Carbon sequestration at the Illinois Basin-Decatur Project: experimental results and geochemical simulations of storage

The Midwest Geological Sequestration Consortium is conducting the Illinois Basin-Decatur Project (IBDP), a large-scale demonstration of carbon sequestration that injected the CO₂ from an ethanol plant into the Mt. Simon Sandstone. Using site-specific data and samples, batch experiments were conducted at reservoir conditions and the reactive transport code TOUGHREACT was used to model the CO₂ migration and interactions in the injection formation. In the model, most of the mineral alteration occurred after the injection was completed and brine displaced the CO₂ at the base of the plume. K-feldspar dissolution led to a nearly 10% increase in porosity which is a maximum estimate of alteration because, the model omits mineral transformations and may underestimate clay precipitation and the effects of grain coatings. The batch experiments recreated these conditions and showed a little alteration. In both the model and experiments, the bulk of the mineralogy remained inert. Calcite precipitated within the modeled plume where the transformation of K-feldspar to clays buffered the pH, though this process only produced minor mineral sequestration. Less-permeable layers in the model baffled the ascent of the CO₂ plume and caused it to spread laterally. The plume did not reach the upper third of the Mt. Simon Sandstone. Both the model and the batch experiments show that the bulk of the Mt. Simon Sandstone will undergo little change due to CO₂ injection, and the batch experiments show the feldspar dissolution in the model is likely limited.