Numerical Modeling Of Rock Hydraulic Fracture Based On Cohesive Crack

This paper introduced the application background of hydraulic fracturing technology. The research situation of rock fracture mechanics and numerical modeling of hydraulic fracture have been presented in this thesis. This paper summarized the basic theory of rock mass and the basis of fracture mechanics briefly,introduced rock mass parameter such as porosity,saturability,effective stress and permeability, analyzed the coupling analysis between permeability and stress,flow seepage law in porous media,the stress equilibrium equation and seepage flow equation of continuity, Pore pressure cohesive model,cohesive law for hydraulic fracture was developed in this thesis.This paper presented a numerical method to solve the hydraulic fracture in rock. Based on cohesive elements, a pore pressure cohesive fracture model was developed. The criterion for fracture initiation of quadratic nominal stress and fracture propagation of critical energy release rate is applied to decide the law of fracture initiation and fracture propagation. In the numerical study, the frccture propagations of different fluid viscosity and rock modulus were simulated and analyzed. The influence of fluid viscosity on the pressure gradient of fracture surface was analyzed, and the fracture patterns in different rock was also studied. 3D cohesive pore pressure model is established used ABAQUS. The effect of Elastic modulus and injection rate on the parallel crack propagation was obtained in fracturing the two rock cracks.In this paper, some conclusions is obtained after simulation: the greater the viscosity of fracturing fluid is, the faster decline of water pressure along the crack surface is. The fracture was seen as the pore channel or diversion channel determined by the critical width and the critical length. Appropriately increase the viscosity of fracturing fluid will widen the crack length and width.The more elastic modulus of rock is, the wider and the shorter of the fracture. In the process of multiple crack by fracturing, the rock fracture with biger elastic modulus plays a dominant part in the propagation of the crack, it decided the propagation of the crack. The faster the fracturing fluid injection is, the longer the rock fracture. The length of the crack changes significantly, This suggests that fracturing rate is an important factor of the fracture shape.