Upscaling mechanical properties of shale obtained by nanoindentation to macroscale using accurate grain-based modeling (AGBM)

Understanding the mechanical properties of shale is essential for applications such as shale gas extraction, carbon sequestration, and underground mining. To capture the heterogeneity of shale at the microstructural, nanoindentation has been employed to investigate the mechanical properties of shale at the microscopic level, but the relationship between nanoindentation data and macroscale mechanical properties of shale is not well established. This study proposes a novel method to upscale nanoscale mechanical properties to macroscopic scales using accurate grain-based modeling (AGBM). Nanoindentation was conducted on shale minerals, including quartz, feldspar, illite, clinochlore, and calcite, revealing significant variations in their mechanical properties. The cohesion and internal friction angles of these minerals were determined by the dual-indentation technique. AGBM was generated using nanoindentation data and real microstructural details obtained from the TESCAN Integrated Minerals Analyzer (TIMA). Numerical simulations of uniaxial compression tests on the AGBM model predicted Young's modulus of 39.46 GPa and uniaxial compressive strength (UCS) of 66.7 MPa, closely matching experimental values (38.65 GPa and 64.1 MPa, respectively). The AGBM results showed a deviation of less than 5 % from laboratory tests, outperforming traditional homogenization models. The results represent a meaningful stride towards cross-scale data integration and predictive multi-scale physical modeling of shale.