To cease work on a well which is non-productive, to plug off the well with cement plugs and salvage all recoverable equipment. Also used in the context of field abandonment. (Oil & Gas UK)

Acid stimulation

Form of hydrochloric acid is pumped down well hole to enlarge pore space in oil bearing rocks to increase flow and recovery.


Non-hydrocarbon compounds added to or blended with a product to modify its properties (2009/119/EC)

Appraisal Well

A well drilled as part of an appraisal drilling programme which is carried out to determine the physical extent, reserves and likely production rate of a field. (Oil & Gas UK)


A unit of volume measurement used for petroleum and its products (7.3 barrels = 1 ton: 6.29 barrels = 1 cubic metre). (Oil & Gas UK)


One barrel of oil; 1 barrel = 35 Imperial gallons (approx.), or 159 litres (approx.); 7.5 barrels = 1 tonne (approx.); 6.29 barrels = 1 cubic metre. (Oil & Gas UK)


Billion cubic feet; 1 bcf = 0.83 million tonnes of oil equivalent. (Oil & Gas UK)


Billion cubic metres (1 cubic metre = 35.31 cubic feet). (Oil & Gas UK)


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

Blow-out preventers

(BOPs) are high pressure wellhead valves, designed to shut off the uncontrolled flow of hydrocarbons. (Oil & Gas UK)


The hole as drilled by the drill bit. (Oil & Gas UK)

British thermal unit (BTU)

A measure of the heating value of a fuel. (Oil & Gas UK)

Cascade control

A system which automatically starts up or stops units in a predetermined sequence to meet variations in the energy demands being served. The sequence may be changed periodically to ensure that the running time of each unit is approximately equal.(DECC UK)


Metal pipe inserted into a wellbore and cemented in place to protect both subsurface formations (such as groundwater) and the wellbore. A surface casing is set first to protect groundwater. The production casing is the last one set. The production tubing (through which hydrocarbons flow to the surface) will be suspended inside the production casing. (Oil & Gas UK)

Casing string

The steel tubing that lines a well after it has been drilled. It is formed from sections of steel tube screwed together. (Oil & Gas UK)

Chemical dosing

The addition of conditioning chemicals to boiler feed-water or cooling water to protect plant from scaling, blocking, corrosion etc. (DECC UK)

Christmas tree

The assembly of fittings and valves on the top of the casing which control the production rate of oil. (Oil & Gas UK)

Commercial field

An oil and/or gas field judged to be capable of producing enough net income to make it worth developing. (Oil & Gas UK)


The installation of permanent wellhead equipment for the production of oil and gas. (Oil & Gas UK)


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. (Oil & Gas UK)


Taking rock samples from a well by means of a special tool -- a "core barrel".(Oil & Gas UK)

Crane barge

A large barge, capable of lifting heavy equipment onto offshore platforms. Also known as a "derrick barge". (Oil & Gas UK)

Creaming Theory

A statistical technique which recognises that in any exploration province after an initial period in which the largest fields are found, success rates and average field sizes decline as more exploration wells are drilled and knowledge of the area matures. (Oil & Gas UK)


Rock chippings cut from the formation by the drill bit, and brought to the surface with the mud. Used by geologists to obtain formation data. (Oil & Gas UK)


The tower-like structure that houses most of the drilling controls. (Oil & Gas UK)

Development well

A well drilled within the proved area of an oil or gas reservoir to the depth of a stratigraphic horizon known to be productive; a well drilled in a proven field for the purpose of completing the desired spacing pattern of production. (Oil & Gas UK)

Discount factor

The factor used to convert net annual cash flow to present value, depending on the interest rate and the number of years from present. Calculated by a derivation of the compound interest formula: DF = 1 (1 + r/100)n where r = % interest rate and n = number of years from now. (DECC UK).

Discount rate

The annual percentage figure used in discounted cash flow analyses to discount the future value of costs/savings to give a Net Present Value. (DECC UK)


A term used to describe tools, equipment, and instruments used in the wellbore, or conditions or techniques applying to the wellbore. (Oil & Gas UK)


When referring to the oil and gas industry, this term indicates the refining and marketing sectors of the industry. More generically, the term can be used to refer to any step further along in the process. (Oil & Gas UK)

Drill cuttings

The small pieces of rock created as a drill bit moves through underground formations while drilling. (Oil & Gas UK)

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. (Oil & Gas UK)

Dry hole

Any exploratory or development well that does not find commercial quantities of hydrocarbons. (Oil & Gas UK)


Abbreviation for exploration and appraisal. (Oil & Gas UK)


Abbreviation for exploration and production. The ‘upstream’ sector of the oil and gas industry. (Oil & Gas UK)

Enhanced oil recovery (EOR)

A process whereby oil is recovered other than by the natural pressure in a reservoir. Refers to a variety of processes to increase the amount of oil removed from a reservoir, typically by injecting a liquid (e.g., water, surfactant) or gas (e.g., nitrogen, carbon dioxide). (Oil & Gas UK)

Exploration well

Drilling carried out to determine whether hydrocarbons are present in a particular area or structure. Also known as a ‘wildcat well’. (Oil & Gas UK)

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. (Oil & Gas UK)

Fault level

The maximum prospective current that can flow under a three-phase short circuit condition. It should be noted that it can vary according to the point in the system at which the fault occurs. The magnitude of the potential fault level has a major influence on the choice and design of the equipment to be used. (DECC UK)


A geographical area under which an oil or gas reservoir lies. (Oil & Gas UK)

Flaring and venting

Flaring is burning of hydrocarbon gases for commercial or technical reasons. Venting is release of gases to atmosphere.

Formation damage

The reduction in permeability in reservoir rock due to the infiltration of drilling or treating fluids into the area adjacent to the wellbore. (Oil & Gas UK)

Formation pressure

The pressure at the bottom of a well when it is shut in at the wellhead. (Oil & Gas UK)

Formation water

Salt water underlying gas and oil in the formation. (Oil & Gas UK)


A method of breaking down a formation by pumping fluid at very high pressure. The objective is to increase production rates from a reservoir. (Oil & Gas UK)

Gas injection

The process whereby separated associated gas is pumped back into a reservoir for conservation purposes or to maintain the reservoir pressure. (Oil & Gas UK)


Gearing Percentage ratio of debt to net assets. (DECC UK)


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. (Oil & Gas UK)

In-duct burner

A burner comprising an arrangement of fuel nozzles located within a duct along which the combustion air (or oxidant) flows. The fuel nozzles may have their separate supply of cooling or stabilising air. This arrangement is commonly used for supplementary firing of additional fuel using the residual oxygen in gas turbine exhaust as oxidant to boost the exhaust gas temperature before it enters the heat recovery boiler. (DECC UK)

Injection well

A well used for pumping water or gas into the reservoir. (Oil & Gas UK)

Integrated company

Indicates a firm that operates in both the upstream and downstream sectors (from exploration through refining and marketing). (Oil & Gas UK)


The lower section, or ‘legs’, of an offshore platform. (Oil & Gas UK)


A legal document conveying the right to drill for oil and gas, or the tract of land on which a lease has been obtained where the producing wells and production equipment are located. (Oil & Gas UK)

Lifting costs

The cost of producing oil from a well or lease. (Oil & Gas UK)

Metric tonne

Equivalent to 1000 kilos, 2204.61 lbs; 7.5 barrels. (Oil & Gas UK)


A term sometimes used to refer to those industry activities that fall between exploration and production (upstream) and refining and marketing (downstream). The term is most often applied to pipeline transportation of crude oil and natural gas. (Oil & Gas UK)


Million Barrels Oil Equivalent. (Oil & Gas UK)


A mixture of base substance and additives used to lubricate the drill bit and to counteract the natural pressure of the formation. (Oil & Gas UK)

Nameplate rating

The full-load continuous rating of a generator or other electrical equipment under specified conditions as designated by the manufacturer, and written on the nameplate. (Washington State University)

Non-associated gas

Natural gas produced from a reservoir that does not contain significant quantities of crude oil. (Oil & Gas UK)


A mixture of liquid hydrocarbons of different molecular weights. (Oil & Gas UK)

Oil field

A geographic area under which an oil reservoir lies. (Oil & Gas UK)

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. (Oil & Gas UK)

Operating lease

A rental agreement for a fixed period of time during which the risks and rewards of ownership remain with the lessor (i.e. the finance company) rather than the lessee (i.e. the business customer). At the end of the lease period, the equipment is returned to the lessor or, alternatively, it is purchased by the lessee for an agreed sum. (DECC UK)


The company that has legal authority to drill wells and undertake production of hydrocarbons. The operator is often part of a consortium and acts on behalf of this consortium. (Oil & Gas UK)

P&A (plugged and abandoned)

A depleted well or dry hole that has been (typically) filled with cement and marked, with all surface equipment removed. (Oil & Gas UK)


Rock in which oil and gas are found in exploitable quantities. (Oil & Gas UK)


The property of a formation which quantifies the flow of a fluid through the pore spaces and into the wellbore. (Oil & Gas UK)


A generic name for hydrocarbons, including crude oil, natural gas liquids, natural gas and their products. (Oil & Gas UK)


An offshore structure that is permanently fixed to the seabed. (Oil & Gas UK)


A ratio between the volume of the pore space in reservoir rock and the total bulk volume of the rock. The pore space determines the amount of space available for storage of fluids. (Oil & Gas UK)

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. (Oil & Gas UK)

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. (Oil & Gas UK)

Produced water

The water extracted from the subsurface with oil and gas. It may include water from the reservoir, water that has been injected into the formation, and any chemicals added during the production/treatment process. Produced water is also called ‘brine’ (and may contain high mineral or salt content) or ‘formation water’. Some produced water is quite fresh and may be used for livestock watering or irrigation (where allowed by law). (Oil & Gas UK)

Production Drilling

Drilling of wells in order to bring a field into production.

Proven field

An oil and/or gas field whose physical extent and estimated reserves have been determined. (Oil & Gas UK)

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). (Oil & Gas UK)

Recoverable reserves

That proportion of the oil and/gas in a reservoir that can be removed using currently available techniques. (Oil & Gas UK)

Recovery factor

The ratio of recoverable oil and/or gas reserves to the estimated oil and/or gas in place in the reservoir. (Oil & Gas UK)


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. (Oil & Gas UK)

Riser (drilling)

A pipe between a seabed BOP and a floating drilling rig. (Oil & Gas UK)

Riser (production)

The section of pipework that joins a seabed wellhead to the Christmas tree. (Oil & Gas UK)


Drill crew members who work on the derrick floor, screwing together the sections of drillpipe when running or pulling a drillstring. (Oil & Gas UK)


Drill crew members who handle the loading and unloading of equipment and assist in general operations around the rig. (Oil & Gas UK)


A percentage interest in the value of production from a lease that is retained and paid to the mineral rights owner. (Oil & Gas UK)

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. (Oil & Gas UK)


The process of separating liquid and gas hydrocarbons and water. This is typically accomplished in a pressure vessel at the surface, but newer technologies allow separation to occur in the wellbore under certain conditions. (Oil & Gas UK)


A production hiatus during which the platform ceases to produce while essential maintenance work is undertaken. (Oil & Gas UK)


The operation of drilling the first part of a new well. (Oil & Gas UK)

Suspended well

A well that has been capped off temporarily. (Oil & Gas UK)


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. (Oil & Gas UK)


The superstructure of a platform. (Oil & Gas UK)


The exploration and production portions of the oil and gas industry. (Oil & Gas UK)


The injection of water into an oil reservoir to ‘push’ additional oil out of the reservoir rock and into the wellbores of producing wells. (Oil & Gas UK)

Well log

A record of geological formation penetrated during drilling, including technical details of the operation. (Oil & Gas UK)


The equipment at the surface of a well-used to control the pressure; the point at which the hydrocarbons and water exit the ground (Oil & Gas UK)

Wildcat well

A well drilled in an area where no current oil or gas production exists. (Oil & Gas UK)


Operations on a producing well to restore or increase production. A workover may be performed to stimulate the well, remove sand or wax from the wellbore, to mechanically repair the well, or for other reasons. (Oil & Gas UK)