Review of CO2 ocean sequestration technology using hydrate method: Feasibility and influencing factors

CO2 sequestration has gained significant attention as a potential solution to the greenhouse effect caused by massive CO2 emissions from industrial activities and fossil fuels. However, land-based saline aquifer sequestration methods face challenges such as low efficiency, insufficient phase stability and reservoir safety. In contrast, the hydrate method, an ocean sequestration technique, involves introducing CO2 into seabed or depleted mineral sediments under suitable thermodynamic and pore conditions, where water and CO2 molecules form stable, solid, non-stoichiometric crystalline compounds, offering higher efficiency, improved phase stability and enhanced safety. This article systematically reviews the latest advancements in CO2 hydrate ocean sequestration techniques focusing on direct injection and CH4-CO2 replacement methods, in terms of both sequestration efficiency and safety. Sequestration efficiency is affected by many factors. It can be improved by adjusting the sequestration conditions, involving additives, or by combining multiple methods to enhance the reaction's driving force. The hydrate method is considered superior in safety, as the sediment layer gains strength through the cementation of hydrates with sediments, thereby improving reservoir stability. The CH4-CO2 replacement technique maintains the original stable clathrate structure of hydrates, replacing only guest molecules without affecting the cementing structure's stability. Therefore, the hydrate-based sequestration method shows significant potential in effectively balancing efficiency and safety, contributing to the accelerated commercialization of CO2 capture, utilization, and storage (CCUS).