LABORATORY AND MODELING INVESTIGATIONS OF CO2-BRINE-MINERAL GEOCHEMICAL INTERACTIONS IN SHALES MATRICES

Geological Carbon Sequestration (GCS) has great potential to reduce atmospheric carbon emissions and mitigate the effects of climate change. Long term effectiveness of CO₂ sequestration depends on storage security and the physical and chemical trapping mechanisms. Systematic laboratory and modeling studies were conducted to investigate CO₂-brine-mineral interactions in shales matrices. XRD, XRF, LA-ICP-MS, and Raman Spectroscopy were used to assess the changes in mineral contents and elemental composition of hosting rocks after reacting with CO₂. Caprock samples used in the experiments are taken from the Black Warrior Basin with different mineralogy and elemental composition. Conasauga Shale, Neal/Floyd Shale, Chattanooga Shale, and Devonian Shale are some samples that are used. In Conasauga Shale carbonate minerals are dominant and in Neal/Floyd Shale carbonate minerals are in trace amounts. As carbonate minerals are buffers for CO₂-brine-rock interaction changes in pH, alkalinity are changing differently in each sample. CO₂-brine-mineral interactions were examined in temperature ranging from 40 to 100 degree C. Geochemical modeling techniques were used to investigate the interactions of low permeability matrices (i.e., shales) with CO₂ that may influence potential leakage and safety of subsurface storage and sequestration. The geochemical modeling results show that CO₂ partitioning into formation fluids may reduce brine pH and creating conditions favorable for carbonate mineral dissolution. The changing pH conditions would, in turn, affect the adsorption of heavy metals on oxides and sulfides.