New insight into mechanisms of fracture network generation in shale gas reservoir

The generation mechanisms of complex fracture mesh and the mechanism of activating existing natural fractures during shale fracturing are studied based on rock fracture dynamics. It is found that steering conditions should be satisfied at both the left and right ends of a natural fracture to form an intensive fracture mesh after the induced hydraulic fracture reaches the natural fracture; there exists a minimum critical pump rate (critical pump rate) to form an intensive fracture mesh. The critical pump rate increases as the inclination of the natural fracture increases and reaches a maximum value (constant) when the inclination of the natural fracture is 90°. When the inclination of the natural fracture is less than 90°, the critical pump rate first decreases and then increases as the angle between horizontal wellbore and the natural fracture increases; the critical pump rate reaches a minimum value for the natural fractures perpendicular to the wellbore. The critical pump rate increases as natural the fracture length increases and the rock elastic modulus decreases. When hydraulic fractures reopen existing natural fractures, the release of the original shear stress in the fracture surface would lead to the fracture surface slippage, which would greatly enhance the flow conductivity of the natural fracture. Very small or very large inclination of natural fracture is not conducive to fracture activation, best activating result can be reached at 30–60° inclination. Rise in elastic modulus inhibits fracture surface slippage and Poissonʹs ratio has little effect on fracture surface slippage.