CO2 sequestration in depleted methane hydrate deposits with excess water

The recent increase in atmospheric CO2 concentration makes it necessary to investigate new ways to reduce CO2 emissions. Simultaneously, natural gas hydrate mining technology is developing rapidly. The use of depleted methane hydrate (MH) deposits as potential sites for CO2 storage is relatively safe and economical. This method can alleviate the shortage of hydrate displacement gas with CO2. The purpose of this study was to investigate CO2 hydrate formation characteristics during the seepage process-in reservoirs with excess water-and their effect on CO2 storage. The experimental process can be divided into 5 parts: MH formation, water injection, MH dissociation, CO2 hydrate formation, and CO2 hydrate dissociation. Magnetic resonance imaging was employed to monitor the distribution of liquid water, and the effects of different parameters on the formation and dissociation of CO2 hydrates were analyzed. It was found that a state of initial water saturation can effectively control hydrate saturation in artificial MH reservoirs for hydrate reservoirs with excess gas. In the process of CO2 flow, initial water saturation was not the main controlling factor for CO2 hydrate formation. Increasing the flow pressure and reducing the flow rate were beneficial for CO2 hydrate formation. This study is of great significance for advancing the science of CO2 geological storage in the form of deep-sea hydrates.