Rod-pumping system

Abstract

A rod-pumping system is provided. In one embodiment, the system includes a downhole pump positioned in a well and coupled to a well string, such as a sucker-rod string. The system also includes a first hydraulic actuator arranged with respect to the well string so as to enable the first hydraulic actuator to move the well string within the well. The first hydraulic actuator is connected in fluid communication with a second hydraulic actuator. A control pump is connected to both the first and second hydraulic actuators to enable the control pump to alternate between pumping control fluid to the first hydraulic actuator to cause the well string to move in a first direction within the well and pumping control fluid to the second hydraulic actuator to cause the well string to move in an opposite, second direction within the well. Additional systems, devices, and methods are also disclosed.

1 . A rod-pumping system comprising:
 a downhole pump positioned in a well;   a well string coupled to the downhole pump;   a first hydraulic actuator arranged with the well string so as to enable the first hydraulic actuator to move the well string within the well;   a second hydraulic actuator connected in fluid communication with the first hydraulic actuator; and   a control pump connected to the first hydraulic actuator and to the second hydraulic actuator in a manner that enables the control pump, during operation, to alternate between pumping control fluid to the first hydraulic actuator to cause the well string to move in a first direction within the well and pumping control fluid to the second hydraulic actuator to cause the well string to move in an opposite, second direction within the well.   
     
     
         2 . The rod-pumping system of  claim 1 , wherein the control pump is connected to a rod end of the first hydraulic actuator. 
     
     
         3 . The rod-pumping system of  claim 1 , wherein the second hydraulic actuator is connected to at least one accumulator set to counterbalance the full load of the first hydraulic actuator. 
     
     
         4 . The rod-pumping system of  claim 3 , wherein the connection of the control pump to the first and second hydraulic actuators enables the control pump to offset hydraulic balance between the first and second hydraulic actuators. 
     
     
         5 . The rod-pumping system of  claim 1 , comprising sensors to facilitate detection of piston positions in the first and second hydraulic actuators. 
     
     
         6 . The rod-pumping system of  claim 5 , wherein the sensors include proximity switches that facilitate detection of the position of a piston of the first hydraulic actuator and a linear transducer that facilitates detection of the position of a piston of the second hydraulic actuator. 
     
     
         7 . The rod-pumping system of  claim 5 , comprising a controller configured to receive input from the sensors that facilitate detection of the piston positions and to synchronize the first and second hydraulic cylinders. 
     
     
         8 . The rod-pumping system of  claim 1 , comprising an auxiliary pump that enables the introduction of fresh control fluid to a hydraulic circuit that includes the first hydraulic actuator and the second hydraulic actuator. 
     
     
         9 . The rod-pumping system of  claim 1 , wherein the first hydraulic actuator is a double-acting hydraulic cylinder. 
     
     
         10 . The rod-pumping system of  claim 1 , wherein the first hydraulic actuator is coupled to a wellhead installed at the well. 
     
     
         11 . The rod-pumping system of  claim 1 , wherein the well string includes a sucker-rod string that is coupled to a rod clamp that engages the first hydraulic actuator. 
     
     
         12 . A rod-pumping system comprising:
 a slave cylinder mounted on or adjacent to wellhead equipment installed at a well;   a master cylinder connected in fluid communication with the slave cylinder, wherein the master cylinder is counterbalanced with fluid from at least one accumulator and is able to absorb the full load of the slave cylinder; and   a closed-loop hydraulic circuit including a pump connected in fluid communication with the slave cylinder and with the master cylinder to enable the pump to drive a piston in the slave cylinder and a piston in the master cylinder to reciprocate a well string within the well.   
     
     
         13 . The rod-pumping system of  claim 12 , comprising an additional pump that enables hydraulic fluid to be pumped into the closed-loop hydraulic circuit to replace used hydraulic fluid flushed from the closed-loop hydraulic circuit. 
     
     
         14 . The rod-pumping system of  claim 13 , comprising a prime mover coupled to drive both the pump and the additional pump. 
     
     
         15 . The rod-pumping system of  claim 12 , comprising:
 position sensors on the slave cylinder and the master cylinder; and   a controller configured to synchronize the slave cylinder and the master cylinder based on input from the position sensors.   
     
     
         16 . The rod-pumping system of  claim 12 , comprising a downhole pump coupled to the well string. 
     
     
         17 . A method comprising:
 lowering a well string that is positioned in a well and is coupled to a downhole pump within the well by pumping control fluid to a first linear actuator; and   raising the well string by pumping control fluid to a second linear actuator that is connected to the first linear actuator.   
     
     
         18 . The method of  claim 17 , wherein pumping control fluid to the first linear actuator includes pumping control fluid to a rod end of the first linear actuator. 
     
     
         19 . The method of  claim 17 , comprising:
 determining the positions of pistons within the first linear actuator and the second linear actuator; and   synchronizing the first linear actuator and the second linear actuator based on the determined positions of the pistons.   
     
     
         20 . The method of  claim 17 , comprising alternating flow of control fluid between the first linear actuator and the second linear actuator by reversing flow of a bidirectional pump connected to the first linear actuator and the second linear actuator. 
     
     
         21 . The method of  claim 17 , comprising:
 continually flushing control fluid from a hydraulic or pneumatic circuit including the first and second linear actuators and replacing the flushed control fluid with fresh control fluid during operation of the first and second linear actuators; and   maintaining synchronization between the first and second linear actuators during operation.