Abstract:
An electrical system for use with a sucker rod pump includes an electric generator configured to be operated by motion of a sucker rod string. The rod string is configured to transfer motive power to the sucker rod pump disposed in a wellbore. The generator is disposed in the wellbore. The system includes at least one electrically powered device electrically coupled to the generator and disposed in the wellbore.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    Not applicable. 
       STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
       [0002]    Not applicable. 
       BACKGROUND OF THE INVENTION 
       [0003]    1. Field of the Invention 
         [0004]    The invention relates generally to the field of reciprocating (walking beam) type wellbore fluid pumps. More specifically, the invention relates to electric generators and sensing systems usable therewith that are operated by such pumps. 
         [0005]    2. Background Art 
         [0006]    Wellbore fluid pumps include reciprocating (“walking beam” or “sucker rod”) pumps. Such pumps are operated by a prime mover, such as an electric motor or natural gas powered engine disposed at the Earth&#39;s surface. The prime mover operates a crankshaft coupled to a reciprocating beam. The beam is coupled to an assembly of pumping rods (“rod string”) extended into a wellbore drilled into the Earth&#39;s subsurface. A reciprocating pump is coupled to the lower end of the rod string and is anchored at a selected depth in the wellbore. As the walking beam reciprocates, it moves the rod string up and down, causing the movable elements of the pump in the wellbore to move correspondingly. Motion of the pump lifts fluid in the wellbore through a production tubing string to the Earth&#39;s surface. Examples of such pumps are described in U.S. Pat. No. 4,681,515 issued to Allen, U.S. Pat. No. 4,788,873 issued to Laney and U.S. Pat. No. 5,204,595 issued to Opal et al. 
         [0007]    An issue of concern to operators of such wellbore pumps is if the rate at which the pump lifts fluid to the surface exceeds the flow capacity of the Earth formations outside the wellbore. In such cases, the pump may be operated without sufficient fluid to keep it fully submerged (called “pump off”). Pump of can cause extensive damage to the pump, requiring its removal from the wellbore for repair or replacement. Wellbore pump operators therefore go to considerable effort to operate reciprocating pumps to avoid pump off. 
         [0008]    It is known in the art to provide sensing devices in a wellbore and to communicate signals from such sensors to the Earth&#39;s surface without hard wired connection. One such system is described in U.S. Pat. No. 6,899,178 issued to Tubel. A system disclosed in the Tubel &#39;178 patent includes a sensor disposed near the lower end of a tubing string, and a wireless transmitter, such as an acoustic transmitter, in signal communication with the sensor. Signals representative of the sensor measurements are transmitted along the tubing string at selected times and are detected and decoded at the Earth&#39;s surface for concurrent or later use. The system disclosed in the Tubel &#39;178 patent requires a source of electric power. Typically batteries are used for such electric power. Of course, batteries have a limited lifetime, and require that the system is periodically removed from the wellbore for battery replacement. Such removal requires removal of both the rod string and the tubing, making such battery replacement operation difficult and expensive. 
         [0009]    It is desirable to have a source of electric power in a wellbore such that a system such as described in the Tubel &#39;178 patent may be used with a reciprocating pump to monitor fluid level in a wellbore and to maintain battery life so that frequent replacement of batteries is not required. 
       SUMMARY OF THE INVENTION 
       [0010]    An electrical system for use with a sucker rod pump according to one aspect of the invention includes an electric generator configured to be operated by motion of a sucker rod string. The rod string is configured to transfer motive power to the sucker rod pump disposed in a wellbore. The generator is disposed in the wellbore. The system includes at least one electrically powered device electrically coupled to the generator and disposed in the wellbore. 
         [0011]    A method for operating an electrical device in a wellbore according to another aspect of the invention includes moving a sucker rod string along the interior of the wellbore to operate a sucker rod pump. Motion of the rod string is coupled to an electric generator disposed in the wellbore. Electrical power from the generator is used to at least partially power the electrical device in the wellbore. 
         [0012]    Other aspects and advantages of the invention will be apparent from the following description and the appended claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]      FIG. 1  shows a reciprocating wellbore pump having an electric generator coupled thereto. 
           [0014]      FIG. 2  shows the electric generator of  FIG. 1  in more detail and a wellbore wireless sensor system that may be used with the generator. 
       
    
    
     DETAILED DESCRIPTION 
       [0015]    A reciprocating (“walking beam” or “sucker rod”) pump system including a sensing system and one example of an electric power generator is shown schematically in  FIG. 1 . The beam pump system is shown generally at  10  and includes a reciprocating or walking beam mounted by a bearing  22  on a frame  20  which includes a prime mover such as an electric motor or a natural gas powered engine. The prime mover  20  rotates a crank  17  coupled to one end of the walking beam  12  by a connecting rod  16 . Typically the crank  17  will include a counterweight  18  disposed opposite the connection to the connecting rod  16 . The counterweight  18  typically weighs the lever arm equivalent of the weight of a rod string  26  disposed in a wellbore  28  plus one half the weight of a column of fluid from the depth of a pump  38  in the wellbore  28  to the Earth&#39;s surface. Such counterweight, as is known in the at, provides that the overall work performed by the pump system  10  is substantially equalized over the entire range of motion of the walking beam  12 . 
         [0016]    The wellbore  28  typically includes a pipe or casing  30  disposed to the bottom of the wellbore  28  and retained therein by cement. The casing  30  typically includes perforations  32  at selected depths corresponding to the depth outside the casing  30  of a productive formation  34  such as may contain oil and/or gas therein. Fluid enters the casing  30  through the perforations  32 . A production tubing  36  extends from a well head  48  at the Earth&#39;s surface to a selected depth in the wellbore  28 . A reciprocating pump  38  is connected to the lower end of the tubing  36 . The pump  38  is operated by the rod string  26 . 
         [0017]    In the example shown in  FIG. 1 , an electric generator  40  can be disposed in a selected part of the tubing string  36 . Electric power produced by the generator  40  can be used to operate a wireless data transmitter  42 . The wireless data transmitter  42  is typically coupled to the tubing string  36  and includes devices (not shown in  FIG. 1 ) that can convey data signals along the tubing string  36  corresponding to measurements made by one or more sensors, an example of which is shown schematically at  44 . The generator  40  will be explained in more detail below with reference to  FIG. 2 . 
         [0018]    Referring to  FIG. 2 , the generator  40  may include a non-magnetic, electrically non-conductive tubing joint  54  that may be coupled within the production tubing  36 . The joint  54  may be made from fiber reinforced plastic or similar material having the foregoing magnetic and electrical properties. See, for example, U.S. Pat. No. 6,620,475 issued to Reynolds et al. for a description of such fiber reinforced plastic tubing materials. The rod string  26  may include one or more joints therein made from non-magnetic material, such as monel, stainless steel or an alloy sold under the trademark INCONEL, which is a registered trademark of Huntington Alloys Corporation, Huntington, W. Va. One or more permanent magnets  50  may be disposed on the non-magnetic rod string joint  50 . As the rod string  26  is reciprocated by operation of the pump system ( 10  in  FIG. 1 ) the magnets  50  will move correspondingly. One or more wire coils  52  may be wound outside the tubing joint  54 . As the magnets  50  are moved inside the non-magnetic tubing joint  54 , electric current is induced in the coils  52 . 
         [0019]    The coils  52  are electrically connected to circuitry  60  forming part of the data telemetry system  42 . Such circuits  60  may include (none of which is shown separately) power conditioners to convert the current induced in the coils  52  to direct current and energy storage devices such as a Farad size capacitors or rechargeable batteries. The circuits include devices to actuate an acoustic transmitter  62 . The transmitter is actuated to send signals along the tubing string  36  corresponding to signals from one or more sensors  64  in signal communication with the circuits. In the present example, the sensor  64  may be a pressure sensor. A pressure measured by the sensor  64  will correspond to the height of the liquid column in the wellbore ( 28  in  FIG. 1 ). If the pressure drops to a level indicating an unsafe liquid level in the wellbore, the wellbore operator may be advised of this fact by monitoring the pressure measurements transmitted along the tubing string  36  by the telemetry system  42 . 
         [0020]    Because the generator produces electric power whenever the pump system ( 10  in  FIG. 1 ) causes the rod string  26  to move, the circuits  60  may remain energized substantially continuously without the need to remove them to replace batteries, as has proven necessary using wireless telemetry systems known in the art prior to the present invention. 
         [0021]    While the invention has been described with respect to a limited number of embodiments, those skilled in the art, having benefit of this disclosure, will appreciate that other embodiments can be devised which do not depart from the scope of the invention as disclosed herein. Accordingly, the scope of the invention should be limited only by the attached claims.