Wax Deposition during the Transportation of Waxy Crude Oil: Mechanisms, Influencing Factors, Modeling, and Outlook

Wax deposition is an important issue affecting the safe and economical transportation of waxy crude oil via pipelines. Molecular diffusion and aging are considered to be the main mechanisms of wax deposition. However, more and more studies proved the molecular diffusion and aging mechanisms alone cannot fully explain the wax deposition phenomenon. In this Review, the calculation accuracy of wax molecular diffusion coefficient, the wax deposit delay characteristic, deposit formation under zero and negative temperature difference and the change of wax deposit structure were reviewed and discussed. Moreover, the research progress of operating parameters (including temperature, flow, asphaltene, and wax inhibitors) on the wax deposition characteristic were analyzed from the aspect of heat transfer driving force, mass transfer driving force, gelation deposition, and other deposition mechanisms. Furthermore, the development of wax deposition models is summarized and the shortcomings of existing models are discussed from the aspects of wax deposit generation, wax molecules' diffusion, and wax deposit aging in order to efficiently guide the prediction and control of wax deposition in waxy crude oil pipelines.