An experimental and theoretical investigation of slug flow for high oil viscosity in horizontal pipes

Effects of high oil viscosity on slug flow were studied experimentally and theoretically. A 50.8-mm ID indoor facility was used to conduct experiments. A total of 175 slug flow tests were conducted for different superficial oil and gas velocities and viscosities for slug flow in horizontal pipe. The superficial liquid and gas velocities were varied from 0.05 to 0.8 m/s and from 0.1 to 2 m/s, respectively. Pressure gradient, translational velocity, and slug length and frequency were measured in this study. Moreover, a total of 90 tests for drift velocity were performed at different viscosities for inclination angles of 0° to 90°.;A mechanistic model to predict the drift velocity for high viscosity oils was developed for horizontal flow. The model is based on mass and energy balance equations which are solved explicitly. The proposed model was validated against experimental data. Calculated drift velocities matched well with experimental results. A closure model for upward inclined pipe was developed by combining the proposed drift velocity model for horizontal flow and an existing drift velocity model for vertical flow. The model predictions gave good agreement with experimental results. The developed drift velocity model for horizontal pipe, including the effect of liquid viscosity, was implemented into the translational velocity equation. The new equation shows significant improvement in translational velocity prediction for high viscosity oils. The effect of high oil viscosity on slug frequency was investigated for the first time in the open literature. Based on a dimensionless analysis approach, a slug frequency closure model was presented for high viscosity oil in horizontal pipes as a new alternative to existing correlations. The developed closure model gives good prediction results in the laminar flow region.