A study of wax deposition in pipeline using thermal hydraulic model

Wax deposition issue has become one of the primary Flow Assurance challenges for production and transportation of crude oil in the pipeline. The predictions of wax deposited thickness during various operations for crude oil export line and multiphase production line are imperatively required to support the process engineering design and field operations. However, empirical heat and mass transfer correlations, which have been used over the last ten years, give poor predictions for wax deposition thickness, particularly, in multiphase production pipelines under turbulent flow conditions. This paper presents a mechanistic model coupling thermal hydraulic calculations and wax aging model for predicting wax deposition in the pipeline. Finite Element numerical approaches are used and the coupled model of mass balance, momentum balance and energy balance along the pipeline is solved. With calculated flow characteristics, the model is further developed to determine wax deposit on the pipe wall, taking into account long-term aging effects. As a case study, wax deposition in a subsea pipeline is simulated using this model. Effects of wax properties as well as turbulent diffusivity of wax convection on deposition predictions are investigated. The model performance is evaluated against the literature data and predictions from commercial software.