Progress Update: Investigation of Slug Length for High Viscosity Oil-Gas Flow
February 26, 2010
Slug length in pipelines is important for fluids deliverability, flow assurance, and pipeline and surface facility designs. Although several slug length empirical and probabilistic models are available in the literature for light crude oil, there is no such model for high viscosity crude oil. The recently acquired heavy oil slug length data in horizontal pipes at TUFFP (Gokcal, 2008) are carefully evaluated and analyzed in this study. The objective of this project is to understand the effect of high oil viscosity on the average slug length and slug length distribution to develop a high viscosity liquid slug length model. The high-speed video images are analyzed for different parts of the slug flow, namely slug back and front, slug body, and film region at different viscosities. This is to characterize and better understand the slug flow structures. Preliminary results showed that liquid viscosity has significant effect on the structure of slug flow and the slug length.
Based on Dukler et al. (1985) physical model for the minimum slug length, two slug hydrodynamic parameters were identified to control the minimum stable slug length, namely the film height and the time for the redevelopment of velocity profile, i.e. the length of slug mixing region. Liquid viscosity was found to affect both parameters as revealed by the flow visualization analysis. At high oil viscosity, the thick liquid film in front of the slug results in shorter mixing zone and reattachment distance. This shortens the slug length required to achieve a fully developed velocity profile. Based on this analysis, a physical model is proposed.