Frio brine storage experiment—lessons learned

The Frio Brine pilot is a closely monitored, small-volume (1,600 tons), short-duration experiment using injection of CO2 into high-permeability brine-bearing sandstone to test the feasibility of geologic sequestration. The experiment differed from the geoscience and engineering community’s extensive previous experience in injection of CO2 and other fluids into the subsurface. It was, from inception to completion, focused on assessing monitoring strategies. An important objective of this study is to convey lessons learned to the next generation of developers of geologic CO2-injection-pilot projects. For the experiment, CO2 was injected for 10 days 1500 m below the surface. The evolution of the plume was successfully monitored with diverse tools, including downhole pressure and temperature, wireline logging, fluid sampling, cross-well techniques, and vertical seismic profiling. The injection period was brief and the formation was steeply dipping with high permeability; therefore the nineteen months since injection period takes us well into the post injection phase of monitoring. As predicted, CO2 remains stored within the formation. Surface leak detection techniques have thus far failed to detect any clear evidence of leakage except immediately above the injection zone, probably through engineered systems.