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<p>Discontinuities such as lithology interfaces (LIs) and bedding planes (BPs) significantly complicate the mechanisms of hydraulic fracture (HF) propagation in multi-lithology and multi-layered shale reservoirs (MLSR). To investigate how these discontinuities influence HF growth, an improved small-scale true triaxial fracturing simulation system and CT scanning technique were employed to conduct fracturing experiments. Subsequently, a 3D numerical model based on the continuum-discontinuum element method (CDEM) was developed to explore the influence mechanisms of LIs, BPs, minimum horizontal principal stress (σ<sub>h</sub>), and Young’s modulus (E) differences between lithologies, and combined factors on the evolution of HF parameters. The physical experiment results indicate that HF propagates through LIs and BPs in a “step-like” pattern. The HF morphology takes the shape of a “<b>╫</b>” or “╪”, penetrating, offsetting, or terminating at LIs or BPs with a narrow aperture. The numerical simulation shows that when HFs intersect with LIs and BPs, shear failure is dominant. The shear sliding along interfaces causes stress release at the fracture tip, resulting in discontinuities at the fracture front. The effect of σ<sub>h</sub> on HF growth is more significant than that of E. Lithologies with high σ<sub>h</sub> form a pressure barrier, while E indirectly slows the rate of HF growth by influencing the rock stiffness and aperture. HF length extension is more favorable in lithologies with low σ<sub>h</sub>. HFs are more prone to elastic deformation in soft formations, resulting in an uneven and slower extension rate. The tensile-induced stress increases in high E, leading to stress concentration at the LIs, which promotes HF to penetrate the LIs. Furthermore, the elastic deformation of low E contributes to less significant stress concentration, which restricts HF growth. BPs with low σ<sub>h</sub> are less likely to capture HFs, merely delaying the propagation of stress. The findings are expected to provide theoretical support for controlling HF growth during hydraulic fracturing.</p>

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Experimental and Numerical Research on the Mechanism of Hydraulic Fracture Growth for the Multi-Lithology and Multi-Layered Shale Reservoirs

  • 期刊论文

  • 发表日期：

    2025年9月1日

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  • Wenchao Wang,
  • Xinfang Ma,
  • Yushi Zou,
  • Xingwang Zhu,
  • Shicheng Zhang,
  • Li Liu,
  • Peng Yang,
  • Yin Qi,
  • Xiaojia Xue,
  • Wenbin Chen,
  • Jie Bai

摘要

Discontinuities such as lithology interfaces (LIs) and bedding planes (BPs) significantly complicate the mechanisms of hydraulic fracture (HF) propagation in multi-lithology and multi-layered shale reservoirs (MLSR). To investigate how these discontinuities influence HF growth, an improved small-scale true triaxial fracturing simulation system and CT scanning technique were employed to conduct fracturing experiments. Subsequently, a 3D numerical model based on the continuum-discontinuum element method (CDEM) was developed to explore the influence mechanisms of LIs, BPs, minimum horizontal principal stress (σh), and Young’s modulus (E) differences between lithologies, and combined factors on the evolution of HF parameters. The physical experiment results indicate that HF propagates through LIs and BPs in a “step-like” pattern. The HF morphology takes the shape of a “╫” or “╪”, penetrating, offsetting, or terminating at LIs or BPs with a narrow aperture. The numerical simulation shows that when HFs intersect with LIs and BPs, shear failure is dominant. The shear sliding along interfaces causes stress release at the fracture tip, resulting in discontinuities at the fracture front. The effect of σh on HF growth is more significant than that of E. Lithologies with high σh form a pressure barrier, while E indirectly slows the rate of HF growth by influencing the rock stiffness and aperture. HF length extension is more favorable in lithologies with low σh. HFs are more prone to elastic deformation in soft formations, resulting in an uneven and slower extension rate. The tensile-induced stress increases in high E, leading to stress concentration at the LIs, which promotes HF to penetrate the LIs. Furthermore, the elastic deformation of low E contributes to less significant stress concentration, which restricts HF growth. BPs with low σh are less likely to capture HFs, merely delaying the propagation of stress. The findings are expected to provide theoretical support for controlling HF growth during hydraulic fracturing.