R.P. Frey, Shell Oil Company
The North Cross Devonian Unit is located in the Crossett Field at the southern edge of the central basin platform in West Texas. The reservoir is a chalky, siliceous carbonate with 21% porosity, 3 md permeability and has an average pay thickness of 90 feet. There are 17 producers, 6 CO, injectors, 3 residue gas injectors, and 2 TA wells in the unit (Fig. 1). In 1964, residue casing head gas injection was started to" maintain reservoir pressure, and CO, injection was begun in 1972. Response to CO, injection occurred in one well early in 1973 and by late 1974, four wells were showing signs of response. As of the end of 1974, the unit produced 56,000 BOPM, with a GOR of 8000. Figure 2 shows the unit's performance since 1964. To date, the only major operating