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:
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
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.
To unscrew a joint of drillpipe.
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
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
(One billion cubic feet (BCF) = one thousand million
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.
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.
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.
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
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
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
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
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
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.
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
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
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.
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
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.
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
Connate Water The original water content of a reservoir
rock. Connate water reduces the pore-space (porosity)
available to hydrocarbons. Sometimes called Interstitial
Consortium A 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
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-out Total 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
Dealkylation A cracking process whose main product is
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
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.
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
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
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, Diameter 1. 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.
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).
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.
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
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
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
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
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
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
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.
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
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
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.
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
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
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
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
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
The limit of radius of action of an
underwater vessel or vehicle.
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
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
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
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
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
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
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
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).
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.
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
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
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.
Hottap inserting 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
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
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
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
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
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
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
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-
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.
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
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
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.
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
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-
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
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.
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.
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
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
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
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.
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
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
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
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
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
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
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
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.
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
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
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
'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
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
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
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
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
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
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
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
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
A submerged or semi-submerged part of a floating
drilling rig structure designed to assist flotation, containing
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
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
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
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
Production 1. 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
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
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
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
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
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
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
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.
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
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 recovery is 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
Secondary refining process Processes which go
beyond the primary distillation of crude oil into its
Seconds Saybolt Unit of measurement of oil viscosity
mainly used in commercial specifications.
Section of Land (US) One square mile, as defined for
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 Tax A 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
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
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
SOFC Solid oxide fuel cell.
Solid Alkanes Hydrocarbon fractions which are solid at
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
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
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
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
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 Depreciation A 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.
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
Strike 1. The angle of dip or inclination from the
horizontal of rock stratum 2. A strike is also a term for a
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
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
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
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
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
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
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
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
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
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
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
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
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
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:
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
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
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
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
Specific areas where restrictions apply eg Safety zone
(round offshore installation), Danger zone (military activity
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