页岩油气扩散系数及多尺度油气扩散模型研究OA

[Objective]To elucidate the diffusion mechanisms of shale oil and gas in nano-to microscale pore-fracture systems and overcome the limitations of conventional models in cross-scale prediction,this study investigates the diffusion characteristics and controlling factors of shale fluids across multiscale porous media.[Methods]High-temperature and high-pressure diffusion experiments were conducted on matrix and bedding-fractured core samples with varying petrophysical properties.A multiscale diffusion model was developed by coupling fractal theory,a tortuous capillary-bundle representation,and a confinement-corrected Peng-Robinson equation of state to account for pore-size distribution,tortuosity,phase saturation,and nanoscale fluid-wall interactions.[Results]Nanoscale confinement leads to phase-diagram contraction and a leftward shift of the critical point,substantially weakening diffusion capacity in confined spaces.Porosity and permeability are the primary structural controls:when porosity increases from 5.68%to 10.53%,gas and liquid diffusion coefficients increase by approximately one order of magnitude;when bedding-fracture permeability increases from 1.69×10-15 m2 to 404.88×10-15 m2,diffusion coefficients rise by about three to four times.Increasing pressure(10～36 MPa)suppresses gas-phase diffusion but enhances liquid-phase diffusion,whereas higher temperatures(80～115 °C)promote diffusion overall.[Conclusions]The proposed fractal-confinement diffusion model accurately matches the experimental results and reveals key nanoscale mechanisms,including a～10-5 reduction in effective diffusivity relative to bulk fluids and diffusion capacities in fractures that exceed those of the matrix by one to two orders of magnitude.[Significance]This model enables structural-sensitivity analysis and cross-scale prediction of diffusion processes,providing theoretical support for the quantitative characterization of shale-fluid migration and the optimization of reservoir development.