Back Pressure

The pressure existing at the surface on the casing side of the drill string/annulus flow system.

Ball Joint

A ball and socket assembly that has a central through-passage equal to or greater than the internal diameter of the riser. It may be positioned in the riser string to reduce local bending stresses.


The bottomhole assembly (BHA), is the lower portion of the drill string, from the bit to drill pipe. It includes the bit, drill collars, stabilizers and other drilling components.


An uncontrolled release of underground pressure or fluids into the wellbore, or to the surface. Such events can be catastrophic to the surroundings, causing of loss of life, environmental damage, and damage to property.


A blow out preventer (BOP) is a large valve at the surface of a well which closes off the wellbore. It is activated by hydraulic actuators due to loss of pressure control, or due to well interventions.

Box and Pin Stabs

A conventional tool-joint, a mating box and pin assembly which provides pressure-tight mating of two pipe joints.


A contingency well kill operation. Fluid is forcibly pumped into a formation to block well bore fluids or gas reaching the surface, or to force them back into the reservoir. Bullheading can be performed as a contingency operation with minimal advanced planning, however it can present subsequent safety and environmental risks.