Simplified wellbore flow modeling in gas-condensate systems

Predicting long-term reservoir performance with realistic wellbore models is fraught with uncertainty owing to the complexity of two-phase flow. That is because even a calibrated two-phase flow model departs from its expected performance trend when changes in flow conditions occur. These inevitable changes include gas/liquid ratio, wellhead pressure, and flowline pressure with time, among others. Influx of water further exacerbates the prediction problem. This study explores the possibility of using simplified approaches to computing bottomhole pressure (BHP) from wellhead pressure (WHP), measured rates, gravity of producing fluids, and tubular dimensions. BHP computations on three independent data sets comprising 167 gas-condensate well tests suggest that the no-slip homogeneous model applies quite well. Statistical results show that the homogeneous model compares quite favorably with mechanistic two-phase flow models. However, the main advantage of the simplified model is that its recalibration with field data is not required because the gas/oil ratio increases with time, thereby making the model more robust. Most field datasets suggest random error in BHP calculations; uncertainty in rate measurements appears to be the most probable cause. High-GLR systems can tolerate large errors in rate measurements, but low-GLR wells demand greater accuracy. Copyright 2004, Society of Petroleum Engineers Inc.

Simplified wellbore flow modeling in gas-condensate systems Conference Paper