Oil & Gas Terms in Category C


A compound in which chromium has a valence of 6.

Chromate may be added to drilling fluids either directly or as a constituent of chrome lignites or chrome lignosulfonates.

In certain areas, chromate is widely used as a corrosion inhibitor, often in conjunction with lime.


Abbreviation: cement bond log.


A hole dug, usually before drilling of a well, to allow working space for the casinghead equipment.


The part of a pump valve which holds the ball to limit its movement.

Circulating pressure

The pressure generated by the mud pumps and exerted on the drill stem

Clay extender

Any of several substances–usually organic compounds of high molecular weight–that, when added in low concentrations to a bentonite or to certain other clay slurries, will increase the viscosity of the system.

See low-solids mud.

Cavity completion

A completion that uses flow to purposely increase the size of the open hole wellbore.

Casing scraper

Blade tool used to scrape away junk or debris from inside casing; run on pipe or tubing.

Casinghead gasoline

(obsolete) natural gasoline.


In drilling-fluid terminology, a chemical is any material that produces changes in the viscosity, yield point, gel strength, fluid loss, and surface tension.

Complete a well

To finish work on a well and bring it to productive status.

See well completion.


Movement of drilling fluid from mud pits, down drill stem, up annulus, and back to mud pits.


A well capable of producing oil or gas, but temporarily shut in.

Circulation valve

An accessory employed above a packer, to permit annulus-to-tubing circulation or vice versa.

Chase threads

To straighten and clean threads of any king.