Abstract: The wax deposition in waxy crude oil pipelines reduces transportation efficiency and may cause wax blockages, posing significant challenges to pipeline flow assurance. Although extensive research has explored the wax deposition mechanisms, relatively little focus has been given to the rheology governing the formation and evolution of deposits. This paper is a case study of crude oils doped with nanocomposite pour point depressant (NPPD). Using a method that alters rheological properties while maintaining the oil composition, the effects of NPPD on wax deposition characteristics and mechanisms were investigated. The results indicate that the addition of NPPD effectively reduces the gelation temperature of oil, and thus inhibits the formation of the primary condensed oil layers which serve as precursors for wax deposition, consequently slowing the deposition rate. Moreover, the marked reduction in oil viscosity enhances the diffusion of wax molecules within the bulk oil, accelerating the aging process of deposits. This is evidenced by both elevated wax appearance temperature and increased wax content as well as their resultant compact wax-particle structure and large critical carbon number of aging deposits. Furthermore, NPPD can notably reduce the accumulation of resins and asphaltenes in deposits, which is attributed to its compact wax-particle structure, restricting the diffusion of these two components. Despite the increased wax content in NPPD-treated oil deposits, the yield stress shows a significant reduction, with a 91 % decrease observed for 100 μg/g NPPD-doped oil deposits compared to undoped oil deposits.

Key words: waxy crude oil, wax deposition, mechanism, nanocomposite pour point depressant, rheology

摘要： 含蜡原油管道的蜡沉积导致管道输送效率下降,并可导致"蜡堵",一直是输油管道流动保障的难题。目前对蜡沉积机理的研究很多,但从流变学角度对沉积产生与发展过程的研究很少。以纳米降凝剂改性原油为研究对象,通过改变实验油样流变性而保持油样组成不变的技术路线,从流变学视角探究了加剂对蜡沉积和沉积物特性的影响及其机理。研究结果表明:添加降凝剂使油样胶凝温度下降,抑制了作为蜡沉积基础的初始凝油层的生成,从而减缓了沉积速率;添加降凝剂使黏度大幅降低,有利于油流中蜡分子的扩散,从而加快了沉积物老化进程,结果是沉积物析蜡点升高、含蜡量上升因而蜡晶结构致密、老化的临界碳数增大;添加降凝剂对胶质、沥青质在沉积物中的富集有显著抑制作用,这可归因于加剂油较为致密的沉积物蜡晶结构对胶质、沥青质扩散的抑制作用。此外,由于降凝剂对沉积物的改性作用,加剂油沉积物虽含蜡量高但屈服应力却大幅下降,与空白油沉积物相比,加剂量为100 μg/g的加剂油沉积物屈服应力降低91 % 。

关键词: 含蜡原油, 蜡沉积, 机理, 纳米降凝剂, 流变性