A field case study of plunger lift related tubing deformation

Abstract

This study investigates well integrity problems experienced during plunger-assisted gas lift (PAGL) operation of nine wells. The plunger fall motion against the multiphase flow, static gas and liquid are estimated with a drag-based fall model that includes dimensionless parameters of drag coefficient, wall factor, holdup correction. The upstroke stage simulation is conducted considering multiphase flow conditions along the well and two-piece plunger upstroke drag coefficient. Mechanistic models for continuous flow plunger lift have been verified using the field data. The plunger fall velocities against multiphase flow conditions and the plunger upstroke velocity profiles are insignificant compared to sleeve fall velocity during a shut-in. High fall velocities occurred during the fall in the shut-in stage primarily due to high sleeve height (up to 18-in) and low tubing wellhead pressures. The fall velocity of the sleeves was found to be significantly high in mild and severe deformation wells compared to no deformation wells. Consequently, the wells with deformation are exposed to the plungers reaching excessive kinetic energy more frequently. The high plunger fall velocity was concluded to be the root cause of the tubing deformation of PAGL wells and advised to be avoided considering the correlation between repetitive high plunger fall velocity and the wells with tubing deformation.