172271 experimental investigation of gas lift instability and dynamic regulation to control it...
TRANSCRIPT
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172271
Experimental Investigation of Gas Lift Instability and Dynamic Regulation to Control It
Author/presenter: Christer Andre Larsen, NTNU
Co-author: Harald Arne Asheim, NTNU
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Outline
• Short introduction to gas lift and gas lift instability
• Description of stabilization procedure
• Description of laboratory model
• Description of the experimental procedure
• Results
• Discussion
• Conclusion
• Acknowledgements
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172271 · Experimental Investigation of Gas Lift Instability and Dynamic Regulation to Control It · Christer Andre Larsen
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Basics of gas lift
• Pressurized gas is supplied to annulus
• Injected down hole into the production tubing
• The injected gas is mixed with the production fluid, reducing the volumetric density
• Decreased volumetric density increases flow
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172271 · Experimental Investigation of Gas Lift Instability and Dynamic Regulation to Control It · Christer Andre Larsen
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Gas lift instability
• Casing Heading:
• Small pressure variations lead to a dynamic response from annulus
• Large fluctuations in pressure and flow
• Whole production system contributes to the instability
• Can lead to:
• Safety hazard, Production loss, flaring, process shutdown
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172271 · Experimental Investigation of Gas Lift Instability and Dynamic Regulation to Control It · Christer Andre Larsen
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Gas lift instability, cont.Slide 5
172271 · Experimental Investigation of Gas Lift Instability and Dynamic Regulation to Control It · Christer Andre Larsen
• Typical production during Casing Heading instability with the laboratory rig:
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New approach to reduce the fluctuations
• The pressure variations has a natural frequency, which depends on volume and production rate
• By inducing a new frequency to the system, a destructive interference can occur
• In this case this is accomplished by successive opening and closing of the tubing outlet valve or the gas injection valve at a predetermined frequency
• Its effect is investigated by a laboratory rig
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172271 · Experimental Investigation of Gas Lift Instability and Dynamic Regulation to Control It · Christer Andre Larsen
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Laboratory facility
• Air lifts water up a 7.2 m long, 4.2 m high tubing with a 25 mm inner diameter
• A 20 L tank acts as the annulus volume
• Different valves and transmitters regulates and measures the flow in real time
• Data is logged for analysis
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172271 · Experimental Investigation of Gas Lift Instability and Dynamic Regulation to Control It · Christer Andre Larsen
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Experimental procedure
• Water is filled up to a predetermined height
• Supply and injection of gas is started
• Supplied with a constant rate monitored by a rotameter
• Electronic measurement of water inflow rate, annulus pressure and injection rate starts
• Natural frequency of the instability is found by Fourier analysis, and a control of either tubing outlet valve or production valve is started
• Data is logged for analysis throughout the experiment
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172271 · Experimental Investigation of Gas Lift Instability and Dynamic Regulation to Control It · Christer Andre Larsen
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Results
• Control of tubing outlet valve:
• Natural frequency of 0.034 Hz was found (30 sec. period)
• Controlled by a 60 % reduction in valve opening with 0.1, 0.3, 0,7 Hz closing frequency
• Up to 90 % reduction in oscillations depending on control frequency
• No production decrease after control is initiated
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0.1 Hz closing freq.
0.3 Hz closing freq.
0.7 Hz closing freq.
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Results
• Control of injection valve:
• Natural frequency of 0.034 Hz was found as before
• Controlled by a total closing of valve opening with 0.1, 0.5, 0,7 Hz closing frequency
• Up to 80% reduction in oscillations depending on control frequency
• 37% production increase after control is initiated
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172271 · Experimental Investigation of Gas Lift Instability and Dynamic Regulation to Control It · Christer Andre Larsen
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0.1 Hz closing freq.
0.5 Hz closing freq.
0.7 Hz closing freq.
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Discussion
• Scaled down models should be viewed with sobriety
• The laboratory model shows similar trend to reality, giving credibility to the results
• Control of tubing outlet valve most realistic control method
• Both control methods improved stability, with degree of stabilization depending on valve closing frequency
• Best stabilization occurred when the valve control frequency was dominant in the frequency spectrum
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172271 · Experimental Investigation of Gas Lift Instability and Dynamic Regulation to Control It · Christer Andre Larsen
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Conclusion
• The measurements showed that frequency control may be imposed by manipulation of either the injection valve, or the tubing outlet valve
• Imposing a frequency may reduce pressure- and flow variation up to 80-90% and increase production rate up 37%
• The measurements identified destructive frequencies that eradicated the natural instability
• Highest rate improvement was achieved by inlet valve control. However, as the tubing outlet valve is easier accessible, it may be of equal practical interest.
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172271 · Experimental Investigation of Gas Lift Instability and Dynamic Regulation to Control It · Christer Andre Larsen
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Acknowledgements / Thank You / Questions
Presented by the authors are grateful to Aage Sivertsen for help in instrumentation. Yuri Ivanov and Alexei Ctovas provided substantial
assistance to the Russian translation.
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