The Effect of Development of Two-Phase Flow Regimes on the Stability of Gas Lift Systems

Authors: Khalid. M. O. Elmabrok, M. L. Burby, G. G. Nasr

Abstract:

Flow instability during gas lift operation is caused by three major phenomena – the density wave oscillation, the casing heading pressure and the flow perturbation within the two-phase flow region. This paper focuses on the causes and the effect of flow instability during gas lift operation and suggests ways to control it in order to maximise productivity during gas lift operations. A laboratory-scale two-phase flow system to study the effects of flow perturbation was designed and built. The apparatus is comprised of a 2 m long by 66 mm ID transparent PVC pipe with air injection point situated at 0.1 m above the base of the pipe. This is the point where stabilised bubbles were visibly clear after injection. Air is injected into the water filled transparent pipe at different flow rates and pressures. The behavior of the different sizes of the bubbles generated within the two-phase region was captured using a digital camera and the images were analysed using the advanced image processing package. It was observed that the average maximum bubbles sizes increased with the increase in the length of the vertical pipe column from 29.72 to 47 mm. The increase in air injection pressure from 0.5 to 3 bars increased the bubble sizes from 29.72 mm to 44.17 mm and then decreasing when the pressure reaches 4 bars. It was observed that at higher bubble velocity of 6.7 m/s, larger diameter bubbles coalesce and burst due to high agitation and collision with each other. This collapse of the bubbles causes pressure drop and reverse flow within two phase flow and is the main cause of the flow instability phenomena.

Keywords: Gas lift instability, bubble forming, bubble collapsing, image processing.

Digital Object Identifier (DOI): doi.org/10.5281/zenodo.1125167

References:

[1] Hu, B., Characterization of gas-lift instabilities. 2005.
[2] Eikrem, G.O., Stabilization of Gas-Lift Wells by Feedback Control. 2006.
[3] Brill, J.P., Multiphase Flow in Wells. 1987.
[4] Poettman, F.H. and P.G. Carpenter, The Multiphase Flow of Gas, Oil, and Water Through Vertical Flow Strings with Application to the Design of Gas-lift Installations. 1952, American Petroleum Institute.
[5] Zabaras, G.J., Physical Modelling Of Vertical Multiphase Flow: Prediction Of Pressure Gradients In Oil And Gas Wells. 1994, Offshore Technology Conference.
[6] Hasan, A.R. and C.S. Kabir, A Study of Multiphase Flow Behavior in Vertical Wells. 1988.
[7] Kaji, R., B.J. Azzopardi, and D. Lucas, Investigation of flow development of co-current gas–liquid vertical slug flow. International Journal of Multiphase Flow, 2009. 35(4): p. 335-348.
[8] Omebere-Iyari, N.K. and B.J. Azzopardi, A Study of Flow Patterns for Gas/Liquid Flow in Small Diameter Tubes. Chemical Engineering Research and Design, 2007. 85(2): p. 180-192.
[9] Kaji, R. and B.J. Azzopardi, The effect of pipe diameter on the structure of gas/liquid flow in vertical pipes. International Journal of Multiphase Flow, 2010. 36(4): p. 303-313.
[10] Bertuzzi, A.F., J.K. Welchon, and F.H. Poettman, Description and Analysis of an Efficient Continuous-Flow Gas-Lift Installation. 1953.
[11] Gilbert, W.E., Flowing and Gas-lift well Performance. 1954, American Petroleum Institute.
[12] Hagedorn, A.R. and K.E. Brown, The Effect of Liquid Viscosity in Two-Phase Vertical Flow. 1964.
[13] Orkiszewski, J., Predicting Two-Phase Pressure Drops in Vertical Pipe. 1967.
[14] Gould, T.L. and M.R. Tek, Steady and Unsteady State Two-Phase Flow through Vertical Flow Strings. 1970, Society of Petroleum Engineers.
[15] Bin, H. and M. Golan, Gas-lift Instability Resulted Production Loss and Its Remedy by Feedback Control: Dynamical Simulation Results. 2003, Society of Petroleum Engineers.
[16] Nicolas, Y. and E.J. Witterholt, Measurements Of Multiphase Fluid Flow. 1972, Society of Petroleum Engineers.
[17] Asheim, H., Criteria for Gas-Lift Stability. 1988.
[18] Alhanati, F.J.S., et al., Continuous Gas-Lift Instability: Diagnosis, Criteria, and Solutions. 1993, Society of Petroleum Engineers.
[19] Faustinelli, J., A. Cuauro, and G. Bermúdez, A Solution to Instability Problems in Continuous Gas-Lift Wells Offshore Lake Maracaibo. 1999, Society of Petroleum Engineers.
[20] Dentec, C.D., Dynamicstudio2015 manual. 2015.
[21] Peter Griffith, G.B.W., Two-Phase Slug Flow. Journal of Heat Transfer, 1961. Volume 83 (3): p. 307-318.