ABSTRACT:

A connectivity method for pressure estimation in sands and a calibrated velocity-effective stress transform model for shale pressure were integrated with wellbore instability indicators to reduce uncertainty in the predrill PPFG forecast for a highly deviated subsalt well targeting a depleted reservoir. To calibrate the model, measured pore pressure data, logging data, and drilling events were used to accurately interpret pore pressures in offset wells. A fracture gradient model incorporating wellbore strengthening was applied to reduce the risk of losses in the depleted reservoir. The resulting PPFG prediction, including geomechanical analysis, allowed for an optimized well design, and with real-time PPFG monitoring, efficient drilling with minimal operational problems. This highly inclined ~ 60-degree subsalt well, with ~2000 psi depletion, was drilled successfully at a cost savings of 22% compared to recent first quartile wells drilled in the field. The optimized design resulted in the elimination of one intermediate casing string compared to all offset wells.

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