A Model To Predict Liquid Holdup and Pressure Gradient of Near-Horizontal Wet-Gas Pipelines
- Yongqian Fan (ConocoPhillips Co.) | Qian Wang (ConocoPhillips Co.) | Hong-Quan Zhang (ConocoPhillips Co.) | Thomas John Danielson (ConocoPhillips) | Cem Sarica (U. of Tulsa)
- Document ID
- Society of Petroleum Engineers
- SPE Projects, Facilities & Construction
- Publication Date
- June 2007
- Document Type
- Journal Paper
- 1 - 8
- 2007. Society of Petroleum Engineers
- 4.1.5 Processing Equipment, 4.1.2 Separation and Treating, 4.1.6 Compressors, Engines and Turbines, 4.2.3 Materials and Corrosion, 5.3.2 Multiphase Flow, 4.2 Pipelines, Flowlines and Risers, 5.2.2 Fluid Modeling, Equations of State, 4.2.2 Pipeline Transient Behavior, 4.6 Natural Gas, 4.3.4 Scale
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A mechanistic two-fluid model with new closure relationships is proposed to predict liquid holdup and pressure gradient of stratified flow. The proposed closure relationships include correlations of wetted-wall fraction factor, liquid-wall friction factor, and interfacial-friction factor. An iterative calculation procedure is implemented to solve for liquid holdup and pressure gradient for a given set of operating conditions, pipe geometry, and fluid properties.
Two sets of facilities, a small-scale facility with 51-mm internal diameter (ID) and a large-scale facility with 150-mm-ID test sections, were used to tune the model. Superficial gas and liquid velocities were varied from 5 to 25 m/s and 0.00025 to 0.03 m/s, respectively, in the small-scale facility while they were varied from 7.5 to 21 m/s and 0.005 to 0.05 m/s, respectively, in the large-scale facility. The pipe inclination angle varied from -2 to 2°. The liquid holdup was ranged between 0.003 and 0.12, emphasizing the low-liquid-loading two-phase flow.
The tuned model performance was then benchmarked against the high-pressure (up to 90 bar) SINTEF-stratified flow data. The model predictions agreed well with measured values of liquid holdup and pressure gradient. The comparison between the present model and OLGA® (a commercial transient multiphase-flow simulator by Scandpower Petroleum used widely in the petroleum industry) performance was also presented.
Stratified flow with a low-liquid loading (< 1100 sm3/MMsm3) is a dominant-flow pattern in wet-gas pipelines. A good prediction of liquid holdup and pressure gradient is critical to pipeline size selection and the design of downstream facilities (e.g., slug catcher). Model underestimation of pressure gradient will give a smaller pipe size than required, and the transportation capacity will be restricted; model overestimation of pressure gradient will result in an oversized pipeline, worse sweeping characteristics, and possible solids dropout and corrosion issues. In this section, some of the previous work on stratified flow were reviewed.
Taitel and Dukler (1976) proposed a 1D two-fluid model that assumed a flat gas/liquid interface. A Blasius-type equation was used to calculate gas-wall and liquid-wall friction factors. The effect of interfacial shear stress was taken into account. It was assumed that the interfacial friction factor was equal to the gas-wall friction factor for stratified-smooth flow, and 0.014 for stratified-wavy flow. Cheremisinoff and Davis(1979) collected experimental data of air/water flow in a 63.5-mm-ID horizontal-flow loop. The liquid-phase flow was modeled using an eddy-viscosity expression developed for single-phase flow. To simplify the problem, the authors assumed that the shear stress was constant in the liquid region, and liquid velocity was dependent only on radial distance from the pipe wall. Akai et al.(1981) solved the momentum equations for both phases. The turbulence effect was considered by using a modified model, which is applicable to low-Reynolds-number cases. Shoham and Taitel(1984) numerically solved the liquid-phase momentum equation, considering the gas phase as a bulk flow. The eddy-viscosity model was applied to simulate the turbulence effect in the liquid phase. Issa(1988) solved the momentum equations for both gas and liquid phases to calculate pressure gradient and liquid holdup. The author used the two-equation model to simulate the turbulence effect in both phases.
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