Numerical simulation of wax deposition in crude-oil flows in a pipeline

Crude oils are complex mixtures of hydrocarbons including high molecular weight paraffin waxes. When a “waxy” crude oil flows through a cold pipeline whose temperature is below the wax appearance temperature, e.g. in subsea transportation systems, heavy paraffins separate and deposit on the pipe walls. The available prediction methods for wax deposition are essentially empirical, in particular in terms of the description of the fouling removal due to the coupling between the deposit layer and the bulk flow. We present a numerical model to simulate fouling deposition, based on the solution of the Navier-Stokes and energy equations for the oil-fouling mixture using a Volume-Of-Fluid method. Additional transport equations for the waxy and non-waxy components within each phase are solved simultaneously. The wax deposition process is described using a chemical equilibrium model based on the Gibbs free energy. The numerical framework is validated by comparison with experimental wax deposition data from the literature. The model is suitable for parametric studies of the wax deposition process and can be developed further to incorporate the effect of wax inhibitors.