High-pressure gas encountered in drilling deep wells that can cause serious problems of control when the tools are pulled out of the hole in making a trip. The driller must exercise extreme care to prevent loss of control or a blowout. Sufficient mud must be in the hole to provide the hydrostatic head necessary to contain the downhole gas pressure. Sometimes. in order to come out of the hole under high-pressure conditions, the crew must resort to stripping the pipe (q.v.), i.e., removing the drillstring through the wells stack of control valves, the blowout preventer, on the wellhead.
