Progressive Strength Degradation and Mineral Evolution in Tight Sedimentary Rock: Implications for Carbon Mineralization

Carbon mineralization in geological formations is considered one of the most secure and permanent methods for long-term CO2 storage. While extensive studies have focused on reactive basaltic systems, the behavior of tight sedimentary rocks under CO2-rich conditions remains less understood, particularly regarding the coupling between mineral transformations and mechanical stability. This study investigates how mineral composition and micromechanical properties evolve in low-permeability sedimentary rock when exposed to CO2-rich water under simulated reservoir conditions (60°C, 10 MPa) for up to 8 weeks. Using a combination of scanning electron microscopy (SEM) with energy-dispersive X-ray spectroscopy, X-ray diffraction, and nanoindentation, we tracked progressive changes at both the microstructural and mineral scales. Results revealed early dissolution of calcite, minor changes in clay minerals, and stable silicate phases. SEM images showed increasing porosity and surface roughness, while nanoindentation measurements demonstrated a continuous decline in both hardness and elastic modulus over time. These findings suggest that CO2–water–rock interactions in tight formations can lead to significant weakening of the rock framework, even as mineral trapping proceeds. Understanding this coupled chemical–mechanical evolution is essential for evaluating the long-term safety, sealing integrity, and performance of CO2 geological storage in sedimentary environments.