Performance Review of a Large-Scale CO2-WAG Enhanced Recovery Project, SACROC Unit Kelly-Snyder Field

Abstract

Introduction This paper reviews the performance of the CO2-WAG (water-alternating-gas) project conducted at the SACROC (Scurry Area Canyon Reef Operators Committee) Unit since early 1972. Numerous papers published previously describe in great detail the reservoir, previously describe in great detail the reservoir, the CO2 displacement process, the transmission of CO2 to the field, the mechanics of the operation of the project, a progress report through 1975, and other matters. Since detailed descriptions are available of reservoir characteristics, field history before the inception of the CO2 project, planning and design, and facilities installations, these subjects will be reviewed only briefly here. The performance of CO2 project itself since it began in J an. 1972 is emphasized. project itself since it began in J an. 1972 is emphasized. Kelly-Snyder Field, located in Scurry County, TX, is the major unitized field among four continguous fields along the 35- x 5-mile (56.3- x 8.05-km) Canyon Reef formation (Fig. 1). Reservoir and fluid properties are summarized in Table 1.Estimated original oil in place in the SACROC Unit area, based on a volumetric determination, was 2.73 billion STB (434 Mm3). This volume was used for the evaluation and design of the CO2 miscible flood and for early estimates of incremental oil recovery resulting from CO2 processing.In 1973, Chevron Oil Co., SACROC Unit operator conducted a 24-year history match of more than 1,500 wells in Kelly-Snyder Field using a two-dimensional black-oil simulator. On the basis of this study, the estimated original oil in place in the SACROC Unit area was reduced to 2.113 billion STB (335.9 Mm3). History of Kelly-Snyder Field and the SACROC Unit Before the CO2-WAG Project Project The reservoir was discovered in Nov. 1948. Subsequent development was rapid and essentially complete by Nov. 1951 when 1671 producing wells had been drilled. The production and injection history of the field is shown production and injection history of the field is shown in Fig. 2.Early production performance indicated that solution gas drive was the primary producing mechanism and that a pressure maintenance program would be required to prevent excessive loss of reserves. To improve recovery prevent excessive loss of reserves. To improve recovery the operators and royalty owners of Kelly-Snyder Field agreed to unitize to begin pressure maintenance. In 1953, the Texas Railroad Commission approved formation of the SACROC Unit.Water injection into a unique pattern involving 72 center-line injectors began Sept. 1954. Because of increased oil demand and resulting higher allowables, injection capacity had to be added beginning in 1969. During 1969-71, 72 additional wells were converted to injection service, resulting in a total of 144 center-line injectors. Operational of this center-line injection system continues presently. JPT p. 217