Overcoming Uncertainty in Pore-Pressure While Drilling Through Integration of Logging-While-Drilling and Managed Pressure Drilling; a Case Study from the Gulf of Thailand

Abstract High uncertainty in pore pressure trend possesses drilling challenges which pore pressure need to be updated and managed while drilling. The expected pore pressure trend includes pressure ramp and pressure regression in the area based on the offset well profile. Managing mud weight in this pore pressure is a challenging task without tool to update the pore pressure in real-time. Pressure ramp possesses risk of formation kick if mud weight is too low. In the regression trend, casing point to isolate the pressure regression interval need to be optimized. Uncertainty of casing point selection during regression trend could lead to significant overbalance and fracking of the formation. Updating pore pressure trend in real-time becomes critical in this drilling challenge. Managed Pressure Drilling (MPD) and Logging-While-Drilling (LWD) formation testing (FT) are deployed to overcome the challenge of uncertain pore pressure. MPD static pore pressure testing (SPPT) with reducing surface back pressure (SBP) applied is performed to update the pore pressure ramp until max pressure depth where regression trend is expected. During regression trend, LWD FT is performed to acquire pore pressure while SBP is still applied to avoid the kick from max pressure trend above the regression point. Regression trend of pore pressure is updated till limit of differential pressure then section total depth (TD) is decided. After casing isolation from high pore pressure trend, drilling in deeper section is continued with lower mud-weight to optimize differential pressure till TD is achieved. Pore pressure increasing trend was updated with multiple MPD SPPT in multiple sands encountered in expected target layer and LWD FT acquired formation pressure in regression trend after each sand is encountered. Pore pressure trend is closely monitored to identify the regression trend until desired differential pressure is achieved. Casing point for intermediate section was decided which leads to lower mud weight in the deep section for better efficiency in the deep section. Planned TD was achieved by penetrating multiple sand in this appraisal/exploration (A/E) well despite of the uncertainty in pore pressure trend of pressure ramp and regression. Integration of MPD SPPT and LWD FT enabled pore pressure to be updated in both ramping and regression trend in real-time. Proven workflow with integration of MPD and LWD FT enable operators to drill through challenging formation pore pressure trend, uncertainty in drilling window and able to achieve target TD. Best practices of MPD and LWD operation in this pore pressure challenge could be applied for future drilling in the area with such pore pressure trend and thus able to manage the potential risk of drilling in such challenging environment.