Assessment of Production Methods and Locations for CO2 Storage in Seafloor 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.