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AGU: Geophysical Research Letters

 

Keywords

  • electrical conductivity
  • electromagnetic methods
  • gas hydrate
  • ice
  • impedance spectroscopy
  • methane

Index Terms

  • Marine Geology and Geophysics: Gas and hydrate systems
  • Marine Geology and Geophysics: Marine electromagnetics
  • Mineral Physics: Electrical properties
  • Paleoceanography: Greenhouse gases
  • Physical Properties of Rocks: Magnetic and electrical properties

Abstract

GEOPHYSICAL RESEARCH LETTERS, VOL. 38, L09313, 5 PP., 2011
doi:10.1029/2011GL047243

Electrical properties of polycrystalline methane hydrate

Key Points
  • We developed a pressure cell to synthesize and measure sigma of gas hydrate
  • We determined the sigma of CH4 hydrate to be 5 × 10−5 S/m at 0° C
  • Sigma measurements are a factor of ∼4 and Ea is ∼50% lower for CH4 hydrate than ice

Wyatt L. Du Frane

Lawrence Livermore National Laboratory, Livermore, California, USA

Laura A. Stern

U.S. Geological Survey, Menlo Park, California, USA

Karen A. Weitemeyer

Scripps Institution of Oceanography, La Jolla, California, USA

Steven Constable

Scripps Institution of Oceanography, La Jolla, California, USA

John C. Pinkston

U.S. Geological Survey, Menlo Park, California, USA

Jeffery J. Roberts

Lawrence Livermore National Laboratory, Livermore, California, USA

Electromagnetic (EM) remote-sensing techniques are demonstrated to be sensitive to gas hydrate concentration and distribution and complement other resource assessment techniques, particularly seismic methods. To fully utilize EM results requires knowledge of the electrical properties of individual phases and mixing relations, yet little is known about the electrical properties of gas hydrates. We developed a pressure cell to synthesize gas hydrate while simultaneously measuring in situ frequency-dependent electrical conductivity (σ). Synthesis of methane (CH4) hydrate was verified by thermal monitoring and by post run cryogenic scanning electron microscope imaging. Impedance spectra (20 Hz to 2 MHz) were collected before and after synthesis of polycrystalline CH4 hydrate from polycrystalline ice and used to calculate σ. We determined the σ of CH4 hydrate to be 5 × 10−5 S/m at 0°C with activation energy (Ea) of 30.6 kJ/mol (−15 to 15°C). After dissociation back into ice, σ measurements of samples increased by a factor of ∼4 and Ea increased by ∼50%, similar to the starting ice samples.

Received 23 February 2011; accepted 4 April 2011; published 11 May 2011.

Citation: Du Frane, W. L., L. A. Stern, K. A. Weitemeyer, S. Constable, J. C. Pinkston, and J. J. Roberts (2011), Electrical properties of polycrystalline methane hydrate, Geophys. Res. Lett., 38, L09313, doi:10.1029/2011GL047243.

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