Abstract:
A bumper assembly for down-hole use in a well. In one embodiment, the bumper assembly includes a fish neck, a cage, and a progressive rate spring disposed there-between. When a plunger strikes the top of the fish neck, the progressive rate spring dampens the force delivered by the plunger, thereby prolonging the useful life of the plunger and/or the bumper assembly.

Description:
BACKGROUND 
       [0001]    1. Technical Field 
         [0002]    Embodiments of the subject matter disclosed herein generally relate to methods and systems for stopping a plunger at or near the bottom of a well and reducing the impact damage caused thereby. In this regard, one embodiment of the present invention is directed to a bumper assembly that employs a progressive rate spring, which operates by dampening the force delivered (on impact) by the plunger to the top of the bumper assembly, thereby reducing the damage that would otherwise be caused by the impact, and prolonging the life of the plunger and bumper assembly as a result. 
         [0003]    2. Discussion of the Background 
         [0004]    It is well known that production from oil and gas wells can suffer due to the build-up of fluids at the bottom of the well. See e.g., U.S. Pat. No. 6,148,923, which is incorporated herein by reference. Various methods and devices have been developed to remove those fluids so as to improve the well&#39;s productivity. 
         [0005]    One such device is known as a plunger, of which there are many variants known to those skilled in the art. For example, an auto-cycling plunger operates as follows: (1) it is dropped into the well (at the well&#39;s surface), (2) it free-falls down the well until it stops upon impact with the bottom of the well, and (3) it thereafter is caused (by pressure in the well) to travel back toward the surface of the well, pushing a “load” of liquid above it for removal at the well&#39;s surface. The plunger then is allowed to repeat that cycle, thereby ultimately removing enough fluid from the well to improve its production. 
         [0006]    A number of problems have arisen from the use of prior art plungers. For example, due to the typically great distance between the surface and bottom of a well, the plunger travels at a great rate of speed when—due to its free-fall—it reaches and strikes the bottom of the well. Impacts between the plunger and the bottom of the well can be violent, and they often are so violent that damage occurs (either immediately or over time due to repeated use) to either the plunger and/or whatever it strikes at the bottom of the well. 
         [0007]    Bumper assemblies have been designed and placed at or near the bottom of a well to dampen the impact delivered by a free-falling plunger. The operational premise of such bumper assemblies is to sufficiently dampen the impact delivered by the free-falling plunger in a way that reduces damage that would otherwise be caused to the plunger and/or the bumper assembly. 
         [0008]    One such prior art bumper assembly is shown in  FIG. 1 . The bumper assembly is designed to be seated at or near the bottom of a well, where numeral  10  denotes the bottom of the assembly and numeral  20  denotes the top of the assembly. At the top of the assembly is fish neck  30 , and at the bottom of the assembly is cage  40 . Disposed between fish neck  30  and cage  40  is constant rate compression spring  50 . Constant rate compression spring  50  encloses/encircles pull rod  60 , and pull rod  60  is attached at one end to fish neck  30  and at its opposite end it is slideably mounted within the top portion of cage  40 . 
         [0009]    In operation, a plunger (not shown) free-falls down a well until it strikes fish neck  30 . The impact between the plunger and fish neck  30  imparts a downwardly directed force, which causes fish neck  30  and its attached pull rod  60  to move (down) toward bottom  10 . As fish neck  30  and its attached pull rod  60  move (down) toward bottom  10 , pull rod  60  slides through the top portion of cage  40 . This downward movement compresses constant rate compression spring  50 , which effectively absorbs or dampens the force caused by the impact between the plunger and fish neck  30 . 
         [0010]    The object, of course, of using a bumper assembly of this nature is to sufficiently dampen the impact force delivered by the plunger to the bumper assembly such that it reduces the impact damage that might otherwise take place to the plunger and/or the bumper. Such damage can consist of deformation to the plunger and/or the fish neck, or even partial or total destruction of either one or both. While the damage may not occur on the first impact (although it could), the repetitive nature of the operation of these devices often ultimately results in substantial damage to the plunger and/or bumper. 
         [0011]    Replacing damaged plungers and/or bumper assemblies is both costly and time consuming. Moreover, the time it takes to replace either, and especially a bumper assembly, entails “downtime” for the well, which itself imparts undesirable cost and expense. 
         [0012]    Prior art assemblies such as that shown in  FIG. 1  have not been totally effective. For the most part, their ineffectiveness stems from their use in new shale plays. The well characteristics in these new plays vary greatly from conventional oil and gas environments utilizing conventional plunger lift technologies. The bypass plungers used today are heavier and fall at much higher velocities. In other words, while such designs work to some extent, they do not work well enough because damage (as a result of their normal operation) still often results to the plunger and/or the bumper assembly. 
         [0013]    Efforts, therefore, have been made to improve the effectiveness of bumper assemblies and the processes in which they are used. For example, some prior art attempts have involved forging the fish neck and/or plunger from stronger materials such as titanium. 
         [0014]    Other efforts, such as that depicted by  FIG. 2 , have involved placing Belleville washers  70  in cage  40  to receive the bottom of pull rod  60  as it moves through cage  40  in response to the force delivered to fish neck  30  by a free-falling plunger. The Belleville washers  70  absorb some of the force not otherwise absorbed by constant rate compression spring  50 . 
         [0015]    Belleville washers have been used, as opposed to simply using a longer constant rate compression spring (which would absorb more force than a shorter constant rate compression spring), because the limited space afforded by standard lubricators at the top of the well (for inserting the bumper assembly into the top of the well) limits the length a spring can contribute to the overall length of the bumper assembly. In other words, a longer spring would cause the overall length of the bumper assembly to exceed the standard length of the opening at the top of the well for inserting such assemblies. 
         [0016]    Similarly, using larger diameter springs (of the same length), which would absorb more force than an otherwise similar spring having a smaller diameter, are impractical because the standard width of drilling pipe acts as a barrier to using larger diameter springs. 
         [0017]    None of these prior art techniques have proven satisfactory to the inventors of the present invention. 
       SUMMARY 
       [0018]    The present invention addresses the disadvantages and drawbacks of current plungers and bumper assemblies, while still conforming to limitations imposed on their designs by industry standards, such as pipe size and lubricator design. 
         [0019]    As an example, the present invention replaces the traditional prior art constant rate compression spring in a bumper assembly with a progressive rate spring. A constant rate compression spring is a spring whose compression resistance varies linearly along its compression continuum, i.e., from uncompressed to fully compressed, whereas a progressive rate spring is a spring whose compression resistance varies non-linearly at some point in its compression continuum. 
         [0020]    Use of a progressive rate spring in a bumper assembly better dampens the force imparted by a plunger to a bumper assembly than the use of a constant rate spring. For example, due to the outside diameter and length limitations mentioned above, a prior art constant rate spring used in a bumper assembly is designed to withstand impacts not exceeding 333 lbs/in. With the described length limitations, such a spring is limited to 3 inches of travel, thus limiting a constant rate spring to approximately 1,000 pounds of resistive force. A progressive rate spring, on the other hand, can have a 1,000 lbs/in rating, thereby providing three times the resistive force of a conventional constant rate spring. 
         [0021]    This increase in dampening afforded by a progressive rate spring results in less damage to the plunger and/or bumper assembly caused by the free-fall impact delivered by a plunger to the bumper assembly, and because there is less damage to either component, neither one needs to be replaced or repaired as often, thereby saving time, money, and effectively increasing the productivity of the well. 
         [0022]    As will be appreciated by those skilled in the art, variants of the present invention are possible and within the scope of this disclosure, whether expressly identified or not. The scope of the invention is defined only by the appended claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0023]    The accompanying drawings, which are incorporated herein and constitute a part of the specification, illustrate either certain prior art or one or more exemplary embodiments of the present invention. In the drawings: 
           [0024]      FIG. 1  is a cross-sectional diagram of a prior art bumper assembly; 
           [0025]      FIG. 2  is an cross-sectional diagram of a prior art bumper assembly; 
           [0026]      FIG. 3  is an assembly diagram of a bumper assembly using a progressive rate spring. 
       
    
    
     DETAILED DESCRIPTION 
       [0027]    The following description of the exemplary embodiments refers to the accompanying drawings. The same reference numbers in different drawings identify the same or similar elements. The following detailed description does not limit the invention. Instead, the scope of the invention is defined by the appended claims. 
         [0028]    Reference throughout the specification to “one embodiment” or “an embodiment” means that a particular feature, structure or characteristic described in connection with an embodiment is included in at least one embodiment of the subject matter disclosed. Thus, the appearance of the phrases “in one embodiment” or “in an embodiment” (or variants thereof) in various places throughout the specification is not necessarily referring to the same embodiment. Further, the particular features, structures, or characteristics may be combined in any suitable manner in one or more embodiment. The invention, however, is not limited to any one embodiment. 
         [0029]      FIG. 3  illustrates an exemplary embodiment of the present invention.  FIG. 3  shows a bumper assembly for placement in a well. The bumper assembly can be placed at the bottom of the well or anywhere between the top and bottom of the well that the well operator decides. 
         [0030]    Methods and apparatuses for inserting the bumper assembly in the well (whether it be at the bottom or elsewhere) are well known to those skilled in the art and, depending where in the well the assembly is placed, additional attachment equipment (as appropriate) will be attached at the lower end of the assembly. For example, if the assembly is intended to be placed at the bottom of a well, a seating cup hold-down assembly is attached to the lower end of the assembly for seating the assembly in a seating nipple located generally at the bottom of the tubing string. If the assembly is intended to be placed above the bottom of a well, a collar or tubing stop is attached to the lower end of the assembly for holding the assembly in position above the bottom of the well. Both the seating cup hold-down assembly and collar/tubing stops (and their use as described herein) are well-known to those skilled in the art. 
         [0031]    The bumper assembly of  FIG. 3  has a bottom generally denoted at  300  and a top generally denoted at  310 . While a bottom portion of the bumper assembly depicts cage  320 , the configuration of cage  320  need not be identical to that depicted in  FIG. 3 . Moreover, as described above, when the bumper assembly is intended to be placed at the bottom of the well, an extension (not shown but well-known to those skilled in the art) attaches to the bottom portion of the assembly for seating the assembly in the bottom of the well. 
         [0032]    Likewise, while the top of the bumper assembly is denoted as fish neck  330 , the configuration of the top of the bumper assembly need not be identical to that depicted by fish neck  330 . Material for cage  320  preferably is 17-4 stainless steel and material for fish neck  330  preferably is titanium. The outside diameters of cage  320  and fish neck  330  need not be identical, but both must be suitably sized to fit within the drilling pipe used, which typically is 2⅜ inch or 2⅞ inch pipe. 
         [0033]    Disposed between bottom  300  and top  310  of the bumper assembly is progressive rate spring  340 . Spring  340  possesses a compression resistance that varies non-linearly at some point in its compression continuum. Spring  340  operates to dampen any downward force applied to fish neck  330 , whereby the dampening effect increases as spring  340  is further compressed. 
         [0034]    In another embodiment, pull rod  350  is attached (preferably via a roll pin) to fish neck  330 , threaded through spring  340 , and slideably attached to cage  320 . In this embodiment, as fish neck  330  is forced downward (by an impact delivered by a falling plunger), spring  340  compresses and pull rod  350  slides through the top of cage  320  toward end  300 . When the delivered force is fully absorbed, spring  340  decompresses, and fish neck  330  and pull rod  350  return to their original positions. In this manner, fish neck  330  and attached pull rod  350  move in a piston-like fashion, whereby they are pushed down by the force delivered by a falling plunger and pushed up by the decompression force delivered by spring  340 . 
         [0035]    In yet another embodiment of the invention, Belleville washers are inserted in cage  320  so that the bottom of pull rod  350  impacts them either immediately or on its downward movement (as described above) toward end  300 . This increases the dampening effect provided by spring  340 . Alternatives to Belleville washers also could be used, such as a constant or variable rate spring, one or more friction washers through which pull rod  350  slides, or other dampening mechanisms known to those skilled in the art. 
         [0036]    As indicated above, it should be understood that this description is not intended to limit the invention. On the contrary, the exemplary embodiments are intended to cover alternatives, modifications and equivalents, which are included in the spirit and scope of the invention as defined by the appended claims. Further, in the detailed description of the exemplary embodiments, numerous specific details are set forth in order to provide a comprehensive understanding of the claimed invention. However, one skilled in the art would understand that various embodiments may be practiced without such specific details. 
         [0037]    Although the features and elements of the present exemplary embodiments are described in the embodiments in particular combinations, each feature or element can be used alone without the other features and elements of the embodiments or in various combinations with or without other features and elements disclosed herein. 
         [0038]    This written description uses examples of the subject matter disclosed to enable any person skilled in the art to practice the same, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the subject matter is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims.