M. Dong

A comparison of CO2 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 CO2 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 CO2 streams considered were nitrogen (from flue gas) and methane (from recycled CO2). 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–CO2 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 CO2 and blended CO2 containing up to about 12 mol% CH4 or 5 mol% N2.

Alkaline/Surfactant/Polymer (ASP) Flood Potential in Southwest Saskatchewan Oil Reservoirs

Most of the medium oil reservoirs in southwest Saskatchewan are in thin pay zones of less than 8 m. Primary and waterflood methods have reached more than 80% of their estimated oil recovery potential. These medium oil reservoirs are basically untouched by enhanced oil recovery techniques. An initial study was conducted to assess the suitability of Alkaline/Surfactant/Polymer (ASP) flooding for southwest Saskatchewan reservoirs. On the basis of screening criteria in the literature, the regions reservoir conditions, except for some of the formation types, are favourable for ASP flooding. If only sandstone formations are considered for this process, about 49% of the pools in the region are good candidates for ASP flooding. Extensive oil/water interfacial tension and viscosity measurements were taken using screening criteria for surfactant, alkaline, and polymers. A series of sandpack flood tests were conducted in sandpacks to evaluate ASP flooding for the oil. A tertiary oil recovery of 39% IOIP (72% ROIP) was obtained for the test using all three chemicals. These sandpack flood test results showed that a synergistic enhancement among the chemicals did occur in the ASP system for the medium oil with a very low acid number. The results also indicated that, for a medium oil, mobility control was essential and selection of the right surfactant was important.