Abstract:
A drive assembly for powering a rotating rod string  14  passing through a surface wellhead  18  includes a torque conveying housing  32  containing a radially outer member supporting a plurality of outer member magnets and rotated by a motor. A radially inner member  48  supports a plurality of inner member magnets and is rotatable within the outer member, with magnetic forces between the plurality of outer member magnets and the plurality of inner member magnets rotating the inner member magnets and thus the radially inner member. The drive assembly provides a highly reliable sealed construction for rotating in the rod string with minimal risk of fluid leaking from the assembly.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to drives for rotating a sucker rod commonly used in oil and gas operations, which conventionally use a stuffing box to seal fluid in the well. More particularly, this invention relates to a sealed drive for a rotating rod string which drives a downhole progressive cavity pump. 
       BACKGROUND OF THE INVENTION 
       [0002]    Reciprocating downhole pumps have been used in the oil and gas industry for years to raise oil to the surface. In order to direct the oil flow at the surface of the well, a stuffing box is employed to seal around the reciprocating rod string. Stuffing boxes are commonly used for sealing with a reciprocating rod string. 
         [0003]    Progressive cavity pumps rely upon the rotary action of the rod string rather than reciprocating action to power the downhole pump. Stuffing boxes for rotating rod strings commonly use conventional packing material as the sealing element, although some designs employ Chevron-type sealing elements. 
         [0004]    The failure of a stuffing box is environmentally damaging and costly. Most often, failure results in spillage of oil at the well site, and well sites are thus commonly subject to expensive cleanup operations to eliminate hydrocarbons around the area of a well. Stuffing boxes also require a fairly high maintenance, and operators frequently are scheduled to check operating stuffing boxes to ensure that there are no leaks, to eliminate or minimize any leakage that is occurring, and to replace stuffing boxes when necessary. Leakage of a stuffing box thus represents a significant cost of recovering oil from wells which are driven by a downhole pump and a powered sucker rod. 
         [0005]    U.S. Pat. No. 4,372,379 discloses a drive assembly for powering a downhole rotary pump. The drive motor is not directly over the wellhead, and  FIG. 3  discloses the bearings and seals for sealing fluid within the wellhead. U.S. Pat. No. 4,647,050 discloses a stuffing box for a sucker rod pump, and U.S. Pat. No. 5,217,068 discloses another version of a stuffing box for a rotary rod string. U.S. Pat. No. 5,327,961 discloses a drive head for a rotary downhole pump. 
         [0006]    U.S. Pat. No. 5,343,944 discloses a self aligning stuffing box for a pump-jack unit. U.S. Pat. No. 5,567,138 discloses a technique for limiting eccentric deviations of a rotating rod string in a pumping application. U.S. Pat. No. 5,791,411 discloses a wellhead stuffing box for a rotating rod string. U.S. Pat. No. 5,865,245 discloses a stuffing box gland for use with a rod string. U.S. Pat. No. 6,637,509 discloses a wellhead stuffing box support assembly positioned between a production pumping tree and a stuffing box of a wellhead. 
         [0007]    U.S. Pat. No. 6,843,313 discloses a pump drive head with a stuffing box, and U.S. Pat. No. 7,044,217 discloses a stuffing box for a PC pump drive. U.S. Pat. No. 7,055,593 discloses a stuffing box with packing cones for a seal. 
         [0008]    The disadvantages of the prior art are overcome by the present invention, and an improved sealed drive for powering a rotating sucker rod string which drives a downhole progressive cavity pump is hereinafter disclosed. 
       SUMMARY OF THE INVENTION 
       [0009]    In one embodiment, a drive assembly for powering a rotating rod string in a well having a surface wellhead includes a motor having a drive shaft, and a torque conveying housing below the motor and containing a radially outer member supporting a plurality of outer member magnets. A non-magnetic pressure bearing housing includes an upper plate, a radially intermediate member extending downward from the upper plate, and a lower end seal to the wellhead. A radially inner member supporting a plurality of inner member magnets is rotatable within the intermediate member. Magnetic forces between the plurality of outer member magnets and the plurality of inner member magnets rotate the inner member magnets and thus the radially inner member when the motor rotates the outer member. A drive shaft connects the radially inner member and the sucker rod for rotating the sucker rod. 
         [0010]    In another embodiment, the drive assembly for powering a rotating rod string in a well having a surface wellhead includes a torque conveying housing below the motor and containing a radially outer member supporting a plurality of outer member magnets. The radially inner member supporting a plurality of inner member magnets allows magnetic forces between the magnets to rotate the inner member magnets and thus the inner member as the outer member rotates. The radially inner member is rotationally connected to the sucker rod for rotating a sucker rod. A motor within the torque conveying housing rotates the radially outer member, and a pressure bearing housing above the torque conveying housing seals fluid pressure within the wellhead. 
         [0011]    It is a feature of the invention to provide a drive for powering a progressive cavity pump which utilizes static rather than dynamic seals for sealing pressure within the wellhead. A related feature of the invention provide an improved drive for powering a rotating rod string to drive a progressive cavity pump wherein the maintenance required to seal fluid at the wellhead is significantly reduced. 
         [0012]    These and further features and advantages of the present invention will become apparent from the following detailed description, wherein reference is made to the figures in the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]      FIG. 1  is a side view, partially in cross-section, of the components of a drive assembly according to the present invention. 
           [0014]      FIGS. 1A ,  1 B, and  1 C are each enlarged cross-sectional views of a portion of the drive assembly shown in  FIG. 1 . 
           [0015]      FIG. 2  illustrates the coupling between adjacent magnets. 
           [0016]      FIG. 3  illustrates another embodiment of the invention. 
           [0017]      FIG. 4  is a side view, partially in cross-section, illustrating the coupling between the inner and outer magnets. 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0018]      FIG. 1  illustrates one embodiment of a drive between the motor  12  and the upper end of sucker rod  14 . In this case, fluid pressure is blocked from the ambient environment by the non-magnetic pressure bearing housing  16 . A magnet coupling is driven by the motor  12 , which may be either a hydraulic or electric motor. A conventional wellhead  18  thus receives therein the sucker rod  14 , which powers a downhole pump which pumps fluid to the surface through tubing string  20 , which is positioned on hanger  22  within the wellhead. 
         [0019]    Motor  12  is thus concentrically positioned over the wellhead, and drives an outer housing  24  which has an upper shaft end  26 , an upper top plate section  28 , and a sleeve-shaped lower section  30  positioned within the torque conveying housing  32 . The outer housing  24  supports a plurality of circumferentially arranged outer magnets  34 , which are radially outward from the sleeve portion  36  of the pressure bearing housing  16 . The pressure bearing housing  16  includes an upper plate section  38 , a sleeve-shaped portion  36  extending downward from the upper plate  38 , and a lower section  40  secured to torque conveying housing  32 . In this case, the lower section  40  is a flange section, which is sandwiched between a lower surface of the lower flange on the torque conveying housing  32  and the upper surface of support housing  42 , which in turn rests on top of the upper surface of the wellhead  18 . The lower section of the pressure bearing housing  16  is thus sealed to the torque conveying housing and the support housing  42  to prevent fluid from leaking out of the wellhead. 
         [0020]    A coupling drive shaft  44  extends upward from the sucker rod  14 , and includes a spline connection  46  for axial movement of the coupling drive shaft with respect to the upper end of the sucker rod. Mechanisms other than splines may be used for this adjustment purpose. A rotor sleeve  48  as shown in  FIG. 1A  is positioned circumferentially about the coupling drive shaft  44 , and supports a plurality of circumferentially spaced inner magnets  50  thereon. A top bearing  52  and a lower bearing  54  guide rotation of the coupling drive shaft and thus the rotor  48  with respect to the torque conveying housing. Rotation of the outer magnets  34  by the motor  12  thus transmits torque through the non-magnetic pressure bearing housing  16  so as to rotate the inner magnets  50  and thus the rotor  48 , which in turn rotates the coupling drive shaft  44  and the sucker rod  14 . The support housing  42  is sandwiched between the flange  40  of the pressure bearing housing  16  and the upper end of the wellhead  18 , and provides support for the coupling drive shaft  44  and thus support for the sucker rod  14  secured thereto. 
         [0021]    As shown in  FIG. 1C , the flange section  40  of the pressure bearing housing  16  is sealed to the support housing  42  by static seal  82 . Likewise, the support housing  42  is sealed to the wellhead  18  by static seal  84 . Although not needed for pressure containment, the torque conveying housing  32  may be sealed to the flange section  40  of the pressure bearing housing  16  by static seal  86  for mitigation of ingress of debris at the well site. As illustrated in  FIG. 1B , the flanged section within the wellhead  18  is sealed by static seal  88 . 
         [0022]      FIG. 2  illustrates how the inner and outer magnets of the device align themselves.  FIG. 2  further illustrates the non-magnetic pressure bearing housing. Circumferentially spaced inner magnets  50  and the circumferentially spaced outer magnet  34  may thus become aligned, such that rotation of the outer magnets transmits magnetic forces through the non-magnetic pressure bearing housing  16  to the inner magnets, thereby rotating the rotor  48  and thus the drive shaft  44 . The portion  36  of the pressure bearing housing  16  is preferably relatively thin so that the attracting forces of the magnets are maximized.  FIG. 2  further illustrates one or more recovery tubes  52  extending from the wellhead  18 , and/or similar tubes  58  extending from the lower wellhead body  60 , for transferring pumped fluid to a suitable recovery location. 
         [0023]      FIGS. 1 and 2  further illustrate how the motor  12  may be removed to expose the upper end of the outer housing  24 . The torque conveying housing  32  along with the outer housing  24  and the outer magnets  34  may then be removed, thereby exposing the pressure bearing housing  16 . Pressure bearing housing  16  may similarly be removed to expose the rotor  48  and the inner magnets  50 , as well as the upper end of the drive shaft  44 . The significant feature of the invention is that all seals which retain fluid within the drive assembly may be static seals, and in fact may be static seals between the lower flange of the torque conveying housing, the pressure bearing housing, support housing, and the wellhead. The pressure bearing housing  16  may be fabricated from iconel, or any other suitable non-magnetic material. 
         [0024]    Incorporating a magnetic coupling into a PC drive mechanism is certainly feasible with commercially available couplings. Should greater torques be required, one may increase the axial length of the drive assembly, thereby adding more magnets, or increasing the diameter of the drive unit by using larger magnets. 
         [0025]    The present invention essentially eliminates a conventional stuffing box and associated problems. Rather than use a conventional motor/frame that creates a large eccentrically located device on top of the wellhead, the proposed drive assembly offers a lighter motor and drive with its weight centralized above the wellhead. The centralization of the motor/drive over the wellhead will offer much greater safety in handling during installation and maintenance. 
         [0026]    The drive of the present invention may be much lighter than prior art designs. By providing a hydraulic motor, high voltage and high electrical current can be removed from the critical explosion area near the wellhead. No electrical signal or current would have to be transmitted into the pressurized zone of the wellhead. Standard off-the-shelf motors may be adapted to the design, and the pressure is contained with static seals. 
         [0027]      FIG. 3  depicts another version of a drive assembly, which is also centrally located over the wellhead. Again, either a hydraulic or electric motor may be employed. In this design, the pressure bearing zone of the wellhead is incorporated above the motor. 
         [0028]    In the  FIG. 3  embodiment, the sucker rod  14  extends upward through the pressure bearing housing  60  which contains an electric motor  64 , and into the upper pressure bearing housing  62  which contains a sucker rod adjustment device  70 . The sucker rod adjustment adjustment device  70  has ears for rotating the device, thereby axially lowering or raising the sucker rod which is threaded to the device  70 . Upper bearing  68  and a lower bearing  66  centralize the sucker rod within the pressure bearing housing  60  and thus within the electric motor  64  contained in this housing. Torque is transmitted to the sucker rod via the outer sleeve  72  which houses a plurality of circumferentially spaced outer magnets, while the inner sleeve  74  supporting a plurality inner magnets rotates with the rod string  14 . The electric motor  64  thus rotates the outer sleeve  72 , thereby rotating the inner sleeve  74  and thus rotating the sucker rod  14 . Fluid pressure is contained within the pressure bearing housing  60 , but may pass upward through the motor and into the upper pressure bearing housing  62 . 
         [0029]    The sucker rod  14  thus extends through the motor  64 , thereby allowing a region above the motor for placement of the sucker rod height adjustment device  70 . The sucker rod  14  thus extends through the motor  64 , thereby allowing a region above the motor for the placement of a sucker rod height adjustment device  70 . The pressure bearing housing  62  offers a sealing boundary for any pressure inside the wellhead  18 . 
         [0030]    For this embodiment, torque is transmitted from the motor to the sucker rod via a magnetic coupling. The motor is specifically designed with a hollow region along its central axis for accepting the sucker rod, and drives the outer portion of a concentric magnetic coupling. The radially inner portion of the magnetic coupling is mechanically fixed to the sucker rod. In this case, there is no pressure boundary between the coupled sets of magnets, thereby maximizing the efficiency of the magnetic coupling. All seals for this configuration, namely  90 ,  92 ,  94 , and  96 , may be static seals. 
         [0031]      FIG. 4  illustrates the components within the pressure bearing housing  60 . As with the prior embodiment, each of these housings,  72  and  74 , carries a respective plurality of magnets, with the outer housing rotated by the motor  64 , and the inner housing  74  rotated by the cooperative relationship between the inner magnets  75  and outer magnets  76 , thereby rotating the sucker rod string  14 . 
         [0032]    This embodiment also eliminates a conventional stuffing box and its associated problems. The design may be easily centralized with the drive unit and the motor concentrically positioned over the wellhead. Variations of the sucker rod length may be handled by conventional sucker rods adjustment height mechanism. 
         [0033]    Although specific embodiments of the invention have been described herein in some detail, this has been done solely for the purposes of explaining the various aspects of the invention, and is not intended to limit the scope of the invention as defined in the claims which follow. Those skilled in the art will understand that the embodiment shown and described is exemplary, and various other substitutions, alterations and modifications, including but not limited to those design alternatives specifically discussed herein, may be made in the practice of the invention without departing from its scope.