Abstract
SummaryThis paper presents a new comprehensive transient model and dynamic simulator that describe the complicated characteristics of the gas-lift unloading process. The model uses conservation equations of mass, momentum and energy, for both the cocurrent and countercurrent multiphase flow, along with the necessary closure relationships. The effect of liquid flowing back into the formation is also considered. The transient temperature changes in the gaslift unloading process are studied and the transient tubing pressure and two-phase flow parameters are incorporated into the temperature calculation. Two heat transfer mechanisms within the wellbore annulus are considered in the temperature model.An explicit numerical scheme is used for the mass and momentum partial differential equations. A double iteration procedure on both the temperature and pressure numerically solves the three conservation equations simultaneously.Several example calculations are given to illustrate the characteristics of the unloading process and to underscore the unreliability of conventional design methods. Gas-lift instability is also analyzed with the dynamic simulator. In addition, field data from 25 wells support the accuracy of the transient model. Finally, the simulator can be used to perform gas-lift optimal design, stability analysis, and gas-lift operation troubleshooting.
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