Patent Publication Number: US-8535024-B2

Title: Sand plunger for downhole pump

Description:
FIELD OF THE INVENTION 
     The present invention relates to subsurface, or downhole, pumps, such as are used to pump oil and other fluids and bases from 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. A subsurface pump is 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. 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 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 compression chamber between the valves with fluid and then lifts the fluid up the tubing toward the surface. 
     In some wells, sand in the well fluid is a problem. “Sand” as used herein includes particulates that are found downhole, such as actual sand, scale, iron sulfides, etc. The sand abrades the upper parts of the plunger and may even enter between the plunger and the barrel, thereby degrading the fluid seal between the plunger and the barrel. Pump components in a sandy well require frequent replacement. 
     In the prior art, there is a plunger known as the “Farr” plunger that provides some measure of protection against sand. The plunger has a tapered leading edge that contacts sand. However, the plunger is lifted from the lower end. This causes the upper end of the plunger to wobble inside of the barrel and contributes to wear on both the plunger and the barrel. 
     SUMMARY OF THE INVENTION 
     A downhole pump comprises a barrel and a plunger. The barrel has barrel first and second ends and a first one-way valve. The plunger has plunger first and second ends and a second one-way valve. The plunger is located in the barrel so that one of the plunger or the barrel reciprocates with respect to the other of the plunger or the barrel. The plunger has an interior passage therethrough. The plunger second end is interposed between the barrel second end and the plunger first end. The plunger and the barrel form a compression chamber between the first and second one-way valves. The plunger first end has a tapered leading edge. Ports are adjacent to, and located radially inside of, the leading edge. The ports communicate with the passage. A sucker rod string coupling is located at the plunger first end. 
     In accordance with one aspect, the ports are oriented so that fluid exiting the plunger passage is directed toward the leading edge. 
     In accordance with one aspect, the sucker rod string coupling is coupled to a wall between the ports. 
     In accordance with another aspect, the sucker rod string coupling has first and second ends. The sucker rod string coupling second end is coupled to the plunger and is tapered so that fluid can flow out of the ports. 
     In accordance with still another aspect, the sucker rod string coupling and the plunger first end form an integral member that couples to the remainder of the plunger. 
     A plunger has first and second ends and a one-way valve. The plunger has an interior passage therethrough. The plunger first end has a tapered leading edge, with ports adjacent to, and located radially inside of, the leading edge. The ports communicate with the passage. A sucker rod string coupling is located at the plunger first end. 
     In accordance with one aspect, the ports are oriented so that fluid exiting the plunger passage is directed toward the leading edge. 
     In accordance with one aspect, the sucker rod string coupling is coupled to a wall between the ports. 
     In accordance with another aspect, the sucker rod string coupling has first and second ends. The sucker rod string coupling second end is coupled to the plunger and is tapered so that fluid can flow out of the ports. 
     In accordance with still another aspect, the sucker rod string coupling and the plunger first end form an integral member that couples to the remainder of the plunger. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram of a well, shown with pumping equipment. 
         FIG. 2  is a longitudinal cross-sectional schematic view of a prior art pump. 
         FIG. 3  is a longitudinal cross-sectional view of a plunger, in accordance with a preferred embodiment. 
         FIG. 4  is a top end perspective view of the plunger. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     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 device or 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 and a stuffing box  25  on the surface  13 . The sucker rod string  23  is connected to a pump jack unit, or beam pump unit,  24  which reciprocates up and down due to a prime mover  26 , such as an electric motor or gasoline or diesel engine, or gas engine. 
     The pump  21  can be used with a variety of surface drive units besides a beam pump unit  24 . For example, hydraulic pump units can be used, as well as belt type lifting units. Also, the pump can be used with a variety of connecting members besides sucker rods  23 . For example, a wire line can be used. 
       FIG. 2  illustrates a prior art pump  31 . The pump has a barrel  33  and a plunger  35 . The plunger  35  reciprocates with respect to the barrel  33 . The barrel has a standing valve  37  and the plunger has a traveling valve  39 . In the illustrations, the valve cage and other details are not shown. 
     The sucker rod string  23  is connected to the reciprocating member of the pump, which in  FIG. 2  is the plunger. The plunger  35  is connected to a sucker rod or to a valve rod or some other component that is part of the reciprocating string of sucker rods. The connection between the sucker rod string and the reciprocating pump member can be made by a variety of devices, which are referred to herein as couplings. A coupling includes couplings (having box or female ends), bushings (having pin or male ends) and connectors (having both box and pin ends). 
     The plunger  35  is reciprocated by the sucker rod string  23 . As the plunger  35  is raised on the upstroke, the traveling valve  39  is closed and the standing valve  37  is opened, wherein fluid is drawn into the compression chamber  41  between the two valves  37 ,  39 . Thus, on the upstroke, the compression chamber  41  is charged with fluid. The fluid above the traveling valve  39  is lifted toward the surface. As the plunger  35  descends on the downstroke, the traveling valve  39  opens and the standing valve  37  closes, thereby forcing the fluid in the compression chamber  41  into the plunger. 
     The outside diameter of the plunger  35  is sized so as to provide a fluid seal  43  between the plunger and the barrel. The fluid seal is formed by the fluid entering a clearance between the plunger and the barrel. This clearance is typically 0.002-0.008 inches. The plunger  35  has an interior passage  44  for the flow of fluids through the plunger. 
     If the fluid contains sand  45 , the plunger  35  exhibits wear. This is because on the upstroke, the plunger  35  moves up into the sand  45  that is in the fluid column just above the plunger. The top end  47  of the plunger  35  exhibits the most wear from the sand due to the upstroke motion and due to fluid pressure. The column of fluid in the tubing extending to the surface exerts pressure on the top end of the plunger. This fluid pressure tends to force fluid with sand between the plunger  35  and the barrel  33 , independently of the movement of the plunger. 
     With the pump of the present invention, the plunger  51  (see  FIG. 3 ) is modified so as to minimize damage and abrasion caused by the sand. In the description, like reference numbers may be used on like parts or components from figure to figure and between embodiments. 
     The plunger  51  has a top end  47  and a bottom end  55  (in the description, relative terms such as “top” and “bottom” refer to the orientations shown in  FIGS. 1-3 , however, the plunger and pump can be used in other orientations). The barrel  33  likewise has top and bottom ends  57 ,  59  (see  FIG. 2 ). The plunger  51  is located in the barrel  33  so that the plunger bottom end  55  is interposed between the barrel bottom end  59  and the plunger top end  47  (see also  FIG. 2 , which shows plunger and barrel top and bottom ends). Thus, in reciprocating, the plunger bottom end  55  remains inside of the barrel, while the plunger top end  47  may, under certain pump configurations, egress the barrel or remain outside of the barrel. 
     Referring to  FIGS. 3 and 4 , the plunger top end  47  has a leading edge  61 . The leading edge is so called because on the upstroke, this edge is the first part of the plunger outside diameter that contacts sand and consequently is a part of the plunger that is subject to the highest amount of wear from sand. The leading edge  61  is tapered as shown in  FIG. 3  so as to reduce the surface area that contacts sand on the upstroke. Thus, the leading edge forms an annular lip that is small in area. The tapering of the leading edge is accomplished by ports  63  in the top end  47  of the plunger, which ports are located radially inside of the leading edge  61 . Located between the individual ports  63  is a wall (or walls)  65 . The tapering of the leading edge  61  is also caused by the wall  65  being below the leading edge. (The line shown in  FIG. 3  between the leading edge and the wall  65  is for illustrative purposes. The actual part may be fabricated without the line as shown in  FIG. 4 .) The wall  65  forms a shallow bowl or depression inside of the leading edge. The outside diameter of the plunger at the leading edge  61  is the same as the outside diameter for the remainder of the plunger. Thus, the taper is on the inside of the plunger. 
     The ports  63  perforate the wall  65  so as to allow fluid to exit the plunger interior passage. In the preferred embodiment, the ports  63  are angled so that the top end of each port is above and radially outward from the bottom end of the port. This orientation of the ports directs fluid exiting the plunger upwardly and outwardly over the leading edge  61 . Fluid exiting the plunger (flowing up in the orientation of  FIG. 3 ) thus carries away sand that has accumulated on the top end  47  of the plunger. In the preferred embodiment, there are six ports  63  spaced an equal distance apart. However, the number and size of the ports can vary. 
     The top end of the plunger is also provided with a coupling  71  to attach to the sucker rod string (either directly to sucker rods or to a valve rod). The coupling has a top end  73  and a bottom end  75 . The top end  73  is cylindrical and, in the embodiment shown, has a threaded interior  77  for attaching to the sucker rod string  23  (see  FIG. 1 ; in  FIG. 3 , the lower end of sucker rod string is shown schematically). The coupling top end  73  could have instead of a box end as shown in  FIG. 3 , a pin end, with male threads, or the top end  73  could have any alternative coupling or attachment. The bottom end  75  is coupled to the top end  47  of the plunger. The bottom end is tapered in its outside diameter. In the preferred embodiment, the tapering is frusto-conical, wherein the outside diameter of the coupling reduces from the cylindrical top end  73  to the plunger top end  47 . This tapering allows fluid to exit the ports  63 . 
     In the preferred embodiment, the coupling  71  and plunger top end  47  are provided in an integral member  81 . This member  81  couples, such as by a threaded fitting or by soldering, to an end of the plunger  51 . The other end of the plunger is a threaded fitting for receiving the valve cage. Providing the leading edge  61  on a member  81  that is separate from the remainder of the plunger provides advantages in both manufacturing and in use. In manufacturing, the plunger is essentially a tube with a high precision outside diameter and concentricity, while the member  81  requires some chamfering for the tapered leading edge  61  and boring for the angled ports  63 . In use, if the leading edge  61  wears, but the remainder of the plunger remains undamaged, only the upper end member  81  need be replaced. The coupling  71  and plunger top end  47  need not be a single member but can be fabricated from two or more members. 
     During operation, the pump and plunger are reciprocated in a normal manner. On the upstroke, the plunger  51  is pulled up. The tapered leading edge  61  reduces the surface area of the plunger that contacts any sand and the fluid, so that wear on the leading edge and the plunger top end caused by the sand is reduced. The sand may accumulate on the wall  65 . However, on the downstroke, fluid flows out of the plunger through the ports  63 , which fluid washes and carries any sand on the plunger top end away. This washing effect further reduces contact of the sand with the plunger and reduces wear. 
     By coupling the sucker rod to the top end  47  of the plunger, the coupling is strong and is less likely to fail. In addition, the problem of wobble of the plunger top end  47 , experienced by the prior art “Farr” plunger, is eliminated, as the plunger is pulled on the top stroke from the plunger top end. 
     The foregoing disclosure and showings made in the drawings are merely illustrative of the principles of this invention and are not to be interpreted in a limiting sense.