Miscible CO2 injection is one of the most common enhanced oil recovery processes employed worldwide to recover the residual oil left behind after waterflooding. Although continuous miscible CO2 injection (CGI) floods have excellent microscopic displacement efficiency, they often suffer from poor macroscopic sweep efficiency due to mobility effects. In order to mitigate these sweep issues, processes like Water Alternate Gas (WAG) and Simultaneous Water and Gas (SWAG) injection were developed. WAG is the most common mobility control technique employed in the industry and is well understood. However the SWAG process has had fewer studies and is not well understood. There has been very little published either evaluating the performance of SWAG under miscible conditions or comparing the performance of these EOR processes under consistent experimental conditions. This paper presents the results of corefloods used for evaluating the performance of CGI, WAG and SWAG processes using CO2 under conditions that are as consistent as possible to make meaningful comparisons. A series of experiments were carried out to evaluate tertiary coreflood performance: CGI, a 1:1 WAG with slug size of 0.25 pore volumes and the SWAG process at four values for the fractional flow of gas (fg). The SWAG process with an optimal gas fractional flow recovered the most residual oil. CGI had the second best recovery followed by WAG. SWAG floods with suboptimal fg values recovered slightly lower amounts of residual oil. Gas utilization was the least for the SWAG process with optimal fg values followed by CGI.

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