层理页岩水力裂缝扩展特性数值模拟研究

    NUMERICAL SIMULATION OF HYDRAULIC FRACTURE PROPAGATION BEHAVIORS IN BEDDING SHALE

    • 摘要: 为深入探究层理页岩水力裂缝扩展特性,本文通过构建随机分布层理页岩数值模型,系统探究了层理数目、裂隙倾角及应力差对水力裂缝扩展路径与起裂压力的影响。结果表明:层理通过弱面效应主导水力裂缝网络复杂度,中等层理发育下诱导使水力裂缝分叉形成复杂扩展路径,密集层理发育形成单一扩展路径;裂隙倾角45°时水力裂缝与层理面斜交更易形成复杂水力裂缝扩展路径;高应力差抑制层理活化形成纵向主缝,中等应力差时裂缝沿主应力与层理交替扩展,生成密集分叉扩展路径。水力裂缝扩展模式受层理胶结强度控制,呈现三类典型路径:高胶结强度下的穿透性扩展,中等胶结强度下形成“主裂缝穿层扩展-次级裂缝沿层理延伸”的复合扩展路径,低胶结强度下沿层理平面的单一扩展路径。起裂压力受多因素协同控制,层理弱化与高应力差显著降低起裂压力,裂隙倾角45°时因最优几何角度使得周围拉应力最小化,从而导致起裂压力最小。研究结果为层理页岩储层体积压裂的复杂压裂网络机理提供依据。

       

      Abstract: To gain an in-depth understanding of hydraulic fracture propagation in bedded shale,this study systematically investigated the effects of bedding density,fracture inclination,and stress difference on fracture propagation paths and initiation pressure using a numerical model of shale with randomly distributed bedding. The results indicate that bedding plays a dominant role in the complexity of fracture networks due to its weak interfacial properties. Moderate bedding density promotes hydraulic fracture bifurcation,resulting in complex propagation paths,while highly dense bedding tends to guide fractures along a single dominant pathway. At a fracture inclination of 45°,the interaction between hydraulic fractures and bedding planes is most conducive to forming complex fracture patterns. High stress difference suppresses bedding activation,leading to the formation of dominant longitudinal fractures. Under moderate stress difference,fractures propagate alternately along the maximum principal stress direction and bedding planes,resulting in densely branched fracture paths. The bonding strength of bedding interfaces governs the hydraulic fracture propagation mode,which manifests in three distinct patterns: direct penetration through bedding under high bonding strength; a composite path with main fracture penetration and secondary fractures extending along bedding under medium bonding strength; and confinement to the bedding plane under low bonding strength. Fracture initiation pressure is synergistically controlled by multiple factors. Bedding weakening and high stress difference significantly reduce initiation pressure. When the fracture inclination is 45°,the tensile stress around the wellbore is minimized due to optimal geometric configuration,resulting in the lowest initiation pressure. These findings provide valuable insights into the mechanisms underlying complex fracture network formation during volumetric fracturing in bedded shale reservoirs.

       

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