Gas transport properties of compacted bentonite

The gas permeability of the FEBEX and the MX-80 bentonites compacted at dry densities of between 1.4 and 1.8 g/cm(3) with different water contents was measured for different confining, injection and backpressures. It was checked that gas permeability was greatly affected by dry density and water content, decreasing with the increase of both. Gas permeability was mainly related to the accessible porosity (inverse to liquid degree of saturation), through a potential expression with exponent close to 3. The lower gas permeability of MX-80 can be attributed to its finer grain size. For gas pressures below 1.2 MPa no significant effect of the injection or confining pressures on the value of permeability was detected. The Klinkenberg effect was not significant for these materials in the range of pressures applied in the tests.