水平井交替压裂裂缝间距优化及影响因素分析

Fracture spacing optimization for horizontal well alternating fracturing and influencing factors

为使水平井交替压裂在非常规油气储集层中形成大规模高效复杂体积缝网,需对交替压裂裂缝间距进行优化分析。从相邻2条压裂裂缝诱导应力叠加效应对初始水平主应力差的影响出发,建立了裂缝高度不同且缝内净压力也不同的物理模型,提出了交替压裂第一次压裂裂缝和第二次压裂裂缝临界裂缝间距及中间裂缝最佳起裂位置的确定方法。分析发现:前两次压裂裂缝临界裂缝间距随储集层岩石泊松比增大而减小,随裂缝高度和缝内净压力增大而增大;中间裂缝最佳起裂位置距第一次压裂裂缝的距离随储集层岩石泊松比增大而减小,随裂缝高度增大而增大,而缝内净压力对中间裂缝最佳起裂位置的影响较小。通过实例,将改进后的方法与已有方法进行对比分析后发现,改进后的临界裂缝间距和中间裂缝最佳起裂位置较已有方法能更准确地计算出诱导应力场,对非常规油气储集层交替压裂形成高效复杂体积缝网具有指导意义。

For creation of large-scale effective complex fracture networks of unconventional oil/gas plays, fracture spacing for alternating fracturing should be optimized. Started from the effect of total induced stresses on initial horizontal stress anisotropy, the total induced stresses computational model of two adjacent hydraulic fractures with different fracture height and fracture net pressure was built. Subsequently, optimization approaches for critical fracture spacing of the first two hydraulic fractures and optimal fracture initiation position of the third one were proposed. The analysis result shows that critical fracture spacing between the first two hydraulic fractures decreased with the increase of Poisson＇s ratio, and increased with the increase of fracture height and fracture net pressure; the optimal fracture initiation position of the third fracture apart from the first one decreased with the increase of Poisson＇s ratio, and increased with the increase of fracture height. However, fracture net pressure has negligible impact on the optimal fracture initiation position of the third fracture. Finally, with comparison and analysis of a case study, the optimization results of the proposed approaches were proved to be much more advantageous and economic over the existed one, which is of significant guidance for creation of complex fracture networks with alternating fracturing technology in unconventional oil/gas reservoirs.