The Rheology of Swelling Clay Dispersions

Nearly all muds, in drilling applications, contain smectite clay minerals, such as montmorillonite or hectorite, which have the remarkable property of swelling in the presence of water. Such systems are known to exhibit long-term gelation and thixotropic behavior, of great importance in applications, depending on clay volume fraction, particle properties (origin of the clay, surface charge, etc.) and solvent conditions (pH, ionic strength, etc.) [1-6]. Mainly two mechanisms for gel formation of smectite clays have been proposed up to now: electrostatic attraction between the positively charged edges and negatively charged faces of the platelets, resulting in a card-house structure, [7] and long-range electrostatic repulsion between interacting double layers of clay particles [8]. According to recent works, the latter mechanism has appeared to be the most probable one. The rheological results presented in the paper have been obtained with a synthetic hectorite-type clay, namely Laponite, often considered as a model reference smectite clay. The data will be compared to those of the literature.