The applicability of X-ray CT method to the visualization and the analysis of water permeation process were discussed. Here the one-dimensional water permeation tests by using Kimachi sandstone were conducted. The effect of the confining pressure together with the effect of suction was analyzed, and the procedure to evaluate coefficient of permeability was discussed under the assumption that the samples have macroscopically homogeneous structure as for water permeation. It was found from the results of visualization that permeation process is almost uniform and confirmed that the assumption of one-dimensional permeation can be applicable. By applying the introduced technique, the coefficient of permeability was correctly evaluated. The pressure dependency of coefficient of permeability was emerged and the good applicability of X-ray CT to the analysis of permeation phenomena was shown. The heterogeneity of water permeation was also discussed and it was found that the effect of the heterogeneity is negligible in the case of Kimachi sandstone.
X-ray computed tomography (CT) is well known as nondestructive medical imaging technique, which makes it possible to evaluate the attenuation of X-ray at each point within a body, by digitizing shadow pictures taken from various directions and subsequent image reconstruction. This technique has been applied for the measurements of geomaterial properties, such as soils and rock (Arthur, 1971 Verhelst et al., 1995). The migration of fluid fronts in rock has been studied by Cromwell et al. (1984) and the subtraction of CT images has been utilized to identify the water saturation process by Coles et al. (1991) and Sugawara et al (1999). Through these studies, It has been revealed that X-ray CT is an effective tool for visualization of the pore structure and of transitional phenomenon such as water permeation process in rock. The applicability of X-ray CT method to the visualization and the analysis of water permeation process is discussed. Here the one-dimensional water permeation tests by using Kimachi sandstone are conducted and image processing techniques are applied to visualize the water permeation process. In this permeation tests, rock sample is under the hydrostatic pressure condition. Therefore, confining pressure that is equal to the inlet pressure is always acting on the rock sample. The effect of the confining pressure together with the effect of suction is analyzed, and the procedure to evaluate parameters related to the permeation is discussed.
The system of permeation tests is shown in Figure I. As this figure shows, the system is composed of the cylindrical pressure vessel and the temperature and pressure control system located above the pressure vessel. In order to avoid from the attenuation of X-ray, the pressure vessel is made from acrylic resin. Heater and temperature sensor are installed in the pressure vessel and the temperature can be raised up to 60 °c. During the experiments, hydrostatic pressure is always acting on the rock sample, since the inside of pressure vessel is filled with the water and pressurized.