- Copyright ©2006. The American Association of Petroleum Geologists/Department of Environmental Geosciences. All rights reserved.
If CO2 released from fossil fuel during energy production is returned to the subsurface, will it be retained for periods of time significant enough to benefit the atmosphere? Can trapping be assured in saline formations where there is no history of hydrocarbon accumulation? The Frio experiment in Texas was undertaken to provide answers to these questions.
One thousand six hundred metric tons of CO2 were injected into the Frio Formation, which underlies large areas of the United States Gulf Coast. Reservoir characterization and numerical modeling were used to design the experiment, as well as to interpret the results through history matching. Closely spaced measurements in space and time were collected to observe the evolution of immiscible and dissolved CO2 during and after injection. The high-permeability, steeply dipping sandstone allowed updip flow of supercritical CO2 as a result of the density contrast with formation brine and absence of a local structural trap.
The front of the CO2 plume moved more quickly than had been modeled. By the end of the 10-day injection, however, the plume geometry in the plane of the observation and injection wells had thickened to a distribution similar to the modeled distribution. As expected, CO2 dissolved rapidly into brine, causing pH to fall and calcite and metals to be dissolved.
Postinjection measurements, including time-lapse vertical seismic profiling transects along selected azimuths, cross-well seismic topography, and saturation logs, show that CO2 migration under gravity slowed greatly 2 months after injection, matching model predictions that significant CO2 is trapped as relative permeability decreases.
Susan D. Hovorka is a research scientist at the Bureau of Economic Geology, Jackson School of Geosciences, University of Texas at Austin. She served as principal investigator and geologist and research integrator for the Frio Project.
Sally M. Benson is a staff scientist in the Earth Sciences Division at Ernest Orlando Lawrence Berkeley National Laboratory. She co-led the GEO-SEQ consortium in experiment design and provided analysis of pressure transients.
Christine Doughty is a staff scientist in the Earth Sciences Division at Ernest Orlando Lawrence Berkeley National Laboratory and developed numerical models using TOUGH2 to design and interpret experimental results.
Barry M. Freifeld is a mechanical engineer and hydrologist in the Earth Sciences Division at Ernest Orlando Lawrence Berkeley National Laboratory and developed the U-tube and tracer program.
Shinichi Sakurai is a research associate at the Bureau of Economic Geology, Jackson School of Geosciences, University of Texas at Austin and led the log analysis team.
Thomas. M. Daley is a research associate in geophysics at Ernest Orlando Lawrence Berkeley National Laboratory and was a leader in designing, collecting, and interpreting the vertical seismic profiling and cross-well seismic data at the Frio project.
Yousif K. Kharaka is a research hydrologist with the U.S. Geological Survey in Menlo Park, California, and led the geochemical team.
Mark H. Holtz is research associate at the Bureau of Economic Geology, Jackson School of Geosciences, University of Texas at Austin and provided petrophysical data.
Robert C. Trautz is a research associate in hydrogeology in the Earth Sciences Division at Ernest Orlando Lawrence Berkeley National Laboratory and conducted the tracer tests and other field activities.
H. Seay Nance is a research scientist associate at the Bureau of Economic Geology, Jackson School of Geosciences, University of Texas at Austin, and led the surface assessment team.
Larry R. Myer is a geophysicist in the Earth Sciences Division at Ernest Orlando Lawrence Berkeley National Laboratory and co-led the GEO-SEQ team.
Kevin G. Knauss is a geochemist at Lawrence Livermore National Laboratory and provided interactions analysis of fluid-rock.