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Plunger design considerations and selection: Difference between revisions
Plunger design considerations and selection (view source)
Revision as of 11:11, 29 September 2013
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[[Plunger lift]] is used primarily in low rate, high gas-oil ratio (GOR) wells. This page focuses on the features desired in key equipment required to operate a plunger lift operation. | |||
==Plunger design and selection== | ==Plunger design and selection== | ||
Desirable features in a plunger include efficient sealing, reliability, durability, and the ability to descend quickly.<ref name="r1"/><ref name="r2"/> Rarely does a plunger exhibit all these characteristics, though. Usually a plunger that excels at one aspect sacrifices others. A wide variety of plungers is available to accommodate differences in well performance and operating conditions. | |||
===Plunger seal and velocity=== | ===Plunger seal and velocity=== | ||
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*Cause equipment wear | *Cause equipment wear | ||
*Increase well backpressure | *Increase well backpressure | ||
<gallery widths=300px heights=200px> | <gallery widths=300px heights=200px> | ||
File:Vol4 Page 869 Image 0001.png|'''Fig. 1—The importance of plunger velocity. (Taken from Phillips and Listiak.)'''<ref name="r4" /> | File:Vol4 Page 869 Image 0001.png|'''Fig. 1—The importance of plunger velocity. (Taken from Phillips and Listiak.)'''<ref name="r4" /> | ||
</gallery> | </gallery> | ||
Target velocities allow just enough slippage to provide a good seal. | Target velocities allow just enough slippage to provide a good seal. | ||
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===Reliability and durability=== | ===Reliability and durability=== | ||
Reliability refers to the ability of the plunger to repeat performance over time or in adverse environments. Many plungers have internal moving components (e.g., pads, seals, valve rods, and bypasses) that might fail in the presence of sand or corrosive environments. Other plungers (e.g., brush or bar stock plungers) have no internal moving components and generally are more reliable. | Reliability refers to the ability of the plunger to repeat performance over time or in adverse environments. Many plungers have internal moving components (e.g., pads, seals, valve rods, and bypasses) that might fail in the presence of [[Sand control|sand]] or [[Corrosion problems in production|corrosive]] environments. Other plungers (e.g., brush or bar stock plungers) have no internal moving components and generally are more reliable. | ||
Durability is a plunger’s ability to operate over many cycles with minimal wear and breakage. Typically, metal sealing plungers such as pad plungers are longer wearing, whereas brush plungers with fiber sealing elements wear quickly. Small-diameter plungers (for 1 1/4-in. or 1 1/2-in.-outside diameter (OD) tubing) tend to break more easily than larger-diameter plungers (those for 2 3/8-in. or 2 7/8-in.-OD tubing). | Durability is a plunger’s ability to operate over many cycles with minimal wear and breakage. Typically, metal sealing plungers such as pad plungers are longer wearing, whereas brush plungers with fiber sealing elements wear quickly. Small-diameter plungers (for 1 1/4-in. or 1 1/2-in.-outside diameter (OD) tubing) tend to break more easily than larger-diameter plungers (those for 2 3/8-in. or 2 7/8-in.-OD tubing). | ||
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Plungers can be manufactured in a combination of these types. Lengths and diameters also can be adjusted to meet installation requirements. | Plungers can be manufactured in a combination of these types. Lengths and diameters also can be adjusted to meet installation requirements. | ||
'''Bar stock''' | |||
'''Bar | |||
A bar stock plunger ('''Fig. 2''') is a piece of metal (solid or hollow) whose surface is machined with grooves, spirals, or other shapes to create turbulence and thus the seal, between it and the tubing wall. The bar-stock-plunger seal is one of the least efficient available. | A bar stock plunger ('''Fig. 2''') is a piece of metal (solid or hollow) whose surface is machined with grooves, spirals, or other shapes to create turbulence and thus the seal, between it and the tubing wall. The bar-stock-plunger seal is one of the least efficient available. | ||
<gallery widths=300px heights=200px> | <gallery widths=300px heights=200px> | ||
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</gallery> | </gallery> | ||
'''Wobble washer''' | |||
'''Wobble | |||
A wobble washer plunger ('''Fig. 2''') is similar to a length of bolt that is full of loose-fitting washers. Its sealing characteristics are comparable to those of a bar stock plunger, but the side-to-side movement of its loose washers sometimes allows it to travel through tubing anomalies that would stick a bar stock plunger. The wobble washer plunger can be less durable than a bar stock or brush plunger, and should it fail in the well, retrieving all its washers can be difficult. | A wobble washer plunger ('''Fig. 2''') is similar to a length of bolt that is full of loose-fitting washers. Its sealing characteristics are comparable to those of a bar stock plunger, but the side-to-side movement of its loose washers sometimes allows it to travel through tubing anomalies that would stick a bar stock plunger. The wobble washer plunger can be less durable than a bar stock or brush plunger, and should it fail in the well, retrieving all its washers can be difficult. | ||
'''Pad''' | '''Pad''' | ||
Pad plungers are popular because of their durability and efficient seal. A pad plunger ('''Figs. 3''' and '''4''') incorporates spring-loaded metal pads that are fitted on a mandrel that expands to maintain contact with the tubing walls. The pads improve the sealing ability of the plunger by providing less bypass area for gas slippage, but because of this the pad plunger falls more slowly than other plungers. Pad plungers are available with one set or multiple sets of pads. In general, the more sets of pads, the better the seal, but the fit of the pad against the tubing wall also can improve the seal. | Pad plungers are popular because of their durability and efficient seal. A pad plunger ('''Figs. 3''' and '''4''') incorporates spring-loaded metal pads that are fitted on a mandrel that expands to maintain contact with the tubing walls. The pads improve the sealing ability of the plunger by providing less bypass area for gas slippage, but because of this the pad plunger falls more slowly than other plungers. Pad plungers are available with one set or multiple sets of pads. In general, the more sets of pads, the better the seal, but the fit of the pad against the tubing wall also can improve the seal. | ||
<gallery widths=240px heights=200px> | <gallery widths=240px heights=200px> | ||
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File:Vol4 Page 872 Image 0001.png|'''Fig. 4—Pad/brush combination plungers (left to right): brush/brush, brush/pad, pad/pad configurations. (Courtesy of Ferguson Beauregard.)''' | File:Vol4 Page 872 Image 0001.png|'''Fig. 4—Pad/brush combination plungers (left to right): brush/brush, brush/pad, pad/pad configurations. (Courtesy of Ferguson Beauregard.)''' | ||
</gallery> | </gallery> | ||
Sand can create problems for most pad plungers, because the sand has a tendency to deposit behind the pads. When this happens, the pads are unable to retract and the plunger might become stuck. | Sand can create problems for most pad plungers, because the sand has a tendency to deposit behind the pads. When this happens, the pads are unable to retract and the plunger might become stuck. | ||
'''Sealed pad''' | |||
'''Sealed | |||
A sealed pad plunger ('''Fig. 5''') is an improved version of the pad plunger. In a normal pad plunger, gas can slip behind the pads, making the seal less efficient. The improved plunger has seals behind the pads, eliminating gas slippage. The seals may be made up of metal, rubber, polymer, or a tortuous path that creates turbulence behind the pads. Take care that the sealing material is compatible with well fluids. | A sealed pad plunger ('''Fig. 5''') is an improved version of the pad plunger. In a normal pad plunger, gas can slip behind the pads, making the seal less efficient. The improved plunger has seals behind the pads, eliminating gas slippage. The seals may be made up of metal, rubber, polymer, or a tortuous path that creates turbulence behind the pads. Take care that the sealing material is compatible with well fluids. | ||
<gallery widths=300px heights=200px> | <gallery widths=300px heights=200px> | ||
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</gallery> | </gallery> | ||
'''Retractable pad''' | |||
'''Retractable | |||
A retractable-pad plunger seals well when unloading liquid, and falls very quickly. This type of pad plunger is built with a shift rod that enables the pads to retract and expand. The pads retract when the plunger reaches the surface and contacts a strike plate in the catcher. The plunger then has a much smaller than normal OD, which helps it to descend quickly. It might even be able to fall against flow. When the plunger drops to the bottom of the well, the shift rod strikes the plunger stop and causes the pads to expand, readying the plunger to lift the next liquid load. Because of its internal moving parts, the retractable-pad plunger is less durable and can become stuck if the pads fail to expand when the plunger reaches the bottom of the well. | A retractable-pad plunger seals well when unloading liquid, and falls very quickly. This type of pad plunger is built with a shift rod that enables the pads to retract and expand. The pads retract when the plunger reaches the surface and contacts a strike plate in the catcher. The plunger then has a much smaller than normal OD, which helps it to descend quickly. It might even be able to fall against flow. When the plunger drops to the bottom of the well, the shift rod strikes the plunger stop and causes the pads to expand, readying the plunger to lift the next liquid load. Because of its internal moving parts, the retractable-pad plunger is less durable and can become stuck if the pads fail to expand when the plunger reaches the bottom of the well. | ||
'''Brush''' | '''Brush''' | ||
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Brush-fiber material and stiffness affect plunger durability and influence what diameter is chosen. A stiff bristle will wear longer, but can be cut so large that it prevents the plunger from falling. A softer bristle can be built with an oversized brush diameter for increased seal, but tends to wear out more quickly. Material selection is important in wells with high temperatures because some nylon-fiber material melts at higher temperatures. | Brush-fiber material and stiffness affect plunger durability and influence what diameter is chosen. A stiff bristle will wear longer, but can be cut so large that it prevents the plunger from falling. A softer bristle can be built with an oversized brush diameter for increased seal, but tends to wear out more quickly. Material selection is important in wells with high temperatures because some nylon-fiber material melts at higher temperatures. | ||
'''Internal bypass''' | |||
'''Internal | |||
An internal bypass can be built into any type of plunger ('''Figs. 6''' and '''7'''). As with the retractable-pad plunger, in an internal-bypass plunger there is a shift rod that causes the bypass to open at the surface and close at the plunger stop. There are variations of the shift-rod mechanism that require a special lubricator with a permanent rod built into the shock-spring strike plate. An even newer variation is a two-piece plunger, which includes a ball and cylinder that fall separately but rise as a single unit. The bypass also allows the plunger to fall more quickly. These types of plungers sometimes are used without any surface control because of their ability to freely cycle while the well is flowing. | An internal bypass can be built into any type of plunger ('''Figs. 6''' and '''7'''). As with the retractable-pad plunger, in an internal-bypass plunger there is a shift rod that causes the bypass to open at the surface and close at the plunger stop. There are variations of the shift-rod mechanism that require a special lubricator with a permanent rod built into the shock-spring strike plate. An even newer variation is a two-piece plunger, which includes a ball and cylinder that fall separately but rise as a single unit. The bypass also allows the plunger to fall more quickly. These types of plungers sometimes are used without any surface control because of their ability to freely cycle while the well is flowing. | ||
<gallery widths=240px heights=200px> | <gallery widths=240px heights=200px> | ||
File:Vol4 Page 874 Image 0001.png|'''Fig. 6—The internal- | File:Vol4 Page 874 Image 0001.png|'''Fig. 6—The internal-bypass (freewheeling) plunger is capable of falling in gas flow. (Courtesy of Plunger Lift Systems Inc.)''' | ||
File:Vol4 Page 875 Image 0001.png|'''Fig. 7—Ball and cylinder plungers. (Courtesy of Pacemaker Plunger Co.)''' | File:Vol4 Page 875 Image 0001.png|'''Fig. 7—Ball and cylinder plungers. (Courtesy of Pacemaker Plunger Co.)''' | ||
</gallery> | </gallery> | ||
'''Side-pocket mandrel''' | |||
'''Side- | |||
The side-pocket-mandrel plunger ('''Fig. 8''') is designed for use with gas lift side-pocket mandrels. It is longer than other plungers (5 to 20 ft), with seals on both ends, and is used to bridge large inside diameter (ID) increases across gas lift mandrels. Such ID increases can cause excess gas slippage or plunger stall on shorter plungers, preventing operation. The side-pocket-mandrel plunger always keeps either the top or bottom seals in contact with normal tubing ID, allowing a continuous seal in the tubing as the plunger passes through the large ID. This specialty plunger also can be used when a packer, blast joints, subs, or other equipment is installed with an ID that is larger than the tubing ID. | The side-pocket-mandrel plunger ('''Fig. 8''') is designed for use with gas lift side-pocket mandrels. It is longer than other plungers (5 to 20 ft), with seals on both ends, and is used to bridge large inside diameter (ID) increases across gas lift mandrels. Such ID increases can cause excess gas slippage or plunger stall on shorter plungers, preventing operation. The side-pocket-mandrel plunger always keeps either the top or bottom seals in contact with normal tubing ID, allowing a continuous seal in the tubing as the plunger passes through the large ID. This specialty plunger also can be used when a packer, blast joints, subs, or other equipment is installed with an ID that is larger than the tubing ID. | ||
<gallery widths=300px heights=200px> | <gallery widths=300px heights=200px> | ||
File:Vol4 Page 876 Image 0001.png|'''Fig. 8—Side-pocket-mandrel plunger. This plunger is designed to maintain contact with the tubing when passing through gas-lift mandrels or packers. (Courtesy of Ferguson Beauregard.)''' | File:Vol4 Page 876 Image 0001.png|'''Fig. 8—Side-pocket-mandrel plunger. This plunger is designed to maintain contact with the tubing when passing through gas-lift mandrels or packers. (Courtesy of Ferguson Beauregard.)''' | ||
</gallery> | </gallery> | ||
==Evaluation of control methods== | ==Evaluation of control methods== | ||
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Adding microprocessors and plunger-velocity tracking to on/off timers was a major advance in controller technology ('''Fig. 9'''). These automated controllers monitor plunger velocity to continually optimize the well, eliminating the time-consuming trial-and-error process.<ref name="r8"/> | Adding microprocessors and plunger-velocity tracking to on/off timers was a major advance in controller technology ('''Fig. 9'''). These automated controllers monitor plunger velocity to continually optimize the well, eliminating the time-consuming trial-and-error process.<ref name="r8"/> | ||
<gallery widths=300px heights=200px> | <gallery widths=300px heights=200px> | ||
File:Vol4 Page 877 Image 0001.png|'''Fig. 9—Electronic controller. (Courtesy of Ferguson Beauregard.)''' | File:Vol4 Page 877 Image 0001.png|'''Fig. 9—Electronic controller. (Courtesy of Ferguson Beauregard.)''' | ||
</gallery> | </gallery> | ||
The importance of plunger velocity and efficient velocities for various plunger types has been discussed already. In essence, a plunger must travel at the correct velocity to lift liquids efficiently. If the plunger ascends faster than the target velocity, then more energy was available than was required to lift the plunger, either because the liquid load was too small or because pressure buildup was too great for operating conditions. In such a situation, the automated controller would decrease the shut-in time (to decrease pressure buildup) and increase the flow time (to increase the liquid load). | The importance of plunger velocity and efficient velocities for various plunger types has been discussed already. In essence, a plunger must travel at the correct velocity to lift liquids efficiently. If the plunger ascends faster than the target velocity, then more energy was available than was required to lift the plunger, either because the liquid load was too small or because pressure buildup was too great for operating conditions. In such a situation, the automated controller would decrease the shut-in time (to decrease pressure buildup) and increase the flow time (to increase the liquid load). | ||
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===Venting=== | ===Venting=== | ||
All the plunger controllers discussed here can be used with a venting option. With a venting system, the controllers typically will switch to venting if the plunger does not reach the surface in a specified period of time. The manual controller requires an operator to determine when the controller vents. An automated controller uses flowing conditions to determine when and how long the well should vent and, over time, attempts to eliminate venting by making changes to shut-in and flow times. For automated controls, venting is a preventative measure to keep the plunger operating during short periods of high line pressures. Venting is discussed in more detail in | All the plunger controllers discussed here can be used with a venting option. With a [[Flare and vent disposal systems|venting system]], the controllers typically will switch to venting if the plunger does not reach the surface in a specified period of time. The manual controller requires an operator to determine when the controller vents. An automated controller uses flowing conditions to determine when and how long the well should vent and, over time, attempts to eliminate venting by making changes to shut-in and flow times. For automated controls, venting is a preventative measure to keep the plunger operating during short periods of high line pressures. Venting is discussed in more detail in [[Plunger lift applications]]. | ||
This is optional; not found in all installations. | This is optional; not found in all installations. | ||
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This equipment also may be used with tubing/casing-flow plunger lift. The casing purge cycle can be managed more efficiently by determining exactly when the fluid has been transferred from the casing annulus to the tubing. | This equipment also may be used with tubing/casing-flow plunger lift. The casing purge cycle can be managed more efficiently by determining exactly when the fluid has been transferred from the casing annulus to the tubing. | ||
This is optional; not found in all installations. | This is optional; not found in all installations. | ||
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This is optional; not found in all installations. | This is optional; not found in all installations. | ||
<gallery widths=240px heights=200px> | <gallery widths=240px heights=200px> | ||
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File:Vol4 Page 881 Image 0001.png|'''Fig. 12—Plunger-lift controller that incorporates electronic gas measurement and telemetry. (Courtesy of Ferguson Beauregard.)''' | File:Vol4 Page 881 Image 0001.png|'''Fig. 12—Plunger-lift controller that incorporates electronic gas measurement and telemetry. (Courtesy of Ferguson Beauregard.)''' | ||
</gallery> | </gallery> | ||
===Missed-trip protection=== | ===Missed-trip protection=== | ||
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This is optional; not found in all installations. | This is optional; not found in all installations. | ||
=== | ===Swab mode=== | ||
Some controllers incorporate a swab mode, which is used primarily in wells that have been worked over with completion fluids or chemically treated, such that it might be necessary to remove the additional liquids before starting normal plunger operation. In swab mode, the well is shut in immediately upon plunger arrival at the surface. This tends to conserve well pressure and produce many small liquid loads. In this manner, the additional fluids are “swabbed” with the plunger. | Some controllers incorporate a swab mode, which is used primarily in wells that have been worked over with completion fluids or chemically treated, such that it might be necessary to remove the additional liquids before starting normal plunger operation. In swab mode, the well is shut in immediately upon plunger arrival at the surface. This tends to conserve well pressure and produce many small liquid loads. In this manner, the additional fluids are “swabbed” with the plunger. | ||
Controllers operate in swab mode by requiring the plunger to make a preset number of consecutive arrivals at or above the target velocity before flow time is allowed. Shut-in time adjustments usually continue, while flow time adjustments are suspended. When the plunger arrival criterion has been met, the additional well liquids are assumed to be unloaded, and the controller resumes normal operation. | Controllers operate in swab mode by requiring the plunger to make a preset number of consecutive arrivals at or above the target velocity before flow time is allowed. Shut-in time adjustments usually continue, while flow time adjustments are suspended. When the plunger arrival criterion has been met, the additional well liquids are assumed to be unloaded, and the controller resumes normal operation. | ||
This is optional; not found in all installations. | This is optional; not found in all installations. | ||
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===Surface production facilities and equipment=== | ===Surface production facilities and equipment=== | ||
Surface equipment (e.g., separators, heater treaters, and compressors) should be sized to handle the high instantaneous flow rates that accompany cyclical plunger-lift flow. Proper plunger-system operation can minimize these fluctuations (by operating at the minimum shut-in period), but flow rates still will vary. | Surface equipment (e.g., [[Separator types|separators]], heater treaters, and [[compressors]]) should be sized to handle the high instantaneous flow rates that accompany cyclical plunger-lift flow. Proper plunger-system operation can minimize these fluctuations (by operating at the minimum shut-in period), but flow rates still will vary. | ||
Monitor pressures from the wellhead through all surface equipment to the sales point and beyond, and use these pressure nodes to identify and eliminate restrictions and leaks. Piping, connections, valves, check valves, and even chokes sometimes are already in place, and are overlooked when plunger lift is installed. Every restriction increases the pressure necessary to operate the plunger lift and potentially reduces well production. Eliminate leaks upstream of the control valve to enable effective static-pressure buildup. Leaking equipment can allow liquid entry into the wellbore during the shut-in cycle, loading the well or preventing efficient plunger operation. | Monitor pressures from the wellhead through all surface equipment to the sales point and beyond, and use these pressure nodes to identify and eliminate restrictions and leaks. [[Piping and pipeline systems|Piping]], connections, valves, check valves, and even chokes sometimes are already in place, and are overlooked when plunger lift is installed. Every restriction increases the pressure necessary to operate the plunger lift and potentially reduces well production. Eliminate leaks upstream of the control valve to enable effective static-pressure buildup. Leaking equipment can allow liquid entry into the wellbore during the shut-in cycle, loading the well or preventing efficient plunger operation. | ||
Dehydration can be very difficult in single-well applications. If initial rates are too high, glycol could be forced out of the dehydrator and lost. Minimize the loss of dehydration fluid by installing pressure-differential controllers or bypasses or by using desiccant-type dehydrators. | [[Gas treating and processing|Dehydration]] can be very difficult in single-well applications. If initial rates are too high, [[Dehydration with glycol|glycol]] could be forced out of the dehydrator and lost. Minimize the loss of dehydration fluid by installing pressure-differential controllers or bypasses or by using [[Dehydration with deliquescing dessicants|desiccant-type dehydrators]]. | ||
===Measurement=== | ===Measurement=== | ||
Electronic flow measurement ('''Fig. 12''') is very beneficial for plunger-lifted wells. Electronic measurement more accurately records cyclical production rates, increasing the profitability of plunger-lift applications. Dry-flow paper-chart recorders ('''Fig. 13''') are difficult to integrate if production has a wide sweep on the chart or | Electronic flow measurement ('''Fig. 12''') is very beneficial for plunger-lifted wells. Electronic measurement more accurately records cyclical production rates, increasing the profitability of plunger-lift applications. Dry-flow paper-chart recorders ('''Fig. 13''') are difficult to integrate if production has a wide sweep on the chart or over-ranges the recorder, or if the chart time cycle is too long. | ||
<gallery widths=300px heights=200px> | <gallery widths=300px heights=200px> | ||
File:Vol4 Page 882 Image 0001.png|'''Fig. 13—Circular paper-chart recorder. Large, cyclical production swings make measurement more difficult with this type of chart. (Courtesy of Ferguson Beauregard.)''' | File:Vol4 Page 882 Image 0001.png|'''Fig. 13—Circular paper-chart recorder. Large, cyclical production swings make measurement more difficult with this type of chart. (Courtesy of Ferguson Beauregard.)''' | ||
</gallery> | </gallery> | ||
Larger-range springs and orifice plates help to keep differentials within a measurable range. The orifice plate should be capable of measuring the peaks and valleys of the plunger flow. Install as large an orifice plate as possible; as with the motor valve and other surface equipment, an orifice plate that is too small can act as a choke. Small plates also can become bowed or damaged if subjected to high differentials at the beginning of a cycle. | Larger-range springs and orifice plates help to keep differentials within a measurable range. The orifice plate should be capable of measuring the peaks and valleys of the plunger flow. Install as large an orifice plate as possible; as with the motor valve and other surface equipment, an orifice plate that is too small can act as a choke. Small plates also can become bowed or damaged if subjected to high differentials at the beginning of a cycle. | ||
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==See also== | ==See also== | ||
[[ | [[Plunger lift]] | ||
[[ | [[Plunger lift applications]] | ||
[[ | [[Plunger lift design and models]] | ||
[[ | [[Plunger lift installation and maintenance]] | ||
[[ | [[PEH:Plunger Lift]] | ||