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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.

bbl

One barrel of oil;

bcf 

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

Block

North Sea acreage measuring approximately 10 x 20 kms

Blow-down 

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

Blow-out preventers

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

Borehole

The hole as drilled by the drill bit.

Casing

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.

Casing string

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

Christmas tree 

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

Completion 

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

Condensate

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.

Coring 

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".

Cuttings 

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.

Derrick 

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

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.

Downhole 

A term used to describe tools, equipment, and instruments used in the wellbore, or conditions or techniques applying to the wellbore.

Downstream 

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.

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 

Any exploratory or development well that does not find commercial quantities of hydrocarbons.

E&A 

Abbreviation for exploration and appraisal.

E&P 

Abbreviation for exploration and production. The ‘upstream’ sector of the oil and gas industry.

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).

Exploration well 

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

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.

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.

Fracturing 

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

Gas injection 

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

Gas-to-Liquids (GTL) 

The conversion of natural gas to a liquid form so that it can be transported easily. Typically, the liquid is converted back to natural gas prior to consumption.

Hydrocarbon 

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

Jacket 

The lower section, or ‘legs’, of an offshore platform.

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.

mmboe 

Million Barrels Oil Equivalent.

mmcfd 

Millions of cubic feet per day (of gas).

Mud 

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 (NGLs)

The portions of gas from a reservoir that are liquified at the surface in separators, field facilities, or gas processing plants. NGL from gas processing plants is also called liquified petroleum gas (LPG).

Non-associated gas 

Natural gas produced from a reservoir that does not contain significant quantities of crude oil.

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.

Operator 

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.

Payzone 

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

Permeability 

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

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.

Permeability 

A measure of the ability of a rock to transmit fluid through pore spaces.

Platform 

An offshore structure that is permanently fixed to the seabed.

Porosity 

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.

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.

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

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).

Recoverable reserves 

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

Recovery factor 

The ratio of recoverable oil and/or gas reserves to the estimated oil and/or gas in place in the reservoir.

Reservoir 

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.

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.

Separation 

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.

Spud-in 

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

Suspended well 

A well that has been capped off temporarily.

tcf 

Trillion Cubic Feet (of gas).

Topside 

The superstructure of a platform.

Upstream 

The exploration and production portions of the oil and gas industry.

Waterflooding 

The injection of water into an oil reservoir to ‘push’ additional oil out of the reservoir rock and into the wellbores of producing wells.

Well DataStore 

Run by CDA, one of the largest shared online stores of digital well report and log data in the world.

Wellhead 

The equipment at the surface of a well used to control the pressure; the point at which the hydrocarbons and water exit the ground.

Well log 

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

Wet gas 

Natural gas containing significant amounts of liquifiable hydrocarbons.

Wildcat well 

A well drilled in an area where no current oil or gas production exists.

Workover 

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.

WTI 

West Texas Intermediate, a type of crude oil commonly used as a price benchmark.