Novel strategy for reducing the minimum miscible pressure in a CO2–oil system using nonionic surfactant: Insights from molecular dynamics simulations

Abstract

Effective CO2-oil miscibility is a vital factor in optimizing oil production during CO2 flooding and enhancing CO2 storage capacity. This research investigates the impact of various surfactants, temperatures, and pressures on CO2-oil interfacial tension (IFT) through experimental measurements. It also evaluates the reduction in minimum miscible pressure (MMP). Subsequently, molecular dynamics (MD) simulations analyze gas-liquid miscibility, focusing on relative concentration, interaction energy, radial distribution function (RDF), and miscibility degree (Dmix). Results indicate that introducing a compound nonionic surfactant SF significantly reduces IFT and MMP, achieving an impressive 19.59% MMP reduction. Moreover, SF inclusion boosts Dmix by 8.57%, reflecting enhanced miscibility. The highest absolute value of average interaction energy (EInter) is observed, primarily driven by van der Waals interactions. SF's augmented CO2 coordination number contributes to improved Dmix and reduced MMP. SF's nonpolar groups react with CO2, reducing asymmetric forces between phases and lowering IFT. Electronegative fluorine atoms in SF interact with electron-deficient carbon atoms in CO2, heightening CO2 solubility. Elevated system pressure or reduced temperature amplifies EInter, the coordination number, and subsequently enhances Dmix. Experimentally measured MMP results closely align with MD simulations, with an average relative error of 4.63%. This study elucidates CO2-oil miscibility mechanisms on experimental and molecular scales, offering a promising avenue for future CO2 flooding research.