Glossary of Terms  

These are some terms you may find used in relation to our principal assets and businesses.

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.

Associated Gas Natural: gas associated with oil accumulations, which may be dissolved in the oil at reservoir conditions or may form a cap of free gas above the oil.

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

bbl: 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.

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

bcm: Billion cubic metres (1 cubic metre = 35.31 cubic feet).

Biofuel: Solid, liquid, or gas fuel consisting of, or derived from recently dead biological material, most commonly plants. Distinct from fossil fuel, which is derived from long dead biological material.

Blow-out: When well pressure exceeds the ability of the wellhead valves to control it. Oil and gas “blow wild” at the surface.

Borehole: The hole as drilled by the drill bit.

Capex: Capital expenditure.

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.

Coalbed methane: A form of natural gas extracted from coal beds. Also know as Coal Seam Methane.

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

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.

Core sample: A cylindrical sample generally 1-5” in diameter drilled out of an area to determine the geologic and chemical analysis of the overburden and mineral.

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

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

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.

E&A: Abbreviation for exploration and appraisal.

E&P: 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.

Fracturing: 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 Hydrate: A solid form of water that contains a large amount of methane within its crystal structure. Originally thought to occur only in the outer regions of the Solar System where temperatures are low and water ice is common, significant deposits of have been found under sediments on the ocean floors of Earth.

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

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.

Indicated Resource: Mineral deposit for which estimates of the rank, quality, and quantity have been computed partly from sample analyses and measurements and partly from reasonable geologic projections.

Inferred Resource: Mineral deposit in unexplored extensions of the demonstrated resources for which estimates of the quality and size are based on geologic evidence and projection.

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

JORC Code: The Australasian Code for Reporting of Exploration Results, Mineral Resources and Ore Reserves – 2004 Edition

Kerogen: A mixture of organic chemical compounds that make up a portion of the organic matter in sedimentary rocks such as in Oil Shale

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.

mboe: 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.

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

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.

Oil shale: A fine-grained sedimentary rock, containing significant amounts of kerogen (a solid mixture of organic chemical compounds), from which liquid hydrocarbons can be manufactured.

Open-pit mining: A method of extracting rock or minerals from the earth by their removal from an open pit or borrow.

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

Opex: Operating expenditure.

Outcrop: A geological term referring to the appearance of bedrock or superficial deposits exposed at the surface of the Earth.

Overburden: The the term used in mining to describe material that lies above the area of economic interest, e.g., the rock and soil that lies above the coal seam.

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.

Platform: An offshore structure that is permanently fixed to the seabed.

Porosity: 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.

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 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.

Retort: An airtight vessel in which substances (e.g. oil shale) are heated for a chemical reaction producing gaseous products to be collected in a collection vessel or for further processing.

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.

Shale gas: Natural gas produced from shale. Because shales ordinarily have insufficient permeability to allow significant fluid flow to a well bore, most shales are not sources of natural gas.

Spud-in: The operation of drilling the first part of a new well.

Strip Ratio: A measure of how much waste material has to be mined for every volume of mined mineral in an open pit. This is expressed as cubic metres of waste per cubic metre of mineral.

Suspended well: A well that has been capped off temporarily.

tcf: Trillion Cubic Feet (of gas).

Tar sands: Naturally occurring mixtures of sand or clay, water and an extremely dense and viscous form of petroleum called bitumen. Also known as bituminous sands or oil sands.

Tight gas: Natural gas produced from reservoirs that have very low porosities and permeabilities.

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 a “exploration well”.

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


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