胶凝原油试验管路的启动特性

Start-up characteristics of gelled crude oil test pipeline

针对胶凝原油管道停输后再启动压力远低于计算预测启动压力的技术难题,使用管流试验装置研究了胶凝原油管路的启动特性。依据对胶凝原油管道停输启动过程的理解,提出胶凝原油管道存在对应的临界启动剪切率和启动屈服应力。胶凝原油管路启动过程分为控制流量启动过程和控制压力启动过程。控制流量启动过程研究发现,受含蜡原油轻组分影响,试验管路内胶凝原油表现出"韧性"和"脆性"两种特性,"韧性"原油不含轻组分,胶凝结构强度与停输前的预剪切过程、停输静止时间、停输降温幅度、启动温度及启动剪切率相关;"脆性"原油含轻组分,胶凝结构强度主要取决于停输降温幅度和启动温度。胶凝原油的启动屈服应力取决于胶凝结构强度和静态降温过程的体积收缩;试验管路的启动速度与胶凝原油的结构强度和启动剪切率相关。控制压力启动过程研究发现,启动油温越高,试验管路全线启动速度越快;在相同启动油温下,启动压力越低,试验管路全线启动速度越慢;对应相同启动温度,存在临界启动压力。相关研究结果为深入研究胶凝原油停输再启动过程和指导工程实践奠定了理论基础。

Since the actual restart pressures in gelled crude oil pipelines after pipeline shutdown are much lower than the theoretical start-up pressures, the pipe flow test apparatus has been used to study start-up characteristics of such pipelines. With consideration to existing knowledge about the shutdown and start-up of gelled crude oil pipelines, critical start-up shear rates and start-up yield stresses corresponding to gelled crude oil pipelines have been proposed. The start-up procedure for gelled crude oil pipelines can be divided into two stages： start-up with control over flow rate and over pressure. By studying the start-up process with control over flow rate, it was found that gelled crude oil in the test pipeline is characterized by both ＂toughness＂ and ＂brittleness＂ due to the impact of lighter compositions in the waxy oil. Without lighter components, crude oil with ＂toughness＂ has gel structural strength closely related to pre-shearing procedure, shutdown duration, shutdown temperature drop, start-up temperature and start-up shear rate. At the same time, crude oil with lighter compositions and characterized by ＂brittleness＂ may have structural strength predominantly determined by shutdown temperature drop and start-up temperature. The start-up yield stress of gelled crude oil is determined by the structural strength and contraction in volume during static temperature drop. Start-up speed of the test pipeline is determined by structural strength and start- up shear rate of the gelled crude oil. By studying the start-up process with control over pressure, it was found that faster start-up speed can be obtained under higher start-up oil temperature. Under identical start-up oil temperatures, lower start- up pressure may lead to slower start-up speed of the pipeline. There are critical start-up pressures with the same start-up temperatures. Relevant research results provide theoretical basis for studying the shutdown and start-up process of gelled crude oil and guiding the engineering practice. （7 Figures, 10 Tables, 10 References）