CO2 Recovery of Heavy Oil: Wilmington Field Test

Abstract

Summary Champlin Petroleum Co.'s pilot test of the CO, immiscible-drive oil recovery process has been in continuous operation for 50 months in the Wilmington field, Tar zone. Fault Block Ill Unit reservoir. First CO2 injection was in March 1981. The pilot, containing 1,700 acre-ft [2.1 × 10 M ] includes four injection wells and three producers. The reservoir is an unconsolidated sandstone at 2,500 ft [762 m] that contained 920 bbl/acre-ft [0.12 m /M ] of 14 degrees API [0.97-g/cm ] crude oil at the start of the CO2 pilot. This is the first test of immiscible CO2 tertiary oil recovery in a late-life waterflood reservoir. Cumulative water injection before start of the CO2 pilot was three PV's. Through May 1, 1985, 2.1 Bcf [60 × 10 M ] of produced and purchased CO2 had been injected intermittently with water. Cumulative purchased CO2 through May 1, 1985, was 1.5 Bcf [42.5 x 10 m ]. Each of the three producing wells has shown stimulated oil response with production rates producing wells has shown stimulated oil response with production rates increasing an average of seven-fold. One producing well, converted from a former water-injection well, produced 100% water for 5 months after first CO2 injection. The well has since steadily increased in production to over 40 B/D [6.4 m /d] of oil. All produced oil is considered incremental oil since the pre-CO2-flood oil rates were essentially at the economic limit and the wells would soon have been plugged and abandoned. Introduction The Wilmington field, one of the major oilfields that make up the Los Angeles basin, is among the most prolific in the continental U.S. It is located close to the center of the basin (Fig. 1). The initial discovery was made in 1936, and production has been continuous since that time. The Wilmington field is a layered formation consisting of 19 distinct sand bodies. These have been somewhat arbitrarily divided into seven reservoirs located at depths ranging from 2,300 to 4,800 ft [700 to 1460 m]. The lowest zone is the 237 reservoir, overlain in sequence by the Ford, Union Pacific, Lower Terminal, Upper Terminal, and Ranger zones. and finally the shallowest, the Tar zone. These reservoirs vary in gross thickness from 100 to 1,000 ft [30 to 305 m]. A cross section of the field, shown in Fig. 2, illustrates not only the various layered reservoirs but also the many faults that add complexity to the geology and complicate producing operations. The Tar zone. chosen for the CO2 pilot is a Pliocene, unconsolidated sand. The major faults have been used to divide the reservoir into separate unitized operating properties. Oil gravity in the Wilmington field ranges from properties. Oil gravity in the Wilmington field ranges from 13 to 28 degrees API [0.98 to 0.89 g/CM ]. Reservoir temperature increases with depth starting with the Tar zone at 123 degrees F [51 degrees C] and ending with the 237 zone at 226 degrees F [108 degrees C], The low gravity of the crude oil contained in the multilayered, highly faulted reservoirs, coupled with a pollution-conscious urban environment, have created a pollution-conscious urban environment, have created a significant technical and economic challenge to the profitable recovery of a significant fraction of Wilmington's profitable recovery of a significant fraction of Wilmington's original oil in place (OOIP). Primary production was gradually supplemented by waterflooding, initiated in the early 1960's. This water-flood was subsequently expanded in 1973 to a higher-volume flood when the "Big Water" project was put into operation. Although each phase of the production history resulted in profitable oil production, only 30% of the OOIP contained in the numerous reservoirs had been recovered at the start of CO2 flooding. The remaining OIP represents a significant opportunity for profitable application of the proper tertiary oil recovery technology. proper tertiary oil recovery technology. All known EOR processes were screened before the best-chance-of-success process for the shallow Tar zone reservoir was selected. Five processes-polymer flooding, caustic flooding, micellar/polymer, CO2, and steamflooding-were studied in depth. The first three processes have been piloted in adjacent areas of the processes have been piloted in adjacent areas of the Wilmington field. All were less than profitable. yet the miceltar/polymer flood did recover a very significant quantity of tertiary oil. The two remaining processes, immiscible CO2 flooding and steamflooding, appeared to have reasonable chances for profitable operation in this viscous oil reservoir. These two processes-grossly different in both cost of operation and volume of oil recovery-were difficult to evaluate precisely either in the laboratory or by computer simulation. Accordingly, Champlin undertook to field-test both processes in two large-scale pilots to obtain comparative data on steam and CO2 flooding. This paper addresses the analysis, design and operation of the paper addresses the analysis, design and operation of the pilot test for immiscible CO2 flooding. pilot test for immiscible CO2 flooding. Initial recognition of the potential of CO2 for enhancing heavy-oil recovery came from research conducted by Beeson and Ortloff. JPT p. 769