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. Introduction 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. SPEPE P. 183
The tester set initial opening pressure of a gas-lift valve (GLV) and port size are no indication of its injection-gas passage at a given injection-gas pressure for unloading and/or gas lifting a well. The initial test rack opening pressure (Ptro) of a GLV creates an opening force that slightly exceeds the valve’s closing force. The importance of the required injection-gas throughput performance of a GLV for unloading and gas lifting a well increases for very high daily liquid production rate wells and for wells that the workovers are very costly. A test procedure that allows individual injection-gas throughput rate testing of every GLV and check valve prior to being installed in a well is described in this paper. The method includes GLVs with cross-over seats that prevent stem travel probe test measurements. The test requires very little gas volume and is based on a rapid pressure decline (blow-down). Recent computer electronics as National Instruments LabVIEW software and 4 channel data acquisition instrument control hardware can record up to 12,500 pressure readings per second per channel. Test procedures are now possible to dynamically test the gas throughput performance of a GLV in a fraction of a second. GLV replacement can be very costly – even by wireline in wells with subsea wellheads. After setting the Ptro and aging (stabilizing) this set opening pressure, the dynamic blow-down test can be performed on each GLV with check valve. If the GLV passes this test, the valve will have the injection-gas throughput required to unload and/or gas lift the well. Every supplier of gas-lift valves should offer this testing option to the producer.
Each gas lift valve (GLV) is a variable orifice until a fully open port area is attained (under maximum stem travel). As the ball (stem) moves away from the ball/seat contact area, the area open to flow increases until the flow area upstream to the port area equals or exceeds the fully open port area. Laboratory gas dynamic throughput testing indicates that each injection-operated GLV often does not open fully in actual operation, mainly because of the bellows stacking phenomena. As a result, the stem forms a restriction upstream to the flow path. Therefore, actual flow through the GLV can be less than expected. This paper addresses such issues and recommends a simple but effective solution. A modified design for the GLV seat was created to help reduce the required stem travel to generate a flow area equal to the port area. Theoretical calculations confirm the actual gas dynamic measurements and show that the minimum stem travel for the modified design improves from 5 to 58% compared to using a conventional sharp-edged seat. This improvement should have a significant impact on GLV performance. The modified seats for all different ports sizes were manufactured and tested using a benchmark valve test. The experiments showed that for the same stem travel, the new design has a larger flowing area than that of the sharp-edged seat. This paper details the new design, theoretical calculations, and experimental results.
This paper is an analytical study of the flow of fluids through small vertical conduits. Small conduits are defined as 1 ~ -in. nominal diameter tubing size and smaller, and approximately twice this area for annular conduits (i.e., 1-X 21/2-in. annulus and smaller). Experimental data are presented for the 1-X 2-in. and 1~-X 21/2-in. annuli, and the I-in. and 1 ~ -in. tubing, since these represent the small conduit sizes and configurations generally encountered in oilfield applications. Data have been gathered for these conduits for single-phase water, single-phase gas and twophase water-gas mixtures, with particular emphasis on high gas-liquid ratios. Water rates in excess of 2,000 BID and gas rates in excess of 2.5 MMcfID, and two-phase flow ratios in between these two, represent the scope of the data gathered. Existing equations have been applied to predict flowing pressures and compared with experimental data. New correlations have been developed.
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