MODELING OF CO2–WATER–ROCK INTERACTIONS IN MISSISSIPPIAN SANDSTONE AND CARBONATE RESERVOIRS OF KENTUCKY

Mitigating the input of carbon dioxide (CO₂) into the atmosphere is becoming increasingly critical as usage of fossil fuels continues. With the overwhelming majority of electricity coming from coal-fired power plants, Kentucky is a significant producer of CO₂. Pilot tests are underway in Kentucky to further understand the processes involved with sequestering captured carbon into geologic reservoirs including: oil and gas fields, and deep saline aquifers. This study focuses on modeling the subsurface water-rock-CO₂ interactions occurring during carbon sequestration into Mississippian oil and gas reservoirs of western and eastern Kentucky.

New samples (n= 81) and archived data, both collected from oil wells, were used to characterize the chemistry of formation waters from Sugar Creek field in Hopkins County, Euterpe field in Henderson County, and various fields in Leslie County. In addition, 20 core and 17 cuttings samples from the reservoir and overlying cap-rocks in or near these fields were analyzed for bulk and clay mineralogy using X-ray diffraction. Electric logs were used to select sample intervals within the overlying cap-rocks and in the center of the producing zones. Samples from the sandstones include the Cypress, Big Clifty Member (Jackson) of the Golconda Formation, Hardinsburg, and Tar Springs Formations in western Kentucky. The carbonate samples were taken from the Slade Formation/Newman Limestone (Big Lime) of eastern Kentucky.

The chemistry of formation waters directly influences the potential for dissolution of CO₂ into fluids (solubility trapping), as well as influencing mineral-forming reactions (mineral trapping). Using the water chemistry and mineralogic data as inputs, speciation and reaction path models were created using the Geochemist Workbench software to predict the distribution of aqueous species at equilibrium, evolution of fluid chemistry, and reservoir mineralogy as CO₂ is injected into the reservoir. Ongoing work involves comparison of fluid-mineral equilibria and reactions in the sandstone versus carbonate reservoirs to determine the feasibility of long-term carbon capture, as well as comparing model results against actual data collected from pilot sites.