The aim of this work is to evaluate the influence of dispersants additives and anionic surfactants in the apparent viscosity (AV), plastic viscosity (PV), water loss (WL) and filter-cake thickness (FT) of the water based drilling fluids with bentonite clay. The fluids were prepared with 4.86 wt % of bentonite clay and the additives studied in the concentrations of 0.025 g to 0.300 g/24.3 g of dry clay for the dispersants and 0.005 g to 0.300 g/24.3 g of dry clay for the anionic surfactant. The results had shown the filter-cake thickness was significantly reduced by the presence of the anionic surfactant, without, however, to modify the taxes of filtration of studied fluids. As it was waited, it was observed the reduction in the values of AV and PV after treating the fluids with dispersants addictives. Also, the abrupt change in the values of AV, PV and FT of fluids treated with the anionic surfactant in the concentration of 0.100 g/24.3 g of dry clay evidenced that this is very probably the critical concentration micelar of this additive.
drilling fluids; apparent and plastic viscosities; filter-cake thickness; dispersants; anionic surfactant
