Demonstration of CO2 Sequestration in the Frio saline formation

CO2 sequestration is one of the most promising new technologies for the reduction of greenhouse gas emissions.  Saline aquifers can hold several centuries’ worth of carbon emission [1].  However, there is significant concern that CO2 injected into the aquifers may leak into surrounding fresh groundwater reservoirs or back into the atmosphere [2].  There is also fear that CO2 injection will result in increased seismic activity, similar to the fears behind hydraulic fracturing for oil and gas recovery [3].

In order to demonstrate the feasibility of geological storage of CO, 600 metric tonnes of CO2 was injected into the Frio saline formation near Dayton, TX.  The study attempted to answer two fundamental questions related to geologic storage: 1) If CO2 released from the burning of fossil fuels is returned to the subsurface, will it be retained for periods of time significant enough to benefit the atmosphere? 2) Can trapping be assured in formations where there is no history of hydrocarbon accumulation? [4]

CO2 was injected at an approximately constant rate of 3 kg/s for a 10 day period. The pressure of the injection well was measured as a function of time during and after the injection.  Initially the pressure increased rapidly as CO2 displaces brine.  In the post-injection period, the pressure fell back towards the initial pressure of the well.  No CO2 leaked to the monitoring horizon located 15 meters above the injection zone for over one year after injection.  The measured CO2 plume and the changes in the aquifer pH and alkalinity correlated well with model predictions.  The Frio experiment proved that CO2 could be successfully injected into a saline aquifer and would remain trapped, with little risk of leakage. [4, 5]

[1] 2010 Carbon Sequestration Atlas of the United States and Canada – Third Edition. NETL, U.S. Department of Energy, 2010. < >


[3] Sminchak J, Gupta N. “Issues related to seismic activity induced by the injection of CO2 in deep saline aquifers.” < >

[4] Hovorka, S.D., Benson, S.M., Doughty, C., Freifeld, B.M., Sakurai, S., Daley, T.M., Kharaka, Y.K., Holtz, M.H., Trautz, R.C., Nance, H.S., Myer, L.R., Knauss, K.G. “Measuring Permanence of CO2 Storage in Saline Formations: The Frio Experiment.” Environmental Geosciences, vol. 13, no. 2, 2006, pp 105-121.

[5] Kharaka, Y.K., Thordsen, J.J., Hovorka, S.D., Nance, H.S., Cole, D.R., Phelps, T.J., Knauss, K. G. “Potential environmental issues of CO2 storage in deep saline aquifers: Geochemical results from the Frio-I Brine Pilot test, Texas, USA.” Applied Geochemistry, vol. 24, 2009, pp 1106-1112. < >


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