Краткое описание

Conventional waterflooding may fail in the recovery of tight oil reservoirs due to the interaction between the ultra-low-permeability matrix and high-conductivity fractures. Cyclic injection combined extensively with hydraulic fracturing is a promising substitute approach widely used for recovery in such reservoirs. During cyclic injection exploitation, spontaneous imbibition is one of the most important recovery processes in water-wet reservoirs with strong capillary forces. This paper presents a numerical method to effectively model the spontaneous countercurrent imbibition process after extensive hydraulic fracturing. The model helps to provide insight into the oil recovery mechanism in tight oil reservoirs. A discrete fracture model is adopted to precisely model the features of fluid flow inside fractures and the interaction between the matrix and fracture media. Comparisons of the simulation results and experiments show an excellent match. Numerical simulations of the model with different capillary curves and cyclic injection schemes were performed to evaluate the effects of the spontaneous imbibition process on enhanced oil recovery. The simulation results show that the complex fracture network and cyclic injection parameters play an important role in the contributing fraction by spontaneous imbibition of the total oil recovery. The proposed simulation method can be used to optimize the cycle period and well spacing in order to maximize the role of spontaneous imbibition.