Pump control device, oil well with device and method

Abstract

A method of operating an oil well comprises applying through a regenerative variable frequency drive AC electrical energy from a power grid to an AC electric motor to operate a drive mechanism of an oil well pump. The motor speed is regulated in a manner to optimize fluid production and maximize the operational life of the drive mechanism, decreasing motor speed by transferring the electrical energy to the power grid and increasing motor speed by transferring the electrical energy from the power grid to the motor. The drive mechanism has a predetermined stroke cycle and, over the course of each stroke cycle, the motor is operated at different regulated speeds initiated when the drive mechanism is at a predetermined position.

1 . An oil well including
 a pumping unit having a drive mechanism operably connected to an AC electric motor powered by AC electrical energy from a power grid, and   a regenerative variable frequency AC drive that controls the AC electrical energy in the motor to decrease motor speed by transferring the electrical energy to the power grid and to increase motor speed by transferring the electrical energy from the power grid to the motor,   said variable frequency AC drive regulating the motor speed in a manner to optimize fluid production and maximize the operational life of the drive mechanism.   
     
     
         2 . The oil well of  claim 1  where the AC drive is programmed to regulate the instantaneous speed of the motor based on a calculated position of the drive mechanism that is a mathematical function including an estimated speed from a motor controller. 
     
     
         3 . The oil well of  claim 1  where the AC drive is programmed to regulate the instantaneous speed of the motor based on a calculated position of the drive mechanism that is a mathematical function including a measured number of motor revolutions. 
     
     
         4 . The oil well of  claim 1  where the drive mechanism includes a rod moving along a predetermined path of travel and the AC drive is programmed to regulate the instantaneous speed of the motor based on a calculated position of the rod that is a mathematical function including an estimated speed from a motor controller. 
     
     
         5 . The oil well of  claim 1  where the drive mechanism includes a rod moving along a predetermined path of travel and the AC drive is programmed to regulate the instantaneous speed of the motor based on a calculated position of the rod that is a mathematical function including a measured number of motor revolutions. 
     
     
         6 . The oil well of  claim 1  including a well manager that controls the operation of the well and provides a speed reference signal for establishing how many strokes per minute are to be executed by the drive mechanism, the instantaneous speed of the motor being based on the position of the drive mechanism during each stroke cycle. 
     
     
         7 . The oil well of  claim 6  where the position of the drive mechanism for each increment of degree of a 360 degree stroke cycle is established by a calculation, said calculated position determining the instantaneous speed at each degree increment of each stroke cycle so that the real-time speed at each position of each stroke is controlled. 
     
     
         8 . The oil well of  claim 6  where the position of the drive mechanism for each increment of degree of a 360 degree stroke cycle is established by a measured position of the drive mechanism, said measured position determining the instantaneous speed at each degree increment of each stroke cycle so that the real-time speed of the drive mechanism at each position of each stroke is controlled. 
     
     
         9 . An oil well including
 a pump having a drive mechanism operably connected to an AC electric motor powered by AC electrical energy from a power grid, and   a regenerative variable frequency AC drive that controls the AC electrical energy in the motor to decrease motor speed by transferring the electrical energy to the power grid and to increase motor speed by transferring the electrical energy from the power grid to the motor,   said variable frequency AC drive regulating the motor speed in a manner to optimize fluid production and maximize the operational life of the drive mechanism, being programmed to regulate the instantaneous speed of the motor based on position of the drive mechanism, and   a well manager that controls the operation of the well and provides a speed reference signal for establishing how many strokes per minute are to be executed by the drive mechanism, the instantaneous speed of the motor being based on the position of the drive mechanism during each such stroke cycle,   where for each stroke cycle the number of revolutions of the motor is fixed based on individual characteristics of the pump and drive mechanism,   said oil well including control means programmed during initial start-up of the variable frequency AC drive so that said fixed number of motor revolutions correlates to a single stroke of the pump and drive mechanism scaled to 360°.   
     
     
         10 . In an oil well where a drive mechanism for a pump is driven by an AC electric motor to move the pump's rod through a predetermined stroke cycle and a signal generator provides a signal when the rod is at a predetermined position in the stroke cycle,
 an improvement wherein AC electricity from a power grid is transferred to the motor under the control of a regenerative variable frequency AC drive that regulates the instantaneous velocity of the motor over the course of each stroke cycle, the operational control of the AC drive being determined by rod position and said signal, said AC drive programmed to decrease motor speed by transferring electrical energy to the power grid and to increase motor speed by transferring electrical energy from the power grid to the motor.   
     
     
         11 . The oil well of  claim 10  where the instantaneous velocity of the motor is regulated over the course of each stroke cycle, increasing and decreasing the motor speed to maximize fluid production and minimize tension in the rod on the upstroke and maximize tension in the rod on the downstroke. 
     
     
         12 . The oil well of  claim 10  where the variable frequency drive is controlled by a microprocessor that calculates drive chain position as it applies to a long-stroke pumping units, crank (gear box output) position as it applies to a beam pumping units throughout the entire stroke cycle according to the equation
     X=K∫   0   T     o     Vdt    
 where
 X=drive chain position for long-stroke units; crank position for beam pump units based on percent of cycle (0 to 100%) 
 V=motor speed (instantaneous revolutions per minute (rpm) 
 K=scaling constant, 
 T o =time at which “end of stroke” signal is received. 
 
 
     
     
         13 . An oil well comprising
 a pumping unit including a rod extending below ground level into an oil well formation,   an AC electrical motor that moves the rod through a stroke cycle having an upstroke and a downstroke, said motor being operably connected to the rod through a drive mechanism that operably connects the motor to the rod and rotates a drive shaft of the motor through a known number of revolutions with each stroke cycle,   a first sensor that provides an end of stroke signal each time the rod is at an end of the downstroke during each stroke cycle of the rod,   an AC drive that provides electrical energy from an AC power grid to the motor, said AC drive being capable of decreasing motor speed by transferring electrical energy to the power grid and increasing motor speed by transferring electrical energy from the power grid to the motor,   a well manager control unit that controls the operation of the oil well in response to conditions of the oil well and provides for each stroke cycle of the rod a speed signal corresponding to an optimum average motor speed to maximize oil production under the then present well conditions,   said AC drive being controlled by a microprocessor with an input at which the speed signal is received and an input at which the end of stroke signal is received,   said microprocessor being programmed   to vary the instantaneous velocity of the motor based on (i) the speed signal and (ii) a calculated or measured position of the rod over the course of each stroke cycle, increasing and decreasing the motor speed to maximize fluid production and minimize tension in the rod on the upstroke and maximize tension in the rod on the downstroke, a determination of rod position being initiated each time said end of stroke signal is received,   to set the motor at a predetermined minimum speed whenever the rod position indicates a rotation greater than said known number of revolutions and the end of stroke signal has not been received, and   after setting the motor speed at said predetermined minimum speed and once again receiving the end of stroke signal, to vary the instantaneous velocity of the motor based on (i) the speed signal and (ii) a calculated rod position.   
     
     
         14 . The oil well of  claim 13  including a second sensor that monitors tension in the rod and provides a tension signal corresponding to the measured tension, and the microprocessor has an input that receives the tension signal and is programmed to take into account the measured tension in regulating motor velocity. 
     
     
         15 . An oil well comprising
 a pumping unit that has a rod extending below ground level into the well,   an AC electric motor operably connected to the rod to drive the rod through a predetermined stroke cycle,   a sensor that provides a signal each time the rod is at a predetermined position during each stroke cycle, and   a pump control device that regulates the frequency and voltage of AC electrical power from an AC power grid that is transferred to the AC electric motor,   said pump control device including a microprocessor that controls the speed of the motor, said microprocessor programmed to drive the electric motor over the course of each stroke cycle at different speeds as a function of a calculated or a measured rod position, decreasing the motor speed by transferring electrical energy to the power grid and increasing the motor speed by transferring electrical energy from the power grid to the motor.   
     
     
         16 . A control device for an AC electric motor adapted to be operably connected to a pump for an oil well to vary the speed of the motor as the pump moves through an entire stroke cycle, said control device including
 a regenerative variable frequency AC drive that during each stroke cycle converts AC current at a standard frequency and voltage from an AC power grid to a variable AC current and applies the variable AC current to the motor to decrease motor speed by transferring electrical energy to the power grid and to increase motor speed by transferring electrical energy from the power grid to the motor,   said variable frequency drive being controlled by a microprocessor including an input to be placed in communication with a well manager unit that provides an average motor speed signal that indicates increasing and decreasing the average speed of the motor based on conditions of the well and an input to be placed in communication with a sensor that provides an electrical pulse indicating a predetermined pump position that is the same for each stroke cycle,   said microprocessor programmed to provide at an output of the microprocessor a regulating signal for the variable AC current that modulates frequency and voltage of the variable AC current as a function of the average motor speed signal and a calculated or measured pump position over the course of each stroke cycle initiated each time the electrical pulse is received.   
     
     
         17 . The pump control device of  claim 16  where the position is calculated according to the equation
     X=K∫   0   T     o     Vdt    
 where
 X=belt position for long-stroke units; crank position for beam pump units based on percent of cycle (0 to 100%) 
 V=motor speed (instantaneous revolutions per minute (rpm) 
 K=scaling constant, 
 T o =time at which the signal is received. 
 
 
     
     
         18 . The pump control device of  claim 16  where the microprocessor is programmed to operate the motor at a predetermined minimum speed whenever said electrical pulse is not received during any stroke cycle. 
     
     
         19 . The pump control device of  claim 16  including a circuit that controls the waveform of the input AC current to reduce low order harmonic current drawn from the power grid. 
     
     
         20 . The pump control device of  claim 16  including IGBT transistors that are switched on and off in such a manner that results in current flow and voltage that is substantially sinusoidal. 
     
     
         21 . The pump control device of  claim 16  including an inductive and capacitive filter that reduces harmonic voltage distortion caused by switching of a converter circuit directly to the input AC current. 
     
     
         22 . A pump control device that regulates the frequency and voltage of electrical energy from an AC power grid transferred to an AC electrical motor that drives a rod of a pump having a predetermined stroke cycle, said device comprising
 means during each stroke cycle for transferring electrical energy in both directions between the electrical motor and the AC power grid and for providing a controlled variable AC current for driving the electrical motor over the course of each stroke cycle at different speeds at least in part as a function of a calculated or measured the rod position, and   means for initiating operation of motor over the course of each stroke cycle at said different speeds in response to an electrical pulse generated each time the rod is at a predetermined rod position,   said motor speed being decreased by transferring electrical energy to the power grid and being increased by transferring electrical energy from the power grid to the motor and being operated at a predetermined minimum speed whenever the position signal is not received during in any stroke cycle.   
     
     
         23 . A control device that operates an oil well comprising
 means for applying through a variable frequency drive AC electrical energy from a power grid to an AC electric motor operating a drive mechanism of a pump that pumps oil from the well, and   means for regulating the motor speed in a manner to optimize oil production and maximize the operational life of the drive mechanism, decreasing motor speed by transferring the electrical energy to the power grid and increasing motor speed by transferring the electrical energy from the power grid to the motor.   
     
     
         24 . A combination comprising
 a regenerative variable frequency AC drive connected to an electric motor having a rotating drive shaft that drives a mechanism along a predetermined recurring path of travel, and   a control device that controls the operation of the AC drive to direct current to and from a power grid as a function of a calculated instantaneous position of the mechanism along the recurring path of travel,   said control device including a microprocessor adapted to receive a position signal indicating that the mechanism is at a selected recurring position along said path of travel, said microprocessor programmed to calculate the instantaneous position of the mechanism according to the following mathematical formula:
     X=K∫   0   T     o     Vdt    
   where
 X=instantaneous position of the mechanism along the path of travel, 
 V=estimated instantaneous motor shaft speed (revolutions per minute), 
 K=scaling constant, 
 T o =time at which the position signal is received. 
   
     
     
         25 . The combination of  claim 24  where the mechanism moves linearly and reciprocates along the path of travel. 
     
     
         26 . The combination of  claim 24  where the mechanism rotates. 
     
     
         27 . The combination of a long-stroke pumping unit for an oil well and a regenerative variable frequency AC drive that is operably connected to the pumping unit and is programmed to control the operation of the pumping unit in a predetermined manner over the course of each stroke cycle of the pumping unit. 
     
     
         28 . A method of operating an oil well comprising the steps of
 applying through a regenerative variable frequency drive AC electrical energy from a power grid to an AC electric motor operating a drive mechanism of a pump that pumps fluid from the well, and   regulating the motor speed in a manner to optimize fluid production and maximize the operational life of the drive mechanism, decreasing motor speed by transferring the electrical energy to the power grid and increasing motor speed by transferring the electrical energy from the power grid to the motor.   
     
     
         29 . The method of  claim 28  where the drive mechanism has a predetermined stroke cycle and, over the course of each stroke cycle, the motor is operated at the varying regulated speeds initiated when the drive mechanism is at a predetermined position in each stroke cycle. 
     
     
         30 . The method of  claim 28  where the instantaneous position of the mechanism is calculated according to the following mathematical formula:
     X=K∫   0   T     o     Vdt    
 where
 X=instantaneous position of the mechanism along the path of travel, 
 V=estimated instantaneous motor shaft speed (revolutions per minute), 
 K=scaling constant, 
 T o =time at which the position signal is received.