CO2 containment and storage in organic-rich strata ‒ State of the art and future directions

Abstract

Caprocks are crucial for preventing CO2 leakage in carbon storage, but the effects of mineral dissolution and precipitation on caprock properties and CO2 propagation remain debated. This review focuses on the interaction between CO2 and organic matter in shaly caprocks to enhance our understanding of caprock sealing integrity. CO2 acts as a solvent for extracting hydrocarbons from caprocks, but if only light hydrocarbons are extracted while polar compounds remain, the impact on caprock integrity should be minimal. The reaction between CO2 and kerogen poses the greatest risk, with limited evidence suggesting that supercritical CO2 (sCO2) can dissolve trapped hydrocarbons, enhancing penetration and rearranging kerogen structure. CO2-caprock interaction is influenced by various factors. Shales with high total organic carbon (TOC) content and at a mature stage exhibit increased CO2 adsorption and CO2-wet characteristics, facilitating diffusion. Conversely, low TOC shales at an immature stage are water-wet and better suited as caprocks. Conflicting findings on sCO2 exposure's effects on caprocks arise from differing experimental conditions, hindering direct comparisons. Quantitative studies on kerogen changes caused by extraction are essential for understanding long-term caprock integrity and CO2 storage efficiency. Evaluating CO2-kerogen interaction is vital, and comprehensive understanding of CO2-shale interactions requires quantitative investigations into kerogen composition and structure alterations.