海相页岩与陆相页岩体积压裂支撑剂敏感性差异机理探讨

DISSCUSSION ON THE MECHANISM OF DIFFERENCE IN PROPPANT SENSITIVITY BETWEEN MARINE AND CONTINENTAL SHALE VOLUME FRACTURING

页岩体积压裂是储层在地应力与致裂压力联合作用下形成天然裂缝与压裂裂缝相互交错的复杂缝网,现场实践表明这个复杂的缝网破裂演化过程中海相、陆相页岩储层对不同粒径的支撑剂注入具有明显的敏感性差异。通过海陆相页岩露头剖面地质调查、钻井取芯对比分析岩体结构性差异,分析海相、陆相页岩水平井水力压裂施工数据,结合位移间断边界元裂缝网络演化模拟(DFN),揭示海相与陆相页岩体积压裂支撑剂敏感性差异机理。结果表明:陆相页岩呈岩性互层结构,多种岩体结构面发育,具有高度的结构非均质性特征;在相似的工况条件下,支撑剂随高压流体注入陆相页岩储层地面采集压力波动幅度较大,支撑剂对陆相页岩敏感性强于对海相页岩敏感性;海相页岩与陆相页岩岩体结构性差异导致水力压裂过程中的起裂行为、拓展机制、缝网形态的差异化机制,天然裂隙、弱结构面越发育,相同注入条件下压裂液滤失量大缝内净压力越低,水力裂缝平均开度越小;天然裂隙与最大水平主应力夹角越大,水力裂缝沟通天然裂隙之后转向至最大水平主应力方向扩展,转向段裂缝开度越小,容易引起支撑剂聚集沉降,从而造成支撑剂敏感性强。该研究对陆相页岩储层压裂方案优化具有一定现实指导意义。

Volume fracturing in shale formations creates a complex fracture network where natural fractures and induced fractures intersect under the combined effects of in-situ stress and fracture pressure.Field practices have shown that during the fracturing evolution of this complex network,marine and continental shale reservoirs exhibit significant differences in sensitivity to proppant injection of varying particle sizes.Through outcrop profile geological survey and drilling core collection,the structural differences of marine and continental shale rock masses were comparatively analyzed.By analyzing hydraulic fracturing data from horizontal wells,combined with discrete fracture network(DFN)simulation of displacement-discontinuity boundary element,the mechanism of the difference in proppant sensitivity between marine and continental shale volume fracturing is revealed.The results show that continental shale displays a layered lithologic structure with developed various rock structural planes,demonstrating significant heterogeneity.Under similar operating conditions,the ground-collected pressure fluctuates greatly when proppant is injected into continental shale reservoirs with high-pressure fluid,indicating a stronger sensitivity to proppants compared to marine shale.Differences in rock structure between marine and continental shale lead to varied fracture initiation,propagation mechanisms,and fracture network morphology during hydraulic fracturing.The more developed natural fractures and weak structural planes are,the greater the fluid loss and the lower net pressure within fractures under the same injection conditions,resulting in smaller average hydraulic fracture aperture.The larger the angle between natural fractures and the maximum horizontal principal stress,hydraulic fractures will turn and propagate towards the direction of the maximum horizontal principal stress after intersecting with natural fractures.As a result,the apertures of fractures in the turning segments tend to be smaller,which can result in the accumulation and settling of proppants,thereby leading to stronger proppant sensitivity.This study provides practical guidance for optimizing hydraulic fracturing strategies for continental shale reservoirs.