Production Optimization of Gas-Lift System by Using
Wellflo and Dynalift Simulators
Jayant L Sadare
Dr. Faleh T. Al-Saadoon
Texas A&M University-Kingsville
Abstract
This presentation summarizes a study conducted at Texas A&M University-Kingsville of how to optimize production of gas-lifted wells by using the Wellflo and Dynalift simulation software.
Although several commercial software packages can simulate a gas-lifted well, most of them consider steady-state conditions; however the injection of gas through orifices or valves is a dynamic situation. The performance curves generated using steady-state software represent a very specific “operating point”, valid for one set of flowing well-head and bottom-hole pressures for a specific production rate, and under one casing-head injection pressure and gas-lift injection rate scenario. That concept is valid only if the well is producing under perfectly stable conditions. Many wells are producing under unstable conditions and simulation becomes complicated if flowing the wellhead pressure and the production rate are not stable. In other words, there is more than one operating point and the steady-state assumption becomes invalid. In reality, to simulate that condition a transient based simulator is necessary to reproduce all the movements of both fluids inside the tubing and gas-lift valves.
This presentation focuses on the optimization of the amount of gas being injected to lift or produce the same or even more fluids at static as well as dynamic conditions. Some wells producing at very stable conditions can become unstable when reducing the amount of gas being injected. The kinetic energy inside the tubing is reduced and the lifting efficiency decreases to such a point that the well can start loading up liquids, and it decreases its production or eventually stops flowing. The conditions like this can be modeled with steady-state software like Wellflo; by running sensitivities separately. The real advantage of doing the same analysis using a dynamic simulator like Dynalift is the “trouble-shooting” capability, which means not only to predict the well behavior from the production point of view, but also to check and verify the correct functioning of the gas-lift components. This simulator has been originally designed to verify and diagnose gas-lift designs before implementing the actual design in the field.