Determination of the reactivity of clay-fluid systems using liquid limit data

Abstract

The reactivity coefficient, defined as lambda = rhowGsSatheta (rhow is the mass density of water, Gs is the specific gravity, Sa is the specific surface, and theta is the double-layer thickness), has been proposed as a parameter to assess the sensitivity of a clay-fluid system to changes in physical and chemical properties of the pore fluid. In this study, the liquid limit of a clay-fluid mixture, wL, is shown to be related to the reactivity coefficient. Double-layer theory is applied to determine the void ratio at the liquid limit, which is assumed to occur at a stress close to 10 kPa. Liquid limit data were measured for a bentonite clay at different pore-fluid concentrations; other data were collected from the literature. Both measured and collected data followed the proposed simple expression, suggesting that there is a unique relationship between wL and lambda, at least for the three-layer sheet minerals (or for clays with wL > 50). The proposed expression can be used as a simple approach to determine the sensitivity of clay-fluid systems. A parametric study based on the lambda-wL relationship is presented to study the effects of temperature and pore-fluid concentration on the liquid limit.Key words: clay, specific surface, pore fluid, ion concentration, double layer.