Uncertainty in Gas Well Critical Velocity Predictions

Critical velocity in a producing gas well has been defined originally by Turner et al. as the gas velocity to carry small droplets of liquid upward. If you try to produce below the predicted value, the droplets are predicted to fall in the well and accumulate in the tubing and create liquid loading problems. Correlations such as Turner et at., Coleman et al, and results from Shell are compared. It is shown that at low pressures, projections for the required critical velocity differ the most. To provide some additional information on the situation, some low pressure laboratory measurements in 2 3/8's tubing are made and compared to the existing prediction methods. The reader will have a better idea of what accuracy is expected when trying to predict critical gas well velocity or production rate requirements from available correlations.