Exxonmobil Upstream Research Company

Torney M Van Acker

Mark E Ehrhardt

L Donald Maus

A method and apparatus for controlling the riser base pressure and detecting well control problems, such as kicks or lost circulation, during drilling of an offshore well using a gas-lifted riser. The pressure control apparatus preferably includes two separate control elements, one to adjust the pressure at the surface (p ) and the mass flow rate out of the top of the riser ({dot over (m)} ) to compensate for changes in riser base pressure (p ) and the other to adjust either or both of the boost mud flow rate (q ) and lift gas flow rate (q ) to maintain a constant or nearly constant mass flow rate entering the base of the riser ({dot over (m)} ). According to the method of the present invention, the well return flow rate (q ) is preferably determined by directly measuring various other parameters and then computing q from the measured parameters. The computed value of q may be compared to the drill string flow rate (q ) to detect well control problems, such as kicks or lost circulation.

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Fairfax Station, VA, United States of America

Torney M Van Acker