Plunger Fall Velocity Studies in Vertical Wells

Abstract

The objective of this study is to experimentally investigate the fall velocities of several type of plungers in various stagnant liquids and at different dynamic operating conditions. Six different plungers were evaluated, namely, new and used brush, new and used dual pad, new and used spiral, and new two piece type plungers. The experimental studies were carried out using two different facilities. First, a simple plunger setup was used to measure the fall velocity of different plungers. This experimental configuration allows the use of different liquids at stagnant conditions (water, water with flowing air and oil). The experimental results show that plunger fall velocity in water is about 4% of the plunger velocity in air. Under a bubbling column and for all plunger types, the fall velocity fluctuates as the air passes through the plunger yielding, in some cases, an average velocity similar to the water case. The fall velocities in low and medium viscosity oils are 60% and 42% of the average velocity in water, respectively. Second, a comprehensive experimental facility was designed and constructed to study the plunger under dynamic operating conditions (or cycles) and at different fluid pressures (air). When the plunger fall velocity was studied under a cyclic operating conditions, the resultant fall velocity is about 60% of the velocity observed in only air, but 30 times larger than the corresponding velocity in stagnant oil. Comparatively, the fastest conventional plunger is the spiral type, whereas the conventional sealing types (pad and brush) are the slowest ones. In addition, the effect of pressure is substantial and the fall velocity of the plunger rapidly decreases as the gas phase (air) pressure increases. Based on the experimental observations and data analysis, it was found that the fall velocity depends mainly on the type of plunger, air phase pressure, thickness of the liquid film on tubing wall, viscosity of the liquid, and density of the gas phase. Plunger lift is one of the most used deliquification method for gas wells. However, only a few experimental studies have been found in the literature. None of them attempt the comparison of different plungers. This study present a new set of data that helps to understand the behavior of the different types of plungers.