Integrated Geomechanics Analysis for Drilling Wellbore Stability Optimization in Multi-Lithology Formations in Sichuan Basin

Abstract During the drilling process in the Sichuan Basin, complex events such as mud loss and stuck pipe frequently occur. The risk types in multiple formations and different lithologies are intricate, with vertically developed multiple pressure systems and complex overpressure mechanism. The mechanical properties in both vertical and lateral directions under the complex tectonic background are highly heterogeneous, making it difficult to predict the safe mud window for pre-drill wells. To address the challenges of frequent complex drilling events, we analyze the main control factors and distribution of drilling complexity, establish geomechanical models for multi-formation systems with complex lithologies, incorporating elastic modulus, rock strength parameters, pore pressure, and in-situ stress. Wellbore stability is assessed for different formations based on shear and tensile failure criteria and the results of 1-D geomechanical model. We predict overpressure and simulate in-situ stress for multi-formation systems using different models tailored to the overpressure formation mechanisms of various lithologies, and quantitatively predict pore pressure, breakout pressure, fracture pressure, and breakdown pressure based on the integrated geomechanics model. This allows us to determine a reasonable safe drilling mud weight window and develop a drilling map to provide early warnings of drilling risks, thereby supporting the optimization of the drilling process in the study area.