Organic salt brines represent a good alternative to drill through deep productive zones. The literature presents these salts as thermal stabilizers of polymers used in the formulation of drill-in fluids. An extensive study was carried out to evaluate the rheological behavior of formate-based fluids as a function of temperature and density. An analytical expression was developed to correlate shear stresses with temperature for general drilling fluids and a special case of this expression results in a greatly simplified expression that is valid for a number of drilling and completion fluids produced using different alkali-metal salts of formic acid. The advantage of this new approach is the lack of dependence between the proposed correlation and the choice of a rheological model. Unlike man), expressions presented in the literature, the expression proposed and methodology that follows allows the choice of a best-fit model to predict the fluid's rheological behavior as a function of temperature. Experimental results show that formates do improve the thermal stability of polymers. The proposed correlations will soon be incorporated in a wellbore cleaning numerical simulator to compensate for thermal effects.