GEOCHEMICAL REACTIONS FOR SEQUESTRATION OF CO2 IN OHIO'S DEEP SALINE AQUIFERS

Deep saline aquifers are potential long-term repositories for CO2 from power plant emissions. The extent, form, and duration of CO2 storage depend on chemical reactions between the injected CO2, aquifer brines, and formation minerals. The Rose Run sandstone of eastern Ohio is one of Ohio's deep formations that has potential for CO2 injection and storage. The dominant silicate minerals are quartz, orthoclase, albite, and glauconite. Carbonate layers interbedded with the sandstone contain dolomite, calcite, and siderite.

Equilibrium and kinetic geochemical modeling was conducted using Geochemists Workbench™ to simulate the likely geochemical reactions in the Rose Run aquifer. Geochemical modeling of simple and complex mineral-brine-CO2 mixtures makes it possible to evaluate the impact of temperature, pressure, mineralogy, brine composition, CO2-fluid-rock ratio, and CO2 fugacity on mineral dissolution and precipitation, amount of CO2 sequestered, and the form of sequestration.

For 10 kg of typical Rose Run composition and 1 kg of brine and a CO2 fugacity of 60 – 80 atm carbonate precipitation at equilibrium traps 10.5 g of C in 126 g of authegenic dawsonite (NaAlCO3(OH)2), 1.6 g of C in 12 g of authegenic dolomite, and 0.7 g of C in 7 g of authegenic siderite. At lower fugacity of 0-20 atm about 1.7 g of C is trapped in 13 g of authegenic dolomite, a significant amount of siderite dissolves and dawsonite is not precipitated at the completion of reaction.

The modeling indicates that under certain conditions, dissolution of albite, which is a widespread and relatively abundant mineral in the Rose Run sandstone, can lead to mineral trapping of carbon in dawsonite. The extent to which dawsonite traps carbon will depend on the relative timing of dilution of CO2 by flow versus the rate of dissolution of albite. Modeling studies by others predict that the timescales for these processes are of the same order and consequently dawsonite may be a significant phase for trapping CO2 in the deep saline aquifers of the eastern United States.