Gas flooding technologies primarily use carbon dioxide flooding as a method to produce more oil from the reservoir by channeling gas into previously-bypassed areas. CO2 flooding technologies experiment with a number of foams, gels, and thickening agents to improve sweep efficiency. CO2 floods are extensively used in some regions of the U.S., particularly in West Texas and the southern Rocky Mountains. CO2 flooding currently produces about 190,000 BOPD. In the past decade flooding with nitrogen gas, flue gas, and enriched natural gas have also shown some beneficial results by increasing recovery when used to re-pressure reservoirs. Nitrogen and flue gas may be useful in areas where CO2 is not economically available for use.
This schematic illustrates a nitrogen-CO2 flood. This and other cross-sectional illustrations of EOR methods that are in the public domain are available free from NETL.
The fastest-growing EOR method in the United States is carbon dioxide flooding, which entails injecting CO2 in an oil reservoir to “sweep” oil to a producing well. This photograph of a CO2 storage tank and injection skid is featured in the NETL project fact sheet entitled Field Demonstration of Carbon Dioxide Miscible Flooding in the Lansing-Kansas City Formation, Central Kansas, Project No. DE-FC26-00BC15124.
Many reservoirs are not being considered for CO2 flooding or other EOR methods because of their extreme heterogeneity often caused by natural fractures. The degree to which the injected CO2 is transferred through these fractures is critical to a CO2 flood's economics. NETL research seeks to understand these transfer mechanisms and thus improve the sweep efficiency of this promising EOR method. The top figure depicts X-ray images of a CO2 front movement through a fractured core, showing the influence of gravity segregation. The bottom image displays a pressure distribution map with a unique gridding technique feature. Both are featured in the fact sheet entitled Investigation of Efficiency Improvement During CO2 Injection in Hydraulically and Naturally Fractured Reservoirs, Project No. DE-FC26-01BC15361.