Microscopic Mechanism Study on Gas–Crude-Oil Interactions During the CO2 Flooding Process in Water-Bearing Reservoirs

Abstract

The impact of water on CO2 sequestration and enhanced oil recovery processes is significant. In this study, a CO2–water-film–crude-oil–rock molecular system was established. Then, the influence of water-film thickness on the dissolution and dispersion of CO2 and crude oil under different temperature and pressure scenarios was examined through molecular dynamics simulations. The results indicate that water films hinder CO2 diffusion into the oil, reducing its ability to lower oil density. When the thickness of the water film increases from 0 nm to 3 nm, the oil density increases by 86.9%, and the average diffusion coefficient of oil decreases by 72.30%. Increasing the temperature enhances CO2–oil interactions, promoting CO2 and water diffusion into oil, thereby reducing oil density. Under conditions of a 2 nm water film and 10 MPa pressure, increasing the temperature from 100 °C to 300 °C results in a decrease of approximately 32.1% in the oil density. Pressure also promotes oil and water-film density reduction, but its effect is less significant compared to temperature. These results elucidate the function of the water film in CO2-EOR processes and its impact on CO2 dissolution and diffusion in water-bearing reservoirs.