In this study, two-phase flow pressure prediction correlations and mechanistic models for pipelines commonly used in petroleum industry are evaluated against experimental data.
Downward two-phase flow occurs in hilly terrain pipelines, in steam injection wells, as well as in offshore oil and gas production systems. During pipeline design and simulation, experimental data are usually unavailable to calibrate against correlations and models. Sometimes it is difficult to determine which correlation or model to use in predicting pressure gradient in inclined downward flow since there are very a few correlations and models were developed specifically for downward pipe flow.
Experimental data used in this study are from a published paper (Kokal and Stanislav, 1989). Experimental data were gathered from 1-inch, 2-inch and 3-inch pipes with seven inclination angles. Oil and air were used as testing fluids. During the experiment, superficial liquid velocities range from 1.2 to 10 ft/s and superficial gas velocities range from 0.76 to 85 ft/s. The experimental results were plotted as pressure gradient vs. superficial gas velocity for each superficial liquid velocity.
Beggs-Brill, Dukler-Eaton-Flanigan, Dukler-Flanigan, Dukler, Eaton, Eaton-Flanigan correlations and Xiao mechanistic model are evaluated in this study.
The results of this study can be used as guidelines in choosing two-phase flow pressure prediction correlations and models in designing and analyzing downward two-phase flow pipelines.
Downward two-phase pipe flow is a common occurrence in oil and gas production and transportation. Although there are many pipeline correlations and mechanistic models around, during pipeline design and simulation, it is often difficult to determine which correlation or mechanistic model to use.
Correlations and mechanistic models evaluated in this study include Beggs-Brill (BB), Dukler-Eaton-Flanigan (DEF), Dukler-Flanigan (DF), Dukler (D), Eaton (E), Eaton-Flanigan (EF) and Xiao mechanistic (Xiao). Below is a brief description of the correlations and Xiao Mechanistic model.
The Beggs-Brill correlation was developed from experimental data obtained in a small scale test facility. The facility consisted of 1-inch and 1.5-inch sections of acrylic pipe 90 ft long. Fluids used were air and water. The correlations were developed from 584 measured tests for all inclination angles (Brill and Beggs, 1991).
The Eaton correlation was developed from experimental data obtained from a flow system consisting of 2-inch and 4-inch horizontal lines. Correlations were for liquid holdup and two-phase friction factor (Brill and Beggs, 1991).
The Dukler correlation was based on similarity analysis and the friction factor and liquid hold up correlations were developed from field data (Brill and Beggs, 1991).
The Eaton-Flanigan, Dukler-Flanigan and Dukler-Eaton-Flanigan correlations used the Flanigan corrected correlation, where elevation term in the total pressure gradient is neglected for down hill flow (Brill and Beggs, 1991). Eaton-Flanigan uses Eaton correlation with elevation term neglected, Dukler-Flanigan uses Dukler correlation with elevation term neglected, and Dukler-Eaton-Flanigan uses Dukler correlation for friction calculation, Eaton correlation for liquid holdup calculation and elevation term is neglected (Pipesoft-2TM Manual 2, 2007).
The Xiao model is a comprehensive mechanistic model developed for gas-liquid two-phase flow in horizontal and near horizontal pipelines. It has been evaluated against a data bank that includes field data culled from the A. G. A. database, and laboratory data published in the literature (Xiao et al., 1990).