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

Abstract

The semipermeability arising from filtration effects on ionic species at the pore spaces in clay minerals has been recognized as a fundamental transport property of argillites. However, little is known about the dependence of the semipermeability on the confining stress that controls the pore sizes. Thus, we investigated the evolution of the semipermeability during cyclic loading by performing chemical osmosis experiments on siliceous mudstones. Results show that the semipermeability irreversibly increases with increasing confining stress, but once the stress exceeds the past maximum effective burial stress, it reversibly changes in accordance with the change in the stress. The net increase in the semipermeability from the first loading cycle to the last unloading cycle implies the irreversible shrinking of pores that should have expanded owing to stress relief before testing. The reversible change in the semipermeability probably reflects the reversible pore deformation due to the elasticity of argillites in the overconsolidated state.