Summary The flow performance of two nitrogen-loaded gas-lift valves and one combination gas-lift valve was tested under simulated downhole conditions. Set pressures up to 1,500 psig and injection pressures up to 1,650 psig yielded a maximum observed gas flow rate of 3.6 MMscf/D. Pressure-operated valve performance depends on injection pressure for specific production and domepressures, valve geometry, and other factors. Two performance pressures, valvegeometry, and other factors. Two performance characteristics, separated by the test-rack opening pressure, are observed: throttling and orifice flows. Semimechanistic models predict throttling and orifice flow performance. Experimental predict throttling and orifice flow performance. Experimental performance characteristics tune the model for any port size used performance characteristics tune the model for any port size used in the Camco R-20valve. Introduction Ninety percent of domestic wells use artificial lift. Continuous-flow gaslift is popular in wells determined suitable by a feasibility study. This presupposes that the performance of each system component is predictable. This study proposes more reliable empirically based methods of predicting gas flow than are available currently. Most manufacturers recommend treating the gas-lift valve as an orifice; only a few provide empirical evidence. Since its inception in May, 1983, Tulsa U. Artificial Lift Projects (TUALP), an industrially funded research consortium, gave Projects (TUALP), an industrially funded research consortium, gave the study of gas-passage performance of nitrogen-loaded gas-lift valves the highest priority. TUALP studied the performance of two 1.5-in.-OD nitrogen-loaded and one combination gas-lift valve under simulated downhole conditions. This paper summarizes the observed gas-lift valve flow performance characteristics, presents two semi-mechanistic models that predict throttling and orifice flow performance, and defines a procedure for incorporating the models performance, and defines a procedure for incorporating the models into gas-lift designs. Test Facilities. Ref. 1 gives details on the TUALP test facility. Air supplied at a working pressure up to 2,500 psi and a flow rate up to 3.6MMscf/D was used. Operating limits were 2,000 psia and 2.0 MMscf/D. To use the dynamic test facility, one closes the downstream flow-control valves and admits gas to the flow loop by opening the upstream flow-control valves. Once sufficient pressure is applied for the test valve to open and both upstream and downstream pressures equilibrate, the downstream flow-control valves are opened slowly to reduce the downstream pressure and to initiate flow through the test valve. Throughout the test, the upstream flow-control valves are adjusted to maintain constant injection pressure while the downstream pressure is reduced in 25- to 100-psig decrements until either the valve closes or the downstream pressure falls to atmospheric. For each decrement in downstream pressure falls to atmospheric. For each decrement in downstream pressure, flowing conditions are stabilized with the flow-control pressure, flowing conditions are stabilized with the flow-control valves and the data acquisition system is manually prompted to sample and store all the pressure and temperature transducer responses. Note that one can hold either downstream tubing orupstream injection pressure constant during a test. Careful experiments show that results of tests done either way mathematically transform so that either experimental procedure is acceptable. Gas Flow Rate Calculation. The American Gas Assn. calculation procedures is used to compute gas flow rates. Base temperature and procedures is used to compute gas flow rates. Base temperature and pressure are assumed to be 60F and14.73 psia. For natural gas pressure are assumed to be 60F and 14.73 psia. For natural gas calculations, the ratio of specific heats and gas specific gravity must be known to compute the gas expansion factor, Y. Hall and Yarborough and Lee et al. give gas compressibility factors and viscosities. For air flow rate calculations, the ratio of specific heats is assumed to be 1.4 and the specific gravity is 1.0; standard references give viscosities and compressibility factors for dry air. Experimental Data The experimental data were taken for two nitrogen valves, the Camco R-20 and the McMurry-Hughes VR-STD, and one combination valve, the Teledyne MerlaLN-20R. Most tests were conducted with air as the flowing gas, but a few tests were conducted on the R-20 and VR-STD valves with natural gas. Stem displacement tests were performed on the R-20 valve to define the load rate of the bellows performed on the R-20 valve to define the load rate of the bellowsassembly. Test Conditions. LN-20R Valve. This is a wireline-retrievable, 1.5-in.-ODvalve with a combination nitrogen-spring-loading element. For constant upstream or injection pressure, the spring-nitrogen-loading element and the large port causes the flow performance of the LN-20R valve to be sensitive to downstream pressure. Because of its high flow rate capacity, this valve was tested only with the smallest 0.582-in.-ID port. The valve closing pressure was set at 685psig and the test-rack opening pressure at 1,060 psig at 64F. Only 12 dynamic tests were conducted, with pressure at 1,060 psig at 64F. Only 12 dynamic tests were conducted, with injection pressures ranging from 880 to 1,050 psig, because of insufficient capacity of the air supply at the time. R-20 Valve. TheR-20 valve is a wireline-retrievable, 1.5-in.-OD, nitrogen-loaded valve capable of passing and regulating both low and high gas flow rates with small and large ports. Measuring this valve with all available port sizes required I year of flow performance testing. Each port size was tested at valve closing performance testing. Each port size was tested at valve closing pressures set at about 500, 600, 700, 800, 900, 1,000, 1,250, and pressures set at about 500,600, 700, 800, 900, 1,000, 1,250, and 1,500 psig. At least six flow performance tests were performed at each valve closing pressure, with injection pressures that generate a family of three throttling and three orifice flow performance curves. Table 1 summarizes the data acquired from the 476 air flow performance tests on the R-20 valve. performance tests on the R-20 valve. Natural Gas Tests. We tried to test the R-20 valve with natural gas to evaluate the validity of Biglarbigi's theoretical air-to-natural-gas flow rate conversion equation. To conduct the natural gas flow tests, the dynamic test facility was connected between a high-pressure gas well and a low-pressure gas pipeline. Agas well at the ONG Depew Storage Facility in Depew, OK, was selected for tests on the R-20 and VR-STD valves. Two R-20 valves, with a 0. 187- and a 0.3750-in.-ID port, were used. For comparison, the VR-STD valve with a 0. 1875-in.-IDport was chosen because it is similar to the R-20 valve in geometry and construction. Table 2 shows data for 11 flow performance tests. Because a minimal amount of data on natural gas flow performance was obtained on the R-20valves, the air-to-natural-gas conversion equation could not be evaluated effectively with the R-20 valve data. The flow rate conversion equation was evaluated after 11 air flow performance tests on the VR-STD valve to duplicate the natural gas tests at the same test conditions. Valve Performance Characteristics Fig. 1 is a typical family of flow performance curves for the R-20 and VR-STD valves. The separate curves differ by the upstream or injection pressure, which is the intercept on the horizontal axis at the high-pressure end of a curve. SPEPF P. 203
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