胶凝含蜡原油压缩性对管道再启动影响的研究

Effect of compressibility of gelled waxy crude oil on pipeline restart

热含蜡原油管道长时间停输后,温度降低导致原油胶凝且压缩性显著增强。胶凝含蜡原油黏弹-触变特性和压缩性的共同作用对管道再启动特性产生重要影响。本研究改进了已有的黏弹触变模型的不足,更好地表征了胶凝含蜡原油的黏弹-触变特性,进而通过数值模拟,分析了胶凝原油压缩性对最小启动压力、末端见流时间等关键性再启动工程参数的影响。结果表明,随着胶凝原油压缩性增强,最小启动压力降低,相同启动压力下的末端平衡流速增大;再启动过程中,屈服面向下游推进的初始速度等于胶凝原油中的声速,而后逐渐衰减;随着压缩性增强,一方面屈服面向下游推进的初始速度减小,另一方面屈服面推进过程中速度衰减程度加大,两者共同作用导致末端见流时间延长。

Waxy crude oil in pipeline becomes gelled and more compressible because of temperature reduction after prolonged shutdown of the heated oil pipeline. The combined effect of both elasto-viscoplastic thixotropic behavior and compressibility of gelled crude oil plays a critical role on pipeline restart. In the present work, an elasto-viscoplastic thixotropic model was modified to better describe the elasto-viscoplastic thixotropic behavior of gelled waxy crude oil. Then numerical simulations were carried out to investigate the effect of compressibility of gelled crude oil on the restart time and the minimum pressure difference required for successful restart, both of which are of prime importance in engineering practice. The results show that a high compressibility of gelled oil will reduce the minimum pressure difference required for successful restart, and increase the steadystate velocity under given restart pressure. In the initial stage, the propagation velocity of the yield cross-section is equal to the sound speed in gelled crude oil, then gradually decreases during the restart process. With the increase of compressibility of gelled crude oil, the initial propagation velocity of the yield cross-section decreases, while the attenuation of the propagation velocity of the yield cross-section increases. Under this action, the restart time increases.