Experimental and Modeling Studies on Gas Migration in Kunigel V1 Bentonite

Tanai, Kenji ; Yamamoto, Mikihiko*

The knowledge obtained from previous studies are as follows, i) The gas permeabilities are 10mfor the 30wt% sand mixtures at a dry density of 1.6 Mg mand 10to 10mfor the bentonite (100%) at a dry density of 1.8 Mg m, ii) The breakthrough pressure seems to be almost the same as the swelling pressure at constant volume condition, iii) Gas pathways created during the first gas injection period are closed due to bentonite swelling during the resaturation period. For the recent experiment, it is obtained two peak of gas flow rate. In particular, maximum flow rate at secondary peak is obtained apploximately 1667cc min. This peak is probably indicative of generation of cracks in the specimen by particle displacement. Breakthrough pressure (2.5 MPa) is larger than the swelling pressure of the bentonite (swelling pressure is approximately 1.0 MPa at a dry density of 1.6 Mg m). It may be that there is a time lag between the gas pressure change in the clay and expansion of cracks due to large pumping rate (0.05 cc min-1). The gas migration pathways are unstable due to stress condition in bentonite specimen and/or heterogeneity of specimen. The distribution of bulk density in the specimen was measured to demonstrate that X-ray CT was reliable new technique for the non-distructive measurement of gas migration through bentonite specimen. The degree of X-ray attenuation depends on the bulk density of the bentonite specimen. The change in bulk density in this test specimen is not cleared from this test case. These experimental results are probably indicative of migration along preferential pathways rather than uniform flow in the matrix of bentonite specimen.