A simulator has been developed to track two-phase slugs in pipelines transporting liquid and gas mixtures. The algorithm consists of close coupling of a one dimensional hydrodynamic slug flow model with an interface tracking methodology, and solving both simultaneously with an iterative procedure. The tracking scheme is based on propagating the fronts and backs of the liquid slugs to new locations during an incremental time step. New positions of the interfaces determine if a slug will enter the pipeline, exit the pipeline, collapse, merge with a slug ahead of it, or none of the above. The solution procedure determines the locations and the characteristics of all the slug units which exist in the pipeline at a given time.
Data collected in hilly-terrain and horizontal pipes in a large-scale multiphase flow loop were used to validate the slug tracking simulator. The average absolute percent errors in predicting the maximum slug length and inlet pressure were 12.6 and 0.47 respectively. A case study with field data collected on a 14,762 feet, 16 in. pipeline showed that the simulator predicted the maximum slug length and inlet pressure with absolute percent errors of 11.6 and 4.3 respectively. The comparisons are good and provide confidence in using the algorithm and the simulator to model and track two-phase slugs in hilly-terrain pipelines.
The simulator can be used to determine the characteristics of the slug unit used to design separators and slug catchers. It can also be used to analyze the impact of the flow and pressure transients on reservoirs, equipment, and structures, and study the effects of slugging on corrosion rates. The history of each slug in the pipe can be traced by determining if it will grow, shrink, collapse, or remain the same size as it traverses the pipe. During slug tracking, slug lengths are determined by the locations of interfaces instead of a correlation.