Statistical damage constitutive of oil shale considering post-peak stress drop: taking the Seven Member of Yanchang Formation in Ordos#br# Basin as an example
(1. College of Petroleum Engineering, China University of Petroleum (Beijing), Beijing 102249, China; 2. State Key Laboratory of Petroleum Resources and Prospecting, China University of Petroleum (Beijing), Beijing 102249, China; 3. Sinopec Production and Exploration Research Institute, Beijing 102206, China)
Abstract：To elucidate the mechanical properties of oil shale in the Chang 7 Member of the Ordos Basin, triaxial compression experiments were conducted under various confining pressures and bedding inclinations. Based on the characteristics of the stress-strain curves of the Chang 7 Member rocks, a quantitative brittleness evaluation index was proposed. A damage constitutive model, which incorporates post-peak brittle drop, was established by integrating damage mechanics with residual strength and the Drucker-Prager criterion. The results demonstrate that: (1) The deformation of oil shale primarily occurs in three stages: elastic deformation, strain hardening, and strain softening. (2) As confining pressure increases, the compressive strength, residual strength, peak strain, and elastic modulus increase, while brittleness and fracture complexity decrease. (3) Oil shale oriented perpendicular to the bedding planes exhibits higher strength but lower stiffness and brittleness, displaying pronounced anisotropic characteristics. (4) The proposed model effectively accounts for the stress drop rate (brittleness) and outperforms Weibull distribution-based models in predicting the post-peak brittle behavior of rocks, with theoretical curves aligning more closely with experimental stress-strain curves.
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2025, Vol. 44 
