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TUALP Abstract
Tianlu Liao (Doctor of Philosophy in Petroleum Engineering)
Mechanistic Modeling of Intermittent Gas Lift
(256 pp. - Chapter VIII)
Directed by Dr. Zelimir Schmidt, Dr. Dale R. Doty, Dr. Roger N. Blais,
and Dr. Kermit E. Brown
(319 words)
A mechanistic model for intermittent gas lift is presented based on fundamental physical principles. The model consists of ordinary and partial differential equations for each system component in each stage of the intermittent gas-lift process. The model accounts for reservoir inflow performance, fluid properties, and the behavior of the tubing string, casing string, gas-lift valve, surface gas injection choke, and various intermittent gas-lift control mechanisms. The system of equations is solved using the Euler integration method. The model is validated using experimental data obtained from previous investigators. The model's predictions compare well with the experimental measurements. The model is capable of predicting the detailed cyclic characteristics and the performance of a gas-lift system. Therefore, it can be used either to design a new system or to optimize an existing one.
After the model was tested, it was used to perform a systematic sensitivity analysis of the behavior of intermittent gas-lift systems. The injection gas volume per cycle is the most important controlling parameter. The required injection gas volume per cycle defined in this dissertation should always be used. The initial liquid slug to be lifted in terms of tubing load is also an important parameter controlling the efficiency of the system. There is a specific tubing load that optimizes operational efficiency for a given system. The mechanistic model should be used to perform a sensitivity analysis when seeking the most efficient tubing load to be lifted. The effects of other operating parameters are also investigated and presented in the dissertation.
The intermittent and continuous gas-lift methods are compared. Intermittent gas lift should be used for relatively weak wells with low reservoir pressure or low productivity index. Continuous gas lift should be used for high capacity wells with high productivity index or high reservoir pressure. For a given well with a fixed reservoir condition, the determination of whether intermittent or continuous gas lift should be used depends on the system installation.Download dissertation (TUALP members only)
Last updated September 04, 2012