Transient Flow Characterization between Matrix and Natural Fractures in Shale Oil Reservoir

The transient flow between matrix and natural fractures significantly impacts the exploitation of shale oil reservoirs. Existing characterization models, however, primarily target conventional fractured reservoirs, neglecting the specific mechanisms of shale, including nonlinear flow and stress sensitivity. A new characterization model for shale matrix-natural fracture flow is developed by incorporating these critical mechanisms. The shale reservoir flow equations were first constructed considering nonlinear flow and the stress sensitivity of the matrix. Then, the governing equations are solved numerically using a fully implicit scheme. Based on the equations, the dimensionless shape factor for matrix-fracture flow is derived via the material balance method. Our results demonstrate the time-dependent behavior of the shape factor in shale reservoirs, with values lower than in conventional fractured reservoirs except during initial flow periods. More pronounced nonlinear flow characteristics in the shale matrix result in smaller dimensionless shape factors. In addition, increased stress sensitivity in the shale matrix leads to more significant permeability reduction, yielding smaller dimensionless shape factors. An empirical correlation between dimensionless shape factor and dimensionless time is established through multiple numerical simulations and regression analysis. This model improves matrix-fracture flow characterization in shale systems and can be employed in reservoir numerical simulations to accurately predict the well-production performance, which is essential for the efficient exploitation of shale oil.