Hydraulic Oilfield Lift Pump

Abstract

A vertically orientated hydraulically driven oilfield lift pump unit having a simplified hydraulic system. The system uses a pair of single acting hydraulic cylinders in tandem with a pair of double acting hydraulic cylinders interacting with hydraulic accumulators to provide an energy efficient, robust hydraulic system design with a minimum number of components.

1 . A vertically orientated reciprocating oil well pumping unit comprising:
 at least one double acting hydraulic cylinder, mechanically coupled to at least one single acting hydraulic cylinder such that they extend and retract simultaneously to operate the pumping unit,   the cap end of the double acting hydraulic cylinder in close-coupled fluid communication with a fluid end of a hydraulic accumulator, the accumulator having a precharge pressure at least exceeding a loading pressure in the cap end of the hydraulic cylinder when it is fully extended in use and under load;   a hydraulic control valve having a first inlet/outlet port in fluid communication with the cap end of the single acting hydraulic cylinder and the valve having a second outlet/inlet port in fluid communication with the rod end of the double acting hydraulic cylinder, whereby,   when the hydraulic control valve is operated to retract the cylinders, hydraulic pressure is applied to the rod end of the double acting hydraulic cylinder forcing it and the coupled single acting hydraulic cylinder to retract simultaneously, thereby causing the fluid from the cap end of the double acting cylinder to flow back into the accumulator, and,   causing the fluid from the cap end of the single acting cylinder to flow back through the return port of the hydraulic control valve into a hydraulic reservoir.   
     
     
         2 . The vertically orientated surface oil well pumping unit of  claim 1  wherein the four-way hydraulic control valve is pressure compensated. 
     
     
         3 . The vertically orientated surface oil well pumping unit of  claim 1  wherein the pumping unit further comprises a pressure compensated hydraulic pump. 
     
     
         4 . The vertically orientated surface oil well pumping unit of  claim 1  wherein the cap end of the double acting hydraulic cylinder and cap end the single acting hydraulic cylinder are mechanically mounted to a common rigid base plate. 
     
     
         5 . The vertically orientated surface oil well pumping unit of  claim 1  wherein the rod ends of the hydraulic cylinders are mounted to a common rigid end plate. 
     
     
         6 . The vertically orientated surface oil well pumping unit of  claim 1  wherein the accumulators are precharged to a pressure sufficient to hold the load in place with the pump not operating. 
     
     
         7 . The vertically orientated surface oil well pumping unit of  claim 1  wherein when the four-way type hydraulic control valve is operated to extend the cylinders, hydraulic pressure is applied to the cap end of the double acting hydraulic cylinder forcing it and the coupled single acting hydraulic cylinder to extend simultaneously, thereby allowing pressurized fluid from the accumulators to flow into cap end of the single acting cylinder thereby assisting in extending the cylinders. 
     
     
         8 . A vertically orientated reciprocating oil well pumping unit comprising:
 at least one double acting hydraulic cylinder, mechanically coupled to at least one single acting hydraulic cylinder such that they extend and retract simultaneously to operate the pumping unit,   a cap end of the double acting hydraulic cylinder in close-coupled fluid communication with a fluid end of a hydraulic accumulator, the accumulator having a precharge pressure at least exceeding a loading pressure in the cap end of the hydraulic cylinder when it is fully extended in use and under load;   whereby, in operation under load, the power required to extend the reciprocating oil well pumping unit is approximately equal to the power required to retract the reciprocating oil well pumping unit.   
     
     
         9 . The vertically orientated surface oil well pumping unit of  claim 8  wherein the four-way type hydraulic control valve is pressure compensated. 
     
     
         10 . The vertically orientated surface oil well pumping unit of  claim 9  wherein the pumping unit further comprises a pressure compensated hydraulic pump. 
     
     
         11 . The vertically orientated surface oil well pumping unit of  claim 10  wherein the cap end of the double acting hydraulic cylinder and cap end the single acting hydraulic cylinder are mechanically mounted to a common rigid base plate. 
     
     
         12 . The vertically orientated surface oil well pumping unit of  claim 11  wherein the rod ends of the hydraulic cylinders are mounted to a common rigid end plate. 
     
     
         13 . The vertically orientated surface oil well pumping unit of  claim 12  wherein the accumulators are precharged to a pressure sufficient to hold the load in place with the pump not operating. 
     
     
         14 . The vertically orientated surface oil well pumping unit of  claim 13  wherein when the four-way type hydraulic control valve is operated to extend the cylinders, hydraulic pressure is applied to the cap end of the double acting hydraulic cylinder forcing it and the coupled single acting hydraulic cylinder to extend simultaneously, thereby allowing pressurized fluid form the accumulators to flow into cap end of the single acting cylinder thereby assisting in extending the cylinders. 
     
     
         15 . The vertically orientated surface oil well pumping unit of  claim 8  wherein a lowering load is 60% to 90% of a raising the load. 
     
     
         16 . The vertically orientated surface oil well pumping unit of  claim 15  wherein the lowering load is 66% of the raising the load. 
     
     
         17 . The vertically orientated surface oil well pumping unit of  claim 15  wherein the lowering load is at least 75 to 86% of the raising the load. 
     
     
         18 . The vertically orientated surface oil well pumping unit of  claim 12  wherein the accumulators are precharged to different pressures, that are nonetheless sufficient to hold the load in place with the pump not operating. 
     
     
         19 . A hydraulic control valve having a first inlet/outlet port in fluid communication with the cap end of a single acting hydraulic cylinder and the valve having a second outlet/inlet port in fluid communication with the rod end of a double acting hydraulic cylinder to operate a reciprocating pump, whereby,
 fluid pressure from a hydraulic pumping unit provides hydraulic fluid under pressure such that when the four-way type hydraulic control valve is operated to retract the cylinders, hydraulic pressure is applied to the rod end of the double acting hydraulic cylinder forcing it and the coupled single acting hydraulic cylinder to retract simultaneously, thereby causing the fluid from the cap end of the double acting cylinder to flow back into the accumulator, and the fluid from the cap end of the single acting cylinder to flow back through the return port of the four-way hydraulic control valve into a hydraulic reservoir.