Kill line is a high-pressure pipeline in a drilling rig's well control system. It connects the rig's mud pumps to an outlet on the blowout preventer (BOP) stack, typically below one or more of the preventers, through which line drilling fluid can be pumped into the well to control a threatened blowout. During well control operations, kill fluid is pumped through the drillstring and annular fluid is taken out of the well through the choke line, which controls the fluid pressure. If the drillpipe is inaccessible, it may be necessary to pump heavy drilling fluid into the top of the well, wait for gravity to force the fluid to fall, and then remove fluid from the annulus, via both the kill line and choke line. The kill line also provides a measure of redundancy for the operation.
The kill line is not used strictly on a drilling rig, although it is most commonly associated with drilling operations. Kill lines are also installed and used during other well activities, such as completion, workover, and well intervention, whenever a blowout preventer (BOP) stack is in place and well control is required. In these contexts, the kill line serves the same essential function, to providing a high-pressure pathway to pump kill fluid into the well annulus to control formation pressures. While the surface equipment and configuration may vary between drilling rigs, workover rigs, and intervention units, the presence and purpose of the kill line remain fundamentally the same wherever well control operations are necessary.
