储层射孔压裂裂缝起裂与扩展的数值分析

掌握储层水力压裂裂缝的起裂与扩展规律对非常规油气资源开采和提高采收率至关重要。采用水泥砂浆模拟天然页岩,获得了与页岩基本力学参数和断裂韧性一致的相似材料。运用FRANC3D和ANSYS,模拟分析了不同水平应力比和射孔布置方式对水力压裂起裂和扩展的影响。研究表明:利用FRANC3D+ANSYS可以较好地模拟射孔压裂裂缝的起裂和三维空间中的扩展行为。射孔压裂裂缝的起裂压力随水平应力比的增大而减小。射孔方向与最大水平主应力方向一致时起裂压力较小,射孔方向与最大水平主应力成夹角时,裂缝扩展面扭转并趋向于平行最大水平主应力方向。相对于射孔对称排布和交错排布,射孔线性排布时的起裂压力较小。

Numerical study on fracture initiation and propagation of reservoirs subjected to hydraulic perforating

Understanding hydraulic fracturing initiation and propagation in low permeability reservoir is of great significance for exploiting and enhancing recovery of unconventional oil and gas resources. Cement, mortar and quartz sand were mixed to model the natural shale rock. Our laboratory tests proved that, the mechanical properties, especially fracture toughness, were close to those of the natural shale rock. The numerical codes FRANC3D and ANSYS were adopted to probe into initiation and propagation of hydraulic fractures in reservoir rock in different horizontal stress ratio and perforation layout. The simulation and analysis have indicated that:1) Perforation fracturing initiation and propagation in three dimensions are properly simulated by FRANC3D and ANSYS; 2) The initiation fracture pressure de-creases with the increase of horizontal stress ratio; 3) Perforation parallel to the maximum horizontal stress has the smallest initiation fracture pressure. Propagation plane deflection tends to be parallel to the maximum horizontal stress when they are not in parallel; 4) Linearly distributed perforation is supe-rior to symmetric perforation and staggered perforation as it provides the minimum initiation fracture pressure.