Uniqueness, repeatability analysis and comparative evaluation of experimentally determined MMPs

Miscible gas injection processes like CO2 flooding are recommended to be carried out at minimum miscibility pressure (MMP) for effective enhanced recovery of trapped oil. There are several methods for MMP determination, but slim tube and vanishing interfacial tension (VIT) are deployed experimental techniques in this study. Uniqueness and repeatability of slim tube determined MMP was tested by conducting 55 slim tube runs for three different Omani crude oil samples (L-721, MZE and N) using three different coil lengths of constant diameter and three different injection rates. VIT technique accuracy and reliability was evaluated by comparing VIT determined MMPs, for same three considered crude oil samples, with aforementioned different slim tube systems determined MMPs. A trend of decrease in MMP with increase in coil length was found. No unique trend was found between MMP and injection rate. Lowest MMP and highest recovery were observed with highest coil length and lowest injection rate. It may be attributed to more stable displacement process which results in earlier developed miscibility and almost complete displacement of remaining more coil length retained oil. Therefore, both slim tube design and procedure need to be standardized. PVT software predicted MMP close to lower coil length slim tube system determined MMP for sample L-721 and higher coil length measured MMP for sample MZE. VIT approach determined MMPs were found to lie in between the MMPs measured by slim tube system with medium and longer coil lengths for same three oil samples. Since VIT estimated MMPs are in close match with more liable slim tube design determined MMPs, this technique can be utilized as a reliable and cheap alternative compared to more expensive and time consuming slim tube technique for accurate MMP determination without any potential of significant error.