Abstract:
A plunger installation and retrieval tool that incorporates a magnet which magnetically supports a fluid lift plunger during insertion into or retrieval from a lubricator on a natural gas wellhead. The magnet is housed in a magnet holder suspended from an elongate hanger member the upper end of which is connect to a hanger support. An actuation rod slidably extends through the hanger support and through bores in the magnet and magnet holder, such that a downward force applied to the actuating rod will cause the lower end of the actuation rod to project below the magnet and break its magnetic bond with the plunger, thus releasing the plunger from the tool. The tool may be provided with a cylindrical skirt fitting closely around the upper end of the plunger to prevent laterally leading that could break the magnetic bond during plunger insertion and retrieval.

Description:
FIELD OF THE DISCLOSURE 
     The present disclosure relates in general to fluid lift plungers used to remove accumulated liquids from natural gas wells, and in particular to apparatus for installing a fluid lift plunger into the lubricator section of a natural gas wellhead or retrieving a plunger from the lubricator. 
     BACKGROUND 
     Natural gas is commonly found in subsurface geological formations such as deposits of granular material (e.g., sand or gravel) or porous rock. Production of natural gas from such formations typically involves drilling a wellbore to a desired depth within the formation, installing a casing in the wellbore (to keep the wellbore from sloughing and collapsing), perforating the casing in the production zone (i.e., the portion of the well that penetrates the gas-bearing formation) so that gas can flow from the formation into the casing, and installing a string of production tubing inside the casing down to the production zone. Gas can then flow to the surface through the production tubing. 
     Formation liquids, including water, oil, and/or hydrocarbon condensates, are typically present with natural gas in a subsurface reservoir. If the formation pressure (i.e., the pressure of the fluids flowing into the well from the formation) is high enough, it will lift the liquids with the natural gas, and the liquids can be separated from the gas in a separator facility at the surface. However, the formation pressure reduces as more gas is produced from the well, and may eventually become insufficient to lift the liquids. Liquids therefore accumulate in the well and in the production tubing, and since the density of the liquids is much higher than the density of natural gas, the hydrostatic pressure exerted by the column of liquid in the well exceeds the reduced formation pressure, thus preventing the flow of gas from the formation into the well. The well is then said to be “liquid loaded”. 
     Although the well may be liquid loaded, the formation pressure may still be sufficient to lift gas to the surface if the accumulated liquid in the well can be removed, and one well-known way to do that is by using a fluid lift plunger inserted into the production tubing to facilitate intermittent production from the well. Fluid lift plungers come in many different styles. In general terms, however, a fluid lift plunger can be described as a generally cylindrical body, typically made of steel, and having an outer diameter slightly smaller than the inner diameter of the production tubing; i.e., such that the plunger can move freely up and down within the tubing, and will gradually fall by gravity through any liquid that has accumulated in the tubing, but tight enough against the tubing wall to allow the plunger to support and lift a column of liquid without any significant amount of the liquid bypassing the plunger and dropping back down the tubing. 
     To use a plunger lift system in a liquid loaded well, a plunger is inserted into the production tubing and allowed to drop through the accumulated liquid to the bottom of the tubing. The well is then closed in (by closing a shut-off valve on the tubing at the wellhead), thereby allowing pressure in the well to build up; even though the formation pressure may have become partially depleted, it will still gradually pressurize the well, because the well has no means for pressure relief while it is closed in. When the wellbore pressure has built up to a level sufficient to overcome the hydrostatic pressure of the accumulated liquids, the well can be opened up (by opening the shut-off valve) to begin a production cycle. The plunger, sitting at the bottom of the column of liquid in the production tubing, thus becomes exposed to the built-up wellbore pressure, which forces the plunger upward, lifting the liquid column with it. 
     When the column (or “slug”) of liquid reaches the wellhead, it is drawn off through a production flow line above the shut-off valve, while the plunger continues upward into a “lubricator”, which is essentially an extension of the production tubing extending above the flow line. With the liquid thus removed from the production tubing, thereby relieving the hydrostatic pressure on the formation, the well has been “unloaded”. Gas can once again be produced up the tubing until such time as the formation pressure drops and the well becomes liquid loaded again, whereupon the process can be repeated by re-inserting the plunger and closing off the well to let the wellbore pressure build up again. 
     The lubricator serves as a receiver for the plunger when it arrives at the surface after the well has been opened up. A lubricator typically incorporates a spring-loaded “bumper” or other means at its upper end for cushioning the arrival of the plunger, which can be moving upward quite fast by the time it reaches the lubricator. As well, the lubricator will incorporate a “catcher” which prevents the plunger from falling back down the tubing, and which allows the well operator to retrieve the plunger. One common type of catcher comprises a spring-loaded member (conventionally referred to as a “bullet”) that projects into the bore of the receiver but is readily displaced radially outward when contacted by the upward-travelling plunger, thereby allowing the plunger to continue its upward travel. The spring-loaded bullet immediately moves back into the lubricator bore. When the plunger reaches the end up its upward travel (usually by hitting the cushioning spring), it drops down and rests on the bullet. An end cap at the upper end of the lubricator can now be removed to allow retrieval of the plunger for examination and servicing as required. 
     When the time comes to open a closed-in well and begin a new production cycle, the plunger is re-inserted into the lubricator so that it rests on the bullet, and the end cap is tightened onto the upper end of the lubricator. The shut-off valve is opened, and the bullet is retracted from the lubricator bore (by means of an external actuator) to allow the plunger to drop down past the shut-off valve into the production tubing. 
     Many examples of lubricators, plunger “bumpers” and catchers can be found in the prior art; see, for example, U.S. Pat. Nos. 6,148,923 and 6,705,404. 
     For a number of reasons, lubricators commonly extend several feet above the catcher. One reason for this is to accommodate different types of plungers, the lengths of which can vary significantly. In any event, it is common for the upper end of a plunger, resting on or in the catcher, to be disposed a considerable distance below the top of the lubricator, thus making it difficult to retrieve the plunger. The upper end of a typical plunger is formed with a heavy cylindrical flange commonly called a “fishing neck”, with a diameter smaller than the main body of the plunger so that it can be grasped (either manually or with a “fishing” tool of some type) to retrieve or “fish” the plunger from the lubricator. However, this is not always easy to do when the plunger is sitting well down into the lubricator. 
     Installation of a plunger into a lubricator must also be done with care to prevent damage to wellhead components. Particularly in the case of a wellhead having a comparatively long lubricator, a heavy plunger that is simply dropped into the lubricator from a significant height above the catcher can displace or pass through the catcher and then impact the shut-off valve, causing physical damage to the catcher or the valve or both. Accordingly, it is desirable to insert a plunger into a lubricator in a manner that sets the plunger onto the catcher with minimal vertical force, so that the catcher will not be displaced or damaged in the process. 
     For the foregoing reasons, there is a need for improved tools for inserting a fluid lift plunger into the lubricator on a gas wellhead and for retrieving the plunger from the lubricator. 
     BRIEF SUMMARY OF THE DISCLOSURE 
     The present disclosure teaches embodiments of a plunger installation and retrieval tool incorporating a magnet that magnetically engages the upper end of a steel fluid lift plunger and supports the plunger during installation and retrieval into or from a lubricator. The tool includes release means for exerting a force against the plunger to break the magnetic bond and thus release the plunger from the tool. The magnet will preferably be a rare earth (e.g., neodymium) magnet, but other types of magnets (including electromagnets) could be used in alternative embodiments. 
     In a first embodiment, the plunger installation and retrieval tool comprises a magnet holder having a generally cylindrical outer surface and a pocket formed into the lower end of the magnet holder for receiving a magnet. The diameter of the cylindrical outer surface is preferably only slightly smaller than the inside diameter of the lubricator in which it is intended to use the tool. An elongate hanger member is connected to the upper end of the magnet holder and extends upward to connect to a hanger support, which may be provided in the form of a circular or rectilinear plate, or a member of any other suitable configuration. 
     The tool also comprises an actuating mechanism providing means for breaking the magnetic bond between a plunger and the magnet, in order to release the plunger from the tool. In one embodiment, the actuating mechanism comprises a rigid elongate actuating member (alternatively referred to as a plunger release rod) having an upper end retained by the hanger support such that the plunger release rod is longitudinally movable relative to the hanger support within a preset travel range. The upper end of the actuator member is preferably provided with a handle of any suitable design to facilitate operation of the tool. The lower end of the actuator member is slidingly disposed within an actuator channel passing longitudinally through the magnet holder. The actuator channel may pass through the magnet disposed within the pocket in the magnet holder. Alternatively, the actuator channel may pass through the magnet holder at a location radially outboard of the magnet. When the actuator member is moved to the upper limit of its preset travel range, its lower end will be retracted within the magnet holder. When the actuator member is moved to the lower limit of its travel range, its lower end will extend below the bottom of the magnet holder. 
     In an alternative embodiment, the actuating mechanism comprises a flexible elongate actuating member (such as a cable or a solid rod) encased within a flexible housing or sheath. Although being flexible, the sheath has sufficient strength and stiffness such that a compressive force can be applied to the actuating member notwithstanding its flexibility similar to the well-known “Bowden cable” commonly used to actuate throttles and chokes on internal combustion engines, and to actuate hand brakes on bicycles and motorcycles. The embodiment has the advantage of being more compact than embodiments using rigid elongate actuating members, the length of which will be determined by tool&#39;s required operating range (i.e., the distance from the top of the lubricator to the top of a plunger within the lubricator). As well, a flexible actuating member allows an operator to use the tool from a less elevated position relative to the lubricator, thus enhancing operator safety. 
     To install a plunger into a lubricator on a gas wellhead using the tool, the actuator member is raised to retract its lower end into the magnet holder, and then the tool is manipulated such that the magnet engages the top of the fishing neck at the upper end of the plunger. With the plunger thus magnetically supported by the tool, it is lowered into the upper end of the lubricator until the plunger is resting on the catcher inside the lubricator. A downward force is then applied to the plunger release rod (i.e., by moving the handle of the plunger release rod downward toward the hanger support), thereby pressing the lower end of the plunger release rod against the top of the plunger to break the magnetic bond and release the plunger from the magnet. The tool is then withdrawn from the lubricator. 
     In a second and particularly preferred embodiment, a lower region of the cylindrical outer surface of the magnet holder is threaded to receive a cylindrical member (or “fishing neck skirt”) extending a desired distance below the lower end of the magnet holder. The outer diameter of the skirt is preferably only slightly smaller than the inside diameter of the lubricator in which the tool is to be used, while the inner diameter of the skirt is only slightly larger than the diameter of the fishing neck of the plunger with which the tool is to be used. The fishing neck skirt thus acts as stabilizer keeping the plunger axially aligned with the tool such that the upper end of the plunger remains in full contact engagement with the magnet and will not be dislodged by lateral forces that might be inadvertently exerted against the plunger or the tool during plunger installation or retrieval. 
     This second embodiment provides the further advantage of making it possible to use the same tool in lubricators having different inner diameters, and with plungers having fishing necks of different diameters. The outer diameter of the magnet holder can be set to suit the smallest anticipated lubricator diameter, and a variety of skirts can be provided that can all be threaded onto the magnet holder but have different inner and outer diameters to accommodate different combinations of fishing neck size and lubricator size. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments will now be described with reference to the accompanying figures, in which numerical references denote like parts, and in which: 
         FIG. 1  is an isometric view of a plunger installation and retrieval tool in accordance with a first embodiment, shown with the plunger release rod in a retracted position. 
         FIG. 2  is an isometric view of the plunger installation and retrieval tool in  FIG. 1 , shown with the plunger release rod in an extended position. 
         FIG. 3  is an isometric view of the lower portion of a plunger installation and retrieval tool in accordance with a second embodiment, having a removable fishing neck skirt and with the plunger release rod located coaxially with the magnet holder. 
         FIG. 4  is an isometric view of the lower portion of a variant of the plunger installation and retrieval tool in  FIG. 3 , the plunger release rod passing through the magnet holder radially outboard of the magnet. 
         FIG. 5  is a longitudinal cross-section through the plunger installation and retrieval tool in  FIG. 3 , shown inserted into a lubricator with the fishing neck of a plunger magnetically suspended from the tool and stabilized by the tool&#39;s fishing neck skirt. 
         FIG. 6  is a longitudinal cross-section as in  FIG. 5 , but showing the plunger released from the tool subsequent to actuation of the plunger release rod. 
         FIG. 7  is an isometric view of a plunger installation and retrieval tool in accordance with a third embodiment, in which the plunger release mechanism incorporates a flexible plunger release rod encased in a flexible housing. 
         FIG. 8  is an isometric view of the plunger installation and retrieval tool in  FIG. 7 , shown with the plunger release rod in an extended position. 
     
    
    
     DETAILED DESCRIPTION 
       FIGS. 1-3 and 5-6  illustrate a plunger installation and retrieval tool  100  in accordance with a first embodiment. Tool  100  comprises a magnet holder  30  having an upper end  30 U, a lower end  30 L, a generally cylindrical outer surface  31 , a pocket  34  formed into lower end  30 L of magnet holder  30 , and a magnet  40  disposed within pocket  34 . Magnet  40  preferably has a lower surface  41  which preferably (but not necessarily) is planar to facilitate optimally effective magnetic engagement with the upper end of a plunger. Although magnet  40  is shown with its lower surface  41  flush with lower end  30 L of magnet holder  30 , magnet  40  may optionally project below magnet holder  30 . 
     An elongate hanger rod  10  has a lower end  10 L connected to upper end  30 U of magnet holder  30  (for example, by means of a threaded connection  37 ) and an upper end  10 U connected to a hanger support  14 , shown in the Figures, by way of example only, as a circular plate. Whatever form hanger support  14  may take, it will preferably be large enough to prevent tool  100  from accidentally falling completely into a lubricator. 
     Tool  100  also includes an elongate plunger release rod  20  having an upper end  20 U retained by hanger support  14  such that plunger release rod  20  can move longitudinally relative to hanger support  14  within a preset travel range. In the illustrated embodiments, upper end  20 U of plunger release rod  20  is provided with a handle  26  to facilitate actuation of tool  100 . Handle  26  is shown, by way of example, in the form of a ball-like knob, but it could take any of many different functionally-effective forms (including a simple 90-degree bend in rod  20 ). 
     In the illustrated embodiment, longitudinal movement of plunger release rod  20  relative to hanger rod  10  is facilitated by slidably disposing plunger release rod  20  through an opening  16  in hanger support  14 . However, alternative embodiments may use other means for facilitating this movement without departing from the scope of the present disclosure. Tool  100  preferably incorporates means for limiting the longitudinal travel of plunger release rod  20  relative to hanger rod  10 , and any functionally suitable means of doing so may be used without departing from the scope of the present disclosure. By way of non-limiting example, upward longitudinal travel of plunger release rod  20  relative to hanger rod  10  is limited by a first stop element  12  fixed to hanger rod  10  at a selected location along its length, and a second stop element  24  fixed to plunger release rod  20  at a selected location below first stop element  12  on hanger rod  10 , with first and second stop elements  12  and  24  being configured such that second stop element  24  cannot move upward past first stop element  12 . Downward longitudinal travel of plunger release rod  20  relative to hanger rod  10  is limited in the illustrated embodiments by handle  26  contacting hanger support  14 . 
     In  FIGS. 1 and 2 , magnet holder  30  is shown having an externally-threaded lower section  33  and, optionally, an unthreaded section  32  between threaded section  33  and lower end  30 L of magnet holder  30 . However, this is not essential; in alternative embodiments, unthreaded cylindrical outer surface  31  of magnet holder  30  could extend the full length between upper and lower ends  30 U and  30 L of magnet holder  30 . However, preferred embodiments will include threaded section  33  to facilitate connection of a cylindrical skirt  50  as shown in  FIGS. 3 and 4 . As illustrated, skirt  50  has an upper threaded section  52  for threaded engagement with threaded section  33  of magnet holder  30 , and a lower section having a cylindrical bore  54  below threaded section  52 . The diameter of cylindrical bore  54  will preferably be selected to provide a reasonably close-tolerance sliding fit over the fishing neck  72  of a gas lift plunger  70 , as illustrated in  FIGS. 5 and 6 . 
     In the embodiment shown in  FIGS. 1-3 , plunger release rod  20  is coaxial with magnet holder  30 , with hanger rod  10  being generally parallel to plunger release rod  20  but radially offset from it. A lowermost section  22  of plunger release rod  20  is slidably disposed within a coaxial bore  35  in magnet holder  30  and a coaxial bore  42  through magnet  40 .  FIG. 4  illustrates a variant in which hanger rod  10  is coaxially mounted to magnet holder  30 , with plunger release rod  20  being radially offset. In this embodiment, the force by plunger release rod  20  to release plunger  70  from magnet  40  will be offset, but this variant avoids the need to drill or otherwise form a bore  42  in magnet  40  for sliding passage of plunger release rod  20  (or lowermost section  22  thereof, in the illustrated embodiments). This is advantageous because an offset bore  35 ′ can be drilled through the full length of a variant magnet holder  30 ′ as shown in  FIG. 4 . Magnet holder  30 ′ (or  30 ) will typically and preferably be machined from mild steel, which is readily drillable, whereas materials such as neodymium are difficult and costly to drill. Accordingly, the embodiment in  FIG. 4  allows the use of an undrilled magnet  40 ′, which will be less costly than magnet  40  having a bore  42  as in  FIG. 3 . 
     The operation and use of plunger installation and retrieval tool  100  may be readily understood with reference to  FIGS. 5 and 6 , which show a tool  100  in accordance with  FIG. 3  disposed within a lubricator  60  having an inner cylindrical surface  62 . In the illustrated embodiment, the outer diameter of skirt  50  matches the diameter of cylindrical outer surface  31  of magnet holder  30 , and is slightly less than the diameter of lubricator inner surface  62  to provide a small tolerance gap T between skirt  50  and magnet holder  30  and lubricator inner surface  62 . However, this is not essential; as previously noted, in variants of the illustrated embodiment, the diameter of magnet holder  30  could be less than the diameter of skirt  50 , with tolerance gap T being formed only between skirt  50  and lubricator inner surface  62 . 
     In  FIG. 5 , lowermost section  22  of plunger release rod  20  is fully retracted into magnet  40  and magnet holder  30 , and the upper end of plunger  70  is in flush contact with lower surface  41  of magnet  40 , such that plunger  70  is magnetically suspended from magnet  40 . The fishing neck  72  of plunger  70  is fully inserted into skirt  50 , with the cylindrical outer surface  74  of fishing neck  72  snugly constrained by a tolerance fit against cylindrical bore  54  of skirt  50 .  FIG. 5  thus illustrates the condition existing when plunger  70  is being inserted into lubricator  60  before it is released from magnet  40 , or the condition existing just after tool  100  has magnetically engaged plunger  70  for purposes of removing plunger  70  from lubricator  60 . 
       FIG. 6  illustrates the operation of tool  100  to release plunger  70 , such when setting plunger  70  onto a catcher (not shown) within lubricator  60 . The person operating tool  100 , while grasping hanger support  14 , applies a downward force to handle  26  and plunger release rod  20 , thereby urging the lower end of plunger release rod  20  downward against the top of plunger  70  to break the magnetic bond between magnet  40  and plunger  70 . The downward force applied to handle  26  is reacted by hanger support  14  being grasped by the user. Tool  100  may then be withdrawn from lubricator  60 . 
     Tool  100  may optionally be provided with biasing means for biasing handle  26  and plunger release rod  20  toward a retracted position as shown in  FIGS. 1 and 5 , thereby to facilitate engagement of magnet  40  with a plunger  70 . 
       FIGS. 7 and 8  illustrate a plunger installation and retrieval tool  200  in accordance with an alternative embodiment in which the tool actuating mechanism comprises a flexible elongate actuating member  210  encased within a flexible sheath  215  (which functions in part like hanger rod  10  of tool  100 ). As shown in  FIG. 7 , the upper end  215 U of sheath  215  is anchored to a suitable reaction member  225  (analogous to hanger support  14  of tool  100 ) by means of a suitable upper adapter  220 . Similarly, the lower end  215 L of sheath  215  is anchored to upper end  30 U of magnet holder  30  in conjunction with a suitable lower adapter  230  (shown by way of example in  FIG. 8  as a sleeve connected to magnet holder  30  by means of a threaded connection  237 ). Flexible actuating member  210  extends through reaction member  225  and its upper end  210 U is anchored to a suitable handle  240 . The lower end  210 L of flexible actuating member  210  is slidably disposed within bore  35  in magnet holder  30  and bore  42  in magnet  40 , such that lower end  210 L can (similar to lower section  22  of plunger release rod  20  in other illustrated embodiments). Flexible actuating member  210  fits closely within sheath  215 , which laterally restrains flexible actuating member  210  such that a compressive force can be applied to it without buckling. 
     Operation of tool  200  is essentially the same as for the embodiments of tool  100  shown in  FIGS. 1-6 . To release a plunger  70  that is in magnetic engagement with magnet  40 , a downward force is applied to handle  260  (i.e., toward reaction member  225 ) such that lower end  210 L of flexible actuating member  210  exerts a force against the top of plunger  70  to break its magnetic bond with magnet  40 , all as shown in  FIGS. 7 and 8 . Handle  260  can then be pulled upward to a retracted position  240 R (indicated in broken outline in  FIG. 7 ) so that lower end  210 L of actuating member  210  is fully retracted into magnet  40  and magnet holder  30 , thereby readying tool  200  for re-use to set or retrieve a plunger. 
     Graphite or other suitable lubricating material may be introduced into sheath  215  to facilitate easy movement of actuating member  210  within sheath  215 . Tool  200  may optionally be provided with biasing means for biasing handle  240  and actuating member  210  toward a retracted position, thereby to facilitate engagement of magnet  40  with a plunger  70 . 
     It will be readily appreciated by those skilled in the art that various modifications of the present invention may be devised without departing from the scope and teaching of the present invention, including modifications using equivalent structures or materials hereafter conceived or developed. For example, lowermost section  22  of plunger release rod  20  is shown as being of reduced diameter relative to the main portion of plunger release rod  20 , but this is not essential; in alternative embodiments, plunger release rod  20  could be of uniform size throughout its length. Although plunger release rod  20  is shown as a round rod, plunger release rod  20  could be provided in other forms without departing from the scope of the present disclosure. In all illustrated embodiments, magnet  40  and magnet pocket  34  in magnet holder  30  are shown as being of cylindrical configuration, but this is by way of non-limiting example only; other shapes and configurations of magnet  40  and magnet pocket  34  may be used in variant embodiments of tool  100 . 
     It is to be especially understood that the invention is not intended to be limited to any described or illustrated embodiment, and that the substitution of a variant of a claimed element or feature, without any substantial resultant change in the working of the invention, will not constitute a departure from the scope of the invention. It is also to be appreciated that the different teachings of the embodiments described and discussed herein may be employed separately or in any suitable combination to produce desired results. 
     In this patent document, any form of the word “comprise” is to be understood in its non-limiting sense to mean that any item following such word is included, but items not specifically mentioned are not excluded. A reference to an element by the indefinite article “a” does not exclude the possibility that more than one such element is present, unless the context clearly requires that there be one and only one such element. Any use of any form of the terms “connect”, “engage”, “couple”, “attach”, or any other term describing an interaction between elements is not meant to limit the interaction to direct interaction between the subject elements, and may also include indirect interaction between the elements such as through secondary or intermediary structure. Relational terms such as “parallel”, “perpendicular”, “coincident”, “intersecting”, and “equidistant” are not intended to denote or require absolute mathematical or geometrical precision. Accordingly, such terms are to be understood as denoting or requiring substantial precision only (e.g., “substantially parallel”) unless the context clearly requires otherwise. As used in this document, the terms “typical” and “typically” are used in the sense of representative or common usage or practice, and are not to be understood as implying essentiality or invariability.