Method and apparatus for controlling bottom hole pressure in a subterranean formation during rig pump operation

A system for maintaining pressure in a wellbore during drilling operations comprising;

• a reservoir conduit extending from, a reservoir and having a controllable variable valve provided therein, wherein drill fluid flows from the reservoir through the reservoir conduit and the controllable variable valve to a drill string disposed in the wellbore and further flows from the drill string into an annulus defined between the wellbore and the drill string, wherein the drill fluid returns from the annulus as return fluid;
• a return conduit through which the return fluid flows from the annulus toward a backpressure control device;
• backpressure pump in fluid communication with the reservoir conduit via the controllable variable valve, the backpressure pump pumping the drill fluid from the reservoir to the return conduit at a location along the return conduit upstream of the backpressure control device;
• and a controller configured to determine a backpressure set point based on one or more measurements taken from the system.

A system for maintaining pressure in a wellbore during drilling operations comprising:

• a reservoir conduit extending from a reservoir and having a three-way fluid junction provided therein;
• a first drill fluid line extending from the three-way fluid junction to a drill string disposed in the wellbore;
• wherein drill fluid flows from the reservoir through the reservoir conduit, the three-way fluid junction, and the first drill fluid line to the drill string and further flows from the drill string into an annulus defined between the wellbore and the drill string, wherein the drill fluid returns from the annulus as return fluid;
• a return conduit through which the return fluid flows from the annulus toward a backpressure control device;
• a second drill fluid line extending from the three-way fluid junction to a backpressure pump, the backpressure pump pumping the drill fluid from the reservoir conduit to the return conduit at a location along the return conduit upstream of the backpressure control device;
• and
• a controller configured to determine a backpressure set point based on one or more measurements taken from the system.