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TUALP Abstract
Lackner, Gemot (Doctor of Philosophy in Petroleum Engineering)
The Effect of Viscosity on Downhole Gas Separation in a Rotary Gas
Separator
(198 pp. - Chapter VIII)
Directed by Dr. Zelimir Schmidt and Dr. Dale R. Doty
(326 words)
The presence of free gas at pump intake adversely affects the performance of an electrical submersible pump (ESP) system, often resulting in low efficiency and causing operational problems. One method of reducing the amount of free gas that the pump has to process is to install a rotary gas separator.
The objective of this study is to investigate experimentally and theoretically the influence of fluid physical properties on the downhole separation process emphasizing fluid viscosity.
An existing full scale experimental facility (Tulsa University Artificial Lift Projects (TUALP) two-phase flow loop) was modified and new experimental data were gathered. Mineral oils and air were the working fluids. The experimental matrix covered a wide range of operational conditions, e.g., liquid flow rates up to 2700 bpd, gas-liquid ratios up to 3 00 scf7stb and system pressures up to 300 psig. The tests were conducted using a commercial 400 series REDA rotary gas separator that was installed in a 50' tall 7" (6.3" I.D.) casing section.
The theoretical development of the mathematical model (which is based on physical principles only) focused on the appropriate formulation of the turbulent two-phase flow phenomena associated with the separation process. The turbulent effects can be viewed as an additional turbulent or eddy viscosity that must be accounted for. A twolayer mixing-length turbulence model was adopted for this type of high speed rotational two-phase flow. The numerical solution of this two-phase flow problem followed well established single-phase flow numerics.
The result of the present study indicates that there are two regions of separation efficiency that have a pronounced transition between them. In one the rotary gas separator is very effective (separation efficiencies between 80 % and 1 00 %) and in the other it is not effective at all (separation efficiencies between 30 % and 5 5 %). The location of the transition depends on fluid physical properties, operational conditions and complex geometries.
The experimental data and the theoretical model agree well. Fluid viscosity, in the range of investigation (1 cp to 50 cp at 1 00 °F), is found to have little influence on gas separation efficiency, indicating that the additional viscosity due to turbulence dominates.Download dissertation (TUALP members only)
Last updated September 04, 2012