Capillary- Sealing Efficiency of Mica- Proxy Caprock for CO₂/H₂ Geologic Storage in the Presence of Organic Acids and Nanofluids

Toward a diversified low-carbon future, the geological storage of carbon dioxide (CO2) and hydrogen (H2) is regarded as a key enabler for an industrial -scale implementation. However, many geological formations, such as depleted oil and gas reservoirs, can contain inherent traces of organic molecules that dramatically affect their storage capacities and caprock sealing efficiency. Hence, using the right analysis to accurately determine the caprock sealing efficiency and storage capacity in the presence of organics is crucial for a secure and safe storage process. This study analyzed the sealing potential of a proxy caprock (mica) by calculating the capillary entry pressure and static column height of CO2 and H2 using previously published contact angle measurements. In addition, the effects of key parameters such as pressure (up to 25 MPa), temperature (308 K, 323 K, and 343 K), and pore throat size ( r = 5 nm and 10 nm) were demonstrated, along with those of organic acids (lignoceric acid C24, stearic acid C18, lauric acid C12, and hexanoic acid C6) and alumina nanofluids, on the wettability, capillary sealing efficiency, and static column height of the gas. The results indicated that the sealing efficiency and storage capacity for CO2 and H2 decrease with the increase in pressure and surface concentration of organic acid but increase with the increase in temperature. The analysis demonstrated a theoretical inverse relationship between the capillary entry pressure and the pore throat radius. Thus, the smaller the pore size, the more suitable the conditions for sealing and storage capacity. Furthermore, the wettability and sealing efficiency of the organic -aged mica/CO2 system were improved by the addition of nanoalumina, with an optimal nanofluid concentration of 0.25 wt%. In a nutshell, this work has provided a detailed theoretical workflow for assessing the influence of various parameters on the wettability, sealing efficiency, and storage capacity of mica substrates (as a proxy caprock) for the safe and secure geological storage of H2 and CO2.