TOUGHREACT modeling of the fate of CO2 injected into a H2S containing saline aquifer: The example of the Wabamum Area Sequestration Project (WASP)

Abstract

Abstract The Devonian Nisku formation in central Alberta is potentially a suitable aquifer for CO2 sequestration. As with many Devonian aged aquifers in the Western Canada Sedimentary Basin, it contains H2S from thermochemical sulfate reduction. In spite of this, the Devonian Nisku represents a potentially desirable location as it is at the correct depth to ensure that CO2 is in the supercritical phase, it has multiple impermeable and low permeability barriers and there is very little hydrocarbon production in the formation. This paper presents a modeling study of the injection phase of CO2 into a saline aquifer in the Devonian Nisku formation at Wabamum Lake in Central Alberta. The object of the study is to evaluate the differences and problems, if any, between injection into a brine with an ambient amount of dissolved H2S and without dissolved H2S. The simulation covers a CO2 injection period of 50 years at a rate of 1 Mt/year. A one dimensional, radial symmetric model was used with a uniform carbonate composition. The mineral composition was from the Upper Nisku formation and a water composition from a producing water well in the Nisku formation. The model found that injected CO2 was stored as ionically trapped bicarbonate in a region of varying widths, 300 m wide after 1 year of injection to 3000 m wide after 50 years of injection represents from 2% to 3% of injected CO2. Small amounts are also trapped as calcite and dolomite. The H2S in solution does exsolve as gas during injection but this result is inconclusive due to the small amount of dissolved H2S present in the ambient brine. Overall, there were no noticeable differences between the models with and without ambient H2S in the brine.