Formation and Dissociation of Gas Hydrates in a Seafloor Process Simulator

Clathrate hydrates are solid crystalline structures in which water hydrogen-bonded cages are stabilized by the presence of gas molecules inside the cages. The conditions for the formation and stability of gas hydrates involve pressures much higher than atmospheric and temperatures a few degrees above the freezing point of water. Natural gas hydrates can be found in coastal sediments or the permafrost, and their exploitation constitutes an attractive future source of energy. CO2 hydrate has been considered as a medium for ocean carbon storage. In this presentation, we will examine interfacial effects on hydrate formation and dissociation. Hydrate is formed either in sediment or in the water column in a 72-L vessel, the ORNL Seafloor Process Simulator (SPS). SPS is made of hastelloy and allows pressures up to 3,000 psi. It has several windows for monitoring devices including thermocouples, pressure and sound velocity transducers, and video cameras. The conditions of hydrate formation and dissociation with respect to the thermodynamic stability diagrams are examined for different types of gas hydrates and for different media.