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

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.

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.

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.