Effect of Medium Oil Viscosity on Two Phase Oil Gas Flow Behavior in Horizontal Pipes
Authors: Sarica Cem , Pereyra Eduardo Javier , Brito Rosmer 
Published: May 2013

Abstract
There are significant amount of fields operating with medium viscosity oils(10 cP&lt;µO&lt; 180 cP) Moreover, some of the oils produced from offshore fields can have medium range viscosities when they are exposed to cold sea temperatures. Current two-phase flow models are based on experimental data with low (10 cP&lt;µO) and high (µO&gt;180 cP) viscosity liquids. Therefore, existing mechanistic models need to be verified or improved with medium liquid viscosity experimental results. Effect of liquid viscosity on gas-liquid two phase flow is still not well understood. In the past, most of the studies focused on low (10 cP&lt;µO) viscosity liquids. Significant changes has been observed for high viscosity conditions (µO&gt;180 cP) but no experimental studies for medium oil viscosities has been reported. Thus, there is a need for experimental investigation of medium viscosities in order to characterize the two-phase flow behavior for the entire range of possible viscosities.
A systematic experimental program on medium oil viscosities (39 cP&lt;µO&lt;166 cP) is presented in this study. The experiments are performed using a flow loop with a test section of 50.8-mm ID and 18.9-m-long horizontal pipe. The range of superficial liquid and gas velocity are 0.01 m/s to 3.0 m/s and 0 to 7.0 m/s, respectively. Two-wire capacitance sensors are used to measure the liquid holdup. Visual observation and high speed video recordings are used for flow pattern identification. Effect of viscosity on pressure gradient, liquid holdup and flow pattern is reported. It is observed that the stratified smooth region shrinks when the oil viscosity increases. Dispersed bubble flow presents larger bubble concentration at the top of the pipe as compared with low viscosity case. Acquired experimental data are used to evaluate existing mechanistic models and discrepancies are reported as function of oil viscosity.

Introduction
Gas-liquid two-phase flow in pipes is a common occurrence in the petroleum industry production and transportation of oil and gas. Accurate prediction of the flow pattern, pressure drop and liquid holdup is imperative for the design of production and transport systems. Two-phase flow presents a complex flow configuration. Flow behavior is function of flow variables such as gas and liquid flow rates, pipe diameter, inclination angle and fluid properties (gas and liquid density, viscosities and surface tension). Previous experimental studies show different two-phase gas-liquid flow behavior for low viscosity oils (20 cP &lt; µO) and high viscosity oils (µO &gt; 200 cP). Pereyra et al. (2012) compiled all the available gas-liquid flow pattern experimental data for different oil viscosity ranging from lower viscosity (1 cP- 7 cP) to high viscosity (140 cP- 700 cP). Of these data points, 8677, 121 and 555 were for low, medium and high viscosities, respectively. Their analysis shows that a few experiments for medium viscosity are available to validate the current flow pattern, pressure drop and liquid hold up models. Thus, there is a need of experimental investigation for medium viscosities oils in order to properly characterize the two-phase flow behavior for the entire range of possible viscosities.