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

A measure of the resistance of rock to the movement of fluids. Rocks may have holes or void spaces in them (porosity), but if these holes do not connect, the permeability can be drastically reduced.

A complex mixture of naturally occurring hydrocarbon compounds found in rock. Petroleum can range from solid to gas, but the term is generally used to refer to liquid crude oil. Impurities such as sulfur, oxygen and nitrogen are common in petroleum.

The disappearance of a porous, permeable formation between two layers of impervious rock. The gradual, vertical thinning of a formation, over a horizontal or near-horizontal distance, until it disappears.

A sufficiently dry gas that will not drop out natural gas liquids when entering the gas pipeline; also, gas with enough pressure to enter high-pressure gas pipelines.

An offshore structure that is permanently fixed to the seabed.

To fill a well’s borehole with cement or other impervious material to prevent the flow of water, gas or oil from one strata to another when a well is abandoned; to screw a metal plug into a pipeline to shut off drainage or to divert the stream of oil to a connecting line to stop the flow of oil or gas.

A measure of the relative volume of void space in rock to the total rock volume. These spaces or pores are where oil and gas accumulate; therefore, a formation containing a high percentage of porosity can contain more hydrocarbons.

Power oil is the process in which crude oil is pressurized at the surface to energize the bottom pump during hydraulic pumping. 

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

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’.

A well which produces fluids (gas, oil or water).

Oil and gas which has not been produced but has been located and is recoverable.