Abstract
Wax deposition is an intrinsic problem existing in the production and transportation of waxy crude oil. In the oilfield, non-metallic pipe especially high-density polyethylene pipe (HDPE) has been widely used to solve corrosion problems due to its excellent performance in intensity and corrosion. However, the wax deposition problem in polyethylene (PE) pipe has never been evaluated using dynamic and systemic apparatus. Only a few studies focus on the wax deposition on the coated polyethylene surface by using the cold finger apparatus in recent decades. In this study, the wax deposition experiments were performed using an in-door flow-loop with detachable PE and stainless steel (SS) test sections under the laminar flow regime at the same time to investigate the difference in wax deposition aging rate between the PE and SS pipes. The wax deposits under different operating conditions in both PE and SS pipes were sampled by three layers to study the aging rate at different radial locations during the wax deposition. The wax precipitation characteristics of the wax deposits were determined by using the differential scanning calorimetry (DSC) method. It was found that the wax contents of the wax deposits in PE pipe were lower than that in the SS pipe. And the difference of the wax content between PE pipe and SS pipe decreases with the depositing duration. Eventually, the wax contents of the wax deposits in PE pipe were almost the same as that in the SS pipe. The heat conduction and heat transfer processes in PE pipe and SS pipe were analyzed. The thermal gradient and the concentration gradient at wall were calculated and combined with the heat and mass transfer of wax during the wax deposition to illustrate the difference in wax content. It was found that the variations of the thermal and concentration gradients have significant effects on the diffusion process of wax molecules within the wax deposit layer and thus changing the aging rate. The comparisons and findings of wax deposition between the two kinds of pipes have provided a significant reference for the application of non-metallic pipe in the oilfield.
