Abstract:
A downhole pump has a barrel and a plunger. The barrel has a first one-way valve and the plunger has a second one-way valve. The plunger is of the box end type. The pump prevents or minimizes gas lock by achieving high compression in the compression chamber between the two valves. The second valve is located close to the bottom end of the plunger. In the second valve, the valve seat is in contact with the seat plug, which seat plug has a seal. Alternatively, the valve seat is incorporated into the seat plug, which seat plug also has a seal. The plunger lacks reliefs at the bottom end and thereby achieves tight tolerances with the barrel, further contributing to high compression.

Description:
This application claims the benefit of U.S. provisional patent application Serial No. 60/909,743, filed Apr. 3, 2007. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to subsurface or downhole pumps such as are used to pump oil and other fluids in bases for oil wells. 
     BACKGROUND OF THE INVENTION 
     When an oil well is first drilled and completed, the fluids (such as crude oil) may be under natural pressure that is sufficient to produce on its own. In other words, the oil rises to the surface without any assistance. 
     In many oil wells, and particularly those in fields that are established and aging, natural pressure has declined to the point where the oil must be artificially lifted to the surface. Subsurface, or downhole, pumps are located down in the well below the level of the oil. A string of sucker rods extends from the pump up to the surface to a pump jack device, or beam pump unit (see  FIG. 1 ). A prime mover, such as a gasoline or diesel engine, or an electric motor, or a gas engine on the surface causes the pump jack to rock back and forth, thereby moving the string of sucker rods up and down inside of the well tubing. 
     The string of sucker rods operates the subsurface pump. A typical pump (see  FIG. 2 ) has a plunger that is reciprocated inside of a barrel by the sucker rods. The barrel has a standing one-way valve, while the plunger has a traveling one-way valve, or in some pumps the plunger has a standing one-way valve, while the barrel has a traveling one-way valve. Reciprocation charges a chamber between the valves with fluid and then lifts the fluid up the tubing toward the surface. 
     The chamber between the standing and traveling valves is referred to as the compression chamber. The standing and traveling valves open and close by differential pressure. For example, when the plunger is dropped (the downstroke), the fluid in the compression chamber is pressurized by the plunger. The fluid in the compression chamber cannot escape by way of the standing valve, because of the one-way nature of the standing valve. The only escape for the fluid in the compression chamber is through the traveling valve. However, in order to open the traveling valve, the fluid in the compression chamber must be pressurized sufficiently to overcome the pressure of the fluid above the traveling valve. 
     In a well that produces both liquid and gas, the pump can become gas locked. In a gas locked pump, the compression chamber contains enough gas to act as a shock absorber, resulting in insufficient differential pressure to open the traveling valve. When gas locked, the pump reciprocates without pumping any fluid. 
     In the prior art, pin end plungers, (which have a pin formed by exterior threads at the plunger lower end as shown in  FIG. 3 ), or box end plungers with external valves (see  FIG. 4 ) are used to minimize gas locking. These plungers use a valve generally attached to the bottom of the plunger. This attached valve introduces uncompressible volumes into the compression chamber, which uncompressible volumes are located around the valve, around the seat plug and internal of the seat plug. These uncompressible volumes make it more difficult to achieve a high compression ratio in order to overcome gas locking. 
     In another form of the prior art, a box end plunger (see  FIG. 4A ) is configured with an internal valve comprised of an insert, ball, seat, o-ring, spacer, and seat retainer. This arrangement is an improvement over the other prior art but still introduces unnecessary, uncompressible compression chamber volume in the spacer and the external turned-down length at each end of the plunger. These volumes also make it more difficult to achieve a high compression ratio in order to overcome gas locking. 
     Thus, there is a need for a high compression pump that can operate in gas locked wells. 
     SUMMARY OF THE INVENTION 
     The present invention provides a downhole pump, which comprises a barrel and a plunger. The barrel has a first one-way valve. The plunger has first and second ends, with a passage that extends between the first and second ends and a counterbore in each end. A second valve is located in one of the counterbores of the first or second ends. The second valve comprises an insert with a ball located in the insert, a seat adjacent to the insert, and a seat plug in contact with the seat. The seat plug has a channel therein with a pressure seal in the channel. The seat plug couples to the inside of the plunger so as to form a box end. 
     In accordance with another aspect of the present invention, the plunger has an outside diameter that is substantially the same along its length. 
     In accordance with still another aspect of the present invention, the plunger is reversible. 
     The present invention provides a downhole pump, which comprises a barrel and a plunger. The barrel has a first one-way valve. The plunger has first and second ends, with a passage that extends between the first and second ends and a counterbore in each end. A second valve is located in one of the counterbores of the first or second ends. The second valve comprises an insert with a ball located in the insert and a seat plug in contact with the seat. The seat plug has a channel therein with a pressure seal in the channel. The seat plug has a seat for the ball. The seat plug couples to the inside of the plunger so as to form a box end. 
     In accordance with another aspect of the present invention, the plunger has an outside diameter that is substantially the same along its length. 
     In accordance with still another aspect of the present invention, the plunger is reversible. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram of a well, shown with pumping equipment. 
         FIG. 2  is a longitudinal partial cross-sectional view of a downhole pump. 
         FIG. 3  is an exploded view of the lower end of a prior art pin end plunger and valve. 
         FIG. 4  is an exploded view of the lower end of a prior art box end plunger and external valve. 
         FIG. 4A  is an exploded view of the lower end of a prior art box end plunger and internal valve. 
         FIG. 5  is a perspective exploded view of the plunger of the present invention, in accordance with a preferred embodiment. 
         FIG. 6  is a perspective view of the assembled plunger of  FIG. 5 . 
         FIG. 6A  is a perspective view of the lower end of the assembled plunger of  FIG. 5 , shown cut away. 
         FIG. 7  is a cross-sectional view of the lower end portion of the plunger of the present invention. 
         FIG. 8  is a cross-sectional view of the lower end of the prior art plunger of  FIG. 4A . 
         FIG. 9  is a perspective exploded view of the plunger of the present invention, in accordance with another embodiment. 
         FIG. 10  is a perspective view of the assembled plunger of  FIG. 9 . 
         FIG. 11  is a cross-sectional view of the lower end portion of the plunger of  FIGS. 9 and 10 . 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In  FIG. 1 , there is shown a schematic diagram of a producing oil well  11 . The well has a borehole that extends from the surface  13  into the earth, past an oil-bearing formation  15 . 
     The borehole has been completed and therefore has casing  17  which is perforated at the formation  15 . A packer or other method (not shown) optionally isolates the formation  15  from the rest of the borehole. Tubing  19  extends inside of the casing from the formation to the surface  13 . 
     A subsurface pump  21  is located in the tubing  19  at or near the formation  15 . A string  23  of sucker rods extends from the pump  21  up inside of the tubing  19  to a polished rod at a stuffing box  25  on the surface  13 . The sucker rod string  23  is connected to a pump jack unit  24  which reciprocates up and down due to a prime mover  26 , such as an electric motor, a gasoline or diesel engine, or a gas engine. 
       FIG. 2  illustrates a typical downhole pump  27 . In  FIG. 2 , valve inserts or cages and other details are not shown. The pump  27  has a barrel  29  and a plunger  31  which reciprocates inside of the barrel. The barrel  29  has a standing valve  33  and the plunger has a traveling valve  35 . 
     The plunger is reciprocated inside of the barrel by the sucker rods  23 . As the plunger  31  is raised on the upstroke, fluid is drawn into a compression chamber  37  located between the two valves  33 ,  35 . The fluid contains liquid  39 , such as oil and condensate, and gas  41 , such as natural gas, air or vacuum. The gas  41  may be separated from the liquid  39  as shown in the drawing, or it may be in solution with the liquid. 
     In the prior art, plungers have pin ends or box ends. In a pin end plunger  43  (see  FIG. 3 ), the lower end of the plunger has external threads  45 . The lower end of the plunger has a bore  53  which extends the length of the plunger  43 . An external valve is attached to the lower end of the plunger. The valve has a cage  55 , a ball  57 , a seat  59  and a seat plug  49 . The cage  55  has internal threads  56  that are threaded onto the lower end threads  45  of the plunger  43 . The seat plug  49  retains the ball  57  and the seat  59  inside of the cage  55 . The seat plug  49  forms a metal-to-metal seal with the cage  55 . 
     In a box end plunger  61  (see  FIGS. 4 and 4A ), the lower end of the plunger has internal threads for receiving the external threads of the valve components.  FIG. 4  shows a box end plunger  61  having external valve components. The valve is similar to that shown in  FIG. 3 , having a cage  55 A, a ball  57 , a seat  59  and a seat plug  49 . The upper end of the cage  55 A has exterior threads  67  to engage the interior threads  63  of the plunger  61 . A passage  71  extends between the two ends of the plunger  61 . The passage  71  is larger than the passage  53  of the pin end plunger  43 . In addition, the lower end of the plunger  61  has reliefs  83  machined therein to decrease the outside diameter of the plunger at the lower end. The reliefs  83  compensate for wall movement; when the cage  55 A is screwed into the passage  71 , the wall of the plunger lower end bulges out. The reliefs  83  are 1/32″ deep as measured on the diameter. The reliefs  83  extend over an inch from the ends of the plunger. The plunger  61  is reversible with both ends having reliefs  83  and capable of functioning as either a top end or a bottom end. 
     The plungers  43  and  61  (shown in  FIGS. 3 and 4 , respectively) have an uncompressible space or volume around the outside diameter of the cage  55 ,  55 A. Due to the difficulty and expense of manufacturing concentric threads  56 ,  67  with the diameter of the cages and of manufacturing concentric threads  45 ,  63  with the diameter of the plunger, the cages are made with a slightly reduced outside diameter. This avoids wear of the cage on the barrel. The cages have a reduced outside diameter, relative to the plunger outside diameter, of about 1/32 to 1/16 inches. This gap between the cage and the barrel creates a space or volume that cannot be compressed. Other uncompressible volumes are around the seat plug  49  and internal of the seat plug. 
     Still another prior art box end plunger  61 A is shown in  FIG. 4A . The plunger  61 A has internal traveling valve components. The lower end of the plunger has a counterbore  69  which communicates with a passage  71 . The passage  71  of the box end plunger is larger than the passage  53  of the pin end plunger. The counterbore  69  receives the valve insert  73 , the valve ball  75 , the valve seat  77  and a spacer  79  with an o-ring seal  80 . This plunger  61 A has uncompressible volumes in the spacer  79 , in the external turn-downs, or reliefs  83 , at the ends, and internal of the seat plug  65 . 
     The present invention provides a pump with a box end plunger that makes the compression chamber small at the bottom of the downstroke (when the compression chamber is at its smallest volume), thereby achieving high compression in the compression chamber  37  (see  FIG. 7 ). The high compression in turn causes the traveling valve to open even with large amounts of gas, thereby preventing or minimizing gas lock. The plunger is also suitable for use with heavy crude or in high flow wells. 
     The plunger  81  of the present invention is illustrated in  FIGS. 5 ,  6  and  6 A. The plunger  81  is a hollow tube, having a passage  84  therethrough. The plunger has two ends  85 ; each end has a counterbore  87  formed therein. At one end, the top end, retainer components are inserted. At the other end, the bottom end, traveling valve components are inserted. Each end of the plunger has a reduction in outside diameter of about 0.005 inches, extending ⅜ inch from the end, to account for slight swelling of the diameter on the plunger end when the valve components are inserted and tightened into the plunger. This reduction in diameter is so small as to be substantially the same as the diameter along the remainder of the plunger, and after the valve components are inserted, the diameters are even more so substantially the same. 
     The retainer components are a spacer  89  and a retainer  91 . The spacer  89  is a hollow tube, typically unthreaded. The retainer  91  is also a hollow tube, with external threads  93  on at least one end, which end is threaded into one of the plunger counterbores  87 . The retainer couples to the sucker rod string  23 . The retainer  91  and the spacer  89  can be a single component as shown, or can be two separate components. 
     The traveling valve components are a valve insert  95 , a valve ball  97 , a valve seat  99  and a seat plug  101 . The insert  95  is inserted into the counterbore  87  at one end of the plunger. The insert abuts a shoulder  105  (see  FIG. 7 ). The insert  95  has openings  107  (see  FIG. 5 ) in the sides to allow fluid to flow past the ball  97  when the valve is open. The ball  97  is put into the insert  95 . The seat  99  then follows so as to abut the bottom end of the insert. The seat plug  101  is inserted into the counterbore  87 . The seat plug  101  contains an o-ring seal  103  that seals against pressure. Other types of pressure seals can be used, such as o-rings with backup seals, cup type seals and x-type seals. 
     The seat plug  101  has exterior threads  109  (see  FIG. 7 ) to engage interior threads  111  in the counterbore  87 . The interior threads  111  of the counterbore extend from the open end of the counterbore toward the shoulder  105  for a distance that is substantially the same as the threaded length of the seat plug  101 . The seal  103  contacts an unthreaded, or smooth, surface of the counterbore  87 . The seat plug  101 , which is a hollow ring, typically has a hexagonal or square shape for the lower part of its interior bore so as to receive a tool that installs and removes the plug from the plunger end. The seat plug  101  has around its inner end a circumferential channel  113 . The channel  113  receives the o-ring  103 . When the seat plug  101  is installed into an end of the plunger, the seat plug contacts the seat  99  and the o-ring  103  is compressed between the seat plug and the valve seat  99  and forms a seal. Additionally a seal is accomplished in counterbore  87 . 
     Although the channel  113  has been described as between two parts (namely the seat plug  101  and the seat  99 ), the channel can be within a single part. For example, the channel can be entirely on the seat plug, wherein the channel takes on the form of a groove. 
     With the plunger of the present invention, the traveling valve  97 ,  99  is located close to the bottom end  1   15  of the plunger. Comparing the plunger  81  of the present invention ( FIG. 7 ) with the prior art box end, internal valve plunger  61  ( FIG. 8 ), the difference in spacing of the valve seats  99 ,  77  from the bottom of the plunger is noticeable. The box end plunger  81  of the present invention is able to achieve high compression because of the reduced spacing between the traveling valve components and the standing valve components  1   16 . 
     In addition, the plunger of the present invention has minimal or no relief at the bottom end  115 . This makes the clearance between the plunger end and the barrel smaller and tighter than the plunger  61 A of  FIG. 4A . In addition, the clearance between the plunger end and the barrel is smaller and tighter than the plungers  43  and  61  of  FIGS. 3 and 4  which have gaps (due to manufacturing tolerances) between the cages and the barrel. As a result, the plunger  81  can achieve higher compressions. With a standard conventional plunger, a compression ratio of about 34:1 can be achieved. With the plunger of the present invention, a compression rate of about 45:1 can be achieved, an increase of 33% in compression ratio. If the plunger is used in conjunction with a high compression standing valve, the compression ratio is higher still. 
     Furtherstill, the two ends of the plunger  81  are reversible. Each end can function as either the top end or the bottom end. When the plunger is installed into a downhole pump, the top end will wear faster than the bottom end. The plunger can be pulled from the well and the plunger reversed and reinstalled. What was the bottom end, with little or no wear, is now the top end. The amount of wear relative to the reliefs  83  is small by an order of magnitude or so. Thus, a worn top end can be used as a bottom end and still achieve high compression due to tight tolerances with the barrel. 
       FIGS. 9-11  show the plunger  121  in accordance with another embodiment. In this embodiment, the seat plug functions as both a seat for the valve ball and also as a holder for the seal. In the description that follows, like reference numbers designate like parts or components in the various embodiments. 
     The box end plunger  121  is similar to the plunger  81  described with respect to  FIGS. 5-7 . The plunger  121  has a passage  83  therethrough and two ends  85 , with each end having a counterbore  87  formed therein. The plunger  121  is reversible. At one end, the top end, retainer components, in the form of a spacer  89  and a retainer  91 , are inserted. At the other end, the bottom end, traveling valve components are inserted. 
     The traveling valve components are a valve insert  95 , a valve ball  97  and a seat plug  123 . The insert  95  abuts a shoulder  105  in the counterbore  87 . 
     The seat plug  123  has a seat  125  for the valve ball  97 . The seat plug  123  also has a circumferential channel  113  around the inner end. The channel  113  receives the seal  103 . 
     The seat plug  123  is a hollow ring, with a square or hex shape for its inner bore. The seat plug has exterior threads  109  that engage interior threads  111  of the counterbore  87 . 
     Assembly involves inserting the insert  95  into the counterbore  87 , then the ball  97  and then the seat plug  123 . The seat plug has the seal  103  in the channel  113 . When the seat plug  123  is installed and tightened into the plunger, the seat plug contacts the insert  95 . The seal  103  is compressed between the insert  95  and the seat plug  123  and forms a seal. When the valve is closed, the ball  97  is in the seat  125 , as shown in  FIG. 11 . When the valve is open, the ball is off of the seat. 
     Locating the valve seat  125  and the seal  103  on the seat plug  123  serves to further reduce the volume of the compression chamber when the plunger is at the bottom of the downstroke, thereby achieving high compression. The plunger  121  has minimal or no relief at the bottom end to further minimize the volume of the compression chamber. 
     Thus, the present invention provides a box end plunger that achieves high compression. Consequently, gas lock of the pump is minimized or even eliminated. The plunger is reversible to increase wear and useful life, making the plunger more cost effective to use. 
     The plunger of the present invention can be used in tubing pumps or insert pumps. The plunger can reciprocate or the barrel can reciprocate. 
     The foregoing disclosure and the showings made in the drawings are merely illustrative of the principles of this invention and are not to be interpreted in a limiting sense.