Mechanical behavior of carbonate rock from the Dengying Formation under simulated 10000-m-depth temperature-stress conditions

Ultra-deep carbonate reservoirs experience coupled high temperature and high stress, but the relative roles of stress and temperature in controlling deformation and failure remain insufficiently quantified. Same-formation outcrop analogs from the Sinian Dengying Formation, Sichuan Basin, were tested at 25–200 °C and 0–220 MPa using a servo-controlled 300 °C/300 MPa triaxial system, with strain measurement, computed tomography (CT) imaging, and energy analysis. Confinement exerted a much stronger control than temperature. At 200 °C, increasing confining pressure from 0 to 220 MPa increased peak strength by 413.5%, peak axial strain by 427.1%, and total input energy by 2962%, while delaying dilation from 63% to 98% of peak stress. Heating from 25 to 200 °C reduced peak strength by 26.0% at 0 MPa but by only 15.3% at 220 MPa, indicating that confinement suppressed thermal strength degradation; elastic modulus decreased by 10.5% and 51.9%, respectively. Failure shifted from tensile-dominated cracking at 0–60 MPa to mixed tensile-shear failure at 120 MPa and localized shear failure at 180–220 MPa. Persistent post-peak stress drops indicate localized brittle to semi-brittle instability rather than stable ductile flow. A temperature-corrected Hoek-Brown-type criterion was further established, providing an intact-rock strength boundary for wellbore stability evaluation.