Characteristics of a Retrograde Condensate Reservoir Containing a Large Quantity of Carbon Dioxide

The literature possesses limited data on reservoirs containing an appreciable quantity of carbon dioxide. The primary purpose of this paper is to present the fluid characteristics of a retrograde condensate system containing approximately 92 per cent carbon dioxide. The text includes the basic PVT studies as well as a discussion of surface separation equipment and problems associated with testing and producing the reservoir. Included also are geological and engineering characteristics of the reservoir and a review of corrosion problems. General Description of Area About eight miles northeast of Walden, Colo., in the North Park basin, there are at present four commercial oil fields producing from the Muddy, Dakota, Lakota and Morrison sands of Cretaceous age. These fields are not very significant in size, but each field is on a separate anticlinal structure, and the apparent variation in the nature of their reservoir fluids is quite unusual. Fig. 1 is a map of the area showing the four producing fields. The average elevation of this general area is 8,200 ft. This discussion will deal with the most recently discovered area situated in the South McCallum field, which produces condensate with a large quantity of carbon dioxide from the Muddy, Dakota and Lakota sands. The reservoir fluid is 92 per cent CO2, 3 per cent nitrogen and 5 per cent hydrocarbons. This area, more specifically referred to as the Ballinger-Federal, was discovered in Oct., 1958 with the completion of Gulf Oil Corp.'s Ballinger-Federal No. 1, C-SW-SE Section 8–9N–78W, Jackson County, Colo., for a calculated absolute potential of 39,400 Mcf of CO2 and 542 B/D of 480 gravity condensate. The condensate is an almost clear liquid with a light golden color. A second well was completed in Dec., 1958 for a calculated absolute potential of 101 MMcf of CO2 and 1,390 B/D condensate. The produced GOR initially was approximately 72, - 600 cu ft/bbl. Both wells tested water in the Morrison sand at the approximate depth of 5,400 ft and are completed in the Muddy, Dakota and Lakota sands between 4,980 and 5,345 ft. Production from the three sands is commingled in the wellbore. The two wells are presently being produced at the rate of 200 B/D each.