FTIR Analysis of CO₂ Saturation on Carbonate-Rich Shales: Implications for Seal Integrity

Rising atmospheric CO2 levels are a key driver of climate change, leading to severe environmental consequences, such as extreme weather, rising sea levels, and ecosystem disruptions. While CO2-induced geochemical reactions in shale formations have been widely studied, little experimental research has focused on their effects on shale caprock surface chemistry. This study investigates how gaseous and supercritical CO2 (ScCO2) alter the chemical composition and functional groups of carbonate-rich shales by using Fourier transform infrared (FTIR) spectroscopy. Results show that both treatments modify shale surface chemistry, with ScCO2 exerting a more pronounced effect due to its higher density and solvent power at elevated temperatures. Aromatic hydrocarbons are more effectively extracted while oxygen-containing groups exhibit temperature-dependent changes. ScCO2 also enhances the removal of aliphatic hydrocarbons, while hydroxyl groups show a steady increase with ScCO2 exposure. These findings are crucial for assessing the shale caprock integrity, which is essential for CO2 storage applications. The study underscores the role of temperature in enhancing CO2 mobility and reactivity, making ScCO2 a more efficient extracting agent. Overall, this research advances carbon capture and storage (CCS) efforts by improving our understanding of the interactions of CO2 with geological formations, contributing to the development of effective CO2 sequestration strategies.