A fundamental model of wax deposition in subsea oil pipelines

Wax deposition in subsea pipelines is a significant economic issue in the petroleum industry. A mathematical model has been developed to predict the increase in both the deposit thickness and the wax fraction of the deposit using a fundamental analysis of the heat and mass transfer for laminar and turbulent flow conditions. It was found that the precipitation of wax in the oil is a competing phenomenon with deposition. Two existing approaches consider either no precipitation (the independent heat and mass transfer model) or instantaneous precipitation (the solubility model) and result in either an overprediction or an underprediction of deposit thickness. By accounting for the kinetics of wax precipitation of wax in the oil (the kinetic model), accurate predictions for wax deposition for both lab‐scale and pilot‐scale flow‐loop experiments with three different oils were achieved. Furthermore, this kinetic model for wax precipitation in the oil was used to compare field‐scale deposition predictions for different oils. © 2011 American Institute of Chemical Engineers AIChE J, 2011Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87116/1/12517_ftp.pd

Wax deposition modeling of oil/water stratified channel flow

Wax deposition modeling becomes complicated when multiphase flow is involved. Empirical heat and mass transfer correlations are unreliable for multiphase deposition modeling and full scale computational fluid dynamics calculations require expensive computational intensity. In this work, numerical methods are used to study wax deposition in oil/water stratified flow through a channel. A unidirectional flow analysis is used to calculate the nonisothermal hydrodynamics and mass transfer. It was found that the change in the position of the oil/water interface throughout the channel must be taken into accounted for the mass balance to be valid. Unfortunately, this change has not been accounted for in all previous studies. In addition, the growth of the wax deposit as a function of time along with the effect of oil/water flow rate ratio is discussed. The presence of water significantly reduces the severity of wax deposition by altering the heat and mass transfer characteristics. © 2010 American Institute of Chemical Engineers AIChE J, 2011Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/83460/1/12307_ftp.pd