ABSTRACT
Shear tests using a coaxial cylinders viscometer were performed in order to determine the rheological properties of xanthan gum dispersions with sodium bentonite in the presence of different concentrations of sodium chloride (NaCl) and a fixed concentration of calcium chloride (CaCl2) at room temperature. The dispersions rheology with different concentrations of NaCl and sodium bentonite were prepared by fixing the xanthan gum and CaCl2 concentrations of 0.47% and 0.455% respectively (both mass percentages) using deionized water. The dispersions showed a good fit to modified power rheological model (Herschel-Bulkley) by non-linear regressions. A Central Composite Design was made for two levels. The independent variables were sodium bentonite and sodium chloride concentrations and the dependent variables were the yield point (τ0), the consistency index (k) and the flow index (n). Samples were prepared with stirring 24 hours in advance and the measurement of the rheological curve points were obtained by Haake viscometer. The results of the analysis showed that the yield stress is strongly influenced by the concentration of bentonite while the consistency and flow indexes are influenced by both sodium chloride and sodium bentonite concentrations. These results show that it is possible to improve the performance of clay drilling fluids through manipulation of salts and clay content.
Keywords:
Drilling fluids; bentonite; rheology.
