Deep sea NMR: Methane hydrate growth habit in porous media
and its relationship to hydraulic permeability, deposit
accumulation, and submarine slope stability

R. L. Kleinberg, C. Flaum, and D. D. Griffin
Schlumberger-Doll Research, Ridgefield, Connecticut, USA

P. G. Brewer, G. E. Malby, and E. T. Peltzer
Monterey Bay Aquarium Research Institute, Moss Landing, California, USA

J. P. Yesinowski
Naval Research Laboratory, Washington, District of Columbia, USA

Journal of Geophysical Research (2003) 108(B10) 2508. doi:10.1029/2003JB002389.

Received: 2003 January 3.
Revision received: 2003 May 22.
Accepted: 2003 July 3.
Published: 2003 october 9.


ABSTRACT

Review of the literature reveals that the nature of pore-scale interactions between gas hydrates and porous media remains a matter of controversy. To clarify the situation, nuclear magnetic resonance (NMR) measurements have been made on methane hydratebearing sandstones. The samples were synthetically prepared within the gas hydrate stability zone, at or near the seafloor in Monterey Bay, California. The method simulated natural hydrate deposition by gas flows that are not in thermodynamic equilibrium with the surrounding earth. The efficiency of hydrate production was variable, as has been observed elsewhere. When substantial hydrate saturations were achieved, NMR relaxation time measurements indicated that hydrate tended to replace water in the largest pore spaces. The relative permeability to water, as determined by an NMR-based correlation, was significantly reduced. The magnitude of this reduction was also consistent with formation of hydrate in the centers of pores, rather than with hydrate coating the grains. The growth habit suggested by these results is consistent with creation of hydrate nodules and lenses in coarse, unconsolidated sediments. It is also consistent with scenarios in which methane gas is delivered efficiently to the atmosphere as a result of seafloor slope failure, thereby strengthening global warming feedback mechanisms.

© 2003 by American Geophysical Union.


Acknowledgements

We gratefully acknowledge C. Straley and M. B. Helgerud for discussions and Straley for providing us with data on the relaxivity of the water-hydrate interface in advance of publication. We also thank C. Ruppel for permission to cite her work prior to publication. J. P. Y. acknowledges support to National Research Laboratory (NRL) from the Office of Naval Research. The success of the experiments depended on the skill and patience of the captain and crew of the R/V Western Flyer and the pilots of the ROV Tiburon.


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