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<p>To gain deeper insight into the formation mechanisms of complex fracture networks in heterogeneous coal, this study incorporates the strain-softening behavior and material heterogeneity of coal to develop a hydro-mechanical-damage (HMD) coupling model for hydraulic fracturing, based on the continuum damage mechanics (CDM) framework. Microscopic and macroscopic heterogeneity were incorporated into the numerical model using statistical methods. Using the COMSOL with MATLAB computing platform, this study investigates the effects of the homogeneity coefficient, fracturing fluid viscosity, and natural fractures on the morphology, propagation path, and failure modes of hydraulic fractures in heterogeneous coal under varying horizontal in-situ stress differences. The results indicate that, with increasing horizontal in-situ stress difference and degree of heterogeneity, the deviation distance of fractures from the central axis increases, the propagation paths and surface morphologies of fractures become more complex, and the proportion of elements experiencing shear damage rises. Tensile fractures initiate around the fracturing borehole and gradually propagate outward, inducing shear damage in the surrounding regions; additionally, shear micro-damage is observed in areas distant from the main fracture paths. Fracturing fluids with higher viscosity promote fracture propagation away from the central axis but reduce the stimulated reservoir area and the proportion of elements experiencing shear failure. Greater horizontal in-situ stress differences and higher fracturing fluid viscosity reduce fracture complexity and increase the proportion of elements in a tensile strain-softening state. The high-permeability natural fractures elevate the pore pressure in the matrix around natural fractures through fluid channeling, which in turn products greater tensile damage elements in the matrix around the natural fractures. The simulation results provide new insights into the formation mechanisms of complex fracture networks in heterogeneous coal and offer theoretical guidance for the optimization of field hydraulic fracturing parameters.</p>

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Macro-and-Micro Heterogeneous Influence on Fracture Morphology and Failure Modes during Hydraulic Fracturing of Coal: A Coupled Hydro-Mechanical-Damage Model

  • 期刊论文

  • 发表日期：

    2025年11月14日

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  • Kang Yang,
  • Yunpei Liang,
  • Quangui Li

摘要

To gain deeper insight into the formation mechanisms of complex fracture networks in heterogeneous coal, this study incorporates the strain-softening behavior and material heterogeneity of coal to develop a hydro-mechanical-damage (HMD) coupling model for hydraulic fracturing, based on the continuum damage mechanics (CDM) framework. Microscopic and macroscopic heterogeneity were incorporated into the numerical model using statistical methods. Using the COMSOL with MATLAB computing platform, this study investigates the effects of the homogeneity coefficient, fracturing fluid viscosity, and natural fractures on the morphology, propagation path, and failure modes of hydraulic fractures in heterogeneous coal under varying horizontal in-situ stress differences. The results indicate that, with increasing horizontal in-situ stress difference and degree of heterogeneity, the deviation distance of fractures from the central axis increases, the propagation paths and surface morphologies of fractures become more complex, and the proportion of elements experiencing shear damage rises. Tensile fractures initiate around the fracturing borehole and gradually propagate outward, inducing shear damage in the surrounding regions; additionally, shear micro-damage is observed in areas distant from the main fracture paths. Fracturing fluids with higher viscosity promote fracture propagation away from the central axis but reduce the stimulated reservoir area and the proportion of elements experiencing shear failure. Greater horizontal in-situ stress differences and higher fracturing fluid viscosity reduce fracture complexity and increase the proportion of elements in a tensile strain-softening state. The high-permeability natural fractures elevate the pore pressure in the matrix around natural fractures through fluid channeling, which in turn products greater tensile damage elements in the matrix around the natural fractures. The simulation results provide new insights into the formation mechanisms of complex fracture networks in heterogeneous coal and offer theoretical guidance for the optimization of field hydraulic fracturing parameters.