Experimental Study on How Hydrophobic Tubing Modifies Gas Wells Liquid Unloading

Abstract

Experimental and theoretical studies on liquid unloading in gas wells show that the critical gas velocities for carrying droplets upward is much smaller than the critical gas velocity for carrying liquid film upward. The latest studies show that the hydrophobic coating can change solid surface wettability, reduce contact area between liquid droplet and solid surface, and can promote the droplet formation from liquid film in annular flow. It is speculated that tubing with a hydrophobic wall can reduce the critical gas rate of liquid unloading under certain production conditions. However, how hydrophobic tubing modifies gas wells liquid unloading is still unknown. This study presents the experimental results of air-water two phase flow in hydrophobic pipe. First, a hydrophobic coating was sprayed on the inner wall of a transparent pipe, and an experimental loop with a height of 8 m and an inner diameter of 40 mm was built for air-water two phase flow. A comparative experiment was conducted in the pipe with and without hydrophobic coating. The influence of hydrophobic coating on flow pattern characteristics, flow pattern transition conditions, pressure gradient, liquid holdup, droplet entrainment fraction, and critical gas velocity were measured. The mechanism of hydrophobic coating improves the liquid carrying capacity of gas stream has been revealed from multiple perspectives.