Determination of miscibility conditions by vanishing interfacial tension between CO₂ and crude oil

Injecting recovered CO₂ from fuel gases into the reservoir crude oil at or near the condition of miscibility is one of the main methods to realize CO₂ sequestration and utilization. Minimum miscibility pressure (MMP) is often considered as a key parameter for the design of a gas injection project. In this paper, the interfacial tension between CO₂ and four kinds of reservoir crude oil were measured by the pendant drop method at stratum temperature, and the MMPs for the four kinds of reservoir crude oil were determined directly with visually observed miscibility appearance as 24.12 MPa, 24.81 MPa, 26.87 MPa and 31.69 MPa, respectively. At the same time, the polynomial extrapolation method was also used to determine their MMPs. The results showed that the error of MMPs determined by polynomial extrapolation method was within 3%, and corresponding to lower error value at higher MMP. It indicated that MMP determined by vanishing interfacial tension had the advances of low error and cost, convenience and easy operation.