Insight into the oil–water seepage mechanism based on shale stress deformation: A numerical simulation approach

In shale reservoirs, organic matter (OM) and inorganic matter exhibit different deformation behaviors under stress. Their heterogeneous distribution leads to complex oil–water flow during the fracturing production process. In this study, a conceptual shale model with varying total organic matter content (TOC) is developed. A novel aspect is the consideration of shale stress deformation coupled with fluid flow, based on which the oil–water seepage mechanism is investigated. Simulation results demonstrate that the high TOC matrix swept by water during the soaking stage can be effectively mobilized, and the flow rate of oil briefly increases. During the soaking stage, pore pressure in the shale matrix increases. The fluid-induced stress on OM leads to deformation, which expands additional oil–water flow channels and creates favorable conditions for fluid exchange between isolated or small pores within the matrix. The elastic energy stored in deformed OM is released during production, which provides energy supplement for the flow of shale oil and helps to maintain a higher oil production in the later stage. Additionally, the influences of Young's modulus, shale permeability, fracture spacing, and matrix distribution on oil recovery efficiency are analyzed. The results are expected to provide a deeper understanding of the oil–water seepage mechanism and clarify the favorable conditions for hydraulic fracturing exploitation.