Accurate control over bottomhole pressure during drilling is essential as the industry meets increasingly challenging drilling environments such narrow drilling margin formations, HPHT wells and fractured formations.
To increase the accuracy of the control over bottom hole pressures during drilling, a fully automated prototype system consisting of a hydraulics simulator, a computer controlled choke manifold and a pump as part of the mud return system has been developed and tested.
Rather than mud density alone, the system uses a reduced density mud in combination with a variable back-pressure at the annulus exit to achieve the required downhole pressure. The system is able to substantially compensate downhole pressure variations induced by the drilling operation by varying the surface back-pressure.
A number of possible advantages are associated with the use of the system:
Reduction of formation impairment
Reduction of mud losses
Reduction of formation fluid influx
No flat time during weight-up/down
Potential to reduce number of casing strings
Automatic kick circulation
A successful experimental program has been conducted on a real size test well in preparation of a field test sequence.
The system was easily retrofitted to the existing test rig and normal drilling procedures were minimally impacted.