HYDRATE FORMATION GAS PERMEABILITY VARIATIONS IN GAS-FILLED SOILS UPON HYDRATE FORMATION AND FREEZING: AN EXPERIMENTAL STUDY

Variations in gas permeability of laboratory-formed sand samples exposed to hydrate saturation and freezing are studied experimentally. The experiments are performed in a specially designed system to evaluate the permeability of pressurized wet disperse materials during formation and dissociation of pore gas hydrates, as well as during freezing and thawing of hydrate-bearing samples. Permeability depends on the fraction of pore water converted to hydrate, and the dependence is different as a function of lithology and initial water saturation. Consuming 70–80 % of pore water by hydrate formation reduces the gas permeability of sand and silt with the initial water content 14–18 % by one or two orders of magnitude. Freezing of hydrate-bearing samples makes their permeability times lower upon freezing of residual pore water and additional hydrate formation.