Numerical study of near-wellbore hydraulic fracture propagation

Abstract

Hydraulic fracturing is a major technique used to stimulate shale gas development. In this paper, the fracture propagation path, critical water pressure and deflection angle during the hydraulic fracturing process are analyzed using the maximum tangential strain and incremental crack growth method. After verifying the present numerical method by using published experimental results, this method applied to study the effects of the stress anisotropy coefficient, the perforation length and angle, the water injection pressure and Poisson’s ratio on both the fracture propagation path and the critical water pressure. Furthermore, the effect of T-stress on the crack extension trajectories under different loading conditions is analyzed. The parameter analysis indicates the following: the greater the stress anisotropy coefficient and perforation length, the sooner the fracture reorients to the direction of horizontal stress. A perforation angle that approximately aligns the perforation with the direction of the horizontal stress is recommended to decrease the near-wellbore tortuosity and critical water pressure. The critical water pressure increases with the stress anisotropy coefficient and perforation angle, whereas the perforation length exhibits the opposite trend. The grey relative analysis indicates that the perforation angle is the most important controlling factors in complicating the hydraulic fracture propagation path near-the wellbore. The fracture propagation path is not significantly affected by Poisson’s ratio under high-pressure water injection. In addition, T-stress can significantly affect the fracture propagation path of closed fractures; however, its effect can be ignored for open fractures. The conclusions obtained from this research are important to gain a better understanding of the near-wellbore hydraulic fracture growth process under various conditions.