A unit of volume measurement used for petroleum and its products.

To vent gas from a well or production system. Wells that have been shut in for a period often develop a gas cap caused by gas percolating through the fluid column in the wellbore. It is often desirable to remove or vent the free gas before starting well intervention work.

An uncontrolled flow of reservoir fluids into the wellbore, and sometimes catastrophically to the surface. A blowout may consist of salt water, oil, gas or a mixture of these. Blowouts occur in all types of exploration and production operations, not just during drilling operations.

A large valve at the top of a well that may be closed if the drilling crew loses control of formation fluids. These high pressure valves are designed to shut off the uncontrolled flow of hydrocarbons.

A borehole is a narrow shaft, bored in the ground, either vertically or horizontally. A borehole may be constructed for many different purposes, including the extraction of water or other liquid (such as petroleum) or gases (such as natural gas). As well as pumping petroleum from an underground well through a borehole, liquid or gas can be pumped into it, for that process, or for underground storage of unwanted substances.