A Multi-Scale Fracture Modeling Framework Driven by Integrated Reservoir Geomechanics and Seismic Attribute Analysis: A Case Study from the Northern Luzhou Shale Gas Play

Abstract: Accurate construction of multi-scale fracture models is essential for optimizing hydraulic fracturing design, predicting sweet-spot distribution, and improving shale gas recovery in deep, structurally complex reservoirs. The Wufeng–Longmaxi shale in the northern Luzhou area is characterized by strong tectonic deformation, lithological heterogeneity, and fracture development across multiple scales. To address these challenges, this study proposes an integrated multi-scale fracture modeling framework that couples reservoir geomechanics, multi-attribute seismic analysis, and microstructural characterization. First, pre-stack seismic inversion was performed to derive elastic parameters, including P-impedance, Vp/Vs ratio, and density, which were further used to construct 3D mechanical property volumes such as brittleness index, Young’s modulus, and Poisson’s ratio. Curvature attributes and ant-tracking analysis were applied to delineate zones of enhanced structural deformation and large-scale fracture corridors. Second, triaxial rock mechanics experiments and CT-based digital core analysis were conducted to calibrate lithology-dependent failure criteria and layer-parallel anisotropic mechanical parameters for siliceous and calcareous shales, forming the basis of a heterogeneous geomechanical model. Finite-element simulations were then used to resolve the present-day in-situ stress field and quantify fracture openness, density, and orientation under mechanical–stratigraphic constraints. Results show that: (1) a NW–SE trending high-curvature anticline dominates the northeastern study area, where brittle siliceous shale (brittleness index > 0.65) accounts for 58%, and the maximum horizontal stress (NW 130°–150°) provides favorable conditions for fracture development; (2) large-scale fractures (>10 m) are controlled by curvature ridges and fault transfer zones, while mesoscale fractures (1–10 m) correlate positively with the product of brittleness index and bedding density, and (3) microscale fractures (<1 mm) exhibit strong coupling with TOC-rich domains (TOC > 3.5%). Integrating curvature volumes, ant-tracking results, geomechanical simulations, and microfracture fractal parameters yields a hierarchical workflow linking macroscopic structural guidance, mesoscale mechanical response, and microscale pore–fracture attributes. Field validation shows that the predicted fracture-rich zones match production performance with an accuracy of 82%. The L202 well, deployed using this workflow, achieved a post-fracturing daily gas rate of 2.3×10⁵ m³, 37% higher than adjacent wells. This integrated methodology overcomes the limitations of single-scale modeling and provides a robust framework for 3D shale gas reservoir evaluation and development in complex structural domains.

Keywords: Multi-scale fracture modeling; reservoir geomechanics; seismic attribute integration; in-situ stress; Luzhou area