Patent ID: 7562723
Filing Date: 2009-07-21
Classification: E21B

Abstract:
1. A method for determining existence of a well control event by controlling formation pressure during the drilling of a borehole through a subterranean formation, comprising: selectively pumping a drilling fluid through a drill string extended into a borehole, out a drill bit at the bottom end of the drill string, and into an annular space between drill string and the borehole; discharging the drilling fluid from the annular space proximate the Earth's surface; selectively increasing annular space fluid pressure to maintain a selected fluid pressure proximate the bottom of the borehole by applying fluid pressure to the annular space, the selective increasing including controlling an aperture of an orifice functionally coupled to an outlet of the annular space; monitoring the aperture of the orifice; and determining existence of a well control event when the aperture changes and a rate of the selective pumping remains substantially constant.