Prediction of yield stress of waxy gels in pipelines using scaling theory and crystallization kinetics

The development of a novel coupled kinetic and rheological model for paraffinic wax oil gelation is presented. The crystallization kinetics was studied by differential scanning calorimetry, and the rheological properties were obtained by dynamic oscillatory tests. The mass fraction of the crystallized wax, critical elastic strain, storage modulus in the Hookean region, and yield stress were obtained for model oils with 2.5, 5.0, and 7.5 wt% wax at cooling rates of 0.5, 0.75, and 1.0 degrees C/min. By applying such cooling range to the waxy oils, it was possible to verify the effect of this variable on fractal dimensional analysis using well-known scaling models for the first time. The scaling models used were successfully applied to conciliate the new gathered data enabling the dis-cussion of their microstructural characteristics. From the kinetic and rheological behavior observed, simulations of waxy oil gelation during a pipeline shutdown were also performed. The yield stress evolution was estimated from zero to 14 days of quiescent cooling. With the aid of this novel methodology, the pressure needed to restart the flow and the time for maintenance services without pipeline blockage could be estimated based on the radial yield stress profile, providing a more accurate measurement than the direct extrapolation of yield stress mea-surements for field pipelines.

Automated summary

This study presents a novel coupled kinetic and rheological model for paraffinic wax oil gelation. The crystallization kinetics was investigated using differential scanning calorimetry, while the rheological properties were determined through dynamic oscillatory tests. The effect of cooling rate on fractal dimensional analysis was examined for different wax concentrations. The gathered data were successfully reconciled using scaling models, allowing for the discussion of microstructural characteristics. Additionally, simulations of waxy oil gelation during a pipeline shutdown were conducted based on the observed kinetic and rheological behavior.