Experimental examination of the relationships among chemico‐osmotic, hydraulic, and diffusion parameters of Wakkanai mudstones

Abstract

Sequential permeability and chemical osmosis experiments on Wakkanai mudstones were performed to explore the relationships between the semipermeability of clayey rocks and the hydraulic and diffusion parameters as well as the pore structure characteristics. The wide ranges in osmotic efficiency (0.0004-0.046) and intrinsic permeability (8.92 × 10 À20 to 1.24 × 10 À17 m 2 ) reflect the variation in the pore size distributions of the Wakkanai mudstones. A regression analysis between osmotic efficiency and permeability shows that the osmotic efficiency is proportional to the inverse of permeability, suggesting that the permeability is indeed indicative of the degree of semipermeability. Osmotic efficiency was determined invariant with the effective diffusion coefficient for the Wakkanai mudstones (3.59-8.36 × 10 À11 m 2 /s) due to their small osmotic efficiencies (≤0.046). The wide variation in osmotic efficiencies and pore structure characteristics of Wakkanai mudstones indicates that the nanoscale pores enable semipermeability in Wakkanai mudstones. However, the pressure evolution caused by chemical osmosis is limited by the connected wide pores that are the main conduits for water, thus dissipating the osmotic pressure buildup induced by the semipermeability of nanoscale pores.

Effects of Confining Stress on the Semipermeability of Siliceous Mudstones: Implications for Identifying Geologic Membrane Behaviors of Argillaceous Formations

“…To estimate the effective surface charge densities, Γ s , the specific surface area ( A s ) and cation exchange capacity (CEC) were measured for the remains of the cores by the Brunauer‐Emmett‐Teller method (Brunauer et al, ) and by the column leaching method, respectively. A s and the CEC are 66.8 m 2 /g and 23.5 cmol/kg, respectively, for the sample taken from the depth of 401 m and 52.6 m 2 /g and 24.9 cmol/kg, respectively, for the sample from 698 m. Γ s calculated from A s and the CEC are 0.34 and 0.46 C/m 2 for the samples taken from the depths of 401 and 698 m, respectively, indicating that the potential membrane effects of our samples were comparable to that of other argillites (Takeda et al, , and references therein). The pore characteristics were evaluated by HRTEM and by mercury intrusion porosimetry.…”

“…Since evidence for the geologic membrane behavior of argillites has been obtained from in situ borehole experiments in the Pierre Shale performed by Neuzil (), the semipermeability has been extensively investigated for other argillites including Opalinus Clay (Horseman et al, ; Noy et al, ), Boom Clay (Garavito et al, ), Callovo‐Oxfordian argillite (Cruchaudet et al, ; Gonçalvès et al, ; Gueutin et al, ; Rousseau‐Gueutin et al, , , ; Tremosa et al, ), and Wakkanai mudstones (Takeda et al, ). However, few attempts have been made to clarify the stress dependence of the argillite semipermeability, whereas the other transport properties of argillites, such as the permeability and diffusivity, have already been shown to be stress dependent (e.g., Dong et al, ; Kwon et al, ; Rahman et al, ; Selvadurai & Jenner, ; Uehara et al, ; Van Loon et al, ; Yang & Aplin, ).…”

Responses of chemically active and naturally fractured shale under time‐dependent mechanical loading and ionic solution exposure

“…Ewy tested 9 clay‐rich shale samples under humidity control and brine contact and showed the distinct relationships among the saturation, suction, and volume change. There are also direct measurements of rock poromechanical and chemo‐electro parameters (Rousseau‐Gueutin et al for membrane coefficient of Callovo‐Oxfordian argillite samples; Takeda et al for permeability, chemical diffusion coefficient, and membrane coefficient of Wakkanai mudstone samples). Bunger et al implemented the triaxial test on millimeter‐scale shale samples.…”

Semipermeable Membrane Properties and Chemomechanical Coupling in Clay Barriers

“…The effective pore size, i.e., the average value representative of macroscopic volume of porous medium, was estimated by using the simple mass balance equation given by Neuzil (2000) valid in a plane-parallel conceptual model for the porous media and which is written as (Takeda et al, 2013), Bearpaw formation (4) (Cey et al, 2001), and Bulldog, North sea, Pierre II, Muderong shales (@) (Bunger et al, 2014). The maximum concentration was used since osmotic efficiency decreases with salinity, the lower value controls the measured osmotic flux.…”