HR: 0830h
AN: OS51B-0845    [PDF]
TI: Nucleation and Growth of Gas Hydrate in Natural Seawater
AU: * Holman, S A
EM: sah@mdswater.com
AF: Marine Desalination Systems, 1120 Connecticut Ave. NW Suite 461, Washington, DC 20036 United States
AU: Osegovic, J P
EM: josegovic@mdswater.com
AF: Marine Desalination Systems, 1120 Connecticut Ave. NW Suite 461, Washington, DC 20036 United States
AU: Young, J C
EM: jimyoung@mdswater.com
AF: Marine Desalination Systems, 1120 Connecticut Ave. NW Suite 461, Washington, DC 20036 United States
AU: Max, M D
EM: mmax@mdswater.com
AF: Marine Desalination Systems, 1120 Connecticut Ave. NW Suite 461, Washington, DC 20036 United States
AU: Ames, A L
EM: aames@mdswater.com
AF: Marine Desalination Systems, 1120 Connecticut Ave. NW Suite 461, Washington, DC 20036 United States
AB: Large-scale nucleation of gas hydrate takes place when hydrate-forming gas and seawater are brought together under suitable pressure-temperature conditions or where dissolved hydrate-forming gas in saturated or near-saturated seawater is chilled or brought to higher pressures. Profuse formation of hydrate shells on gas bubbles and nucleation of at least five different forms of gas hydrate have been achieved in fresh natural seawater. Growth of masses of solid gas hydrate takes place when hydrate-forming gas reactant dissolved in seawater is brought into the vicinity of the hydrate. The gas concentration of the enriched water in the vicinity of hydrate is higher than the hydrate equilibrium gas concentration. Hydrate growth under these conditions is accelerated due to the chemical potential difference between the enriched water and the hydrate crystals, which induces mass flux of dissolved hydrate forming gas into new hydrate crystals. As long as water enriched in the hydrate-forming gas is circulated into the vicinity of the hydrate, growth proceeds into the water space. Experimental approaches for growth of examples of solid masses of hydrate are presented. Results of these experiments provide an insight into the growth of gas hydrate under natural conditions where interstitial water in marine sediments is captured by burial from open seawater, and where solid gas hydrate forms on the seafloor. By using fresh natural seawater, which is a chemically and materially complex fluid, our experiments in pressurized, refrigerated reactors should closely track the growth history of solid hydrate in the natural environment. In our model for hydrate growth in sediments, nearly complete pore fill by diagenetic hydrate can best be accomplished by nucleation of hydrate at a point source within the pore water or at a particular point on sediment particulate, with growth outward into the water space that is refreshed with ground water having high concentrations of hydrate-forming gas. Best growth can be achieved by circulation of water through constricting pore space although dissolved gas will also migrate along diffusion gradients.
DE: 1806 Chemistry of fresh water
DE: 1823 Frozen ground
DE: 3022 Marine sediments--processes and transport
DE: 4806 Carbon cycling
DE: 4820 Gases
SC: Ocean Sciences [OS]
MN: 2003 Fall Meeting