Two new quantitative technical criteria for determining the minimum miscibility pressures (MMPs) from the vanishing interfacial tension (VIT) technique

Abstract

In this paper, two new quantitative technical criteria are developed to determine the minimum miscibility pressures (MMPs) from the vanishing interfacial tension (VIT) technique: the linear correlation coefficient (LCC) criterion and the critical interfacial thickness (CIT) criterion. Six series of dynamic interfacial tension (IFT) tests for the dead and live light crude oil–CO2 systems are conducted under different test conditions. The MMP is determined when the LCC is smaller than 0.990 or the interfacial thickness is smaller than 1.0nm for the first time. The determined respective MMPs of 12.9MPa and 13.2MPa for the dead and live light crude oil–CO2 systems from the VIT technique agree well with the MMPs of 12.4–12.9MPa for the former system from the coreflood tests and fairly well with 15.2–15.4MPa for the latter system from the slim-tube tests. In addition, the specific effects of three experimental factors on the determined MMPs are studied by applying the two new quantitative technical criteria: (a) the initial vs. equilibrium IFTs; (b) the oil composition; and (c) the initial gas–oil ratio (GOR). The measured initial other than equilibrium IFTs are found to be sufficiently accurate to determine the MMP from the VIT technique. This is because the pendant oil drops used in the dynamic IFT tests are so small that they can be saturated with CO2 almost instantaneously. The live light crude oil pre-saturated with CH4-dominated hydrocarbons has a slightly higher MMP in comparison with the dead light crude oil. Moreover, the initial GOR effect on the MMP is found to be negligible in a lower GOR range (1:1–10:1 in volume) or in a large CO2 concentration range (31.76–94.69mol%). It becomes pronounced in a higher GOR range (200:1–4000:1 in volume) or in an extremely small range of high CO2 concentrations (98.79–99.99mol%).