Study of Paraffin Wax Deposition in Seasonally Pigged Pipelines

Abstract

Waxy crude oil pipelines are pigged periodically to scrape the adhered wax deposit from the pipe wall and remove it from the pipeline. If wax deposition on the pipe wall is not too severe and there is not much change in pipeline throughput due to wax deposition in winter, a pigging operation in winter is inadvisable because a “paraffin blockage” may occur during pigging due to a lower operating temperature. Seasonal pigging of this pipeline is advisable if the crude oil is piped at ambient temperature in summer and the wax deposit on the pipe wall accumulated during winter is eroded by the oil flow. The pipeline should be pigged during high temperatures in summer rather than in winter. A semi-empirical wax deposition model developed by our laboratory is used to predict the wax deposit distribution along the pipeline in different seasons and the volume of pre-pigging deposit on the pipe wall, and a seasonal pigging program is recommended. An experimental method consisting of determination of the gel point of wax-contaminated oil ahead of the pig is developed to calculate the volume of wax deposits removed by the pipeline pigging operation under actual field conditions to test the model. The wax content in the crude oil is determined from the gel point. The relative discrepancy between the predicted and the field experimental pigging operation data is 12.3%.