This paper presents the novel approach used in drilling, running liner and cementing a development well across multiple reservoir with high pore pressure heterogeneity that has historically caused drilling hazards like differential stuck pipe, losses, well control and slow rate of penetrations.
Having depleted reservoirs and high-pressure reservoirs in the same hole section of well-A dictates that the mud weight must be higher than the higher reservoir pressure, which puts high differential pressure on the depleted reservoir and causes differential stuck pipe and losses. The uncertainty in determining the pore pressure adds another challenge as the mud weight must be higher than the expected pore pressure. Managed Pressure Drilling (MPD) addresses these challenges by enabling determining the pore pressure while drilling and adjusting the Equivalent Circulation Density (ECD) to be with the minimum overbalance.
MPD allowed drilling the section with (12.0 ppg) mud weight instead of the conventional mud weight (15.7 ppg). This has reduced the differential pressure between the depleted formation and the other formations significantly and enhanced the rate of penetration while balancing the well. It also proved that verifying the well's prognosis for pressure is essential in avoiding drilling hazards. Constant Bottom Hole Pressure (CBHP) mode of MPD was used to maintain the same ECD while drilling and connection to avoid well influx during pumps off events by compensating the annular friction pressure loss by surface back pressure. MPD was utilized too in running the 7″ liner and cementing it as a guarantee if the mud weight was too low to stabilize the well. The operation was carried out without safety or quality issue. The MPD system performance was with zero nonproductive time and the hole section was drilled shoe-to-shoe without any change the Rotating Control Device (RCD). This application showed an alternative preventive solution to differentially stuck pipe instead of the reactive one.
The approach explained in this paper is the first of its kind in ADNOC Onshore field. It involved altering the mud weight program strategically for more adaptive approach in dealing with drilling hazards like differential stuck pipe, losses and well control. The scheme involving MPD for running liner and cementing is the first ever in United Arab Emirates.