Crack Initiation Characteristics Of Tension-shear Complex Mode Subjected To Water Pressure

The calculation of critical water pressure and the judgement of crack model are two important contents in the research of hydraulic fracture, and fracture mechanics has comparative advantages in solving the two problems. The paper, which based on fracture mechanics, stduies crack characteristics of the single crack and the crack tip by combining theory and numerical calculation.By considering the influence of water pressure and the secondary non-singular terms, the solutions of critical water pressure and crack initiation angle are derived, which based on the generalized maximum tensile stress criterion. Crack angle, confining pressure, T-stress, and fracture process zone on critical water pressure and crack initiation angle is analyzed. Using ANSYS software to calculate crack tip stress intensity factor, then critical pressure and critical deflection angle can be calculated according to the fracture criterion. The effect of perforation inclination angle, perforation length, the radius of wellbore and the principal stress difference on crack initiation characteristics of the crack tip of perforation was analyzed.The results show that the critical water pressure increases and crack initiation angle decreases with the increase of the radius of fracture process zone and confining pressure. Using the ANSYS finite element software for numerical simulation of crack in artifacts is can ensure the accuracy of calculation. Ki decreases with the increase of crack angle, when Kn increases at first then decreases. For the fracture of tension-shear complex mode, the critical water pressure decreases and crack initiation angle increases with the increase of the perforation length and radius of wellbore. Meanwhile, the critical water pressure and crack initiation angle increase with the increase of principal stress.