A new technique of vanishing interfacial tension for miscibility determination

Abstract

A new technique is presented in this paper to enable rapid and cost-effective determination of minimum miscibility pressure and composition. This new technique, called the Vanishing Interfacial Tension (VIT) technique, consists of measuring the interfacial tension between the injected gas phase and the crude oil at the temperature of the reservoir and at varying pressures and/or enrichment levels of the gas phase. These interfacial tension measurements are carried out by computer digitization of the image of the profiles of the sessile and pendant drops of crude oil enclosed in the surrounding medium of injection gas. By fitting these actual drop profiles with the iterative solution of the Laplace capillary equation, the value of interfacial tension is obtained at each pressure or enrichment level. By making a plot of the interfacial tension against the independent variable (either pressure or enrichment), accurate values for the minimum miscibility pressure (MMce:simple-para) or composition (MMC) are then obtained by extrapolation to zero interfacial tension. The paper provides experimental evidence for the validity of the new VIT technique by comparing the results with slim-tube displacement tests. While the slim-tube technique requires 4–6 weeks for obtaining MMP or MMC, the VIT technique yields the MMP in about 4–6 h, and MMC in about 16–24 h. The paper also presents an application of the VIT technique to optimize injection gas composition for an Alberta field project. The Alberta Energy and Utilities Board (a Government of Alberta agency) has accepted the optimized composition based on the VIT technique.