The Law Of Wax Deposition And Determination Of Pigging Circle For Waxy Crude Oil Pipeline

The high waxy crude oil is transported with heating process in De-Su pipeline. Withthe production decline in oil field, the pipeline throughput decreases gradually so that itis easily transferred into the unstable area and results in congelation. The wax moleculecrystallizes and deposits continuously on the pipe wall during the transportation, theactual flow and flow resistance can be decreased and increased respectively as a result.Therefore, based on the calculation of pipeline throughput and the prediction of pipelinewax deposition rate, the economic pipeline pigging circle must be determined and theparaffin removal must be done regularly in order to ensure the safety of the pipelineoperation. The following aspects are discussed in this paper. Firstly, the rheologicalproperties such as the viscosity-temperature relationship, thixotropy and yield stress ofwaxy oil in De-Er united station was tested to analyze the effect of heating and shearinghistory on waxy crude oil condensation point, the variation of the flow pattern and theflow state of waxy crude oil in pipeline was studied. Secondly, the concepts and thecalculation method of pipeline safety throughput can be brought out from the point offlowing in low temperature for hot oil pipelines and the hydraulic characteristicsconstraints, then the variation rules of pipeline safety throughput were worked out due todifferent operation modes including output oil temperature, environment temperature, thethickness of wax deposition and etc. Thirdly, the wax deposition rate was calculatedunder different flow and output oil temperature according to the wax deposition model ofwax deposition coefficient method which was fitted by the indoor loop experiment data.Fourthly, the period optimized model was established by taking the piping cost as anobjective function for the purpose of determining the pigging circle of De-Su pipelineunder different flow, season and oil temperature. Finally, the program of the waxdeposition rate calculation and the pigging circle optimized solution were organized byusing the Matlab graphical user interface.