WaterRF Project: Gulf Coast System

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).

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