含砾砂岩储层重复压裂新方法及机理分析

New Method to Refracture Conglomerate Formation and Mechanism Analysis

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,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,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。研究结果表明:变排量压裂方式能有效增加裂缝复杂程度,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可增大裂缝数量,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能充分利用各阶段压裂液的特性,最终形成复杂的裂缝网络。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。

Repeated fracturing technology is widely used in the development of old oilfield,especially for tight sandstone,shale,and other typical reservoirs.The effectiveness of refracturing in gravel sandstone reservoirs remains unclear.To produce complex fracture networks in gravel sandstone reservoirs,a new dynamic refracturing method of in-phase refracturing in variable injection rate with different fracturing fluids was proposed,with which the fracture bifurcation could be promoted and could the effective stress of rock be significantly reduced by permeable fracturing fluid.In addition,the applicability of this method was verified on artificially prefabricated gravel sandstone specimens in a true triaxial fracturing simulation experiment.The results show that the new method effectively increases the complexity of fracture network,and the number of fractures produced is at least 3 times those by constant injection fracturing,and the number of hydraulic fractures is three times that using single type fracturing fluid.The new method can make full use of each type of fluid in various stages,and eventually form a complex fracture network.This study provides a certain reference for refracturing of gravel sandstone reservoirs to generate complex fractures.