Knowledge of electrical properties of GH-bearing media is useful in hydrate pros­pecting and monitoring HBS undergoing changes during gas production. Either electrical conductivity or permittivity can be used to distinguish between water and non-water pore filling materials such as hydrate and gas. Electrical conductivity is dominated by the conductivity of the pore fluid; however, surface conduction must be considered for high surface area sediments [81]. Under conditions where hydrate forms or dissociates, the pore fluid conductivity will change due to freshening (hydrate dissociation) or ion exclusion (hydrate formation). Because the effect of ionic concentration is much weaker for the permittivity, this may be the more reli­able indicator in many circumstances. The systematic examination of the effects of THF hydrate on the electrical properties of various media [104, 106] provided use­ful qualitative insights, but applicability to methane systems has not been deter­mined. No comprehensive study has been performed for methane HBS, studies on which has been limited to measurements of electrical resistivity of a few samples [182-185].

5.2.3 Geophysical Properties: Wave Velocities and Attenuation

These are critically important in the exploration, detection, and production monitoring of GH. Compressional (P-) and shear (S-) wave speeds have been measured in a variety of medium/hydrate combinations [6, 219], but these did not involve CH4 and the results have qualitative value for HBS studies. Waite et al. [208] measured the P — and S-wave velocities of methane hydrates in Ottawa sand at different SH. These hydrates were formed using the excess gas method and cemented the grains of the sand, resulting in very stiff samples. No systematic tests examining P — and

S-wave velocities for a variety of porous media types at a range of methane SH and pore-filling habits have been published, but such tests are now in progress.