A CO2 Tertiary Recovery Pilot Little Creek Field, Mississippi

Abstract

Abstract A field test of the CO2 displacement process for tertiary oil recovery is being conducted by Shell Oil Company and its working interest partners in the Little Creek field, Mississippi. The objective of the test is to more clearly assess the potential for fieldwide application of this process. potential for fieldwide application of this process. Preliminary results are encouraging. Preliminary results are encouraging Introduction It has been recognized for some time that approximately 55 million barrels of oil will remain in the Little Creek field's sole producing horizon at depletion of primary and secondary (waterflood) reserves. With this significant target, Shell Oil Company initiated an investigation into possible tertiary recovery methods for Little Creek over 12 years ago. After considerable research, a pilot test of the most prospective method was initiated in 1973. This paper describes the pilot and reviews its performance through June 1977. Preliminary conclusions concerning the CO2 recovery Preliminary conclusions concerning the CO2 recovery method at Little Creek are presented. FIELD HISTORY The Little Creek field was discovered by Shell Oil Company in January 1958. The field is located in Southwestern Mississippi, approximately 100 miles northwest of New Orleans, Louisiana (Figure 1). The development and waterflooding operations of this deep sandstone oil reservoir were documented by Cronquist. The lone producing horizon in the field is a lower Tuscaloosa (Upper Cretaceous) "Q-Q2" sandstone whose productive extent is about 6,200 acres. The oil accumulation is contained in a combination structural-stratigraphic trap created by a winding belt of sand traversing an elongate structural nose now buried to a depth of about 10,750 feet (10,350 feet subsea). Figure 2 shows the structural interpretation for the reservoir. The original oil-in-place volume was estimated at 101.9 million stock tank barrels. Cumulative production is now 46.8 million barrels of oil. production is now 46.8 million barrels of oil. Table 1 summarizes average reservoir and fluid property data. property data. The field was voluntarily unitized to permit initiation of a peripheral line drive waterflood in 1962. This supplemental recovery operation was very successful (see Cronquist)—increasing oil recovery from the field by about 21.7 million barrels. Waterflooding operations were discontinued in February 1970. Production from a gradually declining number of wells has continued since then. Figure 3 shows the primary and waterflood production history of the field. In August 1973 preliminary operations were initiated for a CO2 miscible displacement field test at Little Creek. In February 1974 CO2 injection began into a quarter nine-spot pilot area in Section 1 of the Little Creek Unit with operations continuing to date. PILOT DESIGN PILOT DESIGN Prior to initiating the CO2 pilot, considerable theoretical and laboratory investigation efforts had been expended. A physical model study of the tertiary miscible process had been pursued as well as miscibility tests with several natural gases and mixtures of these gases. Computer simulations of various operational methods and alternate well patterns were also conducted. Based on the patterns were also conducted. Based on the knowledge accumulated from this effort, the decision was made to field test the CO2 miscible displacement process at Little Creek. The pattern choosen was process at Little Creek. The pattern choosen was an inverted nine-spot, which appeared to yield the best process recovery efficiency of those patterns available with existing field development. A semiconfined quarter nine-spot symmetry element was selected for the pilot test as representing a reasonable compromise between acceptable pilot costs and the optimum pilot design. The reservoir geometry in Section 1 of the field (Figure 4) seemed particularly suited for conducting the pilot. The reservoir shale-out boundary, as defined pilot. The reservoir shale-out boundary, as defined by several local dry holes, provided natural confinement of fluid movement to the east and south.