Numerical analysis of the hydraulic fracture communication modes in fracture-cavity reservoirs

Abstract

The fracture-cavity carbonate reservoirs in the Tahe Oilfield in China are mainly exploited by fracturing. We need the hydraulic fractures to communicate with caves to create a flow channel. However, due to the existence of the fracture-cavity systems, the hydraulic fracture propagation morphology is complicated, while the propagation characteristics are not clear. To analyze the hydraulic fracture propagation in fracture-cavity carbonate formations, based on the discontinuous discrete fracture model, we developed a solid-seepage-freeflow coupled fracturing model for fracture-cavity formations, which can simulate the complex interaction behavior of fractures and caves. Based on the simulation results, we found the interaction rule between hydraulic fractures and fracture-cavity systems: the stress concentration around caves is the main factor that determines the fracture propagation path. Deflection due to stress concentration is usually not conducive to communication, while natural fractures distributed around caves could break the rejection action. Increasing the hydraulic energy in the hydraulic fracture can make fracture propagate directly and reduce the influence of deflection. The steering fracture formed by temporary plugging is beneficial to the communication of fracture-cavity systems in the non-principal stress direction. According to the simulation results of different fracture-cavity characteristics, we raised four optimization communication modes for fracture-cavity carbonate formation to provide references for fracturing optimization design and parameter optimization.