Characterization of Oil/Water Flows in Horizontal Pipes
- Maria A. Vielma (Schlumberger) | Serdar Atmaca (U. of Tulsa) | Cem Sarica (U. of Tulsa) | Hong-Quan Zhang (U. of Tulsa)
- Document ID
- Society of Petroleum Engineers
- SPE Projects, Facilities & Construction
- Publication Date
- December 2008
- Document Type
- Journal Paper
- 1 - 21
- 2008. Society of Petroleum Engineers
- 4.3 Flow Assurance, 4.2 Pipelines, Flowlines and Risers, 4.1.2 Separation and Treating, 5.3.2 Multiphase Flow, 2.5.2 Fracturing Materials (Fluids, Proppant), 4.2.3 Materials and Corrosion, 3.1 Artificial Lift Systems, 4.1.5 Processing Equipment, 3.3.1 Production Logging, 4.6 Natural Gas, 3.1.7 Progressing Cavity Pumps
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The dynamic characteristics of oil/water flow systems have not been understood fully. The need for improved designing methods has led researchers toward its continuous investigation. The objective of this study was to characterize oil/water flow through experimental data. The tests were conducted in a 2-in. horizontal test section using tap water and mineral oil (density=0.85 g/cm3 and viscosity=15 cp), with superficial velocities ranging from 0.025 to 1.75 m/s. Data were acquired on flow patterns, pressure drop, phase fraction, and droplet size as a function of flow patterns and were used in characterization of the flow and performance evaluation of an oil/water model. A high-speed video camera was used to identify flow patterns and measure droplets, and ten conductivity probes were used to obtain phase distributions. This paper provides new experimental data on pressure drop, holdup, phase distribution, and droplet-size distribution in oil/water flows that can lead to better modeling and design of dispersed systems. Moreover, the new data provide new information on droplet sizes that can have significant impact on separator design. Data comparisons were performed against the data of Trallero (1996). Three probabilistic distributions were tested for fully dispersed flows. A Sauter mean-diameter (SMD) analysis was conducted across the pipe diameter. Droplet-size data were used to evaluate existing models such as Hinze (1955), Kubie and Gardner (1977), Angeli and Hewitt (2000), and Kouba (2003). An empirical correlation to predict the SMD profile of droplets across the pipe cross section was developed for flow pattern of dispersed oil in water (o/w) and water. Log-normal distribution was the best probabilistic distribution for representing the data for fully dispersed systems. The empirical correlation gave acceptable results. More data are needed to validate the results. Model comparisons revealed that none of the models could represent the experimental data accurately. This paper provides significant insight into oil/water flows in horizontal pipes. The results are significant for the design of pipelines and separators. Moreover, the interpretation of production logs in horizontal wells relies heavily on the flow behavior.
Two-phase liquid/liquid flow can be defined as the simultaneous flow of two immiscible liquids. It can be encountered in a wide range of industries, including the oil industry, where it commonly occurs in the production and transportation of oil and water during the later years of production.
When heterogeneous fluids are flowing together, they are characterized by the existence of diverse flow configurations and flow patterns, or a geometrical arrangement of the phases in the pipe. The flow patterns differ from each other in the spatial distribution and the position of the interface, resulting in different flow characteristics, such as velocities, holdup profiles, and pressure gradients. These internal-flow structures depend on variables such as flow rates of both liquids, pipe geometry, and physical properties of the liquids involved.
The flow characteristics of oil-water mixtures are generally different from gas/liquid systems. The differences in characteristics are caused mainly by the large momentum-transfer capacity, small buoyancy effects, lower free energy at the interface, and smaller dispersed-phase droplet size in liquid/liquid flows (Trallero et al. 1997). Therefore, the characteristics of gas/liquid flow cannot be applied directly to oil/water flow in most cases. Generally, knowledge of the distinctive features of oil-water systems, together with those of gas/liquid systems, can be used in the future for understanding the more complex case of gas/oil/water mixtures, which occur daily in petroleum-industry production systems.
From the different existing flow patterns in oil/water flows, stratified flow in particular has received the most attention because the low flow velocities and well-defined interface favor both experimental and theoretical investigations. For fully dispersed systems, information is available mainly from studies in stirred vessels. The available information is even more limited for the intermediate flow patterns between stratified and fully dispersed flows (Lovick et al. 2000).
The pressure drop for two-phase liquid/liquid pipe flows depends strongly on the flow regime and, hence, on the distribution of the two liquids in the cross-sectional area of the pipe. Turbulent mixing in the pipe can be sufficient to disperse the initially separated phases so that dispersions are formed, resulting in higher pressure drops. The flow behavior of dispersions of oil and water depends on the volume fraction and the droplet distribution of the dispersed phase (Nädler and Mewes 1997). Droplet size depends on the competition between breakup and coalescence phenomena. Knowledge of droplet size and distribution would improve understanding of dispersed systems and contribute to better design and modeling of them.
Experimental data on average droplet size exist mainly for low dispersed-phase concentrations, where a variety of measuring techniques can be used. Few studies have looked at high concentrations, and most of them involved surfactant-stabilized emulsions. That available data on average droplet size and its distribution are limited, especially in unstable dispersions at high dispersed-phase volume fractions, is partially a result of the difficulty in performing such measurements.
|File Size||3 MB||Number of Pages||21|
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