Fluid flow and chemical transport in clay-rich media implicated by pore geometry and connectivity

粘土を主体とする媒体中の地下水流動と物質移行の間隙形状と連続性に基づく評価

Hu, Q.*; Wang, Q. M.*; Zhao, C.*; Zhang, T.*; Iltaf, H.*; 舘 幸男  ; 深津 勇太  

Hu, Q.*; Wang, Q. M.*; Zhao, C.*; Zhang, T.*; Iltaf, H.*; Tachi, Yukio; Fukatsu, Yuta

Fine-grained and clay-rich mudrocks play an important role in the long-term performance of a geological repository for storing high-level nuclear wastes and petroleum production in shale formations. However, low-permeability mudrocks whose pores are poorly interconnected are known to have anomalous diffusion properties that strongly impact long-term net diffusion. The complex pore structure involving predominantly nano-sized pore space is related to compaction and diagenesis from the maturation process of organic matter-rich mudrocks at deep depths, leading to a much smaller effective porosity. Working with various clay minerals, shallow clayey sediments of Wakkanai formation around Horonobe URL in Japan and Opalinus clay of Mt. Terri URL in Switzerland, as well as various deep shales (Barnett, Eagle Ford and Wolfcamp from Texas), using a wide range of sample sizes, this multi-approach and -scale work utilizes a complementary suite of techniques for pore structure characterization (e.g., mercury intrusion porosimetry, small angle X-ray/neutron scattering, scanning electron microscopy), gas diffusion, batch sorption and column transport. The experimental results show that deep mudrocks has a much poor pore connectivity than the shallow ones, and the effective porosity, diffusion coefficients, sorption coefficients are also dependent upon the sample sizes used in the measurement.