Characterization of the wax precipitation in Mexican crude oils

This paper reports the theological and thermodynamic characterization of the wax formation phenomenon in three Mexican crude oils where the effect of waxes and asphaltenes content on wax precipitation and theological behavior of crude oils is evaluated and discussed. Wax appearance temperature is measured by using differential scanning calorimetry, rheometry and densitometry. The wax precipitation curves were obtained by fourier transform infrared spectroscopy. Pour point temperatures were evaluated according to the ASTM-D97 method, whereas gelation temperatures were determined by theological experiments made with a controlled-stress rheometer. Waxes of the crude oils were separated and characterized by gas chromatography/mass spectrometry and differential scanning calorimetry. The methods used in this work for the wax appearance temperature determination showed to be sensitive to the crude oil composition. Results showed that the presence of asphaltenes impacts significantly the liquid-solid equilibrium and rheological behavior of the crude oils studied whereas the wax melting temperature was a key factor to evaluate the propensity of crude oils to present wax precipitation problems. (C) 2011 Elsevier B.V. All rights reserved.