The ''S'' sand Reservoir B CO2 pilot was designed to demonstrate the feasibility of a downward CO2 displacement in a steeply dipping, high temperature and high pressure Gulf Coast reservoir. Research results show that CO2 injection is not a miscible process at the S Sand Reservoir B (SRB) conditions but a CO2-crude oil vaporization process. Vaporization means that the CO2 strips and replaces hydrocarbon components from the crude. The stripping is enhanced with repeated contacts with fresh CO2. Results of experiments indicate that CO2 diluted with five to ten percent of plant gas (primarily methane) would result in a miscible-like displacement process. It also appears that based on slim tube experiments alone, undiluted CO2 might be the most efficient material for the SRB field test. Under SRB reservoir conditions, CO2 not diluted with light hydrocarbons is more dense than the reservoir oil. Fortunately, process mechanisms can work to the benefit of displacement stability. Upon mixing SRB oil and CO2, two phases are formed. The CO2 rich vapor phase is less dense than the liquid phase. Based on a zero dimensional analysis and the phase behavior study results, the vertical displacement by CO2PG or CO2 alone should be gravity stable at the expected flood conditions. A mixture of five percent by volume of plant gas and 95 percent CO2 is the recommended injection system for this field test. This dilution should allow gravity forces to augment the vaporization process.

Shell, in conjunction with the United States of America Department of Energy, is conducting a gravity stable displacement field test of the miscible CO2 process. The test is being conducted in the portion of a fault sealed reservoir lying below a subsea depth of -12,750 feet. Injection of the CO2 slug at the producing gas-oil contact commenced in October 1978. Injection of the 860 MM cubic foot slug was completed in February of 1980. The slug of CO2 was moved downward through the watered out sand by production of downdip water. The leading edge of the displacement has reached the producing perforations and production of the oil column commenced on January 26, 1981. Conventional cores and the log-inject-log technique were used to determine residual oil saturation in a well drilled as the pilot producer. Pulsed neutron logging devices have been used to detect the CO2 slug and monitor its subsequent movements in the vicinity of the production well. The monitor logs indicate the thickness of the oil column had increased during the displacement to the production perforations located 130 feet below the level of CO2 injection. The 23 foot oil column remaining at initiation of the project had apparently grown to 57 feet. PVT samples production data indicate CO2 has penetrated the oil column and free gas is being produced with the oil. However, the qualitative measurements of the logs do not indicate a large gas or CO2 content in the oil column.