Patent Publication Number: US-7584784-B2

Title: Reciprocating pump drive apparatus

Description:
This invention relates to pumps for pumping fluid from underground reservoirs, such as oil wells, and in particular to a reciprocating drive apparatus for a pump. 
   BACKGROUND 
   A common type of pumping unit used in oil well applications includes a downhole pump located in an underground reservoir, and connected to the surface by a string of sucker rods. A drive apparatus on the surface is connected to the top of the rod string and moves the rod string up and down in a reciprocating manner to drive the pump and pump fluid to the surface. 
   One common type of reciprocating drive for use with such pumping units is disclosed for example in U.S. Pat. No. 4,949,784 to Evans. The drive comprises a motor driving an eccentric arm to cause a pump am to move up and down, and the top end of the rod string is connected to the end of the pump arm. 
   It is also well known to use a hydraulic cylinder to cyclically extend and retract to reciprocate the rod string. U.S. Pat. Nos. 4,512,149 to Weaver and 4,761,120 to Mayer et al. disclose such a reciprocating drives where the hydraulic cylinders are oriented vertically, while U.S. Pat. No. 4,530,645 to Whatley et al. discloses such a reciprocating drives where the hydraulic cylinder is oriented horizontally. 
   A consideration when designing a reciprocating drive for such oil well pumping units is the need to move the drive apparatus away from the top of the well to provide access for service rigs to be set up over the well head to provide periodic maintenance such as is usually required on oil wells. Such maintenance often requires that a service rig be positioned to pull the rod string and the downhole pump out of the well. Considerable time and equipment is typically required to disassemble and/or move existing prior art drives sufficiently to allow the service rig to be set up in the required location. 
   SUMMARY OF THE INVENTION 
   It is an object of the present invention to provide a reciprocating drive apparatus for oil well pumps and the like that overcomes problems in the prior art. 
   In a first embodiment the present invention provides a reciprocating drive apparatus for connection to a top end of a rod string to drive a downhole pump located in a well. The apparatus comprises a plate adapted to be fastened to a top end of a well head assembly of the well, and a mast is attachable to the plate in a substantially vertical working position. A hydraulic cylinder is operatively connected to a source of pressurized hydraulic fluid and is attached to the mast such that when the mast is in the working position the hydraulic cylinder is oriented substantially vertically, and such that the hydraulic cylinder can extend and retract in response to a controller. A tether is adapted to be fixed to the well head at a fast end thereof and is adapted for attachment to the top end of the rod string at a second end thereof. The tether is configured such that the hydraulic cylinder engages the tether to move the second end of the tether up and down as the hydraulic cylinder extends and retracts. 
   In a second embodiment the present invention provides a reciprocating drive apparatus for connection to a top end of a rod string to drive a downhole pump located in a well. The apparatus comprises a plate adapted to be fastened to a top end of a well head assembly of the well. A mast comprises a pair of beams and is pivotally connected to the plate such that the mast can be moved from a substantially horizontal idle position to a substantially vertical working position. At least one fastener is operative to secure the mast in the working position. A hydraulic cylinder is operatively connected to a source of pressurized hydraulic fluid and has a barrel thereof attached to the beam and substantially in alignment with the beams such that a piston of the hydraulic cylinder extends and retracts from a top end of the barrel in response to a controller. A wheel member is rotatably attached to a top end of the piston about a substantially horizontal rotational axis. A tether is adapted to be fixed to the well head at a first end thereof, and extends upward over and engaging the wheel member, and then downward to a second end thereof adapted for attachment to the top end of the rod string. 
   In a third embodiment the present invention provides a reciprocating drive apparatus to drive a downhole pump located in a well. The apparatus comprises a plate fastened to a top end of a well head assembly of the well, and a mast pivotally connected to the plate such that the mast can be moved from a substantially horizontal idle position to a substantially vertical working position. At least one fastener is operative to secure the mast in the working position. A hydraulic cylinder is operatively connected to a source of pressurized hydraulic fluid, and is attached to the mast such that when the mast is in the working position the hydraulic cylinder is oriented substantially vertically, and such that the hydraulic cylinder can extend and retract in response to a controller. A tether is fixed to the well head at a first end thereof and is attached at a second end thereof to a top end of a rod string extending down the well to the downhole pump. The tether is configured such that the hydraulic cylinder engages the tether to move the top end of the rod string up and down as the hydraulic cylinder extends and retracts. 
   The apparatus is simple and economical, and can be scaled up down as required for particular applications. Generally it is contemplated that the apparatus of the invention will be used with about a 20-30 horsepower gas engine, running on natural gas from the well. Because of its economy, and the ease of installation, and the case of removal to allow access for well servicing, it is contemplated that many oil wells with small production can be profitably maintained in production. 

   
     DESCRIPTION OF THE DRAWINGS 
     While the invention is claimed in the concluding portions hereof, preferred embodiments are provided in the accompanying detailed description which may be best understood in conjunction with the accompanying diagrams where like parts in each of the several diagrams are labeled with like numbers, and where: 
       FIG. 1  is a schematic perspective rear view of an embodiment of a reciprocating drive apparatus of the present invention; 
       FIG. 2  is a schematic perspective front view of the embodiment of  FIG. 1 ; 
       FIG. 3  is a schematic side view of the embodiment of  FIG. 1 ; 
       FIG. 4  is a top view of the plate of the embodiment of  FIG. 1 . 
   

   DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS 
     FIGS. 1-3  illustrate a reciprocating drive apparatus  1  of the present invention for connection to a top end of a rod string  3  to drive a downhole pump located in a well  5 . The apparatus  1  comprises a plate  7  adapted to be fastened to a top end of a well head assembly of the well  5 . In the illustrated embodiment, the plate  7  is attached to the well head flange  9  at the top of the casing  11  of the well  5 . The hardware  13  of the well head assembly, comprising valves and the like, is located above the plate  7 . 
   Also as illustrated in  FIG. 4 , the illustrated plate  7  comprises right and left sections  7 R,  7 L such that well head bolts  15  on a right side of the well head flange  9  can be removed and then replaced through flange bolt holes  14  in the plate section  7 R to install the right section  7 R, and then well head bolts  15  on a left side of the well head flange  9  can be removed and then replaced through flange bolt holes  14  in the plate section  7 L to install the left section  7 L. The plate  7  can thus be fastened to the well head flange  9  on existing wells without the need to disturb the hardware  13  of the well head assembly. Well tubing and the rod string  3  extend through the central aperture  17  in the plate  9 . 
   A mast  21  is attached to the plate by fasteners such as bolts  23  such that the mast  21  is oriented in a substantially vertical working position as shown in  FIGS. 1 and 2 . While it is contemplated that the mast  21  could be raised and maneuvered into the required vertical working position on top of the plate  7  by a boom truck or like equipment,  FIG. 3  illustrates the mast  21  pivotally connected to the plate  7  about a pivot axis PA. 
   When the plate  7  has been attached to the well head flange  9 , the mast  21  can be connected by hinge pins  25  to hinges  27  welded to the plate  7  and the bottom of the mast  21  while lying down in a substantially horizontal idle position IP as illustrated in  FIG. 3 , and then raised to the substantially vertical working position WP by a boom truck or the like. The hinges  27  are configured such that once the mast  21  has been raised to the working position WP article, fastener apertures  29  in the bottom of the mast  21  are aligned with corresponding apertures  29  in the plate  7 ′ and fasteners such as bolts  23  may be inserted to secure the mast  21  in the working position WP article. 
   The pivotal connection of the mast  21  to the plate  7  allows the mast  21  to be maneuvered to connect the hinges  27  while it is lying down, a substantially easier operation than maintaining the mast  21  upright while aligning the fastener apertures  29 . Also, when in use, the pivotal connection of the hinges  27  allows the operator to simply remove the bolts  23  to lay the mast over to one side, or all the way down to rest on the ground, to allow access to the well head assembly for service rigs or the like. One the service is complete, the mast can be simply raised again to the working position WP article and the bolts  23  re-installed. 
   A hydraulic cylinder  33  is attached to the mast  21  and operatively connected to a source of pressurized hydraulic fluid. Typically the source will be provided by an engine driving a hydraulic pump, and will include appropriate valves and piping as is known in the art. 
   The hydraulic cylinder  33  is attached to the mast such that when the mast is in the working position WP article, the hydraulic cylinder  33  is oriented substantially vertically, and such that the hydraulic cylinder  33  can extend and retract in response to a controller  30 . A tether  34  is fixed at a first end thereof  34 A to the well head flange  9 , or to some other convenient location fixed with respect to the ground such as the plate  7  or a lower portion of the mast  21 . The opposite second end of the tether  34 B is attached to the top end of the rod string  3 . The tether  34  is configured such that the hydraulic cylinder  33  engages the tether  34  to move the second end  34  B of the tether  34 , and thus the rod string  3 , up and down as the hydraulic cylinder  33  extends and retracts. 
   In the illustrated embodiment the mast  21  comprises a pair of beams  35 , and the barrel  37  of the hydraulic cylinder  33  is attached between the beams  35  and substantially in alignment with the beams  35 . The piston  39  of the hydraulic cylinder  33  extends and retracts from a top end of the barrel  37 . A wheel member  41  is rotatably attached to the top end of the piston  39  about a substantially horizontal rotational axis and engages a tether  34 . Depending on the tether being used the wheel member  41  will typically be provided by a pulley, sprocket or like member appropriate to the tether  34 . 
   In order to maintain the hydraulic cylinder  33  in alignment, a carriage  45  is attached to the top end of the piston  39 . Carriage wheels  47  are mounted on opposite faces  49  of the carriage  45 . The carriage rollers or wheels  47  roll up and down inner faces  51  of the beams  35 , and recesses on the faces  49  of the carriage  45  engage corresponding ribs  53  extending from the inner faces  51  of the beams  35 . The carriage  45  is thus movable up and down in a path maintained in alignment with the beams  35 . The wheel member  41  is rotatably mounted to the carriage  45 . 
   In the illustrated embodiment the first end  34 A of the tether is fixed to the well head flange  9  by attachment to a tether bracket  55  bolted to the plate  7 . A portion  57  of the illustrated tether  34  is provided by a cable that is passed through the tether bracket  55  and clamped. An upper end of the cable portion  57  is connected to a link chain portion  59  of the tether  34  that is configured to pass smoothly over a pulley providing the wheel member  41 , and down to the second end  34 B that is attached to the top end of the rod string  3 . 
   The mast  21  and the plate  7  are configured such that when the second end  34 B of the tether  34  is attached to the top end of the rod string  3  the tether  34  is oriented substantially vertically between the top end of the rod string  3  and the wheel member  41 . The vertical configuration is seen in  FIG. 3 . Lateral stresses on the rod string  3  are avoided and the tether moves the rod string  3  vertically as the hydraulic cylinder moves the wheel member  41  vertically up and down. 
   The controller  30  includes upper and lower limit switches  61  configured such that at upper and lower ends of a stroke of the hydraulic cylinder  33 , pressurized hydraulic fluid is directed to reverse a direction of travel of the piston  39 . The stroke location on the mast  21 , and the length of the stroke, can be set as desired by the operator. The hydraulic cylinder could be either a single or double acting cylindrical. Appropriate pump capacities, orifices, and the like will be provided to control the speed of the ascent and descent of the piston  39  to that satisfactory for driving the connected pump. 
   The foregoing is considered as illustrative only of the principles of the invention. Further, since numerous changes and modifications will readily occur to those skilled in the art, it is not desired to limit the invention to the exact construction and operation shown and described, and accordingly, all such suitable changes or modifications in structure or operation which may be resorted to are intended to fall within the scope of the claimed invention.