Paper: Miscible Displacement By High-Pressure Gas At Block 31

The world's first large-scale miscible displacement project by high-pressure gas injection has produced 130,000,000 bbl, almost double the original estimated primary recovery of 69,000,OOO bbl, at the University Block 31 field in Crane County, Tex. Early injection-production history is shown on Fig. 1. The field-wide project began in 1952, and will keep the unit on stream well into the future, with ultimate recovery efficiency estimated at 60%. Infill drilling has helped boost daily production to 16,000 bbl, highest producing rate since gas injection began in 1949. Atlantic Richfield (formerly The Atlantic Refining Co.) discovered Block 31 in 1945. Operators agreed to reinject produced gas into the Devonian reservoir in 1949 for partial pressure maintenance. The field was unitized in August, 1952, with Atlantic Richfield as the unit operator. Others include Phillips Petroleum Co., Champlin Petroleum Co., and Continental Oil Co. Extensive research indicated that oil recovery could be improved substantially by miscible displacement through high-pressure gas injection. Waterflooding was impractical because of the low permeability of the Devonian formation. The reservoir contains five producing horizons, of which the Devonian at 8500 ft is dominant. The miscible project, which began in 1952, includes 86 oil producing wells and 24 gas injection wells. Eighty acre spacing was used to develop the 7840-acre unit. Devonian gas injection is based on a 320-acre nine spot pattern. The Devonian formation is a crystalline limestone, interspersed with chert. Average porosity is 15% and average permeability is 1 md. Gross thickness is 1000 ft. There are three reservoirs in the Devonian column: Upper, Middle, and Lower. The major reservoir is the Middle. The trapping mechanism is a northeast to southwest trending anticline with the south end cut by a normal fault. Flanks of the anticline are delineated by a water-oil contact.