Abstract:
A method for generating power in a wellbore includes moving an actuator; inducing an oscillating stress on a piezoelectric component with the actuator; and generating a voltage with the piezoelectric component in response to the induced stress on the piezoelectric component.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    This application is a divisional application of U.S. application Ser. No. 11/728,760, filed Mar. 27, 2007, the contents of which are incorporated by reference herein in their entirety. 
     
    
     BACKGROUND 
       [0002]    For nearly a century, pump jacks have been used in the production of hydrocarbons from downhole formations. Such jacks are seen atop many oil fields, their rhythmic movements common. It is well known how the pump jacks work, which is by moving sucker rods up and down within the wellbore. For the same near century, the pumps have worked very well doing precisely that, pumping. 
         [0003]    More modern well systems while still employing pump jacks also are instrumented extensively downhole. This requires substantial amounts of available power in the downhole environment. Power is for the most part delivered from the surface but due to the small amount of available space in the hole, allocation of such space is a source of trepidation. Since the hydrocarbon recovery art is always in search of improved means to produce hydrocarbons, any reduction in components needed within the cross-section of the wellbore would be well received. 
       SUMMARY 
       [0004]    A method for generating power in a wellbore includes moving an actuator; inducing an oscillating stress on a piezoelectric component with the actuator; and generating a voltage with the piezoelectric component in response to the induced stress on the piezoelectric component. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0005]    Referring now to the drawings wherein like elements are numbered alike in the several Figures: 
           [0006]      FIG. 1  is a schematic view of a pump jack; 
           [0007]      FIGS. 2-6  are each schematic views of a piezoelectric power generation arrangement utilizing the pump jacks in different positions. 
       
    
    
     DETAILED DESCRIPTION  
       [0008]    In order to enhance understanding of the invention applicants have elected to describe briefly the components of the tool followed by a discussion of its operation. 
         [0009]    Referring to  FIG. 1 , a pump jack  10  is illustrated schematically. One of skill in the art will recognize a walking beam  12  and sucker rod  14  extending into a wellbore  16 . The pump jack  10  as is known, reciprocates the sucker rod up and down in the wellbore. The sucker rod  14  of the pump jack is the only portion of the pump jack that is modified in connection with the invention and therefore other components of the pump jack need not be described in detail. Also to be noted is that although a pump jack is utilized herein as a source of movement, other sources of similar movement could be substituted while maintaining the benefits of the inventive concept. 
         [0010]    Referring to  FIG. 2 , a power generation arrangement  20  for use in combination with a reciprocating source such as a pump jack is illustrated. The arrangement includes a housing  22 , within which is disposed at least one piezoelectric component  24  which may be a single piezoelectric element or a plurality of elements in a stack. The component  24  is in physical force transmission contact with a resilient member (stress inducer)  26 , illustrated as a coil spring, but could be any device similarly capable of oscillatory movement. Spring  26  is in operable communication with a magnetic element  28 , which may be a rare earth magnet or may simply be a ferrous element. The magnetic element  28  is also in operable communication with another resilient member  30  (also illustrated as a coil spring for convenience but as noted for spring  26 , other devices capable of oscillatory movement are equally applicable). Spring  30  may be the same or different from spring  26 , providing that the desired oscillatory motion of magnetic element  28  and associated mechanical compression of component  24  is preserved. Spring  30  is bounded by a compression cap  32  in the illustrated embodiment but could alternatively be bounded by another piezoelectric component (not shown) that essentially would be a mirror image of the component  24 . In such an arrangement, power generation would occur based upon movement of the magnetic element  28  in both axial directions. 
         [0011]    Through an inside dimension of all of the foregoing components is at least one sucker rod  14  or sucker rod extension  34  having at least one magnetic element  36  disposed thereat. Magnetic element  36  may be a magnet or simply a ferrous element providing that either it or the magnetic element  28  is in fact a magnet. At least one of the two magnetic elements  28  and  36  must provide a magnetic field for operability of the invention. It is to be noted that the sucker rod  34  is used in an exemplary manner and is not a limitation of the invention. Any support for the magnetic element  36  that is an oscillatory structure itself is substitutable. Magnetic element  36 , if indeed a magnet, is to be attractively polarized relative to magnetic element  28  such that a strong attractive force is generated between the magnetic elements. Further noted is that at portions of the sucker rod  34  other than at the at least one magnetic element  36 , there is disposed a non-magnetic sleeve  38 . Sleeve  38  that functions to align the magnetic elements and the sucker rod to ensure that they remain non-contacting in nature thereby reducing frictional losses otherwise caused by magnetic attraction of the magnetic element  28  to the sucker rod  34 , which is usually a metal, or actual contact between magnetic elements  28  and  36 . 
         [0012]    As one of skill in the art should recognize the sucker rod  34  moves up and down pursuant to the motion of the walking beam pictured in  FIG. 1 . This movement is harnessed as taught herein not only for its original purpose of pumping stubborn well fluids to the surface but to generate power for downhole devices as well. 
         [0013]    Referring to  FIGS. 2-6  as a sequence of drawings showing the device in different positions, the operation thereof will become clearer. As magnetic element  36  draws nearer magnetic element  28  the attractive magnetic fields they exhibit (or one field attracting the ferrous element of the other) begin to draw magnetic element  28  toward magnetic element  3   6 , to some extent overcoming spring  26  in compression and spring  30  in tension. This movement of magnetic element  28  will impart a compressive load, through spring  26  to component  24  thereby creating an electrical potential in component  24 . Since the magnetic element  36  is moving towards magnetic element  28 , it should be understood that the magnitude of the compressive load on the component  24  for this movement is small and consequently the potential generated is small. As the sucker rod continues, its movement uphole and as illustrated in  FIG. 3 , the magnetic elements  28  and  36  align and thereby are at the highest attractive force therebetween. Yet farther uphole movement of sucker rod  34  draws magnetic element  28  to compress spring  30  while extending spring  28 . This continues, since the magnetic elements are engineered to have a greater attractive force to each other than the springs  26  and  30  have spring force to separate them, until the spring  30  is substantially maximally compressed. After such compression, illustrated in  FIG. 4 , magnetic element  36  is moved farther uphole with sucker rod  34  thereby misaligning the magnetic elements and thus reducing the attractive forces therebetween. At a point, the attractive force between magnetic element  28  and magnetic element  36  is overcome by the spring force of springs  30  and  26 . As this occurs, springs  30  and  26  propel magnetic element  28  back toward component  24  as illustrated in  FIG. 6 . This motion, as one of skill in the art should appreciate, presents a relatively large compressive load on the component  24  thereby generating a large electrical potential. Further, because of the springs of  30  and  26 , the magnetic element  28  will oscillate causing a number of compressions on the component  24 , each developing an electrical potential. Since the oscillations diminish in magnitude with each cycle, the compressive load is also reduced but some of the benefit is still achieved by oscillatory motion until magnetic element  28  is magnetically “bound” again to magnetic element  36  (or another similar magnetic element if the sucker rod stroke is long enough to create multiple actuations due to magnetic interaction using multiple magnetic elements  36 ). A capacitor  40  is electrically connected to the piezoelectric component  24  to store the potential generated by the disclosed system for use when needed. 
         [0014]    As was noted hereinabove, a pump jack is but one source of movement for a system such as that disclosed. Further, and also as noted, in an alternative embodiment, compression cap  32  could be substituted by an additional piezoelectric component so that oscillatory compressive loading on both springs  30  and  26  will produce potentials. This will increase available power downhole from the system as described. In addition hereto, rapid unloading of the component  24  will create a voltage as well. This voltage may be made usable by employing a rectifier bridge  42  in the electrical circuit connected to the component  24 . 
         [0015]    While preferred embodiments have been shown and described, modifications and substitutions may be made thereto without departing from the spirit and scope of the invention. Accordingly, it is to be understood that the present invention has been described by way of illustrations and not limitation.