Fracture Interaction during Temporarily Plugging Staged Fracturing

Temporarily plugging staged fracturing technique has been successfully applied in unconventional reservoirs.Using XFEM-based CZM  (cohesive zone model based on the extended finite element method) , a 2D capturing stress interference and coupling fluid –solid model was established to investigate the process of the technique. The key points are as follows: (1) The diameter of the whole model was 1000m. The enriched zone is a square with the length of 200 m. The whole model has 162299 nodes and 161901 elements. The quality of meshes meets the requirement of XFEM convergence. (2) plugging efficiency of diverting agents is simulated by changing injection rate. (3) the boundary condition of propped fractures is maintained by surface pressure, change of which simulates filtrate loss rate; (4) heterogeneity along horizontal well is simulated by setting various properties surrounding the subsequent fractures. The simulation results reveal that: (1) in-situ stress contrast affects the extent of the stress alteration zone, while in-situ stress magnitude impacts fracture length and width; (2) proper plugging efficiency will help to achieve even treated effect along the horizontal well; (3) with the augment of formation permeability, the extents of stress reversal and reorientation become small, thus subsequent fractures tend to propagate along the direction of maximum principle stress. (4) Young modulus and tensile strength have a great influence on propagation path, propagation rates, fracture length and width .