页岩气井压后返排动态模拟研究

Research on Dynamic Simulation of Fracturing Fluid Flowback in Shale Gas Wells

压裂液返排动态是影响页岩气井水力压裂后产能效果的重要因素。从页岩气井压后压裂液流动机理出发,讨论了压裂液分布区域和特征,利用数值模拟手段描述了压裂液在裂缝系统中的流动,并深入分析了压裂液滞留在裂缝和地层中的机理。根据页岩气水力压裂可能产生的裂缝形态,压裂液分布在高导流主缝、分支缝及压裂液侵入裂缝面周围的页岩基质,在返排过程中,裂缝与基质之间的渗流能力级差、重力分异造成在高导流裂缝的压裂液滞留,气水两相相对渗透率差异为影响分支缝压裂液返排的主要因素,而基质毛管压力则是阻碍基质侵入带压裂液流动的主要原因。开展对页岩气井压后返排动态研究,对于认识页岩气井压后返排率与裂缝系统形态特征的关系极为重要,同时,也为制定合理的返排制度提供了相应的理论指导。

The flowback performance of fracturing fluid is one of significant factors impacting post-fracturing productivity of shale gas wells.Initiated with the flowback mechanism of fracturing fluid,the distribution area and features of fracturing fluid were discussed.Flow of the fracturing fluid in fracture system was described using numerical simulation,and the mechanisms of fracturing fluid retention in both fracture and formation were deeply investigated.According to the potential fracture geometry that could be induced by hydraulic fracturing in shale gas formations ,the fracturing fluid after fracturing distributes at high conductivity primary frac- tures,branch fractures and shale matrix surrounding fracture faces.During the process of flowback,permeability difference and gravity segregation between fracture system and shale matrix result in fracturing fluid retention in high conductivity fractures,and liquid-gas two phase relative permeability is the main factor affecting the fracturing fluid flowback in the branch fractures ,however matrix capillary pressure is the main reason for the fracturing fluid retention in the invaded matrix.Research on flowback performance after fracturing in the shale gas wells is significant to know the relationship between flowback rate and fracture morphological characteristics after fracturing in the shale gas wells,meanwhile it provides corresponding theoretical guide for reason- able flowback design.