Main Controlling Factors of Fracture Network Formation of Volume Fracturing in Shale Reservoirs and Its Evaluation Method

Volume fracturing in shale reservoirs can effectively connect the natural fractures for forming fracture network system.It can enormously improve the productivity of shale gas,and obtain the economic benefits of shale gas exploitation as soon as possible.Thus,the fracture network formation of volume fracturing is particularly important.On the basis of the literature research of volume fracturing research findings and shale's test data around the world,research shows the fracture network formation of volume fracturing is mainly influenced by three controlling factors.① According to quality of shale reservoirs,higher brittle mineral contents of rock and Young modulus,lower fracture toughness,Poisson's ratio,strain energy release rate,and reservoir sensitivity(good fracture-ability)will be constructive to easier formation of fracture network.② According to favorable geological background conditions,lower stress anisotropy,better developed natural fractures and smaller approaching angle can be good for better extension and propagation for hydraulic fractures extending into network.③ According to opportune engineering conditions of fracturing operations,including the pressure and orientation of fracture initiation,the performance of proppant and fracturing fluid and fluid volume and pump delivery of fracturing and so on,their rational use will be more helpful to the formation of fully propagated fracture-network.Additionally,the evaluation methods of the above controlling factors are laboratory experiments,numerical simulation software and fracturing monitoring.This study has important theoretical value and practical significance to the understanding of shale reservoir's fracture-network formation mechanism and can improve the science of shale reservoir fracturing design.