| The effect of high oil viscosity on upward two-phase gas-oil flow behavior in vertical pipes was experimentally and theoretically studied. A total of 149 air-high viscosity oil and 21 air-water experiments were conducted in a 50.8 mm ID vertical pipe. Six different oil viscosities, namely, 586, 401, 287, 213, 162, and 127 mPa·s, were used. The superficial liquid and gas velocities were varied from 0.05 m/s to 0.7 m/s and from 0.5 m/s to 5 m/s, respectively.;Flow pattern, pressure gradient, average liquid holdup, translational velocity, slug liquid holdup, slug frequency, and slug length were measured and analyzed in this study. Moreover, an experimental facility analysis and a theoretical investigation on observed positive pressure gradient region were conducted. The investigation showed that the positive frictional pressure gradient phenomena can exists for low gas and liquid velocities in upward two-phase vertical flow without violating the second law of thermodynamics.;The experimental results were also used to evaluate different flow pattern maps, mechanistic models, and correlations for two-phase flow and slug characterization. Significant discrepancies between experimental and predicted results were observed for pressure gradient, slug frequency, and average slug length.;A new slug liquid holdup closure model was developed for high viscosity liquid upward two-phase vertical flow. The model is a function of the Froude number and inverse viscosity number. The proposed model was validated against independent experimental data, and showed very small errors for high viscosity. The proposed model showed better performance than the existing models for high viscosity upward vertical flow.;Based on a dimensionless analysis approach, a new slug frequency closure model was presented for high viscosity liquid upward two-phase vertical flow. The model is a function of Froude number and viscosity number. Using the experimental data, the proposed model showed significant improvement in prediction for high viscosity. |
