In-situ stress prediction methods for continental shale oil reservoirs based on rheological models

Continental shale oil reservoirs typically exhibit strong heterogeneity, high clay content, and complex structural configurations, which result in significant deviations in conventional in-situ stress prediction methods. Parameters calibrated based on measured data struggle to represent reservoir spatial heterogeneity, and models based on elastic constitutive relationships often neglect the impact of clay rheology (e.g., stress relaxation and creep) on in-situ stress. To improve the accuracy of in-situ stress field characterization in continental shale oilreservoirs and support efficient development decision-making, a new in-situ stress prediction method driven by rheological constitutive behavior was established. The YPD pre-stack inversion method was used to directly invert elastic parameters, reducing chain errors in modulus conversion. Total organic carbon (TOC) content was employed as a criterion for overpressure mechanisms, and a segmented modified Eaton's method was applied to predict pore pressure. A multilayer thin-plate bending theory was derived, and elastic parameters and structural curvature were utilized to predict local structural strain, thereby strengthening the characterization of reservoir heterogeneity and structural differences. Rheological models such as Maxwell model were used to represent creep and stress relaxation phenomena of rock under long-term loading, and a viscoelastic constitutive equation characterizing rock rheological behavior was derived, establishing an in-situ stress prediction method based on the rheological model. By integrating seismic data with geomechanical models, a workflow for rheology-based in-situ stress prediction in continental shale oil reservoirs was established. Application in continental shale oil blocks of the Bohai Bay Basin demonstrates that the predicted in-situ stress magnitude exhibits a relative error of less than 6%, demonstrating a marked improvement in accuracy over conventional methods. The proposed rheological constitutive model effectively quantifies the impact of rheological behavior on stress, overcomes the theoretical limitations of traditional elastic models, and establishes a high-precision, highly adaptable in-situ stress prediction method, thereby providing reliable theoretical support for the optimized design of horizontal wells and fracturing operations in continental shale oil reservoirs.