Geochemical Dynamics in ScCO2-Exposed Raniganj Shales: Probing Depth-Responsive Transformations and Their Significance for CO2 Storage

ABSTRACT In response to the pressing need to combat rising atmospheric CO2 levels, carbon capture, utilization, and storage (CCUS) technologies have gained prominence, with particular relevance to enhanced shale gas recovery (ESGR). This study delved into the geochemical intricacies of the Raniganj shales of the Lower Gondwana Group, investigating their response to supercritical CO2 (ScCO2) exposure through an array of advanced analytical techniques, including X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), Brunauer–Emmett–Teller (BET) surface area analysis, Raman spectroscopy, and scanning electron microscopy with energy-dispersive X-ray analysis (SEM-EDX). The outcomes of this comprehensive analysis unveiled notable transformations within the shale matrix. Notably, there was evidence of Si–O and C–H bond degradation in the shale’s framework and phyllosilicate minerals. Moreover, the precipitation of secondary minerals was observed, suggesting a complex geochemical response to ScCO2. Furthermore, the study highlights a significant increase in shale porosity following ScCO2 exposure, which has promising implications for enhanced CO2 storage. Additionally, a depth-dependent trend in thermal maturity (R0) was evident, underscoring the role of depth in shaping the geochemical response to ScCO2. A significant observation was the reduced impact of ScCO2 on greater-depth shale samples compared to their shallower counterparts. While increased porosity was observed post-ScCO2 exposure, the findings suggest that permeability enhancement may be restricted due to secondary mineral precipitation, pore throat narrowing, and depth-dependent thermal maturity effects. This study highlights how geological factors, especially depth, affect geochemical dynamics in CO2-ESGR, helping to optimize CCUS for carbon storage and shale gas recovery.