Robust Wax Deposition Modeling Incorporating Non-Newtonian Characteristics

Abstract

Wax deposition in sub-sea flowlines during oil production is a well-known problem attributed to the formation of wax crystal induced by ambient cooling. Due to the non-Newtonian characteristics of waxy oil below its wax appearance temperature, the deposit growth can be modeled as a gelation process resulting from the accumulation of wax crystal in the boundary layer, which increases the dynamic yield stress leading to the arrest of flow near the wall or gel−fluid interface. In the present study, we performed wax deposition simulations, both with and without incorporating this non-Newtonian effect and compared them against single-phase turbulent flow wax deposition tests carried out in a 2" flow loop under various conditions. The deposit thickness and wax content evolution with time obtained in the flow loop tests were compared against the simulations. Compared to the conventional molecular diffusion approach, the non-Newtonian approach can capture the time-varied experimental deposit thickness at early and late times across various temperature and flow conditions. The conventional diffusion approach fails to predict the rapid deposit growth resulting from oil gelation that occurs at early times but performs comparably to the non-Newtonian model for cases without gelation.