1 research outputs found
Displacement Mechanism of Oil in Shale Inorganic Nanopores by Supercritical Carbon Dioxide from Molecular Dynamics Simulations
Supercritical
CO<sub>2</sub> (scCO<sub>2</sub>), as an effective
displacing agent and clean fracturing fluid, exhibits a great potential
in enhanced oil recovery (EOR) from unconventional reservoirs. However,
the microscopic translocation behavior of oil in shale inorganic nanopores
has not been well understood yet in the scCO<sub>2</sub> displacement
process. Herein, nonequilibrium molecular dynamics (NEMD) simulations
were performed to study adsorption and translocation of scCO<sub>2</sub>/dodecane in shale inorganic nanopores at different scCO<sub>2</sub> injection rates. The injected scCO<sub>2</sub> preferentially adsorbs
in proximity of the surface and form layering structures due to hydrogen
bonds interactions between CO<sub>2</sub> and −OH groups. A
part of scCO<sub>2</sub> molecules in the adsorption layer retain
the mobility, due to the cooperation of slippage, Knudsen diffusion,
and imbibition of scCO<sub>2</sub>. The adsorbed dodecane are separated
partly from the surface by scCO<sub>2</sub>, as a result the competitive
adsorption between scCO<sub>2</sub> and dodecane, and thus enhancing
the mobility of oil and improving oil production. In the scCO<sub>2</sub> displacement front, interfacial tension (IFT) reduction and
dodecane swelling enhance the mobilization of dodecane molecules,
which plays the crucial role in the CO<sub>2</sub> EOR process. The
downstream dodecane, adjacent to the displacement front, is found
to aggregate and pack tightly. The analysis of contact angle, meniscus,
and interfacial width shows that the small scCO<sub>2</sub> injection
rate with a large injection volume is favorable for CO<sub>2</sub> EOR. The morphology of meniscus changes in the order convex–concave–CO<sub>2</sub> entrainment with the increase of the injection rate. The
microscopic insight provided in this study is helpful to understand
and effectively design CO<sub>2</sub> exploitation of shale resources