Gas lift valves are used in many producing wells to increase or maintain production. The spacing of valves in the well, calculation of opening or closing pressures, and selection of port size all play an integral role in the success of unloading and lifting operations. The design procedures that have been developed through the years include many safety factors; however, some of these were based on erroneous assumptions concerning the flow performance of gas lift valves; subsequently, many problems resulted.
Now that recent developments in gas lift valve mechanics have addressed the importance of using gas lift valve performance testing in predicting a valve's true flow performance, considerably more interest is being shown in this topic. One gas lift valve manufacturer has been furnishing gas lift valve performance data and using the data to perform gas lift valve spacing designs since 1962.
This paper will answer the questions of what constitutes performance data, why there is a need for this data and what types of testing techniques must be conducted to obtain a valve's true flow performance when subjected to subsurface conditions. The methods for performing the tests will also be discussed.
What is gas-lift valve performance? There are many criteria such as temperature sensitivity, corrosion and erosion resistance, stability of set pressure, and vibration suppression that can be used to qualify valve performance, but in the context of this paper, gas-lift valve performance will be defined as "the quantitative measure of a valve's flow rate response to changes in casing and/or tubing pressure for a given set pressure."
Why do we need performance data? The need for gas-lift valve performance data is a requirement of the valve spacing and port sizing technique. All gas lift valve manufacturers, with the exception of one, currently use spacing and port sizing techniques that assume that if the valve is open, it is fully open. This is not necessarily true.