Mitigating the Failure of Downhole Pumps Due to Gas Interference in Coal Seam Gas Wells

Abstract

Coal seam gas (CSG) well operators typically follow an industry rule of thumb 0.5 ft/s liquid velocity to prevent the onset of gas carryover during CSG dewatering operations. However, there is very little experimental data to validate this rule of thumb with only a publication by Sutton, Christiansen, Skinner and Wilson [1] available in the open literature. A review of more general studies on two-phase gas-water flows in vertical pipes and annuli revealed that experimental conditions, especially pipe and annuli diameters, can have a significant impact on development of two-phase flow phenomena. As such, the limited available data may not be applicable due to differences in experimental conditions. This study experimentally investigates the onset of gas carryover using an experimental setup intended specifically for the study of CSG wells. The University of Queensland Well Simulation Flow Facilities were designed to replicate as closely as possible the production zone of a typical vertical CSG well in Queensland, Australia in transparent acrylic pipes to observe two-phase flow behavior in simulated downhole conditions. The annular test section in the rig was constructed of a 7-in casing and 2¾-in tubing. Modification of the experimental setup to include a vertical separator allowed for the detection of gas carryover. Conceptual demonstrations of gas carryover were captured and have been illustrated. The experiments in this study validate the industry rule of thumb of 0.5 ft/s liquid velocity as an appropriate guideline for onset of gas carryover in a casing-tubing annulus dimension similar to a typical CSG well in Queensland.

The experimental study of counter-current two-phase flows in annuli

“…experimentally investigated the onset of liquid flooding, wherein gas is carried downward by the liquid phase, and supported a critical superficial liquid velocity of approximately 0.152 m/s. This cut-off value was validated in Chapter 5 (Wu et al, 2018) and has been included in Figure 3-15 for comparison, showing a good overall agreement with our experimental results. Our results also indicated that the onset of liquid flooding is almost independent of gas flow rate.…”

“…The content of this chapter is based on: Wu, B., Firouzi, M., Rufford, T. E. and Towler, B. (2018) " et al (2006) available in the open literature.…”

“…In addition to studying the counter-current flow regimes, we observed two extremes that collectively form the counter-current flow limitation: gas flooding due to very high gas flow rates and liquid flooding due to very high liquid flow rates. The counter-current flow limitation due to very high liquid flow rates, described as liquid flooding with gas being dragged downward by liquid, was detected using the setup developed in Chapter 5 (Wu et al, 2018) and shown in Figure 3 , allowing liquid flooding to be confirmed when slugs of air and water exit from the vent hose.…”