Characterization of Brazilian Crude Oil Samples To Improve the Prediction of Wax Precipitation in Flow Assurance Problems

The deposition of paraffinic waxes in offshore Brazilian crude oils is a high potential problem in terms of flow assurance. These compounds precipitate when the temperature decreases, causing damage in equipment and operation. Several models have been proposed to determine the wax appearance temperature (WAT) and the wax precipitation curve (WPC) to predict potential wax deposition problems and their magnitude. However, their application is limited because of the scarcity of reliable input data. In this work, WAT and WPC were obtained by a multi-stage fractional precipitation for three Brazilian crude oils. The wax content at −20 °C was obtained using a modification of Burger’s method. Precipitated solid at each temperature was characterized by means of proton nuclear magnetic resonance ( 1 H NMR) to determine the amount of entrapped crude oil. The n -paraffin distribution for the selected crude oils was determined by high-temperature gas chromatography (HTGC), and it was used to predict wax precipitation with a rigorous thermodynamic model. Discrepancies between experimental and predicted results were found, probably related to the presence of non-paraffinic compounds in the studied crude oils. DSC results of some precipitated fractions showed signals that may support this hypothesis. Gas chromatography−mass spectrometry (GC−MS) analysis was used to determine qualitatively the nature of such compounds, but no conclusive results were obtained.