Diffusivity anisotropy in a rhyolite and its relation to pore structure

✍ Scribed by Tadashi Yokoyama; Satoru Nakashima

• Publisher: Elsevier Science
• Year: 2005
• Tongue: English
• Weight: 501 KB
• Volume: 80
• Category: Article
• ISSN: 0013-7952
• DOI: 10.1016/j.enggeo.2005.07.002

✦ Synopsis

The diffusivity anisotropy of ions through rock pore water was evaluated quantitatively by through-diffusion experiments on a rhyolite rock having anisotropic pore structure. The rhyolite has planar flow structure with elongated pore shapes to the flow direction (X-Y plane). Diffusion coefficients of K + ions for the direction perpendicular to this flow structure (Z-direction) were about 5-9 times smaller than those for the orthogonal parallel directions (X-and Y-direction). Pore geometrical analyses on backscattered electron microscopic images indicated that the pore length ratios among the X-, Y-, and Z-direction were roughly 2 : 2 : 1. This shorter pore length for the Z-direction appears to reduce pore connectivity, causing larger tortuosity and smaller diffusivity for this direction. This diffusivity anisotropy needs to be taken into account for precise modeling of diffusion-limited geological processes such as contaminant transport and rock deformation.