Oil & Gas Terms in Category I

Infill drilling

Adding new wells in an existing field within the original well patterns to accelerate recovery or to test recovery methods.

Improved oil recovery or ior

Any of various methods, chiefly reservoir drive mechanisms and enhanced recover techniques, designed to improve the flow of hydrocarbons from the reservoir to the wellbore or to recover more oil after the primary and secondary methods (water and gas floods) are uneconomic.

Insert pump

A sucker rod pump that is run into the well as a complete unit.

Injection gas


A high-pressure gas injected into a formation to maintain or restore reservoir pressure.


Gas injected in gas lift operations.

see gas injection.

Injection valve

A poppet spring-loaded subsurface valve run in on wireline, landed in a profile, to shut the well if injection ceases.

Intermediate casing string

The string of casing set in a well after the surface casing but before production casing is set.

Keeps hole from caving and seals off troublesome formations.

Also called protection casing.

Interfacial tension

The surface tension occurring at the interface between two liquids that do not mix, such as oil and water.

Interfacial tension is caused by the difference in fluid pressures of the liquids.


See feed in.

Insulated flange

A flange which incorporates plastic pieces to separate the metal parts.

Input well

An injection well used for injecting fluids into an underground stratum to increase reservoir pressure.

Initial circulating pressure (icp)

The pressure at which a well that has been closed in on a kick is circulated when well-killing procedures are begun

Inflatable packer

A type of packer used for open-hole work, with inflatable packing elements


An additive used to retard undesirable chemical action in a product.

It is added in small quantities to gasolines to prevent oxidation and gum formation, to lubricating oils to stop color change, and to corrosive environments to decrease corrosive action.

Instrument hanger

A hanger used to lock instruments into seating nipple (pressure/temperature bombs, etc.).

Initial gel

See initial gel strength.