A comparison of CO 2 minimum miscibility pressure determinations for Weyburn crude oil

Abstract

Minimum miscibility pressure (MMP) is often used as a key criterion for screening and selecting suitable solvents for enhanced oil recovery projects. This paper compares the pure and impure CO 2 MMP values determined for a medium oil from Weyburn reservoir located in southeast Saskatchewan, Canada. Three different methods were employed for determining MMP, namely, slim tube experiments, rising bubble apparatus (RBA) tests, and correlations. The contaminants in the impure CO 2 streams considered were nitrogen (from flue gas) and methane (from recycled CO 2). Results of the study indicated that the MMP values measured by the RBA technique agreed well with those measured using the slim tube tests and those predicted using a published correlation. For the Weyburn oil–CO 2 system, a distinct bubble behaviour—tail formation—was observed when the pressure reached or was higher than MMP. These results provide additional experimental experience of using the RBA as an efficient tool of determining the MMP for some solvent gas–medium oil systems. This study also demonstrated that, for the Weyburn reservoir, promising EOR agents (having an MMP below 80% of the reservoir fracture pressure) are pure CO 2 and blended CO 2 containing up to about 12 mol% CH 4 or 5 mol% N 2.