Wax deposition law study for oil transportation pipeline with phase equilibrium

Owing to high pour-point of most waxy crude oil in China, if the wall temperature is below the wax precipitation point through pipeline transportation, wax crystal will appear and deposit with the other components of crude oil on the wall together. This process is commonly known as "wax precipitation". It is the widely existing problem of wax deposition in pipelines during transportation of waxy crude oil. This phenomenon leads to many problems such as pipe plugging, production rate decreasing, pressure drop increasing, fiction increasing and so forth. In the non-equilibrium thermodynamics, wax deposition is a complex coupling irreversible process with diffusion, heat transfer and fluid flow and phase change together. To start with the main factor of several stages, such as dissolution, precipitation, diffusion, deposition and ablation of wax, the physical model of non-equilibrium thermodynamics process on wax deposition in pipeline transportation process was established. Then combined with fugacity and activity coefficients, enthalpy change and entropy change of phase transition process and solid-liquid phase equilibrium model in atmospheric pressure are deduced, the pipeline operation parameters on the effect of wax deposition law in transportation pipeline is explored, thus the theoretical foundation can be provided to make further research on wax deposition with non-equilibrium thermodynamics. © 2013 American Society of Civil Engineers.