Start-up characteristics of gelled crude oil test pipeline

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 startup 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 startup 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.