MODELLING OF WAX DEPOSITION IN OIL PIPES: A DISPERSED MULTIPHASE TURBULENT FLOW APPROACH

Abstract

Crude oils are complex mixtures of hydrocarbons including high molecular weight paraflin 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 paraflins separate and deposit on the pipe walls. The available prodiction methods for wax deposition are essentially empiric, particularly regarding the description of the fouling deposition and removal processes, which depend on the fluid dynamlc interaction between the deposit layer and the bulk flow. In Ibis work, we present a novel theoretical and numerlcal mode! for predicting wax deposition in oil pipes and, more generally, coagulation/deposition processes for a wide range of applications. Unlike other models existing in literature, which are mostly based on a separated lw<>-fluid description of the oil/wax-<Jil flow aod phase-chaoge represented as a deposition process, our model is based on a mixture description, where wax is considered as a suspended phase immersed in crude-oil. Coagulation and dissolution phenomena are modelled with an associated first order kinetic reaction which allows to study arhitrarily complex geometries. Wax ageing (hardening) is solved with a dynamic equation for the viscosity. We show bow Ibis mode! can be implemented in the open-source C++ library OpenFOAM and we present key results for deposition in a variety of pipe shapes.