Experimental Investigation and Modeling of Onset of Liquid Accumulation in Large- Diameter Deviated Gas Wells

Abstract

The challenges related to liquid loading have been observed during flow-back after hydraulic fracturing, as well as during the production phase, and are further aggravated with the high inclination angles found in deviated wellbores. An experimental study was carried out to investigate the onset of liquid loading in a 6-inch production casing at various inclination angles. A unified mechanism model for the onset of liquid loading is developed for a large-diameter production casing. The experimental setup includes a 6-inch acrylic test section which can be inclined from 0° to 90°. The study involves two-phase air-water flow in low liquid loading conditions to simulate a gas well. A dye- injection-system was used to detect the onset of liquid film reversal. The experimental data demonstrates that the major factor that induces liquid accumulation is the liquid film reversal at pipe bottom. The critical gas velocity associated with the onset of liquid film reversal shows a strong function with the inclination angle and liquid flow rate in the current experimental study. Comparison with previous experimental data reveals that it also depends on the gas density and pipe diameter, i.e. it decreases with increasing gas density and increases when pipe diameter increases. Comprehensive model evaluation was conducted in the current study, showing a large discrepancy for inclination angles higher than 45° and few existing models capture all the effects of deviation angle, liquid flow rate, pressure, and pipe diameter. A new model is developed based on the physics of the onset of liquid film reversal, coupled with a new model for the liquid film thickness distribution around the pipe perimeter. It captures well the effects of deviation angle, liquid flow rate, gas and liquid density, viscosity, and pipe diameter on the critical gas velocity, outperforming all other existing models. The experiments in this study provide new insights into the onset of liquid accumulation in large- diameter deviated wells. The new mechanics model fills the critical gap to enhance accuracy when predicting the onset of liquid loading especially for deviated and large-diameter wells. It can be easily implemented, which will benefit the industry practically. It is also applicable to gas condensate pipelines where smaller inclination angles exist.