Effect of Surfactants on the Minimum Miscible Pressure of CO2 with Crude oil from the Chang-8 Oilfield using Molecular Dynamics Simulations

DOI: 10.14800/IOGR.1314

Abstract

CO₂ flooding represents a promising approach for enhancing the recovery of tight reservoirs, facilitating the efficient development of unconventional oil and gas resources while concurrently contributing to CO₂ reduction. This method is of significant importance for the sustainable advancement of energy in China. Both theoretical and empirical evidence indicate that the oil recovery efficiency associated with CO₂ miscible-phase processes markedly exceeds that of non-miscible-phase processes. However, current CO₂ injection technologies often struggle to achieve miscible-phase conditions in various contexts, thus limiting their effectiveness in enhancing recovery from tight reservoirs.

The composite system formed by CO₂ and surfactants presents a novel avenue for optimizing CO₂ flooding technology aimed at improving recovery of tight reservoirs. In this study, a molecular system model was established to characterize the interaction between CO₂ and crude oil specific to the Chang 8 tight reservoir. Molecular dynamics simulations were employed to estimate the miscibility pressure. The surfactant C₁₂PO₆ was introduced to investigate its impact on physical parameters, including intermolecular forces, interfacial tension, and miscible pressure, within the CO₂-crude oil-surfactant system.

The findings demonstrate that the incorporation of surfactants enhances molecular interactions between CO₂ and crude oil, resulting in a reduction of minimum miscibility pressure by 9.36% at a temperature of 344 K. Furthermore, the extent of this reduction is temperature-dependent, with a 10% increase in surfactant efficacy observed as the temperature rises from 323 K to 363 K. This research elucidates the interactions among multiple fluid molecules at the molecular level, revealing the microscopic mechanisms by which the CO₂-surfactant composite system reduces miscibility pressure in tight reservoirs. These insights are poised to advance the development of CO₂ enhanced recovery technologies within China’s tight oil and gas sector.