Dynamic Performance Testing of Single-Element Unbalanced Gas-Lift Valves
- H.W. Winkler (consultant) | G.F. Camp (Arabian American Oil Co.)
- Document ID
- Society of Petroleum Engineers
- SPE Production Engineering
- Publication Date
- August 1987
- Document Type
- Journal Paper
- 183 - 190
- 1987. Society of Petroleum Engineers
- 4.3.1 Hydrates, 4.6 Natural Gas, 5.4.2 Gas Injection Methods, 3.1.6 Gas Lift, 5.1.1 Exploration, Development, Structural Geology, 4.1.4 Gas Processing
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Summary. Reliable predictions of injection gas passage through gas-lift valves are important for unloading and lifting high-capacity wells. This paper outlines the procedure for conducting static and dynamic tests paper outlines the procedure for conducting static and dynamic tests required to evaluate gas-lift valve performance. Limited test results are presented for the 1- and 1 1/2-in. [25.4- and 38.1-mm] unbalanced presented for the 1- and 1 1/2-in. [25.4- and 38.1-mm] unbalanced bellows-charged gas-lift valves with three-ply monel bellows.
Dynamic gas-throughput performance of gas-lift valves is a complex topic because of the many factors that influence valve performance; therefore, the scope of this project is limited to the basic type of single-element gas-lift project is limited to the basic type of single-element gas-lift valve. The primary purpose of this paper is to provide guidelines for testing gas-lift valves rather than to offer specific valve performance data for well installation design. Test equipment and procedures are illustrated and described.
A gas supply was made available in Saudi Arabia for this gas-lift valve test program. A skid-mounted test unit was designed to control and to measure the upstream and downstream pressures and volumetric gas rates across fixtures for installing gas-lift valves and other devices. Benchmark valves and a probe tester were built to obtain vital information related to the characteristics that are unique to a particular type of gas-lift valve.
The valve testing program was divided into several major test phases. Different sizes of gas-lift valve seats were tested to determine discharge coefficients. These seats were tested fully open without restrictions upstream or downstream. Benchmark valves with identical seats as above were installed in an encapsulating tester, and discharge coefficients were calculated for four stem positions that generated equivalent areas less than the fully positions that generated equivalent areas less than the fully open port area and for a fifth position for the fully open port area. The bellows-assembly load rate of the port area. The bellows-assembly load rate of the singleelement, unbalanced, bellows-charged gas-lift valve was established with the probe tester. Volumetric gas-throughput tests were performed with the same gas-lift valve bellows assembly as previously probed and with the identical seat sizes as tested above. Gas-throughput profiles were plotted on the basis of performance data. profiles were plotted on the basis of performance data. Curves of initial injection gas opening pressure vs. production pressure were established for each ball/seat combination pressure were established for each ball/seat combination tested in the benchmark and gas-lift valves. Examples of pertinent data and results of each phase of the test pertinent data and results of each phase of the test program are presented. program are presented. Unbalanced Single-Element Gas-Lift Valves
The most widely used gas-lift valve in the oil industry is an unbalanced single-element injection-pressure-operated valve that operates in the same manner as an unbalanced backpressure gas regulator. This type of valve is offered by all major gas-lift equipment manufacturers. The closing force for a gas-lift valve can be a gas-pressure-charged bellows, a spring in compression or elongated, or a combination of both. The analogy between the unbalanced single-element bellows-charged gas-lift valve and the unbalanced backpressure gas regulator is illustrated in Fig. 1.
"Single-element" implies that the principle components of the gas-lift valve are a bellows-and-dome assembly, stem and tip (the tip is generally a high-quality polished carbide ball), and a metal seat. The entire unit is housed in a valve body that may be threaded for attachment to a tubing mandrel, or the body may include packing and a latch for installation in a wireline-retrievable valve mandrel. "Unbalanced" implies that the production pressure is applied over the ball/seat contact area as an opening force at the instant the gas-lift valve opens or closes. Generally, the primary initial opening force is the injection gas pressure applied over an area equal to the effective bellows area minus the ball/seat contact area.
King filed the original patent for a pressure-operated, unbalanced, single-element bellows-charged gas-lift valve. This type of gas-lift valve became the industry standard soon after its introduction. These valves have been used successfully for 45 years without published dynamic injection-gas-throughput performance. Typical gas-lift installation design calculations include many safety factors to offset this lack of information. In most gas-lift wells, little or no flowing bottomhole pressure drawdown occurs from the top one or two valve stations while control fluids are unloaded. These continuous-flow gas-lift installations were designed to be unloaded and operated efficiently without the need of precise injection-gas-throughput performance of the valve. With the increased worldwide performance of the valve. With the increased worldwide application for gas-lifting high-rate production wells, these design methods proved inadequate.
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