A Reproducible SEM Surface Imaging Protocol for Monitoring Microstructural Changes During Gas–Rock Interactions

Reliable characterization of mineralogical and textural changes in rock samples is essential for understanding fluid–rock interactions, particularly in experimental studies simulating subsurface conditions. This study presents a reproducible protocol for scanning electron microscopy (SEM) analysis of rock surfaces before and after exposure to CO2 under controlled temperature and pressure conditions. The protocol enables the precise relocation of observation areas, allowing a direct comparison of microstructural features such as mineral dissolution, secondary precipitation and porosity evolution. Combining SEM with digital image analysis and expert petrographic interpretation, the method enhances the repeatability and quantitative rigor of comparative studies. The complete experimental workflow (from sample preparation to post‐exposure imaging) is described in detail, emphasizing the importance of spatial referencing and surface preservation. The protocol is demonstrated through a case study involving detrital sandstone samples from the Middle Eocene of the Ebro Basin (Spain), representing potential reservoir rocks. Samples were exposed to supercritical CO2 under controlled conditions (8 MPa, 40°C, 30 days), either dry or in contact with CO2‐saturated brine. Results show that brine‐mediated CO2 exposure led to selective mineral dissolution, grain detachment and increased porosity, indicating relatively high geochemical reactivity. In contrast, dry CO2 exposure caused minimal alteration, suggesting that fluid presence is critical for chemical interaction. The proposed protocol enables detailed discrete‐time surface characterization and provides a robust framework for evaluating rock–CO2 interactions in geological storage settings.