Previsão de propriedades reológicas de géis parafínicos baseada na teoria de objetos fractais

Abstract

The gelation of waxy oils is a meaningful problem in the oil industry, because the gel formed due to the cooling of the oil in the pipe can cause blockage of the line. In this scenario, it is important to have mathematical models that reconcile the kinetics of gel formation with the rheological properties of the fluid to assist in situations of resumption of operation, especially in predicting the yield stress. Therefore, the objective of this work was to study and develop kinetic and rheo- logical models for paraffinic oils from the perspective of fractal object theory. To this end, the kinetics of gel formation was studied through the processing and anal- ysis of polarized light microscopy images and differential scanning calorimetry, and its rheological properties were investigated through dynamic oscillatory stress sweep tests. These tests were carried out using model oils with paraffin fractions of 2.5, 5.0 and 7.5 % wt and cooling rates of 0.50, 0.75, 1.00 °C·min−1. With the experimental data obtained, a kinetic model was developed for predicting the mass fraction of precipitated wax, and this, reconciled through scaling models with the critical de- formation, elastic modulus and yield stress of the gel. The developed models were then applied to a simulation of operational shutdown in a pipeline, through which it was possible to estimate the yield stress in the pipe. The results obtained point to the strong influence of the precipitated wax fraction and the cooling rate on the rheological properties obtained. Thus, with the proposed methodology it was pos- sible to expand the studies performed on a laboratory scale for an application in industry through a mathematical model that integrates the effects of kinetics in the rheological properties of the fluid.