The Role of CO2 Pressure on Chemo-Mechanical Properties of Shales in a Brine-Rich Environment

ABSTRACT: This study examines the chemo-mechanical response of quartz-rich Mancos shale exposed to CO2-rich brine under two pressure conditions, 1000 psi and 1800 psi, at 100°C for 28 days. The objective is to investigate how pressure influences dissolution-precipitation reactions and their impact on mechanical properties. High-speed nanoindentation was utilized to generate spatially resolved mechanical property maps, providing micron-scale resolution of hardness and modulus variations across reacted and unreacted regions. These nanoindentation grids served as the basis for machine learning clustering, which was applied to identify chemo-mechanical transformations by correlating mechanical property variations with volume fraction data obtained from SEM/EDS maps. Results show that at higher pressure, increased dissolution and precipitation led to greater mechanical degradation, reducing hardness and promoting microstructural instability. At lower pressure, salt precipitation was more prominent near the reacted edge, influencing local mechanical properties. The analysis highlights the weakening of Si-O-Si bonds in quartz, altering its mechanical response. These findings enhance understanding of how CO2-induced reactions affect quartz-rich shale integrity, with implications for geomechanical stability. The integration of nanoindentation and machine learning provides a reliable framework for assessing pressure-dependent chemo-mechanical transformations, improving insights into dissolution-precipitation effects on rock stability and mechanical integrity.