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Wellbore Stability Analysis and Drilling Strategy in Depleted Reservoir

A decrease in reservoir pressure leads to change in the in-situ stress acting on the reservoir over the lifetime of the field as oil and gas are being produced. Drilling infill wells in the depleted reservoir may experience a narrow mud weight window due to presence of cap rock, stacked reservoir, and difference in production rate within the reservoir. Wellbore stability issues such as differential sticking, lost circulation, and formation damage that were not expected while drilling the initial production field could occur more frequently while drilling in depleted reservoir, which may contribute to increased drilling time and cost. Wellbore stability analysis and appropriate drilling strategies are required to overcome these drilling risks associated with depleted reservoirs for successful drilling operations. This paper describes the theoretical background of wellbore stability, drilling strategies, and case histories, i.e., managed pressure drilling and wellbore strengthening techniques, to drill through depleted reservoirs successfully.