水平井分段多簇限流压裂数值模拟

Numerical simulation of limited entry technique in multi-stage and multi-cluster horizontal well fracturing

李扬 2 邓金根 2 刘伟 2 闫伟² 曹文科 2 王鹏飞 2

中国石油大学（北京）石油工程学院，北京 102249 中国石油大学（北京）油气资源与探测国家重点实验室，北京 102249）

水平井分段多簇压裂是目前非常规储层开发的有效手段，但现场生产测试结果表明，相当一部分的射孔簇对产量完全无贡献。文中基于CZM模型和伯努利方程建立了考虑射孔孔眼摩阻的多簇裂缝同时起裂与扩展的有限元计算模型，对不同射孔参数情况下裂缝的同时扩展进行了计算模拟，得到了不同时间5簇裂缝的扩展形态，以及井底压力、各簇裂缝缝口压力和进入各簇裂缝的压裂液流量等随时间的变化规律。模拟结果表明：当射孔孔眼摩阻较低时，初期5簇裂缝同时起裂，后期由于应力干扰加强，中间3簇裂缝停止扩展并逐渐闭合，压裂液不再进入中间3簇射孔，成为无效射孔簇；非均匀射孔簇摩阻之间的差异能够有效平衡裂缝之间的应力干扰，使多簇裂缝同时起裂扩展并减缓多簇裂缝扩展的不均衡性；中间簇比侧边簇射孔数量只需多出2~3个就可以有效改变裂缝扩展形态，提高储层改造效果。该有限元计算模型对现场多簇水力压裂施工参数设计具有一定的指导意义。

Multi-stage and multi-cluster fracturing is one of the most powerful techniques for exploiting unconventional reservoirs. However, production logging analysis of many wells indicates that considerable number of perforation clusters do not contribute to production. In this paper, a multiple fracture simultaneous initiation and propagation finite element model, which takes perforation pressure drop into account, is developed based on the cohesive zone model(CZM) and Bernoulli′s equation and applied for simultaneous propagation simulation of 5 clusters with different perforation parameters. The evolution of the fracture geometry and the variation of bottom-hole pressure, fracture inlet pressure and fracture inflow rate with time are obtained. The results show that 5 clusters simultaneously initiate and propagate at the beginning of the fracturing treatment with low perforate pressure loss whereas the center and sub-center fractures are gradually closed in subsequent time and stop propagation due to stress shadow. These three middle fractures become invalid fractures because the fracturing fluid no longer enteres. Perforation pressure loss during the limited entry fracturing can counterbalance the stress interference during the hydraulic fracturing. In spite of the uneven fracture length, each cluster among the stage can successfully initiate and propagate and the total length of fractures has been improved significantly. Compared with the side clusters, only 2 or 3 more perforation center clusters can change the final fracture geometry and improve the fracturing effect. This finite element model may be useful for the parameter design of multiple hydraulic fracturing.

10.6056/dkyqt201701016