Research on Shale Fracture Propagation Control Based on the Perforation Sealing Law of Ball Sealer

Abstract During shale gas well fracturing, the equilibrium of fracture propagation is poor due to the influence of formation heterogeneity and stress interference between fractures. Wellbore temporary plugging is an effective measure to control fracture propagation. However, in temporary plugging fracturing, perforation and temporary plugging parameters mainly rely on empirical design. Under the same parameters, the temporary plugging effect and production of different fracturing sections in the same well are quite different, which reflects the law of ball sealer sealing and the law of fracture propagation are unclear. To solve the above problems, this paper built a CFD-DEM horizontal wellbore temporary plugging model, analyzes the migration and sealing characteristics of ball sealer, and forms the judgment conditions for sealing perforation holes. On this basis, an adaptive temporary plugging fracture propagation model is built by coupling the perforation flow distribution model and the phase field fracture propagation model. This model can realize the adaptive calculation of the sealing position of the ball sealer and the fracture propagation path after temporary plugging. Based on the field parameters of Weiyuan shale gas block in Sichuan Basin, the simulation of wellbore temporary plugging fracture propagation under multi-cluster perforation conditions was carried out. The results show that the fractures at the heel side and toe side propagate faster under the uniform perforation mode. Additionally, the simulated ball sealer sealing results show that the ball sealer preferentially seals the perforation holes at the toe side. After temporary plugging, the propagation of fractures at the toe side are inhibited, and the propagation of fractures at the heel side are over-propagated. Therefore, we propose a variable number perforation mode, the number of perforation holes in each cluster gradually increases from heel side to toe side, to control the fracture propagation. The simulation results show that in this mode, the fractures at the toe side propagate preferentially after fracturing, and the fractures at the heel side propagate slowly. In the process of temporary plugging, the fractures at the toe side are preferentially sealed, thereby accelerates the propagation of slow-propagation fractures at the heel side, ultimately forming an overall more balanced fracture morphology. This study was applied in WH6 well in Weiyuan shale gas block. Compared with the well section after temporary plugging of uniform perforation, the fracture propagation equilibrium coefficient of the well section after temporary plugging of variable number perforation increased by 41.3 %, the perforation cluster sand influx variation coefficient decreased by 38.7 %. The findings of this study are of great significance to guide the optimization design of perforation scheme and temporary plugging scheme of horizontal wells, which is helpful to improve the reservoir simulation effect.