Molecular dynamics simulation of sub- and supercritical water extraction shale oil in slit nanopores

MD simulation on the process of supercritical water extraction of shale oil in silica nano-slit was carried out in this paper. Oil molecules extraction was a coupled-process of desorption and diffusion. Supercritical water exhibited a higher extraction rate for adsorbed oil than subcritical water. Temperature showed a positive effect, dominating the desorption process, while pressure acted as an inhibitor, with the benefit of increasing the temperature (623–823 K) being 3.4 times greater than that of decreasing the pressure (15–35 MPa). An increase in temperature promoted extraction by reducing adsorption stability and enhancing diffusion, and an increase in pressure advanced start time of desorption by enhancing oil-water interaction and prolonged complete desorption time by inhibiting diffusion. Oil component diffusion mainly depended on molecular weight and solvent polarity. The diffusion direction of oil in nano-slit was mainly parallel to the slit surface under surface adsorption.