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Wax crystallization processes are investigated using differential scanning calorimetry, near-infrared spectroscopy, and nuclear magnetic resonance spectroscopy. The performance of a chemical additive is assessed using calorimetry and NMR. Heat flows of model waxy oils are obtained using differential scanning calorimetry, providing the wax appearance temperature and crystallization profiles. The effect of cooling rate, wax content, asphaltene, and chemical additive on the wax appearance temperature is investigated. The wax appearance temperature increases with increasing wax contents. The wax appearance temperature decreases in the presence of chemical additive, effectively increasing the instantaneous supersaturation. Furthermore, near-infrared spectroscopy and nuclear magnetic resonance spectroscopy are utilized to determine wax appearance temperature. The NMR experiments quantify liquid and solid fractions at thermal equilibrium conditions, effectively circumventing the need for dynamic thermal techniques.

Thermal behavior of waxy oils is investigated using the techniques of thermogravimetric (TG) analysis and differential scanning calorimetry (DSC). Model waxy oils and real waxy crude oils are utilized. Decomposition temperatures of waxy oils are obtained using TG analysis. The effects of thermal history, wax content, and additive on the gelation process of waxy oils are investigated using DSC. The DSC method provides a measure of wax solubility as well as solid fraction. An integration method and a computation method are utilized to predict solid fraction. In addition, wax crystallization onset points are obtained at the cooling rates ranging from 1 to 20 °C min−1. Similarly, wax dissolution endset points are obtained at heating rates ranging from 1 to 20 °C min−1. Extrapolated onset and endset points yield wax precipitation temperature and wax dissolution temperature, respectively. Subsequently, wax solubility curves are obtained using thermodynamic computations. A wax precipitation temperature method and a wax dissolution temperature method combine thermodynamic phase behavior with onset/endset points to predict solid fraction. Both the wax precipitation temperature method and the wax dissolution temperature method can predict solid fraction of waxy oil samples. The wax precipitation temperature method and the wax dissolution temperature method are accurate when the temperature is close to the wax appearance temperature. A heat-integration method provides accurate values of the solid fraction at temperatures significantly below the wax appearance temperature. Therefore, integration method and wax precipitation temperature/wax dissolution temperature method are combined to predict solid fraction. The effect of solid fraction on yield stress is also investigated using differential scanning calorimetry and rheometry. Finally, a new solid fraction dependent gel strength model is obtained for shut in and restart of waxy crude oil pipelines.