Comparison of consecutive and alternate hydraulic fracturing in horizontal wells using XFEM-based cohesive zone method

Abstract

Abstract Combining multistage hydraulic fracturing and horizontal drilling is a highly effective method of increasing the production rates of unconventional reservoirs. The openings of propped transverse fractures in horizontal wells cause the reorientation of the stress in their neighborhood. This, in turn, affects the direction of propagation of the subsequent fractures. It is desirable to minimize the fracture spacing while also ensuring the growth of transverse fractures in multi-fractured horizontal wells, in order to improve reservoir drainage. In this paper, we present a two-dimensional fully coupled pore pressure-stress model based on the extended finite element method in conjunction with the cohesive zone method for simulating consecutive fracturing and alternate fracturing for a typical field case corresponding to low-permeability reservoirs. It is shown that the stress interference increases with the number of fractures created and also depends on the sequence of fracturing. The in-situ stress difference has a significant impact on the extent of the stress interference zone. The magnitude of in-situ stress affects the fracture length and width. The local in-situ stress in the near-tip region is redistributed with fracture propagation. In contrast to the consecutive fracturing method, the alternate fracturing method allows for the fracture spacing to be lowered, owing to the propagation of a middle fracture between the previous two fractures. These results offer new insights on the optimization of fracture spacing and should act as a guide for fracture design, helping improve the production rates in unconventional reservoirs.