Integrated Geomechanical Study for Hole Stability, Sanding Potential, and Completion Selection: A Case Study From Southeast Asia

A full scale geomechanical study was carried out to evaluate hole stability during drilling and production, and sanding potential of Lower Miocene oil bearing sands in horizontal wells with planned open hole completion in a Malay Basin field, offshore Malaysia. Drilling information, well logs and rock mechanical test results were used to determine in situ stresses, pore pressure and rock mechanical properties in the field. This paper highlights the use of geomechanics principles integrated with sound drilling and completion practices to achieve and deliver highly productive wells in the field. An analytical 3D elastic-shear failure model and a 2D elasto-plastic yield zone growth model were used to evaluate the sanding risk over life of field conditions. Using conservative critical sand failure parameters, both the elastic and elasto-plastic sanding models indicate that the risk of sand production during the life of field would be very low to none; therefore, no sand control would be required for the planned horizontal wells. 2D elasto-plastic hole stability modelling, using Mohr-Coulomb failure criteria, showed that the sandstone sections should remain stable over the life of field in an open hole (barefoot) completion, even with water cut. However, the stability of intra-reservoir shales in a barefoot completion might be at risk under high reservoir pressure depletions, if no depletion occurs in shales. Planned horizontal wells were drilled successfully with no major drilling problem by using the recommended mud pressures and good drilling practices, confirming the reliability of the geomechanical model and wellbore stability analysis. The wells were completed with predrilled liners to minimise the risk of hole instability in shales. The wells are currently producing sand free with the planned drawdowns while water cut is approaching 70%, confirming the accuracy of sand production predictions. Integration of geomechanical analysis with rational engineering judgment and practices resulted in avoidance of unnecessary sand prevention installations which could be expensive and have adverse effects on well productivity.