A Waterflood Induced Fracture Simulation Model for Naturally Fractured Low-Permeability Reservoirs

摘要

Waterflood induced fractures are the new features affecting the reservoir heterogeneity in low-permeability reservoirs. Due to the high injection pressure, waterflood induced fractures will generate and propagate when the formation pressure exceeds fracturing pressure during the waterflood process of low-permeability reservoirs. Waterflood induced fractures will interact with natural fractures and create high permeable flow channels. Conventional reservoir simulation models often fail in simulating the waterflooding of low-permeability reservoirs without considering the effect of reservoir pressure on the fractures. Current fracture models based on Perkins-Kern-Nordgren (PKN) model only focus on the simulation of the propagation of a single fracture without considering the interaction between waterflood induced fractures and pre-existing natural fractures. Therefore, based on the analysis of field data and the mechanism of waterflood induced fractures, a comprehensive wateflood induced fracture simulation model for naturally fractured low-permeability reservoirs is established. Compared with the existing models, this waterflood induced fracture model can simulate the process of occurrence, propagation and closing of waterflood induced fractures due to the effect of high injection pressure and complex in-situ stress. The model considers the interaction between induced fractures and natural fractures, including slippage and crossing. The fracture model is coded in a module of a reservoir simulator. The simulation results shows that waterflood induced fractures worsen the reservoir heterogeneity, greatly increase the water cut of production well and lower the oil production rate. The model can simulate the impact of waterflood induced fractures on waterflooding and optimize well patterns in low-permeability reservoirs to improve sweep efficiency and oil recovery.