The Huff-n-Puff site in south central Illinois was the first CO2-Sequestration test for the Midwest Geological Sequestration Consortium in the Illinois Basin. This was a small-scale CO2 injection pilot program to test equipment, monitoring techniques, logistics and enhanced oil production. Approximately 43 tons of CO2 were injected into the Cypress sandstone formation (~1550 ft deep) over a period of 5 days and shut in for two weeks before oil extraction. The isotopic composition of gases and aqueous samples from the site were determined to help detect migration of CO2 from the injection well to surrounding production wells and to shallower freshwater aquifers and the vadose zone. The δ13C of the injected CO2 was -35 ‰. The d13C of the CO2 associated with the formation brines averaged around -23 ‰. A major increase in the percentage of CO2 was observed at one of the production wells 182 days after the first day of injection as indicated by a large CO2 concentration (94 %) in the gas sample collected. The δ13C of this CO2 was very negative, -32.5 ‰, representative of the injection gas. Prior to this, small increases in CO2 concentrations were observed at the same production well that also showed -33 ‰ δ13C values, suggesting a small amount of injected CO2 may have bled to this production well even before 182 days. An alternative explanation for these early events may be oxidation of hydrocarbons to produce such negative δ13C values but %O2 remained very low. The δ13C of the dissolved inorganic carbon (DIC) for the aqueous samples collected indicated isotopic equilibration began to be established in the injection well between the CO2 and DIC but not in the production wells. This data suggests the small amount of gas that bled or was pulled through the formation brines to the production wells was out of geochemical equilibrium with the brines. There was no indication of CO2 migration to the shallow monitoring wells or vadose zone probes adjacent to the injection and production wells.
|Original language||English (US)|
|State||Published - 2010|