reading assignment 2- oil and gas glossary

170 SPEAKING OIL & GAS

Glossaryacidise injecting acid solution down a well to dissolve carbonate rocks in a reservoir, or improve the fl ow of hydrocarbons to the well.

acoustic log a measurement of the velocities of sound waves imparted to a formation in a well and used mainly for determination of rock porosity.

anomaly a divergence from the background levels of physical or chemical properties of an area under survey.

anticline an upfold in rock strata producing an arch or dome structure. One of the most common hydrocarbon traps.

API American Petroleum Institute. API gravity is a standard method of measuring density of crude oils and is expressed in degrees.

appraisal well a well or wells drilled to follow up a discovery and evaluate its commercial potential.

assay a mini distillation process carried out in a laboratory to determine the exact composition and the physical properties of crude oil.

associated gas natural gas found as part of or in conjunction with other constituents of crude oil, as opposed to gas found on its own.

AVO amplitude variation with offset. This is a variation in seismic refl ection amplitude with a change in the distance between the energy source and the geophone/hydrophone. It indicates differences in lithology and fl uid content in rocks above and below the refl ecting layer.

ballast extra weight taken on to increase a ships stability to prevent rolling and pitching. Most ships use seawater as ballast. Empty tank space is fi lled with inert (non-combustible) gas to prevent the possibility of fi re or explosion.

barite a sulphate of barium used to add weight to drilling fl uids.

GLOSSARY 171

barrel (bbl) measure of crude oil equal to 42 USA gallons, 35 Imperial gallons or 159 litres. Takes its name because the fi rst oil produced in the USA was stored and transported in wooden barrels.

basin a dip in the earths crust usually fi lled or being fi lled with sediment. It is a basic concept in petroleum geology.

bathymetry relates to the measurement of water depths, usually referring to the ocean.

bentonite a type of clay often added to drilling fl uid because of its swelling properties when added to water.

bit the cutting part of the drilling equipment.

blowout when downhole pressure overcomes the weight of drilling fl uid and rises in a well to the surface out of control. An underground blowout is where the overpressuring enters another formation higher in the well, but before it reaches the surface.

blowout preventer a system of valves and rams set in a well which can be closed successively to counteract the uncontrolled rise of oil or gas from a reservoir below.

boe barrels of oil equivalent. A fi gure used when expressing the combined volume of oil and gas reserves.

bright spot a point on a seismic profi le which shows up brighter than surrounding traces because of an increase in amplitude of seismic waves passing from hydrocarbons to water within the pores of a rock.

calliper log a measurement of the diameter of a well.

cap rock an impermeable layer of rock that traps or halts the upward movement of oil and gas, forming the top or cap of a reservoir.

casing steel pipe screwed together to line the inside of a well bore and cemented into place.

casing shoe a heavy section steel tube fi tted to the lower end of a casing string to protect the end of the string from damage when running into a well.


cat cracking a secondary refi ning process which uses heat and the presence of a catalyst to crack apart the molecules of the various components of crude oil obtained from the primary distillation process to form refi ned petroleum products.

cement bond log a measurement of the strength and bonding of cement to the casing in a well.

choke a valve or valves used to control the fl ow of hydrocarbons from a well by changing the diameter of the orifi ce.

Christmas tree the system of valves and controls placed at the wellhead.

CIF cost including freight, where the seller of a cargo of petroleum or petroleum product provides the transport to its destination.

city gate the point at which high pressure pipelines deliver natural gas to low pressure pipelines for distribution to individual users.

closure a term used to indicate that a trap exists in the subsurface and there are no avenues for hydrocarbons (if present) to escape.

completion the fi nal preparations to ready a well for production.

concession an arrangement whereby an oil company is given exclusive permission by a government to explore a large portion of a country over a long period of time in return for an agreed percentage of any oil or gas production that results.

condensate hydrocarbons which are gaseous in a reservoir, but which condense to form a liquid as they rise to the surface where the pressure is much less.

conductor the fi rst casing string in a well.

coning this occurs when an oil well is produced at excessive rates. The reduction in reservoir pressure may draw up water underlying the oil and gas can be drawn down from an overlying gas cap.

coring an operation whereby a sample of rock being drilled is allowed to pass through the centre of a special bit and be collected in a core barrel mounted directly behind it.

GLOSSARY 173

crown block an assembly of sheaves at the top of the drilling derrick of a rig over which the hoist lines are passed.

cuttings the broken pieces of rock formed by the bit during drilling. These are fl ushed up the well and examined by the well site geologist to determine the type of formations being drilled.

darcy the unit of measurement of permeability of rock.

delineation well see appraisal well.

development well a well drilled specifi cally into a previously discovered fi eld for the purpose of producing oil or gas.

deviated well a well whose path has been deliberately diverted from the vertical.

diamond bit a drill bit with impregnated diamonds as the cutting edge.

dipmeter an instrument lowered down the well to measure the dip of the drilled formations relative to the well.

directional well see deviated well.

distillation the refi ning process of separating crude oil components by heating and subsequently condensing of the fractions by cooling. The basic principle in refi ning is that of heating crude oil until various vapours or gases boil off, and then condensing them to form a condensate or distillate. The fi rst to boil are the very light, dry gases; then highly volatile natural gasoline, kerosene, gas oil, light lube oil stock, and so on until heavy resin is left. This resin is broken up by other, more sophisticated processing.

distribution cost usually refers to the cost of transporting gas to the consumer through low pressure pipelines and includes a fee for the pipeline owner.

distribution system usually refers to the network of low pressure gas pipelines delivering gas to individual consumers.

downstream refers to all petroleum operations occurring after delivery of crude oil or gas to refi nery or fractionation plant.


downtime the time an operation is postponed, usually due to bad weather or mechanical failure.

draw-works the hoisting winch for handling drill pipe and casing on a rig.

drill collar the top of a well, usually a cemented section from which the conductor pipe is hung.

drill pipe steel pipe screwed together and used to carry and rotate the drilling tools in a well and to permit the circulation of drilling fl uid.

drill stem test a valved test tool is lowered down a well on the end of the drill string to a specifi c reservoir formation and the valve opened to admit formation fl uids.

drill string the column of drill pipe lengths screwed together.

drilling fl uid see drilling mud.

drilling line the wire cable on a rotary rig, one end of which is wound around the drum of the draw-works and the other passes through the crown and travelling block sheaves to a fi xed point on the derrick frame. As the wire round the drum is wound in or paid out, it is the means of raising and lowering the travelling block.

drilling mud (drilling fl uid) is the suspension of minerals and chemicals in oil or water which forms the well circulatory system.

drillship a ship-shaped marine exploration drilling vessel usually with its own means of locomotion.

dry gas natural gas (methane and ethane) with no signifi cant content of heavier hydrocarbons.

dry tree a subsea wellhead where the equipment is enclosed in a water-tight chamber.

dynamic positioning a method of keeping an offshore drilling rig on location without anchors using computer-controlled propellers around the vessels hull.

GLOSSARY 175

electric logs measurement of rock properties (e.g. resistivity, radioactivity) down a well which leads to determination of the rock types.

ethane a component of natural gas and the basic feedstock for petrochemical industries.

extended reach well a well in which the horizontal distance from the wellhead to the target location is much greater than the vertical depth to the reservoir horizon.

farminee a company which earns an interest in an oil and gas permit from the company holding the lease. This may be done through a direct cash payment, a share trade or, more usually, by agreeing to pay all or some of the costs of a seismic survey, a drilling program or a development project on that permit.

farminor a company holding the exploration or production rights in a permit which agrees to bring in another company to help defray the costs of its work program in return for allowing the newcomer to take a percentage interest in the permit.

farm-in/out an arrangement between one or more parties and the company or group holding a lease title to an exploration or production area whereby the former pays to earn an interest in the permit. Payment may be in cash or in the form of a work program.

fault a break or fracture in the earths sub-strata where one side of the break moves relative to the other.

FEED front end engineering and design. This process provides defi nitive costs and technical data on a proposed project to enable a decision on fi nal commitment to construction.

fi shing to retrieve equipment which has fallen into or is caught in the well.

fl aring the practice of burning off waste gas or oil as a safety measure in a refi nery or during a test of an exploration well. It is rarely done during production as associated gas is used or returned to the reservoir.

fl at spot a fl at trace on the seismic profi le indicative of a fl uid interface in the subsurface.


FOB free on board, where a buyer of a cargo of petroleum or petroleum product arranges the shipping from the sellers port.

formation interval test see wireline test.

FPSO a fl oating production storage and offtake (offl oading) vessel

fraccing a process used to improve the permeability of a tight reservoir. A specially blended fl uid, charged with proppants like sand or aluminium pellets, is pumped down a well at high pressure to force passageways into the rock. The proppants keep them open once the pressure is released.

gas cap the natural accumulation of associated gas in the top of an oil reservoir.

gas oil a medium distilled oil from the refi ning process that is intermediate between light lubricating oils and kerosene. Used to produce diesel fuel and in heating and air conditioning systems.

gas/oil ratio (GOR) the ratio of gas to oil by volume, measured during a production test.

gazettal the advertisement of permits by the government calling for applications for exploration licences.

geophones microphones used in seismic surveys to electronically pick up returning shock waves and pass them on to the recording equipment.

geo-steering a modern drilling technique in which a hydraulic motor turns the drilling bit independently of the drill string. A bend in the motor housing enables the trajectory of the well to be changed as the full weight of the drill string bears down on the bit.

gross pay the total thickness of a reservoir rock, including the impervious layers which do not contain hydrocarbons.

guyed tower a type of offshore production platform surrounded by a series of cables anchored in the sea bed to hold it in place, much like the guy ropes of a tent.

GLOSSARY 177

heavy crude crude oil with high viscosity and high specifi c gravity. The API classifi es heavy oil as crudes with a gravity below 22.3 API.

hedging forward selling of petroleum shipments at a price believed to be competitive when the physical cargo is available.

heli-rig a land rig capable of being broken down into loads small enough to be carried by a helicopter. Usually used in inaccessible terrain to replace land transport.

horizontal drilling a technique for deviating wells through up to 90 degrees from the vertical, usually to produce thin reservoirs by exposing more of the oil zone to the well perforations.

hydrocarbon kitchen the part of a sedimentary basin containing mature petroleum source rocks. A general term for conditions deep in the subsurface rich in organic sediments which, with the necessary burial history (heat and pressure) generate signifi cant amounts of hydrocarbons.

hydrophones the marine equivalent of geophones.

infi ll drilling production wells drilled between existing wells to increase hydrocarbon recovery. Often the wells are drilled to reach oil or gas stranded by the rising water drive in a reservoir and unable to fl ow to the original wells.

injection well a well through which water or gas is injected to maintain reservoir pressure.

in situ (in place) refers to total oil or gas reserves contained in a reservoir in the ground as opposed to those reserves which may be recovered.

isogals contour lines drawn through points of equal gravity values and referring to the gal which is the unit of gravity measurement.

jacket the leg section of an offshore production platform, so called because it surrounds and protects the well conductors as well as supporting the deck and its equipment.

jack-up a type of mobile drilling rig which jacks its legs down to the sea bed and then hoists its deck and drill fl oor above the sea surface.


jet bit a drilling bit with nozzles through which fl uids like air, mud or water are forced under pressure, thus breaking up the formation to be penetrated.

J-lay an offshore pipe laying technique in which the pipeline is lowered vertically to the sea bed from the lay barge and then allowed to bend in a J-curve shape as the vessel moves forward adding new sections of pipe.

joint venture a group of companies or individuals who share the cost and rewards of exploring for and producing oil or gas from a permit.

kelly hexagonal or square pipe about 15 metres long attached to the top of the drill string and turned by the rotary table. It is used to transmit the twisting movement from the rotary machinery to the drill string and thus the bit.

kelly bushing a piece of equipment which fi ts around the kelly at the point where it passes through the rotary table. It is often used as a datum from which to measure the depth of a well.

kerogen the organic matter which is the base for the formation of oil or gas.

kick a sudden infl ux of high pressure into a well, usually experienced while drilling.

kill the process of increasing drilling fl uid weight to control a potential blowout.

landmen generally only applicable in the USA where the rights to subsurface minerals are often owned by private individuals. These individuals are entitled to ask for a royalty on any oil or gas production from their portion of the subsurface. These subsurface rights began by being attached to the surface landholding of the original landholder. However, they can be bequeathed or sold and onsold separately to the surface rights, such that after a period of time it is diffi cult for an oil explorer to trace who actually owns the rights in question and who to deal with when negotiating royalties. Landmen are employed by the oil explorers specifi cally to unravel the paper trail and fi nd the royalty holders in the lease they want to drill.

GLOSSARY 179

lay barge a specially designed vessel used to lay a pipeline along the sea bed.

lease a specifi c area of land or sea bed marked out by a government and usually put up for tender. The successful bidder is given exclusive right to explore for oil and gas for a specifi ed length of time provided it upholds the work program mentioned in the winning bid and obeys the set conditions of the leasehold agreement.

light crude generally refers to crude oil with an API gravity of 30 degrees or more.

liner steel tube of small diameter extending into a producing reservoir from the bottom of the last string of casing in a well.

lithology a study of the rock types in a given region, including descriptions of mineral content.

LNG liquefi ed natural gas.

LNG train the liquefaction of natural gas to form LNG is carried out in a refrigeration unit that has four main elements in the cooling cycle a compressor, a condenser, a pressure-expansion valve and an evaporator. A single liquefaction unit is called a train. An LNG plant may comprise just one train. Larger plants comprise a number of trains arranged side by side each doing exactly that same liquefaction task.

logging tools devices lowered down a well to measure various parameters and properties of the formations being drilled (electric loop).

LPG liquefi ed petroleum gas, usually refers to propane and butane.

marine riser the conductor pipe for offshore wells. It extends from the drill fl oor to the sea bed.

marker crude a commonly traded crude oil in a particular region that is used as a quality standard to price other crudes.

mercaptans compounds of carbon, hydrogen and sulphur found in sour crude and natural gas which have a strong, repulsive odour. They are re-introduced in small amounts as a safety measure so that the presence of sales (retail) gas can be detected by smell.


migration the movement of oil/gas from a petroleum source rock into and then within a reservoir rock.

monkey board the small platform high in the derrick of a rig occupied by the derrickman when guiding stands of drill pipe and casing to and from storage racks during drilling operations.

moonpool the open hole in the centre of the hull of a drillship through which drilling takes place.

mud logging this includes routine geological examination of drill cuttings from a well, plus a record of the variations in drilling rate, mud pumping pressure, depths of formation changes and an analysis of the mud for oil and gas traces.

naphtha a collective name given to a range of distillates covering the heavier end of the gaseous fuel and the light end of the kerosene range.

net pay the aggregate thickness of only those parts of the reservoir which contain and produce hydrocarbons.

nuclear logs a measurement of gamma rays and thermal neutrons from downhole formations which can be used to determine rock porosity and lithology.

on stream in production.

open hole refers to a well which has no casing or which is cased only to the top of the reservoir section.

operator the company which organises the exploration and production programs in a permit on behalf of all the interest holders in the permit.

override interest this occurs when a company holding the permit sells all its working interest to an incoming party in return for an agreed percentage of the proceeds from any commercial discovery.

P1 reserves see proved reserves.

P2 reserves see probable reserves.

P3 reserves see possible reserves.

GLOSSARY 181

packer a device (often rubber) which seals off a section of the well during testing.

paper crude crude oil which is sold on the futures market, but which will not be physically produced for several months or longer.

pay zone a formation within a reservoir containing producible hydrocarbons.

percussion drilling a system whereby the drill bit penetrates rock with a hammer action. The drill can either be dropped using its own weight and gravity or it can be pressure driven into a rock face.

perforations holes punched through the casing of a well at the pay zone to allow oil and gas to enter the well.

permeability the degree to which fl uids can move through a rock.

permit an area of specifi ed size within a sedimentary basin which is licensed or allocated to a company or companies by the government for the purpose of exploring for and producing oil and gas. In Australia separate licences are issued for exploration and production.

petroleum resource rent tax (PRRT) a form of profi t-based tax which applies after a producing oil/gas project has reached a set rate of return. The tax itself is levied at specifi ed percentage. Usually exploration and development costs can be deducted from cash fl ow so they are recouped before tax trigger or threshold is reached.

pig a mechanical device sent through a pipeline to scour the inside walls or to run internal checks on the integrity of the line.

plug a seal deliberately placed in a well to prevent escape of high pressure material from the substance after it has been abandoned. Usually plugs are of cement.

plugged and abandoned where all the reservoir and high pressure zones in a well are sealed off with cement so that no fl uids can escape after the drilling rig leaves the location.


porosity a measure of the pore space within a rock and expressed as a percentage of volume.

possible reserves those unproved reserves which analysis of geological and engineering data suggests are less likely to be recoverable than probable reserves. In this context, when probabilistic methods are used, there should be at least a 10 per cent probability that the quantities actually recovered will equal or exceed the sum of estimated proved plus probable plus possible reserves. [Society of Petroleum Engineers, www.spe.org]

probable reserves are those unproved reserves which analysis of geological and engineering data suggests are more likely than not to be recoverable. In this context, when probabilistic methods are used, there should be at least a 50 per cent probability that the quantities actually recovered will equal or exceed the sum of estimated proved plus probable reserves. [Society of Petroleum Engineers, www.spe.org]

production platform a fi xed facility on an offshore fi eld from which development wells are drilled. It carries all the associated processing plant and other equipment needed to keep the wells fl owing and treat the oil and gas once it reaches the onboard wellheads, as well as accommodation. See also jacket.

production sharing contract see PSC.

production test a test conducted in a well to assess its production potential by measuring pressures and fl uid volumes produced through various choke sizes at specifi ed time intervals.

production well see development well.

proppant (propping agent) a granular substance such as sand grains, aluminium pellets, glass balls and in the early days even walnut shells, that are carried in suspension in a fl uid that is injected into a formation at high pressure during a well fraccing program to improve the permeability of a reservoir. The proppant keeps the newly made fractures open when the fl uid is withdrawn.

GLOSSARY 183

proved reserves are those quantities of petroleum which, by analysis of geological and engineering data, can be estimated with reasonable certainty to be commercially recoverable, from a given date forward, from known reservoirs and under current economic conditions, operating methods, and government regulations. If deterministic methods are used, the term reasonable certainty is intended to express a high degree of confi dence that the quantities will be recovered. If probabilistic methods are used, there should be at least a 90 per cent probability that the quantities actually recovered will equal or exceed the estimate. [Society of Petroleum Engineers, www.spe.org]

PSC production sharing contract, where an oil company is contracted to explore for and produce oil and gas under pre-set arrangements to share the proceeds with the host government or its national petroleum company.

recovery factor the amount of oil or gas that can be recovered from a reservoir is considerably less than the total volume of hydrocarbons actually in place. Recovery factor is expressed as a percentage of the total reserves believed to be in place.

refi nery an installation that manufactures fi nished petroleum products from crude oil, unfi nished oils, natural gas liquids and other hydrocarbons.

reservoir a rock or formation which holds hydrocarbons within the pore spaces between individual grains.

retention lease a permit enabling a company to keep ownership of a hydrocarbon discovery that is not commercial at the time of discovery, but that may be in the future if parameters change, such as a higher oil price or the discovery of signifi cant new fi elds nearby.

rolling cutter bit a bit with hardened steel or tungsten carbide teeth of varying lengths and spacings mounted on three roller cones.

rotary drilling a system whereby a bit is forced against a rock face and mechanically rotated to penetrate the various formations.


rotary swivel the part of a rotary drilling rig which connects the travelling block to the drill string.

rotary table a fl at plate in the drill fl oor which is turned mechanically at varying speeds and directions imparting the rotary action to the drill string which passes through its centre.

roughneck a rig worker who handles the drill pipe and other equipment on the drill fl oor.

round trip the complete operation of pulling out the drill string from a well (for instance to change a bit) and then running it back into the well.

roustabout a general labourer on a rig.

safety case where government sets broad safety goals to be attained at industrial facilities and the companies concerned develop the most appropriate methods for achieving those goals. The basic tenet is that the ongoing management of safety is the responsibility of the operator and not the regulator.

sales gas natural gas that is sold into the distributor/retail market after being treated to remove impurities.

sand lenses porous sandstone reservoirs that are completely surrounded by fi ne-grained impervious rocks. The lenses are often buried river beds or deltas.

sedimentary cycle the period encompassing an encroachment of the sea over the land and then a subsequent withdrawal of the sea.

seep a point where migrating oil or gas, not already trapped, reaches the earths surface.

seismic survey a method of determining the subsurface features by sending sound waves into the various buried rock layers in the earth and measuring the time they take to return to the surface.

GLOSSARY 185

semi-submersible an offshore drilling vessel which has its deck supported by columns fi xed to pontoons which can be ballasted below the wave action and provide a stable drilling base.

shale shaker equipment near the rig fl oor which separates the drill cuttings from the drilling mud.

side wall coring is the extraction of a small core of rock from the side of a drill hole. It is obtained by lowering a percussion gun to the required depth and fi ring a small core tube into the well wall. The core in the tube is then pulled back to the surface.

sidetracking when a well is deliberately deviated around an obstruction or branched off part way down a completed well to reach another part of the reservoir.

slim hole drilling drilling a hole where 90 per cent of its length has a diameter of seven inches (180 millimetres) or less. The smaller hole and casing sizes result in reduced costs and are sometimes used in the initial phase of an exploration drilling program.

slug catcher a device which uses a very long length of pipe to create a pressure drop in an incoming natural gas pipeline suffi cient to allow slugs of associated heavier hydrocarbons like condensate to drop out and be separated from the gas fl ow.

sour crude crude oil that contains appreciable amounts of sulphur compounds.

spot market the sale of individual shipments of crude oil priced at the international market rate at the time of sale.

spud date the date when drilling of a well begins.

spud in to begin drilling. To start a well.

stinger a ramp or boom mounted on the stern of a lay barge used to gradually lower the pipe onto the sea bed.


stratigraphy a description of the rock formations in sequence from top to bottom in a sedimentary basin.

streamer the string of cable with hydrophones attached which is towed behind a vessel during an offshore seismic survey.

structure in oil industry terms it refers to a feature within the earths crust with the potential to trap migrating hydrocarbons.

submersible a form of fl oating drill rig which can be ballasted down to sit on the sea fl oor or lake fl oor during marine drilling mode. The term can also refer to a remote-controlled or a manned submarine used in inspection and maintenance offshore.

subsea completion a production wellhead which is placed on the sea bed instead of on a platform at the surface.

suspended a well is suspended when it is likely to be re-entered at a later date, either to continue drilling or to run a test of a reservoir that was not possible or convenient during the original drilling. The well is suspended by setting cement plugs that can be drilled out when re-entry takes place.

sweet crude crude oil that is free of sulphur compounds.

tension leg platform a type of fl oating offshore production facility that is tethered to the sea bed with steel cables and uses its buoyancy to keep the cables tight (in tension).

term contracts when shipments of a particular crude oil or condensate are contracted and sold to one buyer or group of buyers for a specifi c period of time (often 510 years) at a negotiated price which is set at a differential to the fl oating price of a bench mark crude.

thin stringers a term referring to oil and gas reservoirs that measure a few metres or less in thickness.

three dimensional seismic survey (3D) a survey with seismic lines set out in close grid pattern to gain better resolution of detail in an area.

GLOSSARY 187

tight a term indicating that a formation has little permeability.

time map a plan of mapped horizons from the seismic sections where the contours connecting equal values in times of waves reaching the geophones are plotted on the grid map for the survey. To convert this to a geological map, velocity measurements are used to change time to depth values.

toolpusher the chief driller in charge of operations on the rig fl oor.

top drive a drilling system where a motor is attached to the top of the drill string in the rig derrick to impart a rotary action directly, rather than use a kelly and rotary table.

trap a formation in the earths subsurface which prevents the onward migration of hydrocarbons.

travelling block a large pulley with sheaves at the top end that allow the drilling line to pass through and a hook at the bottom end which is attached to the drill pipe. Raising or lowering the drilling line will move the travelling block and the attached drill pipe up or down within the derrick.

tri-cone bit see rolling cutter bit.

tubing see liner.

turbo drill a drill bit which is rotated via a multi-stage turbine mounted at the bottom of the drill pipe. Power to rotate is supplied by the drilling fl uid being pumped down hole from the surface.

underbalanced drilling where the weight of the drilling mud in the well is less than the formation pressure of the rock layers penetrated. This allows formation fl uids to rise up the well to the surface where the fl ow is continuously monitored to detect hydrocarbons.

unitisation agreement where owners of petroleum reserves pool their individual interests in return for an interest in the overall unit which is then operated by a single company on behalf of the group.


up-dip a term referring to any point in a reservoir that is higher up in the structure or trap.

vibroseis a form of survey where the seismic waves are created by mechanically vibrating a steel pad or plate on the earths surface.

wet gas natural gas that contains signifi cant amounts of associated liquid hydrocarbons such as condensate, propane and butane. In terms of quantity, gas is sometimes declared wet when 10 or more barrels of liquid hydrocarbons can be separated from 1 million cubic feet of gas.

wet tree a subsea wellhead where the equipment is exposed to the sea.

whipstock a wedge-shaped piece of equipment placed in the bottom of a well which forces the bit and the drill pipe to deviate from their original direction when drilling is resumed.

wildcat the fi rst well drilled in a new area. It can also mean the fi rst well in a new structure or prospect.

wireline logging an operation to obtain information about the rock formations in the well by lowering a suite of logging tools down the hole on a cable called a wireline.

wireline test a test for hydrocarbons in a formation by lowering a chamber downhole on the end of a wire and allowing reservoir fl uids to fl ow into it.

working interest where a company pays a percentage of a survey, drilling or development program and receives a proportional part of the resultant benefi ts.

workover the re-entry into a completed well for modifi cation or repair and maintenance work.

reading assignment 2- oil and gas glossary

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