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<p>Granite in high-temperature dry-hot rock (HDR) reservoirs exhibits complex crack initiation, propagation, and coalescence governed by mineralogy and mesoscale heterogeneity. We combine laboratory characterization with a PFC3D grain-based model (GBM) of clustered mineral particles to reproduce the macro–meso-mechanical behavior of granite. 30 granite models with different grain-to-particle size ratios (L/R) are created and loaded in uniaxial compression. Acoustic emission (AE) events are extracted during loading and analyzed by moment tensor inversion (MTI) to quantify tensile versus shear cracking. Results show a clear convergence threshold of L/R = 4, beyond which peak strength and damage stress stabilize and AE statistics become insensitive to further resolution increases. The grain size ratio also controls failure patterns: small grains produce lower and more scattered peak strengths, fewer shear-dominated AE events, and macroscopic inclined-shear failure; larger grains lead to higher and more stable strengths, abundant AE activity, and splitting-dominated failure. While different mineral distributions alter crack paths and the spatiotemporal evolution of damage, their effects on peak strength, b value, and AE failure modes remain secondary compared with L/R. This study provides a reproducible, RVE-like resolution criterion for GBM simulations and links AE–MTI descriptors to macroscopic failure, offering practical guidance for model resolution selection and for interpreting AE in HDR-related brittle rock stability assessments.</p>

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Convergence Threshold and Failure-Mode Shift in Granite: Effects of Grain-to-Particle Size Ratio Revealed by PFC3D-GBM and Numerical AE–MT Inversion

  • 期刊论文

  • 发表日期：

    2026年1月7日

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  • Lei Zhang,
  • Jian Zhou,
  • Xiao Peng,
  • Lu-Qing Zhang,
  • Xia-ying Li,
  • Song Wang,
  • Zi-qian Yan,
  • Jiu-zun Wang

摘要

Granite in high-temperature dry-hot rock (HDR) reservoirs exhibits complex crack initiation, propagation, and coalescence governed by mineralogy and mesoscale heterogeneity. We combine laboratory characterization with a PFC3D grain-based model (GBM) of clustered mineral particles to reproduce the macro–meso-mechanical behavior of granite. 30 granite models with different grain-to-particle size ratios (L/R) are created and loaded in uniaxial compression. Acoustic emission (AE) events are extracted during loading and analyzed by moment tensor inversion (MTI) to quantify tensile versus shear cracking. Results show a clear convergence threshold of L/R = 4, beyond which peak strength and damage stress stabilize and AE statistics become insensitive to further resolution increases. The grain size ratio also controls failure patterns: small grains produce lower and more scattered peak strengths, fewer shear-dominated AE events, and macroscopic inclined-shear failure; larger grains lead to higher and more stable strengths, abundant AE activity, and splitting-dominated failure. While different mineral distributions alter crack paths and the spatiotemporal evolution of damage, their effects on peak strength, b value, and AE failure modes remain secondary compared with L/R. This study provides a reproducible, RVE-like resolution criterion for GBM simulations and links AE–MTI descriptors to macroscopic failure, offering practical guidance for model resolution selection and for interpreting AE in HDR-related brittle rock stability assessments.