Patent Publication Number: US-7909589-B2

Title: Downhole pumps with sand snare

Description:
The present invention is a continuation application of U.S. Ser. No. 11/645,872 filed Dec. 27, 2006 now U.S. Pat. No. 7,686,598, which in turn claims the benefit of U.S. provisional application Ser. No. 60/755,916, filed Jan. 3, 2006. 
    
    
     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. 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. 
     SUMMARY OF THE INVENTION 
     The present invention provides a downhole pump. The downhole pump comprises a barrel and a plunger. The barrel has a first 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 has a second one-way valve. The plunger and the barrel form a compression chamber between the first and second one-way valves. The plunger has a first portion with a first seal with the barrel. The plunger has a second portion that forms a balancing chamber between the barrel and the plunger. The plunger second portion has an opening so as to allow communication between the plunger interior passage and the balancing chamber. A wall is located relative to the opening so as to form a sand snare chamber between the balancing chamber and the plunger interior passage. The plunger has a third portion. The plunger second portion is interposed between the plunger first and third portions. The plunger third portion has a second seal with the barrel. 
     In accordance with one aspect of the present invention, the first seal comprises resilient members. 
     In accordance with another aspect of the present invention, the first seal comprises valve cups. 
     In accordance with still another aspect of the present invention, the first seal comprises an outside diameter that forms a fluid seal with the barrel. 
     In accordance with another aspect of the present invention, the second seal comprises an outside diameter that forms a fluid seal with the barrel. 
     In accordance with still another aspect of the present invention, the plunger third portion comprises a spray metal finish on the outside diameter. 
     In accordance with still another aspect of the present invention, the second seal comprises resilient members. 
     In accordance with another aspect of the present invention, the second seal comprises valve cups. 
     In accordance with another aspect of the present invention, the wall extends beyond the opening a distance so as to create a quiet zone between the wall and the plunger second portion. 
     In accordance with another aspect of the present invention, the wall surrounds a circumference of the plunger second portion and the wall extends from the plunger third portion toward the plunger first portion. The opening is located closer to the plunger third portion than to the plunger first portion. 
     In accordance with another aspect of the present invention, the first seal comprises resilient members which are valve cups, the second seal comprises an outside diameter that forms a fluid seal with the barrel. The wall surrounds a circumference of the plunger second portion and the wall extends from the plunger third portion toward the plunger first portion. The opening is located closer to the plunger third portion than to the plunger first portion. The wall extends beyond the opening a distance so as to create a quiet zone between the wall and the plunger second portion. 
     In accordance with still another aspect of the present invention, the first and second seals comprise resilient members. 
     In accordance with still another aspect of the present invention, the second seal comprises resilient members and a fluid seal. 
     The present invention also provides a method of pumping fluid from a sandy downhole well. The plunger is provided with two sets of seals. The plunger is reciprocated with respect to a barrel. Pressure across one set of seals is equalized by venting pressure from an inside of the plunger to an outside of the plunger at a location intermediate the two sets of seals. At the intermediate location, sand from the fluid is captured so as to isolate the sand from the sets of seals. 
     In accordance with one aspect of the present invention, the step of capturing the sand from the fluid further comprises providing a barrier between a location where pressure is vented and the barrel. 
     In accordance with another aspect of the present invention, the step of providing a plunger with two sets of seals further comprises providing a plunger with a first set of seals comprising resilient members and with a second set of seals comprising a fluid seal. 
    
    
     
       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 schematic view of a pump of the present invention, in accordance with a preferred embodiment. 
         FIG. 4  is a longitudinal cross-sectional schematic view of a pump of the present invention, in accordance with another embodiment. 
         FIG. 5  is a longitudinal cross-sectional schematic view of a pump of the present invention, in accordance with still another embodiment. 
         FIG. 6  is a detail longitudinal cross-sectional view of a plunger third portion, in accordance with still another embodiment. 
     
    
    
     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 present invention 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 present invention 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 plunger  35  is reciprocated by the sucker rods  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. 
     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 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  21  of the present invention, the plunger  51  is modified so as to minimize damage and abrasion caused by the sand.  FIG. 3  illustrates the pump  21  of the present invention. Like parts from one figure to another have like reference numbers. Thus, the barrel  33  and valves  37 ,  39  are substantially similar in the two pumps  21 ,  31 . 
     The generally cylindrical plunger  51  has several parts or portions. The plunger  51  has a first portion  53 , a second portion  55  and a third portion  57 . Because the pump  21  is typically oriented vertically, as shown, this orientation will be used to describe the pump. Thus, the plunger first portion  53  is above the second and third portions  55 ,  57 . The plunger second portion  55  is interposed between the plunger first and third portions  53 ,  57 . The pump  21  can be used in a non-vertical orientation, and can even be used in a horizontal orientation. An internal passage  59  extends along the length of the plunger, through all portions  53 ,  55 ,  57 . The internal passage  59  extends from the traveling valve  39  to openings  61  in the upper end of the plunger. These openings  61  communicate with the tubing  19  that extends to the surface. 
     The plunger first portion  53  is equipped with seals  63  around the circumference. The seals  63  form a seal against the barrel  33  inside diameter. In the preferred embodiment, the seals are conventional and commercially available valve cups, although other types of seals can be used. For example, the seals can be of elastomeric material and have a fiber component. Because the seals  63  will be abraded and worn by the sand  45  during pumping operations, a number of seals are used. For example, in one embodiment, twelve valve cups are used, with the valve cups positioned along the length of the plunger first portion  53 . 
     The plunger second portion  55  has a reduced diameter so as to form a balancing chamber  65  in the barrel between the first and third portions  53 ,  57  of the plunger. The plunger second portion  55  has an opening  67  that allows communication between the plunger internal passage  59  and the balancing chamber  65 . The opening  67  is sized large enough so that it will not become blocked or occluded by sand. For example, the opening can be ½ to 1 inch in diameter. A wall  69  extends upward, past the opening  67 , to form a sand snare chamber  71 . The sand snare chamber  71  communicates with the balancing chamber. In the preferred embodiment, the wall  69  extends from the lower end of the second portion toward the plunger first portion. The wall  69  is cylindrical and surrounds the opening  67 . The wall  69 , and thus the sand snare chamber  71 , is located so as to capture sand that enters the balancing chamber  65  by way of the opening  67 . In the preferred embodiment, the opening  67  is located close to the bottom end of the plunger second portion  55 . The wall  69  extends up past the opening for some distance. In a preferred embodiment, the wall  69  extends past the opening  67  five to eight inches. 
     The plunger third portion  57  is cylindrical. The outside diameter of the plunger third portion  57  is slightly smaller than the inside diameter of the barrel  33 . The clearance between the plunger third portion  57  and the barrel  33  is sized so that fluid can enter and provide a fluid seal  43 . This fluid seal is also known as a metal-to-metal clearance seal. In the preferred embodiment, the clearance is 0.002-0.008 inches. The larger clearances are for heavy crude, large plungers or heavy particulate conditions. 
     As one option, the outside diameter of the plunger third portion  57  can be hardened for increased wearability and durability. For example, the plunger third portion can be sprayed with metal such as nickel-based spray powder. The outer spray metal layer is typically 0.01 inches thick on each side, or 0.020 inches in total cross-section. The hardness is typically Rockwall C 50 or C 60. Of course other types of hardening methods and materials can be used, as well as other thicknesses of hardening coats. 
     In the preferred embodiment, the plunger portions  53 ,  55 ,  57  are joined together with couplings. This allows replacement of an individual component rather than the plunger  51  as a whole. In the preferred embodiment, the plunger first portion  53  is joined to the plunger second portion  55  by way of a coupling having female threads that receives an end of the plunger second portion. The same type of coupling is used to join the plunger second portion to the plunger third portion. The plunger second portion is a connecting tube having male threads on each end. These male threads receive the individual couplings. The coupling joining the second and third portions also has external male threads for receiving the wall  69 . The wall  69  can be a length of a small diameter barrel. 
     In operation, the plunger  51  and the barrel  33  have reciprocal motion relative to one another. In a fixed barrel pump, the plunger is reciprocated. In a fixed plunger pump, the barrel is reciprocated. 
     Using as an example a fixed barrel pump, the plunger has a seal provided by the resilient members  63  and another seal  43  provided by the fluid inside of the small clearance. Sand  45  from the tubing enters the top of the clearance between the plunger first portion  53  and the barrel  33 . As the plunger  51  reciprocates, the seals  63  on the plunger first portion  53  isolate the balancing chamber  65  from the remainder of the pump. This minimizes sand from entering the balancing chamber  65  from the top of the overall plunger  51 . Furthermore, during reciprocation, the seals  63  wipe the inside surface of the barrel, wiping sand that may adhere to the barrel. 
     Normally, in prior art pumps, the seals  63  would have a short life and would require frequent replacement. That is why most downhole pumps utilize a plunger that relies on a fluid seal as described with respect to  FIG. 2 . However, the first portion  53  of the plunger has no pressure differential across it. The openings  61 ,  67  provide that the first portion upper end is at the same pressure as the balancing chamber  65  and thus the first portion lower end. This equal pressure across the plunger first portion  53  and its seals  63  greatly reduces the wear on these seals. 
     The opening  67  in the plunger second portion not only equalizes pressure across the seals, but it also allows sand to enter the balancing chamber  65 . However, the sand is captured or snared in order to prevent the sand from contacting the top end of the plunger third portion  57 . The snare is formed by the wall  69  and the sand snare chamber  71 . The wall  69  forms a barrier around the opening  67 . On the downstroke, fluid flows through the internal passage  59  of the plunger  51 . Some sand may pass through the opening  67  and enter the sand snare chamber  71 . The sand snare chamber has little or no fluid flow therein. To the extent that there is fluid flow inside the sand snare chamber  71 , any sand entering through the opening is confined to the sand snare chamber and does not enter the balancing chamber  65 . Thus, the sand is confined and does not contact the barrel  33  in the balancing chamber  65 , nor does sand contact the top end of the plunger third portion  57 . 
     The volume of the sand snare chamber  71  can be large relative to the volume of the balancing chamber  65 . In other words, the wall  69  can be placed close to the barrel  33 . The sand snare chamber  71  is sized sufficiently large so that any volume of fluid flow through the opening  67  is confined within the sand snare chamber  71 . The wall  69  forms a quiet zone above the opening  67 . Any fluid flow into the sand snare chamber  71  is confined to the volume around the opening  67 . In the chamber  71  volume located between the opening  67  and the balancing chamber  65 , little or no flow occurs. In the preferred embodiment, this volume  71 A is located above the opening and is a quiet zone because little or no fluid flow occurs. 
     The plunger third portion  57  forms a fluid seal and carries the pressure differential across it, much like a conventional plunger  35 . 
       FIG. 4  shows another embodiment. The plunger has first, second and third portions  53 A,  55 A,  57 A. The seals between the plunger and the barrel are in a different arrangement from the embodiment of  FIG. 3 . The first portion  53 A uses a metal-to-metal clearance seal or a fluid seal  43 . This is the same type of seal used by the third portion  57  in the embodiment of  FIG. 3 . The third portion  57 A of  FIG. 4  can be a metal-to-metal clearance seal  43 . Alternatively, as shown in  FIG. 4 , the third portion can have seals  63 , which seals are the same as discussed above with respect to  FIG. 3 . 
     The balancing chamber  65  in  FIG. 4  equalizes the pressure across the fluid seal  43 . This minimizes pressure driving sand into the upper end of the fluid seal  43 . The seals  63  on the plunger third portion  57 A wipe the inside of the barrel free of sand on each stroke, extending the useful life of the fluid seal  43 . 
     The embodiment of  FIG. 4 , where the fluid seal  43  is above or uphole relative to the resilient seals  63 , is also useful where the traveling valve  39  is located at or near the upper end of the plunger  51 . In this case, the balancing chamber  65  equalizes pressure across the resilient seals  63 . 
     The present invention splits the function of the plunger into one portion, which provides a seal suitable for sand, and another portion, which provides a seal suitable for fluid. By providing components that are specialized to their function, the life of the overall plunger is prolonged in sandy wells. 
       FIG. 5  shows another embodiment of the pump. The plunger has first, second and third portions  53 B,  55 B,  57 B. The first portion  53 B and the third portion  57 B have resilient seals  63 . Providing resilient seals on both the upper and lower plunger portions  53 B,  57 B eliminates slippage. Slippage occurs in a fluid seal  43 ; the fluid slips through the clearance between the barrel and the plunger for lubrication purposes. Slippage also allows the entry of sand into the clearance between the barrel and the plunger. The sand causes wear. Resilient seals have no slippage and consequently allow no sand into the clearance between the plunger and the barrel. There is hardly any wear on either the first or the third plunger portions  53 B,  57 B. 
       FIG. 6  shows a plunger third portion  57 C, in accordance with another embodiment. The plunger third portion  57 C has two types of seals. One type is resilient seals  63 . The resilient seals are located at one end of the third portion  57 C and prevent the entry of sand into the clearance between the plunger and the barrel. The other type of seal is a fluid seal  43 , which is located along the remainder of the length of the plunger third portion  57 C. The outside diameter of the third portion changes to accommodate the types of seals. Thus, the outside diameter of the plunger is smaller at the resilient seals  63  than at the fluid seal  43 . 
     Thus, a combination of resilient seals and fluid seals can be used. Resilient seals prevent the entry of sand into the clearance between the plunger and barrel. Providing a balancing chamber reduces the pressure differential across the resilient seals. Fluid seals are better suited to wear when subjected to pressure differentials but exhibit wear due to sand. 
     The invention can be utilized on insert-type pumps and tubing-type pumps. The invention can be used on stationary barrel-type pumps, regardless of whether the barrel is top anchored or bottom anchored. The invention can also be used on traveling barrel-type pumps. 
     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.