Numerical Simulation of Oil Displacement by Fracturing Imbibition in Horizontal Shale Oil Wells

Abstract

To improve the production prediction accuracy of fractured horizontal shale oil wells and optimize parameters such as shut-in time and fracturing fluid volume, a mathematical model of oil-water two-phase flow considering the whole process of fracturing fluid injection, shut-in imbibition, and well-opening production was built. Its numerical solution was obtained with the control volume finite element method, and the oil-water displacement between the matrix and fractures by imbibition was simulated to obtain the dynamic changes of the oil-water pressure field, velocity field, production, and water cut. The characteristics of oil displacement by fracturing imbibition were analyzed, and the shut-in time and fracturing fluid volume were optimized. In addition, the effects of matrix permeability and fracture network complexity on oil displacement by imbibition were examined. The research results show that in the case of a larger capillary force and longer shut-in time, the water cut is lower and the imbibition stimulation effect is more noticeable. The increase in fracturing fluid volume can promote the production of oil displacement by imbibition, while it will raise the water cut at the same time. Thus, the reasonable fracturing fluid volume can be determined by the increments of water cut and production. The optimal shut-in time is affected by the capillary force, matrix permeability, and fracture network complexity. To be specific, the capillary force and matrix permeability determine the imbibition velocity, while the fracture network complexity regulates the imbibition area. The model built in this paper can provide references for the optimal design of horizontal shale oil well fracturing.