ANALYSIS OF PALEO-MIGRATION OF CO2 USING SATELLITE IMAGERY, CORRELATION OF GEOPHYSICAL AND FIELD DATA IN AN EFFORT TO DETERMINE TOP SEAL INTEGRITY, WITH IMPLICATIONS FOR CO2 SEQUESTRATION

Injection of carbon dioxide (CO₂) at depth into stacked saline aquifers separated by low permeability shale units has been proposed as a viable method to reduce the amount of anthropogenic CO₂ released into the atmosphere. Large anticlines in Central Utah are natural analogs for a class of injection sites. The shale-siltstone sections may act as hydrostratigraphic trapping mechanisms which can be utilized as natural reservoirs, capable of storing large volumes of injected CO₂. In most cases migration of CO₂ to the surface is inhibited by the presence of a low permeability top seal, but in some cases the integrity of the top seal is compromised by the presence of fractures and faults. Evidence of paleo-fluid migration along fractures and faults is preserved in many formations throughout Utah in the form of bleached host rock, and calcite fill in both open and closed fracture systems. Analysis of Landsat-7 and Advanced Spaceborne Thermal Emission and Reflection (ASTER) imagery using common ratios and various band combinations to highlight distinct alteration features is useful in identifying areas in which the migration of CO₂ through a formation is preserved. Areas in which alteration of host rock is identified by Landsat-7 and ASTER imagery is evaluated both macroscopically and microscopically, and compared to areas in which no fluid alteration of host rock is observed. Field and lab measurements are correlated to the geophysical data acquired from the drilling efforts in the area. The correlated data provides insight into the sealing capacity of a potential CO₂ sequestration site. An increase in fracture density is observed in shale which overlies potential injection reservoirs in areas where paleo-migration of CO₂ is present. The transition from sandstone to shale along fractures and faults show a continuation of bleached host rock, and calcite filled fractures across the transition.