1. Steacie Institute for Molecular Sciences, National Research Council of Canada Ottawa, Ontario, Canada K1A 0R6
2. School of Earth and Ocean Sciences, University of Victoria, Victoria, Canada V8W 3P6
3. Naval Research Laboratory, Washington DC 20375, USA
4. Institute of National Measurement Standards, National Research Council Canada, Ontario, Canada K1A 0R6
5. Present addresses: New Energy Research Department, Korea Institute of Energy Research, 71-2, Daejeon 305-343, Korea (Y.S.); Department of Environmental Engineering, Konju National University, Chungnam 330-717, Korea (J.L.).

Correspondence to: John A. Ripmeester¹ Correspondence and requests for materials should be addressed to J.A.R. (Email: john.ripmeester@nrc-cnrc.gc.ca).

Abstract

Natural gas hydrates are a potential source of energy¹ and may play a role in climate change² and geological hazards³. Most natural gas hydrate appears to be in the form of 'structure I', with methane as the trapped guest molecule⁴, although 'structure II' hydrate has also been identified, with guest molecules such as isobutane and propane, as well as lighter hydrocarbons^{5, 6}. A third hydrate structure, 'structure H', which is capable of trapping larger guest molecules, has been produced in the laboratory⁷, but it has not been confirmed that it occurs in the natural environment. Here we characterize the structure, gas content and composition, and distribution of guest molecules in a complex natural hydrate sample recovered from Barkley canyon, on the northern Cascadia margin⁸. We show that the sample contains structure H hydrate, and thus provides direct evidence for the natural occurrence of this hydrate structure. The structure H hydrate is intimately associated with structure II hydrate, and the two structures contain more than 13 different hydrocarbon guest molecules. We also demonstrate that the stability field of the complex gas hydrate lies between those of structure II and structure H hydrates, indicating that this form of hydrate is more stable than structure I and may thus potentially be found in a wider pressure–temperature regime than can methane hydrate deposits.

MORE ARTICLES LIKE THIS

These links to content published by NPG are automatically generated.