Estudo do comportamento reológico de suspensões aquosas de bentonita e CMC: influência da concentração do NaCl.

The properties of drilling fluids have a very significant effect on the sucessful of a well completion and the project costs.The experimental study was conducted based on the determination and analysis of the curves of shear stress and shear rate of aqueous suspensions composed of bentonite and carboxymetil cellulose at different concentrations of NaCl.The rheological behaviour of carboxymetil cellulose suspensions 0.5% w/w at NaCl concentrations in the range of 0 to 4% w/w from 14 to 26 °C was studied.The experimental results allow the rheological characterization of these solutions as pseudoplastic fluid.It was observed that the addition of NaCl to CMC solutions changes its rheological behaviour significantly.In addition, the rheological behaviour of 4,8% bentonite suspensions with 0,5% carboxymethyl cellulose at different concentrations of NaCl in the range of 0 to 4% was studied.The characterization of these solutions showed thixotropic behaviour and a strong dependence on the salt concentration.The study was complemented with a comparative analysis of the results obtained by using a coaxial cylinders rheometer model Brookfield and the FANN Model 35 A viscometer, usually employed in drilling fluids analysis.The analytical solutions allowed a more detailed interpretation of the values described in the standard resulting in an equivalence between the measured values obtained in the field and in the Brookfield rheometer despite the differents shear rate ranges.