Evaluation and Design of a CO2 Miscible Flood Project-SACROC Unit, Kelly-Snyder Field

Abstract

Investigations of alternative methods for improving recovery in the SACROC Unit showed that an inverted nine-spot miscible flood program consisting of injecting CO, driven by water would be the most effective and economical. Under such a scheme, the predicted ultimate recovery would be some 230 million barrels more than is expected from the original water injection program. program. Introduction The Kelly-Snyder field, discovered in 1948, is one of the major oil reservoirs in the U. S., having approximately 2 3/4 billion bbl of oil originally in place. The early performance history of the field indicated that the primary production mechanism was solely solution gas drive, which would probably result in an ultimate recovery of less than 20 percent of the original oil in place. The SACROC Unit was formed in 1953, and in Sept. 1954 a massive pressure maintenance program was started. Water was injected into a center-line row of wells along the longitudinal axis of the reservoir. This program, together with controlled production under unitized operations, has effectively rebuilt bottom-hole pressure, restored a large portion of the reservoir to liquid-saturated conditions, and stabilized producing GOR's at near solution levels. producing GOR's at near solution levels. Although the performance of the water injection program was very encouraging, technical program was very encouraging, technical representatives of the major Unit owners were constantly investigating potential methods of improving the ultimate oil recovery over that expected from the water injection program. In 1968, a technical committee, investigating potential alternatives, recommended that a water-driven potential alternatives, recommended that a water-driven slug of carbon dioxide be used to miscibly displace the oil in the non-water-invaded portion of the reservoir and that a pattern injection program be developed in this area to implement the slug process and improve ultimate oil recovery. This paper presents a summary of the methods used in evaluating alternatives and designing the final program of CO2 injection, which was begun in early 1972. Reservoir The Kelly-Snyder field, in Scurry County (West Texas) is the major unitized field among four contiguous fields along the 35- X 5-mile Canyon Reef formation. The formation is a Pennsylvanian age limestone occurring at an average depth of 6,700 ft and is a northeast-southwest trending massive reef buildup with thinner, gently sloping flanks. Formation thickness varies from an average of 800 ft on the crest of the structure to less than 50 ft on the flanks, and averages 213 ft over all. The SACROC Unit constitutes about 98 percent of the Kelly-Snyder field and includes 1,256 wells and just under 50,000 acres. The unitized reservoir is generally bounded on the east and west by porosity development and on the northeast and southwest by offsetting units. An oil/water contact, although poorly defined in some areas, occurs throughout most of the Unit area. Only very limited water influx was detected during pressure depletion, indicating a relatively small aquifer in the immediate area. A summary of basic reservoir data is given in Table 1. Reservoir oil was initially undersaturated at an original BHP of 3,122 psig, and had a solution gas content of slightly under 1,000 scf/STB and a bubblepoint pressure of 1,805 psig. P. 1309