The objective of this study is experimental and theoretical investigation of the fall mechanics of continuous flow plungers. Fall velocity of the two-piece plungers with different sleeve and ball combinations and bypass plungers are examined in both static and dynamic conditions to develop a drag coefficient relationship. Dimensionless analysis conducted including wall effect, inclination and liquid holdup correction of fall stage. The fall model is developed to estimate fall velocities of the ball, sleeve, and bypass plungers. Sensitivity analysis is performed to reveal influential parameters to the fall velocity of continuous flow plungers.

In a static facility, four sleeves with different height, weight, and OD, three balls made with different materials and a bypass plunger are tested in four different mediums. The wall effect on settling velocity is defined, and it is used to validate the ball drag coefficient results obtained from the experimental setup. Two-phase flow experiments were conducted by injecting gas into the static liquid column and liquid holdup effect on drag coefficient is observed. Experiments in a dynamic facility are used for liquid holdup and deviation corrections. The fall model is developed to estimate fall velocities of the continuous flow plungers against the flow. Dimensionless parameters obtained in the experiments are combined with multiphase flow simulation to estimate the fall velocity of plungers in field scale.

Reference drag coefficient values of plungers are obtained for respective Reynold number values. Experimental wall effect, liquid holdup and inclination corrections are provided. The fall model results for separation time, fall velocity, total fall duration, and maximum flow rate to fall against are estimated for different cases. Sensitivity analysis showed that the drag coefficient, the weight of plungers, pressure, and gas flow rate are the most influential parameters for the fall velocity of the plungers. Furthermore, the fall model revealed that plungers fall slowest at the wellhead conditions for the range of gas flow rates experienced in field conditions. Lower pressure at wellhead had two opposing effects; namely, reduced gas density, therefore reducing the drag, and gas expansion, increased the gas velocity, therefore increasing the drag.

Estimating fall velocity of continuous flow plungers is crucial to optimize ball and sleeve separation time, plunger selection and gas injection rate for plunger assisted gas lift (PAGL). The fall model provides maximum flow rate to fall against, which is defined as the upper operational boundary for continuous flow plungers. This study presents a new methodology to predict fall velocity using drag coefficient vs. Reynolds number relationship, wall effect, liquid holdup, deviation corrections and incorporating multiphase flow simulation.

You can access this article if you purchase or spend a download.