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There are multi-scale fractures formed by hydraulic fractures and natural fractures in shale gas reservoirs, and the fluid flow and geo-stress field distribution in the reservoir show high heterogeneity and anisotropy under the influence of multi-scale fractures, which brings new challenges to Coupled Flow and Geomechanics numerical simulation. To address these issues, this paper proposes a new numerical simulation method for coupled flow and geomechanics simulation method employing multi-scale fracture model. In the flow mechanics model, natural fractures and secondary fractures induced by hydraulic fracturing are treated as equivalent continuous media, while the primary hydraulic fractures are treated as discrete fractures, establishing a dual-porosity medium + embedded discrete fracture model (DPM + EDFM) hybrid numerical model. In the rock geomechanics mechanics model, the flexibility superposition method is used to equate multi-scale fractures to an increase in element flexibility, and the pseudo-continuous medium method is employed to account for the impact of the anisotropic stiffness model on the stress–strain relationship, thus establishing a rock constitutive model that considers multi-scale fractures. Furthermore, the fracture aperture and conductivity coefficient are updated according to the stress evolution to realize the two-way coupling of fluid flow and rock geomechanics models. A comparative analysis was conducted between this method and fully equivalent models (DPM) as well as fully discrete fracture models (EDFM). The results of the study indicate that: ① Due to the influence of fractures, the equivalent stiffness of the rock decreases, and this varies at different positions and in different directions. ② As extraction proceeds, the 3D in-situ stress in the shale reservoir decreases, the effective stress increases, and consequently, the fracture aperture and permeability decline, resulting in a faster decline in the productivity of production wells. Taking a shale gas well group in the Sichuan Basin, China as an example, in the near-well region, the average fracture aperture decreased by a margin of up to 25.1%, and fracture permeability decreased by up to 48.9%; The heterogeneity and anisotropy of the reservoir pore pressure distribution were also enhanced; Compared to non-coupled simulations, the productivity of production wells decreased by 20.3%. The role of geomechanics effects in productivity evaluation cannot be ignored.

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A Novel Coupled Flow and Geomechanics Simulation Method Employing Multi-Scale Fracture Model

  • 会议论文

  • 发表日期：

    2025年

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  • Jun-chao Li,
  • Bin Su,
  • Cheng Dai

摘要

There are multi-scale fractures formed by hydraulic fractures and natural fractures in shale gas reservoirs, and the fluid flow and geo-stress field distribution in the reservoir show high heterogeneity and anisotropy under the influence of multi-scale fractures, which brings new challenges to Coupled Flow and Geomechanics numerical simulation. To address these issues, this paper proposes a new numerical simulation method for coupled flow and geomechanics simulation method employing multi-scale fracture model. In the flow mechanics model, natural fractures and secondary fractures induced by hydraulic fracturing are treated as equivalent continuous media, while the primary hydraulic fractures are treated as discrete fractures, establishing a dual-porosity medium + embedded discrete fracture model (DPM + EDFM) hybrid numerical model. In the rock geomechanics mechanics model, the flexibility superposition method is used to equate multi-scale fractures to an increase in element flexibility, and the pseudo-continuous medium method is employed to account for the impact of the anisotropic stiffness model on the stress–strain relationship, thus establishing a rock constitutive model that considers multi-scale fractures. Furthermore, the fracture aperture and conductivity coefficient are updated according to the stress evolution to realize the two-way coupling of fluid flow and rock geomechanics models. A comparative analysis was conducted between this method and fully equivalent models (DPM) as well as fully discrete fracture models (EDFM). The results of the study indicate that: ① Due to the influence of fractures, the equivalent stiffness of the rock decreases, and this varies at different positions and in different directions. ② As extraction proceeds, the 3D in-situ stress in the shale reservoir decreases, the effective stress increases, and consequently, the fracture aperture and permeability decline, resulting in a faster decline in the productivity of production wells. Taking a shale gas well group in the Sichuan Basin, China as an example, in the near-well region, the average fracture aperture decreased by a margin of up to 25.1%, and fracture permeability decreased by up to 48.9%; The heterogeneity and anisotropy of the reservoir pore pressure distribution were also enhanced; Compared to non-coupled simulations, the productivity of production wells decreased by 20.3%. The role of geomechanics effects in productivity evaluation cannot be ignored.