Assessment of a Thermodynamic Model To Describe Wax Precipitation in Flow Assurance Problems

One of the most important problems related to flow assurance is the deposition of paraffinic waxes present in crude oils. These compounds may precipitate when temperature decreases during oil production, transport through pipelines or storage, causing problems in flowlines and equipment that could in the most severe cases stop crude oil production. 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 experimental information, such as detailed crude oil characterization, the experimental WPC, and the wax composition. In this work, experimental WAT and WPC for three crude oils with differences in chemical structure were determined through a multistage fractional precipitation procedure. The trapped crude oil of the precipitated mixtures at each temperature was determined by a H-1 nuclear magnetic resonance (NMR) technique, so that the true amount of wax precipitated at each temperature was obtained. Differential scanning calorimetry was also used to determine WAT and WPC. The n-paraffin distribution for the selected crude oils was determined by gas chromatography (GC) techniques, and it was used to predict wax precipitation with a rigorous thermodynamic model available in commercial software. Predictive capabilities of the considered model were tested by comparing the experimental and predicted values of WAT and WPC, obtaining reasonable agreement.