Pressure Effects on Pressure Gradient and Liquid Holdup in Two-Phase Oil-Gas Low-Liquid-Loading Flow in Horizontal Pipes

An experimental study is conducted in a 6-in. inner diameter (ID) high-pressure facility to investigate the pressure effects on two-phase oil-gas low-liquid-loading flow in horizontal pipes. The investigated flow characteristics include pressure gradient and liquid holdup. Total of 247 tests are conducted at five different operating pressures: 200, 250, 300, 350 and 400 psig. The test fluids are nitrogen and mineral oil (Isopar-L). Superficial oil velocity ranges from 0.01 to 0.05 m/s, while superficial gas velocity ranges from 1.6 to 16.7 m/s depending on the operating pressures. Differential pressure transmitters, quick closing valves, visualization system, and dual Wire-Mesh Sensors (WMS) are used to acquire the data. The experimental data are analyzed and compared with the model predictions. Suggestions are made to improve the existing model. It is found that the operating pressure clearly affects pressure gradient. The effects of operating pressure on liquid holdup are insignificant for the investigated range. The performances of the transient multiphase-simulation software OLGA High Definition (Biberg et al. (2015)), standard OLGA version 2015 (Bendiksen et al. (1991)), the Tulsa University Fluid Flow Project (TUFFP) Unified Model version 2015 (Zhang and Sarica (2003)), and Xiao et al. (1990) models are tested against the acquired pressure gradient and liquid holdup data. The results from all models are in good agreement with experimental liquid holdup and pressure gradient data for stratified wavy flow. OLGA v2015 and TUFFP Unified Model v2015 have performed the best for annular flow. Modification of the interfacial velocity in the interfacial shear stress term in TUFFP Unified Model v2015 is suggested to partially account for the effects of the operating pressure. The new model predictions are compared with the experimental data from this study and studies from other sources. Significant improvements in the model predictions are observed in comparison with the TUFFP Unified Model v2015. Experiments at high pressures are very limited because of the high cost of these experiments. This paper provides a unique experimental data set for two-phase flow in a 6-in ID horizontal pipe at high operating pressure. In addition, the model comparison and development are given in this paper.