(1) The proper plugging and abandoning of a well in compliance with all applicable regulations, and the cleaning up of the wellsite to the satisfaction of any governmental body having jurisdiction with respect thereto and to the reasonable satisfaction of the operator.(2) To cease efforts to find or produce from a well or field.(3) To plug a well completion and salvage material and equipment.    


(1) The act or process of reducing the intensity of pollution.(2) The use of some method of abating pollution.   


The space between: (1) The casing and the wall of the borehole.(2) Two strings of casing.(3) Tubing and casing.   

Appraisal Well    

A well drilled as part of an appraisal drilling program which is carried out to determine the physical extent, reserves and likely production rate of a field.   

Associated Gas   

A well drilled as part of an appraisal drilling program which is carried out to determine the physical extent, reserves and likely production rate of a field.   


A unit of volume measurement used for petroleum and its products (7.3 barrels = 1 ton: 6.29 barrels = 1 cubic meter).   


One barrel of oil; 1 barrel = 35 Imperial gallons (approx.), or 159 litres (approx.); 7.5 barrels = 1 ton (approx.); 6.29 barrels = 1 cubic meter.   


Billion cubic feet; 1 bcf = 0.83 million tons of oil equivalent.   


Billion cubic meters (1 cubic meter = 35.31 cubic feet).   


An acreage sub-division measuring approximately 10 x 20 kms, forming part of a quadrant. e.g. Block 9/13 is the 13th block in Quadrant 9.   


Condensate and gas is produced simultaneously from the outset of production.   


When well pressure exceeds the ability of the wellhead valves to control it. Oil and gas "blow wild" at the surface.   

Blow-out preventers (BOPs)   

Are high pressure wellhead valves, designed to shut off the uncontrolled flow of hydrocarbons.   


The hole as drilled by the drill bit.   


A casinghead.   


Pipe cemented in the well to seal off formation fluids or keep the hole from caving in.    

Casing string   

The steel tubing that lines a well after it has been drilled. It is formed from sections of steel tube screwed together.   

Central estimate   

A range of exploration drilling scenarios from which the following activity levels, based on recent historical experience, are adopted as the central estimates.   

Christmas tree   

The assembly of fittings and valves on the top of the casing which control the production rate of oil.   

Commercial field    

An oil and/or gas field judged to be capable of producing enough net income to make it worth developing.   


The installation of permanent wellhead equipment for the production of oil and gas.   


Hydrocarbons which are in the gaseous state under reservoir conditions and which become liquid when temperature or pressure is reduced. A mixture of pentanes and higher hydrocarbons.   


Taking rock samples from a well by means of a special tool -- a "core barrel".   

Crane barge   

A large barge, capable of lifting heavy equipment onto offshore platforms. Also known as a "derrick barge".   

Crude Oil    

Liquid petroleum as it comes out of the ground as distinguished from refined oils manufactured out of it.    

Cubic foot   

A standard unit used to measure quantity of gas (at atmospheric pressure); 1 cubic foot = 0.0283 cubic meters.   


Rock chips cut from the formation by the drill bit, and brought to the surface with the mud. Used by geologists to obtain formation data.   


To increase the distance below a specified reference datum.   


The tower-like structure that houses most of the drilling controls.   

Development phase    

The phase in which a proven oil or gas field is brought into production by drilling production (development) wells.   


(1)To bore a hole, Also see Drilling(2)An implement with cutting edges used to bore holes.   

Drilling rig   

A drilling unit that is not permanently fixed to the seabed, e.g. a drillship, a semi-submersible or a jack-up unit. Also means the derrick and its associated machinery.   

Dry Gas   

Natural gas composed mainly of methane with only minor amounts of ethane, propane and butane and little or no heavier hydrocarbons in the gasoline range.   

Dry hole   

A well which has proved to be non-productive.   


Abbreviation for exploration and appraisal.   


Abbreviation for exploration and production.   

Enhanced oil recovery   

A process whereby oil is recovered other than by the natural pressure in a reservoir.   

Exploration drilling   

Drilling carried out to determine whether hydrocarbons are present in a particular area or structure.   

Exploration phase   

The phase of operations which covers the search for oil or gas by carrying out detailed geological and geophysical surveys followed up where appropriate by exploratory drilling.   

Exploration well   

A well drilled in an unproven area. Also known as a "wildcat well".   

Farm in   

When a company acquires an interest in a block by taking over all or part of the financial commitment for drilling an exploration well.   


A geographical area under which an oil or gas reservoir lies.   


Retrieving objects from the borehole, such as a broken drillstring, or tools.   

Formation pressure   

The pressure at the bottom of a well when it is shut in at the wellhead.   

Formation water   

Salt water underlying gas and oil in the formation.   


A method of breaking down a formation by pumping fluid at very high pressures. The objective is to increase production rates from a reservoir.   




Gas Condensate.   

Gas field    

A field containing natural gas but no oil.   

Gas injection    

The process whereby separated associated gas is pumped back into a reservoir for conservation purposes or to maintain the reservoir pressure.   

Gas/oil ratio    

The volume of gas at atmospheric pressure produced per unit of oil produced.   

Geographic Information Systems(GIS)    

A computer system capable of assembling, storing, manipulating, and displaying geographically referenced information.   


A compound containing only the elements hydrogen and carbon. May exist as a solid, a liquid or a gas. The term is mainly used in a catch-all sense for oil, gas and condensate.   

Injection well    

A well used for pumping water or gas into the reservoir.   


The lower section, or "legs", of an offshore platform.   


A well is said to "kick" if the formation pressure exceeds the pressure exerted by the mud column.   

Lay barge    

A barge that is specially equipped to lay submarine pipelines.   

Liquefied natural gas (LNG)   

Oilfield or naturally occurring gas, chiefly methane, liquefied for transportation.   

Liquefied petroleum gas (LPG)    

Light hydrocarbon material, gaseous at atmospheric temperature and pressure, held in the liquid state by pressure to facilitate storage, transport and handling. Commercial liquefied gas consists essentially of either propane or butane, or mixtures thereof.   


Million Barrels Oil Equivalent.   

Mechanical Integrity Test    

The act of setting a packer or retrievable bridge plug above the perforations in a wellbore and applying pressure to the annulus in order to ensure soundness of the casing.   

Metric ton    

Equivalent to 1000 kilos, 2204.61 lbs.; 7.5 barrels.   


Mechanical Integrity Test   


Millions of cubic feet per day (of gas).   


An aperture in the center of a drillship or semi-submersible drilling rig, through which drilling and diving operations can be conducted.   




A mixture of base substance and additives used to lubricate the drill bit and to counteract the natural pressure of the formation.   

Natural gas   

Gas, occurring naturally and often found in association with crude petroleum.   


Natural gas liquids. Liquid hydrocarbons found in association with natural gas.   




Oil and Gas.   


A mixture of liquid hydrocarbons of different molecular weights.   

Oil field   

A geographic area under which an oil reservoir lies.   

Oil in place   

An estimated measure of the total amount of oil contained in a reservoir, and, as such, a higher figure than the estimated recoverable reserves of oil.   


The company that has legal authority to drill wells and undertake the production of hydrocarbons that are found. The Operator is often part of a consortium and acts on behalf of this consortium.   


Rock in which oil and gas are found in exploitable quantities.   


The property of a formation which quantifies the flow of a fluid through the pore spaces and into the wellbore.   


A generic name for hydrocarbons, including crude oil, natural gas liquids, natural gas and their products.   


An offshore structure that is permanently fixed to the seabed.   


The percentage of void in a porous rock compared to the solid formation.   

Possible reserves   

Those reserves which at present cannot be regarded as ‘probable’ but are estimated to have a significant but less than 50% chance of being technically and economically producible.   

Primary recovery    

Recovery of oil or gas from a reservoir purely by using the natural pressure in the reservoir to force the oil or gas out.   

Probable reserves   

Those reserves which are not yet proven but which are estimated to have a better than 50% chance of being technically and economically producible.   

Proven field   

An oil and/or gas field whose physical extent and estimated reserves have been determined.   

Proven reserves   

Those reserves which on the available evidence are virtually certain to be technically and economically producible (i.e. having a better than 90% chance of being produced).   


An operation involving any of the following: (1) Deepening from one zone to another zone.(2) Completing well in an additional zone.(3) Plugging back from one zone to another zone.(4) Sidetracking to purposely change the location of the bottom of the well, but not including sidetracking for the sole purpose of bypassing obstructions in the borehole.(5) Conversion of a service well to an oil or gas well in a different zone.(6) Conversion of an oil or gas well to a service well in a different zone.   

Recoverable reserves   

That proportion of the oil and/gas in a reservoir that can be removed using currently available techniques.   

Recovery factor   

That proportion of the oil and/gas in a reservoir that can be removed using currently available techniques.   


To enter a previously abandoned well.   


The underground formation where oil and gas has accumulated. It consists of a porous rock to hold the oil or gas, and a cap rock that prevents its escape.   

Riser (drilling)   

A pipe between a seabed BOP and a floating drilling rig.   

Riser (production)   

The section of pipework that joins a seabed wellhead to the Christmas tree.   


Drill crew members who work on the derrick floor, screwing together the sections of drillpipe when running or pulling a drillstring.   


Drill crew members who handle the loading and unloading of equipment and assist in general operations around the rig.   

Royalty payment   

The cash or kind paid to the owner of mineral rights.   

Secondary recovery    

Recovery of oil or gas from a reservoir by artificially maintaining or enhancing the reservoir pressure by injecting gas, water or other substances into the reservoir rock.   

Shut In Well   

A well which is capable of producing but is not presently producing. Reasons for a well being shut in may be lack of equipment, market or other.    


A production hiatus during which the platform ceases to produce while essential maintenance work is undertaken.   


Shut In /Temporarily Abandoned   


A wellbore segment extending from a wellbore intersection along a wellbore path to a different wellbore bottomhole from any previously existing wellbore bottomholes.   


The well activity of drilling a new wellbore segment from a wellbore intersection to a new wellbore bottomhole or target.   


The operation of drilling the first part of a new well.   

Surface Location   

The location of a well or facility/measurement point.   

Surface Reclamation   

A restoration of the surface as for productivity or usefulness.   

Suspended well   

A well that has been capped off temporarily.   


Trillion Cubic Feet (of gas).   

Temporarily Abandoned   

The act of isolating the completed interval or intervals within a wellbore from the surface by means of a cement retainer, cast iron bridge plug, cement plug, tubing and packer with tubing plug, or any combination thereof.   


Second-in-command of a drilling crew under the drilling superintendent. Responsible for the day-to-day running of the rig and for ensuring that all the necessary equipment is available.   


The superstructure of a platform.   


Underground Injection Control   

Underground Injection Control   

A program required in each state by a provision of the Safe Drinking Water Act (SDWA) for the regulation of Injection Wells, including a permit system. An applicant must demonstrate that the well has no reasonable chance of adversely affecting the quality of an underground source of drinking water before a permit is issued.    

Well log   

A record of geological formation penetrated during drilling, including technical details of the operation.   

Wildcat well   

A well drilled in an unproven area. Also known as an "exploration well". [The term comes from exploration wells in West Texas in the 1920s. Wildcats were abundant in the locality, and those unlucky enough to be shot were hung from oil derricks.]   


Remedial work to the equipment within a well, the well pipework, or relating to attempts to increase the rate of flow.