Identify the lower limit (pore pressure)
@balance services mapped out the lower limit (pore pressure) by using a DFC process with MPD in conjunction with other pore pressure prediction methods. Constant BHP was maintained during the drilling process by applying a backpressure of up to 800 psi during connections in order to compensate for the annular friction losses while circulating and drilling. This minimized the risk of wellbore breathing as well as the risk of taking a high intensity kick when the pumps were switched off. When there was a need to flow check the well, the backpressure was reduced gradually in stages of 100-200 psi. If the well started to flow, the backpressure was immediately increased to minimize the influx volume, while ramping down the rig pumps prior to shutting in the BOP. A total of 56 DFCs were necessary in order to reach well TD without uncontrolled influx incidents.
Identify and control wellbore breathing/ballooning
Wellbore breathing and formation supercharging, if wrongly interpreted, could easily be identified as a kick and handled incorrectly. The primary strategy by @balance services to minimize wellbore breathing was to maintain a required BHP with MPD. It was more challenging because of the DFCs required to fingerprint the pore pressure. When DFCs were performed, the BHP was reduced by the amount of backpressure applied at the surface. As a compromise, it was decided to limit the amount of backpressure reduction if there was any sign of ballooning, i.e., if the backpressure was reduced to a preset amount but not all the way to zero.