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Title: Southwestern Gas Measurement Short Course
Author(s): [Not Available]
Source: 1965 Southwestern Gas Measurement Short Course (Now called ISHM)
Year Published: 1965
Abstract: The dome of the valve is loaded with gas (usually nitrogen) which fills the bellows to a predetermined pressure. Injection gas, exposed to the valve stem via ports in the valve body, oppose the dome load pressure. With the assist of the fluid column pressure in the producing conduit, acting through the valve seat upon the end of the valve stem, the valve opens and permits injection gas to enter the producing conduit. In this manner the well unloading frequency is dependent upon the rate at which formation fluid enters the well. Dome Loading Valve Tubing Mandrel Bellows Pressure Inlet Port Gas Inlet Port Valve Stem Valve Seat i Casing Figure 3. At certain wells a programmed time cycle surface control (intermitter) is used to schedule injections of lift gas. The pressure of injection gas, in such cases, is sufficient to open lift valves regardless of the fluid column pressure in the producing conduit. Lift valves are generally located on the exterior of tubing mandrels and the tubing is used as the producing conduit. When the fluid volume to be lifted exceeds the tubing capacity, lift valves can be placed inside the tubing and the casing is then used as the producing conduit. LIFT EFFICIENCY Through trial and error it has been found that efficiency of gas lift is related to the velocity of fluid flowing up the well bore. A low lift velocity invites excess liquid fall-back as fluid moves up the conduit. If the lift gas velocity is too great, it tends to jet through the liquid slug, giving a poor lift effect. Though the velocity within the well varies due to submergence and density changes, 900 to 1,000 cubic feet per minute is deemed a most efficient lift rate. This most efficient lift velocity for removing liquid from wells is an important point to remember if one has gas wells which load up with liquid and cease to flow. Liquid problems plaguing gas wells can often be overcome by regulating gas withdrawal rates.

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