Abstract:
The invention relates to a double string pump for pumping liquids to the surface of a hydrocarbon well and especially a hydrocarbon well that is producing both natural gas and liquid fluids. The double string pump includes a hollow tube that raises and lowers the plunger and carries the liquids to the surface and an outer tube receives liquids down into the well to lubricate the moving parts and flush particles from areas prone to wear and back toward the production tube. The natural gas is produced through the annulus between wellbore casing and the outer production tubing string.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a non-provisional application which claims benefit under 35 USC §119(e) to U.S. Provisional Application Ser. No. 61/247,331 filed Sep. 30, 2009, entitled “Double String Pump for Hydrocarbon Wells,” which is incorporated herein in its entirety. 
     
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
       [0002]    None. 
       FIELD OF THE INVENTION 
       [0003]    This invention relates to down hole rod pumps that are typically used to pump liquids from the bottom of a hydrocarbon wells. 
       BACKGROUND OF THE INVENTION 
       [0004]    As one travels through Texas and Oklahoma and other oil producing regions, it is common to see oil wells with rocking beam pumps in action. The beam is rocked like a seesaw by a motor while one end the beam lifts and lowers a sucker rod string to drive the down hole pump. The sucker rod string is typically made up of a number of twenty-five foot to thirty foot steel rod sections connected end to end to form a long string of rods that extend down into the production tubing of a well. The production tubing itself was inserted into the wellbore after the wellbore was drilled and cased. The production tubing is fixed in the wellbore with a down hole rod pump positioned near the bottom. As the sucker rod moves up and down in the production tubing, the pump draws liquids from the wellbore into a chamber of the pump through a first check valve during a first stroke and then pushes the liquids in the chamber through a second check valve during the return stroke. The liquids pass through the second check valve and into the production tubing above the pump so that the liquids are eventually pumped to the surface and are either piped or trucked to market. 
         [0005]    Natural gas wells and many low rate oil wells are sometimes provided with pumps to periodically withdraw liquids that enter the wellbore from the formation and tend to accumulate and slow and eventually stop the production of hydrocarbons the natural gas. The liquid may be water, but may also include hydrocarbon liquids which are sufficiently valuable to collect and transport to market. 
         [0006]    One of the problems associated with pump systems for small volumes of liquids in wells is that any solids, particularly small particles, that are produced tend to collect and cause trouble for the pump. If the liquid volume were substantially higher, the particles would likely be carried to the surface and not collect at the bottom of the production tubing. With low liquid production rates and intermittent pumping, the particles tend to collect in the production tubing on top of the pump and have been known to damage the pumps and pumping systems well short of their expected service life. This can be especially challenging in coal seam gas production wells where the particles tend to be very fine and abrasive and are susceptible of stacking out rod strings by caking up and packing between plungers and barrels and blocking the travel of check valves and other vital pumping equipment. Coal seam gas wells produce water and along with highly abrasive coal fines. 
         [0007]    Many other wells produce sand which is a problem on a much larger scale in terms of total numbers of pumps exposed to particles. Some wells have sand delivered into the formation to hold open the fissures, fractures and perforations to enhance production of gas and liquids. This kind of sand is called proppant. Unfortunately such proppant sand causes many rod pump failures every year as some amounts exit the formation and creates hazard for moving equipment such as the pump in the wellbore. Another type of sand that is even more difficult for pumps to handle is formation sand, often referred to as flour sand. Formation sand is quite fine in nature and very difficult to control due to its fine size and mobility. It is highly abrasive and will wear out the polished surfaces of a pump or bury and stack out the pump. 
       SUMMARY OF THE INVENTION 
       [0008]    The invention more particularly includes a system for producing liquids and solids from the bottom of a natural gas well including a string of production conduit installed in a wellbore where a lower end thereof is near the bottom of the wellbore. The system further includes a pump comprising a barrel and a plunger wherein the barrel is connected to the production conduit near its lower end and a string of hollow rod string is disposed within said production conduit such that a tubing annulus is formed around the hollow rod string where the hollow rod string is connected to the plunger that is positioned within the barrel of the pump for movement up and down the barrel. The system further includes a column of filtered liquid within the tubing annulus on top of the barrel and plunger. 
         [0009]    In a further aspect of the system, check valves are provided within the hollow rod string to prevent particles that might settle in liquid from descending below the check valves and maintaining the particles at a level in the wellbore closer to the surface so that when the pump is operating, the particles are pushed closer and closer to the surface to eventually be fully removed from the well. 
         [0010]    The invention may further be viewed as a process for producing liquids and solids from the bottom of a natural gas well where an open ended string of production conduit is installed in a wellbore with a seating nipple near the open lower end of the production conduit and a pump is installed at the end of a string of hollow rod string where the pump includes a barrel and a hollow plunger and where the hollow plunger is connected to and in fluid communication with the hollow rod string and further includes a traveling valve to admit liquids into the hollow interior of the plunger and wherein the barrel includes a standing valve to admit liquids from below the seating nipple into the barrel. A barrel is connected to the seating nipple and seal the interior of the production tubing from the open lower end of the production tubing wherein a tubing annulus is defined within the production tubing above the seating nipple and outside the hollow rod string. Substantially particle free liquid is provided into the tubing annulus to be in contact with the barrel and the outside of the plunger and as the plunger is raised and lowered, it draws liquids through the standing valve and through the traveling valve and eventually into the hollow rod string. 
         [0011]    In a preferred arrangement, a portion of the liquids are produced through the hollow rod string are directed through a filter and then back into the tubing annulus. 
         [0012]    In another preferred arrangement, gas is produced through gas production annulus and a quiet zone is defined below the seating nipple above the open end of the production tubing and gas that enters the quiet zone is allowed to exit back into the gas production annulus from an upper portion of the quiet zone. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]    The invention, together with further advantages thereof, may best be understood by reference to the following description taken in conjunction with the accompanying drawings in which: 
           [0014]      FIG. 1  is a cross section of a prior art version of a pumping system for pumping liquids to the surface of a natural gas well; 
           [0015]      FIG. 2  is a cross section of a first embodiment of an inventive pumping system shown in a well for pumping liquids to the surface of a natural gas well; 
           [0016]      FIG. 3  is a fragmentary perspective view of the surface of the well showing the arrangement for providing filtered liquid back to the bottom of the production tubing; 
           [0017]      FIG. 4  is a is a cross section of a second embodiment of an inventive pumping system shown in a well for pumping liquids to the surface of a natural gas well; and 
           [0018]      FIG. 5  is an exploded perspective view of a hollow shear tool for providing preferred breakaway for the production systems of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0019]    Turning now to the preferred arrangement for the present invention, reference is made to the drawings to enable a more clear understanding of the invention. However, it is to be understood that the inventive features and concept may be manifested in other arrangements and that the scope of the invention is not limited to the embodiments described or illustrated. The scope of the invention is intended only to be limited by the scope of the claims that follow. 
         [0020]    In  FIG. 1 , a wellbore, generally indicated by the arrow  10 , is shown formed or drilled into the ground G. According to conventional procedures, casing  12  has been inserted into the wellbore and sealed against the wall of the wellbore with cement  15  whereafter perforations  18  have been punched through the casing  12  and through the cement  15  and into a hydrocarbon-bearing formation in the ground G by explosive charges. Hydrocarbons in the hydrocarbon-bearing formation are then enabled to flow into the wellbore  10  through perforations  18  where natural gas and other gases would ascend up the wellbore through annulus  19  while liquids accumulate at the bottom of the wellbore  10 . 
         [0021]    In natural gas wells, liquids that are also produced from the formation tend to slow or block the production of the natural gas into the wellbore  10  so it is generally more productive to maintain the level of liquids below the lowest of the perforations  18 . The liquid level is drawn down by a production system including a pump, generally indicated by the arrow  20  that is associated with production tubing  50 . The pump  20  and production tubing  50  are run into wellbore  10  separately with the production tubing  50  being first inserted into the wellbore  10 . The production tubing  50  is sufficiently smaller than the casing  12  so that gas is easily able to flow up to the surface through annulus  19 . The production tubing  50  also has an open bottom end  51  preferably below the lowest of the perforations  18  and above the bottom of the wellbore  10 . Production tubing further includes a segment  52 , generally called a seating nipple, that includes an inside contour and dimension to receive barrel  30  and seal the barrel in place. Seating nipples typically have a shoulder stop or a reduction of the interior dimension also referred to as “ID”, and a highly machined surface or polished bore for packing seals on barrel  30  to engage into. Thus, the barrel  30  is installed after the production tubing  50 , but may be sealed in seating nipple  52  and therefore sealed and isolating the interior  55  of the production tubing  50  from the annulus  19  of casing  12 . The production tubing  50  is therefore divided into a small segment at the bottom, called a quiet zone  53  and a production path  55  above the seating nipple  52 . 
         [0022]    The pump  20  includes a plunger  30  arranged to move up and down within the barrel  40 . The plunger  30  is attached to the bottom end of a hollow rod string  22  and is able to move up and down within the barrel  40  that is firmly connected or locked into the seating nipple  52 , but it should be understood that the periphery of the plunger  30  and the interior of the barrel  40  are each machined and sized so that any liquid flow around the plunger  30  is substantially restricted. The preferred path for liquids to travel through the barrel  40  is also through the interior of the plunger  30 . Below the barrel  40  is a strainer nipple  42  having a number of holes to allow liquids or gas that is in the quiet zone  53  to pass into the barrel through stranding valve  44 . Standing valve  44  is shown to be a ball and seat, but may be any suitable one-way valve technology. As the plunger  30  is lifted relative to the barrel  40 , liquids are drawn up through the strainer nipple  42  and through standing valve  44  to fill the space in the barrel  40  below the plunger  30 . The plunger  30  includes a travelling valve  34 , that like the standing valve  44 , is shown as a ball and seat, but may be any suitable one-way valve technology. As the plunger  30  is lowered in the barrel  40 , standing valve  44  closes to keep liquid in the barrel but unseat the travelling valve so that the liquids in the barrel below the plunger  30  enter and flow into the plunger  30 . Liquids that were already in the plunger  30  before the plunger began its downward movement in the barrel exit the top of the plunger  30  through one or more vent holes  36 . Liquids that pass out of the vent holes  36  fill the production path  55  and are eventually delivered to the surface. 
         [0023]    In operation, pump  20  operates intermittently to lift liquids out of the bottom of the wellbore  10  so that hydrocarbon production is optimized. A number of operation schemes can be employed, but typically, the pump  20  is started based on elapsed time from the most recent pump operation cycle and continues until a reduced weight of the plunger  30  is detected, meaning that the liquids at the bottom of the well are reduced and that the pump  20  has had a gas break through. One of the problems with this arrangement that has been identified by the inventor is that particles such as sand and grit are going to pass into the and through the pump  20 , but tend to settle back down in the production path  55  during times of inactivity. In some wells, it is common for just a barrel, or two or three barrels to be pumped off the bottom to maintain natural gas production, but these few barrels may not make it to the surface for days or weeks. By the time a certain volume of liquid makes it to the surface, the small entrained solids are quite likely to have settled and even when stirred up, never make it to the surface. These solids collect around the top of the pump  20  and are prone to cause premature failure of the pump by getting into the top of the gap between the outside of the plunger  30  and the inside of barrel  40 . Wear on these highly machined surfaces will likely to cause a pump failure. 
         [0024]    Another problem that comes up with the arrangement shown in  FIG. 1  is called gas lock and it occurs when gas is drawn through the strainer nipple and fills the space in barrel  40  below the plunger  30 . The gas in this tight space can be insufficient to unseat the travelling valve  34  with the weight of the liquid column above the travelling valve  34  in production path  55  pressing down. The contained volume of gas gets repeatedly compressed and decompressed by movement of the plunger  30  in the barrel  40 , but no liquids are conveyed to the surface through the production path  55 . While the pump is unable to reduce the liquid level from the bottom of the wellbore, liquids that are continually produced from the formation eventually choke off the natural gas production through  19 . As the gas flow slows, the liquid flow may diminish and the productivity of the well will eventually be permanently impaired. If particles get into the same space described with the gas lock, the incompressible solids eventually prevent the plunger  30  from reaching the bottom of its travel and reduce the capacity of the pump or cause distortion of the path of the plunger  30  such that the pump eventually fails. 
         [0025]    To alleviate these and other problems identified in the embodiment of  FIG. 1 , a pumping system is shown in  FIG. 2  where similar elements are identified with similar numbers except being three digit numbers with the first digit being “1”. For example, casing  112  in  FIG. 2  is essentially the same element as casing  12  in  FIG. 1 . 
         [0026]    Focusing on the differences between the invention and the embodiment in  FIG. 1  is a plunger  130  is moved up and down inside the barrel  140  by a hollow rod string  125 . The hollow rod valve  125  is similar to sucker rod  22 , but has additional functions and features. The plunger  130  is arranged to convey the liquid up the hollow rod string  125  where the inner diameter of the hollow rod string  22  is much smaller than the production path  55  in  FIG. 1 . Thus, each stroke of the plunger  130  may move the same volume of liquid, but the liquid moves far closer to the surface at a higher velocity so that the entrained solids are more likely to be carried farther up the production path  155  within the hollow rod string  125  during each pump operation cycle. Moreover, check valves, such as shown at  145 , are provided within the production path  155  so that when a pumping cycle is ended and the pump  20  is idled, the particles only settle down to the last check valve each particle may have passed. Ideally, the check valves or ball checks  145  are spaced within the string so that the volume between them does not exceed the volume expected to be pumped during each a pumping cycle so that particles pass through at least one check valve during each pump cycle. Also, with the smaller diameter in the production path  155 , the pump rate should equal or exceed the lift velocity required for the well and re-entrainment of the solids into the liquid flow should be quicker and more certain. 
         [0027]    In one aspect of the invention, hollow rod string  125  is connected to plunger  130  by a hollow shear tool  126 . The hollow shear tool  126 , which will be more fully explained in relation to  FIG. 5 , provides a well operator with a predetermined “weakest link” for the production system in the event that the pump  120  is stuck in the wellbore  110 . In that circumstance, the well operator will know that lifting on the hollow rod string  125  with a tension above the shear strength of the hollow shear tool  126  will cause the hollow shear tool to separate near the pump  120 . The remaining portion of the hollow shear tool  126  is suitable for wireline or other high strength fishing tools to get the pump  120  out of the wellbore. If fishing is not effective, the production tubing may be withdrawn without the complication of also disconnecting the segments of hollow rod string that are inside the segments of production tubing. An operator of a wellbore will prefer a system that is predictable in its failure mode and fails in a manner that minimizes delays to returning to operation. 
         [0028]    A second aspect of the embodiment in  FIG. 2  is that there is now a tubing annulus  160  that is inside the production tubing  120 , and outside the rod string  125 . This tubing annulus  160  is filled with production liquid that has been carried to the surface and filtered. Thus, the plunger  130  has clean liquid around the outside thereof and to the extent that any filtered liquid might pass along the small gap around the outside of the plunger  130  and within the barrel  140 , it would tend to sweep any particles in that gap back into a location where such particles are directed up into production path  155 . Ideally, the level of filtered liquid would extend to the surface so that the pressure head on either side of the plunger is the same or very close to the same. At the end of the pump operation cycle, it is preferred that the plunger  130  is in the “up” position so that if gas had entered the space below the bottom of plunger  130  and above standing valve  144  that some amount of filtered liquid in the barrel  140  would pass through the small gap during the idle time and occupy enough space to unseat the traveling valve  134  before the plunger reaches it full bottom stroke. As long as the travelling valve  134  can be unseated, the gas will quickly pass into the plunger and the gas lock condition will be alleviated without having to undertake substantial intervention. In an alternative embodiment, double standing and double travelling valves may be preferred where fluid travels through a first of the double valves and then through the second. A double valve arrangement provides redundancy in the event that solid particles block open one of the valves. 
         [0029]    While abrasion and wear are the primary concern of the inventor, another aspect of the present invention that may help avoid gas locks is to provide a vent  158  to allow any gas that has entered the quiet zone  53  such as gases dissolved from the hydrocarbon liquid to pass back into the annulus  119  and exit the well  10 . The vent  158  is above the highest opening in the strainer nipple  42  so that the liquid level inside the quiet zone  153  is not lower than the liquid level outside the quiet zone in the annulus  119 . Another strategy to alleviate gas lock is to increase the fluid slippage past the plunger/barrel interface from annulus  160  into barrel  140  to displace traveling valve  134  and push gas into flow path  155 . 
         [0030]    Turning now to  FIG. 3 , a horse-head shaped bracket  171  is positioned at the end of a rocking beam  170  with a linkage  172  connected to the upper end of hollow rod string  125 . As the rocking beam  170  lifts and lowers the bracket  171 , the hollow rod string  125  raises and lowers through packing  173 . Packing  173  seals tubing string against the hollow rod string  125  as the hollow rod string telescopes in and out of the wellbore  110 . A swivel at the top of the hollow rod string connects to a flexible hose  181  to carry liquids produced from the hollow rod string  125  to storage, such as storage tank  185  or to market as indicated by the arrow  186 . Some amount of the liquid is carried back into the wellbore  110  through conduit  182 . Preferably, such liquids will allow solids to settle in the storage tank and to be sure that the recirculated liquids are “clean”, are also filtered by any acceptable filtering technology such as a cartridge filter  183 . The clean liquids are then directed through conduit  184  into piping that leads to the inside of production tubing  150 . Natural gas that has passed up the annulus  119  to the top of the well is directed into gas gathering line  188  to be conveyed to market as indicated by arrow  189 . Before leaving the description of  FIG. 3 , it should be seen and understood how simply the tubing annulus  160  may be maintained with a column of particle free liquids. At times, it may be advantageous to provide additional liquids into the tubing annulus  160  such as chemicals for inhibiting corrosion or scale or dealing with other issues. The tubing annulus  160  may also provide access for injecting hot oil or hot water to alleviate wax buildup or carry lubricants for the pump and other moving equipment downhole. The inventors also see an opportunity to provide clean water down tubing annulus  160  to slurry debris around the pump  120 . 
         [0031]    In another aspect of the invention, the tubing annulus  160  provides other options for dealing with challenges in wellbores. For example, in the event the a well produces a lot of sand, a perforated pipe section may be installed just above the seating nipple to allow clean liquids to descend into the wellbore  112  without interfering with the gas production. Once the clean liquids are past or below the perforations  118 , the perforated section allows the liquids to entrain the sand or solids and provide sufficient liquids to operate the pump  120  continuously. While a full column of clean liquid would no longer be practical once the production tubing  150  is pierced, the primary concern of sand collection would have been addressed. However solids free liquid would either be maintained on top of the pump or would continuously pass by the pump depending on the location of the liquid exit port(s). 
         [0032]    The production tubing  150 , may also be provided with an opening to the annulus  119  to provide a path to direct a chemical treatment such as a scale, corrosion or paraffin inhibitor to a location that is prone to such problems anywhere up or down the length of the wellbore. It should be noted that even hot liquid such as water or oil to enhance production. The tubing annulus  160  provides many new options for addressing a near endless list of challenges in the oil field. 
         [0033]    In one further preferred aspect related to  FIG. 3 , a rod rotator may be installed at the top of the well near the location where the bracket  171  attaches to the hollow rod string  125  to rotate the hollow rod string  125  and spread any wear from the up and down motion evenly around the outside of the sucker  125  for longer rod string life. Also, with the rod string  125  being hollow, it will likely and preferably have a larger diameter than equivalent non-hollow rod string of the same strength and will therefore have a larger radius distributing any load on the inside of the production tubing  150  in a manner that will reduce wear on the production tubing  150 . 
         [0034]    While it should be understood that the invention introduces two tubing strings which enables operators of wells to control the operating environment of the pump  120 . The invention provides a way to flush water or other liquid to the pump from above (through the inside of the production tubing  150 ) or from below the pump through the annulus  119 . In one particular advantage, the seating nipple or short section of pipe may be slotted or ported to provide a path for injection of liquids or chemicals or both into the wellbore anywhere up or down the production tubing  150 . In cold weather circumstances, the string may be warmed with heated liquids injected into production tubing  150  that would thaw any ice that may have formed during a cold night or extended cold period. Some formations produce paraffins that may precipitate into waxy solids when exposed to temperatures below the formation temperature. Solvents may be added to the liquids in the production tubing  150  in the tubing annulus  160  that dissolves the waxy solids. Paraffin control may be accomplished by a combination of heated liquids and solvents. 
         [0035]    It should further be understood that while the adjacent surfaces of the outside of the plunger  130  and inside of barrel  140  are preferably machined with close tolerances to prevent liquids from passing through the gap, some amount of liquids will pass through the gap. In fact, with the arrangement of the tubing annulus  160  providing clean liquids and liquids with additives for paraffin control, lubrication of the pump  120 , control of scale, and other preventive measures, it may be preferable to open the tolerances of the barrel and plunger. This small amount of flow can be described as liquid slippage and opening up the tolerances slightly would increase the pump slippage. Such added pump slippage reduces the potential for gas lock and provides a direct route to lubricate the pump and any places along the production tubing where the hollow rod string comes into contact with the production tubing. 
         [0036]    Turning now to a second embodiment of the present invention shown in  FIG. 4 , similar features are numbered similarly to  FIG. 2  with the first number being “2” rather than “1”. In  FIG. 4 , the tubing annulus  260  is generally kept dry except to periodically flush the pump with clean liquid. Production liquids are allowed into the production tubing  250  through screen  248  and flow upward inside production tubing  250  through perforated sub  249  to surround the barrel  240 . The pump  220  periodically pumps the liquids to the surface though the standing valve  244  and travelling valve  234  as described above. When concern arises that sand or other particulates may be accumulating around the pump  220  or collecting around filter  248 , clean or particle free liquids may be flushed down the tubing annulus  260  to provide more liquid to pump and entrain the sand and also to back flush the filter  248 . A purge check  262  or one way valve is provided at the bottom of the production string to allow the flushing liquid out of the bottom thereof. The purge check  262  is arranged to allow flow out of the bottom of the production tubing  250 , but not permit flow there through into the production tubing  250 . Again, the advantage of this arrangement is that liquid production is carried up the hollow rod string  225  and a tubing annulus is available to provide access to the pump to perform preventive maintenance on the pump  220 . 
         [0037]    Turning now to  FIG. 5 , the hollow shear tool  126 / 226  will be explained. The hollow shear tool  126 / 226  comprises three segments. Base segment  190  includes screw threads  190   a  to attach to the plunger  130 / 230  with ring segment  191  overlying the upper, smaller diameter portion  190   c  of base segment  190 . The ring segment slides down smaller diameter portion  190   c  until it contacts shoulder  190   b . Breakaway segment  192  also slides over smaller the diameter portion  190   c  until holes  194  generally align with groove  198  in smaller diameter portion  190   c . Breakaway segment  192 , like base segment  190  includes screw threads that are arranged to attach to the hollow rod string  125 / 225 . O-rings  196   a  and  196   b  are provided to seal the hollow interior passageway from the outside of hollow shear tool  126 / 226 . With a preselected number of screws screwed into holes  194  and into groove  198 , a predetermined breakaway strength can be provided so that when a tension between the hollow rod string  125 / 225  and plunger  130 / 230  exceeds the predetermined breakaway strength, the breakaway segment  192  will separate from the base portion. The predetermined breakaway strength may be easily tested using conventional machine shop tools such as a press and pressure gauge by removing ring segment  191  and inserting a number of screws  195  and applying compression force until the screws break. The three segments  190 ,  191  and  192  are sized so that when all three are assembled, compression force is translated through the hollow shear tool  126  by their respective ends pressing against the adjacent end. In other words, the bottom end of breakaway segment  192  would press against the corresponding flat end of the ring segment  191  and the bottom end of ring segment would press against the shoulder  190   b  of base segment  190 . The screws  195  would not be expected to carry much, if any compression load in operation. However, with the ring segment  191  removed, the entire compression load between breakaway segment  192  and base segment  190  would, in contrast, actually be carried entirely by the screws  195 . The screws  195 , in the arrangement of the hollow shear tool, should provide the same breakaway strength in compression and tension. The inventor expects that breakaway strengths of roughly 10,000 pounds or 15,000 pounds may be achieved and using stronger or weaker materials would expand the capacity range of such an arrangement. Clearly, the ease at which the breakaway strength may be successively measured should provide confidence in the actual breakaway strength. Unused screw holes are preferably blinded off to reduce the possibility of sand entering the hollow shear tool and potentially altering its performance. 
         [0038]    One interesting aspect of this arrangement is that with the liquids coming to the surface within a hollow rod string, the liquids exit the well pumping system on the “downstroke” of the rod pump. In conventional rod pumps, the liquid production occurs on the “upstroke.” This point may not seem significant, but it does reveal that the present invention is quite different than prior systems. 
         [0039]    Finally, the scope of protection for this invention is not limited by the description set out above, but is only limited by the claims which follow. That scope of the invention is intended to include all equivalents of the subject matter of the claims. Each and every claim is incorporated into the specification as an embodiment of the present invention. Thus, the claims are part of the description and are a further description and are in addition to the preferred embodiments of the present invention. The discussion of any reference is not an admission that it is prior art to the present invention, especially any reference that may have a publication date after the priority date of this application.