Natural CO2 accumulations in the western Williston Basin: A mineralogical analog for CO2 injection at the Weyburn site

F. J. Ryerson, John Lake, Steven Whittaker, James W. Johnson

Research output: Contribution to journalArticlepeer-review


The Devonian carbonates of the Duperow Formation on the western flank of the Williston Basin in southwest Saskatchewan contain natural accumulations of CO2, and may have done so for as long as 50 million years. These carbonate sediments are characterized by a succession of carbonate cycles capped by anhydrite-rich evaporites that are thought to act as seals to fluid migration. The Weyburn CO2 injection site lies 400km to the east in a series of Mississippian carbonates that were deposited in a similar depositional environment. That long-term isolation of natural CO2 can be accomplished within carbonate strata has motivated the investigation of the Duperow rocks as a potential natural analog for storage of anthropogenic CO2 in carbonate lithologies. For the Duperow strata to represent a legitimate analog for Midale injection and storage, the similarity in lithofacies, whole rock compositions, mineral compositions and porosity with the Midale Beds must be established. Here we compare lithofacies, whole rock compositions, mineralogy and mineral compositions from both locales. The major mineral phases at both locales are calcite, dolomite and anhydrite. In addition, accessory pyrite, fluorite, quartz and celestine (strontium sulfate) are also observed. Dawsonite, a potential CO2-trapping mineral, is not observed within the CO2-bearing horizons of the Duperow Formation, however. The distribution of porosity in the Midale Vuggy units is similar to that of the Duperow Formation, but the Marly units of the Midale have significantly higher porosity. The Duperow Formation is topped by the Dinesmore evaporite that is rich in anhydrite, and often contains authigenic K-feldspar. The chemistry of dolomite and calcite from the two localities also overlaps. Silicate minerals are in low abundance (<3%) within the analyzed Duperow samples, with quartz and K-feldspar the only silicates observed petrographically or in X-ray diffraction patterns. The Midale Beds contain significantly higher silica/silicate concentrations (Durocher et al., 2003), but the paucity of mono- and divalent cations that can be derived from dissolution of these silicate minerals likely precludes significant carbonate mineral formation. Hence, physical and solution trapping are likely to be the primary CO2 trapping mechanisms at both sites.

Original languageEnglish (US)
Pages (from-to)S25-S34
JournalInternational Journal of Greenhouse Gas Control
StatePublished - Jun 2013
Externally publishedYes


  • Geologic carbon sequestration
  • Natural analog
  • Natural carbon dioxide accumulations
  • Supercritical carbon dioxide
  • Water-rock interaction
  • Weyburn carbon dioxide injection

ASJC Scopus subject areas

  • Pollution
  • Energy(all)
  • Industrial and Manufacturing Engineering
  • Management, Monitoring, Policy and Law


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