--> Abstract: Chemical Composition of Water and Gases in the Frio Brine Pilot Test: Preliminary Baseline and Post-Injection Results, by Yousif K. Kharaka, William D. Gunter, Seay Nance, and David R. Cole; #90039 (2005)

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Chemical Composition of Water and Gases in the Frio Brine Pilot Test: Preliminary Baseline and Post-Injection Results

Yousif K. Kharaka1, William D. Gunter2, Seay Nance3, and David R. Cole4
1 U. S. Geological Survey, Menlo Park, CA
2 Alberta Research Council, Edmonton, T6N 1E4, AB
3 The University of Texas at Austin, Austin, TX
4 Oakridge National Lab, Oakridge, TN

In a multi-laboratory field experiment to investigate the potential for geologic storage of CO2, ~2,000 tons of refinery CO2 was injected into a 21m sandstone zone of the Frio Formation – an extensive regional petroleum and brine reservoir in the U. S. Gulf Coast. Down-hole and surface formation water and gas samples were obtained from both the injection and the monitoring wells using a variety of sampling tools and methodologies. The drilling fluids were tagged with Rhodamine WT to allow for calculation of the composition of uncontaminated Frio brine. Samples for baseline data were obtained from the injection well immediately after drilling (before casing), and from both wells after perforation, but before CO2 injection. The monitoring well was sampled also during the CO2 injection and 20 days after injection was completed. Results show that the Frio brine is a Na-Ca-Cl type water, with a salinity of 93,000 mg/L TDS, and with low Br/Cl ratios indicating dissolution of halite. The brine is close to saturation with methane (95% of total gas) at subsurface conditions (67oC and 150 bar). After the CO2 reached the monitoring well, the brine salinity of samples increased slightly, but there were major changes in composition, including a sharp drop in pH (6.7 to 5.7) and high increases in alkalinity (100 to 3,000 mg/L as bicarbonate) and dissolved Fe (30 to 1,100 mg/L). Results of geochemical modeling indicate that brine pH would have dropped to lower values, but for the fact that carbonate and iron oxyhydroxide minerals in the Frio were dissolving rapidly.

AAPG Search and Discovery Article #90039©2005 AAPG Calgary, Alberta, June 16-19, 2005