Electrical properties of polycrystalline methane hydrate

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 (sigma). 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 s. We determined the sigma of CH4 hydrate to be 5 x 10(-5) S/m at 0 degrees C with activation energy (E-a) of 30.6 kJ/mol (-15 to 15 degrees C). After dissociation back into ice, sigma measurements of samples increased by a factor of similar to 4 and E-a increased by similar to 50%, similar to the starting ice samples. 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.