Patent Publication Number: US-9429001-B2

Title: Synchronized pump down control for a dual well unit with regenerative assist

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The present application claims priority as a continuation of U.S. patent application Ser. No. 14/231,331, filed 31 Mar. 2014, which is a continuation-in-part of U.S. Provisional Patent Application Ser. No. 61/809,294, filed 5 Apr. 2013, and U.S. patent application Ser. No. 14/231,331, filed 31 Mar. 2014, is also a continuation-in-part to U.S. patent application Ser. No. 14/016,215, filed 2 Sep. 2013, which is a continuation of U.S. patent application Ser. No. 13/608,132, filed 10 Sep. 2012, which issued as U.S. Pat. No. 8,523,533 on Sep. 3, 2013, and wherein each of the forgoing invented by Larry D. Best, inventor of the present application. 
    
    
     TECHNICAL FIELD OF THE INVENTION 
     The present invention relates in general to pump units for oil wells, and in particular to a hydraulic pumping units having a regenerative assist. 
     BACKGROUND OF THE INVENTION 
     Hydraulic pumping units have been provided for pumping fluids from subterranean wells, such as oil wells. The pumping units have hydraulic power units and controls for the hydraulic power units. The hydraulic power units have an electric motor or a gas motor which powers a positive displacement pump to force hydraulic fluid into a hydraulic ram. The ram is stroked to an extended position to lift sucker rods within a well and provide a pump stroke. The ram lifts the weight of the sucker rods and the weight of the well fluids being lifted with the sucker rods. When the ram reaches the top of the pump stroke, the hydraulic fluid is released from within the ram at a controlled rate to lower the weight of the sucker rods into a downward position, ready for a subsequent pump stroke. The hydraulic fluid is released from the ram and returns to a fluid reservoir. Potential energy of the weight of the lifted sucker rods is released and not recovered when the hydraulic fluid is released from within the ram and returns directly to the fluid reservoir without being used to perform work. 
     Hydraulic assists are commonly used in hydraulic well pumping units to assist in supporting the weight of the sucker rods. Hydraulic accumulators are used in conjunction with one or more secondary hydraulic rams which are connected to primary hydraulic rams to provide an upward support force. The hydraulic accumulators are provided by containers having hydraulic fluids and nitrogen pre-charges ranging from one to several thousand pounds per square inch. Although the volumes of the containers are constant, the volume of the nitrogen charge region of the containers will vary depending upon the position of the ram piston rod during a stroke. At the top of an up stroke of the ram, the nitrogen charge region of a connected accumulator will have the largest volume, with the nitrogen having expanded to push hydraulic fluid from within the accumulator and into the secondary rams. At the bottom of a downstroke the nitrogen charge region will be at its smallest volume, compressed by hydraulic fluid being pushed from the secondary rams back into the accumulator. According to Boyle&#39;s Law, the pressure in the charge region is proportional to the inverse of the volume of the charge region, and thus the pressure will increase during the up stroke and decrease during the up stroke. This results in variations in the amount of sucker rod weight supported by the secondary hydraulic rams during each stroke of the ram pumping unit. 
     Drive motors for hydraulic pumps are sized to provide sufficient power for operating at maximum loads. Thus, motors for powering hydraulic pumps for prior art accumulator assisted pumping units are sized for lifting the sucker rod loads when the minimum load lifting assist is provided by the accumulator and the secondary ram. Larger variations in accumulator pressure and volume between the top of the up stroke and the bottom of the downstroke have resulted larger motors being required to power the hydraulic pump connected to the primary ram than would be required if the volume and pressure of the nitrogen charge section were subject to smaller variations. Large motors will burn more fuel or use more electricity than smaller motors. Several prior art accumulator containers may be coupled together to increase the volume of the nitrogen charge region in attempts to reduce variations in pressure between top of the up stroke and the bottom of the downstroke. This has resulted in a large number of accumulator containers being present at well heads, also resulting in increasing the number of hydraulic connections which may be subject to failure. 
     SUMMARY OF THE INVENTION 
     A synchronized dual well variable stroke and variable speed pump down control with regenerative assist is provided for pumping two, four or more wells. Should pump down be encountered in one of the wells, programmable controllers reduce the speed and the stroke of a ram unit for a pumped-down well by the same percentage, to maintain a constant cycle time between up strokes and down strokes such that the ram unit of the pumped down well will remain synchronized with a ram unit of the other well. Preferably the speed and the stroke of the ram unit of the pumped down well will be decreased by 1.5% per stroke when pump down is detected, and will be increased by 3% per stroke until a constant fluid level is reached. 
     A dual well assist for a hydraulic rod pumping units is disclosed which does not make use of secondary hydraulic rams, and which provides both downstroke energy recovery and synchronized variable stroke and speed pump down. Two variable displacement, positive displacement pumps are coupled to a single drive motor. The first pump is connected between a hydraulic fluid reservoir and a first hydraulic ram for a first pumping unit. The second pump is connected between the hydraulic fluid reservoir and a second hydraulic ram of a second pump unit. The first pump and the second pump are each connected to pump control units which automatically control the displacement of each of the pumps and selectively determine whether each of the pumps are operable as a hydraulic motor or a hydraulic pump. Preferably, the first and second pumps are variable displacement, open loop piston, hydraulic pumps which are modified for operating in reverse flow directions, such that the hydraulic fluid may pass from one of the two hydraulic rams, back into the respective pump discharge port, through the pump, through the pump suction port and into a fluid reservoir with the drive shaft for both of the hydraulic pumps and the rotor, or drive shaft, of the drive motor turning in the same angular direction as that for pumping the hydraulic fluid into respective ones of the two rams. Reversing the flow direction of the hydraulic fluid through the pumps selectively uses respective ones of the pumps as hydraulic motors which provides power for turning the other pump. 
     The pump control units determine actuation of the pumps for either pumping fluids or providing a hydraulic motor for turning the other pump, in combination with the power output by the drive motor. The pump control units are programmable controllers and each include a microprocessor which controls hydraulic motor displacement for each pump with feedback from provided by pump/motor displacement, a pressure transducer and a speed sensor. During the up stroke of the first well head pumping unit, the second pump is operated as a motor driven by the first pump and the power motor. The sucker rod load of the second well head pumping unit will in-part drive the second pump. During the down stroke of the first well head pumping unit, the second pump is operated as a pump that charges the second ram and the first pump is operated as a motor driven by the down stroke of the sucker rod load of the first well head pumping unit. This results in recovery of the potential energy stored by lifting the weight of the sucker rod assemblies during the up strokes in each of the wellhead pumping units. The hydraulic fluid from the ram units of the first or second wellhead pumping units are passed through respective ones of the first and second ram pumps in the reverse flow directions, with the pump control units actuating the respective pumps to act as a motor and assist the drive motor in driving the other pump. 
     Recovery of the potential energy from the suck rod weight provides two advantages. First is a lower energy requirement for powering the wellhead pumping units. A second advantage is that the size requirements for drive motors used to power the ram pumps of the wellhead pumping units is reduced, allowing smaller less expensive drive motors to be used. The discharges of both ram pumps are connected to an accumulator, which preferably has a nitrogen pre-charge region. The accumulator may also be engaged to provide additional assist on an up stroke, but is preferably only used for single well operation should one of the wells be taken out of service and shut in. 
     In one embodiment, a hydraulic ram for a ram pumping unit is mounted atop a support frame which has a self-aligning feature to prevent wear of the hydraulic ram. A lower end of the hydraulic ram is provided with a convex, rounded shape such as that of a spherical washer, which engages with a flange having an upwardly facing, dished face providing a concave surface for engaging with the convex surface of the lower end of the hydraulic ram. This provides for several degrees of self-alignment of the hydraulic ram with the applied sucker road load. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
       For a more complete understanding of the present invention and the advantages thereof, reference is now made to the following description taken in conjunction with the accompanying Drawings in which  FIGS. 1 through 19  show various aspects for hydraulic rod pumping units having synchronized dual well variable stroke and variable speed pump down control with regenerative assist, as set forth below: 
         FIG. 1  is a schematic diagram depicting a side elevation view of the hydraulic rod pumping unit during an up stroke; 
         FIG. 2  is a schematic diagram depicting a side elevation view of the hydraulic rod pumping unit during a downstroke; 
         FIG. 3  is a partial top view of the hydraulic rod pumping unit showing three hydraulic rams used in the unit; 
         FIG. 4  is a longitudinal section view of a variable volume piston pump which is operable in both conventional flow and reverse flow directions with the motor shaft continuously moving in the direction for pumping fluid; 
         FIGS. 5-8  illustrate various aspects of two dual well hydraulic ram pump systems providing regenerative assist which powered by a single prime mover or motor; 
         FIGS. 9A and 9B  together provide a flow chart for operation of a dual well system with regenerative assist; 
         FIG. 10  is a schematic block diagram of calibration of stroke position and ram synchronization; 
         FIG. 11  is a schematic block diagram of variable stroke and speed pump down control for the dual well system; 
         FIG. 12  is a pump card illustrating pump down of a well; 
         FIGS. 13-15  show a well pump operating in various pump down conditions; 
         FIG. 16  illustrates multiple well system with regenerative assist power by a single prime mover or motor; and 
         FIGS. 17-19  show a mounting configuration for a hydraulic ram of a pumping unit having self-aligning features between a hydraulic ram and a sucker rod assembly. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIGS. 1 and 2  are schematic diagrams depicting a side elevation view of a hydraulic rod pumping unit  12  having a constant horsepower regenerative assist.  FIG. 1  shows the pumping unit in an up stroke, and  FIG. 2  shows the pumping unit in a down stroke. The pumping unit  12  is preferably a long stroke type pumping unit with heavy lift capabilities for pumping fluids from a well. The ram pumping unit  12  preferably has three single acting hydraulic rams  26 , a sucker rod assembly  10 , and a hydraulic power unit  14 .  FIG. 3  is a partial top view of the hydraulic rod pumping unit  12  and shows the three hydraulic rams  26  connected together by a plate  32  to which the piston rods  30  are rigidly connected. A polished rod  8  is suspended from the plate  32  by a polished rod clamp  50 , and extends through a stuffing box  6  for passing into a well head  4  and connecting to sucker rods  10  of a downhole well pump for lifting fluids from the well. 
     Each of the hydraulic rams  26  has a piston guide  28  and a rod  30  which reciprocate within a cylinder  42 . Preferably, the rod  30  provides the piston element within each of the hydraulic rams  26 , and the piston guide  28  does not seal but rather centers the end of the rod  30  and provides bearings within the cylinder  42 . The only hydraulic connection between the power unit  14  and the ram  26  is a single high pressure hose  48  which connects to a manifold plate  52 , which ports fluid between each of the rams  26  and the hose  48 . The hydraulic power unit  14  includes a drive motor  16 , two variable volume piston pumps  18  and  20 , a fluid reservoir  22 , a hydraulic accumulator  24 , and a control unit  44 . The drive motor  16  may be an electric motor, or a diesel, gasoline or natural gas powered engine. The control unit  44  preferably includes a motor control center and a microprocessor based variable speed pump down system. The hydraulic accumulator  24  preferably is of a conventional type having a nitrogen charge region which varies in volume with pressure. The pump down system monitors the polished rod load and position to make appropriate speed adjustments to optimize production from the well while keeping operational costs at a minimum. The ram pump  18  and the accumulator pump  20  preferably each have a pump control unit  46  mounted directly to respective ones of the associated pumps housings. Valves  96  and  98  are provided for preventing hydraulic fluid from draining from the hydraulic rams  26  and the accumulator  24 , respectively, when the drive motor  16  is not running. 
     The control unit  44  and the two pump control units  46  are provided for controlling operation of the pump  18  and the pump  20 . The control unit  44  and the pump control units are programmable controllers each having a microprocessor and memory for both storing machine readable instructions and executing such instructions. The control unit  44  is preferably a microprocessor-based controller which is provided sensor inputs for calculating the stroke position of the piston rod  30  of the ram  26 , and the polished rod load. The polished rod load is calculated from the measured hydraulic pressure and the weight of the sucker rods  10  at the well head  4 . The control unit  44  will feed control signals to the pump control units  46 , to vary the flow rate through respective ones of the pump  18  and the pump  20 . The pump control units  46  are integral pump controllers which are preferably provided by microprocessor-based units that are mounted directly to respective ones of the pumps  18  and  20 , such as such a Model 04EH Proportional Electrohydraulic Pressure and Flow Control available from Yuken Kogyo Co., Ltd. of Kanagawa, Japan, the manufacturer of the pumps  18  and  20  of the preferred embodiment. The Yuken Model 04EH pump controller includes a swash plate angle sensor and a pump pressure sensor, and provides control of each of the swash plate angles C and D (shown in  FIG. 3 ) to separately control the pressure outputs and the flow rates of the hydraulic fluid through respective ones of the pumps  18  and  20 . 
       FIG. 4  is a longitudinal section view of the variable volume piston pump used for both the pump  18  and the pump  20 . The pump is operable in both a conventional flow direction mode and a reverse flow direction mode, with a drive shaft  56  of the pump  18  and the rotor of the drive motor  16  continuously turning in the same angular direction for both flow directions. The pump  18  has a pump housing  54  within which is the drive shaft  56  is rotatably mounted. The pump drive shaft  56  is connected to the rotor of the drive motor  16  (shown in  FIG. 1 ), in conventional fashion. A cylinder block  58  is mounted to the drive shaft  56 , in fixed relation to the drive shaft  56  for rotating with the drive shaft  56 . Preferably, a portion of the outer surface of the drive shaft  56  is splined for mating with splines in an interior bore of the cylinder block  58  to secure the drive shaft  56  and the cylinder block  58  in fixed relation. The cylinder block  58  has an inward end and an outward end. The inward end of the cylinder block  58  has a plurality of cylinders  60  formed therein, preferably aligned to extend in parallel, and spaced equal distances around and parallel to a centrally disposed, longitudinal axis  90  of the drive shaft  56 . The drive shaft  56  and the cylinder block  58  rotate about the axis  90 . Pistons  62  are slidably mounted within respective ones of the cylinders  60 , and have outer ends which are disposed outward from the cylinders for engaging retainers  64 . The retainers  64  secure the outer ends of the pistons  62  against the surface of a swash plate  66 . The outward end of the cylinder block  58  is ported with fluid flow ports for passing hydraulic fluid from within the cylinders  60 , through the outward end of the cylinder block  58 . A port plate  76  is mounted in fixed relation within the pump housing  54 , and engages the outward, ported end of the cylinder block  58 . The port plate  76  has a first fluid flow port  78  and a second fluid flow port  80 , with the first flow port  78  and the second flow port  80  connected to the pump suction port  82  and the pump discharge port  84 . The suction port  82  and the discharge port  84  are defined according to conventional operation of the pumps  18  and  20 , in moving hydraulic fluid from the fluid reservoir  22  and into the hydraulic ram  26 . The pistons  62 , the cylinders  60  and the cylinder block  58  rotate with a pump drive shaft  56 , with the outer ends of the pistons  62  engaging the swash plate  66  and the ported end of the cylinder block  58  engaging the port plate  76 . 
     The swash plate  66  is mounted to a yoke or a cradle  68 , preferably in fixed relation to the cradle  68 , with the swash plate  66  and the cradle  68  pivotally secured within the motor housing  54  for angularly moving about an axis which is perpendicular to the longitudinal axis  90  of the drive shaft  56 . A bias piston  70  is mounted in the pump housing  54  to provide a spring member, or bias means, which presses against one side of the cradle  68  and urges the swash plate  66  into position to provide a maximum fluid displacement for the pump  18  when the pump  18  is operated in conventional flow direction mode to pump the hydraulic fluid from the fluid reservoir  22  into the hydraulic ram  26 . A control piston  72  is mounted in the pump housing  54  on an opposite side of the pump drive shaft  56  from the bias piston  70  for pushing against the cradle  68  to move the cradle  68  and the swash plate  66  against the biasing force of the bias piston  70 , minimizing fluid displacement for the pump  18 , when the pump  18  operated in the conventional flow direction mode to pump the hydraulic fluid from the reservoir  22  into the hydraulic ram  26 . 
     The swash plate  66  preferably has a planar face defining a plane  86  through which extends the central longitudinal axis  90  of the pump drive shaft  56 . A centerline  88  defines a neutral position for the swash plate plane  86 , with the centerline  88  is preferably defined for the pump  18  as being perpendicular to the longitudinal axis  90  of the drive shaft  56 . When the swash plate  66  is disposed in the neutral position, the stroke length for the pistons  62  will be zero and the pump  18  will have zero displacement since the pistons  62  are not moving within the cylinder block  58 , as the cylinder block  58  is rotating with the drive shaft longitudinal axis  90 . When the swash plate  66  is in the zero stroke position, with an angle C between the swash plate plane  86  and the centerline  88  equal to zero, the pump  18  is said to be operating at center and fluid will not be moved. The angle C between the centerline  88  and the plane  80  of the swash plate  66  determines the displacement for the pump  18 . Stroking the control piston moves the cradle  68  and the swash plate  66  from the neutral position, in which the plane  86  the swash plate  66  is aligned with the centerline  88 , to a position in which the angle C is greater than zero for operating the pump  18  in the conventional flow mode to provide hydraulic fluid to the ram  26 . The larger the angle C relative to the centerline  88 , the larger the displacement of the pump  18  and the larger the volume of fluid moved by the pump  18  for a given speed and operating conditions. 
     If the plane  86  of the swash plate  66  is moved across the centerline  88  to an angle D, the pump swash plate  66  is defined herein to have moved across center for operating the pumps  18  and  20  over center as a hydraulic motor in the reverse flow mode. When the swash plate  66  is moved across center, the pumps  18  and  20  will no longer move fluid from the fluid reservoir  22  to respective ones of the hydraulic ram  26  and the accumulator  24 , but instead will move the hydraulic fluid in the reverse flow direction, either from the hydraulic ram  26  to the fluid reservoir  22  or from the accumulator  24  to the fluid reservoir  22 , for the same angular direction of rotation of the pump drive shafts  38 ,  40  and the rotor for the drive motor  16  as that for pumping hydraulic fluid into the hydraulic ram  26  or the accumulator  24 . With fluid flow through the pump  18  reversed, the pressure of the hydraulic fluid in the hydraulic ram  26  may be released to turn the pump  18  as a hydraulic motor, which applies mechanical power to the drive shafts  38  and  40  connecting between the pumps  18  and  20 , and the drive motor  16 . Similarly, with fluid flow through the pump  20  reversed, the pressure of the hydraulic fluid in the accumulator may be released to turn the pump  20  as a hydraulic motor, which applies mechanical power to the drive shafts  38  and  40  connecting between the pumps  18  and  20 , and the drive motor  16 . 
     Referring to  FIGS. 1 and 2 , a position sensor  36  is provided for sensing the stroke position of the rod  30  within the cylinder  42  of the ram  26 . The position sensor  36  is preferably provided by a proximity sensor which detects a switch actuator  34  to detect when the ram  26  is at a known position, such as at the bottom of the downstroke as shown in  FIG. 1 . The control unit  44  is operable to reset a calculated position to a known reference position which is determined when the sensor  36  detects the ram switch actuator  34 . Then, the control unit  44  calculates the position of the piston rod  30  within the cylinder  42  by counting the stroke of pump  18  and angle of swash plate  66  within the pump  18 , taking into account the volume of the rod  30  inserted into the cylinder  42  during the up stroke. The piston rod  30  acts as the piston element in each of the hydraulic rams  26 , such that the cross-sectional area of the piston rod  30  times the length of the stroke of the rod  30  provides the volume of hydraulic fluid displaced during the stroke length. The angle of the swash plate  66  provides the displacement of the pump  18 . The rpm at which the pump  18  is turned is known by either the synchronous speed of an electric motor, if an electric motor is used, which is most often 1800 rpm, or the speed set by the governor for a diesel or gas engine. The calculated stroke position is reset to a reference position near the bottom of the downstroke for the ram  26 . From the known angular speed and measured angle of the swash plate  66  for selected time intervals, the controller  44  calculates the total flow of hydraulic fluid through the ram pump  18  from the time the piston rod  30  is a the known reference position as detected by the proximity sensor  36 , and then determines the stroke for the piston rod according to the cross-sectional area of the piston rod  30 . 
     During operation of the pumping unit  12 , the load or weight of the piston rod  30  and the sucker rods  10  provide potential energy created by being lifted with hydraulic pressure applied to the hydraulic ram  26 . The potential energy is recaptured by passing the hydraulic fluid from the ram  26  through the hydraulic pump  18 , with the swash plate  66  for the pump  18  disposed over center such that the pump  18  acts as a hydraulic motor to apply power to the pump  20 . The control unit  44  positions the swash plate  66  at the angle D from the centerline  88 , such that the hydraulic pump  18  recaptures the potential energy stored by the raised sucker rods and powers the pump  20  to store energy in the hydraulic accumulator  24 . Then, during the up stroke the potential energy stored in the accumulator  24  is recaptured by passing the hydraulic fluid from the accumulator  24  through the hydraulic pump  20 , with the swash plate  66  for the pump  20  disposed over center such that the pump  20  acts as a hydraulic motor to apply power to the pump  20 . The potential energy from the accumulator  23  is applied to the drive shafts  38  and  40  to assist the drive motor  24  in powering the pump  18  to power the ram  26  during the up stroke. 
     The control unit  44  will analyze data from both pressure on the hydraulic rams  26 , and from the calculated the position of the piston rod  30 , and will adjust the position of the swash plates  66  in each of the respective pumps  18  and  20  to control the motor displacement. This controls the rate of the oil metered from respective ones of the hydraulic ram  26  and the accumulator  24 , thus controlling the down-stroke speed of the ram  26 , the pump  18  and the pump  20 , which provides a counterbalance for the weight of the sucker rod assembly  10  and may be operated to provide a constant horsepower assist for the drive motor  16 . Increasing the displacement increases the speed and decreasing the displacement decreases the speed for the pump  18  and the pump  20 , controlling the horsepower assist during an up stroke of the ram  26 . During up stroke of the hydraulic ram  26 , the drive motor  16  is operated to move the hydraulic fluid through the pump  18 , from the suction port  82  to the discharge port  84  and to the ram  26 . The up stroke speed of the pump  18  is controlled manually or is controlled automatically by a microprocessor-based control unit  44 . During the downstroke of the hydraulic ram  26 , the pump  18  is stroked over center by moving the swash plate  66  over center, and the hydraulic fluid will flow from the ram  26  into the port  84 , through the pump  18  and then out the port  82  and into the reservoir  22 , with the pump  18  acting as a hydraulic motor to drive the drive the pump  20 , which assisted in providing provided power to the pump  18  for the up stroke. During the downstroke, the pump  20  will similarly provide power to assist turning the pump  18 , with the control unit  44  controlling the angle of the swash plate  66  in the pump  20  and thus rate at which hydraulic fluid is released from the accumulator  24  and power is applied to the drive shafts  38  and  40 . 
     The load on the piston rod  30  at various linear positions as calculated by the controller  44  and detection of the down bottom of stroke position by the proximity sensor  36  are also analyzed by the control unit  44  to automatically provide selected up-stroke and downstroke speeds, and acceleration and deceleration rates within each stroke, for optimum performance in pumping fluids from the well head  4 . Should the well begin to pump down, the up-stroke and the downstroke speeds may be adjusted to maintain a constant fluid level within the well. The control unit  44  monitors key data and provides warnings of impending failure, including automatically stopping the pump from operating before a catastrophic failure. The load on the piston rod  30 , or the polished rod load for the sucker rods  10  at the well head  4 , is preferably determined by measuring hydraulic pressure in the hydraulic rams  26 . Sensors may are also preferably provided to allow the control unit  44  to also monitor the speed of the pump drive shafts  38  and  40  and the rotor for the drive motor  16 . 
     The hydraulic pump  18  is a variable displacement pump which is commercially available and requires modification for operation according to the present invention. Pump  18  is commercially available from Yuken Kogyo Co., Ltd. of Kanagawa, Japan, such as the Yuken model A series pumps. Other commercially available pumps may be modified for operating over center, in the reverse flow direction, such as a PD Series pump or a Gold Cup series pumps available from Parker Hannifin HPD, formerly Denison Hydraulics, Inc., of Marysville, Ohio, USA. The Gold cup series pump which uses a hydraulic vane chamber actuator for position a swash plate rather than the control piston of the Yuken model A series pump. The hydraulic vane chamber is preferably powered by a smaller hydraulic control pump connected to the drive shaft of the pumps  18  and  20 , rather than being powered by the pumps  18  and  20 . Hydraulic fluid is passed on either side of a moveable vane disposed in the vane chamber to move the vane within the chamber, and the vane is mechanically linked to a swash plate to move to swash plate to a desired position. In other embodiments, other type of actuators may be used to control the position of a swash plate relative to the centerline, such as pneumatic controls, electric switching, electric servomotor, and the like. The modifications for the pumps required for enabling operation according to the present invention are directed toward enabling the swash plates for the respective pumps to move over center, that is over the centerline, so that the pump may be operated over center in the review flow direction mode. The commercially available pumps were designed for use without the respective swash plates going over center, that is, they were designed and manufactured for operating in conventional flow direction modes and not for switching during use to operate in the reverse flow direction mode. Typical modifications include shortening sleeves for control pistons and power pistons, and the like. Internal hydraulic speed controls are also typically bypassed to allow operation over center. For the Denison Gold Cup series pumps, pump control manifolds may be changed to use manifolds from other pumps to allow operation of the pump over center. Closed loop pumps and systems may also be used, with such pumps modified to operate over center, in the reverse flow direction. 
     The hydraulic pumping unit having a constant horsepower regenerative assist provides advantages over the prior art. The pumping unit comprises a single acting hydraulic ram, without secondary rams provided for assist in lifting the sucker rod string. During a downstroke, the pumping unit provides for regeneration and recapture of energy used during the up stroke. The sucker rod load is used during the downstroke to power a ram pump which a controller has actuated to act as a hydraulic motor and provide useable energy for driving a accumulator pump to charge an accumulator. During the up stroke the pump controller actuates the accumulator pump to act as a motor and fluid released from the accumulator provides power for assisting the drive motor in powering the ram pump to raise the ram and lift the sucker rod string. Preferably, controller operates the pumps to determine the rate at which fluids flows from the ram and through the pump, such as by selectively positioning the swash plates for each of the hydraulic pumps to determine a counterbalance flow rate at which hydraulic fluid flows from the ram back into the ram pump and is returned to a reservoir, and the counterbalance flow rate at which the hydraulic fluid flows form the accumulator back into the accumulator pump and is returned to the reservoir. In other embodiments, valving may be utilized to control flow, or a combination of valving and pump controls. 
       FIGS. 5-8  illustrate various aspects of a dual well system with regenerative assist with two wellhead pumping units connected to one primer move  16 . Referring to  FIGS. 5 and 6 , a dual well regenerative system  100  has wellhead pumping units  102  and  104  with similar components as that of the standard single well pumping unit  12  and hydraulic power unit  14  of  FIGS. 1-4  above, but which requires only one power unit  14  with one prime move  16  to power two separate well head pumps  102  and  104  for two wells. The hydraulic power unit  14  has the two hydraulic pumps  18  and  20 , and the hydraulic accumulator  24 , preferably provided by a nitrogen charge accumulator. The accumulator  24  may be used to store recovered potential energy should the assist from one pumping unit not be fully used for powering the other pumping unit. The shuttle valve  94  connects the high pressure side of the pumping units  102  and  104  to the accumulator  24 . The solenoid valves  98  are also provided on opposite sides of the shuttle valve  94 , and may also be used controlling flow between accumulator  24  and the pumping units  102  and  104  in place of the shuttle valve  94 . Each of the ram pumps  18  and  20  has one of the pump control units  46  integrated with the respective pump housing. A control unit  44  is provided and connected to each of the pump control units  46 , the position sensors  36  and fluid pressure sensors (not shown). 
     The pumping units  102  and  104  are synchronized such that one of the pumping units  102  and  104  will be on an up stroke while the other of the pumping units  102  and  104  is on a downstroke. The potential energy of the lifted weight of the sucker rod assembly of the well on the downstroke is recovered and used to provide assist to the other pumping unit which is on the up stroke.  FIG. 5  shows the pumping unit  102  during a downstroke and the pumping unit  104  on an up stroke. The potential energy stored in the lifted the weight on the sucker rod  8  pushes hydraulic fluid from the hydraulic rams  26  of the pumping unit  102  and turns the pump  18 . The pump  18  is actuated to an over-center condition and acts as a motor for assisting the drive motor  16  in turning the ram pump  20 . The ram pump  20  is in a pump configuration for turning to force the hydraulic fluid into the hydraulic rams  26  of the pumping unit  104 , lifting the sucker rod  8  of the pumping unit  104 . Similarly,  FIG. 6  shows the pumping unit  102  during an up stroke and the pumping unit  104  during a downstroke. The potential energy stored in the lifted the weight on the sucker rod  8  of the pumping unit  104  pushes hydraulic fluid from the hydraulic rams  26  of the pumping unit  104  and turns the pump  20 . The pump  20  has been actuated to an over-center condition and acts as a motor for assisting in turning the pump  18 . The ram pump  18  has been moved back from the over-center condition to operate as a pump and is turned by the ram pump  20  and the drive motor  16  to force the hydraulic fluid into the hydraulic ram  26  of the pumping unit  102 , lifting the sucker rod  8  attached to the pumping unit  102 . Thus, a first one of the wellhead pumping units  102  and  108  during a downstroke will counterbalance the second of the wellhead pumping units  102  and  108  during a downstroke, with the first providing regenerative assist to the second in lifting the respective sucker rods  8 . 
       FIGS. 7 and 8  similarly show a dual well regenerative system  106  with two wellhead pumping units  108  and  110  operated by a single hydraulic power unit  14 . The wellhead pumping units  108  and  110  have similar components as that of the hydraulic pumping units  102  and  104  of  FIGS. 1-6  discussed above, except that rather than providing three rams  26  for each of the ram pumping units  102  and  104 , a single hydraulic ram  26  is inverted and mounted atop a support structure  112  for each of the ram pumping units  108  and  110 . A single hydraulic power unit  14  of  FIGS. 7 and 8  requires only one prime mover for both of the pumping units  108  and  110 , and provides regenerative assist between the two pumping units  108  and  110 . A hydraulic accumulator  24  is also provided, preferably by a nitrogen charge accumulator, for use when one of the two wells is taken out of service. The shuttle valve  94  connects the high pressure side of the wells  108  and  110  to the accumulator  24 . The solenoid valves  98  are also provided on opposite sides of the shuttle valve  94 , and may also be used controlling flow between accumulator  24  and the pumping units  108  and  110  in place of the shuttle valve  94 . The hydraulic accumulator  24  may also be used to store and provide energy as noted above for  FIGS. 1-4 , when the regenerated potential energy recovered from one pumping unit on a first well is greater than the energy required to lift the other pumping unit on a second well. Each of the ram pumps  18  and  20  has one of the pump control units  46  integrated with the respective pump housing. A control unit  44  is provided and connected to each of the pump control units  46 , position sensors  36  and fluid pressure sensors (not shown). 
     The pumping units  108  and  110  are synchronized such that one of the pumping units  108  and  110  will be on an up stroke while the other of the pumping units  108  and  110  is on a downstroke. The potential energy of the lifted weight of the sucker rod assembly on the well on the downstroke is recovered and used to provide assist to the other pumping unit on the up stroke. FIG.  7  shows the pumping unit  108  during a downstroke and the pumping unit  110  during an up stroke. The potential energy stored in the lifted the weight on the sucker rod  8  pushes hydraulic fluid from the hydraulic ram  26  of the pumping unit  108  and turns the ram pump  18 . The pump  18  is actuated to an over-center condition and acts as a motor for assisting the drive motor  16  in turning the ram pump  20 . The ram pump  20  is in a pump configuration for turning to force the hydraulic fluid into the hydraulic ram  26  of the pumping unit  110 , lifting the sucker rod  8  of the pumping unit  110 . Similarly,  FIG. 8  shows the pumping unit  108  during an up stroke the pumping unit  110  during a downstroke. The potential energy stored in the lifted weight on the sucker rod  8  of the pumping unit  110  pushes hydraulic fluid from the hydraulic ram  26  of the pumping unit  110  and turns the pump  20 . The pump  20  has been actuated to an over-center condition and acts as a motor for assisting in turning the pump  18  in cooperation with the motor  16 . The ram pump  18  has been moved back from the over-center condition to operate as a pump and is turned by the ram pump  20  and the drive motor  16  to force the hydraulic fluid into the hydraulic ram  26  of the pumping unit  108 , lifting the sucker rod  8  of the pumping unit  108 . The hydraulic accumulator  24  may also be used to store and provide energy as noted above for  FIGS. 1-4 , when the regenerated potential energy recovered from one pumping unit on a first well is greater than the energy required to lift the other pumping unit on a second well. Thus, a first one of the wellhead pumping units  108  and  110  during a downstroke will counterbalance the second of the wellhead pumping units  108  and  110  during an up stroke, with the first providing regenerative assist to the second in lifting the sucker rods  8 . 
     For a dual regenerative assist an even number of wells is preferably required for proper counterbalance. Although the system can accommodate many wells, it is most practical for four wells since then number of wells increases, the hydraulic power unit gets more complicated, the prime mover size increases, and the distance between wells increases. If the prime mover, or motor, fails or has a problem then all of the wells are shut-down. For example, a cluster with dual well regenerative control with two wells requires that both hydraulic ram pumping units be synchronized so that when one pumping unit is on the up stroke the other pumping unit is on the down stroke. The stored potential energy of the polished rod from the down-stroke well is used to both assist in powering the up stroke of the polished rods in the other well and to provide counter-balance. If one of the wells is shut-down for work-over, a stand-by accumulator can be activated to provide power assist and counter-balance. The prime mover can be an electric motor or gas engine. 
     This system is preferably used for a cluster of wells which are within 150 ft. (50 m) of each other, and it allows a single hydraulic power unit  14  to operate up to four different wells. Each well will have a wellhead ram pumping unit that connects to the hydraulic power unit with a single hose and control cable. In a four well configuration there will be two master/slave systems; with a separate pump control unit for each well. The only differences between the dual or multiple well hydraulic power units is the number of controls based on number of wells and selector valves for activating the accumulator when one of the wells is shutdown. 
     The pump control  44  which interfaces with the control units  46  for each of the hydraulic pumps  18  and  20  preferably has individual microprocessors, one for each well unit, with on-site input means, such as touch screens. The speed of both well pumping units is set with one of the pumping units being controlled a master and the other of the control pumping units being controlled as a slave. The master control unit  44  will control the speed at which the slave pumping unit operates, with feedback from the stroke position of ram of the slave wellhead pumping unit. Each well&#39;s stroke length, variable speed pump-down, and acceleration or deceleration can be independently adjusted as control provided for each well according to different, independent dynamometer cards. Preferably, the master control unit  44  will receive position feedback information for the position of the pumping unit ram controlled as the slave. The master control unit  44  automatically signals the slave pump control unit to adjusts the displacement of the slave hydraulic pump during the down-stroke to match the downstroke speed of the slave hydraulic pump to the up-stroke speed of master well, even if the stroke length of the wells are different. During downstroke of the master well, the displacement of the master hydraulic pump is adjusted to match the speed of the slave hydraulic pump which is operating over center to act as a motor during an up stroke of the slave ramp pumping unit. This makes sure that both units are synchronized to reverse at the same time to control counter-balance and prime mover loads. 
     As an example, a 7874 ft. well has a 1.25 inch downhole pump, a Peak Polished Rod Load of 18,543 lbs, and a Minium Polished Rod Load of about 11,654 lbs, or a load differential of 62%. If Well “A” pumping unit requires 50 HP on the up stroke to lift the polished rod, Well “B” pumping unit is on the down stroke and generating 56% (including inefficiency) or 28 HP through a hydraulic motor that assists well “A”s hydraulic pump. The actions are reversed when the pumps (alternating in acting as hydraulic motors) stroke positions are reversed. The amount of regenerative assist depends upon the maximum and the minimum polished rod load differential and the system efficiencies. The wells are preferably close to each other, spaced apart no more than 150 Ft. (50 m) to allow the hydraulic pump assist to function properly. The following are examples of a test well: 
     
       
         
           
               
               
             
               
                   
               
               
                   
                 CYLINDER 
               
               
                 CYLINDER “A” ON UP STROKE 
                 “B” ON DOWN STROKE 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
            
               
                 PRESSURE:  
                 1968 
                 PSI 
                 PRESSURE: 
                 1237 
                 PSI 
               
               
                 FLOW: 
                 41 
                 GPM 
                 FLOW: 
                 41 
                 GPM 
               
               
                 HP: 
                 50 
                   
                 REGEN HP:  
                 28 
                 HP 
               
               
                 Net Power required:  
                 22 
                 HP 
                   
                   
                   
               
               
                   
               
            
           
         
       
     
     Prime Mover Required:
         25 HP Electric Motor.   30-40 HP @ 1800 RPM Gas Engine (The gas engine should be sized so it does not run fully loaded, this saves fuel and extends engine life.)       

       FIGS. 9A and 9B  together provide a flow chart for operation of a dual well system with regenerative assist. The process begins with a start step  130  and then proceeds to a decision block depicting a step  132  in which a user selects either a single well operation mode or a dual well operation mode. If the single well operation mode is selected in step  32  the process proceeds to step  134  and single well parameters are set in the controller  44 . The system will then proceed to step  136  and the stroke position is calibrated. In step  138  the respective controller  44  will run a single well regenerative system using the accumulator  24  for storing recovered energy during the downstroke and emitting energy for assisting in powering the up stroke, as noted above. 
     If in step  132  the dual well operation mode is selected, the process proceeds to step  140  and dual well operational parameters are set in the controller  44 . In step  142  both of the dual wells  108  and  110  are started. In step  144  the stroke position is calibrated using position sensors  36  and the calculated known volume of the hydraulic fluid passing through the pumps  18  and  20 , which are positive displacement pumps. Then, in step  146  the wells are synchronized so that the up stroke of the ram pumping unit for one well occurs during the downstroke of the ram pumping unit for the other well. If a first ram reaches the top of the up stroke, or downstroke, prior to the second ram, the speed of the first ram is slowed as it begins to stroke in the opposite direction until the other ram reaches the end of its stroke, and the speed of the first stroke returns to its original rate as determined by the controller  44  for the pumps. The flow rates of hydraulic fluids through the respective one of the pumps moving a ram during an up stroke is determined by the swash plate angle which provides the displacement of the pump. 
     In step  148  a pump down point is set for each of the wells, as noted in the pump down discussion set forth below in reference to  FIGS. 13-15 . The process then proceeds to step  150  and pump down for each of the wells is checked, preferably during each stroke of the wells. If pump down is not detected for either of the wells  1  or  2 , the process proceeds to loop an again perform step  150  to check for pump down of both wells. If pump down is detected for one of the wells, the process proceeds to a respective one of the steps  152  and  154  and synchronizes the stroke and the speed of the respective ram for the well which has pumped down. The process will then return back to the step  150  and both wells will be checked for pump down. The process will continue to loop between the steps  150 - 154  until stopped by an operator. 
       FIG. 10  is a schematic block diagram depicting calibration of stroke position and ram synchronization. A positioning system includes top proximity sensors  174  and  184  and bottom proximity sensors  176  and  186  for each ram pumping unit, for determining when the respective rams are disposed in a selected position during a stroke. Pump sensors  172  and  182  are provided in each of the hydraulic pumps for determining the swash plate angles which provide the displacement for each of the pumps. The swash plates are rotated at known angular velocities, provided by the prime mover rotary speed sensors  170  and  180 . Microprocessor controllers  160  and  164  are provided for each pump for calculating positioning of the respective hydraulic ram during a stroke relative to the selected position. The microprocessor controllers  160  and  164  use the stroke position of each ram to determine when one is on the up stroke and one is on the down stroke and controls the pumps displacements to synchronize them so they reverse directions at substantially the same time. Well “1” and Well “2” are synchronized when Well “1” is on the down-stroke, Well “2” is on the up-stroke. The Down Stroke polished rod load on Well “1” forces the ram down pumping the oil back into the hydraulic motor; the microprocessors  160  and  164  control each of the pumps displacement through the displacement controls  162  and  166  for each pump, which controls the respective swash plate angles for each of the pumps which in turn controls the rate of flow of oil from each of the rams for providing counterbalance and the power that assists the prime mover (electric motor or gas engine) and for driving the hydraulic pump that lifts the ram during the up-stroke. 
       FIG. 11  is a schematic block diagram of variable stroke and speed pump down control for the dual well system. The system discussed above in reference to  FIG. 10  is used, with the addition of the input into the microprocessors  160  and  164  of pump pressure transducers  178  and  188  for each respective pump for determining rod load. Pump pressure applied to each of rams can be used in combination with the cross-sectional area of the particular ram to determine the rod load. Rod load from the sensors  178  and  188  is used with position information from proximity switches  174 ,  176  and  184 ,  186  to determine when pump down occurs. The microprocessor controller checks each well for Pump Down on every stroke ( FIGS. 12-15  for pump down characteristics). The black dot  212  shown in  FIG. 12  indicates a rod load and a stroke position target for pump down check. If the rod load stays below this target past the pump off angle, the control takes it as indicating no pump down and increases the stroke length and speed 3% per stroke until it reaches max stroke length and speed setting. If the rod load stays above this target, pump down has occurred and the control reduces the stroke length and speed at the rate of 1.5% per stroke until it reaches the min stroke length setting. The pump down control will increase or decrease the stroke length and speed for each stroke as required to maintain a constant fluid level. 
     For example, if the microprocessor controller for Well  2  detects a Pump-Down condition, the microprocessor controller will reduce the stroke length and the speed for the ram pumping unit for Well  2  during each stroke until no pump down is detected, and then on the following stroke will increase the stroke length and speed until pump down is again detected. The stroke length and the speed are continuously adjusted to maintain a constant fluid level. To keep the wells synchronized; the microprocessor controller will decrease Well  2  speed the same percentage as it reduced its stroke length to match the period time cycle for Well  1 . Stroke Length and Speed will continue to decrease at a rate of 1.5% per stroke or increase at the rate of 3% until a constant fluid level is reached. The other well (Well  1 ) will continue to run at its preset speed and stroke length until it detects a pumped down condition: at which time it will decrease only its speed and Well  2  will increase its stroke length and speed to maintain a constant fluid level and stay synchronized with Well  1 . If Well  1  speed is decreased to the level of Well  2  its stroke length and speed will decrease to stay synchronized with Well  2 . The wells will always stay synchronized no matter which well is pumped-down. 
       FIG. 12  is a pump card illustrating pump down control, showing a plot  200  of rod load in pounds verses rod position in inches. The up stroke of the pump is represented as the upper portion of the plot  200 , running from point  202  at which the traveling valve closes, through point  204  at which the standing valve opens, and then to point  206  at which the standing valve closes. The downstroke is represented by the lower portion of the plot  200 , running from the point  206 , through point  208  at which the traveling valve opens, and then returning to the point  202  at which the traveling valve closes. The right side portion  210  of the plot  200  represents changes in the rod load which are encountered when pump off occurs. The rod load will remain at a larger weight until the traveling valve encounters the fluid level in the pump chamber, and then the rod load will decrease after entering fluid beneath the level of fluid in the pump chamber. The pump-off point  212  represents a point on the plot  200  which is selected as the point to reduce the speed of the pump to allow the fluid level to increase in the downhole pump chamber. The pump-off point  212  is detected when for a particular rod position the rod load is above a rod load at which the traveling valve is submerged. 
       FIGS. 13-15  illustrate a downhole pump  222  suspended on tubing  220  and powered by sucker rods  224 . The pump  222  has a pump chamber  226 , a traveling  228  and a standing valve  230 . The traveling valve  228  has a ball  232 , a ball seat  234  and a flow port  236  which passes through the ball seat  234 . The ball  232  will engage the ball seat  234  to seal the flow port  236 . Flow ports  238  are provide in the upper portion of the traveling valve  228  for passing fluid which passes through the flow port  236 . Similarly, the standing valve  230  has a ball  240 , a ball seat  242  and a flow port  244  which passes through the ball seat  242 . The ball  240  will engage the ball seat  242  to seal the flow port  244 . Flow ports  248  are provide in the upper portion of the standing valve  230  for passing fluid which passes through the flow port  244 . 
       FIG. 13  shows an up stroke and  FIGS. 14 and 15  show a downstroke for the pump  222 .  FIG. 13  show that during the up stroke, the rods  224  lift the traveling valve  228  and the weight of the fluid on top of the traveling valve  228  will seat the ball  234  on the ball seat  236 , closing the traveling valve  228 . In the standing valve  230  the ball  240  will lift off the seat  242 , opening the standing valve  230  and well fluids will flow into the pump chamber  236 .  FIGS. 14 and 15  shows that during the downstroke the traveling valve  228  will remain closed until the liquid level is encountered, at which time the traveling valve  228  will open and the standing valve  230  will be held closed by the traveling valve  228  moving toward the standing valve  230 . Well fluids in the pump chamber  226  will pass through the traveling valve  228 . The cycle will then repeat with the traveling valve  228  moving upward to lift the well fluids which are located above the traveling valve  228 , and the standing valve  230  will again open to pass well fluids into the pump chamber  226 . During the up stroke the pump  222  lifts the fluid that has entered the pump chamber  226  through the standing valve  230  on the previous up stroke, and fluid from the formation enters the pump barrel when the standing valve  230  opens. 
     During the up stroke the traveling valve  228  in the pump plunger closes and the fluid column weight is now on the sucker rods  224  as the fluid is lifted to the surface. The up stroke sucker rod load is the weight of the sucker rod string  224  and the weight of the fluid column being lifted by the traveling valve  238 . During the down stroke the traveling valve  228  will open when it contacts the fluid in the pump barrel  226  and the fluid column weight will transfer from the rod string  224  to the tubing  220 . If the pump barrel  226  did not fill completely during the up stroke the rod load will remain high until the traveling valve  228  reaches the pump fluid level  250 , at which time the traveling valve  228  will open and the fluid column weight will be removed from the sucker rods  224 , as shown in  FIG. 15 . Pump down can be detected by measuring the rod weight at the surface and the position of the pump stroke. A load transducer and stroke position system measures the distance from the top of the stroke to when the rod load changes as the traveling valve  228  opens, this is the pump down point  212  shown in  FIG. 12 , which is used to determine when pump down has occurred to a point which should then be corrected by adjusting the rate at which fluid is being pumped from the well. 
     For Dual Well regenerative operation, two wells are being synchronized to for recovering the downstroke energy of one well to assist in powering the up stroke for the other well. Should Well  2  pump-down, then the controller for Well  1  will continue to operate Well  1  at maximum speed and maximum stroke length until a pump down condition is detected. In response to detecting pump down in Well  2 , the speed and the stroke length of Well  2  are decreased by the same percentage so that Well  2  will remain synchronized with Well  1 . Similarly, should Well  1  pump-down, then in response to detecting pump down the speed and the stroke length of Well  1  are decreased by the same percentage so that Well  1  will remain synchronized with Well  2 . When pump down is not detected for either Well  1  or Well  2 , then the speed and the stroke length for that respective well are increased by the same percentage, up to maximum values, to remain synchronized with the other well. The Well  1  and Well  2  will always stay synchronized, starting and ending their cycles substantially together, no matter which well is pumped-down. 
     In maintaining a constant fluid level in the pump barrel, also referred to as the pump chamber, preferably during pump down detection of a well its Stroke Length and Speed will be decreased at a rate of 1.5% per stroke. When pump down is not detected, the Stroke Length and Speed are increased at the rate of 3.0% per stroke until pump down is detected. In other embodiments, the stroke lengths remain constant and the wells remain synchronized by slowing the speed of the non-pumped down well at the bottom of the up stroke until the pumped down well finishes the downstroke and begins its up stroke. 
     An example of pump down control is shown in Tables A, B and C which list calculated net power requirements with dual well regenerative assist between Well  1  and Well  2 , with Well  2  shown in a various pump down conditions. When pump down is encountered in one of the dual wells, the corresponding pump controller will reduce both the speed and the stroke length of a ram unit for the pumped-down well by the same percentage, to maintain a constant cycle time between up strokes and then down strokes such that the ram unit of the pumped down well will remain synchronized with a ram unit of the other well. Preferably the speed and the stroke length of the ram unit of the pumped down well will be decreased by 1.5% per stroke when pump down is detected, and will be increased, for this embodiment, by 3% per stroke until a constant fluid level is reached. The constant percentage change for the velocity and the stroke length will keep the period for an up stroke and a downstroke constant so that the two wells remain synchronized. 
     Well  1  and Well  2  are preferably synchronized to operate at the same number of cycles or number of strokes per minute, with the up stroke of one well occurring during the downstroke of the other well. Well  1  and Well  2  also have the following operational parameters: 
     Operating Speed: 3 Strokes per Minute (spm) 
     Maximum Stroke Length: 168 inches (14 feet) 
     Peak Polished Rod Load: 20,000 Lbs. (Up Stroke) 
     Minimum Polished Rod Load: 10,000 Lbs. (Downstroke) 
     
       
         
           
               
             
               
                 TABLE A 
               
             
            
               
                   
               
               
                 NET POWER REQUIRED DURING WELL NO. 1 UP STROKE 
               
            
           
           
               
               
               
               
               
               
            
               
                 PUMP DOWN 
                 WELL No. 2 
                 WELL No. 2 
                 WELL No. 1 
                 WELL No. 2 
                 WELL No. 1 
               
               
                 REDUCTION 
                 STROKE 
                 ROD 
                 UP STROKE 
                 DOWNSTROKE 
                 NET POWER 
               
               
                 (Stroke Length 
                 LENGTH 
                 VELOCITY 
                 POWER REQ. 
                 POWER ASSIST 
                 REQUIRED 
               
               
                 and Velocity) 
                 (Inches) 
                 (Feet/Min) 
                 (HP) 
                 (HP) 
                 (HP) 
               
               
                   
               
            
           
           
               
               
               
               
               
               
            
               
                  0% 
                 168 
                 84 
                 53.5 
                 26.8 
                 26.7 
               
               
                 20% 
                 134 
                 67 
                 53.5 
                 21.3 
                 32.2 
               
               
                 40% 
                 100 
                 50 
                 53.5 
                 16 
                 37.5 
               
               
                 50% 
                 84 
                 42 
                 53.5 
                 13.4 
                 40.1 
               
               
                 70% 
                 50.4 
                 25.2 
                 53.5 
                 8 
                 45.5 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE B 
               
             
            
               
                   
               
               
                 NET POWER REQUIRED DURING WELL NO. 2 UP STROKE 
               
            
           
           
               
               
               
               
               
               
            
               
                 PUMP DOWN 
                 WELL No. 2 
                 WELL No. 2 
                 WELL No. 2 
                 WELL No. 1 
                 WELL NO. 2 
               
               
                 STROKE &amp; 
                 STROKE 
                 ROD 
                 UP STROKE 
                 DOWNSTROKE 
                 NET POWER 
               
               
                 VELOCITY 
                 LENGTH 
                 VELOCITY 
                 POWER REQ. 
                 POWER Assist 
                 REQUIRED 
               
               
                 REDUCTION 
                 (Inches) 
                 (Feet/Min) 
                 (HP) 
                 (HP) 
                 (HP) 
               
               
                   
               
            
           
           
               
               
               
               
               
               
            
               
                  0% 
                 168 
                 84 
                 53.5 
                 26.8 
                 26.7 
               
               
                 20% 
                 134 
                 67 
                 42.7 
                 26.8 
                 15.9 
               
               
                 40% 
                 100 
                 50 
                 31.9 
                 26.8 
                 5.1 
               
               
                 50% 
                 84 
                 42 
                 26.8 
                 26.8 
                 0 
               
               
                 70% 
                 50.4 
                 25.2 
                 16 
                 26.8 
                 −10.8 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE C 
               
             
            
               
                   
               
               
                 TOTAL NET MOTOR POWER REQUIRED (FULL CYCLE) 
               
            
           
           
               
               
               
               
            
               
                 PUMP DOWN 
                 WELL No. 1 
                 WELL No. 2 
                 MAXIMUM 
               
               
                 STROKE &amp; 
                 UP STROKE NET 
                 UP STROKE NET 
                 MOTOR POWER 
               
               
                 VELOCITY 
                 POWER 
                 POWER 
                 REQUIRED 
               
               
                 REDUCTION 
                 (HP (kW)) 
                 (HP (kW)) 
                 (HP (kW)) 
               
               
                   
               
            
           
           
               
               
               
               
            
               
                  0% 
                 26.7 
                 26.7 
                 26.7 
               
               
                 20% 
                 32.2 
                 15.9 
                 32.2 
               
               
                 40% 
                 37.5 
                 5.1 
                 37.4 
               
               
                 50% 
                 40.1 
                 0 
                 40.1 
               
               
                 70% 
                 45.5 
                 −10.8 
                 45.5 
               
               
                   
               
            
           
         
       
     
     Without pump down requirements, the dual well regenerative assist would reduce in half the size of the motor required for a single well, from 53.5 horsepower (39.9 kW) motor to 26.7 horsepower (19.9 kW). However, with pump down requiring a reduction in stroke length and corresponding reduction in polished rod velocity to keep the cycle time consistent, to thereby synchronize the pumping units of the two wells, as shown above, a 45.4 horsepower (33.9 kW) rated motor is required, still allowing for a 15% reduction in the rating for the motor used for powering the dual well regenerative assist configuration. 
     For the first example of well data shown in the first rows of Tables A, B and C, pump down has not been detected and the stroke length and velocity of the ram pumping unit for Well  2  has not been reduced. At a stroke length of 168 inches and an operating speed of 3 strokes per minute, the rod velocity for Well  2  will be 84 fpm. Table A shows that during an up stroke of Well  1 , 53.5 hp is required for lifting the ram for Well  1 , during which the downstroke of Well  2  will provide a power assist of 26.7 hp. This will provide a net power requirement of 26.7 hp. Table B shows that during an up stroke of Well. 2, 53.5 hp is required for lifting the ram for Well  2 , during which the downstroke of Well  1  will provide a power assist of 26.8 hp. This will provide a net power requirement of 26.7 hp. The larger of the net horsepower is the same for both wells, 26.7 hp, which will be the minimum power requirement for the motor  16  without a reduction in the speed and the stroke length for the ram pump of Well  2 . 
     In the second example of well data shown in the second rows of Tables A, B and C, the Pump-Down Control for Well  2  has detected a pump-down condition and has reduced the stroke length and speed for Well  2  to maintain a constant fluid level. To keep the wells synchronized, the speed of Well  2 . has been decreased the same percentage as the polished rod stroke length. For Well  2  the Stroke Length and polished rod velocity will continue to decrease at a rate of 1.5% per stroke and increase at the rate of 3.0% until a constant fluid level is reached. In this example, the stroke length and the velocity of the ram pumping unit for Well  2  has been reduced by approximately 20 percent, which maintains the period for the cycle time for Well  2  to maintain synchronization will Well  1 . Table A shows that during an up stroke of Well  1 , 53.5 hp is required for lifting the ram for Well  1 , during which the downstroke of Well  2  will provide a power assist of 21.3 hp. This will provide a net power requirement of 32.2 hp. Table B shows that during an up stroke of Well  2 , 42.7 hp is required for lifting the ram for Well  2 , during which the downstroke Well  1  will provide a power assist of 26.8 hp. This will provide a net power requirement of 15.9 hp. Table C shows the larger of the net horsepower between Table 1 and Table 2 for the 20% reduction in the speed is 32.2 hp, which will be the minimum power requirement for the motor  16  at the 20% reduction in speed and stroke length for the ram pump for Well  2 . 
     In the third example of well data shown in the third rows of Tables A, B and C, pump down has been detected and the stroke length and velocity of the ram pumping unit for Well  2  has been reduced by approximately 40 percent, which maintains the period for the cycle time for Well  2  to maintain synchronization will Well  1 . Table A shows that during an up stroke of Well  1 , 53.5 hp is required for lifting the ram for Well  1 , during which the downstroke of Well  2  will provide a power assist of 16 hp. This will provide a net power requirement of 37.5 hp. Table B shows that during an up stroke of Well  2 , 31.9 hp is required for lifting the ram for Well  2 , during which the downstroke Well  1  will provide a power assist of 26.8 hp. This will provide a net power requirement of 5.1 hp. Table C shows the larger of the net horsepower between Table A and Table B for the 20% reduction in the speed is 37.5 hp, which will be the minimum power requirement for the motor  16  at the 40% reduction in speed and stroke length for the ram pump for Well  2 . 
     In the fourth example of well data shown in the fourth rows of Tables A, B and C, pump down has been detected and the stroke length and velocity of the ram pumping unit for Well  2  has been reduced by approximately 50 percent, which maintains the period for the cycle time for Well  2  to maintain synchronization will Well  1 . Table A shows that during an up stroke of Well  1 , 53.5 hp is required for lifting the ram for Well  1 , during which the downstroke of Well  2  will provide a power assist of 13.4 hp. This will provide a net power requirement of 40.1 hp. Table B shows that during an up stroke of Well  2 , 26.8 hp is required for lifting the ram for Well  2 , during which the downstroke of Well  1  will provide a power assist of 26.8 hp. This will provide a net power requirement of 0 hp. Table C shows the larger of the net horsepower between Table A and Table B for the 50% reduction in the speed is 40.1 hp, which will be the minimum power requirement for the motor  16  at the 50% reduction in speed and stroke length for the ram pump for Well  2 . 
     In the fifth example of well data shown in the first rows of Tables A, B and C, pump down has been detected and the stroke length and velocity of the ram pumping unit for Well  2  has been reduced by approximately 70 percent, which maintains the period for the cycle time for Well  2  to maintain synchronization will Well  1 . Table A shows that during an up stroke of Well  1 , 53.5 hp is required for lifting the ram for Well  1 , during which the downstroke of Well  2  will provide a power assist of 8 hp. This will provide a net power requirement of 45.5 hp. Table B shows that during an up stroke of Well  2 , 16 hp is required for lifting the ram for Well  2 , during which the downstroke Well  1  will provide a power assist of 26.8 hp. This will provide a net power requirement of −10.8 hp, which will not be recovered. Table C shows the larger of the net horsepower between Table A and Table B for the 70% reduction in the speed is 45.5 hp, which will be the minimum power requirement for the motor  16  at the 70% reduction in speed and stroke length for the ram pump for Well  2 . 
       FIG. 16  illustrates a multiple well system with regenerative assist power by a single prime mover  16 . Six hydraulic ram pumping units  262  (three pair) are shown being operated by the single prime mover  16  for pumping fluids form six different wells. The prime mover  16  will typically be a gas engine or an electric motor. Control units  44  are provided for operating each of first pumps  18  and second pumps  20 , each pair of the pumps  16  and  20  corresponding to powering a pair of the hydraulic ram pumping units  262 . Each of the pumping units  262  has at least one hydraulic ram  26 , such as that shown in  FIGS. 5 and 6  and  FIGS. 7 and 8 . The ram pumping units  262  are paired. If one of the ram pumping units  262  is taken out of service, then the accumulator  24  is provided for allowing the working ram pumping unit  262  of a pair to continue with the non-working ram pumping unit  262  of the pair remaining out of service. The shuttle valve  94  is connected to the high pressure side of each respective pair of the pumping units  262  and to the accumulator  24 . More wells than six may be added, preferably in pairs or an additional accumulator is required for mating with a single well if a single well is added to the singular prime mover  16 . The controllers  44  will also preferably provide pump down control, changing the stroke length and the stroke rate by the same percentage for a well being pumped down so that it remains synchronized with a paired well to end and begins each stroke simultaneously with the paired well. 
       FIGS. 17-19  show details of the support structure  112  of  FIGS. 7 and 8  for mounting the hydraulic ram  26  atop the ram pumping unit  108 . The structure  112  is provided with self-aligning features so that the hydraulic ram  26  will align with weight applied by the sucker rods  10 . The structure  112  includes a base  274  and an upper portion  276  which are pivotally connected together at a hinge  278 . Fasteners  280  secure the upper portion  276  in relation to the base  274 . The base  274  has legs  282  which are telescopically adjustable in length by means of turnbuckles which include threaded coupling collars  284 . Upper and lower portions of the legs  282  have external threads which are configured as threads of opposite hand, respectively, and opposite ends of the coupling collars  284  also have threads of opposite hand for mating with corresponding external threads on the legs  282 , such that the upper and lower portions are moved further apart or closer together depending upon the direction of rotation of the threaded couplings  284  around longitudinal centerlines of the legs  282 . Adjustment of the lengths of the legs  282  allow for rough alignment of the upper portion  276  relative to the wellhead  4 . The upper portion  276  has a mounting plate  288  to which the hydraulic ram  26  is mounted. The hydraulic ram  26  is mounted atop the mounting plate  288  and connected to the sucker rods  10  which extend through the tubing nipple  298 , the tubing  290  and into the stuffing box  6 . A spherical mounting configuration  300  is provided to allow the ram  26  to align with a centerline  292  of the tubing  290 , the stuffing box  6  and the wellhead  4 . A projection  296  of longitudinal centerline  296  of the ram  26  can move an angle  294  of approximately two degrees radially, so that the ram will align with the sucker rods  10  when the weight of the sucker rods  10  pull downward on the ram  26 . 
       FIG. 18  shows the spherical mounting configuration  300 . A dished ring  302  is mounted to the top of the mounting plate  288  with a dished face  304  facing upwards. The dished face  304  has a recess  306  which preferably has a concave, spherically shaped profile which tapers in a downward direction. A spherical shaped ring  308  is mounted to the lower end of the hydraulic ram  26 . The ring  308  has a lower face  310  which is conically shaped to define a convex, rounded surface which tapers in a downward direction. The rounded surface defined by the lower face  310  of the ring  308  will preferably fit flush against the rounded surface of the recess  306  in the ring  302  in a sliding engagement, which allows the ram  26  to pivot along the configuration  300  to align in the direction of the load applied by the sucker rods  10 . This will align the rod  30  and the cylinder  42  of the ram  26  with the direction in which the weight of the sucker rods pulls downward, which prevents seal wear for the ram  26  and friction which provides for more efficient operation of the ram  26 . 
       FIG. 19  shows the hydraulic ram  26  mounted atop the upper portion  276  of the support structure  112  to allow sliding movement between the spherical ring  308  and the dished ring  302 . The dished ring  302  is preferably fits in a recess  322  which extends into an upper surface of the mounting plate  288 . A radial clearance  322  of 0.125 inches is preferably provided between the dished ring  302  and the mounting plate  288 , across the recess  322 . The radial clearance  322  preferably extends fully around the sides of the dished ring  302 . The spherical ring  308  is preferably mounted in fixed relation to the ram  26  and the flange  312 . Fasteners  314  extend through holes in the mounting plate  288  and the flange  312  and have ends secured by nuts  316 . Sleeves  318  are mounted around the fasteners  314 , with ends disposed between the mounting plate  288  and the flange  312 . A clearance  320  of approximately 0.080 inches is provided between the upper ends of the sleeves  318  and the bottom side of the flange  312 . The clearances  320  and  322  provide an angle  294  of approximately two degrees for radial, pivotal movement of the centerline  296  of the ram  26  relative to the centerline  297  of the rods  10  and the tubing  290 . 
     A dual well hydraulic rod pumping unit has regenerative assist and synchronized variable stroke and variable speed pump down. Should pump down be encountered in one of the wells, the controllers reduce the speed and stroke of the ram for pumped-down well by the same percentage, such that ram unit the pumped down well will remain synchronized with the ram unit other well. Preferably the speed and stroke of the ram of the pumped down well will be decreased by 1.5% per stroke when pump down is detected, and will be increased by 3% per stroke until a constant fluid level is reached. The dual well regenerative system is preferably provided for wells in pairs, such as two wells, four wells, six wells, etc., in a cluster, and synchronizes a pair of wells so when one is on the up stroke the other one is on the down stroke. The down-stroke polished rod energy from the down-stroke of one well is used to assist the other well during its up-stroke and provide counter-balance. If one of the pair of wells is shut-down for work-over, a stand-by accumulator can be activated to provide power assist and counter-balance. A self-aligning mounting configuration is provided for mounting a hydraulic ram for a pumping unit to a support structure using a conical ring which fits into a dished ring. 
     Although the preferred embodiment has been described in detail, it should be understood that various changes, substitutions and alterations can be made therein without departing from the spirit and scope of the invention as defined by the appended claims.