Analysis of spatial distribution of cracks caused by hydraulic fracturing based on zero-thickness cohesive elements

As the main mining method of shale gas extraction, hydraulic fracturing produces a large number cracks in the target rock, forming effective transportation channels for shale gas.Therefore, it is of importance to study the spatial distribution and factors of cracks.In this paper, zero-thickness cohesive elements are inserted between adjacent solid elements by ins-coh program based on continuous-discontinuous method, obtaining computational model.Considering the fluid-solid coupling in hydraulic fracturing, user subroutines are developed to define the initial field distribution of pore pressure.The flow criterion of fluid and fluid-solid coupling equation are given in the fracturing stage.With the injection of fluid, cohesive elements break down, resulting in coherent space which constitutes transportation channels for shale gas.After verifying the correctness of the method above, a 3D numerical model of hydraulic fracturing is established, combining the geology of shale gas reservoir in some region of southwest China.The results show that this method can simulate the flow of fluid in rock mass under high pore pressure, and the complete failure process of rock mass properly.Finally, through the analysis and comparison of multi-group models studying the effect of injection rate, initial spacing and length of cracks on the final distribution, some guidances on the design of projects are given.