Study On Initial Structural Destruction Properties Of Gelled Crude Oil Pipeline Under Constant Start-up Flow Condition

The initial structure of the gelled crude oil pipeline means the structure that the wholegelled oil has in pipeline at the moment of shutdown end or start-up beginning. Thisstructure formed by experiencing special cooling process, and at the time of restart pipeline,the mechanical response of the different initial structures is not the same, showing adifferent start-up characteristic of the gelled oil. Therefore, the pressure change duringcooling process and start-up process is the best starting point to study the initial structure ofthe gelled crude oil.The pressure changes in the pipe flow experimental loop of Sudan crude duringcooling process were analyzed and summarized. The reasons for the formation of reducedpressure and reduced pressure difference during cooling process were investigated,thinkthat the contraction deformation of pipeline can not keep up with the contractiondeformation of the crude oil during cooling process, so the crude oil (thermal expansion)cold contraction or phase change contraction in the pipeline caused the reduced pressure;when the contraction flow of oil which was oriented by the external force was hindered byincreased viscosity and structural strength of crude oil, the reduced pressure difference wasformed. The viscosity and structural strength of crude oil was increased because thetemperature is decreasing. The reduced pressure and reduced pressure difference wassimulated using computer program.When the reduced pressure during shutdown process reaches the saturated vaporpressure of light components within crude oil at that temperature, light components escapefrom the crude oil and cause voids in the gelled oil initial structure, thus increase thecompression of gelled oil and affect the gelled oil startup characteristics; start-uptemperature is lower, the greater the cooling rate of shutdown, the greater the reducedpressure appears, the more tend to cause the greater voids and a higher gelled oil compression characteristic. Studies on compression coefficient of gelled oil in the laterchapters confirm this.A model for simulating the initial stage of start-up gelled oil pipeline was establishedand the simulation using this model to the start-up initial stage was conducted, we obtaineda pressure transmission speed law in the initial stage of start-up process, found that thepressure transmission speed in the start-up process is not a fixed value, but will experience afast decay process from a high speed to a low steady speed within a short distance frompipeline inlet to somewhere of the pipeline; In the rest majority pipelines, the pressurepropagates at this lowed steady speed.According to the simulating results of start-up model，discovered that gelled oilcompression factor is larger than the compression factor of a Newtonian fluid or of a novoids gelled oil，meanwhile，gelled oil have different compression factor at differentpressure. This is due to the sake of voids presented in the initial structure of gelled oil，thepresence of voids lead to the increase of compressibility of gelled crude oil，and the voidsare compacted as different volume under different compression state，so the compressibilityof gelled crude oil exhibits changing with compression state.