Bentonite swelling characteristics with a hypersaline multi-component pore fluid

Abstract

Swelling characteristics of compacted bentonite when hydrated with a hypersaline pore fluid (332 g/L total dissolved solids; 6.6 mol/L ionic strength) are reported. The pore fluid mimics the multiple constituents and their concentrations found for the Cobourg limestone of the Michigan Basin and is dominated by sodium (25% mole fraction) with some potassium, calcium, and magnesium (10%, 5%, and 4% mole fractions). Measurements of swell pressure for two sodium bentonites when hydrated under conditions of zero volume increase are reported. Swell pressure reached a peak within 10–30 h from the onset of hydration, followed by a continual decrease over 1 year of testing from chemical interaction between the bentonite and pore fluid. After 1 year, the swell pressure of the MX-80 bentonite tested decreased by a factor of nine relative to the peak swell pressure with deionized water when the dry density was 1.6 Mg/m3. Swell pressures increased as dry density increased. However, chemical interactions appear to have more influence on swell pressure than density for the pore fluid examined as a swell pressure of just under 1200 kPa was measured for MX-80 after 1.8 years of hydration when compacted to the highest dry density of 1.8 Mg/m3 examined.