页岩气藏水平井水力压裂裂缝敏感参数数值分析

Numerical analysis of fracture sensitive parameters in a hydraulically fractured horizontal well in layered shale reservoir

在计算页岩气井水平井分段压裂诱导应力和分析缝间干扰机理时,如果将页岩近似为各向同性体,将严重偏离工程实际。文中考虑了页岩弹性各向异性和孔隙渗流应力耦合效应,建立了水平井分段压裂三维有限元数值模型,针对水平井分段压裂方式、页岩力学特性对射孔簇间距的影响规律进行了敏感性研究分析。结果表明,裂缝形成的先后顺序影响裂缝周围诱导应力场,选择压裂方式与顺序压裂方式相比,形成的缝间诱导应力较小,最优缝间距也较小;页岩储层较高的弹性模量会引起较强的缝间干扰,导致缝宽和缝长均减小,页岩弹性模量各向异性越强,最优缝间距越大。所建有限元数值模型克服了仅适用于常规各向同性体诱导应力解析模型的限制,提供了相应的理论参考和技术支持。

It would be extremely deviated from practical engineering situation to consider the formation as an approximately isotropic body when calculating hydraulic fracturing induced stress and analyzing fracture interaction mechanism for horizontal well in shale gas reservoir.Therefore,by incorporating elastic anisotropy and pore hydro-mechanical coupling effect,a 3D finite element model for staged fracturing in horizontal well is developed and the sensitivity of staged fracturing methods and mechanical properties on the optimal fracture spacing of multistage operations are analyzed.The results show that the fracture order influences induced stress field around the fracture,comparing with consecutive fracturing,alternate fracturing produces smaller induced stress between fractures and smaller optimal fracture spacing; A higher Young＇s moduli results in strong interference between fractures and shorter and narrower fractures.The stronger the elastic anisotropy of elastic moduli,the greater the optimal fracture spacing.This finite element model overcomes the restriction of conventional stress-induced analytical model only applicable to isotropic body and can guide field practices more effectively.