Discussion on Carbon Dioxide Minimum Miscibility Pressure Estimation: An Experimental Investigation

Abstract

Abstract Among existing enhanced oil recovery (EOR) processes, carbon dioxide (CO2) flooding is the most widely used. The popularity of CO2 as a miscible agent is due to its characteristics, which result in excellent macroscopic and microscopic efficiencies when miscibility conditions are optimal. In most CO2 flooding studies, these conditions are related to the minimum miscibility pressure (MMP), which is the pressure above which miscibility develops and materializes in recoveries equal to or higher than 90% (Metcalfe and Yarborough,1979). Since the MMP is a quick and convenient tool for conducting screening studies for post-evaluation of miscible projects, many correlations used to estimate the MMP have been developed for various crude oils and are presented in the literature. The problem is that not all correlations reflect the necessary process parameters needed in a typical CO2 flooding project. Correlations that work for reservoirs in North America may not be suitable for reservoirs in the Middle East. This paper addresses the issues related to experimental estimation of the MMP in a large, low-permeability reservoir in the Middle East and the evaluation of correlations as a means of estimating the MMP for a given reservoir. These issues range from the experimental approach and the verification of slim tube results by core flooding experiments to the use of dead versus live oil to estimate the MMP (for instance) or the effect of impurities on the MMP of pure CO2. The use of dead oil instead of live oil to conduct both slim tube and core flooding experiments resulted in errors up to 9%. Also the effect of some gases like nitrogen, hydrogen sulfide, and methane on the MMP of pure CO2 is discussed. Among the correlations tested, only one was found to apply with a reasonable accuracy to CO2 flooding in the reservoir studied. The deviation between live and dead oil MMP slim tube experimental results is also discussed as well as the correction due to contamination of CO2 by other gases.