Constant bottom hole pressure. Bottomhole pressure is kept constant during connections to compensate loss of AFP when the mud pumps are off.


A mechanical device which controls the flow of oil or gas in a well or flowline.

Christmas Tree

Assembled at the top of a completed well both surface or subsea, the Christmas Tree is an assembly of valves, fittings, chokes, and gauges used in monitoring and controlling the flow of hydrocarbons and other fluids from production or injection wells. Their primary function is to control the flow out of the well.


Closed loop drilling.

Connection Gas

A small influx of gas in the drilling fluid when a pipe connection is made.


Term referring to a range of mechanical devices used to provide a pressure containing structural connection between adjacent end fittings. May consist of a flange arrangement bolted to the end fitting, or an assembly comprised of clamped hub, gasket and seal ring(s), pulled into place with hydraulics and locked in.

Conventional Drilling

A conventional drilling operation (also referred to as open-loop drilling ) uses the drilling fluid hydrostatic pressure to balance between the pore and fracture pressure gradients without the assistance of an annular pressure control system. Use of a control head at the surface does not directly imply a rig is using MPD.

Crossover Joints

In Riser gas handling, crossover joints (used with riser flanges) provide integration of the RGH system with the rig’s riser below the tension ring and the termination joint.


Low temperature processing, generally subzero. For LNG this can be as low as -162˚C.