MINERALOGY AND GEOCHEMISTRY OF ARBUCKLE SALINE AQUIFER IN SOUTH CENTRAL KANSAS AND IMPLICATIONS FOR CO2 SEQUESTRATION

With increasing concerns over the impact of CO₂ on global warming, scientists have proposed a probable storage mechanism of CO₂ within saline aquifers. The deep saline aquifer within the Arbuckle formation in south-central Kansas has been proposed as a potential site for geologic storage for CO₂ in a project funded by the US Department of Energy – National Energy Technology Laboratory (NETL) (FED002056). Two wells (KGS 1-32 and 1-28) have been drilled to the basement rock to provide data for a site specific determination of the storage potential of the Arbuckle. The Arbuckle formation (~4100-5100 ft) was cored to provide core plugs for mineralogical analysis and water was collected from 11 depths to define the chemistry of the aquifer brine. Due to extensive heterogeneity found in the core plug samples it is essential to carefully examine and describe the mineralogy of each core for accurate geochemical modeling linking them to evaluate the storage permanence of the aquifer. The dominant mineralogy within the proposed CO₂ injection zone is micritic dolomitic limestone with dispersed cherty nodules dispersed throughout. Presence of extensive fluid enhanced vugs and micro fractures are common at some depths. Thin section and XRD data have provided specific mineral assemblage of each core plug examined in this study. SEM imaging provides microtopography and information on surface area changes after reaction with supercritical CO₂. Water samples were collected from a total of 11 depths throughout the aquifer to describe the changing chemistry of water with depth. Initial chemical analyses of the water show a hypersaline brine (50,000 to 190,000 TDS) dominated by Cl, Na and Ca. Mineralogical description of the formation rocks and geochemical evaluation of the water throughout the depth of the aquifer will constrain geochemical models of an injection scenario. Future work includes laboratory experiments to be carried out at the National Energy Technology Laboratory at formation temperatures and pressures using core plugs and collected brine to identify the major reactions and pathways that can be anticipated when supercritical CO₂ is injected.