Application of the fundamentals of heat and mass transfer to the investigation of wax deposition in subsea pipelines.

摘要

The doctoral study focuses on the development of a rigorous understanding of wax deposition using the fundamentals of heat and mass transfer. First, a state-of-the-art model is developed to account for wax deposition experiments with various operating conditions. It is shown that the predicted deposit thickness can be bounded by two physical limits: no precipitation in the oil and instantaneous precipitation in the oil. The most influential input parameter for the deposition model is the solubility curve of the wax in the oil. A rigorous method was developed to correct previous methods that have over-estimated the amount of precipitating wax molecules. Based on the corrected solubility curve, it was found that the thermal driving force, a term that is frequently highlighted in many deposition studies, is not the best parameter to characterize the driving force for wax deposition. This study found that a more appropriate candidate for predicting the thickness of the wax deposit is the mass driving force, which reflects the interaction between the heat transfer and the solubility curve and can cause discrepancies in the trends for the amount of wax deposit with the change of thermal driving force for different oils.;The subsequent portion of this research is devoted to the study of wax deposition in oil/water stratified flow. First, to provide insights of the effect of the presence of water, a 2D wax deposition model for oil/water channel flow was developed. It was revealed that one had to calculate the change in the oil/water interface position for the correct mass balances of oil and water. The effect of the presence of water is found to reduce the severity of wax deposition by acting as an additional heat source to alleviate the cooling of the oil during its transportation in the sub-sea pipelines.;The deposition wax deposition experiments for oil/water stratified flow showed that gelation as another deposition mechanism can be significant at low oil flow rates. The degree of gelation increases with decreasing the shear stress in the oil phase, which corresponds to a thicker deposit with lower wax fraction in the deposit.