Abstract:
An apparatus incorporating a chemical seal and method for removing fluids from a well is disclosed. The chemical seal is created by a foaming agent which, when in the presence of gas and fluids present in the well, and when agitated by the apparatus, creates foam between the apparatus and the walls of the well in which it operates. The foam improves the seal between the apparatus and the inner wall of the well, improving the efficiency of the apparatus in lifting fluids from the well. Furthermore, the chemical seal improves the distribution of treatment chemicals within the well as it reduces liquid flowback. Automatic recharging or reapplication of the foaming agent and/or treatment chemicals to the apparatus can be accomplished with a chemical application assembly associated with the well.

Description:
[0001]     This is a continuation-in-part application of U.S. patent application Ser. No. 10/630,292 filed on Jul. 30, 2003. 
     
    
     TECHNICAL FIELD  
       [0002]     The present invention relates to petroleum production and has significant application to wells which use plunger lift systems to aid in production from the well. In particular, the invention relates to an improved seal between a plunger used in a plunger lift system and the inside surface of the tubing in which the plunger travels.  
       BACKGROUND OF THE INVENTION  
       [0003]     This invention relates to production from petroleum wells, and in particular, an improvement to the efficiency of plunger lift techniques and an improvement to the efficiency of chemical treatment of wells using plunger lift techniques. The invention will find use in wells which produce either gas or oil, including those using enhanced production techniques such as artificial gas lift. It is anticipated that the invention will find the greatest use in low producing or “stripper” wells, and more particularly in gas wells, thus, the background description and the description of the preferred embodiments of the invention will focus on gas wells.  
         [0004]     As a well matures, the pressure in the formation decreases and the volume and velocity of the gas flow slows. While initially the flow rate and velocity of produced gas may be sufficient to remove the liquids with the gas, at some point the flow rate of gas will be insufficient to carry liquids out of the well. As a result, the liquid loading in the well will increase, and liquid will collect in the bottom of the well. When production by natural reservoir pressure becomes uneconomical, artificial lift techniques can be utilized to increase well production. A number of artificial lift systems are known in the industry, including sucker rod pumps, gas lift techniques and plunger lift techniques.  
         [0005]     Conventional plunger lift systems, which are also known as free piston systems, utilize a plunger (piston) that is dropped into the well by releasing it from a plunger catcher located at the surface. The plunger falls to the bottom of the tubing and onto a bumper or stop at the bottom of the tubing. After the well is shut in and pressure in the well has built, the wellhead is opened to a low pressure line and the high pressure gas located within the well pushes the piston upward to the surface, thereby pushing the liquid on top of the plunger to the surface. This sequence can be repeated by closing the wellhead off and allowing the plunger to fall again to the bottom of the well while pressure in the well is allowed to rebuild. Another technique is the use of a bypass plunger which is designed so as not to require the well to be shut in. U.S. Pat. No. 6,209,637 entitled “Plunger Lift with Multi Piston and Method” relates to this technique.  
         [0006]     Automatic control of plungers used in plunger lift technique is known in the art. Generally, an electronic controller can be utilized which is able to control all of the various valves required to open and close the well, monitor the position of the plunger, and catch the plunger at the surface. Such controllers may, for example use pressure within the well, production flow rate, or travel time of the plunger in order to determine when to perform various operations. Alternatively, an electronic controller may simply operate based on a preset, timed schedule. Electronic controllers are offered by Ferguson Beauregard of Tyler, Tex. and are described at Ferguson Beauregard&#39;s web site located at http://www.fergusonbeauregard.com/lift.shtml.  
         [0007]     The efficiency of a plunger in bringing fluid to the surface is limited somewhat by the plunger&#39;s ability to create a seal with the inside walls of the tubing in which it travels. Ideally, to maximize the seal between the plunger and tubing, a plunger would have a diameter that is as close to the inside diameter of the tubing as possible, thereby minimizing gaps between the plunger and tubing. Unfortunately, obstructions may exist within the tubing, such as sand, crimping from work over operations, tool traps, and the like. Such obstructions could cause the plunger to become stuck in the tubing, thus a smaller diameter plunger may be selected. However, a smaller plunger may tend to leave a gap between the outer surface of the plunger and the inner surface of the production tubing. Thus, it is less able to create an effective seal with the tubing. As a result, when the plunger is rising in the well driving fluids out, these same fluids are able to pass around the sides of the plunger and fall back into the well.  
         [0008]     Previous attempts to address this problem have achieved limited success. For example, attempts have been made to use a plunger fitted with a flexible rubber seal able to engage the walls of the tubing. U.S. Pat. No. 7,080,692 titled “Plunger Lift Tool and Method of Using the Same” to Kegin is illustrative of the rubber seal model. However, these plungers suffer from common drawbacks such as insufficient contact with the tubing, wear (particularly in the case of rubber seal plungers), and the inability to accommodate significant aberrations in the tubing. Thus, there is a need for a plunger which is able to travel in a well with a reduced risk of becoming stuck, while still being able to create an effective seal with the tubing walls.  
         [0009]     Plunger lift assisted wells are known to be susceptible to corrosion, scale, and undesirable deposits of paraffin, petroleum distillates, asphaltines, microbial growth, and other undesirable substances. To address these problems, treatment chemicals such as soap, acid, corrosion inhibitors, solvents for paraffin and petroleum distillates, stabilizers, biocides and other known treatment chemicals are deposited downhole. A number of techniques have been employed to deliver these treatment chemicals, however, these techniques have many drawbacks, such as excessive chemical use, and inefficient application.  
         [0010]     One treatment technique, known as continuous injection, involves the continuous pumping of treatment chemical into the annulus between the tubing and the casing, sometimes through capillary tubes. However, the treatment chemicals themselves are potentially damaging to the production tubing and/or casing, and the use of capillary tubes presents problems associated with installation and maintenance of the tubes themselves. Another treatment technique is a batch treatment technique. However, the batch technique does not provide even distribution of treatment chemical. Many batch and capillary treatment methods rely on the liquids accumulated in the wellbore to dilute the chemicals. As such, the chemicals are generally applied downhole in concentrated form. Unfortunately, the concentrated chemicals can be corrosive to the tubing and casing. Furthermore, in wells where the plunger does not make a good seal with the tubing, fluids which would have been forced out of the well by the plunger lift action will instead flow around the plunger and down the sides of the tubing, washing away treatment chemical, thereby raising the chemical dose necessary for effective treatment. The present invention provides an apparatus and method which is able to evenly distribute treatment chemicals along the inner surface of the tubing and minimize waste of treatment chemicals, damage to the tubing, and disruption to production from the well.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]     The invention will be better understood with reference to the drawings taken in connection with the detailed description which follows:  
         [0012]      FIG. 1  is a cross-sectional area of a well;  
         [0013]      FIGS. 2A, 2B , and  2 C are perspective illustrations of three prior art plungers;  
         [0014]      FIG. 3  is a cross-sectional view of a chemical dispenser removably attached to a plunger;  
         [0015]      FIG. 4  is a cross-sectional view along line  4 - 4  of  FIG. 3 ;  
         [0016]      FIG. 5  is a partial cross-sectional view showing one embodiment of an attachment mechanism between a chemical dispenser and a plunger;  
         [0017]      FIG. 6  is a partial cross-sectional view of another chemical dispenser removably attached to a plunger;  
         [0018]      FIG. 7  is a cross-sectional view of the lower portion of a chemical dispenser;  
         [0019]      FIG. 8  is a partial cross-sectional view of the lower portion of another embodiment of a chemical dispenser;  
         [0020]      FIG. 9  is a cross-sectional view of another chemical dispenser removably attached to a plunger;  
         [0021]      FIG. 10  is a side view of a coiled spring plunger with treatment chemical applied;  
         [0022]      FIG. 11  is a side view of a brush plunger with applied chemical treatment solution;  
         [0023]      FIG. 12  is a side view of a plunger with a chemical dispenser attached;  
         [0024]      FIG. 13  is a cross-sectional view of  FIG. 12  along line  13 - 13 ; and  
         [0025]      FIG. 14  is a partial cross-sectional view of a chemical dispenser.  
         [0026]      FIG. 15  is a side view of a brush plunger with foam and a chemical seal in the well tubing.  
         [0027]      FIG. 16  is a cross-sectional area of a well with an alternate embodiment of the present invention shown.  
         [0028]      FIGS. 17A &amp; 17B  are cross-sectional areas of a well with alternate embodiments of the present invention shown. 
     
    
       [0029]     The drawings illustrate certain preferred embodiments of the invention and like elements have been provided with like reference numerals to corresponding items between various drawings.  
       SUMMARY OF THE INVENTION  
       [0030]     The present invention relates to a method and apparatus for creating an improved seal between a plunger and the inner wall of tubing inserted into a well wherein an artificial lift technique is used. In the method of the present invention, specific types of chemicals, referred to herein as foaming agents, known to produce foam in the presence of wellbore fluids, may be applied to a known plunger, such as a brush or pad plunger in the form of a gel, putty, paste or other suitable form such that a significant portion of the treatment chemical will be retained on the plunger as it is dropped from the well head to the bottom of the wellbore. While the plunger is at the bottom of its travel, foam builds around the plunger as the foaming agent diffuses and reacts with the produced liquids. The foaming may be augmented by produced or artificial lift gas as it bubbles through produced liquids at the bottom of the well. As the plunger returns to the surface, the foam acts as a seal, filling the gaps between the plunger and the inner surface of the tubing. When the plunger is caught in the plunger catcher, additional treatment chemical can be applied to the plunger before it is again dropped to the bottom of the wellbore, thereby ensuring that there will be foaming agent sufficient to create another foam seal on the plunger&#39;s next trip to the surface.  
         [0031]     In another aspect, the invention relates to a method for improving the seal between the plunger or plunger/dispenser apparatus and the inside wall of the tubing in which it operates by using foaming agents which are surfactants or lubricants, or by adding surfactants or lubricants in addition to a foaming agent. The foam created by the foaming agent and/or mixtures of foaming agent with treatment chemical forms a chemical seal, creating a barrier between gas and liquids as the gas tries to bypass the plunger in an upward direction and as the liquid tries to fall backward between the outer surface of the plunger and the inside wall of the tubing. Thus, the invention may allow the plunger to bring a greater volume of fluids to the surface with each trip.  
         [0032]     In another aspect, the present invention relates to a method and apparatus which provides more uniform distribution of treatment chemicals to the inside walls of the tubing inside the well. In particular, in addition to being treated with a foaming agent, the plunger may also have treatment chemical mixed with the foaming agent or be loaded with a treatment chemical. Alternatively, the foaming agent may itself be a treatment chemical. Once the plunger has been released into the well, it may treat the well during its downward travel. In addition, it will fall to the bottom of the well where it will encounter water and/or other fluids. A treatment chemical may then be released into the fluid, diluting it. As the plunger subsequently rises to the surface, the foaming agent will create foam which in turns forms a chemical seal which will force fluids mixed with the now diluted treatment chemicals ahead of it. In the present invention, because the plunger in combination with the foam and chemical seal more efficiently moves the fluid upward, the diluted treatment chemicals in the fluids may be more evenly applied to the inner walls of the tubing.  
         [0033]     In another aspect, the plunger may be a plunger/dispenser apparatus. The apparatus includes an interface area and a dispenser section which includes one or more receptacles for receipt of treatment chemical. The plunger/dispenser may also have a neck for engagement with a plunger catcher, and/or downhole tools.  
         [0034]     In yet another aspect, the chemical dispenser can include a head with an attachment mechanism for attaching to a known plunger, and one or more receptacles for receipt of treatment chemicals. Furthermore, the receptacle may be an elongate chamber having lower ports and upper ports. In a preferred embodiment, a valve is associated with the lower ports to control flow of liquid through the lower ports.  
         [0035]     Alternatively, the valve may be a flexible polymeric sheet which is pressed against the lower ports as the dispenser falls through the wellbore and liquid. When the dispenser comes to rest at the bottom of the wellbore, the flexible sheet will fall away from the lower ports of the dispenser, opening the lower ports to liquid flow so that the chemical within the dispenser can be dissolved into the liquid.  
         [0036]     Also, the dispenser may include an extension or standoff section which allows the receptacle holding the treatment chemical to be positioned below the lower end of the tubing when the plunger assembly comes to rest at the bottom of the well. This allows the treatment chemical to dissolve or diffuse into the liquid located in the near wellbore area, thereby increasing the efficiency of the chemical delivery.  
         [0037]     In another aspect, the treatment chemical, foaming agent, surfactant and/or lubricant may be applied or recharged with a chemical application apparatus. The chemical application apparatus is a modification to wellhead manifold systems used in plunger lift operations. In this embodiment an applicator is positioned in the section of the manifold which receives the delivery system, e.g., plunger, or plunger/dispenser apparatus, or plunger with attached chemical dispenser. The applicator is positioned such that it will be operatively adjacent to the receptacle portion of the plunger, plunger/dispenser or chemical dispenser attached to a plunger. The nature of the applicator can vary depending upon the form of the treatment chemical and/or foaming agent.  
         [0038]     The automated application of foaming agents and/or treatment chemicals to the delivery system is especially suited to the application of gels and paste. In these applications, the applicator can include a nozzle which communicates with an opening in the manifold and is aligned such that it delivers the desired materials to the desired portion of the plunger or plunger/dispenser. The nozzle can be connected to one or more storage tanks via one or more conduits. One or more control valves to control the flow of materials from the one or more storage containers to one or more nozzles can be provided.  
         [0039]     The treatment chemical foaming agent, surfactant and/or lubricant can also be recharged by removing the delivery system from the manifold and recharging manually. This method can be used for any form in which the treatment chemical, foaming agent, surfactant and/or lubricant is used, such as, stick, time release capsules, gel, paste, putty, liquid, emulsion, etc.  
       DETAILED DESCRIPTION  
       [0040]     For purposes of background, an abbreviated discussion of the plunger lift technique will be presented. Those skilled in the art will recognize that there are many variations which have been used in connection with the lift technique and system which is described. While the discussion will focus on gas producing plunger lift wells, the method of the present invention is also suited for use on oil producing wells, and can be modified for variations of the described lift system. Further, those skilled in the art will appreciate that the present invention need not be used to the exclusion of other chemical treatment methods. Costs and other considerations can result in the use of the present invention together with other treatment methods.  
         [0041]     With reference to  FIG. 1 , the gas well  17  will have a wellbore  10  located within petroleum-bearing formation  11  and which typically contains a casing  12  either throughout the entire well or a portion of the wellbore. Extending through a portion of the formation  11  are fractures  15  created by known well stimulation techniques. The wellbore  10  can also contain tubing  14  within the casing  12 . Typically, casing  12  will have one or more perforations  13  which provide a fluid passage between the inside of casing  12  and formation  11 . In a typical arrangement, the well production will flow through the tubing  14  to the wellhead  16 . For gas lift operations the tubing  14  can be provided with a stop  18  and seating nipple  19  at the lower end of the tubing  14 , and a plunger  20  which travels in the tubing  14 , and to the wellhead  16 . In a typical arrangement, a manifold  22  is provided at the wellhead  16  which can have a plunger catch  30  to hold the plunger in place, a lubricator  32 , and a control box  34  to control the flow of gas and liquid from the well by operating the valves  24 ,  26 ,  28  and  250  and related conduits.  
         [0042]     Stop  18  is provided to prevent plunger  20  from falling below the position of the stop  18 . The stop  18  can include a spring  36  or other shock absorbing device to reduce the impact of the falling plunger  20 . The plunger  20  can be of any of the numerous designs which are known in the art or another delivery system as described herein. The plunger  20  provides a mechanical interface between the gas  38  and the liquid  40  present in the well. After shutting the well off at the surface, plunger  20  is allowed to fall to the bottom of the well and rest on the stop  18 . After pressure builds in wellbore  10 , well  17  is opened and the pressure will push plunger  20  and liquid  40  on top of plunger  20  up the tubing  14  to the surface.  
         [0043]     When plunger  20  reaches the top of well  17  it enters or is received by manifold  22 . Manifold  22  can include a shock absorbing spring  42  or other mechanism to reduce the impact of the plunger. A plunger arrival sensor  41  is provided to detect arrival of the plunger  20  at the surface and to activate plunger catch  30  which holds the plunger  20  until a signal is received to release plunger  20 . Control box  34  contains circuitry for opening and closing the appropriate valves  24 ,  26 ,  28 , and  250  during the different phases of the lift process. As known in the art, other valving/piping arrangements may be constructed to accomplish the same functions. By controlling these valves, control box  34  regulates the plunger lift cycle and the application of various materials such as treatment chemicals, surfactants, or lubricants, and, in the present invention, a foaming agent, to the plunger. Furthermore, once arrival sensor  41  signals control box  34  that plunger  20  has been caught by plunger catcher  30 , appropriate materials may be applied to plunger  20  and/or dispensers  65  ( FIG. 3 ),  116  ( FIG. 6 ),  140  ( FIG. 8 ),  162  ( FIG. 9 ), and  220  ( FIG. 14 ) attached to plunger  20 . Following application of chemicals, control box  34  may also release plunger  20  according to its control method.  
         [0044]     The present invention is suitable for use with any known plunger lift system, although in a preferred embodiment, brush or pad plungers are used.  FIGS. 2A, 2B , and  2 C illustrate several prior art plungers, although they are not intended to be all inclusive. Necks  46  are provided in most plungers to provide an area where the plunger can be caught by the plunger catcher, and also to provide an area which may be engaged by a downhole tool in the event the plunger becomes stuck in the tubing. Furthermore, many plungers are provided with a mechanical cleaning apparatus  47  suitable to engage with the walls of the tubing  14 .  FIG. 2A  illustrates a brush plunger  48 . Brush plunger  48  is also provided with necks  46  at each end. In this type of plunger, mechanical cleaning apparatus  47  is brush  50  which may be a flexible nylon brush, a metal fiber brush or a brush made from any other suitable material.  FIG. 2B  illustrates a solid bar stock plunger  52 . In the bar stock plunger, mechanical cleaning apparatus  47  is a plurality of helical grooves or ridges  54  along a portion of bar stock plunger  52 .  FIG. 2C  illustrates a pad plunger  56  in which mechanical cleaning apparatus  47  is pads  58  which are made up of pad plates  60 . The pad plates  60  can be spring loaded so that they expand or contract to maintain contact with the inside of the tubing. The illustrated pad plunger  56  is a two-pad plunger but pad plungers can have one or more pads. The illustrated pad plunger  56  has a neck  46  at the top. However, a neck can also be provided at the opposite end. Each plunger has one or more interface sections  62  which are the portions of the plunger designed to interface with the inside of the tubing.  
         [0045]     Referring now to  FIG. 3 , there is shown another embodiment of a delivery system  64  for chemicals. Only a portion of the plunger  20  is shown. The system  64  is a plunger  20  with an attached chemical dispenser  65 . For purposes of illustration, this is only one embodiment of a chemical dispenser  65 . The plunger  20  can be of any known design which has a neck  46  on the lower end. In this embodiment, chemical dispenser  65  has a head portion  66  and a member  68  which defines a receptacle  70  for receiving treatment chemical  72 . Head  66  defines an opening  74  to receive the lower portion of plunger  20  and the plunger neck  46 . Head  66  includes an attachment mechanism for attaching the dispenser  65  to plunger  20 . For purposes of illustration only, two different attachment mechanisms are shown in  FIG. 3 . One attachment mechanism can be set screw  76  in threaded passageway  78  in head  66 . Alternatively, another attachment mechanism can be a spring loaded bolt  80  in passageway  82 . A spring  84  biases the bolt  80  against the neck  46  of the plunger  20 . A ridge  86  can be provided in the passageway  82  against which the spring  84  rests. To remove head  66 , bolt  80  or screw  76  is retracted depending on the attachment mechanism present. Typically, more than one of the same attachment mechanisms will be used to attach dispenser  65  to plunger  20 , for example, one or more set screws  76 , or one or more bolts  80  will be used.  
         [0046]     The chemical dispenser  65  should securely attach to plunger  20 . In some applications it may be desirable for the chemical dispenser  65  to have some play in the connection between the plunger  20  and the chemical dispenser  65  to permit a slight wobble. Some operators may prefer a more rigid fit, in which case, a portion of the upper surface  90  of head  66  can be a shaped surface which mates with a corresponding surface  92  on the plunger  20  so as to limit the movement of the plunger with respect to the dispenser. In a preferred embodiment, one or more upper ports  94  are provided, and one or more lower ports  96  are provided. Upper ports  94  allow gas and liquid to enter or leave the receptacle  70 . While the plunger is falling in the tubing the primary function of ports  94  is to exhaust any gas and liquid which may enter the receptacle to aid the fall of the plunger. Once the plunger has reached the stop at the bottom of the tubing the upper ports  94 , if below the liquid level, will function to allow chemical contained in the receptacle to diffuse or dissolve into the liquid. Lower ports  96  allow liquid to enter and leave the receptacle  70 . In the illustrated embodiment, the lower ports  96  are on the bottom surface of member  68 ; however, they can also be positioned on the side walls. Preferably, a valve  98  is provided. In the illustrated embodiment, valve  98  is a flexible rubber sheet  100  having a dimension sufficient to cover lower ports  96 . Valve  98  is held in place by a retaining plug  102  which can extend through an opening  104  in the bottom of the member  68 . The purpose of valve  98  is to either restrict or close off the flow of liquid through lower ports  96  as the plunger drops. As the plunger drops in the tubing, the flexible sheet  100  will be pushed against the bottom of the member  68 . This will either completely seal or partially seal off ports  96 . The purpose of valve  98  in this embodiment is to minimize or prevent the flow of fluid through receptacle  70  while the system drops in the tubing. This will prevent or minimize the washing of chemicals out of the receptacle as the chemical dispenser  65  passes through the fluid above the stop of the tubing. Once the delivery system  64  comes to rest on the stop, flexible sheet  100  will fall away from the bottom of member  68  and to a second position  103  (shown in phantom), because there is no force pushing the flexible sheet  100  against the bottom of member  68 . This will allow liquid to enter receptacle  70  and leach the treatment chemical  72  out of receptacle  70 .  
         [0047]      FIG. 3  illustrates an embodiment in which a threaded surface  106  on the bottom of head  66  is provided to engage a threaded surface  108  on member  68 . Threaded surface  108  allows member  68  to be removed from head  66  which facilitates the manual insertion of chemicals into the receptacle  70 . As an alternative, head  66  and member  68  can be one piece and an opening  110  provided through which chemicals can be inserted into the receptacle  70 . In an alternative embodiment, dispenser  65  may receive treatment chemical  72  through passageway  73  (shown in phantom) which passes through plunger  20  and head  66 .  
         [0048]      FIG. 4  is a cross sectional view of  FIG. 3  across line  4 - 4 . It illustrates a plurality of lower ports  96 .  
         [0049]      FIG. 5  shows another attachment mechanism for attaching the plunger  20  to head  66 . In this embodiment, the lower portion of the plunger has a male threaded surface  112  and head  66  is provided with a corresponding female threaded surface  114 . This allows the head  66  to be attached to plunger  20 . Many other connection mechanisms can be used other than those illustrated herein.  
         [0050]      FIG. 6  is a partial view of a chemical dispenser  116 . In this embodiment, a cap  126  having a threaded surface  128  for engaging threaded surface  130  of the wall defining the receptacle  70  is provided. In this embodiment, between head  118  and receptacle section  70  is standoff section  120 . Standoff section  120  has the length L 1  and receptacle section  70  has a length L 2 . For purposes of illustration, only one side of tubing  14  is shown together with stop  18 . In this illustration stop  18  includes a shock absorbing spring  122  which absorbs the impact of the delivery system. Head  118  is provided with a surface  124  which contacts spring  122  of stop  18 . Standoff section  120  has a sufficient length to allow the receptacle  70  to be positioned below the lower end of tubing  14 . This is advantageous because it allows the chemicals in the receptacle to diffuse in the wellbore below the tubing, rather than diffusing inside the tubing. Generally, the treatment of formation  11  will be more effective when the chemical diffuses directly into the space below tubing  14 . Preferably, the chemical dispenser  116  is dimensioned such that at least a portion of it will pass through the stop. An advantage of the present invention is that the assembly can be constructed to place the dispenser at a predetermined location in relation to the stop. Pressure drop occurs across the stop during well operation, and this pressure drop can produce temperature and pressure changes which cause scale deposits to form in the stop. If scale deposits are allowed to build up at the stop, the deposits can become great enough to cause the plunger to become stuck in the stop. If this occurs, it may be necessary to use wireline removal techniques, or a rig to pull the tubing. With the present invention, treatment chemicals are delivered and concentrated in the vicinity of the stop, and thus scale formation can be very effectively treated. Indeed, the dispenser can be configured to come to rest within the stop for treatment of scale, and later reconfigured to add in the standoff section to provide treatment below the stop.  
         [0051]      FIG. 7  shows the lower portion of wall  136  of another embodiment of a chemical dispenser having an area of reduced outer diameter to provide neck  138 . This provides an area which can be engaged by the plunger catcher on the surface.  
         [0052]      FIG. 8  shows the lower portion of another embodiment of a chemical dispenser  140 . In this embodiment, receptacles for treatment chemical in the form of one or more passageways  142  are shown. Chemical sticks  144  can be inserted into the receptacles, or the passageways  142  can be packed with chemical in a paste form or other form.  
         [0053]      FIG. 9  shows an embodiment of plunger  146  which does not have a neck at the lower end, but rather has an annular end  150  which has an inside threaded surface  152 . The chemical dispenser  162  is a tubular member having a reduced diameter portion  164  at the top which has threads on its outside surface  166  for engaging the threaded surface  152  of plunger  146 . Dispenser  162  defines a receptacle  168  for holding chemical  170 . The plunger has lower ports  172  and one or more upper ports  174 . To manually load the dispenser  162  with chemicals, the dispenser  162  is removed from the plunger  146  and the chemicals are inserted through the opening  176  at the top. If desired, such an assembly can also be equipped with a valve to restrict flow into the lower ports. Alternatively, as further described herein, an automatic chemical applicator may be used to recharge chemicals.  
         [0054]      FIGS. 10 and 11  illustrate yet other embodiments of plunger/chemical dispensers. These embodiments use known plungers as carriers for the chemicals.  FIG. 10  illustrates a coiled spring plunger  44 . In this embodiment of the invention, the space between coiled spring  180  of plunger  44  is partially or completely filled with chemical  182 . In  FIG. 11 , a brush plunger  48  is shown. Brush  50  of brush plunger  48  may be advantageously sized such that it engages the inner surface of tubing  14 . By engaging this surface, brush  50  is able to evenly and effectively distribute chemicals along this inner surface of tubing  14 . In this embodiment of the invention, brush  50  of plunger  48  is impregnated with chemical  182 . In this embodiment, chemical  182  can be applied in the form of a spray, paste, or gel. Preferably, it has a consistency which will allow it to be retained on brush  50  as brush plunger  48  falls through tubing  14 . Chemical  182  may be any one or more of the materials discussed herein, such as treatment chemical, foaming agent, surfactant and/or lubricant. The embodiments of  FIGS. 10 and 11  have the advantage of utilizing existing plungers as the delivery system. This embodiment allows for the delivery of chemical along the tubing to prevent or minimize paraffin deposit and build up, as well as physically scraping off some of the paraffin.  
         [0055]     Turning to  FIGS. 11 and 15 , a preferred embodiment wherein plunger  20  is a brush plunger  48  is depicted. Brush plungers  48  are especially suited to the creation of foam  300  and chemical seal  301  of the present invention, although other types of plungers will be able to create foam  300  and will benefit from chemical seal  301 . In the case of a brush plunger  48 , the individual bristles of brush  50  mechanically agitate chemical  182 , which in this embodiment is preferably a foaming agent, applied to plunger  48  to aid in the creation of foam  300 , and chemical seal  301  as brush plunger  48  travels up and down within tubing  14 . Foam  300  advantageously creates chemical seal  301  between brush plunger  48  and the tubing  14  in which it operates.  
         [0056]     Foam  300  and chemical seal  301  are created by the movement of brush plunger  48  relative to the produced gas  38  and liquid  40  as well as through physical contact with the foaming agent  182  all within tubing  14 . In addition to foam  300  formed by gas  38  rising through liquid  40  as brush plunger  48  settles within tubing  14 , as brush plunger  48  moves up tubing  14 , driven by pressure within formation  11 , gas bubbles will tend to rise along with it, generally at a rate that is greater than the rate at which plunger  48  is rising. Simultaneously, liquid  40  resists the push of plunger  48 , and attempts to flow back down tubing  14 . It is the opposing motions of gas  38  and liquid  40 , when mixed with foaming agent  182 , and agitated by brush  50 , that creates foam  300  and chemical seal  301 .  
         [0057]     In another embodiment of the present invention, chemical  182  may be a surfactant, lubricant, foaming agent or some combination of the three. In this embodiment, when chemical  182  includes a surfactant or lubricant, the surfactant or lubricant will act to reduce the amount of friction between the plunger  20  and tubing  14 .  
         [0058]     In yet another embodiment, in addition to chemical  182  which may be a foaming agent, an additional treatment chemical  72  may be applied either to plunger  20 , or to a plunger  20  with chemical dispenser  65 . Once plunger  20  or plunger  20  with chemical dispenser  65  has been released into tubing  14 , it will fall to the bottom of well  10  where it will encounter liquid  40 . Treatment chemical  72  is then released into liquid  40 , properly diluting it. As plunger  20  subsequently rises to the top of tubing  14 , foam  300  will be created. Plunger  20  with foam  300  will force liquid  40 , now mixed with the diluted treatment chemicals  72 , ahead of it. Because foam  300  reduces the amount of liquid  40  which flows around plunger  20  and back down tubing  14 , more treatment chemical  72  is forced through tubing  14 , and because there is less flow back around plunger  20 , less of the diluted treatment chemical will be prematurely washed from tubing  14 . As a result, foam  300  increases the likelihood that treatment chemical  72  is delivered to tubing  14  at a more consistent rate, improving the efficacy of the cleaning mechanism and reducing the amount of treatment chemical  72  required.  
         [0059]      FIG. 12  illustrates plunger/dispenser  190 . Previous embodiments discussed related to a chemical dispenser to be attached to a known plunger and a modification of the known plunger by the application of treatment chemicals known to be useful in the treatment of scale or skin damage near the wellbore  10 .  FIG. 12  relates to an embodiment of a plunger/dispenser in which the device is specifically configured to be both a plunger and a chemical delivery system. The assembly has an upper portion  192  which includes an interface section  194 . The interface section is that portion which is adjacent to the inside wall of tubing  14 . The interface section may be a coiled spring, a brush, pads, wobble rings or other known interface sections. The interface section fits inside the tubing snugly. When the pressure is released from the well and the plunger travels to the surface, the interface section, with foam  300 , serves to retain much of the fluid above the plunger so that it may be pushed out at the well head. Below the interface section is the lower section  196 . The lower section  196  can include any type of receptacle  198  to receive treatment chemicals  72 , such as an absorbent pad or matrix, or other suitable structure as described above. In the illustrated embodiment, the receptacle  198  is a stiff wire mesh, and treatment chemical  72  has been deposited in the interstices between the mesh. A lower port (not shown) can be provided at the bottom, and a series of ports (not shown) can be provided along the length of lower section  196 . Thus lower section  196  defines a receptacle having one or more upper ports and one or more lower ports. This embodiment also has a standoff section  200  for elongating the system such that all or a portion of the receptacle will be below the end of the stop on the tubing. The lower end of the interface section  194  is of reduced diameter to provide surface  202  for contacting stop  18 . A neck  204  is provided on the top.  FIGS. 13A and 13B  illustrate different embodiments of a cross section of  FIG. 12  along line  13 - 13 . In  FIG. 13A  the cross section is a multipoint star design. This design increases the surface area of the dispenser exposed to the well liquid and provides flow paths for the liquid. In  FIG. 1   3 B, the cross section is circular. However, the design may take any one of a multitude of shapes although in the preferred embodiment the chemical receptacle portion  198  of the apparatus  190  is of small enough dimensions to pass through the stop  18  at the bottom of the tubing.  
         [0060]     In addition to previously described embodiments of receptacles, an additional embodiment is illustrated in  FIG. 14 . In the illustrated embodiment the dispenser section  220  is tubular and defines an opening  222 . The opening is partially closed by a removable cap  224 . The cap is annular to provide a retaining ring  226  which extends inwardly to provide a rest to retain a chemical stick  228  within the dispenser. The stick of treatment chemical is inserted into the tubular section and bias spring  230  can be provided to force the stick against the annular cap. Thus, the lower portion of the stick can be exposed to liquid at the bottom of the well and as the end dissolves the spring pushes the remainder of the stick outwardly.  
         [0061]     Referring back to  FIG. 1  in yet another embodiment of the present invention, a chemical application assembly  240  may be included. A section of conduit  242  of the manifold  22  below the lubricator  32  receives the plunger which is caught by plunger catcher  30 . Plunger catcher  30  has a movable pin  244  which can engage a neck on the plunger or the delivery system. When it is desired to release the plunger the pin  244  is retracted to allow the plunger to fall. Designs and construction of plunger catchers and automatic plunger controls are well known in the art.  
         [0062]     Chemical application assembly  240  includes a chemical storage reservoir  246  which is connected by conduit  248  to a valve  250  which is connected to applicator  252 . Applicator  252  can be a nozzle, an open end of conduit, or other device. The selection of the specific applicator will be made taking into account the physical characteristics of the form of the treatment chemical. Once the receptacle section of the dispenser is aligned with the applicator, valve  250  can be opened and treatment chemical  72  or chemical  182  may be forced onto the plunger  20  or into the chemical dispenser  65 . With reference to  FIG. 17 , an alternate embodiment of manifold  22  is shown. In this embodiment, two chemical application assemblies  240  and  240 ′ are shown although more assemblies positioned in different locations along manifold  22  are possible. Here, chemical application assembly  240  is positioned such that it may directly interface with plunger  20  while plunger  20  is retained by plunger catch  30 . Alternatively, a second chemical application assembly  240 ′ is positioned lower on manifold  22  such that it may directly interface with chemical dispenser  65 . Of course, chemical application assembly  240  may be removed leaving only chemical application assembly  240 ′. The specific number and position of chemical application assemblies  240  provided or used for a particular application may be determined by those skilled in the art. These embodiments are provided as examples only, and are not intended to be limiting as there are a number of alternate arrangements possible.  
         [0063]     Any suitable mode of force can be utilized to force treatment chemical  72  or chemical  182 , which as previously discussed could include other treatment chemical, foaming agent, surfactant and/or lubricant, from storage container  246  including pressurizing the storage container  246  or by pumping. However, the use of the chemical application apparatus  240  or a similar apparatus for the application of treatment chemical  72  or other chemicals  182  is not required. Alternatively, the plunger  20  and/or the plunger  20  with chemical dispenser  65  can be removed from manifold  22 , inspected and the chemical agents recharged if needed.  
         [0064]     The apparatus used to carry treatment chemical  72  into the wellbore  10 , be it plunger  20 , chemical delivery system  64 , or any of the other embodiments disclosed herein, can be made out of any material which is suitable for use in the construction of such devices. While necks have been illustrated, any other design known in the art which allows engagement with a recovery tool or with the plunger catcher is acceptable.  
         [0065]     The treatment chemical can be any known treatment chemical. Further, the treatment chemical can be encapsulated in time-release capsules or in water-soluble gels. Treatment chemicals which can be used include paraffin solvents, clay stabilizers, paraffin inhibitors, chelating agents, scale inhibitors, solvents, corrosion inhibitors, acid, biocides and soap. Suitable encapsulated treatment chemicals are described in U.S. Pat. No. 6,279,656 B1 entitled “Downhole Chemical Delivery System for Oil and Gas Wells.” The foaming agent may be any one of a number of chemicals known to produce foam. For example, Champion Technologies of Houston, Tex. offers a number of acceptable products such as Fomatron V-41.  
         [0066]     In yet another embodiment, when the natural pressure within formation  11  is insufficient to maintain the desired volume of production due to increased loading in the wellbore, the production of oil may be enhanced by injecting gas into the produced fluids. In a gas lift technique, gas may be artificially introduced below plunger  20  to raise the pressure below plunger  20  and to aid in lifting plunger  20  and fluid  40  out of tubing  14 . Turning to  FIG. 16 , in this embodiment, a gas lift valve  310  is placed below stop  18 . Gas lift valve  310  is in fluid communication with a compressor  312  located at the surface. Compressor  312  pumps recycled gas produced from the well through conduit  314  and via gas lift valve  310  into tubing  14 . Because gas lift valve  310  is placed below stop  18 , the pumped gas will always be below plunger  20  and will therefore assist in lifting plunger  20  and fluid  40  out of tubing  14 .  
         [0067]     Although the invention has been disclosed and described in relation to its preferred embodiments with a certain degree of particularity, it is understood that the present disclosure of some preferred forms is only by way of example and that numerous changes in the details of construction and operation and in the combination and arrangements of parts may be resorted to without departing from the spirit of the scope of the invention as claimed here.