Wellhead drive brake system

Abstract

The present invention provides in one aspect a braking mechanism for slowing the release of torsional potential energy in a rod string of a wellhead drive system on the shutdown or power failure thereof. The braking mechanism, without using a slip clutch, slows the backspin of the rod string by using the rotational energy of the rod string to turn a fluid pump to pump fluid through a constriction orifice in a closed fluid circuit. The present invention reduces the space required for the braking mechanism and moreover reduces the number of moving parts within the braking mechanism which may reduce the likelihood that the braking mechanism will require maintenance or fail, as well as reduce the manufacturing cost. In another aspect, the present invention provides a wellhead drive system for driving a rotary downhole pump which includes the inventive braking mechanism described above.

1 . For use with a pumping system in which a downhole pump has a rotor which is rotated by a rod string which is in turn rotated by a motor, a braking mechanism for slowing the release of torsional potential energy in the rod string when the motor stops, the mechanism comprising: 
 a rotary member rotationally coupled to the top end of the rod string;    a reservoir containing a dampening fluid;    a fluid pump driven by the rotary member, interposed into a closed fluid circuit with the reservoir, the fluid circuit comprising:    a one-way valve allowing dampening fluid to flow between the reservoir and the fluid pump in a first direction corresponding to normal operation of the downhole pump, the one-way valve including a valve orifice having a valve orifice area that does not substantially restrict the free flow of the dampening fluid during normal operation of the downhole pump; and    a constriction orifice allowing the dampening fluid to flow between the reservoir and the fluid pump in a direction opposite to the first direction, the constriction orifice having an orifice area which substantially restricts the flow of the dampening fluid through the fluid circuit as potential torsional energy is released from the rod string;    whereby if the motor stops the potential torsional energy in the rod string is dissipated by controlled rotation of the rod string in a direction opposite to the first direction.    
   
   
       2 . A wellhead drive system for driving a downhole pump including a rotor comprising: 
 a rod string having a top end and a bottom end, the bottom end being connected to, supporting and rotating the rotor;    a motor providing torque energy for rotating the top end, whereby torsional potential energy is stored in the rod string during operation; and    a braking mechanism for slowing the release of torsional potential energy in the rod string when the motor stops, the mechanism comprising:    a rotary member rotationally coupled to the top end of the rod string;    a reservoir containing a dampening fluid;    a fluid pump driven by the rotary member, interposed into a closed fluid circuit with the reservoir, the fluid circuit comprising:    a one-way valve allowing dampening fluid to flow between the reservoir and the fluid pump in a first direction corresponding to normal operation of the downhole pump, the one-way valve including a valve orifice having a valve orifice area that does not substantially restrict the free flow of the dampening fluid during normal operation of the downhole pump; and    a constriction orifice allowing the dampening fluid to flow between the reservoir and the fluid pump in a direction opposite to the first direction, the constriction orifice having an orifice area which substantially restricts the flow of the dampening fluid through the fluid circuit as potential torsional energy is released from the rod string;    whereby if the motor stops the potential torsional energy in the rod string is dissipated by controlled rotation of the rod string in a direction opposite to the first direction.