Oil field Glossary of Terms


Abandonment Final plugging of wells, and/or permanent

dismantling, etc. of a production platform or other


Absolute Pressure term used to describe the gauge

pressure plus atmospheric pressure

Absorption The ability of a gas, liquid or solid to attract

and retain another substance without chemical

combination. A quantity of such a substance that has

absorbed as much of another as is physically possible is

said to be saturated with it. Some refinery processes use

this ability for instance to separate different hydrocarbons.

Acidization is a process where by pumping techniques,

acid is squeezed into tight and/or damaged reservoirs in

an attempt to improve the well porosity and permeability

and thereby improve the flow of hydrocarbons to the well.

See also Stimulation

Acid Rain  Develops when sulphur oxides (Sox) and

nitrogen oxides (Nox), released by the combustion of

fossil fuels (particularly coal) combine with moisture in the

atmosphere to form sulphurous , sulphuric, nitrous and

nitric acids. Because SOx and NOx are gases and because

the formation of acid rain takes time, acid rain damage

often occurs far from the source of the problem.

Acoustic Log A record of the time taken by an acoustic

(sound) wave to travel over a certain distance through the

geological formations. Also called a sonic log. See also:

seismic survey.

Acreage Area covered by a lease granted for oil and gas

exploration and for possible future production

Acre-foot Unit used to measure the rock volume of an oil

or gas reservoir structure.

Additive   Chemical added to a product to improve its


Adsorption A  separation process for removing impurities

based on the fact that certain highly porous materials fix

certain types of molecules onto their surface.

Advance Payment Finance Finance for exploration and

production provided in return for a first claim on

production. Typical sources of such finance are U.S.

refiners and pipeline companies.

Aggregate                     The mineral matter used together with

bitumen to create asphalt for road construction

Air Gun                   Chamber from which compressed air is released

to produce shock waves in the earth array is the most

common technique used for seismic surveying at sea.

Alcohols  A class of compounds, of which ethanol (the

alcohol of beer and wine) is the best known. They react

with acids to form esters. They are widely used as


Aliphatic Carbons A group of hydrocarbon substances,

including the Alkanes and most of the other fractions

found naturally in crude oil. See Section 10.

Alkanes                   Naturally-occurring paraffin fractions of which

the molecules are based on a "straight chain" of

hydrogen-saturated carbon atoms. See Section 10.




Alkylation A refining process used to produce improved

gasoline components with e.g. lower pollutant effects, and

also in plastics manufacture.

Alluvial Fan A pattern of sedimentary deposit frequently

laid down by streams or rivers where they spread out into

plains. Alluvial fans from past geological eras are potential

reservoir structures.

American Petroleum Institute (API) API is the world's

foremost authority on oil industry standards and practices.

"API Gravity" is a reference system for the density of

crude oils and constituent hydrocarbons.

Ammonia  Manufactured by the direct combination of

hydrogen an nitrogen under pressure over a catalyst.

Anhydrous ammonia is mainly used for the manufacture

of nitrogenous fertilisers.

Anhydrous Without water or dried

Anode See Sacrificial Anode.

Anticline A fold in layered rocks originating below the

surface in the form of an elongated dome. Anticlines make

excellent drilling prospects since any oil in the deposit will

naturally rise to the highest point of the structure because

oil has a lower specific gravity than water. See also:


Anticlinal traps     are essentially formed as a result of a

folding of the strata trapping gas, water or oil contained in

the reservoir rock.

Anti Knock Compounds  Additives such as Tetra Ethyl

Lead (TEL) and Tetra Methyl Lead (M) or Methyl Tertiary

Butyl Ether (MTBE) which tend to prevent gasoline

detonating ("knocking" or "pinking") under compression

instead of burning evenly. This enhances their Octane

Rating. Anti-pollution measures will in future largely

eliminate lead based additives.

Annulus The ring-shaped cavity between two concentric

tubes-e.g. inner and outer strings of casing, or between

casing, or drill pipe, and the well borehole.

Apparent Earning Power (AEP) The apparent Earning

Power of the MOD cashflow.

A.P.I. gravity      An arbitrary scale adopted by the

American Petroleum Institute for expressing the gravity of

oils.  The higher the A.P.I. gravity, the lighter the crude

(i.e. the higher the proportion of lighter fractions the oil


Appraisal well A well drilled as part of a programme to

determine the size and likely yield of an oil or gas field.

Appraisal Well. Before development, a discovery is likely

to need at least two or three such wells.

Aquifer   An underground formation of permeable rock

saturated with water under pressure. For gas storage

applications, an aquifer will need to consist of a

permeable lower layer of rock and an impermeable

upper layer (or ‘cap’), with a cavity for storing gas. Such

formations may be, and frequently are, the same as those

containing oil or gas reservoirs.

Area of Mutual Interest (AMI)  Area where two or

more companies agree to explore exclusively in concert.

Aromatics Hydrocarbons with a ring structure, generally

with a distinctive aromatic odour, and good solvent

properties (e.g. BTX)

Aromatic Hydrocarbons  The group of hydrocarbon

products which include Benzene, Toluene, etc. and

provide feedstock for many of the main petrochemical

processes, as well as high Octane Rating gasoline blends.

So-called from their "sweet" smell. See Section 10.

Artificial Drive                   Methods of producing oil when natural

reservoir pressures are insufficient or have declined, such

as injection of gas or water into the reservoir structure.

Articulated Platform                            A semi-buoyant structure

anchored to the seabed by means of a "Universal" joint

coupling which allows it to "sway" with the forces of the

sea etc. Such structures need less rigid strength than fixed

platforms and so are relatively lighter and cheaper to


Asphalt                   A solid petroleum residue, similar to Bitumen,

Tar and Pitch.

Associated Gas   Natural gas found as part of or in

conjunction with other constituents of crude oil, as

opposed to such gas found on its own. The expression has

come to include natural gas necessarily produced along

with crude oil.

ASTM                  American Society for Testing and Materials. In

conjunction with the API and Institute of Petroleum, they

publish authoritative standards and e.g. calculation tables

used by the oil industry. ("ASTM tables").

Atmospheric pressure The weight of the atmosphere

on the surface of the Earth. At sea level this is

approximately 1.013 bars, 101,300 Newtons per square

metre, 14.7 pounds per square inch or 30 inches of



Back Off 1. In drilling, to pull the drill-string out of, or

partly out of, the borehole.

  1. To unscrew a joint of drillpipe.
  2. To slacken off a line or block.

Ballast   Water taken aboard a tanker, semi-submersible

rig etc. to maintain stability and to distribute load stresses

e.g. in the case of part-cargoes. Modern tankers have

segregated ballast tanks so that the water does not

become polluted with oil.

Barite                     A very heavy substance used as a main

component of drilling mud, to increase its density (mud

weight) and counter-balance pressures



A quantity of 42 US Gallons

(approximately 35 Imperial Gallons). The traditional unit

of measure of oil volume. "Barrelage" is a term for oil flow

quantity measured by volume. See Section 13.

Barrel oil equivalent (boe)                      a term frequently used to

compare gas and oil and to provide a common measure

for different quality gases. It is the number of barrels of

stabilized crude oil, which contains approximately the

same amount of energy as the gas: for example : 5.8

trillion cf. (of lean gas) approximates to 1 billion boe.

Base chemicals                     Basic building blocks for the chemical

industry, which are converted to other chemicals (e.g.

aromatics and olefins converted into polymers).

Basket A hollow tool used to retrieve junk from the well

when fishing. The name is also sometimes given to the

bird cage.

Batter The inward slope of the legs of a steel platform for

stability so that the foot of the jacket covers a larger area

than at deck level.

BCF or BN CF  Billion (109) cubic feet (cf), unit of


BCN or BN CM Billion (109) cubic metres (cm), unit of


Baseload The basic, underlying level of demand, or

system minimum; used in the context of gas supply and

power generation. The opposite of peak load.

Beach price Price applying to gas at landfall, when water

and liquid hydrocarbons have been removed.

Bead The fused metal resulting from a welding operation

or "pass" in a major weld, as in a pipeline. There are

normally three, the root or stringer bead, the filler bead,

and the cap bead.

Bean A choke, the orifice in a flow control valve. To "bean

up" or bean down" means to install a larger or smaller

orifice, or to open or close a variable valve.

Be   is the geological term defining a stratum of any

thickness, and of uniform homogeneous texture.

Benzene The simplest aromatic compound with a ring of

six carbon atoms and six hydrogen atoms; one of the

most important feedstocks for the chemical industry.

Bentonite See Mud.

Biodegradable    Material that can be decomposed or

rotted by bacteria or other natural agents.

Billion     In oil and gas usage, a billion means 101 not

  1. (One billion cubic feet (BCF) = one thousand million

cubic feet).

Biomass conversion     The conversion of biochemically

derived material for the production of energy.

Bird Cage     The small net-enclosed "platform" used

offshore to transfer people by crane from e.g. boat to

platform, or rig.

Bit A drilling bit. Those chiefly in use are the steel roller-

cutter, and the diamond-insert bit for hard formations,

which penetrates by scratching or abrading the rock

rather than by crushing or pulverising like the roller bit.

There is also the annular diamond-insert core bit, for

cutting and retrieving rock samples (in conjunction with a

core barrel). As it rotates, it shears/crushes the rock strata

away to form a well.   Most modern bits are comprised of

three circular cutters (tricone), often studded with hard

metals such as tungsten carbide.

Bitumen   Extremely heavy semi-solid product of oil

refining, made up of heavy hydrocarbons, used for road-

building and roofing. A form of heavy, solid petroleum.

See Asphalt

Black Oil/Black Cargo       Crude oil, or distilled crude

containing the fractions heavier than middle distillates.

Black products   Diesel oils and fuels oils, i.e. products

from the low or heavy end of the distillation process. See

also: white products.

Blind Rams See Blow Out Preventer Pipe Rams.

Block 1. A licence or concession area. It may be almost

any size or shape, although usually part of a grid pattern.

  1. An arrangement of pulley wheels used in lifting, on a

derrick or crane.

Bloom The rainbow-like fluorescence shown by oil for

instance when floating on water.

Blow Down 1. The process of releasing pressure in e.g. a

refinery   pressure   vessel   by   venting  to   atmosphere.

  1. Primary production of a crude oil or condensate

reservoir using the pressure of the associated gas.

Blowout                         Uncontrolled or uncontrollable release of

downhole pressure upward through the wellbore or

casing. Although the main danger is fire, the gases are

also toxic, and in floating operations a gas blowout may

include a threat to the stability of the rig itself. (See Mud).

Blowout Preventer (BOP) An emergency shut-off valve

installed on the wellhead during drilling or testing of a

well, which incorporates hydraulic pipe rams capable of

closing the space around the drillpipe against very high


Boomer                     This    expression normally  refers  to   a

Compressed air, or electrical, source of sound used in

marine seismic survey work.

Borehole A well, especially referring to the face of the

rock outside or below the casing. Test boreholes are also

sunk to examine the suitability of a site for major

foundation work, and to examine geological formations at

points where no hydro-carbons are expected.

Bottled gas                     LPG stored in the liquid state at moderate

pressure in steel containers.

Bottles                     1. Small pressure vessels of various kinds,

especially to absorb pressure fluctuations. 2. Cylindrical

flotation tanks such as those temporarily attached to a

platform jacket during placement.

Bottom-hole etc. The deepest part of a well, thus:

Bottom-hole assembly (BHA) includes the drilling bit, drill

collars, stabilizers and other drilling components run into

the well on the end of the drillpipe. See Drill String.

Bottom-hole payment                       A cash payment to the equity

participants in a well, on its reaching target depth, by

other parties interested in acquiring the information it


Bottom-hole pressure Formation pressures measured at

reservoir depth.

Bottom-hole pump                        (also downhole pump) A pump

installed in the lower end of the wellbore, to increase


Bottom of the barrel See Fuel Oil, Heavy Ends etc.

Bottoms Up Circulation of drilling fluid in a well, until the

bottom hole mud and cuttings reach the surface,

indicating that normal circulation can commence.

Booster station A platform on a section of subsea gas

pipeline, designed to boost the flow of gas.

Bow Thruster A propeller mounted transversely in the

bows of a vessel to assist in docking, manoeuvring and


Box The hollow, or female end in a threaded connection,

such as drillpipe.

Bridge Plug A down hole packer assembly used in a well

to seal off or isolate a particular formation for testing,

acidizing, cementing, etc. Also a type of plug used to seal

off a well temporarily while the wellhead is removed.

Brucker  Capsule     A    circular  escape-and-survival

"lifeboat" designed to be lowered automatically on a single

wire cable after those entering it have sealed the hatches

from within.

Bubble Point                       The pressure at which a saturated

hydrocarbon liquid releases gas out of solution. See also


Bullets Cigar-shaped tanks, usually for the bulk storage

of propane or butane LPG's as liquids under pressure.

Bumper Sub A telescopic joint inserted at the upper end

of the string of drillpipe in floating drilling operations, to

compensate for vertical motion of the rig with reference to

the wellhead on the seabed.

Bund Walls The dam or dyke walls surrounding storage

tanks or e.g. onshore well installations, to contain the

contents in case of rupture or spillage.

Bunker ‘C’ A heavy residual fuel oil obtained as a result

of distillation of crude oil, and used as fuel primarily for

marine steam generation.

Bureau Veritas See Certification.

Burial History See Maturity.

Bury Barge A vessel used to bury completed submarine

pipelines in the seabed. This is done by scouring away the

seabed under the line with high-pressure water jets,

usually mounted on an underwater vehicle known as a

tury sled" or "jet sled". The pipeline settles into the trench

so formed and is covered by resettlement of the seabed


Breakdown Analysis Captures the project's sensitivity to

changes in price, discount rate, RFSU, capex and opex to

the point where the NPV becomes negative. The results

are best displayed in a tornado diagram. Brent blend  A

blend of North Sea crudes, used as an international

marker for crude oil pricing.

British thermal unit (BTU)         The amount of heat

required to raise the temperature of one pound of water

by one degree Fahrenheit.

BTX Abbreviation of the aromatic hydrocarbons, benzene,

toluene and xylene.

Bulk cargo Any liquid or solid cargo loaded on to a vessel

without packaging (e.g. oil or grain).

Bunker fuel Any diesel or fuel oil supplied to fuel a ship's

engines; i.e. to run the ship rather than as cargo to be

transported for sale. The 'bunkers' are the place where it

is stored on the ship.

Butane A hydrocarbon consisting of four carbon atoms

and ten hydrogen atoms. Normally a gas, but easily

liquefied for transport and storage; used in gasolines, and

for cooking and heating. See also: LPG.

Blow-out Preventer (B.O.P.)  is a stacked series of

hydraulically controlled safety valves.  When activated the

valves prevent the flow of formation fluids to the drill rig

in the event of a pressure anomaly being drilled.


Cabletool  Equipment for drilling a well by the outdated

cable method. Specifically, the heavy sharpened bar or

"bit" which penetrates by being repeatedly dropped in the

borehole on the end of the cable.


A tool for checking casing in a well for

deformation before e.g. running drilling tools, which might

become stuck, or packers which might leak. See Section

5: BGT.

Calorific Value     The quantity of heat produced by

complete combustion of unit weight of a material.

Expressed as either calories per gram, or British Thermal

Units (BTU) per pound, or BTU per standard cubic foot of


Capbead See Bead.

Cap Rock                           An impermeable layer of rock above a

discovered or potential hydrocarbon reservoir, providing a

seal to contain the reservoir fluids.

Carbon                   A solid element which exists in many forms,

including diamonds, graphite, coke and charcoal. The

combinations of carbon with hydrogen are known as

hydrocarbons and can consist of very large molecules

(e.g. polypropylenes) or very short ones (e.g. methane).

Carbonate rock                         is a sedimentary rock primarily

composed of calcium carbonate (limestone) or calcium

magnesium carbonate (dolomite), sometimes found as

petroleum reservoirs.

Carbon black A carbon product obtained from liquified

carbon feedstock and used mainly in the rubber industry

(e.g. in tyres).

Carbon Black Carbon derived from petroleum in soot-like


Carbon Dioxide (CO2) Injection                        A method used in

secondary recovery from an oil reservoir, in conjunction

with waterflooding.

Carried Interest                     A commercial arrangement, whereby

expenditures due from one participant in a joint venture

are met by another, usually in exchange for increased

equity or repayment out of production revenues.

Casing Etc. The steel pipes with which a well is lined, for

protection against collapse of the borehole, and unwanted

leakage into or from rock formations, or at the surface.

"Joints" of casing are around 33ft/10m long and are

normally screwed together as they are run into the well.

Particularly in offshore drilling it is normal to set large

diameter casing, (such as 20") called the Conductor (or

surface) Pipe after the well has penetrated the layers

nearest the surface, and cement it into place, after which

the drilling continues with a smaller diameter bit, etc

NB The next string of casing, the "Surface String" is

cemented inside the previous string and down to the new

Casing Point (see below) which may be at, say

1,000/1,500m and forms the base for the wellhead. This is

followed by one or more intermediate strings depending

on the target depth and expected conditions in the well.

Finally the Inner Production String is set and cemented

through the reservoir zone, and perforated to allow

hydrocarbons to enter the well.

Casing Hanger The lug or bracket from which a string of

casing is suspended at the upper end.

Casing Head The flanged top of the casing at the surface

to which the Blowout Preventer is bolted, and, in

production, the wellhead.

Casing Point The depth of the lower end of a string of


Casing Shoe A reinforced section of casing run into a

well at the lower end of a string, to protect against

buckling or deformation.

Casing perforation  To complete an oil well the casing is

perforated in the oil-bearing formation in order to allow

the oil to flow into the well.  This operation is performed

by a tool made up of a number of linked explosive


Casing Tong A large mechanical wrench for screwing or

unscrewing casing joints. (Now usually power-operated).

Catalyst A substance which aids or promotes a chemical

reaction without forming part of the final product. It

enables the reaction to take place faster or at a lower

temperature, and remains unchanged at the end of the

reaction. In industrial processes, nevertheless, the catalyst




must be changed periodically to maintain economic


Cat Cracker See Cracker.

Catenary         The curve assumed by a chain or cable

suspended between two points (e.g. an anchor-chain).

Cat Head The drum of a power winch accessible from a

rig floor or ship's deck for hoisting, pulling and tightening


Cathodic protection    A method employed to minimise

the rate of electrochemical corrosion of structures such as

oil drilling and production platforms, pipelines and storage


Catwalk    A narrow elevated platform or walkway for

access to equipment

Cave-in Collapse of part of the wall of a borehole usually

in a poorly consolidated rock formation.

Cavern Storage     Underground natural or man-made

storage   chambers  in    suitable  impermeable  or

artificially lined rock formations. They may also be

designed for cryogenic storage. See also Jug.

Cellar Deck  1. The deck or floor beneath the working

floor of a drilling rig.

  1. The deck below the main superstructure of an offshore


Cement etc Cement is used to "set" casing in the well

bore and seal off unproductive formations and apertures.

It is also used as a coating to add weight to submarine

pipelines, which might otherwise float or be easily

displaced, particularly when filled with gas.

Cement Bond Log (CBL) The measurement made by a

tool run in a well to measure the extent to which the

cement has bonded with the adjacent surfaces and

provided an effective seal. See Section 5.

Cement Slurry-See Slurry.

Cement Squeeze     in a well is the injection of cement

under pressure between casing and borehole wall,

especially where bonding is poor, to fill any cavities and to

infiltrate the rock to further seal it off.

Centipoise (CP) An unit of measurement of viscosity. It

expresses the force needed to overcome resistance to

flow, and to maintain unit velocity of flow, in a given field.

Centralizers Spacing collars attached to the outside of

casing when run in a well, to keep it central in the bore

and ensure an evenly-shaped annulus in which cement

can circulate and set.

Centrifuge   A separator operating on the principle of

differential acceleration of particles of different mass, an

effect produced by equipment similar to a turbine

"spinning" the feedstock in an enclosed chamber.

Certification (Classification)The process of certifying

the origin, quality, and fitness for use or operation to

given standards of a platform structure, process, item of

equipment etc. It originated in ship construction and

insurance  classification. Hence  major  certification

authorities acceptable to Government agencies etc., are

Lloyds, American Bureau of Shipping, Bureau Veritas and

Det Norske Veritas.

Cetane Number A measure of the performance of diesel

fuel in working conditions (i.e. under compression), similar

to the Octane number used for gasolines.

CF/D cubic feet per day.

Chain Tong A power wrench for tubular connections in

which the pipe is gripped and rotated by an endless chain-

belt running on rollers.

Channeling During production from a reservoir which is

being supported by pressure from contiguous water or

gas, the water or gas tends to travel towards the. well

bore faster through channels or layers of more permeable

rock (see Permeability) by-passing and "holding back"

production from the less permeable rocks.

Check Valve A non-return valve, allowing only one-way


Checkerboard leasing A phrase used in exploration to

describe granting concessions or leases on alternate

blocks. A discovery will tend to increase the value of

contiguous blocks still unlet.

Choke is a steel nipple inserted into the oil production

pipe to restrict the flow of oil from a well.  These nipples

come in varying sizes, and often more than one is inserted

in the production pipe.

CHP                   (Combined Heat and Power) Applied to power

generation this refers to the generation of electricity and

steam (or heat) simultaneously from the same single fuel,

generally to satisfy all the needs of the commercial or

industrial site for which it has been designed. In

circumstances where process heat is not required, the

generated steam can be used to generate additional

electricity in a steam turbine; this is described as

Combined Cycle Power Generation.

Christmas Tree                           The manifold, or arrangement of

pipework connections and valves which is installed on the

wellhead prior to production. As well as outlets for

production, the tree will provide for the injection of mud

to "kill" the well, and for the insertion of downhole

maintenance tools.

Circulation (drilling)The passage of fluids, primarily

drilling mud, down the interior of the drill-stem and back

to surface via the annulus. Reverse Circulation is in the

opposite direction.

City gate This refers to the point where gas passes from

a main transmission system to a local distribution system.

There is not necessarily a change of ownership.

CIF cost, insurance and freight.

Circulation Bottoms-up -see Bottoms-up.

Clastic Rock                      Rock which has been formed from the

sediment and detritus of other rocks e.g. sandstone,

shale, conglomerates, etc.

Clean Cargo  1. Any "white" oils such as gasolines,

naphtha, or middle distillates, from the 1ighter end of the

barrel" i.e. excluding black oils.

  1. Oil with less than 1 per cent basic sediment and water

(e.g. for pipeline shipment).

Closure Four-way (all round) closure or seal is necessary,

over the top and down the gradients on the sides of a

potential reservoir, before it can trap or retain

hydrocarbons. Closure may be structural as in an anticline,

or may be partly due to an impermeable fault, or

stratigraphic trapping or e.g. salt intrusion.

Cloud Point                    The temperature at which paraffin waxes

will solidify and give a cloudy appearance to the oil of

which they form part.

CO Carbon Monoxide

CO2  Carbon dioxide.




Coal gas  Manufactured gas made by the destructive

distillation of bituminous coal. The chief components are

methane (20% to 30%) and hydrogen (about 50%).

Coal Gasification   Conversion of coal into methane, still

at the pilot-plant stage. Conversion in the coal-seam by

downhole process is also under study.

Coating (Pipeline) 1. Cement applied externally, weight-

coating. 2. Anti-corrosion compounds applied internally.

Cofferdam In platform construction, the "floatable" wall

used to seal a dry construction dock. When the dock is

filled with water for platform float-out, the cofferdam is

de-ballasted and floated to one side to allow egress.

Cofferdams have various other uses.

Coke (Petroleum Coke)    Carbon extracted from crude

oil, usually as result of thermal cracking. It is much like

ordinary coke in appearance, but its purity makes it

preferable in several industrial processes such as

aluminium smelting.

Coking  A thermal cracking process to break up large

molecules into smaller ones with the generation of

quantities of petroleum coke.

Combined carrier    Ship that can carry oil or dry bulk


Combined-cycle gas turbine (CCGT) the generation of

electric power by a combination of a gas-turbine cycle and

a steam-turbine cycle.

Combined heat and power (CHP) The combination of

heat and power generation in the same plant. This

method reduces the overall consumption of fuel by

exploiting the otherwise wasted heat from conventional

electricity generation. It provides low-grade heating for

domestic and industrial uses.

Commercial Well A well capable of producing profitably.

Commisioning   Preparatory work, servicing etc. usually

on newly-installed equipment, and all testing prior to full

production testing (see Start up).

Common Carrier      The legal status of some pipeline

companies, primarily in the U.S.A.

Common carriage    1) The transport of gas through a

pipeline system on behalf of a third party. 2) The

obligation on transmission or distribution companies to

allocate gas transport to customers on a pro rata basis,

without discrimination between new and existing clients.

Completion 1. Installation in a well of production tubing

and equipment, wellhead and Christmas Tree.

  1. Fulfilment of a contractual obligation.

Completion Test  The procedure specified in e.g. a

construction contract, or project financing agreement, for

determining whether the plant, field development, etc. in

question meets the operating specifications laid down. A

completion test may in some cases extend over several


Compliant Platform Structure A platform capable of

"swaying" to absorb sea forces. See also Articulated


Compound Chemical term referring to a substance made

up of two or more elements chemically united in fixed

proportions by weight.

Compressor station Used during the transportation of

gas. Gas loses pressure as it travels long distances: to

ensure an even flow it must be recompressed at the

stations located every 60 km to 80 km along the route.

CONCAWE The Oil Companies European Organisation for

Environmental and Health Protection, based in the Hague.

Concession A defined licence area granted to a company

for the exploration of oil and/or gas under specified terms

and conditions and for a fixed period of time.

Concrete Platform See Gravity Structure.

Condensate a light oil which condenses from natural

gas when it encounters normal atmospheric conditions. It

is a high value refinery feedstock, rich in gasoline

compounds and other fractions at the light end of the

crude oil range (high API). It is usually colourless. This can

refer to any mixture of relatively light hydrocarbons which

remain liquid at normal temperature and pressure. There

will be some propane and butane dissolved in it. Unlike

crude oil, there is little or none of the heavy hydrocarbons

which constitute heavy fuel oil. There are three main

sources of condensate: •a) The liquid hydrocarbons which

are separated out when raw gas is treated. This

condensate typically consists of C5 to C8. •b) The liquid

hydrocarbons which are recovered at the surface from

non-associated gas. •c) The liquid hydrocarbons which are

produced from gas/condensate reservoir.

Conductor Pipe                        On land and in offshore jack-up or

platform drilling, this is driven rather than drilled in to the

soil/seabed. In a floating drilling operation, the conductor

extends from the rig down to the wellhead on the seabed.

Conductor pipe provides a guide and access to the well,

and seals off the surrounding sea e.g. to enable circulation

of drilling fluid.

Confirmation Well An early Appraisal or Step-out well.

Coning If an oil well is produced at excessive rates the

reduction in reservoir pressure may tend to draw up

underlying water towards the well in a cone like shape.

Likewise gas can be drawn downwards from an overlying

gas cap.

Connate Water The original water content of a reservoir

rock. Connate water reduces the pore-space (porosity)

available to hydrocarbons. Sometimes called Interstitial


ConsortiumA Joint-Venture enterprise used by the oil

industry as a vehicle for joint operations where a distinct

local legal entity and e.g. joint staffing are required. It

may have the legal status of a partnership, limited

partnership, joint-stock or joint-guarantee corporation etc.

according to local law distinguishable from a light

stabilised crude oil.           Constant Value Money (CVM)  The

same as Real Terms money.

Consumer Price Index (CPI)                      A price index number

applicable to a basket of “typical” consumer goods and


Contingent                        Ideas     Ideas    which   depend   on

implementation of other (enabling) ideas first.

Contaminated Blast                     In a tanker, ballast water which

has become mixed with oil.

Continental Shelf The shelving area covered by shallow

water around major land masses. It may be 50-100

miles/80-200 km in width and merges into the steeper

Continental Slope, and yet steeper Continental Rise which

descends to the ocean floor.

Contract Depth The depth to which a well is to be drilled

under e.g. a turnkey drilling contract.

Core/Core barrel A vertical section of reservoir or other

rock taken in drilling a well, for detailed study and

analysis. In order to retrieve the core as intact as possible,

it is cut from the rock by an annular core bit The central

column of rock passes through the centre of the bit and,

as the bit cuts deeper, is received by a hollow cylindrical

Core Barrel above the bit, where it is retained and




protected by a series of rubber baffles. When the bit has

cut deep enough to fill the core barrel, it is withdrawn

from the hole and the core extracted. In this way the

actual sequence of rock strata is preserved.

Cracker    A refinery plant or process which uses heat

(Thermal Cracker) and/or the presence of a catalyst

(Catalytic Crack under pressure to break down long-

chain-molecule, "heavy fraction" distillates, into more

complex and reactive hydrocarbons such as gasolines. See

also Reforming.

Cracking The process of breaking down large molecules

of oil into smaller ones. When this process is achieved by

the application of heat only, it is known as thermal

cracking. If a catalyst is used as well it is known as

catalytic (cat.) cracking. It is known as hydrocracking if

the catalytic process is conducted in a hydrogen


Creaming Curve  An expression reflecting the fact that

the largest reservoirs in a prospective petroleum province

tend to be found first, followed by a predictable

progressive decrease in the size of discoveries.

Critical Path Analysis A project planning tool normally

used in large construction development projects. It is

based on a "network" of necessary actions of known

sequence and duration, and aims at identifying priority

points at which actions ,"critical to" (holding up other

progress on) the project need improvement or elimination.

Critical pressure  The minimum pressure required to

liquefy a gas at its critical temperature.

Critical temperature    The temperature above which a

gas cannot be liquefied whatever the pressure.

Crown Block The upper fixed pulley assembly at the top

of a drilling derrick.

Crude assay is a procedure for determining the general

distillation and quality characteristics of crude oil.

Crude Oil An unrefined mixture of naturally-occurring

hydrocarbons. Because it is essentially a mixture, the

density and properties of Crude Oil vary widely. Light

Crude normally has an A.P.l. gravity of 300 or more.

Gravities of 200 to 300 include the medium gravity

Crudes, while those below 200 are known as Heavy.

Heavy Oils are found right down to the residual solid

state. See Section 8.

Sour crude has a significant sulphur content: Low-sulphur

crude is described as Sweet.

Cryogenics/cryogenic storage        In oil industry terms

this refers to very low temperature(below -46€C/-50€F)

handling  processing  or   storage  of   hydrocarbon

substances. See also Cavern Storage.

Cubic foot/feet (cf) The amount of gas required to fill a

volume of one cubic foot. Unit of measurement applied to

the volume of gas produced or consumed.

Cubic Metre (CM) Unit of measurement for gas volume.

The amount of gas required to fill the volume of one cubic


Cuttings The small chips or flakes of rock retrieved from

a well by the circulation of the mud. They are studied and

logged by the well-site geologist.

Cut/Cut Point    A "cut" is a hydrocarbon substance or

group of substances extracted from a wider mixture in a

refining process. For instance, primary distillation will

usually yield a Naphtha Gasoline cut, a Middle Distillate

cut, and a Residual Fuel Oil cut, with an "Overhead Cut of

gases. The specific gravity at which each cut is separated

by the process is the Cut Point. Cuts are made with


progressive fineness and accuracy as the oil proceeds

through the refinery.


Daily average send-outTotal volume of gas delivered

during a period of time, divided by the total number of

days in the period.

Daily contracted quantity (DCQ)  The average daily

quantity of gas which is contracted to be supplied and


Daily peak The maximum volume of gas delivered in any

one day during a given period (usually one year).

Daisy Chain A name given to a series of interdependent

contracts for future purchase and sale of oil.

Darcy The unit of measurement of rock permeability, i.e.

the extent to which it will allow a fluid to flow through it.

The permeability of most oil and gas reservoir rocks is

measured in millidarcies, (thousandths of a Darcy).

Data                    Although applied to any factual information, this

term most commonly refers to seismic "data"-the

computer records and output of a seismic survey.

Dead Oil Oil containing no naturalgas.

Dead Weight Tonnage The load-carrying capacity of a

vessel, the "live" weight being the displacement weight of

the unladen vessel.

Dead Well A well which will no longer produce without

further stimulation.

Dealkylation A cracking process whose main product is

aromatic hydrocarbons.

Debutaniser, Depropaniser etc.                            A process vessel

(column) set to "cut' or extract a specific hydrocarbon


Decision Hierarchy A tool to prioritise the issues that

form the core of any quantitative analysis

 Decision Trees                             A logic tree asks critical framing

questions, a decision tree quantifies the available options.

A decision tree is a step-by-step map of future decision

options, the expected spread of outcomes resulting from

those decisions and the likelihood or probability of those

outcomes actually occurring

Decompression/Decompression                            Chamber      The

process of gradually reacclimatising deep divers to surface

pressure conditions. For relatively shallow dives this is

achieved by controlled rate of ascent. For longer, deep, tt

saturation" dives, the divers are recovered under pressure

into a Decompression Chamber where pressure reduction

may take some days.

Deep Rig  A drilling rig designed and equipped to

withstand the loads and pressures associated with drilling

to deep objectives (e.g. over 20,00076,000m).

Deep Well                    See Deep Rig. The deepest so far drilled by

the industry is approximately 30,00079,000m.

Default                    There are many uses of this term, but it is of

major importance in Joint Ventures, whereby a participant

which fails to meet its cash contribution obligations may in

specified circumstances lose rights in the concession in





Deficiency Gas In a "Take or Pay" gas sales contract,

this is an amount of gas which must be paid for although

not taken.

De-Gasser        1. A separator which removes from the

returned mud flow any entrained gases from formations

down the well. Gases can cause a potentially dangerous

reduction in the density of the mud and hence its ability to

contain down-hole pressures.

  1. Any process which removes gases of various kinds from

an oil flow.

Degree day A measure of the extent to which the mean

daily temperature falls below an assumed base, say 65° F.

thus each degree by which the mean temperature for any

day is less than 65°F would represent one degree day. (In

Continental Europe, °C are used instead of °F and the

assumed base temperature is generally taken as 16°C,

equivalent to 60.8°F).

Dehydrator (gas)Equipment for the removal of water

from a gas stream, for instance prior to transfer by


Delineation Well     A name for an appraisal well, usually

one drilled specifically to determine the boundary of a

discovered reservoir.

Demurrage     Originally, charges for keeping shipping

waiting outside the times allowed in the freight contract.

It mainly relates to oil tankers, but can be applied to any

major facility. For instance, Pipeline Demurrage is

chargeable for late delivery to or from a pipeline system.

Dependencies Contingent ideas - ideas which depend on

implementation of other (enabling) ideas first

Depositional environment  The conditions under which

a series of rock strata were laid down.  Depositional

environments are divided into five groups:  marine

(ocean- borne), aeolian (wind-borne), alluvial (river-

borne), deltaic (borne by a river at its delta), and

inter-deltaic (between river deltas).

Depletion etc. Progressive reduction in reserves as a

result of production. Depletion Allowance in some

countries is a type of tax-allowable amortization

recognising this reduction. Depletion Drive is primary

production, i.e. as a result of expansion of reservoir gases

with decreasing pressures.

Depth Map     A relief map of a sub-surface geological

structure where the contours relate to depths from the

surface datum level, (i.e. sea level). This is a further

interpretation of a seismic time map.

Derrick etc. A pylon-like steel tower which provides the

vertical lifting capacity needed for drilling a well. The

Derrick Man is the member of the drilling crew who works

up within the derrick on the tubing board or "monkey

island", a platform where the upper ends of stands of

drillpipe or casing are handled, and hung onto or detached

from the Kelly or hooks. (See Drilling Rig, and diagram).

Derrick barge is a sea-going barge fitted with a larger

crane(s) capable of lifting objects of up to 2,000 tons of

weight.  Such barges are used extensively in lifting heavy

modules on to platforms out at sea.

Derv See Diesel fuel

Desalter Apparatus for removing salt and salt water from

crude oil.

Design Wave The maximum size and frequency of wave

that an offshore structure must be able to withstand.

Deterministic Model The simple cashflow models that

represent each strategy option







Development Any major construction such as a refinery,






Distribution After gas has been processed, it is



or a production project. It has come to mean, or cover,

the whole life of a production project from design to

abandonment. Strictly speaking it refers to the planned,

and actual production of reserves from a reservoir.

Development Well  Any well drilled in the course of

extraction of reservoir hydrocarbons, whether specifically

a production well, or injection well, See also Exploitation


Deviated Well/Hole                             A well whose path has been

deliberately diverted from the vertical. Although relatively

costly to drill, they are used particularly offshore to reach

distant parts of a reservoir from a single platform.

Deviated, or directional drilling up to 60c, to 70c, from the

vertical is now fairly common. Greater deviation is possible

with special equipment-see Horizontal Drilling and Slant


Dewpoint The temperature at which liquid condenses

from a gas at sea level pressure.

Diamond Bit See Bit.

Diapir                    An up-thrust intrusion of lower-density rocks

through overlying formations, e.g. a salt dome.

Diesel fuel (oil)                      A general term covering light fuel oil

derived from gas oil used in diesel engines. Sometimes

called Diesel Engine Road Vehicle (Derv) fuel.

Differential Pressure                          The difference between the

pressure in a well due to the mud column and the

pressure in the surrounding rock at any point. See also


Dip, Diameter1. The inclination from the horizontal of

he top surface of a geological structure. A Dip meter

indicates dip relative to a well bore. See Section 5, HDT.

  1. Measurement of the contents of a tank by lowering a

weight and prepared line into it. See Tank Dipping.

Directional Drilling See Deviated Well.

Dirty Cargo                    Crude oil, or any cargo containing black oil

or residual oils.

Discounted Profitability Index (DPI) A measure of

the NPV generated by a project for every (discounted)

dollar of capital spent.

Discount Factor Calculates the investment or time-value

of money; today's dollar is more valuable than tomorrow’s


Discounting The discounting has the effect of reducing

the value of future income in comparison to the cost of

early expenditure. It takes into account the risk that the

income anticipated in the future is less than that predicted

by discounting its value.

Discovery Well A successful exploration well, or wildcat

The first successful well on a new prospective reservoir


Distillates                     The products of condensation during the

fractional distillation process (gaseous fuels, naphtha,

gasoline, kerosine and gas oils).

Distillation/Distillation Column/Distillate

The process of heating and "flashing" or boiling off

successive fractions (component hydrocarbon substances)

from a crude oil feedstock, or a product of earlier

distillation. A Distillation Column is an elongated vertical

process vessel designed to give optimum physical

separation of required fractions "flashed" inside it. The

products of distillation are known as Distillates.


transported through transmission trunk lines to local

distribution centres, for metered delivery to customers

Ditch Cuttings See Cuttings. Originally retrieved from

the "ditch" of early land-based mudsystems.

Diurnal storage Literally, daily storage. Refers to short-

term or peak storage in pipelines or gas holders, as

opposed to seasonal storage.

Diverter A safety device fitted in the early stages of a

well, instead of a blowout preventer, to divert and vent off

any shallow gas encountered.

Dog-leg        Where a well has been deviated and later

returned to vertical. The expression may also be applied

to any similar double bend in a pipeline or well.

Dog House The Driller's enclosure or shack which serves

as a well-site office and control room.

Domestic Gas (DomGas)         Natural gas, supplied by

pipeline is a mixture of different gases, mostly methane

(85% North Rankin). Other components include ethane,

propane, butane, pentane, carbon dioxide and nitrogen. It

occurs in pressures of 31-49 Mega Pascals in reservoirs on

the North West Shelf.

Dope A grease-like substance used to protect and seal

joint-threads of well tubulars such as casing.

Double bottom tanker A tanker in which the bottom of

the cargo tanks is separated from the bottom of the ship

by a space of up to 2 to 3 metres. The space is empty

when the tanker carries cargo, but full of sea water on the

ballast voyage. See also: double hull tanker.

Double hull tanker    A tanker in which the bottom and

sides of the cargo tanks are separated from the bottom

and sides of the hull by spaces of up to 1 to 3 metres

width or depth. These spaces are empty when the tanker

carries cargo but full of sea water on the ballast voyage.

See also: double bottom tanker.

Down Dip An area of a structure where the top of the

formation is lower (e.g. offshore, deeper below sea level)

than the point under consideration.

Down Hole  Down a well. The expression covers any

equipment, measurement, etc., in a well or designed for

use in one.


"Downstream" is a relative term (the opposite of

"Upstream") in oil industry operations. For instance, a

refinery is "downstream" of a crude oil production unit,

and a petrochemical plant usually downstream of a

refinery. The term has also come to mean all operations

occurring after the delivery or lifting of saleable quality

crude or gas from the production unit or associated

delivery terminal. A "Downstream Company" has no

production of its own.

Downtime     A    period  when   any   equipment is

unserviceable or out of operation for maintenance etc.

Drape structures occur when sediments are deposited

or draped over the physical relief of older rocks.  Such

features can include old fault traps or anticlines.

Drawdown The difference between shut in and flowing

bottom hole pressures.

Drill bit  The part of a drilling tool that actually cuts

through the rock.

Drill Collar See Drill String.

Drill Pipe  Pipe, usually of 3.5 in. to 5 in. outside

diameter, which is supplied in "joints" normally of around


33 fL/10 m. in length, each being fitted with thicker, or

"up-set"' reinforced threaded couplings at each end, 66

male and female" or "pin and box"

respectively. To save time, drill pipe in use but not in the

well is stacked in stands.

Drill Ship A ship-shape offshore drilling rig for exploration

in very deep waters. Although less stable than a semi-

submersible rig it has greater load carrying capacity and is

therefore more self-contained when far from land.

Drill Stem/Drill Stem Test The assembled drill pipe in

the well is known as the Drill Stem, and serves three main

purposes; to rotate the bit; to convey drilling mud or

cement down the well, and to flow to surface the fluids in

primary assessment of a discovery, (Drill Stem

Testing/DST). See also Drill String.

Drill String

The assembly of bit (for penetration) drill collars (for

weight, rigidity and torque transmission), stabilizers (to

ensure straight hole and help transmit torque), and the

length of drillpipe in use in the well. Penetration is

achieved by "weight on the bit, or the weight of the drill

string minus the weight of the equivalent volume of mud

in the well.

Drilling Crew The crew on a drilling rig is supervised by

a senior drilling engineer, known as a "Toolpusher". Other

members of the crew ' include the Driller, in charge of a

shift, who ensures adherence to the drilling programme

and maintenance of the shift's operating log, or 7our

Sheet". He controls the lifting mechanism and hence the

weight on the bit (see Drill String). Other skilled members,

or "Roughnecks" may be Motor men, Derrickmen, Floor

men, Pump men, etc. Partly skilled or unskilled members

are known as "Roustabouts".

In addition a rig crew will incorporate such specialists as

Mud Engineers and Well-site Geologists.

Drilling Fluid See Mud.

Drilling mud                    A mixture of clays, water and chemicals

used in drilling operations to lubricate and cool the drill

bit, carry drilling wastes to the surface, prevent the walls

of the well from collapsing, and to keep the upward flow

of oil or gas under control. It is circulated continuously

down the drill string and up to the surface between the

drill pipe and the wall of the hole.

Drilling Out                      When a well must be deviated or side-

tracked, either as planned or to avoid a fish it is normally

necessary to cut a hole in the casing wall and drill out on

the new path.

Drilling Report Every twenty-four hours the Driller's log

and the geological cuttings log, together with the

observations of the Toolpusher and any other significant

data, are sent, usually by telex, to the Area Drilling

Manager and other interested parties. The report will also

include e.g. usage of materials, stock levels, and

requirements for supplies. See also Drilling Crew

Drilling Rig                       Almost all drilling is now carried out by

rotary rigs. A diagram of a typical offshore rig is shown on

this page. The "Rig" comprises a derrick, a draw-works or

source of power, lifting tackles and blocks, a kelly and

rotary table to rotate the drill string, a mud pump and

mud circulation system, a blow out preventer, and a

system for handling drillpipe, casing etc.

Drilling Tools A term applied generally to any down-hole

accessory including for instance stabilizers, jars, fishing

equipment, and directional drilling apparatus.

Drive Pipe See Conductor Pipe.




Dry Gas  Natural gas, methane and ethane, without any

significant content of heavier hydrocarbon fractions.

Dry gasfield   The production from such a reservoir will

yield dry/lean gas and very small quantities of

condensate; typically less than 10 barrels per million cubic


Dry Hole     An unsuccessful well. Sometimes called a


Dry-trees  See Sub-sea wellheads

Dynamic positioning (DP)         A system of computer-

controlled directional thruster propellers which enables a

"DP" floating rig or drillship to maintain position over a

subsea well without using anchors. It is mainly used in

deep water where anchoring would be impractical, but

may also be used in the vicinity of vulnerable seabed


Dwt (Dead weight tonnage) The weight of cargo,

stores and fuel which a vessel carries when fully loaded.


Economic depletion Progressive reduction in the value

of a producing asset as a result of production. See also

Depletion Allowance.

Economic Life          The date when there is no longer

sufficient return to justify any future investment

Economic Zone The area of the seabed over which an

adjacent state can claim rights of exploitation (currently

up to 200 miles).

ECT Energy Charter Treaty - signed by 45 governments

and the EU in Lisbon, Portugal on 17 December 1994.

ECU European Currency Unit.

Edge water is that water underlying and marginal to oil

and/or gas accumulations.

Effective permeability   The permeability of a rock to

fluid when the saturation of the fluids is less than 100%.

Electric Log See Log.

Electric Swivel powered swivel which rotates the drill

stem from above the rig floor, thus replacing the kelly and

rotary table.

Electro Drill  A bit powered by an electric down-hole

motor which operates without the need to rotate the drill


Element  A chemical term referring to a substance that

cannot be chemically broken down into a simpler form.

Elevators A clamp used in a drilling rig to latch on to and

grip drillpipe, casing, etc., when lifting the EMULSION

Water droplets, each encased in an oil film so that it

cannot break free to separate by gravitation. An Emulsion

treater normally uses heat to break down this resistance

ELSBM  Exposed Location Single Buoy Mooring system is

a semi-submersible structure, designed to enable tankers

to off load oil directly from an offshore oil field.

Emulsion A mixture in which one liquid is dispersed in

another in the form of very fine droplets.

Enabling Ideas Ideas which are necessary for successful

implementation of other ideas








Enhanced recovery is a method(s) applied to depleted

reservoirs to increase the overall recovery factor.  After an

oil well has reached depletion, a certain amount of oil

remains in the reservoir, which enhanced recovery is

targeted to produce.  (See secondary recovery and

tertiary recovery.)

Enhances oil recovery (EOR)

Techniques sometimes described as Tertiary Recovery.

They include, for example, injection of surfactant or

polymer into the reservoir, fireflooding, steam injection,

and microbial action.

Entrained Oil/Gas Small amounts of oil which may form

part of a gas stream, due to the difficulties of separation

at source. Similarly gas may be entrained in a stream of

other fluids.

Environmental                      Impact     Assessment      (EIA)    An

assessment of the impact of an industrial installation or

activity on the surrounding environment, conducted

before work on that activity has commenced. The original

baseline study, a key part of this process, describes the

original conditions.

EOR(Enhanced Oil Recovery) The recovery of oil from a

reservoir other than by the use of natural reservoir

pressure. This can involve increasing the pressure

(secondary recovery) or heating or increasing the pore

size of the reservoir (tertiary recovery). See also:


Equity Crude Crude Oil belonging directly to the equity

participant in the oil field, as opposed to 'Tarmer's crude",

royalty oil, Government participation crude, etc.

Escarpment                          is a cliff or relatively steep slope that

separates level or gently sloping areas of land.

Esters                   Compounds formed by the combination of acids

and alcohols. Feedstock for the chemical industry.

Estimated Date Money                      “What it cost at the estimate

date” – the money type for cost estimates but sometimes

requiring adjustment to the Reference Date.

Ethane                   A hydrocarbon consisting of two carbon atoms

and six hydrogen atoms. Normally a gas, present in most

natural gas occurrences.

Ethanol (ethyl alcohol)                            A chemical formed by

fermentation or synthesis; used as a raw material in a

wide range of industrial and chemical processes.

Ethylene (ethene) An olefine consisting of two carbon

atoms and four hydrogen atoms; a very important base

chemical in the chemical and plastics industries.

EU European Union.

Expansion Loop A bend or loop installed in a length of

pipeline to absorb longitudinal expansion with changes in

outside temperature, the passage of hot oils, etc.

Expected Monetary Value (EMV)                     The risked NPV or

the probability of achieving the project NPV (NPV *

Probability of occurrence). A positive EMV indicates

acceptance of the proposal, a negative EMV indicates

rejection. The higher the EMV, the higher value ranking of

the project.

Exploitation Well A development well, e.g. an oil or gas

producer, or gas or water injector to support production.

Exploration/Exploration Well                             Exploration is the

process of identifying a prospective hydrocarbon region

and structure, mainly by reference to regional, and

specific, geochemical, geological and geophysical (seismic)

surveys. An Exploration Well is a well drilled to test a

potential but unproven hydrocarbon trap or structure




where good reservoir rock and a seal or closure combine

with a potential source of hydrocarbons.

Exposure (or cash sink)The maximum value of the

cumulative RT cash deficit ( in financial reports usually in


"EXPRO" Exploration and Production. (Colloquial).


Facies       In geology, the "appearance" and hence the

composition and characteristics of a rock formation. Cores

are taken from a well, for example, so that the reservoir

facies can be studied. A Facies Trap for hydrocarbons is

one in which the seal or closure is provided by a change in

rock characteristics, a form of stratigraphic trap.

Farmers Crude Landowner's royalty-in-kind.

Farmin /Farmout

In a normal farm-in a company acquires equity rights to a

concession by drilling a well at its own cost for the benefit

of the company or companies "farming-out". For example,

it may drill one well to a stated depth for a 25 per cent

equity in the licence.

Fat Oil/Lean Oil

Saturated or under-saturated oil. "Fat" Oil could, for

example, be saturated with gasolines absorbed from a gas

stream in a refinery. The oil is "lean" when the gasolines

have been distilled out again, and the oil recycled to the

process. See also Lean Gas.

Fault/fault Block     A discontinuity in a rock formation

caused by fracturing of the earth's crust. There are

various causes of fault-fractures such as the movement of

1ectonic plates" relative to each other. In oilfield terms a

Fault Block is a compartment of a rock formation

surrounded or partly surrounded by faults, which may

have sealed in hydrocarbons separately from the rest of

the formation.

Faulting A geological structure consisting of a fracture in

the rock, along which there has been an observable

amount of displacement

Fault traps are caused when a reservoir layer such as

sandstone is faulted and brought against an impervious

rock enabling any oil or gas to collect against the fault.

Field       See Oilfield. A field may also be a gas or gas

condensate field.

Feedstock Raw material for a processing unit.

FERC  Federal Energy Regulatory Commission: the

government organisation in the US whose responsibilities

include regulating the gas industry.

Field appraisal  The process of quantifying reserves

levels and production potential of a newly-discovered

petroleum reservoir, usually by drilling a delineation well.

Filter Cake/Filtrate

Build up of mud solids or filtrate on the wall of a well. This

helps seal and stabilize the rock face, but too much can

cause sticking of the drill string. See also Differential


Fines Small particles of rock or other solid.

Fingering Uneven advance of water and/or gas towards

an oil well due to inconsistent permeability in the


reservoir. When the finger reaches the well oil will tend to

be excluded.

Finger Boards These comprise a rack for the upper ends

of stands of drillpipe.

Finger Pier A jetty at right-angles to the shoreline, so

that tankers can moor to load and unload in deep water.

Finger printing                    Crude oil is a mixture of hydrocarbon

components or fractions and other minerals. The

composition of each crude is different in consequence,

leading to differences in gravity, etc. Nowadays, the

source of a crude - e.g. an oil-spill - can be determined by

analysis known as "finger printing".

Fireflooding A form of Enhanced Oil Recovery in which

otherwise unproduceable heavy oils are ignited in the

reservoir. The cracking effect enables resulting lighter

fractions to be recovered.

Fiscal Costs  The deductions allowed against revenue

when calculating tax – generally royalty, operating

expenses and depreciation.

Fish/Fishing                      Any unwanted object down a well,

commonly the lower end of a drill string which has broken

off. "Fishing" is trying to recover the Fish, using various

attachments to the drill stem or wireline, known as fishing


Five Spot Water Flood                             A standard method of

development where a production well is surrounded by

four water injection wells to "sweep" the maximum

amount of oil towards the producer.

Fixed Bed Catalyst/Fluid Catalyst                          Catalyst which

remains in place in the reactor vessel rather than being

pumped in with the feedstock as with Fluid Catalyst.

Flame Jet Drilling                      The use of a rocket-fuel flame to

penetrate rock by fusing (melting) it. The flame also

glazes and seals the walls of the well with fused rock.

Flange Up                      To connect; to complete; to put into


Flare/Flare Stack                         A vent for burning off unwanted

gases or to burn off hydrocarbons which due to temporary

malfunction or maintenance of process plant, cannot be

safely stored or retained in process vessels. A Flare Stack

is the tower from the top of which the burn-off can safely

take place.

Flash Off  To vaporize or "boil off" a hydrocarbon by


Flash Point The lowest temperature at which a vapour

will burn or explode when ignited.

Flotation collar  This is a specially designed raft, which

enables steel jacket platforms to be transported from the

place of construction to the oil field in a horizontal

position.  When over the proposed offshore location of the

platform, the collars buoyancy compartments are

flooded thereby allowing the platform to swing to a

vertical position.  When the platform has been placed on

the seabed and secured by piles, the flotation collar is

detached and taken back to the shore.

Float/Floating Casing                        A method of inserting heavy

lengths of casing into a well without overstressing joints

and seals due to the weight of the total string. The

bottom end is sealed, and the hollow string then becomes

buoyant in the drilling fluids in the well, which are

gradually displaced. Afterwards the seal is drilled out and

the casing cemented into place.

Floating Production Facility (FPF)A vessel designed

to provide offshore field production control and processing

for smaller fields, more cheaply man a fixed platform. The

tension-leg platform is specifically designed to meet this

need in deeper waters but transport barges, semi-

submersible drilling n . gs, and tankers are all capable of

modification for the purpose depending on water depth

Floating Roof Tank Crude oils (and some Other oils) are

normally stored onshore in tanks whose roofs float on,

and in contact with, the oil, avoiding a cavity in which

volatile and dangerous gases could build up.

Float Out/Floatation/ Floatation Can      The launch or

loading out of jackets or other structures for installation

offshore, on a Flotation barge or other vessel, or in some

cases usirM their own buoyancy.

Flotation Cans are hollow tanks attached to a jacket to

assist buoyancy or help control the lowering to the


Flood   To let or pump water into ballast tanks. See also

Waterflood and Fireflood.

Flotel The floating accommodation used as quarters for

offshore personnel

Flowing Bottom Hole Pressure  Bottom hole pressure

measured at a given flow rate.

Flowline Bundle An integrated assembly of production

pipelines, and hydraulic and/or electrical control

lines, connecting a Subsea satellite well to its parent


Flowmeter/Flow chart A meter to measure the rate at

which a fluid passes a given point. A Flow Chart or

flow graph provides a permanent graphic record usually

over a 24 hour period.

Fluid Cat/Cracking See Catalytic Cracker

Flush Phase        The primary production p h as e of a


Foam Blanket A fire protection device. Inert gas foam is

floated on the surface of liquid hydrocarbons in storage to

exclude contact with air and evaporation of combustible

gases. Foam Blankets are also used in fighting

hydrocarbon fires.

FOB free on board.

Fold is  a flexure of rock strata into arches and troughs,

produced by earth movements.

Footage/Footage rate          Penetration rate in drilling.

Footage Rate may also be a form of remuneration under a

drilling contract. Often referred to as ROP (Rate Of




  1. The limit of radius of action of an 

    underwater vessel or vehicle.

    1. The impact/impression on the seabed of a 1 . ack-up


    Force Field A list of major issues - for and against the


    Formation A rock deposit or structure of homogeneous

    origin and appearance.

    Formation Damage        Damage to the reservoir rock

    around a well due to e.g. plugging with mud, infiltration

    by water from the well, crumbling under pressure or high

    flow rate, etc.

    Fractional distillation See Distillation.

    Fractionating column See Distillation.

    Fractionation   The general name for the process of

    separating a mixture into its constituents or fractions. See

    also: absorption, adsorption, distillation. 

    Formation Density Log See Log.

    Fraction/Fractionator                         A hydrocarbon substance of

    specific molecular composition, or closely related group of

    such substances, extracted from a crude oil or natural gas

    stream, predominantly by distillation in a Fractionating

    Tower or Fractionator.

    Fracturing                    The process of cracking open the rock

    formation around a well bore to increase productivity. This

    is normally done by applying hydraulic pressure down the

    well bore.

    Fraction/Fractionator Gas Chromatography

    A hydrocarbon substance of specific molecular A very

    accurate laboratory method of separating composition, or

    closely related group of such and analysing the

    components of a volatile substances, extracted from a

    crude oil or natural hydrocarbon mixture.

    Free Cash Flow                      The cash flow used in determining a

    projects NPV and IRR. It is the total after-tax cash flow

    generated by a project and available to all providers of

    capital. It is essential to define free cash flow properly to

    ensure consistency between the cash flow and the

    discount rate used to value the project.

    FSU (Floating Storage Unit) A large moored chamber in

    which oil produced from an offshore production platform

    is stored before being transferred to a tanker. See also:

    SBM (Single Buoy Mooring).

    Fuel cell                        An electric cell used to generate electrical

    energy from the reaction of a number of chemicals,

    without the need for combustion and without producing

    noise or pollution. Can use natural gas as a feed-stock.

    Fuel gas                        Refers to gaseous fuels, capable of being

    distributed by pipeline, such as natural gas, liquefied

    petroleum gas, coal gas and refinery gas.

    Fuel oils The heavy oils from the refining process; used

    as fuel for power stations, industry, ships etc. Futures


    The sale and purchase of oil at a price agreed upon

    in advance for delivery at a future date. The seller

    may not yet have the oil and both buyer and seller

    are speculating on how prices will change in the



    Gamma Ray Log/Gamma Gamma Log See Log.

    Gang Pusher Supervisor of a pipe laying crew.

    Gas Cap/Gas cap Drive The natural accumulation of

    associated gas in the top of an oil reservoir. Gas Cap

    Drive, or primary production utilizes the pressure and

    expansion of this gas to drive the oil to the surface.

    Sometimes called Depletion Drive.

    Gas Column See Oil Column/Gas Column.

    Gas Condensate                    Light hydrocarbon fractions entrained

    in gas production which condense into liquid when

    brought to the surface. Changes in reservoir pressures as

    result of production may cause it to condense in the

    reservoir, when much of it may become irrecoverable. See

    Retrograde Condensation.




    Gas/condensate field A reservoir containing both

    natural gas and oil, with a greater proportion of gas.

    Condensate appears when the gas is drawn from the well,

    and its temperature and pressure change sufficiently for

    some of it to become liquid petroleum.

    Gas/condensate ratio         •a) For a gas/condensate

    reservoir this is the ratio of the condensate to the gas. As

    for oil it can be measured in scf per bbl. Alternatively the

    inverse is used and the typical units are bbl per mmscf.

    • b) For a dry gas field only the inverse is normally used.

    Typical units are again bbl per mmscf, but grammes per

    cubic metre may well be used.

    Gas/condensate reservoir A reservoir in which neither

    natural gas nor crude oil is the predominant production

    stream. To increase the recovery of the condensate, the

    gas may be re-cycled for the early years and produced at

    a later date.

    Gas cycling or re-cycling A process in which produced

    gas is re-injected into the reservoir after removal of the

    condensate. This is to maintain the reservoir pressure and

    prevent condensate from "condensing" in the reservoir

    and then becoming difficult to recover. This is called

    retrograde condensation.

    Gas detector An instrument to detect the presence of

    various gases, often as a safety precaution to guard

    against flammable or toxic gases.

    Gasfield A field or group of reservoirs of hydrocarbons,

    containing natural gas, but insignificant quantities of oil.

    Gas gathering system  A central collection point for

    offshore gasfields, with pipelines from a number of fields,

    often owned by a number of different companies. From

    there, the gas is transported to a central processing

    system onshore.

    Gas grid     The term used for the network of gas

    transmission and distribution pipelines in a region or

    country, through which gas is transported to industrial,

    commercial and domestic users.

    Gas Injection   A secondary recovery method by which

    gas is injected into and passed through the reservoir to

    maintain pressure and/or entrain heavier hydrocarbons

    left behind by primary production.

    The reservoir can in this way also serve as storage for

    produced gas until the reservoir pressure can be reduced,

    and the gas sold.

    Gas Kick   Increase of down hole pressure above that

    exerted by the column of drilling fluid in a well, allowing

    gas to escape to the surface. If not controlled this could

    develop into a Blowout.

    Gas lift  One of several methods of artificial lift. A

    mechanical process using the continuous or intermittent

    injection of a gas into the production conduit (tubing or

    casing) to aerate or displace the produced fluids. This

    creates a reduction of the bottom hole pressure of the

    well, increasing or sustaining the flow rate of the well.

    Gas liquefaction The process of cooling natural gas to a

    temperature of -162°C, thereby reducing its volume by a

    factor of 600, and making it liquid. The resulting LNG is

    then transportable by purpose-designed ships (LNG

    carriers) or may be stored in tanks

    Gasohol    A motor fuel which includes a proportion of

    plant alcohol processed from vegetable waste.

    Gas Oil A middle distillate product fraction. See Sections

    8 and 11. 

    Gas/Oil ratio (GOR) The proportional amount of gas to

    oil liquid occuring in production from a reservoir, usually

    expressed as cubic feet per barrel.

    Gas processing The separation of oil and gas, and the

    removal of impurities and natural gas liquids from natural


    Gasser A gas well.

    Gas treatment                       Removal of impurities, condensate,

    hydrogen sulphide and any liquids from the raw natural

    gas contained in a gasfield.

    Gas turbine A turbine propelled by the combustion of a

    compressed mixture of natural gas and air, used for

    power generation.

    Gas oil The medium oil from the refining process; used as

    a fuel in diesel engines, burned in central heating systems

    and as a feedstock for the chemical industry. 

    Gasification The production of gaseous fuel from solid or 

    liquid fuel.

    Gas/oil contact  The interface between the gas cap on a

    reservoir and the underlying oil leg.

    Gas/oil ratio (GOR)  This is the proportion of associated

    gas produced with the oil and is usually expressed in

    standard cubic feet or gas per barrel of oil (SCF/BBL).

    The higher the ratio the more separation facilities are

    required so that the gas can be transported to shore

    separately, flared or re-injected into the reservoir.

    Gasoline The fuel used in cars and motorcycles etc (also

    known as petrol). Naturally occurring gasoline is known as


    Gas well  A borehole sunk into the ground with the

    objective of bringing natural gas to the surface.

    Gate A pipeline valve.

    Gatt The General Agreement on Tariffs and Trade.

    Gauge pressure The pressure which a normal measuring

    device would register. Such devices measure the pressure

    which is in excess of the atmospheric pressure.

    Geared Project                      Project that is (partly) financed with

    outside loans.

    Geochemical Survey Analysis of the hydrocarbon- bearing potential of an area by studying shallow cores and

    subsurface water for evidence of seepage or kerogens.

    Geology/Geologist The study of the history of the earth

    and its rocks. The geologists in the oil and gas industry

    tend to specialise in Sedimentoiogy, Palaeontology and

    other branches of the science relating directly to

    prospectivity for hydrocarbon deposits.

    Geological Column/Geological Eras/Ages                        This is a

    name given to the vertical succession of geological

    deposits from successive eras, found in any specific place.

    These columns vary considerably, but a general reference

    sequence is shown in Section 3. Chiefly of interest to oil

    and gas geologists are those showing evidence of life-

    forms deposited long enough ago to have generated


    Geophones                    Sound wave receivers primarily for onshore

    seismic surveys. See also Hydrophone.

    Geosyncline See Syncline.

    Geophysics/Geophysicist                        Physics applied to the

    measurement of the earth and study of its composition. A


    NOTES in the oil and gas industry usually specialises in

    the interpretation of seismic survey data. 

    Geothermal energy  Energy obtained from the heat

    below the Earth's surface.

    Geothermal gradient The increase of temperature with

    depth in the earth's crust. (About 211F. per 100 feet).


    Thousand megawatts.

    Gin Pole A frame used as a vertical support for hoisting.

    The highest point of a drilling derrick is usually the gin

    pole for working on the crown block.

    GJ Gigajoule: equivalent to one billion (109) joules.

    Gooseneck The curved connecting pipe or nipple on the

    drilling swivel, to which the rotary hose from the

    standpipe is attached.

    Graben          A structure which has become displaced

    downward from its original surrounding geological setting. 

    Grass Roots


    Description of a refinery or other 

    development project where there is no existing plant or

    infrastructure-i.e. construction on a "green field" site.

    Gravel Pack Where the producing formation in a well is

    crumbling or caving into the well bore and plugging the

    perforations, the cavity so formed is filled with fine gravel,

    which supports the formation, and keeps the interior of

    the well clean.

    Gravimeter       An instrument which measures minute

    variations in the earth's gravitational pull at different

    surface points due to the density of the underlying rocks.

    A gravimetric survey uses this principle in the search for

    sedimentary rocks which normally have a relatively low


    Gravimetric survey  Rocks have different densities and

    lie at different depths causing slight variations in the force

    of gravity at the surface.  These are measured by

    gravimeters and enable the geophysicist to collect

    information on the shape and nature of the underlying


    Gravitometer An instrument which measures differences

    in the specific gravity of liquids, and is used to identify

    interfaces between batches of different products in a


    Gravity Platform Structure  Offshore platforms etc.,

    which rely on weight alone to keep them stable and in

    place. They are frequently made of concrete with steel as

    a major component. Steel gravity structures are also used.

    Structures of such size are floated into position, the

    buoyancy being provided by hollow chambers in the large

    base of the platform. Subsequently these are flooded with

    water, and can be used for oil storage.

    Greenfield Often used to refer to a planned LNG facility

    which must be built from scratch; without existing


    Groupshoot A seismic survey shared by several sponsors

    Grout/Grouting   Concrete filling the cavity around e.g.

    steel piles of an offshore platform, as a result of a

    cementing operation similar to setting casing.

    Guide Bas/Lines/Posts         The seabed framework or

    template through which a subsea well is drilled. It is fitted

    with Guide Posts from which Guide Lines extend to the

    surface, and enable the wellhead to be located ready for

    drilling, and for installation and control of e.g. the Blowout


    Gumbo A sticky, clogging mud formed in some wells by

    the mixture of drilling fluid with certain types of shale. 

    Gunk                   The accumulation of rubbish, rust, detritus and

    petroleum deposits that accumulates in a pipeline until it

    is pigged.

    Gun 1. See Perforation. 2. A source of sound for seismic


    Gusher                   An old name for a successful well with a high

    pressure leading to a blowout Now uncommon.


    Hanger See Casing and Tubing.

    Hanging-in the Casing                     Tensioning a string of casing

    while cementing by letting it hang from the wellhead. This

    helps to offset later expansion due to the passage of hot


    Hanging in the slips Suspending drill string or casing

    from slips or wedges placed in the rotary table.

    Hazard Zone                    An area where special safety precautions


    Heading Intermittent flow of oil from a well, usually from

    lack of reservoir gas pressure.

    Heavy fractions Also known as heavy ends, these are

    the oils made up of the large molecules that emerge from

    the bottom part of the fractionating column during oil


    Heat exchanger A process vessel which typically uses the

    passage of one fluid through a set of internal tubes to

    heat up or cool down another fluid in which they are

    immersed. There are many different designs and uses.

    Heat Tracing See Tracing.

    Heave/Heave Compensator                      The vertical motion of a

    floating vessel or platform with the waves. A Heave

    Compensator is installed on floating drilling rigs to

    counteract this movement as regards the drillstring and

    marine conductor.

    Heavy Ends Heavy or residual fractions of a feedstock

    after distillation, etc. Sometimes referred to as the

    "bottom" or "heavy end" of the barrel.

    Helipad                    A Helicopter landing deck or onshore landing


    High (Geological)                        The part or parts of a geological

    structure which are nearer to surface datum/sea 1 evel.

    Hydrocarbons tend to accumulate in "Highs".

    The term is also used on a regional basis, where rocks of

    one geological era are nearer the surface over a broad


    Hold up The quantity of hydrocarbons which is retained,

    in normal operations, in the process lines and vessels of a


    Hole opener A large-diameter drilling bit.

    Hole Temperature Formation temperature at a given

    depth in a well.

    Hooks                   The part of the travelling block of a drilling rig

    from which the swivel and drill string or other load is


    Hook-up                    The activity following offshore development

    installation during which all connections and services are

    made operable f o r commissioning and "start up".




    Horizon The formation at a given depth in a well, usually

    identified by geological age, e.g. "Middle Jurassic


    Horizontal Drilling       A technique for deviating wells

    through up to 900 from the vertical. While the main

    purpose of normal deviated drilling is to "reach" remote

    parts of a reservoir, with horizontal drilling the purpose is

    to keep the well bore within a given productive horizon or

    formation, to increase potential productivity.

    Horst        A structure such as a fault-block, which has

    become up-thrust from its original surrounding geological


    Hot pass A Filler bead-See Bead.

    Hottapinserting a branch line into a pipeline or vessel

    which is still in operation.

    Huff and Puff A steam-injection method of Enhanced Oil


    Hundred year Storm For construction design purposes,

    the worst weather conditions that can be statistically

    predicted within a hundred-year period.

    Hybrid platforms are combination structures of concrete

    and steel with the base and storage area (where

    applicable) constructed in concrete, and the legs and deck

    constructed in steel. The structures remain on location

    under the gravity principle Ð i.e. relying upon its own

    weight to keep it in place on the sea bed.

    Hydrates   Compounds   of    water   with    another

    Substance e.g. natural gas in wells or a pipeline. They may

    cause plugging or corrosion.

    Hydrocarbons are a group of compounds including oil

    and gas which consist primarily of hydrogen and carbon.

    Any compound or mix of compounds, solid, liquid or gas,

    comprising carbon and hydrogen (e.g. coal, crude oil and

    natural gas).

    Hydrocracking    A catalytic cracking process using

    hydrogen and a catalyst.

    Hydrodesulphurisation (HDS)       Process to remove

    sulphur from molecules, using hydrogen under pressure

    and a catalyst.

    Hydrodynamic In the oil and gas industry these studies

    apply mainly to the migration of hydrocarbons in the

    earth's crust.


    The instruments which detect returning sound waves in

    offshore seismic survey sonar operations.

    Hydrostatic Pressure/head The pressure exerted by a

    column of liquid at a given depth, such as that exerted by

    drilling fluid in a well.

    Hydrostatic Testing Press used for re-testing vessels

    by pumping water into them.

    Hydrobaric Welding Chamber      Welding under high

    pressure conditions, i.e. subsea in an air chamber

    (Hyperbaric Chamber) similar in principle to a diving bell.

    Hyperbaric chamber is also the name given to a

    pressurised surface chamber or habitat in which returning

    deep divers are gradually reacclimatised to surface


    Hydrogen  The lightest of all gases, occurring chiefly in

    combination with oxygen in water. Hydrogen combines

    with carbon to form an enormous variety of gaseous,

    liquid and solid hydrocarbons 

    Hydroskimming refinery A refinery with a configuration

    including               only   distillation,  reforming  and   some


    Hydrotreating                            Usually      refers      to       the

    hydrodesulphurisation process, but may also be applied to

    other treating processes using hydrogen.


    Ice Platform An 'ice island' strong enough to support

    drilling operations, artificially created by spraying sea

    water to freeze on top of an existing ice surface.

    Idea Statement A framework which ensures the idea

    itself has been correctly stated and all significant

    parameters addressed

    IEA (International Energy Agency)  Established in

    1974 to monitor the world energy situation, promote good

    relations between producer and consumer countries and

    develop strategies for energy supplies during times of


    Igneous rocks  Rocks formed from the solidification of

    molten magma.

    Impermeable Rock                                   A rock with restricted or

    Poorly communicating pore spaces, such that hydrocarbons

    will not flow through it.

    Impressed Current Protection The active, or 'Anodic'

    method of preventing corrosion in submarine steel

    structures. Unlike the cathodic protection system, the self-

    potential of the structure is counteracted by passing a

    large low voltage current through the surface to be


    Inclinometer A down-hole instrument for measuring the

    angle from the vertical or 'slope' of a deviated well.

    Independent Ideas Ideas which are not required for

    other ideas and do not require any prerequisite ideas

    Independent Producer An expression describing an oil

    producer who sells his production on the market, not

    having his own refining facilities. It has come to be

    applied to all exploration and production companies apart

    from the large vertically integrated ones, and those

    national ly-owned or controlled.

    Inert Gas                      Chemically unreactive gases used to flood

    compartments where there is fire or imminent danger of

    fire. Inert gases are also used in the mixture breathed by


    Infill Drilling Production wells drilled between existing

    wells to increase recovery of hydrocarbons.

    Inflation Factor                      Calculates the purchasing power of

    money; what additional monies are needed to purchase

    the same goods in the future, derived from the Inflation

    Rate, the percent change in some price index from one

    year to the next.

    Inflation Rate The percent change in some price index

    from one year to the next.

    Influence Diagram A tool to assist in identifying factors

    to consider when analysing the alternatives to a particular

    idea. Important in identifying key variables and 

    relationships in the decision problem

    Inhibited Mud Mud containing chemicals to prevent loss

    of water which could damage surrounding formations, and

    cause build up of filter-cake in the well. See Differential


    Injection Well (Injector) Sometimes called an 'input' or

    'service' well. A well through which water or gas is

    injected to maintain reservoir pressure and improve A

    sweep' or areal recovery of reserves.

    In Place Description of the total hydrocarbon content of

    a reservoir, as distinct from 'Reserves' which can be

    'recovered' or produced. Oil or gas in place (01P, GIP)

    before the start of production is known as Oil or Gas

    Originally in Place or Initially in Place. (e.g. STOOIP =

    Stock Tank Oil Originally in Place; G11P = Gas Initially in


    Inside Preventer A blowout preventer which is fitted to

    the inside of the drill-string.

    Instrument Pig A pipeline pig fitted with monitoring and

    gauging devices to check for damage or distortion of the


    Interface The term is widely applied in the oil and gas

    industry as in other industries. However, usage specific to

    oil products is in the interface between two batches of

    different products in a pipeline system. Unless separation

    is critical and maintained by an intervening pig or sphere,

    the products are allowed the small amount of

    commingling that occurs, and the combined product or

    'interface' is drawn off separately at its destination.

    Internal Rate of Return (IRR) Discount rate at which

    the NPV of a project is zero. Also called Earning Power

    (EP) or RTEP. It is used mainly in US companies

    Interruptible gas Gas made available under agreements

    permitting the termination or interruption of delivery by

    the suppliers, usually for a limited number of days in a

    specific period. The opposite is "firm gas".

    Interstitial water       is the water present in the pores

    and/or fractures in the oil or gas- bearing zone of a

    reservoir rock.

    IPIECA International Petroleum Industry Environmental

    and Conservation Association.

    Isobath 1 .          A line connecting points on the sea

    bed of equal depth below the surface-a sea bed contour


    1. in mapping subsurface geology, a line connecting points

    on the top of a formation  of

    equal depth below surface datum/sea level.

    Isochore   In a reservoir a line joining points of equal

    vertical thickness.

    Isomers Compounds which have the same number and

    types of atoms in each molecule, but differ in molecular

    structure, e.g. Butane and iso-Butane, Octane and iso-

    Octane, etc

    Isopach A line joining points of equal stratum thickness.

    Reservoir formations are sometimes mapped in this way.


    Jacket   1. The leg-structure of an offshore steel-piled


    2. A concrete coating applied to add weight  to

    submarine pipelines. (See Cement). 

    Jacket platforms are generally constructed of tubular

    steel, and are kept in position over the oil field by the use

    of steel piles driven into the sea bed.

    Jack Rabbit                     A gauge which is run through casing or

    tubing before use to check for correct sizing and freedom

    from obstruction or distortion.

    Jack-up Drilling rigs, production barges, etc. which once

    floated onto location can raise themselves clear of the

    water by 'jacking' themselves up their legs. They then

    offer the operating advantages of fixed platforms but

    unlike piled steel structures, their stability and load

    capacity depends on the strength and stability of the sea

    bed, and closely underlying strata.

    Jars                   1. Down hole tools inserted in the drill-string when

    fishing to jerk or jar the fish free by repeated sudden

    blows. They may also be used while drilling to avoid the

    drill-string becoming stuck.

    1. Artificially made cavern storage in a salt rock formation.

    Joint A single length of pipe. Coupled or welded to other

    lengths, joints become a string. The term joint may also

    refer to the couplings or joints themselves.

    Joint Operating Agreement (JOA)                          The document

    governing operations in a Joint Venture, of prime

    importance to all participants as under it they secure, or

    may lose, rights to production etc. A typical Joint

    Operating Agreement will include sections to cover most

    or all of the following topics:

    - Scope, Duration, Legal status

    - Interests rights and duties of the Operator and other


    - Management structure and voting procedure

    - Approval of Operating Programmes and Budgets

    - Cash contributions, costs and accounting

    - Control and custody of joint properties and equipment

    - Sole Risk, Default, Withdrawal, Assignment, etc.

    - Disposal of Petroleum

    -                        Confidentiality, Force Majeure, Litigation, etc.

    Joint Venture A common form of risk-sharing in Oil and

    Gas operations, especially exploration and production.

    Although they may have many of the characteristics of

    partnerships and are often referred to as such, they are

    usually legally constituted specifically to avoid partnership

    implications. See also Joint Operating Agreement.


    Down hole tools inserted in the drill-string when fishing to

    jerk or jar the fish free by repeated sudden blows. They

    may also be used while drilling to avoid the drill-string

    becoming stuck.

    2. Artificially made cavern storage in a salt rock formation 

    Joule Unit of measurement. The work done when a force 

    of 1 newton is applied to an object, displacing it through a

    distance of 1 metre in the direction of force.

    JP Fuels                             Fuels produced to specifications for jet

    propulsion (aircraft) use.

    Jug 1. A geophone. A 'jug hustler' is the member of a

    land seismic survey crew who places and retrieves


    Junk 1. Any small unwanted object 'lost' down a well. 2.

    To discard or scrap unwanted equipment. 'Junk condition'

    tubulars, for instance, are no longer fit for their intended


    Junked      A well is cemented in and side-tracked, or

    abandoned, when attempts to retrieve equipment lost

    down hole fail.


    Kelly The 'Square Section' pipe at the top of a drill string

    (sometimes Hexagonal). Another name is the Grief Stem.

    It fits into the 'squared' hole in the rotary table, which in

    turning it imparts torque to the drill string.

    Kelly Cock    An emergency 'blowout preventer' valve

    inserted between the swivel and the kelly.

    Kelly Spinner A mechanism attached to the swivel for

    rotating the kelly in or out of the top joint of drill pipe,

    e.g. when adding another stand.

    Kelly Valve (lower) An automatic valve at the lower end

    of the kelly which closes when the kelly is disconnected

    from the drill-stem, preventing spillage of mud.

    Kerogens Organic material from which oil or gas matures

    with time, under burial temperatures and pressures. They

    differ with origin-e.g. marine seaweeds, or terrestrial

    trees. Of the marine types, the presence of Algal Sapropel

    and Waxy Sapropel in a formation is prospective for oil,

    while of the terrestrial types, Vitrinite is generally

    prospective for gas, and Inertinite is not prospective. In

    addition the degree of reflectivity of Vitrinite samples is

    used as an indication of the maturity of a formation for

    the presence of hydrocarbons.

    Kerosine (kerosene)     A medium-light oil from the oil

    refining process intermediate between gas oil and

    gasoline; used for lighting and heating and as fuel for jet

    and turbo-prop aircraft engines.

    Kick Off To start the planned deviation of a well from the

    vertical. The depth at which this occurs is the Kick-Off

    Point (KOP).

    Kill/Killer Well 1. In normal operations, to kill a flowing

    well is to inject mud, etc, to the density needed to

    overcome reservoir pressure, thus stopping the flow for

    e.g. maintenance or modification work.

    1. Getting under control a well which has 'blown out'. A

    Killer Well is one drilled near a blowout, and deviated into

    or close to the blowout well, to inject mud, etc. to kill it.

    This is usually because the blowout has caught fire.

    Kilocalorie A thousand calories. A unit of heat used in

    the chemical processing industry.

    Kilowatt hour (kWh)   Unit of measurement in electric

    power. One kilowatt hour is equivalent to 0.0949 cubic

    metres of gas. 

    Kitchen A colloquial term for rock deposited, in 

    conditions rich in organic sediments, which with the

    necessary burial history has become a significant source

    of hydrocarbons. These may have migrated to traps


    Knocking A metallic rattling sound in an engine caused

    by a mismatch between the fuel characteristics and the

    engine's design, particularly its compression ratio,

    resulting in pre-ignition (also known as 'pinking').

    Knock-Out Drum  A drum or other process vessel used

    for rapid separation of water, etc. from a stream of


    Knuckle Joint                         A universal joint in a drilling tool for

    deviated drilling which enables the bit to rotate at an

    angle to the existing borehole.


    Landing Casing Lowering a string of casing into a well,

    to rest on the 'step' in the hole where drilling at a smaller

    diameter commences.

    Lay Barge/Pipelay/Pipelay Barge/Lifting                          A vessel

    designed for welding together pipelines and laying them

    on the seabed. A Reel Barge lays previously connected

    lengths of pipe from a reel.

    Lean gas or dry gas                                Gas with relatively few

    hydrocarbons other than methane. The calorific value is

    typically around 1,000 Btu per scf, unless there is a

    significant proportion of non-hydrocarbon gases present.

    Lease                      In the oil and gas industry, a legal instrument

    giving the right to explore/exploit acreage, primarily

    onshore. 'Lease operations' has come to mean any

    exploration production field operation.

    Lens A body of potential reservoir rock enclosed on all

    sides by sealing strata, so-called because frequently lens-




    1. A right to explore for and/or produce 

      hydrocarbons issued by a Government agency, where

      rights to underlying minerals are not the property of the

      landowner. Exploration, drilling, development, etc. may be

      licensed separately, over varying lengths of time. Many

      licences require part-relinquishment of acreage after an

      initial period or "primaty term" and make the operations

      subject to the hydrocarbon policy of the country


      1. Various other forms of permit or authorisation affecting


      Licence block A section of continental shelf area

      bounded by latitude and longitude lines, generally at one

      degree intervals, and subdivided into smaller areas. The

      'licences' are sold to companies giving them oil exploration


      Licence round A period during which a state offers and

      then allocates a number of specified areas within its

      national boundaries to oil companies.

      Lifo The last-in-first-out method of inventory valuation,

      chiefly significant in the oil and gas industry because

      historically the basis of US Tax computations.

      Lifting 1. Collection of a production shipment of crude oil

      etc. at the point of sale. Also covers bulk movements of

      any hydrocarbon against, e.g. contract entitlements.

      1. Stimulating production flow from a well.

      Light Crude Generally applied to crude oil with an API

      gravity of 30 degrees or over. See American Petroleum


      Light Ends                     The least dense, more volatile parts of a

      crude oil stream in distillation.

      Lightening See Lightering.

      Lightering                    A ship-to-ship cargo transfer operation to

      enable a vessel to enter a draft-restricted port.

      Light fractions 

      The low molecular weight, low boiling point fractions that

      emerge from the upper part of the fractionating column

      during oil refining.

      Line Fill The volume of oil or gas which is needed to fill a

      pipeline before any deliveries can be made, representing a

      permanent inventory requirement.

      Line pack The ability to increase the amount of gas in a

      pipeline by increasing the pressure above the normal

      pressure of the system, but still within a safe limit. Used

      as a method of peak or diurnal storage.

      Liquified Natural Gas (LNG) Natural gas that for ease

      of transport has been liquefied by cooling to

      approximately minus 161øC at atmospheric pressure.

      Natural gas is 600 times more bulky than LNG. It is

      predominantly composed of methane.  It is held in a

      refrigerated liquid state under pressure for transportation

      and storage. Natural Gas is processed into LNG by first

      removing carbon dioxide, water and heavy hydrocarbons

      which would freeze (hydrate) at cryogenic temperatures.

      The purified natural gas is then chilled to minus 161

      degrees Celsius at which temperature it condenses into a

      liquid, 1/600th of its original gaseous volume. LNG is clear

      colourless and weighs about half as much as water.

      Lithology The study of rocks and hence the description

      of different formations encountered by a well.

      Live Oil  Crude oil containing volatile gases.

      Lloyds  Chiefly refers to the Certification authority.

      LNG carrier  A tanker specially designed to carry LNG, 

       fitted with insulated pressure tanks made of stainless steel 

      or aluminium. The load is refrigerated to -162°C. 

      LNG terminal  A receiving station for LNG shipments,

      typically with storage and regasification facilities.

      LNG train  An LNG plant comprises one or more LNG

      trains, each of which is an independent unit for gas

      liquefaction. It is more cost-effective to add a train to an

      existing LNG plant, than to build a new LNG facility

      (known as a greenfield project), because infrastructure,

      such as ship terminals, does not have to be built for a new

      LNG train  

      Local Drainage The movement of reservoir immediate

      vicinity of a flowing well.

      Location The site of a well, or other operation.

      Log/Logging etc     There are various applications, but

      chiefly: 1. Written chronological records such as shift logs,

      maintenance logs, tour sheets, and mud logs which also

      record cuttings recovered from a well. 2. Various devices

      for taking measurements of formations, physical

      conditions, and fluids encountered by a well, together with

      the records produced by them. The main types of well

      logs, are  Electrical, Magnetic, Mechanical, Sonic, Nuclear

      Lost Circulation Failure to recover to the surface all the

      drilling fluids at the same rate as they are pumped down a

      well, usually because of escapes into surrounding

      formations. Casing would normally be set through the

      relevant formation before proceeding.

      Liquified Petroleum Gas (LPG)is a light hydrocarbon

      which is gaseous at normal temperatures and pressures.

      LPG is composed mainly of propane and butane  or a

      mixture of the two which may be wholly or partially

      liquefied (as with LNG) under pressure in order to

      facilitate transport and storage. LPG can be used for

      cooking and heating or as an automotive fuel.

      Load factor        In gas contracts, the ratio of the Daily

      Contract Quantity and the maximum daily delivery


      Load-on-top A system of cleaning tanks in an oil tanker

      by collecting washings in one 'slop' tank, allowing the

      water to separate from the oil, then discharging the clean

      water overboard, leaving the oil residues in the tank and

      minimising pollution at sea.

      Logic Tree A framework useful in disaggregating an idea

      into manageable chunks and in focussing work on core

      issues only.

      Logs  See wireline logs.

      Loss Carry-Forward                     A fiscal arrangement whereby

      losses incurred in certain years are offset against profits

      made in later years.

      LTI (Lost Time Injury) A measure of safety performance.

      Luboil Lubricating oil used to grease and ease the

      working of mechanical joints and moving parts.


      Magma The molten material that makes up the Earth's

      crust. When extruded onto the Earth's surface and cooled

      it becomes igneous rock.

      Magnetic Particle Testing  A non-destructive testing

      method whereby the object is magnetised and minute

      particles applied externally. Cracks, etc. can be discerned

      at the surface. Welds in wellheads, etc. can safely be

      examined in situ.

      Magnetic survey A preliminary exploration technique

      based on the relatively low magnetic field of sedimentary

      rocks.  This measures variations in the earths magnetic

      field caused by the presence of rock structures and is

      used to detect sedimentary areas.  This type of survey is

      usually carried out by air.

      Majors The world's largest privately / publicly owned oil

      companies (Shell, Exxon, Texaco, Mobil, Chevron and BP).

      National oil companies can be much larger.

      Make Up / Break Out To assemble/screw together the

      sections of joints of a string of pipe. 'Breaking out' is the


      Manifold An assembly of pipework with several branches

      to gather fluids from, or distribute them to, different

      points. It usually incorporates valves so different flow

      patterns can be selected.

      Marginal A well, development, etc. whose commercial

      profitability is in doubt.

      Market Factor                          A factor in the cost escalator for a

      particular commodity, which recognises that it may

      escalate out of line with inflation due to market


      Marine riser A pipe that connects an offshore platform to

      a sub-sea wellhead or pipeline for drilling or production


      Master Bushing  The collar which fits into the rotary

      table and through which the kelly passes.

      Mat / Mattress                            A structure placed on poorly

      consolidated, soft or unstable seabed as a footing for

      jackup rigs, etc.

      Maturity The function of burial pressures, temperatures,

      and time which determines whether a source of

      hydrocarbons will provide oil or gas.




      Maximum Exposure The maximum cash deficit or the

      maximum amount of money at risk.

      Mean Success Volume (MSV) the weighted average of

      the possible hydrocarbon volumes as represented in the

      Expectation Curve (ibid) above the cut-off volume. The

      latter can be taken as zero, in which case the MSV is the

      weighted average of all technically possible volumes. If an

      economic cut-off volume is used (below which

      development is uneconomic) this results in a higher MSV

      and a lower POS. It is essential therefore to stipulate the

      cut-off used when quoting the MSV.

      MD is the linear distance of a well measured along its

      drilled projection.

      Median Line The boundary between the offshore mineral

      extraction jurisdictions of two states, by convention drawn

      equidistant from the nearest points of land on each side.

      Mercaptans    Strong-smelling compounds of carbon,

      hydrogen and sulphur found in gas and oil. Sometimes

      added to natural gas for safety reasons.

      Metamorphic rocks  Rocks changed considerably under

      the action of pressure, heat, and water has become dense

      and crystalline, e.g. slate, gneiss, marble, etc.

      Meter A mechanical device for automatically

      measuring and recording quantities of gas.

      Methane (CH4) The smallest hydrocarbon molecule with

      one carbon atom and four hydrogen atoms. It is the chief

      constituent of natural gas, but also occurs in coal beds,

      and is produced by animals and the decay of vegetable

      material. It is a light colourless, odourless flammable gas

      under normal conditions. Methane is the first member in

      the alkane (paraffin) series. At atmospheric pressure, it

      liquefies at -162°C.

      Methanol (methyl alcohol)     An alcohol used as a raw

      material in a wide range of industrial and chemical


      Migration 1. Hydrocarbons are often found in formations

      other than those in which their organic source was

      deposited. This movement often over considerable

      distances is known as migration.

      1. A process applied to data recorded, e.g. in a '2-J'

      seismic survey, to adjust for the effects of the "oblique"

      angle at which it was gathered.

      Mill  A bit for cutting through steel obstructions in a

      Well such as 'fish'.

      Milliard Synonymous with billion (109).

      Millidarcy See Darcy.

      Mill Scale  Oxides which form on the surface of a steel

      plate after heating during manufacture.

      Miscible Flooding An injection/displacement process

      developed recently to obtain greater oil recovery in many

      reservoirs. Miscibility is the ability of two or more

      substances to mix, without the existence of an interface.

      The fluids are injected together into a reservoir in a

      secondary or tertiary recovery programme e.g. Gas and

      LPG, or Carbon Dioxide followed by water.

      MJ/MMJ Megajoule; equivalent to one million watts.

      MMBBL Million barrels.

      MMBTU Million British thermal units.

      MMSCF Million standard cubic feet.

      MMSCF/D Million standard square feet per day.

      MOD (Money of the Day): This is the money we get paid

      in and spend. The same amount of MOD buys less and 

      less each year because of inflation. It is also the type of

      money used in tax calculations and in most financial plans

      or budgets.

      MOD inflator The number by which we divide the MOD

      cashflow of a given year to convert it to Real Terms. It is

      the ratio of the price of a “basket” of goods in that year to

      the price in the Reference Year.

      Modules A separate section or box-like compartment of

      the 'top side' of an offshore construction, as far as

      possible self-contained, designed to be lifted into place

      and connected to other modules offshore. Modern large

      capacity cranes have meant that modules can be fewer,

      larger, more efficient, and less costly to the project.

      are packages of equipment for installation on an offshore

      production platform.

      Molecular Sieve                     A process of separating hydrocarbon

      fractions etc. by passing the feedstock through successive

      absorbent substances which offer differing degrees of

      resistance to its passage.

      Molecule The smallest particle to which a compound can

      be reduced without losing its chemical identity.

      Monomer                   A single molecule which can be chemically

      joined into long chains known as polymers. Multinational

      company (MNC) A company with investments and

      operating activities in many countries around the world.

      Monopod A small offshore platform, resting on a single

      columnar 'leg', mainly for small satellite developments in

      shallow waters.

      Moonpool A 'well' in an offshore vessel, open beneath

      the surface of the sea at the lower end, through which

      depending on the vessel's function, the drill-string, risers,

      or divers etc. can be lowered in calm surface conditions

      independent of sea state.

      Motion Compensator                    A heave compensator. Fitted to

      cranes etc. to counteract vertical motion caused by the


      Motor Octane Number See Octane Rating

      Mousehole The tubular 'hole' in the floor of a drilling rig

      in which the next stand of drill pipe is stored ready for

      addition to the drill string.

      MSCF Thousand standard cubic feet.

      MTBE (Methyl Tertiary Butyl Ether) A hydrocarbon

      product significant as one of the major leadfree Octane

      enhancers for gasolines. See Anti Knock Compounds.

      Mud Is the name given to drilling fluid which is mainly a

      mixture of water, or oil distillate, and 'heavy' minerals

      such as Bentonite or Barites. Mud is pumped into a well at

      densities calculated to provide a hydrostatic pressure

      sufficient to overcome downhole formation pressures.

      (See e.g. Gas Kick). In addition, the mud is continuously

      circulated down to the bit, and returns in the annular

      space outside the drill-string, bringing with it rock cuttings

      for inspection and keeping the well clean. It is also

      engineered to maintain a thin protective layer of filter-

      cake on the bore hole wall, without excessive weight

      which would decrease the weight on the bit and hence

      penetration (see Drill String), and also possibly lead to

      differential sticking and formation damage. Mud is

      pumped from the mud pit (or tank) via the standpipe,

      rotary hose and gooseneck to the swivel, and into the drill

      stem. On return from down hole it is recovered and rock

      cuttings removed by the shale shakers before re-

      circulation. To Mud Up is to increase mud weight and

      downhole pressure. To Mud Off is to seal off a formation

      with heavy filter cake. A Mud Log is the record of mud




      make-up and analysis of cuttings recovered. The

      composition of mud used in a well is normally supervised

      by a Mud Engineer.

      Mudline The sea bed, or bed of any body of water where

      drilling is taking place.

      Mud logging  This is the recording of information derived

      from examination and analysis of formation cuttings made

      by  the bit and mud circulated out of the hole.  A portion

      of the mud is diverted through a gas-detecting device and

      examined under ultraviolet light to detect the presence of

      oil or gas.

      Mullett An inexperienced investor in oil exploration.

      Multiphase Flow Simultaneous flow of liquid and gas, or

      of different liquids, through a pipeline or other vessel (e.g.

      oil/gas, gas/water, oil/water).

      Multiple Completion   A well perforated and completed

      to produce simultaneously but independently from more

      than one formation. Also known as a Multipay Well.


      NAFTA  (North American Free Trade Agreement): its

      members currently comprise Canada, Mexico and the

      United States.

      Naphtha     is a volatile, flammable liquid hydrocarbon

      distilled from petroleum and used as a solvent or fuel.

      Native gas is gas originally discovered in a reservoir as

      distinct from injected gas. See also Associated Gas.

      Natural Depletion is producing a reservoir by means of

      its natural press u re-without pressure maintenance. (Also

      Flush Phase, Primary Production, etc.)

      Natural gas    is a gaseous mixture of light hydrocarbons

      comprising predominantly of methane.  It is often found

      with crude oil, when it is known as associated gas. a) A

      mixture of generally gaseous hydrocarbons occurring

      naturally in underground structures. Natural gas consists

      mainly of methane (80%) and significant proportions of

      ethane, propane and butane. There will always be some

      condensate and/or oil associated with the gas. b) The

      term is also used to mean treated gas which is supplied to

      industrial, commercial and domestic users and meeting a

      specified quality.

      Natural gas liquids (NGL)  Light hydrocarbon fractions

      distilled from wet gas streams, usually spiked into crude

      lines for transportation purposes.

      Natural Period is the time that elapses between

      successive occurrences of any phenomenon, such as two

      successive wave-crests or the resulting movements of

      heave, roll, etc. of a floating vessel.

      Neoprene  A mixture of natural and petroleum-based

      synthetic rubber highly resistant to chemical attack.

      Netback  The value of gas sold to the customer at the

      burner-tip, less the cost of transportation through the

      pipeline system and cost of production.

      Net Present Value (NPV)A financial technique which

      estimates the value creation of a project by estimating

      expected cash flows and then discounting these future

      free cash flows at the appropriate risk - adjusted

      opportunity cost of capital. NPVs of different projects are


      Net Profits Interest  A low-risk form of participation in

      which the beneficiary, who is usually 'farming out' his

      interest, makes no further contribution to the cost of

      operations but is entitled to a share of any net profit on

      production revenues after deduction of all costs, including

      in some cases, interest.

      Net Revenue Interest                           Another form of net profits

      interest but normally without deduction of capital costs or

      financial charges.

      Neutron Log  See Log.

      Nipple etc.  A short length of pipe with connections at

      both ends. To Nipple Up is to assemble pipe valves etc.

      especially a blowout preventer. A Nipple Chaser is a

      materials man whose job it is to obtain and have ready for

      shipment to the rig the various tools, supplies, etc.


      Nodding Donkey  The colloquial name for conventional

      onshore wellhead production beam pumps.

      Node The specially strengthened junction of tubular

      components in a conventional steel platform jacket. There

      are several on each leg and also at the meeting of cross-


      Non-associated Sometimes called unassociated gas. Dry

      gas that is not associated with oil in a productive

      reservoir, or where only gas can be produced


      Non Destructive Testing (NDT)  Methods of inspecting

      and testing the quality or integrity of vessels or equipment

      which do not involve removal or testing to destruction of

      representative sections.

      Non-Operator  Any equity participant in a Joint Venture

      operation other than the Operator.

      Non Recourse Financing  Lending to a participant in a

      development project on the security provided by the

      development revenues and assets alone. Sometimes the

      financing covers participations in several development

      projects, which provide mutual security but without

      further recourse to the borrower.

      Nuclear Interface Log  A 'gamma-ray' log. See Log.

      NOx Nitrogen oxides.


      OPEC                     Organization of Arab Petroleum Exporting


      Obligation Well  A well undertaken as part of the

      process of earning a concession.

      Obo Vessel  An Oil/Bulk Ore carrier, a versatile form of


      Observation well  This is a special well drilled to allow

      observation of fluid levels, changes in pressure etc., within

      the reservoir as production proceeds.

      Octane number                     A measure of the resistance to pre-

      ignition (which leads to knocking) of a gasoline.

      Odorant                     Substance such as mercaptan with a

      characteristic smell, added to odourless natural gas or

      NGLs when they are used as s fuel, in order to enable





      OECD  Organisation for Economic Cooperation and

      Development, based in Paris.

      Ofgas Office of Gas Supply, the UK gas industry


      Off-peak The period during a day, week, month or year

      when the load being delivered by a gas system is not at

      its maximum volume.

      Offset Well  A well drilled to 'mirror' a production well

      drilled near the boundary of a neighbouring concession,

      on a common reservoir, in order to secure a due share of


      Offsite Facilities (Offsite)  Ancillary or service plant

      which is distant from the main process plant. (e.g. Water

      treatment, power generation, laboratory etc.)

      It is sometimes applied to service installations in general,

      particularly at refineries.

      Offshore Installation Manager (O.I.M.)  The person

      on an offshore platform with statutory responsibilities for

      safety, etc., similar to those of a ship's captain.

      Offtake The point in a gas distribution system where gas

      is taken by supply pipe to a major consumer.

      Oil-Based Mud  Drilling mud in which the solids are

      suspended in a hydrocarbon distillate rather than water.

      This has operational advantages particularly in deeper or

      technically difficult wells, but can make the detection of

      formation hydrocarbons more difficult.

      Oil Column/Gas Column The vertical distance between

      points of highest and lowest known oil or gas. in a


      Oiler An oil well, particularly an oil discovery well.

      Oil Field  1.  A group of hydrocarbon reservoirs in a

      common geological setting.

      1. A single reservoir, the subject of actual or planned


      Oil gasification The conversion of petroleum into gas to

      be used as a fuel

      Oil Geology  Specialised geology which deals exclusively

      with sedimentary basins and the sources of hydrocarbons.

      Oil in place (OIP) The estimation of the real amount of

      oil in a reservoir, and so a higher figure than the

      recoverable reserves of the reservoir (see recoverable

      reserves and recovery factor).

      Oil Patch  A colloquial reference to exploration and

      production activity.

      Oil Province  See Petroleum Province.

      Oil shale A compact sedimentary rock impregnated with

      organic materials (mainly kerogen) which yields oil when



      Oil Spill  Any accidental emission of liquid hydrocarbons,

      from general shipping, oil tankers, or operations onshore

      or offshore.

      Oil String  The inner or production string of casing in a


      Oil/water contact (OWC)       The lower end of the oil

      column in a reservoir with underlying water.  This may be

      graduated or occur in formations where it is hard to


      Olefins A class of hydrocarbons, including ethylene and

      propylene, of particular importance as feedstock to the

      chemical industry. See also: polypropylene. 

      On-Line 1.  Any vessel or equipment which is a normal

      and permanent part of the operation (e.g. an online


      1. 'On Line' can also mean in working order, serviceable.

      On Stream  When production is flowing, or plant is in


      On The Brake  In control on the rig floor, e.g. the driller.

      On the brake refers to the control of weight-on-the-bit

      etc. (See Drill String)

      OPEC                  Organisation of Petroleum Exporting Countries.

      Formed in 1960, its member countries are Algeria,

      Ecuador, Gabon, Indonesia, Iran, Iraq, Kuwait, Libya,

      Nigeria, Qatar, Saudi Arabia, United Arab Emirates and


      Open Flow Producing a well without chokes or beans.

      Unrestricted              production  normally  for   testing  or

      maintenance purposes.

      Open Hole  An uncased section of well borehole.

      Operating Interest An equity interest in concession,

      which pays an appropriate share of the costs and receives

      an equivalent share of residual income after prior charges

      such as royalties.

      Operator A company, organisation or person with the

      legal authority to drill wells and extract hydrocarbons. A

      drilling contractor may be employed to undertake the

      drilling itself. The operator is often part of a consortium,

      and acts on its behalf.

      OPOL (Offshore Pollution Liability Agreement) An industry

      co-operative insurance and self-insurance scheme

      between operators in the European continental shelf and

      adjacent coastal areas covering costs of major pollution

      clean up.

      Opportunity Focal Point (OFP)                             Responsible for


      Option Value                    A way of valuing a project's addition to

      flexibility in decision making that is not caught by strict

      NPV analysis. Types of flexibility to be valued include the

      option to defer an investment, to expand (or contract) the

      scale of a project, to abandon a project, or to start up and

      shutdown an ongoing operation. Asset options are

      especially valuable in valuing businesses that develop and

      extract natural resources.

      Organic/Organic Chemicals  Substances derived from

      living organisms, such as oil in the natural state.

      Orifice Meter  An instrument which measures the flow of

      a fluid in a pipeline by monitoring a controlled flow

      through a small aperture.

      0-Ring  A ring shaped gasket for flanged pipe joints.

      Orogeny  The process of shrinking, cooling and

      'wrinkling' of the earth's crust, leading to the formation of

      mountains, synclines, anticlines etc.

      Outcrop  The appearance of occurrence of a rock

      formation at the surface

      Overheads  1. The 'light ends' produced from the top of a

      distillation vessel.  2.  Standing expenses not related to, or

      variable with, specific operations.

      Overlift  Collecting more crude oil etc. than a production

      participant or purchaser is entitled to at any one time. See

      also Underlift

      Overriding Royalty  A royalty payment from production

      revenues before any deduction for costs, taxes, etc.

      Overshot  A fishing tool with a socket to fit over, enclose,

      and grip the top end of the fish for pulling out. 

      Packer  A seal used to isolate a section of a well, e.g. for

      testing or production from one of several formations.

      Packers are also used in operations such as cementing

      and acidizing.

      Palaeontology  The study of fossil organisms related to

      their geological setting.

      Palynology  The study of pollens and plant spores.

      Identification of fossilised forms of these in a geological

      formation can help determine the environmental origin of

      sedimentary rock, and periods of exposure as land rather

      than sea bed.

      Paraffin UK name for a premium kerosine; used in lamps

      and space heaters.

      Participation  This usually refers to rights retained by a

      state when granting a concession, primarily to acquire

      part of the production at stated terms, but sometimes also

      to participate on a full equity basis in any production


      Pay-As-You-Go Date The date the project starts to pay

      its own way.

      Pay Out  When accumulated revenue from an operation

      equals the accumulated cost to date including investment

      cost.  This is normally expressed as a period of years from

      starting to earn revenue.

      Pay Out Time The time that the original investment has

      just been recovered.

      Pay Sand is the producing formation, often one that is

      not actually sandstone.  It is also called pay, pay zone,

      and producing zone.

      Pay String The production or inner string of casing.

      Pay Zone/Horizon A formation containing producible


      Peak load The maximum load produced or consumed by

      a unit in a stated period of time.

      Peak lopping See peak shaving.

      Peak shaving Increasing the normal supply of gas from

      another source during emergency or peak periods.

      Perforate     is to pierce the casing wall and cement to

      provide holes through which formation fluids may enter or

      to provide holes in the casing so that materials may be

      introduced into the annulus between the casing and the

      wall of the borehole.  Perforating is accomplished by

      lowering into the well a  Perforating Gun(cylindrical

      tool) loaded with explosive charges which are triggered

      opposite the pay zone, perforating the casing in many


      Permeability    is the degree to which a rock will allow

      liquid or gas to pass through it.  It is a function of the

      shape of the capillary pore spaces and the degree to

      which pores are connected.

      Petrochemical    A chemical derived from petroleum or

      natural gas (e.g. benzene, ethylene).

      Petrol See Gasoline.

      Petroleum The general name for hydrocarbons, including

      crude oil, natural gas and NGLs. The name is derived from

      the Latin oil, oleum, which occurs naturally in rocks, 

      Petroleum Engineer A specialist in the properties and

      behaviour of hydrocarbons in their natural reservoirs and

      under production conditions.  While a geologist normally

      provides estimates of hydrocarbons-in-place, a petroleum

      engineer would normally provide the estimate as to how

      much of it could be produced (recoverable reserves)

      under what conditions, and at what rate.

      Petroleum Province A large area where reservoirs show

      common origins and characteristics.

      Petrology The study of rocks, their origin, chemical an

      physical properties and distribution.

      PH  A scale of alkalinity or acidity running from 0 to 14,

      with 7 representing neutrality, 0 maximum acidity and 14

      maximum alkalinity.

      Pig etc  Bullet-shaped, cylindrical or spherical capsules

      which are inserted into a pipeline flow and travel along it

      with the fluid.  Their primary purpose is to scrape the

      pipeline clean of rust, wax or other deposits, or in a gas

      pipeline, slugs of liquid from low points in the line.

      Caliper Pigs also measure the pipeline as they travel,

      and ‘smart’ or ‘intelligent’ pips contain various instruments

      to monitor pipeline condition and integrity.                     Pig

      Launchers                    and Pig Traps    are the arrangements of

      valves etc through which pigs are inserted into and

      extracted from a line.

      Piling refers to the steel ÒpinsÓ which are driven through

      specially designed slots on a jacket platform, and into the

      sea bed, often down to a depth of 150 feet (45 metres) or


      Pillow Tanks Collapsible synthetic rubber/fabric storage

      tanks which can be easily transported and deployed in eg

      military operations or difficult terrain.

      Pin                       1.  See Piling  2. The ‘male’ end in a threaded


      Pinch-Out The thinning out and disappearance over a

      distance of a formation eg an oil bearing sandstone

      between layers of impermeable rock.

      Pinch-out trap  See stratigraphic traps. 

      Pinger                         A source of sounce (eg an ‘air gun’) for an 

      underwater seismic survey.

      Pinking See Knocking.

      Pipe Clamp In drilling, a collar fitted to a string of pipe to

      stop it dropping if the slips fail to hold it.

      Pipe Facing Machine                         A machine for cleaning and

      preparing the butt ends of pipe joints for welding.

      Pipeline A tube for the transportation of crude oil or

      natural gas between two points, either offshore or


      Pipeline capacity                     The amount of oil or gas required to

      keep a pipeline full, or the amount that can be passed

      through a pipeline over a given period of time.

      Pipe Rack   Where stands of drill pipe are stacked

      vertically in a derrick ready for use.  Racks or frames are

      also sometimes used to store tubulars horizontally in yards

      and on offshore decks, and when transporting them


      Pipe Ramp  A sloping ramp from the pipe storage area

      up to the working floor of a drilling rig.

      Pipe Rams  Hydraulic rams in a blowout preventer which

      are shaped to fit around the drill-stem and seal the

      annulus.                 Blind Rams          are designed in extreme

      emergency to shear through the drill pipe and seal the

      well completely. 

      PLAT An official concession map in the USA – hence any

      official concession map.


      A fixed for floating offshore structure from which wells are

      drilled. Drilling platforms can become production platforms

      once the wells are producing oil.

      Platform equipment refers to all the equipment on a

      production platform.  The equipment includes such items

      as: module shells; accommodation areas; helicopter

      decks; water and gas separators; scrubbers; pumps;

      compressors; boilers; heating; ventilating and burning

      equipment; sewage   treatment  plants;   electrical;

      communication; navigational; fire-fighting and safety

      systems; well-head and hydraulic shut-down systems;

      cranes and flare stack.

      Platforming  A catalytic reforming process using a

      platinum catalyst.

      Plenum  An enclosure such as a control room where for

      safety reasons, the air pressure is kept higher than

      outside, to prevent infiltration by inflammable or

      poisonous gases.

      Plugging and abandoning a well (P&A)            On the

      completion of a well which is not to be immediately re-

      entered the operator will P&A, which is seal the well or

      part of with cement.

      Pogo Plan         A financing arrangement for high cost

      exploration. The investors usually take stock etc in a

      company set up for the purpose.

      Polycyclic Hydrocarbons  Hydrocarbons whose carbon

      atoms from a ring or rings eg Cyclohexane.

      Polyethylene A polymer formed by the joining of

      ethylene molecules; one of the most important plastics.

      Polymer     Two or more molecules of the same kind,

      combined to form a compound with different physical

      properties eg Polyethylene.

      Polypropylene A polymer formed by joining propylene

      molecules. See also: olefins.



      1.  A flat-bottomed vessel (“barge”) for

      transporting structures etc to an offshore installation site

      1. A submerged or semi-submerged part of a floating

      drilling rig structure designed to assist flotation, containing

      ballast tanks.

      Pool  1.  An Oil Pool is a reservoir or group of reservoirs

      sharing a common pressure system  2. In a refinery or

      blending plant, the Gasoline Pool is the average Octane

      value of the gasolines produced/available.

      Pop Up Buoy/Recall Buoy A buoy which is normally

      submerged but will surface in response to an acoustic

      signal.  Often used to mark the position of wellheads.

      (Also, colloquially, “Yoo hoo” buoy)

      Porosity          is the proportion of a rocks total volume

      occupied by voids between the mineral grains.

      Possible reserves An estimate of possible oil and/or gas

      reserves based on geological and engineering data from

      undrilled or untested areas.

      Posted Price      Official price of a type of crude oil for

      export from some producing countries.  Historically, they

      were the basis of tax assessment rather than the price

      actually paid.

      Post Implementation Review (PIR)            To compare

      implementation results against budget/plan, and to draw

      out and document lessons learnt. 

      Potentially Commercially Recoverable Reserves

      Reserves which can be commercially developed under not

      too high oil price scenarios. For this purpose it may be

      considered that Unit Technical Costs associated with

      developing the discovery should not exceed the current

      reference PSV.

      Pour point The temperature below which an oil tends to

      solidify and will no longer flow freely.

      Pour Point Depressant (PPD)Chemical compounds

      added to very viscous or waxy oil to prevent it thickening

      at low temperatures to the point where it will not flow.

      PPM Parts per million.

      Prairie-Dog Plant A small, basic distillation plant for use

      in remote production areas to extract locally needed fuels

      from the crude oil.

      Present Value (PV) The PV of an amount to be received

      at a specified future date is the amount of money we

      would need now which, after adding interest annually until

      the future date, would grow to equal the amount to be


      Pressure                    The force exerted by one body on another,

      either by weight (gravity) or by the use of power.

      Measured as force over area, such as newtons per cubic


      Pressure Bomb A down hole pressure recording capsule

      used in well monitoring.

      Pressure Habitat A sealed chamber in which divers can

      rest between shifts without decompression.

      Pressure Maintenance The process of keeping reservoir

      pressure at the optimum level during production, normally

      by water or gas injection to replace fluids extracted.

      Pressure Vessel A tank or process chamber built to hold

      fluids under pressure whether for production, refining or

      other purposes.

      Primary migration  Nearly all sedimentary rocks contact

      a small percentage of organic materials from which the

      petroleum could be formed.  As pressure from overlying

      layers compacts these source rocks, the oil or gas

      droplets are squeezed out and joined together to form

      globules large enough to flow under pressure.

      Primary recovery occurs when the oil is produced as a

      result of natural reservoir pressure. See also: secondary

      and tertiary recovery.

      Primary Refinery Process The distillation of crude oil

      into its major components for further processing or sale ie

      LPGs and gases, naphtha, middle distillates, residual fuel


      Primary Team                             The initial period of an oil or gas

      concession, during which, if the operator’s obligations are

      fulfilled, rights to a second term, often over a reduced

      area, can be acquired.  See also Relinquishment.

      Probable reserves                        An estimate of oil and/or gas

      reserves based on penetrated structures, but needing

      more advanced confirmation to be classified as proven


      Producer Price Index                               The price index number

      applicable to wholesale prices

      Production1.  The full scale extraction of hydrocarbon

      reserves               (also   the    reserves   extracted)      2.

      Refinery/petrochemical operations resulting in a yield of


      Production Casing String  The innermost steel lining of

      a well cemented in place and perforated for production in




      the pay zone. Note that production tubing is inserted

      inside this casing.

      Production Payment Loan  A loan repayable out of

      production from a well o r field.

      Production Plateau  The period during which a field is

      capable of producing at or near its maximum average


      Production Platform/Facility  Production platforms are

      of varying types depending on environment (water depth

      etc. and reservoir needs). Semi-submersible and ship-

      shaped vessels developed from the respective off-shore

      drilling rig concepts are also used as production facilities.

      where several inter-dependent platforms are clustered in a

      development they are known as a Production Complex.

      Production Testing  A production test concerns the

      capability to produce (productivity) of a well and its

      effects on the reservoir produced. A production test may

      continue for several months where extensive data is

      necessary prior to final commitment to development

      expenditures etc.

      Production Tubing String  The string of pipe installed

      inside the cased production well, to a point just above the

      reservoir through which the fluids are produced. It may be

      2" to T' diameter or more, depending on the production

      flow and pressures anticipated.

      Production Well/Producer  A development well

      specifically for the extraction of reservoir fluids.

      Production Wellhead and Tree  The assembly of

      casing head, tubing head, connections and well-control

      valves fitted to a producing well. The "Christmas Tree" is

      the name given to the complete assembly of valves,

      connecting flanges etc.

      Productive Horizon  A pay zone. See also Horizon.

      Productivity Index The continuous productive capacity

      of a well. The Index is measured as volume produced

      (e.g. barrels per day) divided by the drop in pressure

      (p.s.i.) to achieve that flow rate starting with a "shut in"


      Profiling  Shallow seismic surveying by echo-sounder


      Project finance    A method of financing in which the

      lender has a claim to receive loan repayments only out of

      the revenues earned by the project he helped finance. In

      this type of finance, the lender has no recourse to the

      borrower's other assets.

      Project Screening Value (PSV) the reference value of

      a standard crude (eg Dubai) as advised from time to time,

      and used for the economics screening in project


      Propane (C3H8 or C3) A hydrocarbon, small quantities

      of which are found in natural gas, consisting of three

      carbon atoms and eight hydrogen atoms; a gas under

      normal conditions. Used as automotive fuel and for

      cooking and heating purposes. At atmospheric pressure,

      propane liquefies at -42°C. See also: LPG.

      Proppants     Sand, gravel or other particles or “beads”

      used in hydraulic fracturing of a formation, to allow oil to

      flow more freely by wedging into the cracks etc created

      and preventing them re-closing.

      Proprietary Data      Primarily data obtained from the

      owner of a seismic survey record under confidentiality

      undertaking.  It can also include all confidential

      information acquired as part of sole or joint operations. 

      Prorationing                          Restriction of production in a multi-

      concession system in proportion to field capacities and

      ownership interests.   This may be by government

      regulation or due to a period of under-capacity or eg

      maintenance in a pipeline system.

      Propylene (propene)  An olefin consisting of a short

      chain of three carbon atoms and six hydrogen atoms; a

      very important base chemical for the chemical and plastics


      Proven reserves                     The quantity of oil and gas estimated

      to be recoverable from known fields under existing

      economic and operating conditions.

      PTD  Prognosed or predicted total depth of a well.

      Pull-in  Winching the end of a subsea pipeline or flowline

      into a connecting chamber or wellhead, or through a “J”

      tube riser guide to the platform deck.

      Pulling Casing Retrieving casing from a well (where

      possible) before abandonment.

      Pulling Out Retrieving and stacking the drill-string on

      reaching target depth.

      Pup Joint A joint of a pipe of non-standard length, to

      make up a string of tubulars to an exact required total


      Purging                    Cleaning the interior of pipes and vessels to

      eliminate inflammable matter, usually with a “safe” gas

      such as nitrogen.

      PVT Pressure/Volume/Temperature data usually related

      to a test of a reservoir formation or well.

      Pyramid Statement A communications tool to ensure a

      well supported and structured case is presented which

      follows a Recommendations - Synthesis - Analysis - Data



      Quadrillion                            In the oil and gas industry, the U.S.

      definition is used, e.g. 1015            not 1024 as internationally


      Quiet Rig                          A drilling rig insulated and equipped to

      operate with minimum disturbance of sensitive onshore

      environments such as built-up areas.




      A document giving up an interest in a


      concession or lease.

      Q Unit                      A unit used in overall assessment of energy

      resources. It is equal to 1T1 British Thermal Units (BTU).


      Rabbit  A small pig for flowlines.

      Racking Board  See Tubing Board.

      Radioactive Log  See Log

      Ram  See Pipe Rams

      Rathole  A hole in the drilling floor in which the kelly joint

      is kept when not in use. 

      Raw natural gas Natural gas containing impurities and

      unwanted substances such as; water, nitrogen, carbon

      dioxide, hydrogen sulphide gas and helium. Before the gas

      is marketed, these are removed.

      Real Terms (RT) Money RT money is simply a tool that

      we use in economics. It is imaginary money that retains

      its buying power over time. In today's RT money, $5

      would buy a decent hamburger, it will also buy a decent

      hamburger in 10 years time providing that the demand

      has not been distorted by a shortage of beef cattle or a

      change in eating habits.

      Real Terms Earning Power (RTEP)The discount rate

      of a project at which its NPV is zero. If the RTEP exceeds

      a project's cost of capital the NPV is positive; if the RTEP

      is less than the discount rate the NPV is negative.

      Reamer  A bit designed to enlarge a borehole.  It may be

      included in the drill string just above a conventional bit.

      Recall Buoy  See Pop-Up Buoy

      Recycling (Gas)      Re-injection of produced gas into a

      gas/condensate reservoir to maintain pressure for

      optimum recovery of condensates.

      Recovery factor is the ratio of the recoverable oil and/or

      gas reserves to the oil and/or gas in place in a reservoir.

      Recoverable reserves     Of the total oil in place only a

      proportion can be ultimately recovered, the amount being

      dependent on the permeability of the rock, the properties

      of the oil and the type of natural drive available.  At the

      extremes between 10% and 80% of the original oil in

      place can be recovered in primary phase, but the norm is

      20-30%.  Thereafter, depending on the success of

      secondary recovery techniques the figure can be further

      improved upon, but the final figure for recoverable

      reserves will only be known once the field is in production.

      While this often results in an upgrading of the estimated

      recoverable reserves, there are many instances when the

      reverse has been true.

      Reef  A reservoir, usually limestone, deposited in marine

      conditions.  As the name implies, it is frequently

      elongated, and early high production may not be

      sustained without pressure support.

      Reef effect The increase in marine life on and around an

      offshore structure.

      Reel Barge    A vessel for laying underwater pipelines

      form a rotating drum large enough to hold a continuous

      length of pre-welded pipeline.

      Re Entry  Inserting the drilling, testing or logging string

      etc into the wellhead. 

      Reference Year As far as inflation is concerned this is

      the year on which the Real Terms money is based. RT

      money maintains the purchasing power that money has at

      the middle of the Reference Year. It is common to choose

      the year in which the Reference Date for PV calculations

      falls. If this is done, the “base” dates for inflation and for

      Present Value coincide.

      Refinery   A complex of facilities where crude oil is

      separated into light or heavy fractions, which are then

      converted into useable products or feedstocks.

      Reforming   A process which improves the anti-knock

      quality of gasoline fractions by modifying the molecular

      structure. When achieved by heat and pressure the

      process is known as thermal reforming, and as catalytic

      reforming when aided by a catalyst. See also: Knocking.

      Reid Vapour Pressure (RVP) A standard oil industry

      measure of vapour pressure in psi at 100°F (38°C).                                                                                                           Relief Well  A second well deviated from a safe distance 

      to a bottom-hole location close to a “blowout” well and

      produced so as to reduce the pressure in the blowout.

      See also Killer Well.

      Relinquishment  It is a common feature of government

      concessions or licences that at the end of the primary

      term a proportion, commonly half, of the area concerned

      must be released by the licensee (relinquished).  This

      encourages early exploration activity to identify the most

      highly prospective parts of the concession.

      Renewable                       energy     Energy  resources  that   are

      continually available or can be replenished (e.g. solar,

      wind, wave, biomass, hydroelectric, geothermal).

      Reserves                      See; proven reserves, probable reserves,

      possible reserves and recoverable reserves.

      Reserves-to-production ratio For any given well, field

      or country. The length of time that reserves would last if

      production continued at its current rate, at the current


      Reservoir  A porous, fractured or cavitied rock formation

      with a geological seal forming a trap for producible

      hydrocarbons.  A common exploration maxim is that a

      prospective target must possess a related source rock,

      structure and seal.

      Reservoir Engineer  A Petroleum Engineer specialising

      in the behaviour or potential behaviour of reservoirs and

      their fluids under production conditions.

      Reservoir Pressure  The pressure at reservoir depth in a

      shut-in well.

      Residual Oil  The dense, viscous "Heavy Ends" of the

      barrel, remaining after extraction of higher-value


      Retrograde Condensation  In some reservoirs mainly

      deep gas/condensate reservoirs, (gas/oil ratio between

      5,000 and 100,000 cu. ft. per barrel) where temperatures

      and pressures are high, a progressive decrease in

      reservoir pressure as result of production will gradually

      lead to separation of liquids (heavier molecules) from

      natural gases in the reservoirs. These liquids are mainly

      lost to production, being by passed" by the more mobile

      gas. "Recycling", reinjection of produced gas to maintain

      pressure, is used to postpone this problem until an

      acceptable proportion of recoverable liquids has been


      Reworking a Well  Maintenance work on a well to

      stimulate production. This may involve cleaning out silt

      deposits etc., or stimulation techniques such as fracturing

      or acidizing.

      Rig  A collective term to describe the permanent

      equipment needed for drilling a well. It has come to

      include the onshore and offshore vehicles, mobile

      platforms, or vessels on which the equipment is installed.

      Rig Manager  Also Rig Superintendent, Rig Boss. The

      senior individual onsite in a drilling operation. He may also

      be an Offshore Installation Manager.

      Ring Fence  A fiscal segregation of revenues and profits

      from oil and gas production to prevent costs and losses

      from other corporate activities being offset against them,

      and production tax revenues "lost" thereby.

      Riser  A pipe through which fluids flow upwards, as from

      a subsea wellhead or gathering pipeline to the deck of a

      platform. Risers may be rigid or flexible (the latter more

      common for floating production facilities).

      Roller Bit  A rotary drilling bit which penetrates by

      pulverising the rock with its toothed wheels.

      Rotary Bit  See Bit.

      Rotary Hose  The mud supply hose from the standpipe

      to the swivel.

      Rotary Table  The heavy turntable at the centre of a

      drilling rig floor, which is rotated by the main rig power

      supply, and in turn rotates the kelly.

      Roughneck  See Drilling Crew.

      Round Trip  Recovering the drill string from the bottom

      of the well to the surface and returning it to continue

      drilling. This may be e.g. to replace the bit "Tripping" is

      arduous and interrupts "making hole".

      Roustabout  See Drilling Crew.

      Royalty/Royalty Oil  Royalties are payable on

      operations which are subject to prior rights of other

      parties, such as land owners of production leases, patent

      proprietors of refinery processes, etc.  Royalty Oil is taken

      by those to whom royalties are due 1n kind" in place of

      cash payment.

      Running-In/Running Casing  Inserting any tubular or

      tool into a well is known as "running-in". Assembling and

      lowering in a string of casing is "running casing".


      Sack   Cement, mud chemicals and other solids used in

      drilling are supplied to the rig and measured into the well

      in Sacks (SAX).

      Sacrificial Anode     In a cathodic protection system, a

      block or bar of non-ferrous metal attached to the

      submerged part of a steel structure is gradually eroded in

      prevention of structural corrosion.

      Safety Boat  A small vessel, employed to remain in the

      vicinity of an offshore installation for emergencies such as

      “man overboard”.

      Sales gas     Raw gas, after processing to remove LPG,

      condensate and carbon dioxide. Sales gas consists of

      methane and ethane.

      Salt Dome  See Salt traps

      Salt traps   results from the intrusion of salt rocks into

      overlying sediments.  This intrusion often takes the form

      of cylindrical, steeply conical or mushroom-shaped masses

      of rock.  Porous formations if present are truncated and

      effectively sealed by the salt plug.  The salt plug, where it

      fails to penetrate upwards, can still have the effect of

      causing sedimentary folding, which could result in

      anticlinal traps.

      Sandstone is a detrital, sedimentary rock composed of

      individual grains of sand (commonly quartz) that are

      cemented together by silica, calcium carbonate, iron

      oxide, and so forth.  Sandstone is a common rock in which

      petroleum and water accumulate.

      Sapropel  See Kerogen

      Satellite Development/Platform/Well  An installation

      dependent on the existence and services of a gathering

      platform/facility.  They are usually relatively small but

      profitable because of the lower capital investment

      required per barrel of reserves.

      Satellite Navigation/Communications

      Communications satellites are now extensively used to

      “fix” or locate positions offshore to the accuracy necessary

      for oil and gas operations.

      Saturated Hydrocarbons                         Hydrocarbon molecules

      which cannot absorb any more hydrogen atoms without

      subdividing to release carbon valencies for further


      Saturated Oil  See Saturated Hydrocarbons, Fat Oil etc.

      Saturation Diving                    Diving performed over long periods

      at high submerged pressures.  Instead of depressurising

      after each shift, the diver lives in a pressure chamber

      either below the surface or hoisted onto the diving

      support vessel.  See also Decompression Chamber.

      SBM (Single Buoy Mooring) Also known as single point

      mooring (SPM), this consists of a single floating chamber

      moored near an offshore production platform to serve as

      a connection to a tanker. It has no storage capacity. See

      also: FSU (Floating Storage Unit).

      SCF standard cubic feet.

      Scouring  The process by which tides and currents carry

      away loose sedimentation etc from around a fixed object

      on the seabed such as a platform leg or pipeline.

      Scout  A person employed to glean information on results

      of seismic surveys and wells in an area.

      Scraper  A device for cleaning the inside of casing in a

      well, or as with a Scraper Pig, the inside of a pipeline.

      Scratchers                         Collars with wire “bristles” fitted to the

      outside of casing to remove filter-cake from the well bore

      and help ensure a good cement bond.

      Screen  A tubular “sieve” inserted into a well bore to hold

      back loose sand and rock, while letting oil and gas enter

      the well.

      Scrubber A separator for removing liquids and solids

      from a gas stream.

      Scrubbing                   The process of purifying a gas or liquid by

      washing it in a contact vessel.

      Seal  See Reservoir.  An impermeable fault or stratum of

      rock beneath or behind which hydrocarbons can


      Secondary migration Long globules of oil are forced

      through pore spaces in the rock by the force of moving

      water.  It is usually forced upwards being lighter than

      water until it emerges at the surface or is trapped under a

      cap rock to form an accumulation of oil or gas.

      Secondary Porosity                           Porosity developed after the

      original deposition of a formation, for instance by the

      action of water on soluble components of the rock, or well

      stimulation techniques.  The flow of fluids through a

      reservoir               under  production conditions can   cause

      development of secondary porosity.

      Secondary recoveryis used to supplement or replace

      primary recovery.  Various techniques are used, the most

      important being the injection of water or re-injection of

      gas to maintain reservoir pressure.  In modern practice

      secondary recovery is used earlier in the life of the field

      than was the practice in the past as this gives more

      control over production and better overall recovery from

      the field.

      Secondary refining process                             Processes which go

      beyond the primary distillation of crude oil into its

      component fractions.

      Seconds Saybolt Unit of measurement of oil viscosity

      mainly used in commercial specifications.




      Section of Land (US)  One square mile, as defined for

      leasing purposes.

      Sedimentary basin/sedimentary rocks An area which

      in past geological era has been depressed, acquiring

      deposits of sedimentary rocks such as sands, silts or

      limestones.  These are formed from detritus or erosion etc

      of exposed formations and deposited in land or seabed

      depressions or as eg wind-formed desert dunes.  See also

      eg Alluvial Fan.

      Seismic obligation   A seismic survey committed to in

      winning award of a concession.

      Seismic survey      The collection of stratigraphic data

      obtained by creating shockwaves through the rock strata.

      Reflection of these waves from anomalies within the

      earths surface are electronically recorded at surface.

      These recordings are then analysed to produce a

      stratigraphic representation of the surveyed area.

      Self Potential/SP Log  See Log

      Semi-submersible rig A floating platform moored on

      location by anchors to the sea bed.  Stability in the water

      is achieved by submerged pontoons.  The latest models

      have been designed to operate in water depths of up to

      1,500 feet (450 metres) although most of the existing

      generations are limited to nearer 500 to 600 feet (150-180


      Send-out   The quantity of gas delivered by a plant or

      system during a specified period of time.

      Separators       Processing equipment which splits the

      wellhead fluid into separate oil, water and gas streams.

      Service Factor  The proportion of time available during

      which a piece of equipment or whole installation is, or can

      be expected to be, fully effective.  Ineffective time or

      “downtime” may be due to weather, maintenance needs


      Service/Supply Base The port installation from which

      an offshore drilling or production operation is maintained.

      Service Well  See Injection Well

      Set Back/Pick Up   Tubulars removed from a well are

      “set back” in the racks (see Tubing Board), and “picked

      up” for re-running into the well.

      Setting Point (Casing)The depth to which a string of

      casing is set and cemented.

      Seven Sisters  The seven most influential oil companies

      in the development of oil as a major force in world

      politics, namely BP, Gulf, Royal Dutch/Shell, Standard Oil

      New Jersey (Exxon), Standard Oil California (Chevron),

      Standard Oil New York (Mobil) and Texaco.

      Severance TaxA production tax in some areas of the


      Shale/Shale Oil  Very fine-grained “muddy” sedimentary

      rock with low porosity and consequent poor reservoir

      potential.  Oil Shales or     Kerogen Shales contain

      Bituminous deposits which if found at the surface can be

      extracted by heating (Shale Oil).

      Shale Shakers See Mud.  Screens for extracting rock

      cuttings from circulating drilling mud.

      Ship-to-Ship transfer (STS) The transfer of crude oil or

      products from one ship to another while both are at sea.

      Ship or Pay (SOP)          In hydrocarbon transportation

      agreements, the obligation to pay for the transportation of

      an agreed minimum quantity per year. It ensures payment

      of the reserve capacity of the system whether it is used or

      not (usually called “Take or Pay”). 

      Shoe                     The strengthened fitting on the lower end of a

      string of casing to protect the tubulars and help direct the

      cement to the annulus.

      Shoestring Sand  Thin often elongated streaks of

      reservoir sand completely surrounded by impermeable


      Short Trip  A trip during which the drill string does not

      reach the surface.  It may, for instance, be withdrawn

      from down hole into previously set casing for protection.

      Shotgun Tank  A tall, narrow separator column used in

      onshore “stripper” production.

      Shotpoint  See Seismic survey.

      Shut-in field Any field brought onstream which is not

      currently producing.

      Shut-in pressure  The pressure in a shut-in well; static


      Sialic Layer                     The upper layer of the earth’s crust, in

      which prospective reservoirs are found, so called from the

      predominance of Silicon and Aluminium in its composition.

      Sidescan Sonar  Acoustic survey equipment towed close

      to the seabed, used for surveying pipelines – see Sonar.

      Side-Track/Side-Tracked Well A well re-drilled from

      an intermediate depth.  Wells are re-directed or

      sidetracked for various reasons but usually because of

      technical problems deeper in the original well.

      Sidewall Coring  Obtaining rock samples from the sides

      of a well bore using a special tool.

      Signalling Pig  see Pig

      Single Anchor Leg Mooring (SALM)                         A compliant

      monopod version of the SBM tanker-loading buoy, used in

      deeper water.  (see Single Buoy Mooring)

      Single Buoy Mooring (SBM/SPBM)                        A single-point

      buoy mooring for loading and unloading tankers.  The oil

      is fed to or from the centre of the SBM from below, and

      the mooring gear and loading hoses can swivel above the

      buoy through a full circuit.  The tanker moors bows-on,

      and “weathervanes” around the buoy, presenting the

      minimum frontal area to the combined forces of wind and


      Sitting on a well  This usually describes the role of the

      well-site geologist.

      Situation - Complication - Resolution Statement A

      logic framework that assists both in framing the idea and

      communicating the solution - especially useful to assist in

      arriving at the "day 1" answer

      Sizing Pig  See Pig

      Skidding the rig  Moving the derrick to a position above

      another wellhead or “slot” where a well is to be drilled or

      worked over etc.

      Skimmer  Equipment for removing a surface alyer of oil

      from an oil spill, or from an effluent water separator tank

      designed for the purpose.

      Skin factor An expression representing the effects on

      production well pressures and flows of eg formation


      Slant drilling/slant rig                          Drilling a well from a non-

      vertical surface position.  Used offshore to reach distance

      parts of shallow reservoirs where depth is insufficient for

      normal deviated drilling.

      Slim –Hole drilling  Reducing the cost of a well, where

      technically feasible, by the use of specifically designed

      smaller diameter equipment.




      Sling/Pipe Sling  A wire or rubber and fabric strop used

      in lifting tubulars.

      Slips  Metal wedges which are “set” in the annulus at the

      drilling floor to grip and support tubulars while sections

      are added or removed.

      Slop tank      Temporary storage for oil-contaminated


      Sloughing Crumbling or disintegration of the wall of a


      Slug/slug catcher        An accumulation of liquid eg

      condensed water, in a low point of a gas pipeline.  Slugs

      tend to accumulate when flow rate is low or interrupted.

      A slug catcher is a large separator for removing the slug

      at its destination without disrupting the gas flow.

      Slurry               1. A mix of cement and water used in

      drilling/cementing  2. Solid particles or crushed fragments

      in a liquid for pipeline transportation.

      Smoke point  A part of the specification for JP Fuels.

      Snubbers Tackle for exerting a downward force on a

      string of tubulars when inserting it into a well against very

      high pressures.

      SOFC Solid oxide fuel cell.

      Solid Alkanes  Hydrocarbon fractions which are solid at

      normal temperatures.

      Sole Risk  A provision in Joint Ventures whereby the only

      participant wishing to incur the costs of an activity eg

      drilling a well, may, under certain conditions, proceed with

      the well at its own cost, and thereby secure enhanced

      rights to any oil or gas found.  Sole risk development is

      also theoretically possible but very rare.

      Solution gas Natural gas which is dissolved in the crude

      oil within the reservoir.

      Solvent Common name for a liquid which is capable of

      dissolving or dispersing other substances.

      Solvent extraction  A refinery process where a solvent

      is used selectively to isolate and remove part of the

      process flow.

      Sonar         “Sound and Ranging”.  The use of sound echoes

      to locate objects underwater.

      Soup  Nitro-glycerine.  It is used in explosive fracturing of

      a down hole formation.

      Source rocks     The majority of evidence leads to the

      conclusion that hydrocarbons originated from the organic

      matter of muddy sediments deposited in depressions in

      the sea floor where the water was stagnant and lacking in

      oxygen.  Frequently these are clays or shales and such

      sediments are known as source rocks.

      Sour oil/gas  Oil or gas with a relatively high content of

      (odorous, poisonous or corrosive) sulphur compounds

      such as Hydrogen Sulphide. Sour gas is usually treated

      with triethanolamine to remove the unwanted elements.

      Source rock  The sediment/rock in which fossil deposits

      are formed into hydrocarbons which may then migrate

      into different porous formations.  See also Kitchen.

      SOx Sulphur oxides.

      SPACE       Computer programme which produces an

      expectation curve of recoverable hydrocarbons, using

      Monte Carlo techniques. This is the successor to PAQC

      and PADE and includes access to a global data base (as

      PAQC does).

      Spacing pattering The density of development drilling

      on a reservoir, expressed in acres per producing well.

      S.P.A.R.                     A very large manned SBM incoprorating oil




      Part of an echosounder for gauging the 

      thickness of soft seabed deposits.

      Spear  A “fishing” tool for recovering downhole tubulars

      by penetrating and gripping them from the inside.

      Specific Gravity The ratio of the density of a substance

      at a particular temperature to the density of water at 4øC.

      Spider                         A power-operated set of slips for gripping


      Spider Deck  The lowest deck on an offshore drilling rig,

      below the rig floor.

      Spider Diagram                      A chart showing the sensitivity of a

      project’s NPV (or other economic indicator such as VIR) to

      variations in one parameter at a time.

      Spinner  A powered spanner or wrench for gripping and

      rotating drill pipe when screwing or unscrewing the joints.

      Previously the “spinning chain” was wrapped around each

      joint in turn and pulled on the cathead (winch) to rotate it.

      Splash Zone  The part of an offshore structure which is

      regularly exposed alternatively to atmosphere and water

      or spray and is consequently highly prone to sale and rust


      SPM See SBM.

      Spool/spool piece  A short section of pipe with flanges

      or thread-connections at each end thus appearing “spool

      shaped”.  It may be of any length required to make up

      pipeline or casing to an exact required length.

      Spot charter A one-voyage tanker charter or one-well

      rig charter, as opposed to a time-charter.

      Spot market  An international market in which oil or oil

      products are traded for immediate delivery at the current

      price (the 'spot price').

      Spotting  Placing cement etc accurately at a certain lvel

      in a well.

      Spread                     This has come to mean any complete set of

      equipment and ancillary vessels or vehicles, for a

      designated task eg pipelaying spread, diving spread.

      Spud  To start drilling a new well (or re-start)

      Spud can                          The end of each leg of a jack up rig or

      platform designed to penetrate the seabed and give a firm

      foundation for operations.

      Spur lines generally small diameter pipelines connecting

      a production facility to either a terminal platform or to a

      main pipeline leading to the shore.

      Squeeze                         Inserting cement under pressure into the

      poorly sealed annulus of a well, past the existing material.

      Squib Shot  An explosion set off in a producing well to

      stimulate production.  See Stimulation and Soup.

      Stab/Stabbing Board  To make a connection: to insert

      one device into another eg one stand of drillpipe into the

      string in the hole. To do this the derrick-man stands on

      the Stabbing Board high in the derrick.

      Stabilizer  1.  A distillation column for stabilizing crude oil

      1. Part of a drill-string, a tool with external things to give

      rigidity to the string  3. External fins on the hulls of

      shipping to minimise motion due to the sea  4. One of the

      columns or “legs” of a semi-submersible rig, which

      contains ballast compartments for stabilizing motion.

      Stabilized crude oil  Crude oil from which gases volatile

      at normal surface conditions have been removed, meeting

      commercial sale specifications.

      Stabilized well  A well in which the formation pressure is

      balanced by the weight  of the mud column in the well.

      Stack      1.  A vertical vent, chimney or flare  2. The 

      process of laying up an out-of-work rig or other

      equipment  3. A compilation of seismic signals in the

      processing of survey data.

      Standby rig rate       The daily charter rate for a rig in

      readiness but not incurring drilling costs.

      Stand of pipe  A short length of drill pipe pre-assembled

      to save time in operations and stored vertically in the

      derrick ready for use, usually in lengths of three joints or

      “Thribbles”, “Fourbles” and “Twobles” are also known.

      Standpipe     The fixed pipe taking mud from the mud

      pumps under pressure, up to the level of the rotary hose

      and swivel.

      Start up         The process of introducing feedstock to

      commissioned and tested plant and working it up to

      production capacity and efficiency.

      Steam injection/steam flooding Techniques used to

      lower the viscosity of residual oil in the reservoir and

      assist it to flow to a well.  See also Enhanced Oil


      Stenching The process whereby odourless natural gas is

      given a smell for safety reasons by injecting small

      quantities of organic sulphur compounds, typically at the

      rate of 30 ppm. See also odorant.

      Step out well An appraisal well, specifically aimed at

      locating the lateral limits of the reservoir discovered.

      Sticking  Jamming of the drill string in the well borehole

      caused usually by a high differential pressure and a build-

      up of mud solids on the rock face.

      Still  A primitive distillation unit.

      Stimulation Methods such as acidizing (chemical) or

      fracturing (pressure) or explosions designed to break up

      “tight” low permeability reservoir rock in the vicinity of a

      well so that oil can flow freely into the bore.

      Stinger  In offshore pipelaying, the long submerged ramp

      which supports the length of recently welded pipe curving

      between the pipe lay-barge and the seabed, thus avoiding

      undue stressing, deformation or even the collapse of the


      Stock tank oil  Stabilized crude oil

      Stopcocking          Intermittent production from nearly

      exhausted or low-productivity wells, to allow time for

      pressure to build up while shut in.

      Stoppel A temporary plug inserted in a pipeline under


      Storage facilities     For natural gas, these fall naturally

      into two categories, according to the IEA. The first is

      seasonal storage sites, which comprise aquifers (including

      depleted oil and gasfields); salt caverns; mined caverns;

      and disused mines. For peak storage, gasholders -

      originally used to store town gas - and linepacking are

      used. In addition, LNG storage tanks exist for either

      baseload or peak-shaving duties, depending on the

      market. of organic sulphur compounds, typically at the

      rate of 30 ppm. See also odorant.

      Storm choke In a producing well, an automatic down

      hole valve which closes with excessive flow rate or

      pressure drop.  An emergency safety valve.

      Stovepipe pipelaying On-site assembly of lengths of

      pipe, normally by welding. 

      Straddle packer                      A rubber packer or seal isolating a

      section of a well for production testing of the formation in


      Straight-Line DepreciationA scheme in which assets

      are depreciated in equal amounts over a number of years.

      Straight-run A description applied to a product of crude

      oil that has been made by distillation with no chemical


      Strake, Helical                       A spiral external fin to strengthen a


      Strapping  The process of calibrating a storage tank for

      measurement of its contents. 

      Strata                         (Stratum)/stratigraphy


      predominantly horizontal layers of rock of a homogeneous

      type such as sedimentary deposits.  Subsequent local

      geological events may have tilted, rotated, folded or even

      inverted strata.                  Stratigraphy         is the pattern of

      succession of rock strata in an area, represented

      diagrammatically by a Stratigraphic or geological column.

      Stratigraphic trap                      is a structure where the “trap” is

      provided by layers of impermeable but possibly

      homogeneous rock rather than the geometrical “shape” of

      the rock formation.  They are consequently difficult to

      identify at the exploration stage.

      Strategy Table A structured approach to determining

      which strategy options overlap for various decision


      Stratigraphic traps                      occur where sedimentary layers

      have changed in characteristic.  For instance a deposit of

      coarse sand near shore may given place to finer grained

      sediment in deeper water and as these will vary in

      permeability an apparently isolated reservoir can occur.

      Another case would be where a sand layer wedges out

      onto an impermeable clay or shale and becomes isolated

      from its own sedimentary layer.  The latter type of trap is

      sometimes known as a pinch-out trap.

      Stream  The general flow of hydrocarbons from reservoir

      to finished product.  Processes relatively earlier in

      sequence are described as “upstream” and later

      “downstream: ie a refinery is upstream of a filling station

      but downstream of a production well.  However, all the

      extractive activities preceding shipment of stabilized crude

      oil or sales gas are collectively known as “upstream”, and

      a company operating only in these activities is known as

      an “upstream company”.  See also Onstream and Stream


      Stream day                    A day when plan is onstream, excluding

      planned downtime etc.  Used in expressing plant

      throughput capacity (eg 50,000 barrels per stream day).

      Streamer                        A long cable towed behind a survey ship

      carrying hydrophones for receiving seismic survey or

      sonar signals.

      Strike                          1.  The angle of dip or inclination from the

      horizontal of rock stratum  2.  A strike is also a term for a

      discovery well.

      String  See Joint, Drill-string, Casing etc.  Any number of

      connected joints of tubulars run in the well.

      Stringer bead or pass  See Bead.

      Stripping: stripper well                          A nearly exhausted well,

      normally defined as having production of less than 10

      barrels per day.

      Structure                    1.  A geological formation which, if sealed

      against leakage, could be a potential structural or

      stratigraphic trip for hydrocarbons 2.  A man-made load- 

      bearing construction such as an offshore platform, usually

      designed by structural engineers.

      Structural trap  A structure such as an anticline or fault-

      block in which a volume of reservoir rock is sealed above

      and on all sides by impermeable strata and/or faults.

      Stuck pipe  See Sticking

      Sub         1. A non-standard fitting of adaptor

      1. A sub-assembly
      2. A component tool in a drilling string.

      Submersible    A manned or remotely control vessel

      designed to operate completely submerged. 

      Sub sea enclosure  A sealed subsea chamber installed 

      over eg a subsea wellhead, providing access to it in

      normal surface atmospheric conditions.

      Sub-sea wellheads           In certain circumstances it is

      expedient to install a sub-sea wellhead to drain all or part

      of a deposit.  These are essentially wells drilled from a

      mobile drilling rig and completed with a series of valves

      and blow-out preventers on the sea bed.  This wellhead

      equipment is then connected to a central collecting area

      (either a platform, or a semi-submersible rig) by flexible or

      rigid pipelines.  If the wellhead equipment remains

      exposed to the sea it is called a wet-tree, but if it is

      encapsulated in a chamber under atmospheric pressure, it

      is a  dry-tree.

      Sub surface safety valve        A strong choke type valve

      installed in a development well, designed to seal the well

      in emergency until surface control has been resorted.  Also

      known as “Down-hole Safety Valve”.

      Success Ratio  The proportion of exploration wells which

      encounter significant hydrocarbons.      Commercial

      success ratio      is the smaller proportion encountering

      reservoirs of development potential.

      Super port  A port capable of accepting supertankers for

      loading or unloading.

      Superstructure  The deck, modules, and other parts of

      an offshore platform installed on the jacket or leg-section.

      Sometimes referred to as the “Top-sides”.

      Supertanker  A colloquial term for Very Large and Ultra

      Large Crude Carriers.  See ULCC and VLCC.

      Supply boat/ship/vessel  Vessels specially designed to

      carry loads to offshore installations and participate in

      loading/unloading by crane (or hose for water and fuels).

      They may also participate in eg anchor handling of the

      installation. They are highly manoeuvrable and robust.

      Surface string  See Casing.

      Surfactant A detergent or emulsifier, various of which

      are used in the oil industry.  Surfactants are increasingly

      used injected ahead of water in a waterflood system to

      overcome by capillary action the forces whereby the oil

      adheres to the rock grains.

      Surge tank  A vessel, provided at points in a pipeline or

      other flowline to accommodate temporary “surges” in

      pressure/fluid volumes due to timing differences in the

      opening or closing of valves, operation of pumps etc at

      either end of its section of line.

      Surveyor’s transit  A Theodolite.

      Survival capsule    A type of totally enclosed “life boat”

      used on some oil and gas installations.  See Brucker

      Capsule etc.

      Suspended well     A well, usually a successful discovery

      well, which is left temporarily sealed or plugged to be re-

      entered for further testing or for production purposes.


      Sustainable development The meeting of present

      needs without compromising the ability of future

      generations to meet their own needs.

      Swabbing 1. Reducing pressure in a well to clean or

      stimulate it (or inadvertently)  2. Colloquially, to obtain

      information from someone.

      Swage Nipple                     An adaptor for connecting tubulars of

      different diameters.

      Sweetening See Sour oils.

      Sweet gas Natural gas containing very small amounts of

      hydrogen sulphide gas and carbon dioxide. Sweet gas

      reduces sulphur dioxide emissions into the atmosphere.

      Swing                    The amount by which the rate of gas to be

      supplied under a contract at any one time may differ from

      the daily contracted quantity at the buyer's choice.

      Swivel  The rotary bearing from which the kelly and drill

      string are suspended.

      Syncline A geological formation “opposite” in shape to an

      anticline eg saucer-shaped with the edges higher than the

      centre.  Although on a local scale synclines provide poor

      structural traps for hydrocarbons, on the larger scale of a

      sedimentary basin or sub-basin they are prime exploration


      Synthetic gas                     Methane-rich gas manufactured from oil

      or coal that has the same basic characteristics and

      chemical composition as natural gas. After treatment to

      remove carbon dioxide, it is suitable as low-calorific town



      Tail ends  Overlaps in the distillation characteristics of oil

      fractions resulting in a mixture of the products in that 

      vaporisation range. 

      Tail gas  Residual gas from a refinery or other processing


      Take-or-pay A contractual clause obliging a gas buyer to

      pay the seller for a contracted amount of gas in a fixed

      period, whether or not he takes physical delivery of it.

      Tank bottoms  Fluid in a tank below the pump

      suction/outlet, not normally evacuated.

      Tank dipping  The initial action in determining the

      contents of storage tanks.  A prepared weighted line is

      lowered through a “well” in the roof of the tank, and the

      level of the contents and/or underlying water marked.

      The volume represented by the difference in level is then

      calculated by reference to tank tables.

      Tanker  Any mobile storage unit for the bulk transport of

      crude oil, gas or products (eg road tanker, rail tanker) but

      normally refers to marine transport.

      Tank farm  An area at a refinery, terminal or storage

      depot dedicated to storage tanks and their safety

      requirements for surrounding space and spillage

      containment devices (see Bund Walls).

      Tank tables  The result of strapping a tank.  Calibration

      tables for an individual storage tank by the use of which

      the depth revealed in tank-dipping or gauging can be

      converted to a volume of contents.

      Taper mill  A pointed or tapered bit for cutting through

      tubular steel junk in a well. 

      Taper tap  A fishing tool similar in design to a normal

      taper tap.  It is screwed into the upper end of a tubular

      “fish” to enable recovery to the surface.

      Tapping a line  Cutting into a pipeline to install a branch

      connection.  See also Hot Tap.

      Tar  See Asphalt.

      Tariff  Any volume-based or tonnage-based rental charge

      for the use of an installation of equipment eg pipeline

      tariff, processing tariff.  As distinct from royalties tariffs

      are payable to the owners of the installation.

      Tar sands       Mixture of sand, water and heavy

      hydrocarbons; a   potential  alternative  source  of


      Tax Factor Can be used in-place of rigorous earnings and

      taxation calculations to calculate the after-tax values of

      both revenue and cost inputs. The expression of a given

      sum of money in a given year as an amount with

      equivalent purchasing power in the Reference Year.

      TCF  Trillion (1012) cubic feet.

      T/D Tonnes per day.

      TD  Total depth of a well.

      Tectonics  The process of formation and evolution of the

      earth’s solid surface crust.  “Plate tectonics” relates to

      the formation and movement of the “plates” of which the

      crust is composed.

      Telemetry  Remote instrumentation systems, so that for

      instance subsea well or satellite development platform

      temperatures, pressures etc can be read and recorded


      Temperature bomb A capsule containing instruments

      for measuring temperature down a well.

      Template    This usually refers to a structural framework

      within which subsea wellheads are grouped.  It may also

      refer to a prepared foundation or “mattress” for soft or

      shifting seabed on which a jackup rig etc can be stably


      Tensioners Various types of device to maintain 

      controlled tension on a marine riser or one of the “tethers”

      of a tension-leg platform.

      Tension Leg Platform (TLP)        A semi-submersible

      platform which is moored or “tethered” vertically to

      anchor points on the seabed.  After tethering, the

      platform is deballasted to allow its buoyancy to place the

      tethers under pre-determined tension.  This has the effect

      of eliminating vertical “heave” of the platform but allowing

      some lateral compliance with sea forces.  Its main

      advantages are adaptability to increasing depth, minimal

      offshore “hook-up” work and ease of removal, at some

      cost in load-bearing potential compared with a fixed


      Terajoule or TJ One trillion (1012) joules.

      Terminal This usually refers to a loading or unloading

      facility in a transportation system for oil or gas eg

      pipeline-to-tanker, tanker-to-refinery, trunk pipeline-to-

      distribution pipelines, pipeline-to-rail tanker, refinery-to-

      road tanker.  The term also covers associated processing

      and storage facilities.

      Tertiary recovery is a recovery method used to remove

      additional hydrocarbons after secondary recovery methods

      have been applied to a reservoir.  Sometimes more hydro-

      carbons can be removed by injecting liquids or gases

      (usually different from those used in secondary recovery

      and applied with different techniques) into the reservoir 

      Terminal An onshore transit installation that receives and

      stores crude oil and products from offshore production

      facilities via pipeline and / or tankers.

      Testing  See Drill stem testing, Hydrostatic testing, Non-

      Destructive testing, Well testing etc.

      Tethered Platform  A variant of the tension-leg


      Thermal cracking                        A refinery process whereby the

      larger, heavier molecules in crude oil or its residue are

      broken down into lighter products by heating under


      Thermal recovery                      Enhanced Oil Recovery based on

      heating the oil in the reservoir by steam injection or sub-

      surface combustion (fire flood).


      A device for taking samples of fluid from 

      intermediate levels in a storage tank consisting o fa small

      container on a line with a remotely controlled inlet.  It is

      inserted through the "thief hatch” in the tank roof.

      Thief zone  A porous, fractured or vuggy formation in a

      well, into which drilling fluid escapes.  It must be plugged

      or lined with casing.

      Third-party access (TPA)                         A TPA regime obliges

      companies operating gas transmission or distribution

      networks to offer terms for the carriage of gas on their

      systems by other gas distribution companies or particular


      Thixotrophy  The quality of fluids such as drilling mud

      and some clays to set when left undisturbed but to

      become fluid again when force or pressure is applied.

      This can be important in selecting eg jack up drilling sites

      as well as in mud engineering.

      Thread protector  A cape which is fitted over the ends

      of casing, tubing etc when not in use to protect the

      connections from damage and corrosion.

      Through flow line (TFL)  A system for inserting

      workover tools or instruments into a subsea well

      completion through the production gathering line or


      Thrusters  Fixed or “steerable” (direction or azimuth)

      propellers on a vessel which enable it to be manoeuvred

      with great accuracy.

      Thumper  See Vibrator: Vibroseis

      Tie-in  The action of connecting one pipeline to another

      or to equipment.  Hence “pipeline tie in” commonly

      describes the connection itself.

      Tight hole  1. A well regarding which information is

      restricted as highly confidential, usually in a competitive

      situation.  Communication is frequently in code  2.

      Occasionally used to describe a well from which

      production is restricted by low permeability or “tight” rock

      in the reservoir formation.

      Time charter  Rental of a rig or vessel, based on a rate

      for more than one voyage or well etc.

      Time map  A contoured map of a subsurface geological

      formation based on the time taken to reflect seismic

      impulses                  rather      than      the      subsequently

      computed/interpreted depths on a depth map.

      Tongs                     Tools for gripping and turning tubulars when

      making up or breaking out joints.  Now frequently power


      Tonne A metric tonne is 1000 kg (2205 pounds), a long

      ton is 2240 pounds, a short ton 2000 pounds. 

      Tonnes of coal equivalent (TCE)             A method of

      assessing the work or calorific value of different sources of

      energy in terms pertaining to one tonne of coal.

      Tonnes of oil equivalent (TOE) A method of assessing

      the work or calorific value of different sources of energy in

      terms pertaining to one tonne of oil.

      Toolpusher The chief engineer of a drilling crew, with

      overall responsibility for the rig in the field.

      Topped crude Crude oil from which the light fractions

      (naphtha and lighter) have been distilled off in a “Topping


      Torque    The turning force applied to any rotation eg

      rotary drilling, making up casing, tightening flange bolts


      Total Depth (T.D.) 1. The target depth for a well  2. 

      The achieved (drilled) depth in a well at any one time.

      Tour  1.  Drilling or other shift – usually 12 hours  2.  Any

      longer period of duty, such as say, 2 weeks offshore, or a

      period of assignment to a remote or foreign location.

      Tour sheet  The log of a drilling shift with details of all

      operations, materials and equipment used, and conditions

      encountered in the well.  Pronounced “Tower Sheet”.

      Town gas Gas piped to consumers from a gas plant. It

      can comprise manufactured gas, as well as natural gas for


      Tornado Diagram A method of presenting the range of

      uncertainties on key variables and their priority.

      Tracing A system of steam pipes or electric elements

      fitted to vessels or pipelines to keep them warm so that

      very heavy viscous crude oil, for instance, will flow freely.

      Transducer An instrument for converting one form of

      energy into another – for instance enabling acoustic

      signals to be used in controlling a subsea well.

      Transmission The transport of large quantities of gas at

      high pressures, often through national or regional

      transmission systems. From the latter, gas is transferred

      into local distribution centres, for supply to customers, at

      lower pressures.

      Transmission pipeline         A    network  of   pipelines

      distributing natural gas from an onshore station, via

      compressor stations, to storage centres or distribution


      Transponder An acoustic device which on receiving a

      pre-set acoustic signal, transmits a response.  When fitted

      to a subsea wellhead, for example, this enables a rig to

      position itself very accurately for drilling or re-entry.

      Trap A geological structure in which hydrocarbons build

      up to form an oil or gas field. See also: structural trap.

      Travelling block The pulley block suspended from the

      crown block of a drilling rig, from which the hooks and

      swivel are in turn suspended.

      Tray  One of a series of perforated horizontal partitions in

      a distillation column designed to condense and draw off

      specific fractions of rising hydrocarbon vapour.

      Trillion  The Oil and Gas industry commonly uses the US

      definition, namely one million million 1012    (TCF – Trillion

      Cubic Feet).

      Trip  See Round Trip and Short Trip.

      Trip gas    High pressure gas in a well which must be

      carefully controlled when withdrawing the drill string

      (making a trip). 

       True Vertical Depth (TVD) The vertical distance below 

      surface datum reached by a deviated well.

      Trunk lines                      Long distance pipelines, as distinct from

      field, gathering or branch lines.

      Tubing/tubing head                          Wells are normally produced

      through tubing which is installed inside the casing in a

      well.  The              tubing head, similar to the casing head, is

      installed at the wellhead on the production tubing, seals

      off the annulus between casing and tubing, and carries

      the connections for production flowlines.  This assembly

      incorporates a tubing hangar similar to a casing hangar.

      Tubing board  See Derrick. 



      Covers all oilfield tubular materials but 

      primarily drill pipe, casing and production tubing.

      Turbine flowmeter                       An instrument which measures

      rates of flow in a pipeline by the electric current generated

      by a small rotor inserted in the line.

      Turnaround The process of completely overhauling a

      refinery, or piece of equipment.  A refinery will undergo a 

      shutdown and a turnaround every few years.  Turnaround

      is also the time taken to receive, load or unload and

      release a tanker of any kind.

      Turnkey contract A fixed price contract for 

      Underwater Habitat  An air chamber or structure such


      construction, drilling a well etc with the contractor taking

      risk of non-completion.  A true “turnkey” involves the

      contractor funding the operation until startup.

      Turret moored production facility                       In this design, a

      production turret (a cylindrical buoy) is built into a cavity

      similar to a moon-pool in a floating ship-shaped

      production facility.  The turret is connected to subsea

      wellheads by flexible hoses, and is moored in a fixed

      orientation.  The ship/facility, containing process storage

      and offloading equipment, is free to rotate or

      “weathervane” around the turret to present an optimum

      profile to wind and sea.

      TVD  (True vertical depth).  The linear distance measured

      perpendicular between an imaginary horizontal line drawn

      through a well surface location and any subsequent

      measured depth point.

      Twist of                       Severing of the drill pipe due to fatigue or

      excessive torque.

      T/Y tonnes a year.


      UKCS United Kingdom Continental Shelf.

      ULCC   Ultra large crude carrier. An extremely large

      ocean-going tanker, over 300,000 metric tonnes dwt, used

      to transport crude oil.

      Ullage The space in a tank not occupied by its contents.

      Used as a measure of storage space still available.

      Ultimate Cash Surplus                       The value of the cumulative

      cashflow at the end of the project life.

      Ultra large crude carrier (ULCC) A crude oil tanker,

      often defined as having a deadweight tonnage or cargo

      capacity of 350,000 tonnes or more.

      Ultrasonic testing  A non-destructive testing method in

      which ultrasonic waves – (sound waves of frequencies too 

      Unassociated gas  See Associated Gas. 

      Unbundling The separation of the gas transport, storage

      and merchandising functions.

      Unconformity trap    This type of trap occurs when a

      series of rocks are deformed and raised above sea level

      and then eroded away.  When once again depressed

      below sea level the truncated ends are covered and sealed

      by horizontal beds which, if impermeable, provide a cap

      for any hydrocarbon accumulations which form in the

      truncated layers.

      Underlift       A situation where a participant in a joint

      production venture fails to take its full share of production


      agreed limits of overlift/underlift necessary with eg

      periodic tanker shipments, oil underlifted may be deemed

      to be forfeited or “left in the ground” for pro rata benefit

      of all.  These provisions are intended to prevent any

      participant using joint storage to maximise profit on

      market fluctuations, to the detriment of others.  See



      A rotary drilling bit which can be 

      expanded downhole to enlarge the well bore.  See also


      as a diving bell in which divers etc can live while not

      working, or a chamber where work can be carried out

      such as subsea enclosure or hyperbaric welding chamber.

      Unit/Production Unit etc               When a reservoir is

      discovered to extend into more than one concession or

      licence area, it is common for the participants in the areas

      concerned to negotiate a mutual development, sharing all

      costs and production in proportion to the hydrocarbons in

      place or reserves in each area.  The participant with the

      largest equity share in the combined Unit is usually

      selected as  Unit Operator to undertake the common

      development and the negotiated basis of operations is the

      Unit Agreement, a form of Joint Operating Agreement

      which also normally provides for adjustment to

      participants shares if the reservoir is later found to underly

      the areas in different proportions from those initially


      Unitisation    occurs when stockholders of petroleum

      reserves pool their individual interests in return for an

      interest in the overall unit, which is then operated by one

      company on behalf of the group.  Unitisation leads to

      increased efficiency from maximising production and

      minimising development and producing costs.

      Universal Coupling  A joint which permits rotation from

      one shaft to be transmitted to another in a different plane.

      See, for instance, Knuckle Joint.

      Unsaturated Oil See Saturated Hydrocarbons, Fat Oil


      Unstabilized Oil  See Stabilized Oil.

      Updip      An area of a structure where the top of the

      formation is higher (eg offshore, nearer sea level) than

      the point under consideration.

      Uplift    A fiscal device to compensate for the effect of

      inflation on depreciation.

      Upset  The thickening or increased diameter at the joints

      of tubulars to provide the necessary strength.

      Upstream   Those activities relating to the exploration,

      production and delivery to an export terminal of crude oil 


      Vacuum distillation  Distillation of heavier fractions, at 

      a pressure well below atmospheric pressure and at

      accordingly reduced temperatures, thus saving fuel costs,

      and avoiding breakdown or “cracking” of the feedstock


      Value of Information Information is only valuable if it

      will influence the decision. The value of information is

      determined                 from     a      decision    tree      as:

      VOI = EMV (perfect information) - EMV (without perfect


      Vapour pressure The pressure exerted by the vapour

      from a substance, and also the pressure required to

      prevent a liquid from vaporising.

      Variable load  The operating load of equipment, fuel etc

      carried by a floating platform as distinct from its own

      unladen displacement.  Its capacity for variable load is

      similar to deadweight tonnage in a ship.

      Vertical integration                       In the oil industry, the process

      whereby an operating company amalgamates with

      operations further upstream and/or downstream (see

      Stream) in order to obtain greater commercial security by

      avoiding intermediate market fluctuations.

      Vertical Moored Platform  A tethered leg platform.

      Very large crude carrier – VLCC  Crude oil tanker with

      cargo capacity of around 175,000 dwt or over.  See also


      Vibrating screen  A sieve-like part of the shale-shakers

      for separating rock cuttings and mud return from a well.

      Vibroseis/Vibrator  Onshore seismic survey based on a

      mobile vibrating energy source rather than on percussion.

      It is used where roads or terrain will accept the vehicles.

      Visbreaking  A refinery process for cracking and thereby

      reducing the viscosity of fuel oils.

      Viscosity/viscous Stickiness, i.e. the resistance that a

      liquid has to motion or flow; it normally falls as the

      temperature rises.

      Viscosity index A measure of the relationship between

      temperature and viscosity of an oil.

      Vitronite  See Kerogen

      VLCC  (Very large crude carrier) A large ocean-going

      tanker, over 200,000 metric tonnes dwt, used to transport

      crude oil.

      Volatile/volatility  The readiness with which a liquid

      converts to its gas state.  Highly volatile liquids include the

      “light” hydrocarbon fractions.

      Vortex flowmeter  An instrument for measuring flow-

      volumes based on the principle that a solid body in a flow

      stream sheds vortices with increasing frequency as flow

      speed increases.

      Vugs  Cavities in certain types of sedimentary rocks, often

      egg-sized or larger.

      Vulcanisation The cross-linking of polymer chains with

      sulphur to improve the characteristics of rubbery



      Wall cleaner/scraper  See Scratchers



      Washing-in a well      Cleaning a well by replacing the

      drilling mud with water or distillate.

      Wash out  Water leaks into the drilling mud downhole.

      Wash over A fishing tool which is designed to fit over

      the end of the “fish” before gripping it.

      Water-based mud  Drilling fluid based on suspension of

      solids such as Bentonites in water.  See also Oil based


      Water Coning  See Coning.

      Water Drive        Where a hydrocarbon reservoir is in

      contact with an underlying water table, the formation

      pressure will “drive” the water into the rock pores vacated

      by produced fluids, thus tending to maintain reservoir

      pressure and assist production.

      Watered-out is when a production well is shut-in due to

      its unacceptably high proportion of water production.

      Waterflood is a method of secondary recovery in which

      water is injected into a reservoir in order to remove

      additional quantities of oil that would be left behind after

      primary recovery.

      Water injection              See Secondary Recovery and


      Watering out             When the proportion of water in

      production from a well is so high that it must be shut in.

      Water saturation  The proporation of water in the pore

      spaces of a reservoir.  See Porosity.

      Water separation              Removing the water from a

      production flow of oil or gas.  There are several

      techniques including settlement, heating and electrostatic

      precipitation particularly for breaking down water-oil


      Water table   The level in the earth below which rock

      pores are saturated with water.

      Watt The basic unit of electrical power, defined as one

      joule per second.

      Wave period   The time separating successive crests of

      similar waves passing a given point.

      Wave recorder      An instrument which measures and

      records the height and frequency of waves.

      Wax           A solid or semi-solid material derived from

      petroleum distillates or residues; used for various

      purposes including candles and polishes.

      Weather window            The period of relatively good

      (summer) weather within which a given offshore

      operation can take place.  A weather window can also

      occur in winter, but is usually hard to predict and of short


      Weathering         1. Permitting crude oil to stabilize by

      venting its volatile fractions to atmosphere (not now

      practised)  2. The process acting on exposed geological


      Weevil An inexperienced and therefore accident-prone

      oilfield worker. 


      Weight indicator                     A large instrument on the rig floor

      which displays the weight of the drill string, and hence the

      pressure on the drilling bit.

      Weld fillet In welding overlapping surfaces, the weld

      makes a fillet in the angle formed by the end of the


      Welding bug                     Welding head of an automatic welding


      Well                          A hole drilled in rock from the surface to the

      reservoir in order to explore for, or extract, oil or gas.

      Well completion The process of equipping a well for

      development use as a producer, injector etc, eg casing,

      perforating, running tubing, fitting wellhead equipment

      etc.  The expression also covers the equipment installed.

      A well may for example be described thus:  “Type of

      completion – Upper Jurassic Producer”.

      Wellhead 1.  Descriptive of a location or function rather

      than a specific item of equipment  2. The control

      equipment fitted to the top of the well, consisting of

      outlets, valves, blowout preventers etc. See also:

      Christmas tree.

      Wellhead platform An offshore platform designed to

      support only wellheads and associated piping, production

      fluids being transferred to a shore gathering station or

      nearby platform for processing.  Sometimes called a

      Drilling Platform, if equipped with an integral rig and

      drilling facilities.

      Well permit                       Government permission to drill a well.

      Obtaining this is frequently a detailed process.

      Well program The engineering design and technical/

      operational plan for drilling a well, completing and testing

      (as applicable).

      Well servicing                                 Bringing a completed well into

      production, and subsequent maintenance “workovers”.

      Well shooter  An explosives expert who uses downhole

      explosions to stimulate production.

      Well symbols  Conventional symbols used in mapping to

      show location and type of well.

      Well testing  Testing in an exploration or appraisal well

      is directed at estimating of reserves in communication with

      that well, in addition to well productivity.

      Testing in a production well also monitors the effects of

      cumulative production on the formation.  Tests basically

      consist of a series of measurements of pressures, fluid

      flows and temperatures down hole (PVT) in a controlled

      sequence of “flowing” and “shut-in” periods for recovery

      of stable reservoir conditions.  The time taken to recover

      is also recorded.

      Various forms of well stimulation may also be built into

      the sequence.  Tests will also include the functioning of

      well equipment.

      Wet gas  Natural hydrocarbon gas containing significant

      amounts of naturally liquid hydrocarbons.

      Wet tree  A subsea wellhead “tree” which is exposed to

      the water rather than enclosed.

      Wet weld Underwater welding as opposed to normal

      atmospheric welding or hyperbaric chamber welding.

      Whipstock  A tool for deviated drilling, basically a wedge-

      shaped block which is lowered into the well to divert the

      bit onto a chosen path at an angle to the original hole.

      Whitaker capsule  A type of survival capsule.




      White oil/white cargo  Clean or distilled petroleum, or

      products not including heavy “black” residues nor crude


      White products Gasoline, naphtha, kerosene and gas oil,

      i.e. products from the high or light end of the distillation

      process. See also: black products, light fractions.

      Wide cut     A product of crude oil distillation in which

      several fractions are combined usually at the heavy

      distillate/residual fuel oil end of the range.

      Wildcat   Refers to an exploration well drilled without

      complete geological knowledge of the locality.

      Wildcat well An exploratory well drilled without detailed

      knowledge of the underlying rock structure.

      Window mill    A downhole cutting tool used to cut an

      aperture laterally in the casing to sidetrack

      or deviate the well.

      Wireline logs Electrical devices run down a well on a

      steel cable.  The equipments response is used to

      determine rock lithology, permeability, porosity, formation

      fluid type, cement bond effectiveness, etc.

      Wobbe Index An expression of the heating value of a

      gas flame, used in gas marketing.  It is derived by dividing

      the gross calorific value of the fuel by the square root of

      its specific gravity, expressed in eg megajoules per cubic

      metre or BTU per cubic foot.

      W.O.C. Time  Time when a rig is “waiting on cement” to


      Working interest  A full “equity” interest in an oil or gas

      concession, as distinct from, for instance, a royalty

      entitlement or net profits interest.

      Workover        A maintenance job on a well usually to

      replace equipment or to stimulate production.

      Worldscale rates    A schedule of nominal freight rates

      against which tanker rates for all voyages, at all market

      levels, can be compared and readily judged.

      W.O.W. time  Time when a rig or installation vessel etc

      is “waiting on weather” to moderate before operations can



      Xaloy A low friction alloy used for facing drilling tools



      Yield  The total amount of product of a refinery process

      or of all products of all processes of a refinery compared

      with the equivalent amount of feedstock.  A “Refinery

      Yield” for a given crude oil feedstock and refinery will

      include a table of amounts of all products derived from a

      barrel or tonne of crude minus the refinery’s own

      usage for fuel, flaring and other losses.  Since refineries

      commonly use several feedstocks simultaneously, such a

      yield is often measured or predicted on the basis of

      adding incremental feedstock to a fixed throughput.











      Yield point  The force needed to start a fluid flowing i.e.

      to overcome its viscosity or thixotropy.


      Zeolytic catalyst                       A type of catalyst used in catalytic


      Zone                       1. The interval between two depths in a well

      containing a reservoir or other distinctive characteristics

      1. Specific areas where restrictions apply eg Safety zone

      (round offshore installation), Danger zone (military activity

      area) etc.



      Standard Reference Fuels and Equivalents


      Basic Energy Units


      1 British Thermal Unit = 0.252 kcal= 1.055 kJ

      1 kilocalorie= 3.968 Btu = 4.187 kJ

      1 kilojoule= 0.948 Btu= 0.239 kcal

      1 barrel oil equivalent= 5.8 million Btu 

      1 tonne oil equivalent = 10 million kcal

      1 tonne coal equivalent = 7 million kcal

      1 therm= 100,000 Btu  1 therm = 1000 kcal

      1 kilowatt-hour= 3412 Btu = 3600 kJ