Api rp 11v2 2001 (2008) (american petroleum institute)

11V2/E2 Gas lift Valve Performance Testing API RECOMMENDED PRACTICE 11V2 SECOND EDITION, MARCH 2001 REAFFIRMED APRIL 2008 Copyright American Petroleum Institute Provided by IHS under license with API[.]

Definitions

2.1.2 A p : Area based on the nominal port diameter (in 2 ) [cm 2 ].

2.1.3 A s : Area based on the diameter where the stem con- tacts the seat (in 2 ) [cm 2 ].

2.1.4 B lr : Bellows assembly load rate as per Section 4 (psi/ in.) [kPa/cm].

2.1.5 C v : Flow Coefficient as per Section 5.

2.1.6 dP: Differential pressure as defined in context (psi) [kPa].

2.1.7 dx: Distance stem has moved from seat (in.) [cm].

2.1.8 F k : Specific heats factor equal to k/1.40.

Provided by IHS under license with API

2.1.9 H: A factor determined by the manufacturer to calculate the upstream test pressure for the Constant Injection Pres- sure Test

2.1.10 k: Ratio of specific heats of lift gas.

2.1.11 P1: Upstream gage pressure of test section (psig)

2.1.12 P2: Downstream gage pressure of test section

2.1.13 P vst : Pressure required to achieve LST of GLV.

2.1.14 P iod : Operating injection gage pressure at valve depth (psig) [kPag].

2.1.15 P o : Upstream gage pressure for a constant downstream gage pressure and near zero gas flow rate (psig) [kPag].

2.1.16 P pd : Flowing production gage pressure at valve depth (psig) [kPag].

2.1.17 P vc : Measured or calculated upstream gage pressure when the downstream pressure is equal to the upstream pressure and near zero gas flow rate at 60°F (15.5°C) (psig)

[kPag].Referred to as Valve Closing Pressure at 60°F.

2.1.18 P vcT : Measured or calculated upstream gage pressure when the downstream pressure is equal to the upstream pressure and near zero gas flow rate at a known temperature

(psig) [kPag].Referred to as Valve Closing Pressure at temperature.

2.1.19 P vo : Measured or calculated gage pressure applied over the area A b minus A s required to initiate flow through a valve with zero gage pressure downstream at 60°F (15.5°C

(psig) [kPag].Referred to as Valve Opening Pressure at 60°F.

The Valve Opening Pressure at Temperature (P voT) is defined as the measured or calculated gage pressure applied over the area difference between A b and A s, necessary to initiate flow through a valve This measurement is taken with zero gage pressure downstream at a specified temperature, expressed in pounds per square inch gauge (psig) or kilopascals (kPag).

2.1.21 q: Measured flow rate in cubic feet per hour at SC

2.1.22 q gi : Measured flow rate in thousands of cubic feet per dayat SC (MSCFD) [SCMD].

2.1.23 S g : Specific gravity of gas (Air = 1.0).

2.1.24 T1: Upstream gas temperature of test section (°F)

2.1.25 T v : Temperature of valve at depth (°F) [°C].

2.1.26 x: Pressure ratio The measured differential pressure across the test section divided by the absolute upstream pressure (dP/(P1 + 14.7)).

The pressure drop ratio factor, denoted as $X_t$, represents the maximum pressure ratio ($x$) for a specific upstream pressure, beyond which a reduction in downstream pressure does not enhance the flow rate Critical flow is achieved when the product of $F_k$ and $X_t$ is equal to or greater than the pressure ratio.

Abbreviations

ASME American Society of Mechanical

ANSI American National Standards Institute

CIPT Constant injection pressure test

CPPT Constant production pressure test

GST Geometric Stem Travel for full opened condition

ISA Instrument Society of America

LST Maximum effective stem travel from probe test

MSCFD Thousands of standard cubic feet per day

SC Standard Conditions assumed to be 14.73 psia (101 kPa) and 60°F (15.5°C)

SCFD Standard cubic feet per day

SCMD Standard cubic meters per day

Introduction

This section details the essential testing facility for gas-lift valve evaluation, which necessitates a high-volume, high-pressure gas source It is recommended that the gas storage capacity be a minimum of 100 cubic feet (approximately 3 cubic meters) and that the pressure should reach at least 1500 psig (kPa).

When constructing the facility, it is essential to comply with local, state, and national codes and practices The gas-lift valve testing system, which includes piping, valves, and surge vessels, will operate under high pressure gas Therefore, the fabrication, testing, and selection of valves must align with the established codes that regulate piping systems and vessels.

Surge or other vessels with diameters exceeding 6 in (152 mm) should adhere to ANSI/ASME Sec VIII D1-89, Rules for Construction of Pressure Vessels Division 1 or Sec VIII D2-89,

Rules for Construction of Pressure Vessels Division 2—Alter-

`,,```,,,,````-`-`,,`,,`,`,,` - native Rules.These rules provide requirements for design, fabrication, inspection, and certification of applicable vessels.

The piping consisting of materials, wall thickness, and related pressure ratings, should adhere to ANSI/ASME

B31.8-89, Gas Transmission and Distribution Piping Systems and subsequent addenda.Piping material should be specified as Grade B Flanges should adhere to ANSI/ASME B16.5-88,

Pipe Flanges and Flanged Fittings and errata; valves are covered by ANSI/ASME B16.34-88, Valves—Flanged,

Note: API valves and flanges could be used but are covered by API

Spec 6D Specification for Pipeline Valves (Steel Gate, Plug, Ball, and Check Valves).These API flanges may not be interchangeable with ANSI/ASME flanges.

The design pressure for piping, valves, flanges, or pressure vessels should be at least 20% greater than the highest pressure anticipated during the gas-lift valve tests.

When utilizing a test stand for flow rate measurements, the maximum potential error in calculations is around 6%, with the possibility of achieving even lower error rates.

General Description

The flow test system includes, as a minimum, items shown in Figure 1 and listed below:

Test Specimen

The test specimen consists of the components as listed below and shown in Figure 2.

1 The fully assembled test valve including the manufacturers recommended reverse flow valve.

3 Installed and latched in a compatible receptacle.

The valve should be in the fully assembled condition as sug- gested by the manufacturer.Replacement of the external V-ring packing stacks with an alternate sealing means is permissible.

The latch should be compatible with the receptacle and valve

Figure 1—Basic Flow Test System Schematic

The valve receptacle must be compatible with both the valve and latch, ensuring effective sealing above and below the valve inlet ports It is essential to document the inlet port area of the receptacle along with the minimum annular flow area between the receptacle and the valve inlet port.

The test specimen consists of the components as listed below and shown in Figure 3.

1 The fully assembled test valve including the manufacturers recommended reverse flow valve.

2 Threaded to a compatible receptacle for attachment to the test facility.

Test Section

The test section must encompass the test specimen and all fixtures situated between the upstream and downstream pressure measurement devices It is essential that the flow path remains unobstructed, avoiding any chokes, close radius elbows, or tees Additionally, elbows should maintain a minimum radius of 4 inches (10.16 cm) Compliance with these guidelines is illustrated in Figures 4 and 5.

The upstream test section of the specimen must not exceed 24 inches (60.96 cm) in length and should have a minimum inside flow diameter of 1 inch (2.54 cm) It is essential that this section is connected to the test specimen in a way that allows for an unobstructed annular chamber around the inlet ports This chamber must extend at least ½ inch (1.27 cm) above and below the inlet ports and maintain an annular width of no less than ¼ inch (0.64 cm).

The downstream test section must not exceed 24 inches (60.96 cm) from the test specimen and should have a minimum inside diameter of 1.5 inches (3.81 cm) It is essential that the centerlines of both the specimen and the downstream section are parallel and concentric Additionally, there should be a straight extension of at least 6 inches (15.24 cm) starting from the test specimen.

Throttling Control Valves

Upstream and downstream throttling control valves are used to control the pressures acting on the test section.There is no restriction as to the style of these valves.

Figure 2—Wireline Retrievable Test Specimen Figure 3—Tubing Retrievable Test Specimen

Figure 4—Test Section Example for Wireline Retrievable Valves

Both control valves should be of sufficient flow rate and pressure capacity to exceed the flow rate and pressure capacity of the test specimen.

Pressure Surge Protection

Implementing pressure surge protection on both the upstream and downstream sides of the test section is essential This protection serves to mitigate the impact of pressure surges that can arise from valve performance Such surges can lead to significant damage to pressure gauges and transducers, adversely affecting the control and monitoring capabilities during testing.

Surge tanks provide essential surge protection by being integrated into the test system outside the test section They must maintain independent full pressure communication with both upstream and downstream pressures affecting the test section Additionally, optional control valves can be installed in the plumbing that connects the pressure surge tanks to the test system.

The volume of the pressure surge tanks should be no less than 2 ft 3 (0.057 m 3 ).It is preferred that the downstream pres- Figure 5—Test Section Example for Tubing Retrievable Valves

`,,```,,,,````-`-`,,`,,`,`,,` - sure surge tank have twice the volume of the upstream pressure surge tank.

Alternative surge protection systems that reduce pressure surges in the test specimen to no more than 10 psig/sec (69 kPa/sec) are also permitted.

Flow Measurement

The flow measurement instrument and/or method may be any device which meets the specified accuracy.

The flow rate must be measured with an accuracy that does not exceed an error of ± 6% of the actual flow rate Additionally, the resolution and repeatability of the measurement method should be within ± 1% of the actual flow rate It is essential to select and maintain the measuring instrument properly to ensure the required accuracy, as outlined in AGA Report No 3.

ANSI/API MPMS 14.31-1990, or GPA 8185-90 Part 1 methods of flowrate calculation along with a certified meter run will satisfy these recommendations.

Pressure Taps

Two pressure taps are essential for measuring the upstream and downstream pressures on the test specimen Their placement determines the start and end points of the test section Additionally, the geometry of the taps must adhere to the dimensions specified in Figure 6.

The upstream and downstream pressure taps should be located as near as possible to the test specimen but should be no more than 24 in (60.96 cm) from the test specimen.

For optimal placement on a horizontal run, the upstream and downstream taps must be positioned above a horizontal plane that aligns with the pipe's centerline, ensuring that the tap centerline is perpendicular to the pipe centerline.

Pressure Measurement

For optimal performance, pressure and pressure differential measurements must be chosen to ensure that errors remain within ± 1% of the actual value It is essential to calibrate pressure measuring devices regularly to uphold the required accuracy standards.

The upstream and downstream test section pressure measurement should be visually displayed continuously to the operators controlling the test pressures at the test section.

A method must be established to generate a hardcopy report of the pressures recorded at both the upstream and downstream pressure taps in the test section This report should ensure that the pressure readings are accurate within ± 2% of the measurement devices.

Edge of hole must be clean and sharp or slightly rounded, free from burrs, wire edges, or other irregularities In no case shall any fitting protrude inside the pipe.

Temperature Taps

Two temperature taps are essential for accurate measurements: one should be positioned on the upstream side of the test section, while the other is necessary for the flow rate measurement device Additionally, an optional temperature tap can be installed on the downstream side of the test section.

The upstream temperature tap must be positioned on the upstream side of the test section, while the temperature tap for flow rate measurement should be placed according to the manufacturer's guidelines Although the placement of an optional downstream temperature tap is not mandated, it is advisable to position it on the downstream side of the test section if utilized.

When located on a horizontal run, the temperature taps should be located above a horizontal plane extending through the centerline of the pipe.

Temperature Measurement

The devices used to measure gas temperature should not have an error exceeding ± 2°F (± 1.1°C) of actual value.

The gas temperature should be measured at the flow rate measurement device and on the upstream portion of the test section.

A means should be provided to produce a hardcopy report of the temperatures measured at both the flow rate measurement device and at the upstream portion of the test section.

This means should report temperatures within an accuracy of ± 2% of the temperature being measured.

Equalizing Valves

To conduct the tests effectively, it is essential to equalize the upstream and downstream pressures beforehand An equalizing valve is strategically placed between the upstream and downstream test sections, enabling the bypassing of the test specimen.

Gas Supply

For this test procedure, it is essential to use air or another compressible gas as the primary fluid Vapors that may condense at the vena contracta of the specimen are not suitable Additionally, precautions must be taken to prevent the formation of liquids or solids in the gas supply during testing.

Documentation

To demonstrate compliance of the test apparatus with the recommendation, it is essential to provide the following information Data Form 1 serves as a convenient tool for this purpose.

1 Schematic identifying the layout and location of items 1–8 of 3.2 and signed by the person in charge of testing.

The detailed drawing of the test section includes critical measurements such as the distance from the upstream test section to the test specimen and the distance from the downstream test section to the test specimen It also specifies the number and size of receptacle inlet ports, along with the annular flow area between the valve and receptacle for wireline retrievable fixtures Additionally, the drawing highlights the location and size of the annular chamber surrounding the test specimen.

3 Type and capacity of throttling control valves.

4 Type and size of surge protection.

5 Type and accuracy of flow measurement device.

6 Type and accuracy of pressure measurement devices.

7 Type and accuracy of pressure recording hardcopy device.

8 Type and accuracy of temperature measurement devices.

9 Type and accuracy of temperature recording hardcopy device.

4 Gas-lift Valve Probe Test

Introduction

The Gas-lift Valve Probe Test aims to assess the relative stiffness of a gas-lift valve and measure the maximum effective stem travel When gas pressure is applied to the tester, it acts on the entire area of the valve bellows, causing the stem to lift off the seat As the pressure increases, the stem rises further By utilizing the Valve Probe Tester, accurate measurements of stem travel in relation to pressure can be obtained, with results that can be tabulated and plotted The tester depicted is just one example, and various devices can be employed to perform this test.

Plotting pressure on the ordinate and stem travel on the abscissa produces a nearly straight line for effective stem travel The slope of this line reflects the "stiffness" of the valve, providing a numerical value that quantifies this characteristic.

API Recommended Practice 11V2 Data Form 1

1 Schematic of test apparatus attached (Y/N).

2 Detail drawing of test section attached (Y/N).

Dimension from test specimen to upstream pressure gauge.

Dimension from test specimen to downstream pressure gauge.

Number of receptacle inlet ports.

Diameter of receptacle inlet ports.

Annular flow area between valve and receptacle.

Dimension from OD of test specimen to ID of annular chamber around test specimen.

Dimension from test specimen inlet ports to annular chamber seal.

Flow capacity of upstream control valve at full open position.

Flow capacity of downstream control valve at full open position.

4 Type of upstream pressure surge protection.

Type of downstream pressure surge protection.

5 Type of flow measurement device.

Type of Accuracy of flow measurement device.

6 Upstream pressure measurement device Accuracy

Downstream pressure measurement device Accuracy

Differential pressure measurement device Accuracy

7 Method of reporting and recording pressure measurements.

Accureacy of pressure measurement recording device.

8 Upstream temperature measurement device Accuracy

Downstream temperature measurement device Accuracy

9 Method of reporting and recording temperature measurements.

Accuracy of temperature measurement recording device.

The Bellows Assembly Load Rate (B lr ), measured in psig/in (kPa/cm), refers to the slope of the bellows assembly, which encompasses both the bellows and the gas-lift valve mechanism This assembly applies a load to keep the valve stem seated A higher load rate results in a "stiffer" valve, while a lower load rate leads to a "softer" valve.

By varying the opening pressure of the same valve, whether through dome charge or spring setting, we can compare how these adjustments impact the load rate of the bellows assembly This analysis allows for a better understanding of the relationship between dome charge pressure, spring settings, and the performance of the valve under different opening pressures.

The maximum effective stem travel and bellows assembly load rate serve as practical metrics for comparing various valve types, assessing the same valve under different load conditions, and designing gas-lift installations.

Equipment Required

4.2.1 Gas-lift Valve Test Stand

Several typical test stands have been previously described in

The test stand must be equipped with a system to control and measure the pressure exerted on the gas-lift valve sleeve An example of an appropriate test stand for conducting the probe test is illustrated in Figure 7.

The sleeve must effectively transmit pressure from a source to the valve without any leaks, ensuring that the source pressure is communicated both above and below the valve seat when the valve is in a closed position.

4.2.3 Gas-lift Valve Position Measurement Device

The measurement method must be capable of determining the stem position within ± 0.005 in (.127 mm).

The micrometer probe depicted in Figure 7 is engineered for precise measurement of stem travel in relation to the pressure exerted on the bellows It integrates a micrometer with an electrically conductive probe that connects to the valve stem while remaining insulated from the valve body The probe's attachment to the micrometer barrel ensures that any micrometer adjustment corresponds directly to the probe's movement This device is designed to fulfill measurement accuracy standards, although alternative methods for stem position measurement are available.

The gauge used to measure pressure should have an accuracy such that measurement errors are no greater than ± 0.5% of value.

Probe Test Procedure

Nitrogen charged valves and combination valves, which include both spring loaded and nitrogen charged types, must undergo probe testing at opening pressures of 800 psig (5515 kPa), 1200 psig (8274 kPa), and also at the maximum pressure recommended by the manufacturer.

Spring loaded valves should be probe tested at the manufacturer’s maximum recommended opening (P vo ) or closing pressure (P vc ).

Attach the position measurement device (micrometer/probe assembly) to the valve.Insert the valve and position measurement device into the proper sleeve in the valve test stand.

To measure resistance using the micrometer/probe assembly, connect the ohmmeter by attaching one lead to the micrometer barrel and the other lead to the gas-lift valve, as illustrated in Figure 7.

4.3.3 Calibrate the Position Measurement Device

Adjust the position measurement device so that it makes contact with the valve stem when the valve stem is seated and there is no pressure on the test sleeve Make sure to record the micrometer reading.

The stem travel will be calculated by subtracting the micrometer reading at zero pressure from each subsequent reading as the pressure increases, as indicated on the data sheet.

Slowly increase the pressure on the test sleeve until the position measurement device shows that the stem is no longer in contact with the seat This pressure indicates the point at which the valve begins to open when the test pressure is applied across the entire area of the bellows (P vcT) Be sure to record this pressure.

With reference to the micrometer/probe assembly, this is indicated on the ohmmeter as a significant increase in the resistance reading.

4.3.4.2 Increase the pressure to the test sleeve in aconve- nient increment such as 10, 15, 20, or 25 psig (69, 103, 138, or 172 kPa).

Note: If the test pressure increment inadvertently exceeds the target pressure DO NOT REDUCE to the target pressure; instead, record the pressure obtained and continue with the test.

4.3.4.3 Adjust the position measurement device to determine the new stem position.

To measure the valve stem's position accurately, advance the probe using the micrometer barrel until it makes contact with the tip of the valve stem, which will be indicated by a noticeable drop in the ohmmeter resistance reading.

4.3.4.4 Record the pressure, and the stem position using

4.3.4.5 Repeat steps 4.3.4.2 through 4.3.4.4 using the same pressure increment.These pressure increments should yield at least five recordings within the range of the maximum effective stem travel.

4.3.4.6 Decrease the pressure to the test sleeve in a convenient increment such as 10, 15, 20, or 25 psig (69, 103, 138, or 172 kPa).

Before reducing the pressure in the micrometer/probe assembly, ensure to retract the probe rod by reversing the micrometer barrel sufficiently to avoid contact of the stem tip during the pressure decrease.

If the test pressure inadvertently falls below the target pressure, do not attempt to increase it back to the target Instead, document the pressure recorded and proceed with the test.

4.3.4.7 Adjust the stem position measurement device to determine the new stem position.

To measure the valve stem's position, advance the probe using the micrometer barrel until it makes contact with the tip of the valve stem, which will be indicated by a noticeable drop in the ohmmeter resistance reading.

4.3.4.8 Record the pressure, and the stem position using Data Form 2.

Repeat the procedures outlined in steps 4.3.4.6 to 4.3.4.8, applying the same pressure increments until the valve stem is seated, ensuring the initial micrometer reading is within ± 0.005 inches It is essential to document at least five stem positions within the maximum effective stem travel range.

Determining Valve Load Rate

To visualize the data, plot the pressure readings on the vertical axis and the stem position readings on the horizontal axis using linear coordinate paper, as illustrated in Figure 8.

Figure 8 illustrates two distinct regions with varying slopes Slope A represents the effective usable travel range of the valve, while Slope B indicates the travel range where the bellows encounters significant resistance, rendering it typically unusable This additional resistance is often caused by various factors, predominantly "bellows stacking."

The region of Slope A should extend from zero stem travel to the point where the slope of the load rate data turns sharplyupward. This point will be visually determined.

4.4.2 Draw the best-fit straight line to the data of the region corresponding to Slope A.See Figure 9

To calculate the slope of the best-fit straight line, use the formula: Slope = (P1 - P2) / dx, as illustrated in Figure 9 This slope represents the Bellows Assembly Load Rate of the valve, denoted as $ B_{lr} $.

4.4.4 The Bellows Assembly Load Rate (B lr ) documentation must include a graph showing ALL the data points, the best-fit straight line, and the B lr calculation.

Determining Maximum Effective Stem Travel

ing for zero travel from each of the subsequent readings as the pressure is increased.

Slowly increase the pressure on the test sleeve until the position measurement device shows that the stem is no longer in contact with the seat This pressure indicates the point at which the valve begins to open when the test pressure is applied across the entire area of the bellows (P vcT) Be sure to record this pressure.

With reference to the micrometer/probe assembly, this is indicated on the ohmmeter as a significant increase in the resistance reading.

4.3.4.2 Increase the pressure to the test sleeve in aconve- nient increment such as 10, 15, 20, or 25 psig (69, 103, 138, or 172 kPa).

Note: If the test pressure increment inadvertently exceeds the target pressure DO NOT REDUCE to the target pressure; instead, record the pressure obtained and continue with the test.

4.3.4.3 Adjust the position measurement device to determine the new stem position.

4.3.4.4 Record the pressure, and the stem position using

4.3.4.5 Repeat steps 4.3.4.2 through 4.3.4.4 using the same pressure increment.These pressure increments should yield at least five recordings within the range of the maximum effective stem travel.

4.3.4.6 Decrease the pressure to the test sleeve in a convenient increment such as 10, 15, 20, or 25 psig (69, 103, 138, or 172 kPa).

Before reducing the pressure in the micrometer/probe assembly, ensure to retract the probe rod by reversing the micrometer barrel sufficiently to avoid contact with the stem tip during the pressure decrease.

If the test pressure inadvertently falls below the target pressure, do not attempt to raise it back to the target level Instead, document the pressure recorded and proceed with the test as planned.

4.3.4.7 Adjust the stem position measurement device to determine the new stem position.

4.3.4.8 Record the pressure, and the stem position using Data Form 2.

Repeat the procedures outlined in steps 4.3.4.6 to 4.3.4.8, applying the same pressure increments until the valve stem is seated, ensuring the initial micrometer reading is within ± 0.005 in It is essential to document at least five stem positions within the maximum effective stem travel range.

To visualize the data, plot the pressure readings on the vertical axis and the stem position readings on the horizontal axis using linear coordinate paper, as illustrated in Figure 8.

Figure 8 illustrates two distinct regions with varying slopes Slope A represents the effective usable travel range of the valve, while Slope B indicates the travel range where the bellows encounters significant resistance, rendering it typically unusable This increased resistance is often caused by various factors, predominantly "bellows stacking."

The region of Slope A should extend from zero stem travel to the point where the slope of the load rate data turns sharplyupward. This point will be visually determined.

4.4.2 Draw the best-fit straight line to the data of the region corresponding to Slope A.See Figure 9

To calculate the slope of the best-fit straight line, use the formula: Slope = (P1 – P2) / dx, as illustrated in Figure 9 This slope represents the Bellows Assembly Load Rate of the valve, denoted as $B_{lr}$.

4.4.4 The Bellows Assembly Load Rate (B lr ) documentation must include a graph showing ALL the data points, the best-fit straight line, and the B lr calculation.

4.5 DETERMINING MAXIMUM EFFECTIVE STEM TRAVEL

4.5.1 The maximum effective stem travel is the greatest travel obtainable within the region of Slope A as shown in Figure 9.

Note: See Appendix C for detail explanation of Load Rate and Max- imum Effective Stem Travel calculation.

Documentation

The following documentation should be available to demonstrate the execution of the probe test per this section.Data Form 2 is a convenient method for recording the data.

1 Assembly drawing of the probe test equipment.

2 Type and accuracy of the pressure gage.

3 API designation of tested valve, manufacturers part number and dated assembly drawing of valve.

1 Assembly drawing of probe test apparatus attached (Y/N).

2 Type of pressure measurement device Accuracy

Manufacturers part number for valve.

Dated assembly drawing of valve attached (Y/N).

Valve set pressure Pvo or Pvc?

Test Pressure (psig) Actual Corrected

5 Graph attached showing test pressures and stem positions (Y/N).

Graph showing best-fit straight line (Y/N).

6 Bellows assembly load rate (Blr) psig/inch

4 Test data including: a Valve set pressure. b Test pressures. c Stem positions.

5 Graph showing: a Tested pressures and stem positions. b Best fit straight line.

6 Bellows assembly load rate (B lr ).

9 Person in charge of the test.

Introduction

The purpose of this procedure is to determine a gas-lift valve’s flow capacity as a function of the valve’s stem travel.

Accurate calculations of gas and liquid passage at various pressure conditions can be achieved through proper testing The flow rate of the valve, as determined in this section, is dependent on the geometry and is specific to the configuration of the test specimen.

The described test method necessitates the regulation of both upstream and downstream pressure Practical experience indicates that achieving reliable data may require some practice Tests demonstrate that a gradual and consistent change in pressure during the test results in more accurate data compared to abrupt pressure changes.

There are two effective testing methods: the traditional method, which maintains a constant upstream pressure while abruptly altering the downstream pressure, and the ramp method, which keeps the upstream pressure steady while gradually adjusting the downstream pressure When executed correctly, both methods yield reliable results.

The traditional approach necessitates system stability prior to taking any measurements, typically signaled by minimal or no fluctuations in flow rate over a set duration Although this method can be time-consuming, it can be effectively executed using manually read gauges or through transducers and data acquisition systems.

The ramp method requires that the system time constant be determined (Appendix D) and that the data be collected by transducers and data acquisition equipment.

Tests indicate that gradual changes in pressure using the ramp method produce more accurate data compared to the traditional method, which involves abrupt pressure changes This improvement in accuracy is largely attributed to the ability of the system to respond more effectively to slow and steady pressure variations.

`,,```,,,,````-`-`,,`,,`,`,,` - tester to determine when the system is stable when using the traditional method.

When tests are performed using the specified test stand, the maximum potential error in calculating flow coefficients is around 9%, while the maximum potential error for the critical pressure ratio factor is approximately 11%, though it may be lower.

Test Specimen

The test specimen should include the following components.

A modified valve incorporates a mechanism for positive mechanical adjustment of the valve stem relative to the seat, ensuring that this feature does not disrupt the normal flow path Additionally, if the valve is designed to include a reverse flow valve, it is essential that the manufacturer's recommended reverse flow valve is included in the valve assembly.

A compatible latch is securely threaded to the valve, and it can be modified for easy access to the stem adjustment feature, provided that such modifications do not compromise the latch's ability to securely attach to the valve or anchor the latch/valve assembly to the compatible receptacle.

3 The valve and latch shall be inserted into a compatible receptacle.

The test specimen should include the following components.

A modified valve incorporates a feature that enables positive mechanical adjustment of the valve stem relative to the seat, ensuring that this adjustment does not interfere with the normal flow path Additionally, if the valve is designed to include a reverse flow valve, it is essential that the manufacturer’s recommended reverse flow valve is included in the valve assembly.

2 The valve attached to a compatible receptacle.

The stem adjustment feature should enable precise measurement of the stem's position relative to the seat within a tolerance of ± 0.003 inches (± 0.076 mm) A fully closed position is defined when the flow rate through the valve is below 200 SCFD (5.66 SCMD) during testing.

`,,```,,,,````-`-`,,`,,`,`,,` - pressure conditions At this position, the measurement of the stem position with respect to the seat is 0.000 in (0.00 cm).

Each specific valve design and stem/seat configuration requires testing of at least five stem positions It is essential to conduct at least one test with the stem positioned within 10% of its maximum effective travel from the seat, as well as one test with the stem at 100% of its maximum effective travel.

See 4.5 for a definition of maximum effective travel.

A minimum of three more stem position tests should be conducted at stem positions greater than 10% and less than

90% of maximum effective travel.These three stem positions should be chosen to obtain flow capacity data in the range of travel where flow rate is changing significantly.

Flow Coefficient Tests

See Section 2 of for abbreviations and definitions.

For each stem position, it is essential to test at least five well-spaced pressure ratios (x) Analyzing the test data may necessitate further testing; refer to section 5.4 for clarification on this requirement.

Measurements will be taken for each tested pressure ratio (x), including flow rate, upstream test section gas temperature (T1), upstream test section pressure (P1), downstream test section pressure (P2), and stem position.

Flow measurement should be made per 3.7, pressure measurements per 3.9, and temperature measurements per 3.10.

Stem position measurements should be made per 5.2.3.

Before each test, it is essential to equalize both upstream and downstream test section pressures (P1 and P2) to a level exceeding 100 psig (689 kPa) Additionally, the pressure gauges for both sections must display readings within 2% of one another, and the flow measurement device should indicate a flow rate of less than 200 SCFD (5.66 SCMD).

To initiate flow in the test section, ensure that the pressure ratio (x) is maintained below 0.05 Data should be recorded according to section 5.3.3 When employing the ramp testing method, data points will be automatically captured In contrast, when using the traditional method, it is essential to stabilize the flow at this pressure ratio prior to data recording.

If using the traditional method, the data can be automatically recorded when using data acquisition equipment

To achieve critical flow, the pressure ratio (x) must be increased until it is observed that the flow rate remains constant despite a constant upstream pressure and a decreasing downstream pressure.

When using the ramp method, this is accomplished by holding the upstream pressure constant while slowly and continuously dropping the downstream pressure.(see Appendix

D for an explanation concerning the rate of pressure change). Record the data per 5.3.3.

In the traditional method, the upstream pressure is maintained at a constant level while the downstream pressure is adjusted to a new value, followed by a stabilization period for the system Data should be recorded in accordance with section 5.3.3.

At least three pressure ratios (x) should be recorded, falling between 10% and 90% of the critical flow pressure ratio (x) specified in section 5.3.3 Additional pressure ratios (x) can also be tested within this range.

Figure 10—Modified Valve for Flow Coefficient Test

Data Evaluation

This section outlines the method for assessing the test data obtained from the procedure detailed in section 5.3 The evaluation will produce the flow coefficient (\$C_v\$) and the pressure drop ratio factor (\$X_t\$) corresponding to a specific value at a defined stem travel.

For each pressure ratio tested, find the product of Y*C v using the following equation.

Plot the calculated values of \$Y \cdot C_v\$ on linear coordinate paper, with \$Y \cdot C_v\$ on the vertical axis and the pressure ratio (\$x\$) on the horizontal axis Fit a best-fit straight line to the data If any test data point deviates by more than 5% from the line, conduct additional tests near that pressure ratio to determine if the specimen displays anomalous behavior.

Data collected at low pressure ratios and minimal stem displacements may lack accuracy If there are at least five additional data points that meet the specified criteria, the questionable data points can be disregarded.

The value of C v shall be read from the graph as the point on the vertical axis where the fitted straight line intersects the vertical axis.Note point A on Figure 11.

5.4.5 Determination of Pressure Drop Ratio Factor (X t )

A horizontal line is drawn from the vertical axis at a value of \$Y \cdot C_v = 0.667 \cdot C_v\$ until it meets the fitted straight line From this intersection, a vertical line is extended down to the horizontal axis, where the value of \$X_t\$ is determined at the point where the vertical line intersects the horizontal axis, as illustrated by point B in Figure 11.

Alternatively, the following equation could be used to determine X t if the slope (M) of the straight line is known:

The value of the expansion factor (Y) is calculated as:

Figure 11—Flow Capacity Data Evaluation

The expansion factor (Y) must be between 0.667 and 1.0 Additionally, if the value of x exceeds F k * X t, then x should be set to F k * X t.

5.4.7 Record of Flow Coefficient (C v ) versus Stem

A linear graph should be created to illustrate the flow coefficient (C v ) in relation to stem travel, with C v plotted on the vertical axis and stem travel on the horizontal axis The stem travel axis should start at 0.000 inches and extend to the maximum effective travel of the stem, as specified in section 4.5.

Each tested point should be marked with a symbol A curve can be fitted to the data points using the manufacturer's recommended methods to derive untested flow coefficients Refer to Figure 12 for an illustration of the flow coefficients plotted against travel.

5.4.8 Record of Pressure Drop Ratio Factor (X t ) versus Stem Travel

A linear graph should be created to illustrate the pressure drop ratio factor ($X_t$) against stem travel, with $X_t$ plotted on the vertical axis and stem travel on the horizontal axis The stem travel axis should start at 0.000 inches and extend to the maximum effective travel of the stem, as specified in section 4.5.

Each tested point should be marked with a symbol A curve can be fitted to the data points using the manufacturer's recommended method to derive untested pressure drop ratio factors Refer to Figure 13 for an illustration of critical pressure ratios plotted against travel.

Use Of Cv And Xt Test Data

The flow coefficient shall be used in the following equation to compute flow rate. where x = (P iod – P pd )/(P iod + 14.7).

In the above equation, use the actual pressure ratio (x) if it is less than F k *X t , otherwise, use F k *X t as the value of x

5.5.1 Example For Using C v and X t to Compute Flow Rate

To determine the flow rate through a gaslift valve, it is essential to know the stem travel corresponding to the pressure conditions This can be achieved using the Simplified Method outlined in Appendix A or through alternative correlations.

Figure 12—Flow Coefficients vs Stem Travel

Flow Coef ficients q gi 32.64*C v * P( iod +14.7)*Y * x( / S( g * T( v +460)*Z1))

`,,```,,,,````-`-`,,`,,`,`,,` - calculates stem travel.You must also know the ratio of specific heats of the media used to test the flow coefficients.

• Figure 12 is a graph of the C v versus travel for this valve.

• Figure 13 is a graph of the X t versus travel for this valve.

• Test media ratio of Specific Heats = 1.4.

2 From Figure 13 determine the X t for the valve at a travel of 0.020.Read X t = 0.45.

3 Determine the ratio (F k ).The test media used a gas with a specific heat ratio of 1.4.Natural gas has a specific heat ratio of 1.3 therefore, F k = 1.3/1.4 = 0.928

4 Determine if valve isin critical flow.If x is greater than

In the case where the valve is choked, the flow rate should be calculated using the formula $X_t \cdot F_k$ instead of $x$, where $X_t \cdot F_k = 0.45 \cdot 0.928 \cdot 0.417$ Since the actual pressure ratio of 0.1478 is lower than the critical pressure ratio factor of 0.417, the valve is not in critical flow Therefore, the actual pressure ratio factor can be utilized to compute both the flow and the expansion factor.

6 From Figure 12 determine the C v for the valve at a travel of 0.020.Read C v = 0.40.

7 Compute the compressibility factor for pressure 1000 and temperature = 150 Z1 = 0.95

Documentation

The following documentation should be available to record the execution of the test per this section.Data Form 3 is a convenient form to record the data.

1 The API designation of the tested valve and the manufacturer’s part number and dated assembly drawing.

2 A drawing of the modified valve.

3 Maximum effective travel of valve (See 4.5).

Figure 13—Critical Pressure Ratio vs Stem Travel

Manufacturers part number for valve.

Dated assembly drawing of valve attached (Y/N).

2 Drawing of modified valve attached (Y/N).

3 Maximum effective travel of valve (per paragraph 4.5).

4 Type of flow measurement device Accuracy

5 Upstream pressure measurement device Accuracy

Downstream pressure measurement device Accuracy

Differential pressure measurement device Accuracy

6 Upstream temperature measurement device Accuracy

Upstream psig Downstream psig Diff psi Upstream Temp Flowrate

Pressure ratio (x) Y*Cv +5% limit -5% limit

Coefficients of best-fit straight line A B

10 Graph showing data points and best-fit straight line attached (Y/N).

12 Pressure drop ratio factor (Xt).

13 Graph of flow coefficient versus stem travel attached (Y/N).

14 Graph of pressure drop ratio factor versus stem travel attached (Y/N).

4 Type and accuracy of flow rate measurement.

5 Type and accuracy of pressure measurement.

6 Type and accuracy of temperature measurement.

8 Test data to include the following at each test point: a Test section upstream pressure (P1). b Test section downstream pressure (P2). c Test section upstream temperature (T1). d Flow rate.

9 Calculation of the following variables: a Pressure ratio for each test point (x). b Product of Y*C v for each test point as per 5.4.2. c Coefficients of best fit straight line (i.e., coefficients

The equation $Y \cdot C \cdot v = A \cdot x + B$ represents the best fit line for the data Additionally, a 5% upper limit and a 5% lower limit for each data point are established using this best fit straight line as a reference.

10 Graph of data points and best fit straight line.

13 Graph of flow coefficient (C v ) versus stem travel.

14 Graph of pressure drop ratio factor (X t ) versus stem travel.

15 Location of test facility and test facility operator.

17 Date tested and person in charge of testing.

Introduction

Two test methods will be described.

The Constant Production Pressure Test (CPPT) involves conducting a live valve test by maintaining a constant production pressure at various levels while adjusting the injection pressure This method allows for the evaluation of the gas lift valve's performance in response to changes in injection pressures.

The Constant Injection Pressure Test (CIPT) involves conducting a live valve test by maintaining a constant injection pressure while varying the production pressure This method allows for the assessment of the gas lift valve's performance in response to changes in production pressures.

Figure 14—Typical Plot Data from Constant Production Pressure Test (CPPT)

Injection—Gas Casing Pressure (psig)

Tests must be conducted in a facility that meets the standards outlined in Section 3 The Gas-lift Valve (GLV) under evaluation can be either nitrogen charged, spring loaded, or a combination of both It may operate based on Injection Pressure (IPO) or Production.

Pressure Operated (PPO) and it must comply with the test specimen in 3.3.

See Section 2 for abbreviations and definitions of several terms that follow.Figure 16 shows typical GLV performance characteristics on a three-dimensional graph of Upstream

Pressure (P1), Downstream Pressure (P2) and Flow Rate (q gi ).

The ability to plot data from either a Constant Injection Pres- sure Test (CIPT) or a Constant Production Pressure Test

In October 1991, the API 11V2 Work Group confirmed the CPPT on a three-dimensional graph Figure 16 demonstrates the movement of a GLV from the throttling flow regime, transitioning through an intermediate phase, and ultimately reaching the orifice flow regime.

When P1 is increased, and q gi and P2 are viewed as a vertical plane, this plane will correspond to a specific value of P1 Similarly, when q gi and P1 are analyzed as a vertical plane, it will represent a specific value of P2, which can be illustrated as one of the dashed isobar lines.

Figure 16 illustrates the outcomes of a constant production pressure test (CPPT), represented by dashed isobar lines indicating constant production pressure (P2) while varying the injection pressures (P1) Additionally, it presents the results of a constant injection pressure test (CIPT), depicted by solid line curves that serve as isobars for constant injection pressure (P1) as production pressures (P2) are adjusted.

There are two effective testing methods: the traditional approach, which maintains a constant upstream pressure while suddenly altering the downstream pressure, and the ramp method, which keeps the upstream pressure steady while gradually adjusting the downstream pressure When executed correctly, both methods yield reliable results.

The traditional method necessitates system stability before taking any measurements, typically signaled by minimal flow rate fluctuations over time Although this approach can be time-consuming, it is feasible with manually read gauges When employing the traditional method, data acquisition techniques can be utilized to obtain readings effectively.

The ramp method requires that the system time constant be determined (Appendix D) and that the data be collected by transducers and data acquisition equipment.

Research indicates that gradual pressure changes (ramp method) during testing produce more accurate results compared to sudden pressure shifts (traditional method) This improvement is largely attributed to the tester's enhanced ability to assess system stability with the ramp method.

Figure 15—Typical Plot of Data from Constant Injection Pressure Test (CIPT) of Gas-lift Valve

Flow Performance Test Documentation

6.2.1 Valve Description:Record the manufacturer’s name and an assembly or part number designation for the tested valve.Include the version number of the valve or date of manufacture.

6.2.2 Stem-Seat and Bellows Dimensions:Record effective bellows area, port ID, stem-tip description and seat-bevel configuration.

6.2.3 Valve Specifications:Record ratio of stem-seat contact area to effective bellows areas (A s /A b ).

6.2.4 Profile of Equivalent Flow Area versus Stem Travel:

The article defines a curve that illustrates the relationship between equivalent flow area and stem travel, based on the surface area of the frustrum of a right circular cone, as detailed in section 6.2.2 This curve extends from zero stem travel to a maximum equivalent flow area that matches the port area, indicating the fully open stem travel An example of this relationship is depicted in Figure 17.

6.2.5 The test rack set pressure of the valve must be defined in psig at 60°F.The valve set pressure may be the P vo or P vc as designated by the manufacturer.

6.2.6 A probe test of the valve as defined in Section 4 must be performed and a copy of Data Form 2 included with the documentation.

Preparation For Constant Production Pressure Test (CPPT)

To determine the increase in injection pressure during constant production pressure tests, it is essential to establish the maximum valve stem travel (VST) The maximum VST is defined as the lesser value from the analysis.

`,,```,,,,````-`-`,,`,,`,`,,` - either the Loadrate Stem Travel (LST) or Geometric Stem

The travel (GST) and LST of the valve are determined through probe testing, as detailed in Appendix C and measured in Section 4 GST is influenced by the physical geometry of the valve stem tip, typically a carbide ball, and its seat, as outlined in section 6.2.4.

To achieve an equivalent surface area, the valve seat must generate a frustrum of a right circular cone, with the stem tip moving away from its seat, that matches the valve port area.

6.3.2 Calculate the required maximum increase (dP) in the upstream test section pressure (P1) above the initial valve opening pressure (P o ) to achieve maximum valve stem travel

VST for a constant downstream test section pressure (P2).

The maximum increase in injection pressure (dP) remains constant for a specific GLV across all P2 values When the maximum VST meets or exceeds the LST, the dP increase above the valve closing pressure (P vc) is utilized in calculations to reach the LST from the probe test Conversely, if the VST is equal to or greater than the GST, the GLV bellows load rate (B lr) from the probe test, along with the GST, is incorporated into the calculations.

To calculate the incremental delta pressure (dP) values above the upstream initial valve opening pressure (P_o) for tests conducted at a constant downstream test section pressure (P2), it is recommended to use a minimum of four equally spaced test dP values across the entire range This should include the maximum dP (Max dP) calculated in section 6.3.2 For instance, the test dP values can be set at 25%, 50%, and 75% of Max dP, along with Max dP itself.

To determine the valve opening pressure (P voT) of the gas-lift valve, install it in the test fixture and set the downstream test section pressure (P2) to 0 psig (0 kPa gauge) at the tester gas temperature Be sure to record the P voT results.

6.3.5 Since the tested valve closing pressure (P vcT ) can be difficult to accurately measure in the test fixture, calculate the

P vcT for selecting the values of downstream test section pressures (P2) in 6.3.6 by using the following equation:

To determine the full operational range of the injection-pressure-operated valve, calculate at least four equally spaced downstream test section pressures (P2) based on the valve closing pressure (P vcT) Recommended values for P2 include 20%, 40%, 60%, and 80% of P vcT.

Performing The Constant Production Pressure Test

6.4.1 Adjust the upstream and downstream control valves for a near zero gas rate through the gas-lift valve for the calculated downstream test section pressure (P2).Record the

Figure 17—Geometric Flow Area vs Port Size

For VST = LST: Max dP= {1.2 probe dP( )}⁄{1–A s ⁄A b }

For VST = GST: Max dP= 1.2 VST( )B lr

`,,```,,,,````-`-`,,`,,`,`,,` - upstream initial valve opening pressure (P o ) and its corresponding P2

6.4.2 Calculate the upstream test section pressure (P1) based on the upstreaminitial valve opening pressure (P o ) for the set constant downstream test section pressure (P2) from

6.4.1 and the value of delta pressure (dP) from 6.3.3.

6.4.3 Increase the upstream test section pressure (P1) to the

After achieving stable flow conditions, document the necessary values on Data Form 4 to determine the stabilized gas flow rate, the upstream test section gas temperature (T1), P1, and ensure that P2 remains constant for each subsequent higher P1 test An alternative method is also outlined in the guidelines.

Appendix D outlines the procedure for increasing the upstream test section pressure (P1) from the initial pressure (P0) to P1 = P0 + Max dP through a slow and continuous ramp The duration of the test should exceed five time constants, and it is essential to maintain a consistent slope during the pressure increase.

To verify the valve opening pressure at zero downstream pressure (P voT), conduct a final test after the highest upstream test section pressure, based on the maximum differential pressure from section 6.3.2, while maintaining a constant downstream test section pressure (P2) If the P voT deviates by more than 0.5% from the previously tested value in section 6.3.4, it is necessary to repeat the test starting from section 6.4.3 for the last recorded P2.

6.4.5 Select the next downstream test section pressure (P2) and repeat 6.4.1 through 6.4.4 until the final constant P2 test series has been concluded.

Plot the upstream initial valve opening pressure (\$P_o\$) as described in section 6.4.1, and calculate the gas flow rate (\$q_{gi}\$) for each test Graph the data by plotting the upstream test section pressure (\$P_1\$) against \$q_{gi}\$ for each constant downstream test section pressure (\$P_2\$) The resulting curves will resemble those illustrated in Figure 14.

Performing Constant Injection Pressure Test (CIPT)

6.5.1 Place the test specimen in the test section as defined in 3.4.Measure the valve opening pressure at temperature

(P voT ).Record P voT and the temperature.Since the valve closing pressure (P vcT ) can be difficult to accurately measure in the test fixture, calculate the P vcT as follows:

To charge the basic flow test system with valve opening pressure at temperature (P voT), ensure that the equalizing control valve (ECV) is closed after the system is charged The gas lift valve (GLV) will remain open with P voT present both upstream and downstream.

6.5.2.1 Adjust the upstream pressure to P1 = P voT – (0.1)* (P voT – P vcT ) while reducing downstream pressure (P2) from

P voT to 0.9 P1.Stabilize P2 at 0.9 P1.Record the proper values as indicated on Data Form 4.

To achieve accurate measurements, systematically decrease the downstream pressure (P2) in equal increments until at least six flow rates are stabilized and recorded, ensuring that the gas flow valve (GLV) is closed or that P2 is reduced to zero psig.

In the probe test, it is crucial to maintain a decreasing mode for P2 If you inadvertently exceed the desired P2, do not return to it; instead, stabilize at a slightly lower P2.

An alternative method outlined in Appendix D involves gradually reducing the downstream test section pressure (P2) from P1 to zero psig This process should be executed slowly and continuously, with the test duration exceeding five time constants It is essential to maintain a consistent slope during the pressure decrease, and at least six flow rates should be recorded throughout the ramp test.

6.5.2.3 The upstream pressure (P1) must be maintained within 5 psi of target value while testing at the downstream pressures (P2) above.

6.5.2.4 Check P voT after the test.It must be within 0.5% of initial P voT Record this P voT and the temperature at the end of the test.

6.5.2.5 Recharge the basic flow test system to an upstream pressure:

Reduce downstream pressure (P2) to 0.9 P1 and stabilize. Record the proper values as indicated on Data Form 4.Repeat 6.5.2.2 through 6.5.2.4.

R ECOMMENDED P RACTICE FOR G AS -L IFT V ALVE P ERFORMANCE T ESTING 25

API Valve Identification: Set Pvo= psig at 60°F

Vendor name, assembly number, and description

Bellows area= sq in Stem-seat area= sq in Port Bore= in.

Probe test date: Max EffectiveTravel= in for ∆Ρ= psi

Avg Bellows assembly load rate= psi/in Name of technician:

Performance test date: Meter tube ID= in Gas GravityTime begin test: Pvot= psig Time end test: Pvot psig

Gas Orifice Meter Tube Data Gas-lift Valve Fixture Data

6.5.3 Test the valve at upstream pressures (P1) greater than the valve opening pressure (P voT ) (the orifice flow regime).

Calculate a maximum dP above P voT using 6.3.1 and 6.3.2.

Reduce downstream pressure (P2) to 0.9 P1 and stabilize.

Record the proper values as indicated on Data Form 4.Repeat

6.5.2.2 through 6.5.2.4.Obtain at least two P2’s that are less than half the upstream pressure.

Reduce downstream pressure (P2) to 0.9 P1 and stabilize.

Record the proper values as indicated on Data Form4.Repeat

6.5.2.2 through 6.5.2.4.Obtain at least two P2’s that are less than half the upstream pressure.

If the valve manufacturer designs the valve specifically for use in a well under throttling flow conditions, they may choose to utilize only a minimal portion of the maximum differential pressure as outlined in section 6.5.3.1.

6.5.4 Plot the data.The plot will have the form shown in

Figure 15.Be sure to include the valve closing pressure (P vcT ) as an integral part of the plotted data.

6.5.5 Data accumulation If data is accumulated manually, use the convenient Data Form 4.

To predict valve performance under untested conditions, it is essential to develop models or correlations based on test data This RP outlines the necessary tests and their execution to gather the information required for model development The tests can be utilized wholly or partially to create a model, and recommendations on the number of tests needed for effective model development are provided in the subsequent sections.

Probe Tests

Section 4 outlines the procedure for determining a valve's bellows assembly load rate (B_lr) and the maximum effective travel of the valve stem, including the number of tests to be conducted and the specific set pressures for testing.

Flow Coefficient Tests

Section 5 outlines the procedures for determining a valve's flow coefficient (C v ) and pressure drop ratio factor (X t ) based on the maximum effective valve stem travel It recommends the number of tests needed to assess the valve's complete operational range When executed properly, these procedures will yield data relevant for any pressure range and type of gas.

Gas-lift Valve Performance Tests

Section 6 outlines the necessary procedures to determine the dynamic performance characteristics of a valve at a specified set pressure To create an accurate model, it is essential to conduct additional tests at various set pressures The testing should be carried out on a valve set at a minimum of three distinct pressures: the manufacturer's minimum and maximum recommended pressures, along with an intermediate pressure It is important that these set pressures are at least 200 psig (1379 kPa) apart For instance, a valve designed for operation within a specific range should adhere to these testing guidelines.

600 psig (4137 kPa) and 1800 psig (12410 kPa) should pref- erably be tested at 600, 1200, and 1800 psig (4137, 8274, and

Use Of Test Data

The test procedures outlined earlier provide ample data to create a model for valve performance, enabling predictions of gas passage under various conditions Two example models are included in Appendices A and B, with the potential for additional models, though they are not detailed in this article.

Appendix A presents a simplified model based on test data from Sections 4 and 5, which includes assumptions about stem position during flowing conditions This model may not be suitable for predicting gas passage in all scenarios It does not require data from Section 6; however, if such data is available, it can enhance the model by accounting for dynamic pressures within the valve, leading to improved accuracy The process of utilizing Section 6 data to refine the simplified model is not covered in this discussion.

Appendix B presents a model that utilizes test data gathered in Section 6, based on statistical correlations from various dynamic valve tests Notably, this model operates independently of the data collected in Sections 4 and 5.

The model described in the following paragraphs is simplified and will use the data collected in Sections 4 and 5.This model is based on the following assumptions.

1 The measured downstream pressure at the test section is assumed to work on the ball/seat contact area.

2 The areas acted upon byboth upstream and downstream pressure remains constant.

3 The static force balance equation is used to determine the stem position.

As port sizes increase, the error in calculated stem position also rises For ports measuring 3/16 inches or smaller, the accuracy of flow rate predictions is approximately ±30% This accuracy assessment is derived from a limited comparison of tested values from a 1-inch IPO valve, and it is important to note that accuracy may vary for different types of valves.

An improvement to the simplified model would also include the data obtained in Section 6 to more accurately define dynamic stem position during flowing conditions.

To determine the valve's static stem position under expected subsurface pressure and temperature conditions, utilize the static force balance equation, incorporating the valve's travel and load rate For instance, the static force balance equation applicable to a nitrogen or spring-loaded valve can be expressed accordingly.

The flow coefficient (\$C_v\$) can be determined from the graph of \$C_v\$ versus stem travel, as calculated in section A.2 Additionally, the pressure drop ratio factor (\$X_t\$) is obtained from the graph of \$X_t\$ versus stem travel, also based on the static stem travel computed in A.2.

Use the following formula to calculate flow rate:

1 where x = (P iod – P pd )/(P iod + 14.7) or F k *X t whichever is less 1 ,

Y = 1 – [x/(3*F k *X t )] and F k = k/1.40 1 , k = Ratio of specific heat of lift gas.

A.5 Example of use of Simplified Method

When utilizing a 1-inch IPO valve with a 3/16-inch port, the upstream pressure (P iod) is measured at 925 psig, while the downstream pressure (P pd) is at 450 psig The valve's pressure drop (P vo) is recorded at 825 psig, with a temperature of 150°F at depth and a gas specific gravity of 0.65 For reference, Figure 12 illustrates the Flow Coefficient curve, and Figure 13 presents the Critical Pressure Ratio curve.

To compute the P voT at a temperature of 150°F, it is advisable to use a manufacturer’s temperature correction chart for more accurate results If such a chart is unavailable, an approximate method can be applied Additionally, it is essential to refer to a chart of the compressibility factor for nitrogen to determine the value of Z.

To calculate the stem position, apply the static force balance equation For a P vcT of 837, the valve exhibits a load rate of 935 psig/in It is essential to utilize the load rate tested by the valve manufacturer at the specified temperature The effective stem travel for this valve is 0.085 inches, and it is advisable to use the manufacturer's maximum effective stem travel whenever feasible.

The computed stem travel of 0.049 does not exceed the maximum effective stem travel of 0.085 However, if the computed stem travel were to exceed the LST, the LST should be utilized in subsequent calculations.

1Instrument Society of America Standard S75.02 or latest revision.

P vcT * A b +B lr * A b *dx=P iod * A( b –A s )+P pd * A s dx = [P iod * A( b –A s )+P pd * A s –P vcT * A b ]⁄B lr * A b q gi 2.64*C v * P( iod +14.7)*Y * x⁄((T v +460)*S g *Z)

P voT = Ptro*Z * Temperature at depth( +460)⁄(60+460)

P vcT = 919* 0.31( –0.0276)⁄0.317psig dx = [P iod * A( b –A s )+P pd * A s –P vcT * A b ]⁄B lr * A b d x [925* 0.31( –0.0276)+450*0.0276–837*0.31]⁄935* 0.31=0.049

Use Figure 12 as the flow coefficient curve.Compute the

C v using the curve fit for a stem travel of 0.049.

If the stem travel exceeds 0.095 in., then the maximum C v should be used rather than the computed C v In our case, this does not occur, so use C v = 0.774.

Use Figure 13 as the Critical Pressure Ratio Factor curve.

Compute X t using the curve fit for a stem travel of 0.049.

To assess whether the valve is in critical flow, compare the value of $ x $ to $ X_t $ If $ x $ exceeds $ X_t $, which is 0.40 in this case, then the valve is indeed in critical flow Given that the actual pressure ratio is 0.505, which is greater than $ X_t $, it confirms that the valve is in critical flow, necessitating the use of $ X_t $ for calculating the flow rate.

4 Compute the compressibility factor for natural gas at

925 psig and 150F or obtain from a chart.

This method developed by TUALP (Tulsa University Arti- ficial Lift Projects) and has been documented in the literature.

This method offers an alternative to the simplified model outlined in Appendix A, and it is important to note that the TUALP model does not incorporate load rate data measured according to Section 4.

This appendix outlines a cost-effective method for predicting the dynamic performance of gas-lift valves operated by injection pressure The proposed procedure is derived from a comprehensive study of gas-lift valve performance.

Tulsa University Artificial Lift Projects 1-10

The study on injection operated gas-lift valves focused on expected accuracy by analyzing the standard error of the estimate and qualitatively reviewing data patterns Notably, the most significant percentage deviations between the model and experimental data appear at the extremes of the flow rate curves, although the absolute deviations remain relatively small The findings presented provide a conservative upper bound for all port sizes across the data range.

These uncertainties are based on numerous tests Some

3967 data points were taken on 1 inch valves, including 1560 on the Camco BK, 477 on the Camco BK 1, 1112 on the

McMurry-Hughes JR-STD, and 818 on the Teledyne-Merla

An additional 2,590 data points were collected for the Camco R-20 1.5 inch valve, alongside more limited data for the McMurry-Hughes VR-STD and the Teledyne-Merla LN-20R These data points were distributed across a diverse range of flow conditions and port sizes.

For the 1 inch valves there were 158 orifice flow curves and

Tiêu đề	Gas-lift Valve Performance Testing
Trường học	American Petroleum Institute
Chuyên ngành	Petroleum Engineering
Thể loại	Recommended Practice
Năm xuất bản	2008
Thành phố	Washington, D.C.

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Số trang	60
Dung lượng	633,26 KB