Relevance. The article is devoted to the study of drilling fluid thickeners based on biopolymers within the framework of power rheological models. The diversity of these models and the multiplicity of approximation purposes for them make it difficult to choose a specific model. Aim. To study the rheological properties of some thickening solutions using the Carreau–Yasuda model. Methods. Analysis of measured rheological viscosity profile data for aqueous solutions of xanthan gum and their approximation using the Carreau–Yasuda rheological model to obtain additional rheological parameters that expand the information characteristics of thickeners. A feature of calculating the nonlinearity index using the Darley method is revealed: if the ratio of the rotational viscometer readings is , the calculated value of the nonlinearity index becomes equal to or greater than one with a measured viscosity profile corresponding to the viscosity profile of a pseudoplastic fluid. The studies were conducted taking into account the requirements for drilling fluids: high viscosity at low shear rates, increased removal capacity, a sharp decrease in viscosity when flowing in narrow gaps, low values of the filtration index. Results and conclusions. The authors have proposed a method for calculating the consistency and nonlinearity indices for approximating the measured viscosity values of pseudoplastic fluids in the case of . Approximation of the viscosity values of the studied thickener solutions based on the considered biopolymers using the Carreau–Yasuda model gives a more accurate result compared to other power models. As is known, the removal capacity of a drilling fluid improves with an increase in its viscosity at low shear rates. The efficiency of assessing the removal capacity of a thickener solution when modified with potassium and sodium chlorides is shown using one of the parameters of the power model, namely, the consistency index of the solution.