Effect of Pressure on the Crystallization of Crude Oil Waxes. II. Evaluation of Crude Oils and Condensate

Laboratory analyses of the formation of wax deposits in crude oil are generally performed at atmospheric pressure on stabilized samples without the presence of light components. Therefore, the effects of two important factors that influence the solubility of waxes, namely, light fractions and pressure, are not considered. As a consequence, the results may not reflect what really happens in production lines and equipment. In this work, we evaluated five Brazilian crude oil samples and one condensate, recombined with different gases and under varying pressures, using the high-pressure microcalorimetry technique (HP mu DSC). The samples were characterized with regard to the distribution of waxes by the number or carbon atoms to correlate with the results for wax appearance temperature (WAT) and crystallization enthalpy. The results indicate that rising pressure causes the WAT to rise as well and the recombination with gases composed mainly of light hydrocarbons reduces the WAT. Methane has the greatest influence on the oils containing higher amounts of macrocrystalline waxes, an effect that is stronger at higher pressures. Nitrogen does not act as a solvent of the paraffins present, whether of the macro- or microcrystalline type. Fractions lighter than C3, contained in the saturation gas mixtures, are more efficient in the solubilization of waxes, mainly those with lower molar masses. Variations in temperature and enthalpy of crystallization depend upon the pressure, composition of the gas (or mixture of gases), and composition of each crude oil.