Numerical investigation of dimethyl ether impacting the gas–oil minimum miscibility pressure in CO2-enhanced oil recovery: Insights for water-free and water-saturated conditions

Dimethyl ether (DME) has emerged as a promising additive in CO2-enhanced oil recovery (EOR), and the minimum miscibility pressure (MMP) is pivotal for flooding strategies. However, research on DME's impact on MMP is limited. This study undertakes a comprehensive investigation into the effects of DME on the gas–oil MMP during CO2 flooding, considering water-free and water-saturated scenarios. First, a two-phase multiple-mixing-cell method (MMC) with a rapid MMP estimation technique is adopted to analyze the influence of DME concentration on MMP without water. Subsequently, an improved three-phase MMC method is developed for scenarios involving water. The Peng–Robinson equation of state with the Huron–Vidal mixing rule (PR+HV) is used to model the system accurately. Our findings reveal that a proper amount of DME can significantly lower the MMP. When the initial MMP without DME is less than the oil's saturation pressure, increasing DME further will raise the MMP. Moreover, a continuous increase in the DME concentration in the injected gas can shift the miscibility mechanism from multi-contact to first-contact miscibility. This novel observation has significant implications for CO2 flooding strategies. Additionally, water has a negligible effect on MMP, allowing water-free MMP results to be used in water-present situations, thus simplifying calculations. Overall, this research provides a reliable framework for assessing the impact of DME on MMP and highlights the importance of a rational DME concentration for achieving optimal MMP reduction in EOR processes.