Shale oil flow mechanisms during fracturing-soaking-producing process studied by Lattice Boltzmann simulation

Shale oil is one of the most potential and strategic alternative oil resource in China. It’s of great significance to clarify the fluid distribution and evolution laws in porous media for enhancing the recovery of shale oil during the fracturing-soaking-producing process. In this work, a multi-component multiphase lattice Boltzmann model was adopted to study the shale oil flow mechanism during fracturing-soaking-producing process. Firstly, the accuracy of the model was verified using Laplace’s law, contact angle, and stratified flow. Then, based on the scanning electron microscope (SEM) image of Jiyang shale, the structure of the shale porous medium was constructed including the distribution of fracture and matrix pores. Subsequently, the lattice Boltzmann model was used to simulate the fracturing-soaking-producing process of shale porous media, and the fluid distribution characteristics at different stages were analyzed. Then the effects of different soaking time, reservoir wettability and drainage rate were explored further. The results show that the fracturing fluid will seep into the matrix pore and replace the oil phase under the action of capillary force during the soaking stage, and with the increase of soaking time, the backflow rate of fracturing fluid return tends to decrease; the water-wet core has a better development effect than the neutral and oil-wet cores, and the utilization rate of fracturing fluid and the degree of crude oil utilization in the matrix are higher; the higher drainage rate will make the pore pressure drop rapidly, which is not conducive to the development and production of the shale oil. The fluid flow mechanisms during the shale oil fracturing-soaking-producing process are investigated from a pore-scale perspective, which provides support for the formulation of a reasonable production schedule for shale oil wells.