A bed or deposit composed throughout of substantially the same kind of rock; often a lithologic unit.

Each formation is given a name, frequently as a result of the study of the formation outcrop at the surface and sometimes based on fossils found in the formation.

A tubing sub made of abrasion-resistant material and used in a tubing string where turbulent flow may cause internal erosion.

The tendency of certain producing formations to react adversely with invading filtrates.

The pressure at which a well is circulated during well-killing procedures after killweight mud has filled the drill stem.

This pressure is maintained until the well is completely filled with killweight mud.

An assembly of tools made up on drill pipe that is lowered into the hole to retrieve lost or stuck equipment.

Also call a fish assembly.

A casing in which the outside diameter of the joint is the same as the outside diameter of the casing itself.

A procedure by which acid is forced into a formation under pressure high enough to cause the formation to crack.

The acid acts on certain kinds of rocks, usually carbonates, to increase the permeability of the formation.

Compare matrix acidizing.

The amount of fluid that can be delivered through a permeable filter medium after being subjected to a set differential pressure for a set length of time.

A projecting rim or edge (as on pipe fittings and openings in pumps and vessels), usually drilled with holes to allow bolting to other flanged fittings.

Pressure at the bottom of a well that is shut in.

The pressure at which a formation will break down, or fracture.

Distance between well head and point to which fluid rises in the well.

A device to monitor rate of fluid from the annulus.

The gradient needed to initiate a fracture.

To pump drilling fluid into the wellbore while the pipe is being withdrawn to ensure that the wellbore remains full of fluid even though the pipe is withdrawn.

Filling the hole lessens the danger of a kick or of caving of the well or the wellbore.