Injecting carbon dioxide (CO₂) into underground geo-structures, such as depleted oil and gas reservoirs, reduces man-made CO₂ emissions into the atmosphere or removes what is already there. Studies have identified the risks of CO₂ leaks from these underground geo-structures through wellbores back into the atmosphere due to the high mobility of CO₂ in gaseous and supercritical states. This work aims at proposing a novel method of CO₂ storage using the Joule–Thomson cooling effect to effectively produce CO₂ hydrates on seafloors, with an objective to avoid the leakage risks of storage in depleted oil and gas reservoirs. Through the combination of thermodynamic data, analysis of hydrate stability, and engineering design with established working parameters, this study proposes an innovative concept and an enabling process for CO₂ placement onto seafloors for safe storage. The results of case analysis of typical seawater conditions reveal that the appropriate seafloor depth ranges for different applications (>1900 m for liquid CO₂ and 700–1900 m for CO₂ hydrate). An engineering design procedure for real applications is outlined.

Disposing carbon dioxide (CO2) in seafloor environment in its hydrate form provides an efficient means of CO2 storage in virtually unlimited quantity. The process requires that the in-situ condition be above the hydrate forming pressure and below the hydrate forming temperature and the bulk CO2-hydrates have densities greater than seawater density for gravitational stability. The objectives of this study are (1) to find an efficient method for generating stable CO2-hydrates, (2) to identify the required equipment for efficient production of CO2-hydrates, and (3) to identify the required water depth in various seawater environments for CO2 injection. The first objective was achieved using a windowed reactor to observe the rising-settling behavior of generated CO2-hydrates. CO2-injection into chilly water phase and water-injection into cold CO2 phase were both investigated in various pressures and temperatures. CO2-injection into chilly water phase was found to generate bulk CO2-hydrates of density less than water density due to the excess CO2 trapped in the bulk hydrates. Water-injection into cold CO2 phase was found to generate bulk CO2-hydrates of density greater than water density due to the excess water trapped in the bulk hydrates. The second objective was achieved by designing a complete set of equipment to be installed on a ship with an open-bottom reactor assembly attached to the ship. The third objective was achieved by cross-plotting hydrate-forming pressure curve versus seawater hydrostatic pressure curve for seven seas and the Arctic Ocean. Result shows that the minimum required seawater depth varies from 120 m in the Arctic Ocean to 650 m in the Mediterranean Sea environment.

Disposing of carbon dioxide (CO₂) in the seafloor environment in its hydrate form provides an efficient means of CO₂ storage in virtually unlimited quantity. The process requires that the in situ condition be above the hydrate-forming pressure and below the hydrate-forming temperature and that the bulk CO₂ hydrates have densities greater than seawater density for gravitational stability. The objectives of this study are (1) to find an efficient method for generating stable CO₂ hydrates, (2) to identify the required equipment for efficient production of CO₂ hydrates, and (3) to identify the required water depth in various seawater environments for CO₂ injection. The first objective was achieved using a windowed reactor to observe the floating and settling behavior of generated CO₂ hydrates. CO₂ injection into the chilly water phase and water injection into the cold CO₂ phase were both investigated at various pressures and temperatures. CO₂ injection into the chilly water phase was found to generate bulk CO₂ hydrates of density less than that of water due to the excess CO₂ trapped in the bulk hydrates. Water injection into the cold CO₂ phase was found to generate bulk CO₂ hydrates of density greater than that of water due to the excess water trapped in the bulk hydrates. The second objective was achieved by designing a complete set of equipment to be installed on a ship with an open-bottom reactor assembly attached to the ship. The third objective was achieved by cross-plotting the hydrate-forming pressure curve versus the seawater hydrostatic pressure curve for seven seas and the Arctic Ocean. Results show that the minimum required seawater depth varies from 120 m in the Arctic Ocean to 650 m in the Mediterranean Sea environment.