含砾砂岩储层重复压裂新方法及机理分析

重复压裂技术广泛应用于老油田开发过程,尤其适用于致密砂岩、页岩等典型储层,而含砾砂岩储层中重复压裂方法的有效性还有待研究。针对重复压裂含砾砂岩储层产生复杂裂缝网络的压裂方法问题,基于动态载荷促进裂缝分叉、易渗透压裂液明显降低岩石有效应力的作用机理,本文提出“变排量、分阶段多压裂液组合”的重复压裂方法。为验证该方法的合理性,本文以人工预制的含砾砂岩试件为实验对象,通过变排量、分阶段注入不同性质压裂液进行了室内真三轴压裂模拟实验,总结了压裂机理。研究表明：变排量压裂方式产生的裂缝条数至少是定排量压裂方式产生裂缝条数的3倍;分阶段多压裂液组合压裂方法产生水力裂缝的条数是单一类型压裂液压裂产生裂缝条数的3倍。变排量、分阶段多压裂液组合的压裂方法将对含砾砂岩储层进行重复压裂产生复杂裂缝具有一定的借鉴意义。

New Method to Refracture Conglomerate formation and Mechanism Analysis

Refracturing technology is widely used in the development of old oilfield, especially for typical formations such as tight sandstone and shale. The efficiency of refracturing methods in sandstone mixed conglomerate formations remains to be studied. In terms of fracturing method of fracturing sandstone mixed conglomerate formation, based on the mechanism of dynamic load to promote fracture branching and fracturing fluid penetrating to reduce the effective stress, this paper proposed "variable injection rate, staged different fracturing fluids" refracturing method. To verify the rationality of the method, the sandstone mixed conglomerate formation was taken as experimental specimen, and the indoor true triaxial fracturing simulation experiments were conducted by using variable injection rate and different fracturing fluids. The mechanisms of refracturing at each stage were summarized. The research showed that the number of fractures produced by the variable injection rate fracturing method was at least 3 times more than that of the constant injection method. The number of hydraulic fractures generated by the multi-fracturing fluid combined fracturing method was 3 times more than that of the constant injection method. The fracturing method with variable injection rate and staged multi-fracturing fluid can provide a certain reference for refracturing the sandstone mixed conglomerate formation to produce complex fractures.