Fundamental Study of Wax Deposition in Crude Oil Flows in a Pipeline via Interface-Resolved Numerical Simulations

This work presents a fundamental analysis of the mechanisms governing wax deposition and removal in crude oil transportation pipelines. We utilize a numerical framework where oil and deposit are treated as two immiscible phases, and the volume-of-fluid (VOF) method is adopted to resolve the unsteady dynamics of the free interface. Deposition is modeled locally at the oil-deposit interface via a chemical equilibria model, here adapted to the VOF method. Deposit ageing is included via a thixotropic rheological model. The results emphasize that the deposit pattern may appear as a uniform axisymmetric film covering the pipe wall or be completely stratified. Although different mechanisms of deposit mobilization may occur, the removal rates correlate well with the Reynolds number of the bulk flow and the viscosity of the deposit layer. The simulation data are used to benchmark closure laws for the velocity and temperature within the film, and a prediction method for the steady-state deposit thickness is proposed.