Supercritical CO2-Induced Mineral Transformations in Shale: Implications for Permanent Carbondioxide Sequestration

Global energy demands and atmospheric CO2 mitigation needs drive the search for solutions. This study explores the potential for mineralogical sequestration of CO2 in shale formations. Two Oklahoma shale samples, Sample R1 (reservoir proxy) and Sample D1 (caprock proxy), were exposed to supercritical CO2 (scCO2) at 2000 psia and 140°F for 30 days using a flow-through closed-loop system. Pre- and post-exposure analyses employed Raman Spectroscopy, Scanning Electron Microscopy (SEM), and Energy Dispersive Spectroscopy (EDS) to assess mineralogical and structural changes. Raman spectroscopy use to assess the presence of organic matter, carbonates, and silicates. SEM-EDS quantified elemental shifts, including Ca, Mg, Na, Fe, K, and Al, providing evidence of mineral reactivity. Carbonate and feldspar dissolution, along with elemental redistribution, suggests the potential for secondary carbonate precipitation, with spectral and compositional shifts indicating carbonation. Organic matter acted as a reactive site, enhancing CO2 interaction through adsorption among other mineralization pathways. These findings offer insights into the mechanisms of shale's geochemical response to scCO2, reinforcing its viability for carbon capture and storage (CCS) in unconventional reservoirs while addressing key energy and environmental challenges.