Hydraulic oil well pumping system, and method for pumping hydrocarbon fluids from a wellbore

Abstract

A hydraulic oil well pumping system is provided. The system uses a pump to exert hydraulic pressure against a reciprocating piston over a wellbore. The piston is connected to a rod string and downhole pump for pumping oil from a wellbore. The system includes an electronic control system that controls movement of the piston as it moves between the upper and lower rod positions by cycling the hydraulic system between (i) an “upstroke” condition wherein the pump is pumping oil through the oil line into the hydraulic cylinder to move the piston to its upper rod position, and (ii) a “neutral” condition wherein the pump is no longer pumping oil into the hydraulic cylinder, but is allowing oil to flow back through the oil line in response to gravitational fall of the piston. The control system is programmed to cycle based upon a volumetric calculation of hydraulic oil in the cylinder without reference to position sensors along the wellhead. Wellhead conditions or placement of the hydraulic cylinder inside the wellbore may prohibit attaching physical sensors at the wellhead. A method for pumping oil from a wellbore using such a system is also provided herein.

I claim: 
     
         1 . A hydraulic oil well pumping system, comprising:
 an elongated hydraulic cylinder;   a piston that is movable between upper and lower rod positions within the cylinder;   a rod string that is mechanically connected to and that extends downwardly from the piston, the rod string being configured to extend into a wellbore for pumping oil from the wellbore;   a prime mover;   a hydraulic pump that is powered by the prime mover;   a control valve that moves between upstroke and downstroke flow positions;   an oil line connecting the pump and the hydraulic cylinder, the directional control valve being positioned in the oil line so that it can direct flow between the pump and the cylinder;   a fluid reservoir for containing hydraulic fluid to be supplied to the pump;   a reservoir line that transmits hydraulic fluid from the cylinder to the reservoir;   an electronic control system that controls movement of the piston as it moves between the upper and lower rod positions by cycling the valve between (i) an “upstroke” condition wherein the pump is pumping fluid through the oil line and into the hydraulic cylinder to move the piston to its upper rod position, and (ii) a “neutral” condition wherein the pump is no longer pumping fluid into the hydraulic cylinder, but is allowing hydraulic fluid to flow back through the oil line in response to gravitational fall of the piston; and   wherein the electronic control system is programmed to cycle based upon a volumetric calculation of hydraulic fluid in the cylinder without reference to position sensors along the wellhead.   
     
     
         2 . The hydraulic oil well pumping system of  claim 1 , wherein the pump is a hydraulic pump. 
     
     
         3 . The hydraulic oil well pumping system of  claim 1 , wherein the hydraulic fluid is a refined oil or an aqueous fluid. 
     
     
         4 . The hydraulic oil well pumping system of  claim 3 , wherein:
 the system further comprises a filter placed along the reservoir line to filter the hydraulic fluid in the reservoir.   
     
     
         5 . The hydraulic oil well pumping system of  claim 1 , wherein:
 the prime mover is an electric motor or an internal combustion engine; and   the rod string is mechanically connected to the piston through a polished rod.   
     
     
         6 . The hydraulic oil well pumping system of  claim 1 , further comprising:
 a dual-chambered tank comprising an upper chamber, and a lower chamber immediately below the upper chamber, wherein the directional control valve and the downstroke control valve reside in the upper chamber and the fluid reservoir resides in the lower chamber.   
     
     
         7 . The hydraulic oil well pumping system of  claim 1 , wherein the electronic control system controls movement of the piston based on (i) at least one of volume and rate of hydraulic fluid sent to the cylinder during the “upstroke” valve condition, (ii) at least one of volume and rate of fluid returned from the cylinder during the “neutral” valve condition, or (iii) both. 
     
     
         8 . The hydraulic oil well pumping system of  claim 7 , wherein the electronic control system sends a signal to cause the pump to vary its output, to cause a valve to adjust its proportional flow, or to change an operating speed of the prime mover based upon either (i) one or more of a relative volume and rate of fluid that has moved into the hydraulic cylinder, or (ii) an absolute volume of fluid that has moved into the hydraulic cylinder, during the “upstroke” valve condition. 
     
     
         9 . The hydraulic oil well pumping system of  claim 1 , wherein the electronic control system sends a signal to cause the directional control valve to change flow paths of the hydraulic fluid and to initiate a down stroke of the piston rod based upon (i) one or more of a relative measurement of a volume and rate of fluid that has moved into the hydraulic cylinder, or (ii) an absolute volume of fluid that has moved into the hydraulic cylinder, during the “upstroke” valve condition. 
     
     
         10 . The hydraulic oil well pumping system of  claim 1 , further comprising:
 a downstroke control valve that chokes the flow of hydraulic fluid from the cylinder back to the reservoir to limit the rate of flow of hydraulic fluid.   
     
     
         11 . A method of pumping oil from a wellbore, the wellbore having a bore extending into an earth surface, and the method comprising:
 providing an elongated hydraulic cylinder;   providing a piston that is movable between upper and lower rod positions within the cylinder;   mechanically connecting the piston to a rod string such that the rod string extends downwardly from the piston and into an oil well;   providing a hydraulic pump that is powered by a prime mover;   connecting the pump and the hydraulic cylinder with an oil line that transmits hydraulic fluid from the pump to the cylinder;   providing a control valve that moves between upstroke and downstroke flow positions;   providing a fluid reservoir for containing hydraulic fluid to be supplied to the pump;   providing a reservoir line that transmits hydraulic fluid from the cylinder to the reservoir;   using an electronic control system, controlling movement of the piston as it moves between the upper and lower rod positions by cycling the pump between (i) an “upstroke” condition wherein the pump is pumping hydraulic fluid through the directional control valve, through the oil line and into the hydraulic cylinder to move the piston to its upper rod position, and (ii) a “neutral” condition wherein the pump is no longer pumping hydraulic fluid into the hydraulic cylinder, but is allowing fluid to flow back through the oil line and through the down stroke control valve in response to gravitational fall of the rod string;   reciprocating the piston and mechanically connected rod string in order to pump fluid from the wellbore; and   wherein the electronic control system is programmed to cycle based upon a volumetric calculation of hydraulic oil in the cylinder without reference to position sensors along the wellhead.   
     
     
         12 . The method of  claim 11 , wherein the pump is a hydraulic pump. 
     
     
         13 . The method of  claim 11 , the hydraulic fluid is a refined oil or an aqueous fluid. 
     
     
         14 . The method of  claim 11 , further comprising:
 providing a filter along the reservoir line to filter the hydraulic fluid in the reservoir.   
     
     
         15 . The method of  claim 11 , wherein:
 the prime mover is an electric motor or an internal combustion engine; and   the rod string is mechanically connected to the piston through a polished rod.   
     
     
         16 . The method of  claim 11 , the electronic control system controls movement of the piston (i) based on at least one of volume and rate of hydraulic fluid sent to the hydraulic cylinder during the “upstroke” valve condition, (ii) based on at least one of volume and rate of fluid returned from the hydraulic cylinder during the “neutral” valve condition, or (iii) both. 
     
     
         17 . The method of  claim 16 , wherein the measurement of at least one of fluid volume and rate is based upon (i) pressure differential upstream versus downstream of a fixed orifice placed along the oil line, (ii) a flow meter, (iii) a fluid level in the reservoir, or (iv) a combination thereof. 
     
     
         18 . The method of  claim 11 , wherein controlling the movement of the piston comprises sending a signal from the electronic control system to cause the pump to vary its output, to cause a valve to adjust its proportional flow, or to change an operating speed of the prime mover based upon either (i) one or more of a relative volume and rate of fluid that has moved into the hydraulic cylinder, or (ii) an absolute volume of volume of fluid that has moved into the hydraulic cylinder, during the “upstroke” valve condition. 
     
     
         19 . The method of  claim 11 , wherein controlling the movement of the piston comprises sending a signal from the electronic control system to cause the valve to redirect flow and to initiate a down stroke of the piston rod based upon (i) one or more of a relative measurement of a volume and rate of fluid that has moved into the hydraulic cylinder, or (ii) an absolute measured volume of fluid that has moved into the hydraulic cylinder, during the “upstroke” valve condition. 
     
     
         20 . The method of  claim 11 , wherein the control system generates an electrical signal that alters the flow path of the hydraulic fluid during the “upstroke” condition and again alters the hydraulic flow path of the hydraulic fluid during the “neutral” condition. 
     
     
         21 . The method of  claim 11 , further comprising:
 providing a down stroke control valve that chokes the flow of fluid from the cylinder back to the reservoir to limit the rate of flow of hydraulic fluid.   
     
     
         22 . A method of determining location of a hydraulically actuated piston within a cylinder disposed over a wellbore, comprising:
 determining a volume of hydraulic fluid needed to fill a hydraulic cylinder during a piston upstroke;   measuring a dynamic rate for filling the cylinder during the upstroke using a pump and an oil line providing fluid communication between the pump and the cylinder;   based upon the determined volume and rate, determining a first time for filling the cylinder during the upstroke;   determining a second time for draining the fluid from the cylinder through a down-stroke control valve, the down stroke control valve having a sized orifice for reducing a rate at which the piston falls during draining;   using an electronic control system, controlling movement of the piston as it reciprocates between upper and lower rod positions by cycling the valve between (i) an “upstroke” condition wherein the pump is pumping oil through the directional control valve, through the oil line and into the hydraulic cylinder to move the piston to its upper rod position over the first time, and (ii) a “neutral” condition wherein the pump is no longer pumping oil into the hydraulic cylinder, but is allowing oil to flow back through the oil line and through the down stroke speed control valve in response to gravitational fall of the piston during the second time, wherein the cycling is performed without reference to position sensors along the wellhead;   monitoring hydraulic fluid pressure in the oil line during the first time and the second time; and   reciprocating the piston and mechanically connected rod string in order to pump oil from the wellbore.   
     
     
         23 . The method of  claim 22 , further comprising:
 determining a position of the piston during the upstroke based upon (i) one or more of a relative volume and rate of hydraulic fluid injected by the pump during the “upstroke” condition, (ii) the absolute volume of fluid injected by the pump during the “upstroke” condition, or (iii) the ratio of a pressure reading in the oil line to a baseline pressure representing a pressure value just before the piston has reached a mechanical top of its upstroke.   
     
     
         24 . The method of  claim 22 , further comprising:
 sending a signal from the electronic control system to cause the pump vary its output, to cause a valve to adjust its proportional flow, or to change an operating speed of the prime mover based upon the location of the piston during its upstroke.   
     
     
         25 . The method of  claim 22 , further comprising:
 calculating a position of the piston during the down stroke based upon (i) one or more of a relative volume and rate of hydraulic fluid drained from the hydraulic cylinder during the “neutral” condition, (ii) the absolute volume of hydraulic fluid drained from the hydraulic cylinder during the “neutral” condition, or (iii) when the pressure reading in the oil line has reached a value of substantially 0, indicating a mechanical bottom of the piston's down stroke.   
     
     
         26 . The method of  claim 25 , further comprising:
 sending a signal from the electronic control system to cause the pump to vary its output, to cause a valve to adjust its proportional flow, or to change an operating speed of the prime mover based upon the location of the piston during its down stroke.   
     
     
         27 . A dynamometer card for a hydraulically actuated rod pumping system having a piston, a rod string that moves with the piston, a hydraulic pump, and a cylinder dimensioned to contain hydraulic fluid, the dynamometer card comprising:
 an “x”-axis representing a piston position within the cylinder; and   a “y”-axis representing fluid load applied on a downhole pump during a pumping cycle; and   wherein the piston position is calculated based on (i) one or more of a relative measurement of a volume and rate of fluid that has moved to and from the cylinder, or (ii) an absolute measured volume of fluid that has moved to and from the cylinder, and without reference to a position sensor located at least one of at and near a wellhead.   
     
     
         28 . The dynamometer card of  claim 27 , wherein the hydraulically actuated rod pumping system further comprises:
 a directional control valve that moves between upstroke and downstroke flow positions;   an oil line connecting the pump and the hydraulic cylinder, the directional control valve being positioned in the oil line so that it can direct flow between the pump and the cylinder;   a fluid reservoir for containing hydraulic fluid to be supplied to the pump;   a reservoir line that transmits hydraulic fluid from the cylinder to the reservoir;   a down stroke control valve that chokes the flow of hydraulic fluid from the cylinder back to the reservoir to limit the rate of flow of hydraulic fluid; and   an electronic control system that controls movement of the piston as it moves between upper and lower rod positions by cycling the valve between (i) an “upstroke” condition wherein the pump is pumping fluid through the oil line and into the hydraulic cylinder to move the piston to its upper rod position, and (ii) a “neutral” condition wherein the pump is no longer pumping fluid into the hydraulic cylinder, but is allowing hydraulic fluid to flow back through the oil line in response to gravitational fall of the piston.   
     
     
         29 . The dynamometer card of  claim 27 , wherein the fluid load is calculated using hydraulic pressure and effective cylinder area.