From Bureau of Economic Geology, The University of Texas at Austin (www.beg.utexas.edu).
For more information, please contact the author.

AAPG Annual Convention, Calgary, Alberta, Canada, June 19–22, 2005

Frio Brine Pilot: Field Validation of Numerical Simulation of CO2 Storage

Susan D. Hovorka, Christine Doughty, Shinichi Sakurai, and Mark Holtz

Abstract:

For the Frio Brine Pilot we injected 1,600 tons of supercritical CO2 into a brine-saturated formation 1,500 m below surface and measured transport between two wells 30 meters apart though a moderately homogeneous, high permeability (2.5 Darcy) sandstone. Modeling using TOUGH2 with parameters based on detailed study of petrophysics predicted that breakthough of CO2 to the observation well would occur in 2.5 to 6 days. During the injection phase of the field experiment, breakthough of CO2 occurred 30 percent earlier than predicted. Logging using the Schlumberger reservoir saturation tool determined that by the fourth day after the initiation of injection, the plume thickness was half what and that saturation in preferred flow zones was higher than had been predicted by the model showing that factors favoring rapid flow such as high permeability zones or gravity override were larger than predicted. As injection continued for 9 days, plume thickness increased by addition of CO2 in the lower part of the plume, culminating with an observed saturation profile similar to that predicted by the model. CO2 saturation was variable but was estimated to be in excess of 50% of porosity.

Post injection saturation changes observed as CO2 migrated though the steeply dipping sandstone under gravitational forces appears to reverse the trend observed during injection. Continued observation will yield information about saturation history significant to understanding CO2 trapping mechanisms. Downhole pressure and temperature proved to be sensitive indicators of plume behavior, showing changes in plume as CO2 saturation changed before and after breakthough.