Metodologia de ajuste de parâmetros de modelos de fluido viscoelástico diferenciais com base em dados reológicos

Abstract

In this work a methodology for parameter fitting of the Maxwell, PTT, Giesekus and FENE-P constitutive equations from rheological data is developed. An important application of this study is the correct characterization of viscoelastic fluids, which allows, for example, reliable numerical simulation involving such fluids, once the parameters and models used will correctly describe the studied fluids. The proposed methodology has shown to be effective, since results from other works have been reproduced and there was agreement between experimental data and results predicted by rheological models. The linear viscoelastic model was able to predict with good accuracy the values of the storage and loss moduli obtained from small- amplitude oscillatory tests. Among the three non-linear models analysed, the Giesekus and FENE-P models were able to approximate the viscosity behavior of the drilling fluid BRMUL 116 as a function of the shear rate. The use of these models is therefore recommended for numerical simulations of drilling fluids. It is concluded that results obtained from linear viscoelasticity experiments must not be extended to shear flow parameter fitting, so the relaxation spectrum should be recalculated for such experiments. Although viscoelastic effects have been observed in drilling fluids, such effects are not very relevant when compared to polymer solutions.