Glossary

Obligatory wells

exploration wells that an operator undertakes to drill in a given area as a condition for being allocated an exploration licence. Also known as commitment wells.

Octane

the saturated hydrocarbon (alkane) with eight carbon atoms in its molecule (C8H18); the eighth member of the paraffin series - a liquid under normal conditions.

Odorant

substance such as mercaptan with a characteristic smell, added to odourless natural gas or NGLs when they are used as fuel, in order to aid detection.

Offtake

the point in a gas distribution system where gas is taken by supply pipe to a major consumer.

Ofgas

Office of Gas Supply, the UK gas industry regulator.

Oil

a mixture of liquid hydrocarbons of different molecular weights.

Oil field

a geographical area under which an oil reservoir lies.

Oil gasification

the manufacture of gas from oil for use as a fuel

Oil in place (OIP)

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

Oil pipeline

a pipeline used to pump crude or refined oil between two places, either offshore or onshore.

Oil shale

a compact sedimentary rock impregnated with organic materials (mainly kerogen) which yields oil when heated

Oil slick

a layer of oil floating on the surface of the sea; generally caused by some sort of accident or spillage, but which is sometimes caused by natural seepage from the ocean floor.

Oil trap

geological structure of any type which traps migrating hydrocarbons, thereby causing an oil field to form.

Olefins

a class of hydrocarbons, including ethylene and propylene, of particular importance as feedstock to the chemical industry.

OPEC

Organisation of Petroleum Exporting Countries. Formed in 1960, its member countries are Algeria, Ecuador, Gabon, Indonesia, Iran, Iraq, Kuwait, Libya, Nigeria, Qatar, Saudi Arabia, United Arab Emirates and Venezuela.

Open hole

the lower section of the borehole that does not have casing.

Operator

the individual or company responsible for the exploration, development, and production of an oil or gas well or licence. The operator is often part of a consortium and acts on behalf of the consortium.

Option

the right to obtain, within a certain period of time, other rights, e.g. a company that has the right to obtain exploration rights in a particular block is said to have an option thereon.

Outstep well

see step out well

Overshot

a fishing tool for recovering lost drill pipe or casing.