Sensitivity of Slug Flow Mechanistic Models on Slug Length

Slug flow is one of the common flow patterns in gas and oil production and transportation. One of the closure relationships required by the multiphase flow mechanistic models is slug length correlation. There are several closure relationships proposed in the literature as function of pipe geometry, pipe diameter, and inclination angle, and to a lesser extent to the flow rates and fluid properties. In this paper, we show that most of the frequently used mechanistic models are insensitive to slug length information. The only exception to this is identified as the Zhang et al. (2003, “Unified Model for Gas-Liquid Pipe Flow via Slug Dynamics—Part 1: Model Development,” ASME J. Energy Resour. Technol., 125, pp. 266–272). The unified model shows sensitivity at high gas flow rates, while displaying a negligible sensitivity at low gas flow rates. In conclusion, the slug length closure relationship is not crucial for pressure loss and holdup calculations. It can be speculated that the success of the unit cell slug flow modeling approach could be attributed to insensitivity of the models to slug length considering the highly probabilistic nature of the slug length.