Experimental and numerical investigation on the chemical osmotic and poroelastic behaviors of mudstone

Abstract

Mudstone is supposed to behave as suitable caprock due to its low permeability, and is also known to show semipermeable membrane characteristics. Therefore, better understandings on the coupled processes among groundwater flow, solute transport, and deformation of mudstone are highly warranted. In this study, laboratory-scale experiment was conducted by using a mudstone sample collected from Tokamachi, Niigata Prefecture. The sample which was saturated with low NaCl concentration solution was in contact with higher NaCl concentration solution, and circumferential strains were measured by fiber-optic strain sensor. About 150 με of contractional strain was observed by applying ca. 15g/L of concentration difference. Type curves to explain transient strain behavior were developed by using the numerical model which can handle coupled chemical osmotic and poroelastic behaviors, and it was found that, except for the latter stage of the experiment, strain behaviors were quite well fit with the type curves. It was also possible to estimate some of the physical properties of the sample from the fitting result.