Comparative Evaluation of a New Gas/Oil Miscibility-Determination Technique

A new experimental technique of vanishing interfacial tension (VIT) has been reported in recent literature for quick and cost-effective determination of gas/oil miscibility. However, this technique has been criticized because of the perceived absence of compositional-path specification and lack of confirmation against standard gas/oil systems. In this paper, we address these concerns by conducting interfacial-tension (IFT) measurements at elevated pressures and temperatures in two standard gas/oil systems and at varying molar compositions of gas and oil in feed mixtures. Though gas/oil ratio was found to have an impact on mass-transfer rates, the IFT between gas and oil was unaffected in the two standard gas/oil systems as the fluid phases approached equilibrium. This indicates compositional-path independence of gas/oil IFTs measured at near-equilibrium conditions; hence, miscibilities determined using the VIT technique. The minimum miscibility pressures (MMPs) determined using the VIT technique acceptably matched (within 5 to 8%) with the reported slim tube miscibilities for both the standard gas/oil systems. These experimental results clearly support wide use of the VIT technique for rapid and cost-effective determination of MMPs and minimum miscibility enrichments (MMEs) in improved-oil-recovery applications.