This paper describes the implementation and performance of the industry's first Clearfork CO2 flood - Shell's South Wasson Clearfork Unit (SWCU) located in the Permian Basin of West Texas. CO2 injection began in 1986 using a high water-alternating-gas (WAG) ratio (8:1), low volume (8% hydrocarbon pore volume) flood,- or "CO2 augmented" waterflood. The intent of the flood was to increase our understanding of the Clearfork formation before committing to a larger scale CO2 flood.
The performance of the "CO2 augmented" waterflood has met expectations. After 3-1/2 years of CO2 injection, enhanced oil production had increased to 450 BOPD,- or 7% of Unit production. CO2 injectivity was comparable to water injectivity, and no significant decrease in the WAG water injectivity was observed. Encouraged by the success of the CO2 augmented waterflood, a 2:1 WAG CO2 flood was approved and implemented in the northern half of the CO2 flood area in the spring of 1990.
Through 1991, roughly 3% of a hydrocarbon pore volume of CO2 has been injected at SWCU, and the cumulative enhanced oil recovery matches the- original projections. The performance of the CO2 flood to date has been influenced by reservoir heterogeneity, injection pattern modifications, waterflood operating practices, and gas processing constraints.