Gas Lift equipment selection is based on a few variables: tubing size, casing size, and surface capabilities. Depending on the drift ID of the casing and size of tubing, the selection of 1” or 1-1/2” valve will be chosen. Because conventional gas lift equipment has the valve made up on the outside of the gas lift mandrel, the OD of the station (mandrel + valve) is necessary in determining what valve size will fit within the drift of the casing.
After valve size has been selected, port size of the valves is determined. Port size of the valve directly affects the rate at which gas can be injected and what casing drops are needed to ensure closure of valves during the unloading process.
To determine the port sizes, the surface well head pressure is heavily considered. The higher the well head tubing pressure at surface, the more gas injection rate needed for the gas lift system. The lower the tubing pressure is, the less gas injection rate needed.
The most common port sizes for U.S. gas lift operations are 3/16” and 1/4". The larger the port size, the larger rate of gas that can be passed through. As a rule of thumb, 3/16” can pass up to 500 MCFD and 1/4" up to 1000 MCFD.
Utilizing the Turner Equation, a critical flow rate is calculated to determine the rate of total gas coming up the tubing that is necessary to prevent fall back. Using the critical flow rate plus the rule of thumb for port size, the optimal port size is then chosen.
Once valves and port sizes are chosen, the complete the gas lift system design can be completed utilizing information about the reservoir, wellbore, and production data.
To request a quote on equipment or for technical assistance, please use our contact form or call us at 1-800-348-7742 and request to speak with a Gas Lift engineer.