Study On Initiation And Expansion Of Symmetrical Double Perforation And Single Perforation With Wellbore

Hydraulic fracturing is a measure of increasing production in oil and gas production.Research on hydraulic fracturing focuses on cracking theory,crack initiation and crack propagation.When the weight function method is used to solve the crack tip strength factor,the geometry and load variables that affect the stress intensity factor are separated.Once the weight function is determined,the stress intensity factor of the crack can be calculated under arbitrary load,which is highly efficient and flexible.Based on the weight function method and the maximum circumferential stress criterion,the fracture criterion of the symmetrical double cracks and single crack model established,and the test and simulation results have been verified.Using matlab software to edit the critical water pressure and the fracture initiation angle program,and to analyze the influence of different parameters on perforation initiation of the model.the finite element software ANSYS was used to simulate the crack propagation of the symmetrical double cracks and single crack model at a perforation of 45 degrees under different parameter combinations,the influence of wellbore water pressure,the difference of principle stress and perforation length and hydraulic pressure reduction factor within the crack were analyzed,in addition,the crack initiation characteristics and extension trajectory of the two models under the same parameters were compared and analyzed.The results show that in the range of small perforation inclination angle and large a/R parameter,critical water pressure decreases with increasing lateral pressure coefficient and a/R coefficient of the model,larger perforation inclinations and smaller a/R parameters have opposite rules.The critical fracture initiation angle increases with the increase of the parameter a/R and the horizontal stress difference of the model,but the symmetry of crack angle is destroyed by high water pressure.The smaller the water pressure in the wellbore and the reduction factor of the hydraulic pressure in the crack and the larger the lateral pressure coefficient of the principal stress of the model,the faster the crack propagation trajectory tends to crack from 45° to the horizontal principal stress direction,but the effect of perforation length on crack propagation trajectory is not obvious.The symmetric double cracks and single crack model has similar law in the initiation and propagation characteristics.