Abstract:
An improved, unattended, liquid pumping device for oil and gas wells featuring a bellows controlled flow valve that opens and closes at preset pressures. The liquid pumping device may operate within a liner suspended into the well. The liquid pumping device may also include sealing elements configured to deform radially to allow the pumping device to pass through restrictions in the well or liner.

Description:
FIELD OF THE INVENTION  
       [0001]     The invention relates to an autonomous pressure actuated liquid pump for use in gas and oil wells. In particular, it relates to liquid lift pumps in which well pressure, acting against an internal bellows or diaphragm, causes an internal flow control valve to open or close thereby releasing or shutting-in well gas flow. More particularly, the present invention relates to the use of such pumps with a liner that is inserted into open hole and large diameter gas and oil wells.  
       BACKGROUND  
       [0002]     The economic viability of marginal petroleum wells, often referred to as stripper wells, depends on the well&#39;s product flow and pressure capacity and the rate at which undesirable liquids (i.e., brine) infiltrate the well. Removing liquid from gas or oil stripper wells has been accomplished with pump jacks or casing plungers in cased wells, while siphon strings or tubing plungers have been used in small diameter tubing. However, economic viability has restricted most applications to passive liquid removal techniques.  
         [0003]     In large diameter casings (3″ or larger), casing plungers, such as the one disclosed in U.S. Pat. 6,851,480 have had some success in improving the economic viability of stripper wells. However, variations in ID, at each new section of casing, or at joints, or at collars, cause a potential stopping point for a plunger descending a well. These variations in the ID also creates pressure leakage areas that could potentially stop a plunger on its upward travel. Interconnect discontinuities also provide natural trapping areas for well contaminants, such as salt rings, that worsen the descending and ascending plunger problems.  
         [0004]     Due to the problems associated with ID variations in a well, casing plungers may become stuck in the well. Bringing a casing plunger to the surface when it is stuck in the well may require venting the well to dump tanks to provide additional pressure differentials. Often lubricants and salt dissolving chemicals are added to free stuck plungers and at times retrieval gear is brought in to fish-out stuck plungers. All of these efforts to retrieve a stuck casing plunger increase the downtime of the wells and increase well tender man-hours.  
         [0005]     Many mechanical devices have been proposed for accomplishing the sealing of casing and tubing plungers used in 2″ inside diameter and larger applications. Petro-chemical well environments however are quite corrosive and contaminating for mechanical linkages and small moving parts. Thus the industry has standardized on molded, flexible, friction cups to provide the sealing function in full size well casings and tubing, while brushes rather than cups are sometimes used for small diameter tubing applications they are not applicable to larger diameter configurations. Several different implementations of flexible cups are being used but they are not designed for operating in tube configurations in which the inside diameter is reduced 5 to 20% in section-to-section couplers and well head connectors.  
       SUMMARY OF THE INVENTION  
       [0006]     This invention provides a self-actuating solution to overcome the shortcomings of the prior art devices. According to one aspect, the invention provides  10  a system for pumping fluid from a well. The system includes an elongated hollow tubing insertable into the casing of a well, and a casing plunger operable within the hollow tubing. A seal may also be provided to form a fluid tight seal between the liner and the casing of the well.  
         [0007]     According to another aspect, the invention provides a method for pumping fluid from a well. The method includes the step of suspending a liner into the casing of a well. A pump is placed into the liner such that the pump descends through the liner into the liquid. The pump is automatically closed in response to a pressure differential at the pump, such that the pump forms a fluid seal to substantially impede fluid flow around the pump in the liner. The pump is raised along with a column of fluid in the liner in response to a build up of fluid pressure from closing the pump. The pump is then automatically opened in response to a decrease in pressure below the pump relative to the pressure above the pump.  
         [0008]     According to yet another aspect, the invention provides an improved seal for a pump for pumping fluid from a well. The seal forms a fluid-tight seal between the pump housing and an internal surface of the well. The seal comprises first and second sealing elements that are axially spaced apart from one another, and which project radially outwardly. A fluid passage extends through the pump housing, having an inlet port below the seal and a discharge port above the seal. A pressure sensitive valve disposed within the fluid passage automatically closes when a pressure on the valve system is greater than a closing pressure, and automatically opens when the pressure on the valve system is less than an opening pressure. 
     
    
     BRIEF DESCRIPTION OF THE DRAWING  
       [0009]      FIG. 1  is a view of a well-pumping system according to the present invention;  
         [0010]      FIG. 2  is a cross sectional view of the pumping device of the well-pumping system illustrated in  FIG. 1 ;  
         [0011]      FIG. 3  is an enlarged cross-sectional view of the well head of the will pumping system illustrated in  FIG. 1 ;  
         [0012]      FIG. 4  is an enlarged cross-sectional view of a tail stop of the well-pumping system illustrated in  FIG. 1 ;  
         [0013]      FIG. 5  is an enlarged fragmentary cross-sectional view of a connector for a liner in the well-pumping system illustrated in  FIG. 1 ;  
         [0014]      FIG. 6  is an enlarged cross-sectional view of sealing elements of the pumping device illustrated in  FIG. 2 . 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0015]     Referring now to  FIGS. 1 and 2 , a system for pumping liquid out of a well is illustrated. The system preferably includes a liner  30  that hangs from the top of a well  5 . A pump in the form of a casing plunger  60  forms a fluid-tight seal with the interior wall of the liner  30 .  
         [0016]     To pump fluid out of the well, the liner  30  is lowered into the casing of the well. The liner  30  is fed into the well until the bottom end of the liner sinks into the fluid in the well. The pump is then inserted into the liner and lowered through the liner, so that it sinks into fluid in the well. Once the fluid pressure in the liner above the pump exceeds a threshold, the pump  60  seals-off the liner. In doing so, the device seals in the gas in the well, causing the fluid pressure below the pump to build up. The fluid pressure below the pump then drives the pump upwardly along with the fluid above the pump. As the pump  60  is driven upwardly, the fluid above the pump is discharged through discharge lines  19 ,  21  connected to the well  5 . When the pump reaches the top of the well, the gas pressure below the pump drives the pump out of the liner and into a receiver  15  that maintains the pump above the lower discharge line  21  while gas from the well flows from the liner and through the lower discharge line. When the flow of gas from the well diminishes, the pump  60  is again lowered through the liner to pump more fluid out of the well.  
         [0017]     The raising and lowering of the pump  60  is controlled automatically in response to the fluid pressure in the well. Specifically, the pump  60  includes a valve  70  that controls the flow of fluid through the pump. A biasing element  80  controls the operation of the valve  70 . More specifically, the biasing element  80  biases the valve  70  into an open position. When the valve  70  is open, the pump  60  descends into the well, and fluid flows through the pump. The rate of descent is limited by the friction between the pump and the well walls and flow restrictions through the pump. When the pump reaches the liquid level in the liner  80 , it continues to descend, but at a reduced rate.  
         [0018]     When the pressure differential across the pump  60  exceeds a threshold (closing threshold) related to the biasing force of the biasing element, the valve  70  automatically closes so that fluid can no longer flow through the pump. As described above, the fluid pressure in the well builds up and then drives the pump upwardly. At the top of the well  5  the pump  60  is displaced into a receiver assembly  60  that maintains the pump. While the pump is maintained in the receiver, the gas pressure in the well dissipates as gas flows through the lower discharge line  21 . When the fluid pressure across the pump drops below a threshold (opening threshold), the biasing element  80  automatically opens the valve  70  and the pump  60  descends again into the well. In this way, the pump automatically descends and ascends within the well to pump fluid from the well.  
         [0019]     Referring to  FIG. 3 , the liner  30  will be described in greater detail. The liner  30  need not be used in each system in which the pump  60  is used. However, in certain applications the well is not suited for use with a pump, such as a casing plunger. For instance, the well may be an open hole well that only has a casing for the first few hundred feet of the well, therefore, most of the well does not have a casing that the pump can seal against. Alternatively, the casing diameter may be too large or lack pressure integrity for the operation of the pump. In such instances, the liner  30  may be incorporated.  
         [0020]     The liner  30  is an elongated hollow tubing. The liner may be a single length of tubing, however, preferably the tubing is comprised of a plurality of separate sections that are connected together. Accordingly, preferably each section of liner has fittings  32  at each end to connect the different sections using couplers  38 . As discussed further below, packing material  25  is used to maintain a fluid-tight seal between the well casing and the liner. If a section of tubing needs to be added to the tubing, the packer seal  25  is relaxed so that the tubing coupler  38  can pass into the well casing. The tubing coupler is then repositioned around the tubing  30 .  
         [0021]     Referring to  FIG. 5 , the fittings are illustrated in greater detail. The fitting provides a sufficient seal to maintain the pressure build up within the liner during use of the device. In addition, the fitting  32  provides a connection having sufficient tensile strength to support the load of the liner. Specifically, since the liner may need to extend thousands of feet into the well, the weight of the liner becomes significant. In the present instance, the approximately 4000 feet of the liner weighs approximately 5,000 pounds.  
         [0022]     The fitting  32  comprises an external ferrule  33  and an insert  34 . The liner  30  is disposed between the ferrule  33  and the insert  34 . The ferrule  33  is then crimped down onto the insert to fixedly attach the liner  30  to the fitting  32 . As shown in  FIG. 5 , the end of insert  34  flares outwardly forming an externally threaded portion  35 . The threaded portions are used to connect the sections of the tubing. More specifically, a collar  38  (shown in  FIG. 4 ) having internal threads engages the threaded portions  35  of fittings from two sections to connect the two sections.  
         [0023]     The tubing may be formed of a variety of materials, including metal or plastic. Preferably, the conduit is configured so that the conduit can be spooled and shipped on large reels (8 to 12 feet in diameter) prior to insertion into the well. Although a variety of plastic tubing can be utilized, in the present instance, the plastic tubing is a polymer plastic including fiber bands and tension straps to support the weight of the tubing and the operational pressures.  
         [0024]     The liner  30  extends into the well so that the liner is within the casing  10 . The liner may extends down into the well beyond the casing or in some applications, the liner may terminate within the casing. The liner is connected to the well at the well head in such a manner as to provide a fluid-tight seal between the casing  10  and the liner  30 .  
         [0025]     Referring to  FIG. 3 , the connection of the liner to the well head is illustrated in greater detail. The fitting  32  at the top end of the tubing threadedly engages a hanger  23  having a mounting flange  24  on the well head. The mounting flange cooperates with a flange  17  on the receiver  15  to attach the receiver to the well head. Packing material or a packer  25  is positioned between the liner  30  and the casing  10  to seal off the annular space between the interior wall of the casing  10  and external wall of the liner  10 . The packer  25  provides a fluid-tight seal between the casing and the liner  30  that is able to maintain the seal under the fluid pressures created during operation of the pump  60 . In this way, when the casing plunger  60  seals off the liner to shut in the well, the packer  25  prevents gas or other fluid from leaking out of the well between the casing and the liner. The packer  25  may be formed from any of a number of materials, such as elastomeric polymer.  
         [0026]     Tubing sections are added to the liner until the lower end of the tubing extends into the fluid in the well. Typically, the casing includes a perforated section toward the bottom of the well. The perforations are holes through the sidewalls in the casing that allow the marketable fluid(s) in the ground to pass through the casing and then up the well. However, undesirable fluid, such as brine may accumulate in the well and extend above the perforated section, thereby reducing the delivery of desired fluid(s). The pump  60  may be used to remove the undesired fluid so that the level of such fluids is below the perforations thereby improving the flow of the marketable fluid(s). Accordingly, it is desirable to extend the tubing sections into the well so that the bottom end of the liner  30  extends to, or below the level of the perforations in the casing. In this way the pump can be used to pump fluid out of the well at the level of the perforations. In other words, the liner may be positioned so that the pump descends through the liner to a point at or below the perforations, and then automatically closes to lift the fluid to the surface as described previously. By doing so, the pump may lift sufficient undesirable fluid to reduce the fluid level to a level below some or all of the perforations in the perforated section.  
         [0027]     A tail cap  40  attached to the lower end of the tubing  30  prevents the casing plunger from descending out of the liner in the event that the casing plunger does not close before reaching the bottom of the liner. The tail cap  40  comprises an externally threaded portion that is connected to the tubing  30  with a coupler  38 , similar to the manner in which sections of the tubing are connected. The tail cap  40  comprises a plurality of orifices  42  that allow fluid to flow from the well  5  into the liner  30 . Additionally, a bumper stop  45  in the tail cap  40  operates as a cushion to decelerate the casing plunger  60  as the casing plunger bottoms out on the tail cap. The bumper stop comprises a rod  47  having a flared head, and a biasing element, such as a compression spring  48 . The rod and spring are disposed within a cylindrical housing  49  that fits over a cylindrical nipple  44  formed on the inside of the tail cap  40 .  
         [0028]     Referring now to  FIG. 2 , the details of the pump  60  will be described in greater detail. The pump  60  includes an elongated substantially hollow cylindrical housing  62 . A lower housing  65  is fixedly attached to the lower end of the cylindrical housing  62 . An end cap  75  closes the lower end of the lower housing. Preferably, the lower end cap  75  is releasably connected with the lower housing  65 . In the present instance the lower end cap  75  is threadedly connected to the lower housing. A plurality of holes in the lower end cap  75  form inlet ports  76 , so that fluid can flow into the pump  60  through the inlet ports  76  when the pump descends into the well.  
         [0029]     A top cap  90  is attached to the upper end of the housing  62 . The top  90  has a central bore providing a fluid path. The lower end of the top cap  90  is attached to the upper end of the housing  62 . Preferably the top cap  90  is releasably connected to the housing; and in the present instance, the top cap  90  has external threads that mate with internal threads in the housing  62  to attach the top cap to the housing.  
         [0030]     The upper end of the top cap  90  is generally open, and preferably includes an internally threaded portion for mounting a stem  68 . The stem  68  preferably has an externally threaded portion cooperable with the top cap  90  to releasably attach the stem to the top cap. In this way, the stem threads into the top cap thereby sealing the upper end of the top cap.  
         [0031]     As shown in  FIG. 2 , a plurality of holes through the sides of the top cap  90  provide outlet ports  92 . In this way, fluid flowing through the pump  60  flows through the top cap  90  and out the outlet ports  92 .  
         [0032]     A plurality of sealing elements or cups  85 ,  86  disposed around the housing provide a fluid-tight seal between the housing and the inner wall of the well  5 . The cups  85 ,  86  are disposed between the inlet ports  76  at the bottom of the pump  60  and the outlet ports  92  at the top of the pump. The cups  85 ,  86  are elastomeric elements having a central bore. The cups  85 ,  86  are spaced apart axially from one another by a spacer  88 . The spacer  88  is an elongated cylindrical collar having an internal diameter slightly larger than the external diameter of the housing.  
         [0033]     The cups  85 ,  86  and spacer  88  are captured on the housing between a locking ring  95  and a lip that is the formed by the top edge of the lower housing  65 . Specifically, an internal annular shoulder of the lower cup  86  abuts both the top edge of the lower housing, and the locking ring  95  threaded onto the top cap  90  engages the top edge of the upper cup  85 .  
         [0034]     The locking ring  95  is a threaded collar or nut that cooperates with external threads on the top cap  90 . In this way, the locking ring  95  is operable to tighten down or compress the cups  85 ,  86 . Since the cups  85 ,  86  are formed of elastomeric material, preferably a metal washer is disposed between the locking ring  95  and the upper cup  85 . The metal interface between the locking ring and the washer facilitates turning the ring to tighten down on the cups  85 ,  86 .  
         [0035]     During use, the cups may wear and need to be replaced. Accordingly, preferably the pump  60  is configured so that the cups  85 ,  86  can be readily removed and replaced without disassembling the pump. Therefore, in the present instance the top cap  90  is preferably configured so that it need not be removed to replace the cups. Specifically, preferably the exterior diameter of the top cap  90  is small enough to allow the cups to slide over the top cap. In particular, preferably the external diameter of the top cap  90  is approximately the same as, or less than, the external diameter of the housing.  
         [0036]     Referring now to  FIG. 6 , the lower cup  86  is illustrated in more detail. The lower cup  86  comprises a generally cylindrical body  102  and a pair of spaced apart seals  104 ,  106  in the form of circumferential flanges that project outwardly from the body. The body  102  and the seals  104 ,  106  may be formed of separate materials. However, in the present instance the body and the seals  104 ,  106  are a unitary piece of molded elastomeric material. The seal  104 ,  106  are formed of material that is resiliently deformable radially. In the present instance, each flange has an axial thickness “t” and a radial width “w”. The width “w” is greater than the thickness “t” and the width may be twice the thickness “t”.  
         [0037]     The seals  104 ,  106  form a fluid-tight seal, sealingly engaging the casing of the well, or if a liner  30  is used. Additionally, the seals  104 ,  106  are configured to form a sliding seal with the interior wall of the casing or the liner, if used. Since the flanges  104 ,  106  are spaced apart, the flanges sequentially seal the well when the cups encounter a restriction in the path that the pump is traveling (i.e. the casing or the liner). For instance, as described above, the liner  30  may be formed of a number of sections connected together by fittings  32 . As shown in  FIG. 5 , the insert  34  of the fittings  32  creates a restriction in the internal diameter of the liner. Preferably the fitting is relatively thin and only restricts the diameter minimally. Nonetheless, the fitting creates a restriction. As the casing plunger  60  travels upwardly after shutting in the well, the upper seal  104  engages the fitting  32  first, and deflects radially inwardly. The upper seal  104  is configured to maintain a seal with the liner even as the seal deflects radially inwardly. However, even if the restriction deflects the upper seal in such a way that releases a portion of the sealing engagement between the upper seal and the liner, the lower seal  106  maintains the seal with the liner to prevent leakage past the cup. Subsequently, as the lower seal  106  encounters the restriction, the upper seal  104  maintains the seal with the liner in the event that the lower seal loses sealing engagement with the liner.  
         [0038]     As described above, the cups  85 ,  86  are configured to maintain a seal while passing through a constriction in either the casing or the liner, if one is used. Similarly, if a liner  30  is used, the wall of the liner may become out of round. For instance, when the liner is spooled onto a reel, the liner may flatten to become more of an oval or eccentric cross-section rather than a circular cross-section. The cups are formed so that the seals  104 ,  106  deform radially and/or axially to conform to the oval or eccentric cross-section of the liner. In this way, the cups are able to maintain a sliding fluid-tight seal with the out of round interior of the liner.  
         [0039]     Configured as described above, the cups  85 ,  86  are able to maintain a sealing engagement with the casing or the liner if one is used, while being able to deflect sufficiently to allow the casing plunger to pass through a restriction in the liner or casing. More specifically, the cups are configured such that the seals deflect radially inwardly sufficiently to pass through a restriction of 5-20% of the diameter of the casing or liner.  
         [0040]     Referring to  FIG. 2 , the valve  70  controls the flow of fluid through the housing  62 . In  FIG. 2 , the valve  70  and biasing element  80  are shown in elevation. The valve  70  comprises a valve element  72  that cooperates with a valve seat  73  to form a fluid-tight seal. Preferably, the valve element  72  is formed of an elastomeric material. The valve seat  73  is preferably a tapered annular surface formed in the interior wall of the lower housing.  
         [0041]     When the valve is closed, fluid does not flow through the pump. In addition, since the cups  85 ,  86  provide a fluid-tight seal between the housing  62  and the wall of the well  5 , fluid does not flow around the pump. Accordingly, when the valve  70  is closed, the pump  60  operates as a seal, sealing the well closed. This allows a pressure differential to build up across the tool. Specifically, when the valve is closed, the pressure below the cups increases relative to the pressure above the cups.  
         [0042]     The biasing element  80  is a pressurized bellows that bias the valve  70  toward an open position in which fluid can flow through the pump through the inlet and outlet ports  76 ,  92 . The bellows  35  are operable to expand and contract vertically. The lower end of the canister is generally open, having an annular flange extending radially inwardly to form a lip.  
         [0043]     The bias of the bellows  80  is controlled in part by the fluid pressure within the bellows. A cavity is formed within the bellows and a fill valve attached to the housing of the bellows controls the flow of fluid into the bellows. In this way, the bellows can be charged by filling the bellows with pressurized air through the fill valve. As the bellows are filled with pressurized air, the bellows expand outwardly, displacing the valve element  72  downwardly.  
         [0044]     The bellows  80  compresses in response to hydrostatic pressure on the bellows when the pump is in the liquid in the well. As the bellows compresses, the valve  70  closes. The stroke of the valve element  72  between the opened position and the closed position corresponds to the compression of the bellows from the charged length to the compressed length when the valve  70  is closed.  
         [0045]     Referring to  FIG. 1 , an upper discharge line  19  and lower discharge line  21  are connected to the well  5  for receiving the fluid from the well. The upper discharge line  19  extends between the well  5  and the lower discharge line  21 . Preferably, the lower discharge line  21  is approximately twice as large in diameter as the upper discharge line  19 . The opening from the well  5  to the upper discharge line  19  is vertically spaced along the well from the opening to the lower discharge line  21  a distance that is greater than the distance from the point that the lower cup  86  seals with the well to the point that the upper cup  85  seals with the well. In this way, when the device  60  is at the top of the well the upper and lower cups  85 ,  86  form seals with the walls of the receiver between the upper and lower discharge lines  19 ,  21 . In this way, fluid from the well flows through the liner  30  and to the lower discharge line  21  while the pump  60  is disposed in the receiver.  
         [0046]     A check valve  75  is disposed along the upper return line. The check valve  75  is configured to allow higher pressure fluid in the upper discharge line  70  to flow into the lower discharge line  80  and to impede fluid flow from the lower discharge line up into the upper discharge line. In this way, the fluid in the upper discharge line remains at a lower pressure than the fluid in the lower discharge line. An upper shut-off valve  72  is provided on the upper discharge line  70  to shut-off the upper discharge line, and a lower discharge valve  82  is provided to shut-off the lower discharge line. The shut-off valves  72 ,  82  may be any one of a number of types of valves, such as a ball valve.  
         [0047]     When the friction cups  85 ,  86  pass above the lower discharge line  80 , the shut-in well gas pressure discharges into the lower discharge line. The flow control valve  70  in the pump remains in the closed position as the shut-in pressure dissipates. The check valve  75  provides separation between the pressure above the pump (i.e. above the friction cups  85 ,  86 ) and the dissipating shut-in pressure in the lower discharge line  80 , thereby maintaining a positive pressure differential across the pump  60 . The gas pressure in the well is sufficient to support the pump to maintain it in the receiver until the valve  70  opens. As the fluid pressure in the well decreases below the preset pressure differential across the pump (from the high shut-in pressure), the flow control valve  70  opens. When the valve is opened, the pressure differential across the pump approaches zero and the pump descends into the well for additional liquid pumping.  
         [0048]     It will be recognized by those skilled in the art that changes or modifications can be made to the above-described embodiments without department from the broad inventive concept of the invention. It should therefore be understood that this invention is not limited to the particular embodiments described herein but is intended to include all changes and modifications that are within the scope and spirit of the invention as set forth in the following claims.