GEOCHEMICAL MODELING OF MT. SIMON BRINE EXTRACTION AND REINJECTION FOR PLUME PRESSURE MANAGEMENT

Removing brine from a reservoir in which CO₂ sequestration is ongoing or has taken place is a potential technique for influencing plume shape and compensating for increases in reservoir pressure. However, disposing of the brine produced from the reservoir may be problematic. In this study, we examine the geochemical effects of extracting and treating brine from the Mt. Simon Formation, a widespread and current sequestration target, and then reinjecting it into the Potosi Formation.

We modeled several scenarios that might occur following the brine extraction. The brine could simply be reinjected or it could go through a series of treatments to lower the concentration of scale-forming species and then be reinjected. Based on the geochemical model results, the removal of brine does cause some mineral precipitation as the extracted brine cools and is exposed to oxygen. This result matches changes seen during sampling.

The Potosi unit proposed for reinjection is a karstic dolomite with high permeability. The brine chemistry used came from the nearest available sample at the Illinois Basin Decatur Project injection site. In the model results, the carbonates and pyrite in the Potosi react with injected brine leading to changes in mineralogy and brine composition. The calculated changes vary depending on if the flow is considered as being in a single or dual-porosity system.