The Initial Startup Wave Velocity in Isothermal Pipeline With Compressible Gelled Crude Oil

Summary The results of pipe-flow experiments show that the advancement velocity of pressure is considerably slower than the transient-pressure-wave velocity during the startup of pipeline with compressible gelled crude oil under constant flow rate. The startup wave velocity that dominates the advancement velocity of pressure in pipeline with compressible gelled crude oil was described and explained, and the essential difference between the startup wave velocity and the transient-pressure-wave velocity was also described in detail. The startup wave front marks the substantive commencement of breakdown of gel structure, and also indicates when the flow rate starts to become stable in the pipeline segments passed through during startup under constant flow rate, so it is a crucial factor affecting the calculation of startup pressure. In this paper, the efficient numerical formulas to compute the startup wave velocity were deduced on the basis of the analysis of 1D flow of viscoplastic media in elastic pipeline. The reliability of the formulae was verified by the well agreement between the calculated values and the results of pipeline startup experiments carried out with the N-Y gelled crude oil. These formulas facilitate scientific analysis for the safe and economical operation of pipeline transporting waxy crude oil. During the initial startup of pipeline with compressible gelled crude oil under constant flow rate, the startup wave velocity is considerably slower than the transient-pressure-wave velocity, decreases with the increase of the propagation distance and the gel strength of crude oil, and increases with the increase of startup flow rate (the volume elastic/plastic coefficient of gelled crude oil and the ratio of the wall thickness to the inside diameter of the pipeline). It is noticeable that the formulae deduced in this paper are not limited to the pipelines with gelled crude oil. They are also applicable to most kinds of pipelines transporting compressible viscoplastic fluid with strong structure.