Effect of Methyl Orange and Methylene Blue on the Wettability of Organic Acid Aged Sandstone and Carbonate Formations: Implication for CO2 and H2 Geo-Storage.

Abstract Underground storage of carbon dioxide (CO2) and hydrogen (H2) in geological formations has been considered an effective method for the energy transition towards a low-carbon industry. The wettability of the rock is a significant parameter for underground gas storage, determining both the storage capacity and containment safety. This study focuses on using two chemicals, methyl orange (MO) and methylene blue (MB), as wetting agents at different concentrations (10 to 100 mg/L) to change rock wettability and improve the storage capacity of CO2 and H2. To achieve this, the contact angle measurement technique was utilised to measure the advancing (θa) and receding (θr) contact angles under reservoir conditions, with a constant pressure of 13 MPa for the hydrogen system and 20 MPa for the CO2 system, temperatures of 25°C and 50°C, and a brine salinity of 0.3 M NaCl. To mimic reservoir conditions, the surfaces of both calcite and quartz samples were treated with stearic acid before being exposed to the wetting agent chemicals. Although the surfaces of these treated samples are hydrophobic, modifying their surfaces with even a very trace concentration of MO or MB significantly alters the wettability from hydrophobic to hydrophilic. This demonstrates that the presence of organic acids can affect the storage capacity of CO2 and H2 in reservoir rock. However, injecting even a very diluted amount of MO or MB into sandstone and carbonate geological formations can increase CO2 and H2 storage capacity.