GEOCHEMICAL AND MINERALOGICAL CHARACTERIZATION OF THE ARBUCKLE AQUIFER: STUDYING MINERAL REACTIONS AND ITS IMPLICATIONS FOR CO2 SEQUESTRATION

The deep saline aquifer in south-central Kansas has been proposed as a potential site for geologic storage for CO₂. Two wells (KGS 1-32 and 1-28) have been drilled to the basement to provide data for a site specific determination of the storage potential of the Arbuckle. The entirety of the Arbuckle (~4100-5100 ft) was cored to provide rock samples for description and flow cell experiments. Petrographic examination of formation rocks reveal a dolomitic aquifer with an abundance of chert. Argillaceous zones and Fe sulfide minerals are prevalent throughout the injection zone and create extensive heterogeneity seen in core samples. Large (<cm) vugs and micro fractures are common at some depths. Thin section study has revealed a diversity of textures that could facilitate reactions with CO₂ and XRD data have provided specific mineral assemblages of core plugs throughout the proposed injection zone. Brine samples were collected from drill stem tests and swab tests at 13 depths within the Arbuckle and overlying Mississippian aquifer to describe the changing chemistry with depth and to provide baseline data for future monitoring after injection. Chemical analysis by HR-ICP-MS and ICP-OES show a hyper saline brine (range~50,000 - 190,000 TDS) dominated by Na, Ca, and Cl ions. Concentrations of major elements increase with depth while redox sensitive species show fluctuations revealing the impact of microbial communities on the equilibrium of the brine system. The proposed injection zone is reducing, as evident from high concentrations of released H₂S gas during sampling, a high Fe II/III ratio and a Eh value of (~)-169 mv. Reduced Fe has been studied as an important element in carbonation reactions in saline aquifers and high concentrations of Fe II in the injection zone brine could facilitate mineralization reactions. Isotopic variation of ¹⁸O and ²H with depth suggest the Arbuckle has limited vertical connectivity. The presence of a baffle zone between 4300` and 4550` is also suggested from nuclear magnetic resonance logs and whole core porosity measurements. A baffle zone within the Arbuckle would inhibit upward migration of a CO₂ plume. Extensive characterization of the Arbuckle aquifer has been paramount to designing a cutting edge monitoring program to determine potential CO₂ leaks and impacts on freshwater resources.