Brine

Completion fluid (aka work-over fluid) is a fluid used to complete the well and is normally a salty solution made up of e.g. chlorides or bromides, which is also called Brine, as must be free of any solids. Completion fluid should be compatible with the innate formation fluids and rock, as another type of fluids (e.g. drilling fluids) can damage the productive zones. In addition to cleaning the wellbore, after the drilling is finished, completion fluid is used to control the pressure down-hole, prior to and while well-completion operations are in progress.