Numerical evaluation of refracturing fracture deflection behavior under non-uniform pore pressure using XFEM

Refracturing has become an important technique for tapping old wells to stabilize and improve well performance. However, due to inaccurate well selection and formation selection for refracturing and inadequate prediction of refracturing fracture propagation, refracturing effectiveness sometimes may be diminished. Hence, the objective of this paper is to establish a numerical model to efficiently simulate the processes of first fracturing, injection and production, and hydraulic refracturing. The extended finite element method (XFEM) is first applied. Then, a five-spot well pattern is considered, which couples the angle of the well array to the maximum horizontal principal stress with the angle of the perforation orientation. Afterward, we optimize the refracturing orientation under non-uniform pore pressure conditions. Fracture length and fracture deflection angle are utilized as evaluation indicators. Results indicate that the orientation of refracturing is not recommended to follow the injection well and the optimal perforation area exists when the direction is along the middle of the two injection wells. Long fractures with large deflection angles can be obtained along the mid-line of the well array in a clockwise as well as a counter-clockwise direction of 15°, leading to a higher reservoir modification area. In addition, fractures tend to propagate into areas of high pore pressure. This work provides a useful model including the dynamic propagation of fractures during refracturing after initial fracturing and production operations, which can assist operators optimize the fracturing process.