Nanoconfined Water Effect on CO2 Utilization and Geological Storage

Understanding nanoconfined water effect on CO2 utilization and storage has tremendous implications in academic research and practical applications, especially for extremely low-permeability shale reservoirs. Here, a new nanoscale-extended cubic-plus association equation of state is developed by including the confinement effects and intermolecular interactions, based on which the phase behavior and interfacial tension of the pure water and water-CO2 system are accurately calculated. Moreover, three important parameters, caprock-sealing pressure, maximum storage height, and storage capacity, are quantitatively determined for assessing the potential for the CO2 storage. On the basis of the results from this study, the negative effect of nanoconfiend water can be substantially reduced or even converted to be positive for the CO2 utilization and storage in the shale reservoirs due to the extremely small pore scale as well as the associated strong confinements and intermolecular interactions. Overall, this study supports the foundation of general practical applications pertaining to CO2 utilization and geological storage in unconventional low-permeability shale formations with existence of nanoconfined water. Plain Language Summary CO2 utilization and geological storage is an emerging topic in energy and environmental community. Nanoconfined water, either from the natural connate or anthropogenic injected/residual source, is an inevitable topic for CO2 utilizations and storages in geological media. However, most existing theories/methodologies specialized in CO2 utilization and geological storage are restricted to the conventional large-scale porous media without water effect, which may lose effectiveness/accuracy for extremely confined geological media, for example, shale formations. On the other hand, supplies of geological sites with conventional pore scale are badly limited; meanwhile, abundant geological media with unconventional extremely small pores are available and appropriate for CO2 utilization and storage worldwide. This study initially proposes a theoretical method to characterize the CO2 utilization and geological storage at the nanometer scale and investigate the associated nanoconfined water effect. Qualitative and quantitative analyses fill the knowledge gap of the nanoscale water and CO2 behavior. Also, solid scientific results/supports from this study are provided for various academic researches and practical applications, such as the energy and environment and biotechnologies. Therefore, as a comprehensive work consisting of fundamental research and practical applications, this paper shares a wide readership on the areas of science and engineering concurrently.