Summary The translational velocity, velocity of slug units, is one of the key closure relationships in two-phase flow mechanistic modeling. It is described as the summation of the maximum mixture velocity in the slug body and the drift velocity. The existing equation for the drift velocity is developed by using potential flow theory. Surface tension and viscosity are neglected. However, the drift velocity is expected to be affected with high oil viscosity. In this study, the effects of high oil viscosity on drift velocity for horizontal and upward inclined pipes are experimentally observed. The experiments are performed on a flow loop with a test section 50.8 mm ID for inclination angles of 0° to 90°. Water and viscous oil are used as test fluids. Liquid viscosities vary from 0.001 to 1.237 Pa•s. A new drift velocity model is proposed for high oil viscosity for horizontal and upward inclined pipes. The experimental results are used to evaluate the performances of proposed model for drift velocity. The calculated drift velocities are compared very well with the experimental results. The proposed model could be easily implemented into translational velocity equation. It should improve the existing two-phase flow models in the development and maintenance of heavy oil fields. Introduction High-viscosity oils are produced from many oil fields around the world. Oil production systems are currently flowing oils with viscosities as high as 10 Pa•s. Current multiphase flow models are largely based on experimental data with low viscosity liquids. Commonly used laboratory liquids have viscosities less than 0.020 Pa·s. Multiphase flows are expected to exhibit significantly different behavior for higher viscosity oils. Gokcal et al. (2008b) observed slug flow to be the dominant flow pattern for the high-viscosity oil and gas flows. The knowledge of the slug flow characteristics is crucial to design pipelines and process equipments. In order to improve the accuracy of slug characteristics for high-viscosity oils, new models for slug flow are needed such as translational velocity. Translational velocity is composed of a superposition of the bubble velocity in stagnant liquid (i.e. the drift velocity, vd, and the maximum velocity in the slug body). The research efforts have been focused on the drift velocity in horizontal and upward inclined pipes.

The flow of oil-water for different inclination angles (0 o , ±1 o , ±2 o and -5 o ) was studied through the analysis of high-quality experimental data on flow pattern, pressure gradients, water holdup and phase distribution (Atmaca (2007). A total of 324 tests were conducted in a 0.0508-m. ID 21.1 m. long, inclinable test section using tap water and mineral oil (with a density of 0.85 gr/cm 3 and viscosity of 15 cp) with superficial velocities ranging from 0.025 m/s to 1.75 m/s.Oil-water flow in the petroleum industry is a common occurrence during production and transportation of gas-oil-water in pipes. Facilities design is strongly dependent on the flow behavior. The specific applications include design and troubleshooting of flow lines and wells, separator design, interpretation of production logs, etc.Non-intrusive high-speed camera technique was used to determine the flow patterns at various conditions. Experimental flow pattern maps were compared against Trallero (1995) and Zhang and Sarica (2006) models. Trallero model predicted the most flow pattern boundaries well except stratified flow pattern. For most of the cases, the pressure gradients were over predicted by the Zhang and Sarica model. Quick closing valves are used for holdup measurements giving phase slippage information. For the low superficial velocities, slippage behavior was observed very clearly for upward and downward flow. For the high superficial velocities, slippage effects were diminished. Representative phase distributions, and interface boundaries were observed for different flow conditions by examining conductivity probe data.This paper provides significant insight in phase distribution and slippage behavior. The results presented in this study are applicable not only to oil-water flow but also to three-phase gas-oil-water flow models.

Oil/water flow is a common occurrence during production and transportation of petroleum fluids through pipes. Understanding of oil/water pipe flow behaviors is crucial to many applications including design and operation of flow lines and wells, separation, and interpretation of production logs. In this study, the oil/water pipe flow was experimentally investigated for different inclination angles (0 o , ±1 o , ±2 o and -5 o ). A total of 324 tests were conducted in a 0.0508-m (2-in.) ID 21.1-m (69.6-ft) long test section using tap water and mineral oil with superficial velocities ranging from 0.025 to 1.75 m/s. The experimental results include observations of flow patterns and phase distributions, and measurements of water holdups and pressure gradients. A high-speed video system was used to observe the mixing status between oil and water and to determine the flow patterns at various flow conditions. Quick closing valves were used to measure the phase holdups and to demonstrate the slippage between oil and water with the water cut to water holdup ratio. The experimental results of flow pattern transitions, water holdups, and pressure gradients are compared against predictions of the Zhang and Sarica (2006) model. The model performance is analyzed based on the experimental observations and the modeling considerations. Recommendations are presented for future model improvement.