Effect of pH and electrolyte on the rheology of aqueous Wyoming bentonite dispersions

The influence of pH between 7.5 and 10.5, for 5% and 6.42% aqueous Wyoming bentonite dispersions and of NaCl for 2%, 5% and 6.42% of Wyoming-bentonite in water for a range of salt concentrations up to 1.0 M has been investigated. The dispersions were prepared according to American Petroleum Institute procedures and rheological data were obtained with a Couette viscometer. Data were represented very well by the Herschel–Bulkley model for all experimental conditions.The effect of pH and electrolyte concentration is significant, affecting the type of association of the montmorillonite particles thus influencing the rheology, the three Herschel–Bulkley parameters and the apparent viscosity. There is a maximum of the yield stress, flow consistency index and apparent viscosity at the natural pH of the dispersions, while there is monotonous decrease of these parameters with increasing salt concentration. Various scenarios of particle associations are discussed and comparison with similar data from literature is also performed.