Underbalanced drilling(UBD) operations are being utilized with increasing frequency as a means of reducing invasive formation damage, minimizing problems with differential sticking and lost circulation, and increasing rates of penetration in many drilling operations, etc. However, experience has indicated that during many operations, a wide underbalance pressure, such as pipe connection in conventional jointed pipe drilling operations, mud pulsed MWD program, tripping operations, etc. So, it is difficult to maintain a condition of continuous underbalance pressure throughout the complete operation, resulting in fluid losses to the formation and possible significant damage.
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