Wax and Wax–Hydrate Deposition Characteristics in Single‑, Two‑, and Three-Phase Pipelines: A Review

In the oil pipeline transportation system, wax deposition will reduce the effective circulation area, weaken the overall pipeline transportation capacity, and even block the pipeline, which seriously threatens the safety of the pipeline flows. In the actual production of oil fields and the transportation of oil products, except for the single-phase waxy crude oil, under most conditions, operations are performed using multiphase mixed transportation, so it is necessary to determine the wax deposition characteristics in those pipeline systems. In this Review, three new wax deposition mechanisms proposed in recent years and several typical experimental devices were summarized, the wax deposition in oil–water and oil–gas flow systems and the wax–hydrate coupling deposition in oil–gas–water flow system flows were concluded; the mathematical models were also categorized based on the three flow systems. Meanwhile, it highlighted the fact that, in the two-phase flow, because of the complexity of the flow pattern and the presence of the second interface on the wax deposition process, independent theoretical research on the mechanism of wax deposition is particularly necessary; based on this, a more-accurate wax deposition prediction model can also be developed. For the coupled deposition of wax-hydrate in the three-phase flow system, experimental instruments such as FBRM, PVM and molecular dynamics simulations could be used to study the distribution characteristics and interaction rules of wax crystals and hydrate particles from a microscopic perspective. On the other hand, the mechanism of wax crystal and hydrate coupling deposition by additives such as antiwax agents, hydrate inhibitors, antipolymerization agents, and pipeline transportation conditions can be investigated experimentally to better control the deposition process during pipeline operation and ensure the safe flow in the transportation system.