LABORATORY SCALE CO2 FLOW EXPERIMENTS UNDER SUPERCRITICAL CONDITIONS TO MODEL HYDROGEOCHEMICAL REACTIONS AND MINERALOGICAL CHANGES IN THE SALINE ARBUCKLE AQUIFER : IMPLICATIONS FOR CO2 SEQUESTRATION

The deep saline aquifer in south-central Kansas has been proposed as a potential site for geologic storage of CO₂. The entirety of the Arbuckle (4176-5160 ft) was cored to provide rock samples (two wells-KGS 1-32 and 1-28) for description and flow cell experiments. Formation cores show heterogeneity throughout the injection zone. The dominant mineralogy in the proposed CO₂ injection zone is dolomitic limestone with sporadic large cherty nodules. Presence of extensive vugs and micro fractures are common at some depths. Thin section and XRD data have provided the specific mineral assemblage of each core plug. Drill stem test water samples were collected from 8 depths throughout the aquifer to describe the changing chemistry of brine with depth. Initial chemical analysis show a hypersaline brine (range~50,000 - 190,000 TDS) dominated by Cl, Na and Ca. Elemental ratios of Cl:Br, Na:Cl and Ca:Sr are what is expected of a typical saline aquifer system. The swabbed water from 5010 to 5020 ft gave a constant pH of 4.76 for the entire period of pumping and field results show high sulfate concentrations (>200 mg/L). Initial laboratory experiments carried out at the National Energy Technology Laboratory at in-situ T and P using formation core plugs and collected brine (formation water) help identify the major reactions that can be anticipated when supercritical CO₂ is in place. Formation brine is injected into the core plugs and supercritical CO₂ is added thereafter. The effluent is collected over a 24 hour time period and analysed by ICP-OES and IC for major and trace elemental changes. The flow experiments at supercritical T and P allow us to determine extent of mineral carbonation, mineral dissolution reactions and observed breakthrough curves help constrain reaction rates. Major reaction kinetics between CO₂, brine and rock were determined by geochemical modeling and provide insight into how the chemistry of the brine will be affected in short and long term after CO₂ injection.