Hydrodynamics of Continuous Flow Plunger Lift

Abstract

AbstractThe distinctive characteristic of continuous flow plungers (CFP) is the ability to complete a plunger cycle without a pressure buildup period. The hydrodynamics of the fall and upstroke stages of the CFP lift is vital to determine operational envelope, select plunger, and optimize gas lift. This paper presents the results of an experimental and theoretical study conducted to develop fall and upstroke models with dimensionless parameters.The fall motion of four sleeves with different height, weight, and outer diameter, three balls made from different materials, and a bypass plunger were tested in the static facility with four different fluids. The wall effect on settling velocity was defined, and drag coefficient results for balls were validated with the literature. The liquid holdup effect on the drag coefficient was investigated by injecting gas into the static liquid column. The 40-ft long dynamic facility is utilized to investigate fall and upstroke stages of a two-piece plunger for different gas and liquid flow rates. Experiments were performed with the deviation angles up to 40 degrees.The drag coefficients of plungers for respective Reynolds numbers, the liquid holdup correction, and the wall effect on the settling velocity were obtained. The fall model was developed with dimensionless parameters for conventional and continuous flow plungers, which can estimate primarily fall velocity and maximum flow rate to fall against. The fall model was coupled with multiphase flow simulations for sensitivity analysis, and the results showed that plungers fell slowest at the wellhead in field conditions. Furthermore, upstroke experiments demonstrated the effect of gas and liquid flow rates and outer diameter, height, and weight of the sleeve on the plunger upstroke velocity. The model predictions for the upstroke stage match with experimental results from the dynamic facility, and it is further developed to estimate upstroke velocity, liquid slug removal from the wells in field conditions. The fall and upstroke models were used together to determine the operational envelope for CFP lift and plunger assisted gas lift (PAGL) for different plunger types. The liquid unloading mechanism of the CFP lift was also discussed.The study is unique in defining the hydrodynamics of continuous flow plunger lift and PAGL operations. The models are constructed with dimensionless parameters allowing applicability to the field conditions. The experimental results also contribute to plunger selection and design. The study provides a better understanding of when to use and how to use continuous flow plunger lift.