Leakage-Resolved Transient Full-Wellbore Modeling of Plunger Lift in Deviated Wells

Summary

Transient plunger-lift models are widely used to simulate cyclic deliquefication. Most existing models are developed and validated for vertical wells and typically neglect leakage during the upstroke, although leakage is a major source of error in dynamic predictions. In deviated wells, the concentric-clearance assumption fails. Plunger-tubing interaction becomes more complex, and plunger-lift dynamics are not well understood. This study focuses on plunger lift under deviated-well conditions. A leakage-resolved transient modeling framework is developed by explicitly accounting for nonconcentric plunger-tubing distribution and inclination-controlled gas-liquid leakage. High-resolution volume-of-fluid (VOF) simulations and laboratory experiments show that liquid leakage varies nonmonotonically with inclination angle and reaches a maximum near a critical angle due to competing gravity-driven backflow and shear-induced entrainment. Based on this mechanism, a mechanistic leakage closure is formulated to predict both liquid leakage and gas slippage. Then, the leakage closure is coupled with a time-stepping full-wellbore transient algorithm that resolves plunger dynamics along the measured well trajectory. The leakage model matches published variable-angle measurements within ±15%. Field data from a horizontal shale-gas well in the Sichuan Basin further validate the coupled algorithm. Predicted plunger displacement and velocity agree well with measurements, with mean absolute errors of 7.88% and 11.82%, respectively. Compared with cycle-resolved models developed for vertical wells that neglect leakage, the proposed coupled algorithm improves prediction accuracy and can be used to quantify leakage losses, diagnose dynamic mismatch, and optimize operating pressure, cycle timing, and plunger-lift performance in deviated wells. It provides a physics-based tool for analyzing leakage behavior and optimizing plunger-lift operations in deviated wells.