老井开发对加密井水力压裂裂缝扩展的影响规律

随着页岩气的开发,对已有水平井井网加密将会是后期开发的关键。老井的持续开采会引起地层孔隙压力和地应力的重新分布,地应力的重新分布对裂缝扩展行为和路径造成显著影响。为了探究地应力的重新布对裂缝扩展行为的影响机制,本文基于块体离散元数值模拟方法,针对老井开采后地应力场变化对加密井水力裂缝扩展的影响特征开展研究。本研究综合考虑了注液速率,压裂液粘度、地应力梯度和初始地应力场等因素对水力裂缝扩展的影响。结果表明,老井引起的地应力降低会导致新井水力裂缝向老井偏移。提高注液速率,增大压裂液粘度可以有效降低地应力非均匀导致的水力裂缝偏移问题。地应力梯度越大、初始地应力越高,水力裂缝的偏移率越高。本研究对页岩气水平井加密方案制定具有一定的理论指导意义。

Influences of development of old wells on fracture propagation from hydraulic fracturing of infill wells

With the development of shale gas, infilling the existing horizontal well pattern is the key to later development. Continuous exploitation of old wells will cause redistribution of pore pressure and in-situ stress. The redistribution of in-situ stress has a significant impact on the fracture propagation behavior and path. In order to explore the influence mechanism of in-situ stress redistribution on fracture propagation behavior, based on the block discrete element numerical simulation method, the influence characteristics of the change of in-situ stress field on the hydraulic fracture propagation of infill wells were studied. In this study, the effects of injection rate, fracturing fluid viscosity, in-situ stress gradient and initial in-situ stress on hydraulic fracture propagation were considered. The results show that the decrease of in-situ stress caused by old wells will lead to the migration of hydraulic fractures from new wells to old wells. Increasing injection rate and fracturing fluid viscosity can reduce hydraulic fracture migration caused by non-uniform in-situ stress. The larger the in-situ stress gradient and the higher the initial in-situ stress field, the higher the hydraulic fracture migration rate. This study has a certain theoretical significance for the formulation of shale gas horizontal well infill program.