Monitoring CO2 storage in brine formations: lessons learned from the Frio field test one year post injection

Frio field test one year post injection Susan D. Hovorka , Shinichi Sakurai, Yousif K. Kharaka, H. Seay Nance, Christine Doughty, Sally M. Benson, Barry M. Freifeld, Robert C. Trautz, Tommy Phelps, and Thomas M. Daley ABSTRACT The Frio Brine pilot is a closely monitored, small-volume (1,600 tons), short-duration experiment using injection of CO2 into a high-permeability brine-bearing sandstone of the Frio Formation east of Houston, Texas, to test the feasibility of using this technique as a method to reduce atmospheric buildup of greenhouse gases. For the experiment, pure CO2 was injected for 10 days 1500 m below surface. Because the injection period was brief and the formation was on the flank of a steeply dipping structural compartment, a year since injection takes us well into the postinjection phase of monitoring. Key findings are relevant to the design of the next experiments: (1) Understanding site hydrogeology is critical for designing a successful project . (2) Numerical simulation of flow is essential to guided site selection, well design, and tool selection. (3) Successful geochemical techniques include detection of CO2 breakthrough at the observation well, evolution of formation waters as CO2 interacted with rock and brine, and recovery of tracers to quantify CO2 saturation. (4) Field measurements of saturation using time-lapse neutron logging, cross-well seismic, and vertical seismic profiling (VSP) were successful in measuring CO2 plume evolution. (5) Models and conceptualization suggest that significant CO2 is trapped post injection as relative permeability to gas decreases over time (two-phase trapping); measurements confirm the correctness of this process. (6) An innovative sampling devise, the U-tube, provided high-frequency, minimally altered, samples of two-phase fluids in the wellbore during injection . (7) Complex and rapidly changing surface environments and interference among test elements create challenging conditions to monitor for CO2 leakage in groundwater and soil. Geochemical monitoring in the sandstone above the injection interval provided better signal. BIOGRAPHICAL SKETCH Susan D. Hovorka is a Research Scientist at the Bureau of Economic Geology, Jackson School of Geosciences, The University of Texas at Austin. She is the chief scientist of the Gulf Coast Carbon Center (www.gulfcoastcarbon.org), an academic-industry consortium seeking an economic basis on which to move forward on carbon sequestration. Currently she is leading a team in a Frio Brine field pilot CO2 injection to assess the cost, safety, and effectiveness of geologic sequestration as a mechanism for reducing atmospheric greenhouse gas emissions. She is also actively facilitating exchange between applied scientists and citizens, with a focus on precollege students and teachers. Contact: Gulf Coast Carbon Center at the Bureau of Economic Geology, Box X, The University of Texas at Austin, Austin TX 78713-8924, Phone: 512-4714863, Fax: 512-471-0140, E-mail: [email protected] .