A mathematical model and numerical simulation of waterflood induced dynamic fractures of low permeability reservoirs

Based on abundant data of low permeability oilfields, dynamic fractures were conceptualized and their evolution, including cracking, extending and closing, were analyzed. A new model that describes the dynamic changes of fracture shape and properties was established and a software module was developed. The simulation results show that dynamic fractures cracked once the injection pressure was higher than the formation fracture pressure, and then extended continually, which showed a periodic variation relationship with the formation pressure and the injection volume. After the moderate injection, dynamic fractures remained the open status in a relatively long time, but then the whole fractures tended to close quickly, and these phenomena indicate that the dynamic fractures were significantly affected by the production condition. The presence of dynamic fractures provides a channel for the injection water. With the gradual extension of dynamic fractures, the injection water forms a narrow range of displacement, which leads to the severe imbalance of water flooding, aggravates the heterogeneity of low permeability reservoirs, and significantly affects the water cut rising rules of wells in all directions. However, dynamic fractures also show a positive effect on the establishment of an effective displacement system between the injection wells and the production wells.