A Single CO2 Injection Well Minitest in a Low-Permeability Carbonate Reservoir

Abstract

Summary A CO2 minitest was conducted in a high-oil-saturation, low-permeability, carbonate reservoir. Incremental oil production exceeded 4,100 bbl (652 m ) as a result of the injection of 1,500 tons (1360 M ) of CO2. Few problems were encountered in planning and conducting, this field test. Introduction The U.S. DOE Morgantown Energy Technology Center has studied eastern U.S. oil reservoirs for many years. The goal of these studies has been the more complete recovery of oil through the application of secondary and enhanced oil recovery (EOR) methods. This test was one of a series of CO2 injection projects conducted by or in cooperation with the U.S. DOE (formerly U.S. ERDA) in West Virginia. The Hilly Upland oil field in north-central West Virginia was selected for this study because it presented a unique opportunity to investigate the effects of CO2 injection in a primary recovery reservoir with naturally flowing wells. The objectives of the project wereto determine the feasibility of injecting CO2 into a low-permeability reservoir,to increase oil recovery, andto obtain first-hand field experience with the CO2 displacement process, problems, etc. The information and experience trained should be of value in the design of future EOR projects using CO2 as the displacing medium. This work was conducted in cooperation with the Allegheny Land and Mineral Co. (AL and M) in Clarksburg, WV, which owns and operates the leases and which, as prime contractor, performed most of the field work. History Although one very old, depleted oil well was located at the extreme western edge of the productive area, the field actually was discovered in 1963 when Rhodes No. 1. Permit No. LEW-1103D, was drilled on an adjacent property east of the project area. The first Hilly Upland well was drilled on AL and M leases in 1968. The project area, approximately 10 acres (40 500 m), is defined as that part of the field including Wells A-359, A-361, A-390, and the injection well, Al- 1 (Fig. 1). The old well (unnumbered) and Wells A-527 and A-389 also were monitored, but no evidence of the effects of CO2 injection was found in them. Among the wells in the project area, initial flowing production of individual wells after stimulation ranged from 5 to 22 STB/D (0.8 to 3.5 stock-tank m /d). Peak field production of 6,100 STB (970 stock-tank m ) was reached in 1970. The field production rate had declined to 3 STB/D (0.5 stock-tank m /d) per well when CO2 injection was started in Sept. 1976. Cumulative production from the project area at that time was 28,500 STB (4530 stock-tank M ). No form of artificial lift had been used in the field up to that time. One additional well (A-527) was drilled and cored in Feb. 1975 north of the project area into the gas cap and was completed as a gas well. This well's cumulative oil production was less than 10 bbl (1.6 m). The test area had the advantages of relatively new wells, and the reservoir had high oil saturations. A permeability pinchout adjacent to the test area helped contain the injected fluids. The reservoir is less than 2,000 ft (610 m) deep, so well drilling and operations were relatively inexpensive. The reservoir was, however, relatively complex. There were fractures present, and these were characterized through extensive studies. Geology The Hilly Upland oil reservoir occurs in the Greenbrier limestone formation of middle Mississippian age. JPT P. 1781^