HR: 1340h
AN: OS43A-0606    [Abstracts]
TI: Conditions for Fromation of Oceanic Natural Gas Hydrate Deposits
AU: * Max, M M
EM: mmax@mdswater.com
AF: Marine Desalination Systems, 1601 3rd St. South, St. Petersburg, FL 33701 United States
AB: Despite the widespread nature of oceanic natural gas hydrate and associated gas concentrations on continental margins, natural gas hydrate has yet to be proven to be an economically viable unconventional gas resource. In part, this is because unequivocal models for the formation of economic hydrate deposits do not yet exist and there is no exploration methodology for identifying the high-grade hydrate sweet spots that will constitute economic hydrate deposits. At this time, it appears that the most commercially viable high-grade hydrate deposits consist of naturally permeable strata that hosts a high proportion of solid hydrate filling of original porosity. The different means by which hydrate grows and the optimum conditions for the maintenance of a strong growth dynamic provide a key to predicting the location of potential hydrate deposits. Hydrate has been produced from natural seawater, which is a close approximation of connate water in marine sediments, and a variety of Hydrate Forming Gases (HFG) using several different types of crystallizers in laboratory experiments. The crystallizers have been developed to test a broad range of hydrate growth conditions by controlling pressure, temperature (or temperature gradients), and HFG saturation levels. Growth has been achieved in both aqueous and gaseous media. These results provide insight into formation of natural gas hydrate and may constrain the search for economic hydrate deposits Natural gas hydrate forms in one of three main growth modes in aqueous media; mineralizing solutions, diffusion in aqueous media, and solid diffusion. When the relative potential for growth of these modes are assessed along with geological and ground (pore) water provincing, the most likely locations within the gas hydrate stability zone (GHSZ) for recoverable hydrate natural gas deposits may be identified. The most rapid mode for growth of solid hydrate takes place on the seafloor in the presence of venting. Natural gas-rich fluids and natural gas produce strongly oversaturated seawater in which hydrate will grow rapidly upon cooling by heat transfer with seafloor water. The growth dynamic for incorporation of dissolved hydrate-forming reactants in seafloor hydrate is at a maximum under these conditions and acts in such a way that hydrate grows out into the seawater growth media, which is in effect the mineralizing solution, resulting in large volumes of solid hydrate. Within marine sediments, the same growth dynamic occurs where pore water percolation can deliver a large volume of dissolved HFG that will rapidly be incorporated in growing hydrate as the saturated water is chilled in the GHSZ. These mineralizing solutions cause the diagenetic hydrate mineral deposits to form. In an open groundwater system where the water can rise in porous strata into the GHSZ, and where water movement is restricted, diffusion of dissolved natural gas into the GHSZ in the aqueous media will also be associated with a strong growth dynamic that naturally leads to the formation of solid hydrate and high pore fill. Movement of gas into the GHSZ leads to the formation of hydrate shells on gas bubbles or hydrate-sheathed secondary porosity. In this case or where gas is in direct contact with a hydrate-sediment mixture having essentially no permeability, further hydrate growth is only possible by diffusion of either gas and water through the solid hydrate or an additional supply of hydrate-forming gas (HFG)-saturated water, which is a slower process and does not offer the same potential for high pore filling.
UR: http://www.mdswater.com/
DE: 1009 Geochemical modeling (3610, 8410)
DE: 1034 Hydrothermal systems (0450, 3017, 3616, 4832, 8135, 8424)
DE: 1050 Marine geochemistry (4835, 4845, 4850)
DE: 1099 General or miscellaneous
DE: 1829 Groundwater hydrology
SC: Ocean Sciences [OS]
MN: Fall Meeting 2005