Numerical study of simultaneous growth of multiple hydraulic fractures from a horizontal wellbore combining dual boundary element method and finite volume method

Horizontal well and multi-stage hydraulic fracturing have been extensively used to extract unconventional oil/gas. The fracture pattern created from the multiple fractures determines the surface area of the reservoir in contact with the wellbore, thus influencing the overall quality of the multi-stage fracturing. Therefore, a good understanding of the HF propagation behavior is of importance for designing the perforation layout. In this paper, a new fully coupled hydraulic fracturing model is developed by combining the dual boundary element method (DBEM) that describes the rock matrix deformation and the finite volume method (FVM) that simulates the fluid flow in the fracture. The DBEM applies displacement boundary integral equation to one crack surface and traction boundary integral equation to the other. The model presented is first validated against the existing semi-analytical and numerical solutions for single and two fractures in the infinite domain. Then the impact of spacing, in-situ stress difference and injection parameters on the competitive growth behavior between multiple HFs is investigated. A parameter formulated in terms of the ratio of fluid volume allocated to different fractures is proposed to be the indicator of simultaneous or preferential propagation. The results show that less isotropic in-situ stress and a larger fluid viscosity or injection rate tend to facilitate simultaneous growth of multiple fractures, in which the influence of the in-situ stress difference is enhanced while that of the injection parameters is weakened when increasing the fracture spacing.