Geomechanical assessment of underbalanced coil tubing drilling (UBCTD) campaign in depleted deep carbonate reservoirs: A new opportunity at onshore Kuwait

ABSTRACT: This study presents a comprehensive analysis of hole stability and outlines the de-risking approach for the planned underbalanced coil tubing drilling (UBCTD) in the prolific Lower Jurassic Middle Marrat Formation of Kuwait, located at depths exceeding 14000 ft. Through elasto-plastic failure modeling, the analysis examines the failure characteristics of the horizontal wells, quantifying the extent (width) and the severity (hole size/shape) of expected failure during UBD operation. Geomechanical modeling reveals wide but shallow breakouts with up to 1.5" enlargement in less depleted intervals under the planned underbalance conditions, while the heavily depleted zones can exhibit yielded broken zone equivalent of 18% of the original well bore. An estimate of expected extra solids due to rock failure ranges from 12% to 25% of the original hole volume, which should be accounted for in the effective hole-cleaning operation and optimizing drilling parameters. This study also delves into critical sensitivities, uncertainties, and risk mitigation approaches to enhance operational outcomes, drilling efficiency and eventually production enhancement opportunity.