GEOCHEMICAL AND EXPERIMENTAL INVESTIGATION TO ASSESS THE FEASIBILITY OF CO2 STORAGE WITHIN THE ARBUCKLE AQUIFER, KANSAS

The Arbuckle aquifer in south-central Kansas is currently being evaluated as a site for CO₂ storage. Three wells have been drilled into this carbonate aquifer to determine the feasibility for safe, long-term storage of CO₂. Two test wells were drilled in Wellington, now the site of a small-scale CO₂ injection pending approval by EPA. A third well, Cutter KGS #1, was drilled in SW Kansas as a western calibration site located 350 km from Wellington. At these sites three geologic zones are of interest: the Mississippian zone investigated for enhanced oil recovery purposes, a potential baffle zone in the upper Arbuckle that could help impede vertical CO₂ migration, and the Arbuckle injection zone. At both Cutter and Wellington DST and swabbed waters were used for hydrochemical characterization and comparison of the brines. δ¹⁸O vs. δD ratios indicate limited vertical zonation of water within Cutter, unlike at Wellington, which remarkably shows the presence of in-between baffle zones. δ¹⁸O-δD ratio vs. Cl^-helps confirm this while also suggesting a single water origin at Cutter. At Wellington Ca/Mg vs. Ca/Sr ratios show that the upper Arbuckle waters trend towards calcite recrystallization, while the lower Arbuckle shows more of a dolomitization trend. At Cutter these same ratios show a higher dolomitization trend. At both locations overall increasing TDS with depth allows for higher rate and availability of reacting ions.

Experimental work at Lawrence Livermore National Laboratory investigated a carbonate core (fine-grained dolomite, moderately fractured with chert infillings including a large chert nodule (~2cm)) being simultaneously injected with CO₂ and formation brine to model a simulated in-situ injection. Initial dissolution appears to have occurred along the dolomite/chert boundary after the experiment. Dissolution along mineral boundaries and fractures and determinations of change of net porosity and permeability are currently being measured by X-ray CT scans. Geochemical modeling is used to confirm mineral saturation states and reaction kinetics for similar lithologies in Cutter. These experimental results and geochemical modeling predictions will complement one another, and will allow for an accurate understanding of what occurs before, during, and after CO₂ injection.