Lift system

Abstract

A hydraulic lift system comprises a plurality of hydraulic cylinders with pistons therein, having piston rods that are mechanically interconnected so that the pistons and piston rods move upwards and downwards in unison. A hydraulic fluid communication sub-system is operable to deliver fluid from a source of pressurized hydraulic fluid to at least a first cylinder to drive the pistons through an upstroke, from the source of pressurized hydraulic fluid to a second cylinder to drive the pistons through a downstroke, and from the first cylinder to the second cylinder. A hydraulic fluid flow control system selectively directs fluid from the source of pressurized hydraulic fluid either to the first cylinder to drive the pistons upwardly or to the second cylinder to drive the pistons downwardly. During the downstroke, hydraulic fluid flow control system directs hydraulic fluid from the first cylinder to the second cylinder help drive the pistons downwardly.

What is claimed: 
     
         1 . A hydraulic lift system comprising:
 a source of pressurized hydraulic fluid;   a plurality of hydraulic cylinders, each one of said cylinders having a piston therein with a piston rod of said piston extending from an end of each one of said hydraulic cylinders, wherein said piston rods are mechanically interconnected so that said piston rods and said pistons of each of said hydraulic cylinders are operable to move upwards and downwards in unison with each other;   a hydraulic fluid communication sub-system operable to deliver fluid from said source of pressurized hydraulic fluid to at least a first cylinder of said plurality of hydraulic cylinders to drive said pistons in an upward direction through an upstroke; said hydraulic fluid communication sub-system also operable to deliver hydraulic fluid from said source of pressurized hydraulic fluid to a second cylinder of said plurality of hydraulic cylinders to drive said pistons in a downward direction through a downstroke; said hydraulic fluid communication sub-system also operable to deliver hydraulic fluid from said first cylinder to said second cylinder;   a hydraulic fluid flow control sub-system operable to: (a) selectively direct hydraulic fluid from said source of pressurized hydraulic fluid to said first cylinder to drive said pistons in an upward direction to provide an upstroke; and (b) alternatively, selectively direct hydraulic fluid from said source of pressurized hydraulic fluid to said second cylinder to drive said pistons in a downward direction to provide a downstroke; and (c) during said downstroke direct hydraulic fluid from said first cylinder to said second cylinder to assist said second cylinder in driving said pistons in said downward direction during said downstroke.   
     
     
         2 . A system as claimed in  claim 1 , wherein said second cylinder has an upper chamber and a lower chamber separated by a common piston, and wherein said hydraulic fluid is operable to be communicated to said upper chamber to provide a force from above said piston during said downstroke. 
     
     
         3 . A system as claimed in  claim 2  wherein said piston rods both extend from a lower end of their respective cylinders and wherein said piston rods are operable to be interconnected to a reciprocating mass. 
     
     
         4 . A system as claimed in  claim 3  wherein said reciprocating mass comprises a sucker rod operable to be interconnected to a down-well pump in a well. 
     
     
         5 . A system as claimed in  claim 2  further comprising a counterbalance subsystem operable to supply a pressurized counterbalance fluid to said lower chamber of said second cylinder, said counterbalance fluid operable to provide a force from below said piston in said second cylinder during said upstroke and said downstroke, said counterbalance fluid counteracting at least some the gravitational force associated with said reciprocating mass. 
     
     
         6 . A system as claimed in  claim 5 , wherein said counterbalance fluid comprises a pressurized inert gas. 
     
     
         7 . A system as claimed in  claim 6  wherein said gas is nitrogen. 
     
     
         8 . A system as claimed in  claim 6 , wherein said counterbalance system comprises a reservoir operable for storing a supply of said pressurized inert gas. 
     
     
         9 . A system as claimed in  claim 8  wherein said reservoir is in communication with said lower chamber of said second cylinder. 
     
     
         10 . A system as claimed in  claim 5 , wherein said counterbalance sub-system comprises:
 a counterbalance cylinder with a counterbalance piston therein defining a hydraulic fluid chamber containing a hydraulic fluid and a counter balance fluid chamber, containing a pressurized inert gas,   a fluid communication line connecting said hydraulic fluid chamber in fluid communication with said second hydraulic cylinder, such that said pressurized fluid and said counterbalance piston exert pressure on said hydraulic fluid in said hydraulic fluid chamber, urging said piston of said second hydraulic cylinder in an upward direction.   
     
     
         11 . A system as claimed in  claim 5 , wherein a reciprocating mass is interconnected to said piston rods of said first and second cylinders and wherein said system is operable such that said reciprocating mass is driven upwards and downwards by said upstroke and said downstroke of said piston rods of said first and second cylinders, and wherein said counterbalance subsystem is operable to urge said piston of said second hydraulic cylinder upwardly with a force substantially equal to a substantial portion of the gravitational force acting downwards associated with said reciprocating mass. 
     
     
         12 . A system as claimed in  claim 1 , wherein said hydraulic fluid flow control sub-system comprises a three-state valve being operable to selectively direct said hydraulic fluid from said first cylinder to said second cylinder to assist said second hydraulic in driving said pistons in said downward direction during said downstroke. 
     
     
         13 . A system as claimed in  claim 12 , wherein said hydraulic fluid flow control sub-system comprises one or more relief valves. 
     
     
         14 . A system as claimed in  claim 13 , wherein said one or more relief valves comprises at least one hydraulically piloted valve. 
     
     
         15 . A system as claimed in  claim 14 , wherein said one or more relief valves comprises at least one valve that is electrically biased to a closed. 
     
     
         16 . A system as claimed in  claim 1  further comprising a controller operable for controlling the operation of said hydraulic fluid flow control sub-system. 
     
     
         17 . A system as claimed in  claim 16  wherein said source of pressurized hydraulic fluid comprises a pump and further wherein said controller is operable for controlling the operation of said pump. 
     
     
         18 . A system as claimed in  claim 1 , wherein said second cylinder has an upper chamber for receiving said driving fluid such that said second cylinder is operable to drive said piston of said second cylinder downwardly and said at least one first cylinder has a lower chamber for receiving said driving fluid such that said first cylinder is operable to drive said piston of said first cylinder upwardly. 
     
     
         19 . A system as claimed in  claim 1 , wherein:
 said plurality of hydraulic cylinders comprises said first and second cylinders and further comprises a third cylinder;   said hydraulic fluid communication sub-system is operable to deliver fluid from said source of pressurized hydraulic fluid to both said first cylinder and said third cylinders such that said first and third cylinders are operable to drive said pistons in an upward direction through an upstroke; and   said hydraulic fluid flow control sub-system is operable to: (a) selectively direct hydraulic fluid from said source of pressurized hydraulic fluid to said first cylinder and said third cylinder to drive said pistons in an upward direction to provide an upstroke; and (b) alternatively, selectively direct hydraulic fluid from said source of pressurized hydraulic fluid to said second cylinder to drive said pistons in a downward direction to provide a downstroke; and (c) during said downstroke direct hydraulic fluid from said first cylinder and said third cylinder to said second cylinder to assist said second cylinder in driving said pistons in said downward direction during said downstroke.   
     
     
         20 . A system as claimed in  claim 19  wherein said second cylinder is positioned between said first and third cylinders. 
     
     
         21 . A system as claimed in  claim 20  wherein said second cylinder is transversely aligned between said first and third cylinders. 
     
     
         22 . A system as claimed in  claim 21 , wherein said second cylinder has an upper chamber for receiving said driving fluid for driving said piston of said second cylinder downwardly. 
     
     
         23 . A system as claimed in  claim 22 , wherein each of said first and third cylinders has a lower chamber for receiving said driving fluid for driving said pistons of said first cylinder and third cylinders upwardly. 
     
     
         24 . A system as claimed in  claim 18  wherein a cross-sectional area of said upper chamber in said second cylinder is approximately double the cross-sectional areas of said lower chamber in each of said first and third cylinders. 
     
     
         25 . A system as claimed in  claim 1 , wherein said piston rods are interconnected to a sucker rod of a well pump, and wherein said system is operable to operate said well pump in a shaft of a well. 
     
     
         26 . A system as claimed in  claim 21 , wherein said piston rods are interconnected to a sucker rod of a well pump, and wherein said system is operable to operate said well pump in a shaft of a well. 
     
     
         27 . A system as claimed in  claim 26 , wherein said second cylinder is axially aligned with said sucker rod and wherein said first and third cylinders are transversely spaced a substantially equal distance on either side of said second cylinder whereby rotational forces acting on said sucker rod can be substantially eliminated. 
     
     
         28 . A system as claimed in  claim 27  wherein said piston rods of each of said first, second and third cylinders are interconnected to a common carriage and said common carriage is interconnected to said sucker rod. 
     
     
         29 . A system as claimed in  claim 1  wherein said hydraulic fluid flow control sub-system comprises a plurality of valve devices interposed between said plurality of cylinders and said source of pressurized hydraulic fluid. 
     
     
         30 . A system as claimed in  claim 29  wherein plurality of valve devices comprises at least one electronically operated valve device. 
     
     
         31 . A system as claimed in  claim 30  further comprising a controller, and wherein said controller is operable to control said at least one electronically operated valve device. 
     
     
         32 . A system as claimed in  claim 1  further comprising a controller operable to control at least a component of said hydraulic flow control sub-system. 
     
     
         33 . A system as claimed in  claim 1  further comprising a reservoir for said hydraulic fluid, said reservoir being in fluid communication with said hydraulic fluid communication sub-system, such that hydraulic fluid may be communicated to said reservoir. 
     
     
         34 . A system as claimed in  claim 33  wherein said hydraulic flow control sub-system is operable to direct the flow of hydraulic fluid to said reservoir from said second cylinder during said downstroke. 
     
     
         35 . A system as claimed in  claim 32  further comprising a reservoir for said hydraulic fluid, said reservoir being in fluid communication with said hydraulic fluid communication sub-system, such that hydraulic fluid may be communicated to said reservoir. 
     
     
         36 . A system as claimed in  claim 35  further comprising a controller operable to control at least a component of said hydraulic flow control sub-system, and wherein said controller is operable to control the flow of hydraulic fluid to said reservoir from said second cylinder during said downstroke. 
     
     
         37 . A method of reciprocating a down-well pump in a shaft of a well, said method comprising:
 a) pumping a pressurized fluid into a lift chamber of a first hydraulic cylinder to lift a carriage coupled to said down-well pump and to a piston of said first hydraulic cylinder;   b) pumping a pressurized fluid into a lowering chamber of a second hydraulic cylinder having a piston coupled to said carriage, to lower said carriage;   c) connecting said lift chamber in fluid communication with said lowering chamber such that pressurized fluid is expelled from said lift chamber into said lowering chamber during said lowering.   
     
     
         38 . A method as claimed in  claim 37 , said method further comprising:
 urging said piston of said second hydraulic cylinder in an upward direction using an inert gas counterbalance cylinder to offset at least a portion of the weight of said carriage, said down-well pump and masses reciprocated therewith.   
     
     
         39 . A lift system comprising
 a pump for supplying a flow of pressurized driving fluid;   at least one upward driving cylinder having a movable piston rod;   at least one downward driving cylinder having a movable piston rod; said piston rods of said upward driving cylinder and said downward driving cylinder being interconnected to each other such that said piston rods of both said upward driving cylinder and said downward driving cylinder are operable to move upwards and downwards in unison with each other;   a driving fluid communication sub-system operable to deliver a flow of driving fluid supplied by said pump from said pump to said upward driving cylinder to drive said piston rods in an upward direction in an upstroke;   said driving fluid communication sub-system also operable to deliver a flow of driving fluid supplied by said pump from said pump to said downward driving cylinder to drive said piston rods in a downward direction in a downstroke; and said driving fluid communication sub-system also operable to deliver a flow of driving fluid in said upward driving cylinder from said upward driving cylinder to said downward driving cylinder during said downstroke;   a fluid direction control sub-system operable to: (a) in a first mode of operation to direct a flow of driving fluid from said pump to said upward driving cylinder to drive said pistons in an upward direction to create an upstroke; (b) in a second mode of operation to direct a flow of driving fluid from said pump to said downward driving cylinder to drive said pistons in a downward direction to create a downstroke; and (c) in said second mode of operation, to also direct a flow of driving fluid from said upward driving cylinder to said downward driving cylinder during said downstroke, such that during said downstroke, said driving fluid is delivered from said upward driving cylinder to/towards said downward driving cylinder to assist said downward driving cylinder in driving said pistons in said downward direction during said downstroke.   
     
     
         40 . A method of moving a reciprocating mass upwards and downwards, said method comprising
 a) providing a pump for supplying a flow of pressurized driving fluid;   b) providing at least one upward driving cylinder having a movable piston rod interconnected to said reciprocating mass;   c) providing at least one downward driving cylinder having a movable piston rod interconnected to said reciprocating mass; said piston rods of said upward driving cylinder and said downward driving cylinder being interconnected to each other such that said piston rods of both said upward driving cylinder and said downward driving cylinder are operable to move upwards and downwards in unison with each other;   d) providing a driving fluid communication sub-system for delivering a flow of driving fluid supplied by said pump from said pump to said upward driving cylinder to drive said piston rods in an upward direction in an upstroke and for delivering a flow of driving fluid supplied by said pump from said pump to said downward driving cylinder to drive said piston rods in a downward direction in a downstroke, said driving fluid communication sub-system also for delivering a flow of driving fluid in said upward driving cylinder from said upward driving cylinder towards said downward driving cylinder during said downstroke;   e) providing a fluid direction control sub-system;   f) directing a flow of driving fluid from said pump to said upward driving cylinder to drive said pistons in an upward direction to create an upstroke to thereby move said reciprocating mass upwards;   g) directing a flow of driving fluid from said pump to said downward driving cylinder to drive said pistons in a downward direction to create a downstroke; and simultaneously also directing a flow of driving fluid from said upward driving cylinder to said downward driving cylinder during said downstroke, such that during said downstroke, said driving fluid is delivered from said upward driving cylinder to said downward driving cylinder to assist said downward driving cylinder in driving said pistons in said downward direction during said downstroke, to thereby move said reciprocating mass downwards.   
     
     
         41 . A method of operating a lift system, wherein lift system comprises:
 a pump for supplying a flow of pressurized driving fluid;   at least one upward driving cylinder having a movable piston rod:   at least one downward driving cylinder having a movable piston rod; said piston rods of said upward driving cylinder and said downward driving cylinder being interconnected to each other such that said piston rods of both said upward driving cylinder and said downward driving cylinder are operable to move upwards and downwards in unison with each other;   a driving fluid communication sub-system for delivering a flow of driving fluid supplied by said pump from said pump to said upward driving cylinder to drive said piston rods in an upward direction in an upstroke and for delivering a flow of driving fluid supplied by said pump from said pump to said downward driving cylinder to drive said piston rods in a downward direction in a downstroke, said driving fluid communication sub-system also for delivering a flow of driving fluid in said upward driving cylinder from said upward driving cylinder towards said downward driving cylinder during said downstroke;   a fluid direction control sub-system operable to: (a) in a first mode of operation to direct a flow of driving fluid from said pump to said upward driving cylinder to drive said pistons in an upward direction to create an upstroke; (b) in a second mode of operation to direct a flow of driving fluid from said pump to said downward driving cylinder to drive said pistons in a downward direction to create a downstroke; and (c) in said second mode of operation, to also direct a flow of driving fluid from said upward driving cylinder to said downward driving cylinder during said downstroke;   and wherein said method comprises:   a) directing a flow of driving fluid from said pump to said upward driving cylinder to drive said pistons in an upward direction to create an upstroke;   b) directing a flow of driving fluid from said pump to said downward driving cylinder to drive said pistons in a downward direction to create a downstroke; and simultaneously also directing a flow of driving fluid from said upward driving cylinder to said downward driving cylinder during said downstroke, such that during said downstroke, said driving fluid is delivered from said upward driving cylinder to said downward driving cylinder to assist said downward driving cylinder in driving said pistons in said downward direction during said downstroke.