A New DSC-Based Method to Determine the Wax Porosity of Mixtures Precipitated from Crude Oils

Abstract

Wax precipitation is one of the most important problems in flow assurance. The correct prediction of the wax appearance temperature (WAT) and the wax precipitation curve (WPC) is essential to anticipate potential solutions for this problem. The determination of both WAT and WPC requires reliable data on the amount of precipitated wax and the trapped crude oil remaining in these mixtures. The estimation of the latter is difficult due to the scarcity of experimental methodologies. In this work, a method based on differential scanning calorimetry (DSC) was developed to determine the trapped crude oil of precipitated mixtures. The WPCs were experimentally determined by fractional precipitation and DSC analysis for a variety of crude oils. The comparison of these curves requires the correction of the former by subtracting the trapped crude oil remaining in the precipitated mixtures. The trapped crude oil was calculated using two methods: one based on proton nuclear magnetic resonance (1H NMR) previously developed and the other based on DSC, developed in this work. This method considers that the gel formed when decreasing the temperature contains not only solids, but also occluded crude oil. The values of trapped crude oil estimated by both methods were used to correct experimental WPC. The comparison between corrected WPC and those obtained by DSC analysis showed the superiority of DSC over 1H NMR to calculate the amount of trapped crude oil.