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Effects of Clay Swelling or Shrinkage on Shale Caprock Integrity
- Publisher: European Association of Geoscientists & Engineers
- Source: Conference Proceedings, 80th EAGE Conference and Exhibition 2018, Jun 2018, Volume 2018, p.1 - 5
Abstract
During CO2 injection and storage, the exposure of shale caprock to dry supercritical CO2 can lead to clay dehydration and shrinkage. This has been proposed as a potential leakage risk for shale caprocks during CO2 storage. We report permeability measurements on pressed tablets of smectite and a smectite-quartz mixture, aimed at directly observing the effects of mineral composition, confinement, hydration, and exposure to CO2 on the permeability of clay-rich materials. Our results indicate that confinement and mineral composition have a strong impact on permeability. Furthermore, hydration always lead to a decrease in CO2-permeability, which varied from less than one to several orders of magnitude depending on sample mineral composition and confinement. Exposure of a hydrated sample to (a flow of) dry supercritical CO2 did not result in a long term increase in permeability, as might be expected as a result of dehydration-induced shrinkage. Subsequent drying of the hydrated samples at elevated temperature outside the vessel did result in a return of permeability to the original dry values. When combined, our results suggest that clay shrinkage is not a significant CO2 leakage mechanism in shale caprocks, though further tests, including longer exposure to a flow of supercritical CO2, are required.