Permeability evolution of claystones and other sealing materials for CO2 storage: role of confining stress and time

Carbon Capture and Storage (CCS) is a promising approach that has been increasingly utilized for reducing atmospheric carbon dioxide (CO2) levels. The long-term security of CO2 sequestration in saline aquifers depends on the integrity of overlying sealing units, while the transmissive properties of multi-barrier sealing systems remain to be further elaborated. This study investigates the permeability of claystones and compares them with other low-permeability lithologies (evaporites, tight sandstones, and tight limestones, 1 × 10− 17 − 1 × 10− 21 m² at 30 MPa) as well as casing cements (1 × 10− 16 − 1 × 10− 22 m² at 30 MPa) under CO2 storage conditions. Permeability was measured using helium gas and, for selected samples, with CO2. The stress-sensitivity of Klinkenberg-corrected permeability was assessed under confining pressures of 10–30 MPa, and pressure sensitivity coefficients (γ-values) were determined. Time-dependent effects were evaluated by maintaining samples at 30 MPa (approximately 2 km depth of effective pressure) confining pressure for 5–8 days. Results indicate that claystones reduce permeability by approximately one order of magnitude after 3–5 days, while casing cements decrease permeability by two orders of magnitude in 3 days. ... mehrThese findings highlight the necessity of allowing caprock samples to equilibrate under targeted effective stresses for at least three days to obtain reliable permeability measurements. Furthermore, our measured permeability varies distinctly across lithotypes (shales, evaporites, tight sandstones, and tight limestones), spanning 2 to 6 orders of magnitude at low confining stresses, necessitating the site- and lithotypespecific assessment of sealing unit permeability.