Interest in geologic sequestration of CO2 in deep brine formations in the Gulf Coast is considerable because globally this region is the eighth-largest emitter of CO2. Previous studies evaluated the impact of injecting 1,600 tons of CO2 into the Frio Formation at 1,500-m depth (Kharaka et al., 2006). Injection of CO2 resulted in reduction in pH (6.5–5.7) and increases in alkalinity (100–3,000 mg/L as HCO3) and Fe (30–1,100 mg/L) (Kharaka et al., 2006). Modeling analyses indicate that reduction in pH was buffered by dissolution of carbonates and iron oxyhydroxides. Later work by Kharaka et al. (2009) indicates that corrosion of pipes and well casing contributed to the increase in Fe concentrations.
Current CO2 sequestration studies at the Bureau of Economic Geology (The University of Texas at Austin) are being conducted in Cranfield, Mississippi (Figure 3), which is located near the town of Natchez in Adams County, Mississippi, ~15 mi east of the Mississippi River. Cranfield field, discovered in 1943. consists of a simple anticlinal four-way closure, having a large gas cap surrounded by an oil ring (Mississippi Oil and Gas Board, 1966). The reservoir is in the lower Tuscaloosa Formation at depths of >3,000 m. From the 1940's through the 1960's Cranfield field produced ~62 million bbl of oil and ~670 million cf of gas and is being retrofitted for tertiary oil recovery. CO2 injection into the reservoir began in July 2008. More recently, researchers at the Bureau of Economic Geology, have begun injecting CO2 in the saline formation downdip of the reservoir. The team is monitoring CO2 migration and fate through an array of dedicated tools to thoroughly understand CO2 behavior in the subsurface. Sediments at the Cranfield site generally consist of loess (~2 m thick) underlain by alluvial sands and clays (Figure 4). It is an ideal system for evaluating impacts of potential CO2 leakage into an aquifer that typifies the Gulf Coast system.
Another field test of impacts of CO2 injection on groundwater quality will be conducted in the Texas Gulf Coast in Helena (Figure 3).
The following provides background information and the tasks.
- Program Overview
- Gulf Coast System
- Regulatory Issues
- Significance to Water Utilities
- Research Approach
- Task 1.0: Laboratory Batch Experiments
- Task 2.0: Modeling Design of Field Push-Pull Tests
- Task 3.0: Conduction of Push-Pull Tests in the Field
- Task 4.0: Modeling of Field Experiments
- Task 5.0: Communication
- Quarterly Reports, Publications, and Data