A thermal–mechanical coupled DEM model for deep shale reservoir: the effects of temperature and anisotropy

This paper presents a new thermal–mechanical coupled numerical approach to investigate the effects of temperature and inherent anisotropy on deep reservoir shale. The proposed method combines the discrete element method (DEM) with thermal expansion algorithm to capture the thermal behavior of deep reservoir shale. Anisotropic characteristics are reproduced by replacing linear parallel bonds dipping within a specific angle range with smooth-joint contacts. The effectiveness of the proposed coupled model is validated by comparing simulation results with experimental observations, focusing on the specimen responses and crack patterns. The modeling analysis shows that high confining stress conditions result in increased peak strength, elastic modulus, and residual strength. Conversely, high temperature treatment induces micro thermal damage, leading to a degradation of macro mechanical properties. Our numerical simulations suggest that shale exhibits ductile characteristics in high temperature and high pressure deep reservoir environment. To explore the applicability of the proposed approach, a parametric study is conducted to investigate micro parameters related to model anisotropy. Influence mechanisms and suggestions for parameter values are presented in detail. Finally, based on the constructed coupled approach, the thermal response of the model and corresponding particle-scale mechanisms are explored. The obtained conclusions could provide guidance for calibrating thermal-related parameters and offer theoretical explanations for DEM-based rock material simulations considering temperature effects.