Miscible CO2 Injection Project In A West Texas Carbonate Reef

Performance predictions of the proposed miscible CO2 injection project for the Wellman Field, Terry County, Texas were made using an enhanced oil recovery process numerical simulator. The study investigated the potential of injecting a relatively small, gravity stable CO2 slug with nitrogen as the drive gas into the crest of the cone-shaped reservoir. The effects of slug size, injection rate and reservoir pressure were evaluated for an optimum future operating plan. The differences in fluid densities at reservoir conditions were conducive to gravity segregation of the nitrogen, CO2 and miscible oil bank. Assuming that most of the produced CO2 would be reinjected, a CO2 slug as small as 15% of the initial hydrocarbon pore volume appeared to be sufficient to mobilize the remaining recoverable oil in-place. Oil production performance during the early years of the project was similar for CO2 injection rates of 10 MMSCF/D and 20 MMSCF/D so the lower rate case appeared economically more attractive. Since the massive carbonate reef, having a vertical oil column of over 800 feet, exhibited no major barriers to impede horizontal or vertical fluid flow, an excellent sweep of the reservoir was predicted in all cases. The results of this study indicated that the concept of the proposed CO2 flood was reasonable and could provide an economic tertiary oil recovery process for the Wellman Field.