Note: Descriptions are shown in the official language in which they were submitted.
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SYNCHRONIZED DUAL WELL VARIABLE STROKE AND VARIABLE SPEED
PUMP DOWN CONTROL WITH REGENERATIVE ASSIST
INVENTOR(S)
[0001] Larry D. Best, a resident of the City of Springtown, in Wise County,
Texas, United
States of America, and a citizen of the United States of America.
TECHNICAL FIELD OF THE INVENTION
[0002] The present application relates in general to pump units for oil wells,
and in particular
to a hydraulic pumping units having a regenerative assist.
[0003]
BACKGROUND OF THE INVENTION
[0004] 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.
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[0005] 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'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.
[0006] 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.
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SUMMARY OF THE INVENTION
[0007] 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.
[0008] 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.
[0009] 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
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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.
[0010] 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.
[0011] 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 rod load.
[0011a] Accordingly, in one aspect the present invention resides in a dual
well hydraulic
pumping unit for removing well fluids from a first well and a second well,
comprising: a
prime mover having a rotary drive shaft for turning in a first angular
direction; a reservoir for
a hydraulic fluid; a first sucker rod assembly disposed in the first well for
removing the well
fluids from the first well; a first ram connected to said first sucker rod
assembly for moving
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in an upstroke and moving said first sucker rod assembly from a downward
position to an
upward position, and moving in a downstroke with said first sucker rod
assembly moving
from said upward position to said downward position; a second sucker rod
assembly
disposed in the second well for removing the well fluids from the second well;
a second ram
connected to said second sucker rod assembly for moving in an upstroke and
moving said
second sucker rod assembly from a lowered position to a raised position, and
moving in a
downstroke with said second sucker rod assembly moving from said raised
position to said
lowered position; a first ram pump connected to said rotary drive shaft, said
first ram pump
having a first ram pump suction port connected to said reservoir and a first
ram pump
discharge port connected to said first ram for during the upstroke of said
first ram
transferring the hydraulic fluid into said first ram and moving said first ram
from a
downward position to an upward position, and during the downstroke of said
first ram pump
transferring the hydraulic fluid into said reservoir; a second ram pump
connected to said
rotary drive shaft, said second ram pump having a second ram pump suction port
connected
to said reservoir and a second ram pump discharge port connected to said
second ram for
during the upstroke of said second ram transferring the hydraulic fluid into
said second ram
and moving said second ram from a lowered position to a raised position, and
during the
downstroke of said second ram pump transferring the hydraulic fluid into said
reservoir; and
at least one control unit adapted for controlling flow rates of the hydraulic
fluid through said
first ram pump and said second ram pump, and adapting said first ram pump for
pumping the
hydraulic fluid into said first ram during the upstroke and during the
downstroke passing the
hydraulic fluid from said first ram into said reservoir and turning said
rotary shaft in said first
angular direction to power said second ram pump in response to pressures
within said first
ram provided by the weight of said first sucker rod assembly in combination
with said prime
mover, and adapting said second ram pump for pumping the hydraulic fluid into
said second
ram during the downstroke of said first ram and the upstroke of said second
ram and turning
said rotary shaft in said first angular direction to power said second ram
pump in response to
pressure within said second ram provided by the weight of said second sucker
rod assembly
in combination with said prime mover.
[0011b] In another aspect the present invention resides in a method for
operating a pumping
unit, comprising the steps of: providing a first hydraulic ram and a first
sucker rod assembly,
the first sucker rod assembly and the first hydraulic ram are located at a
first well and
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configured for lifting well fluids from within the first well, and a second
hydraulic ram and a
second sucker rod assembly, the second sucker rod assembly and the second
hydraulic ram
are located at a second well and configured for lifting well fluids from
within the second
well; further providing at least one control unit, a drive motor, a first ram
pump, a second
ram pump, a reservoir for a hydraulic fluid, wherein the control unit, the
drive motor, the
reservoir, the first ram pump, and the second ram pump are configured for
moving the
hydraulic fluid between the reservoir, the first hydraulic ram and the second
hydraulic ram
for lifting and lowering respective ones of the first and second sucker rod
assemblies;
connecting the first ram pump, the second ram pump and the drive motor to a
rotary shaft for
rotating in one angular direction during both upstrokes and downstrokes of the
first and
second hydraulic rams; releasing the hydraulic fluid from the first hydraulic
ram into the first
ram pump and to the reservoir, and thereby providing mechanical power in
combination with
the drive motor for turning the rotary shaft which powers the second ramp pump
to move the
hydraulic fluid into the second hydraulic ram; releasing the hydraulic fluid
from the second
hydraulic ram into the first ram pump and to the reservoir, and thereby
providing mechanical
power in combination with the drive motor for turning the rotary shaft which
powers the
second ramp pump to move the hydraulic fluid into the second hydraulic ram;
controlling the
flow of the hydraulic fluid from the first hydraulic ram, through the first
ram pump and into
the reservoir, and the flow of the hydraulic fluid from the second hydraulic
ram, through the
second ram pump and into the reservoir; and wherein first potential energy is
recovered from
the first sucker rod assembly when disposed in a lifted position and used to
operate the
second ram pump for assisting in the upstroke of the second hydraulic ram, and
second
potential energy is recovered from the second sucker rod assembly when
disposed in a lifted
position and used to operate the first ram pump for assisting in the upstroke
of the first
hydraulic ram.
DESCRIPTION OF THE DRAWINGS
100121 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
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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
5 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; and
FIG. 16 illustrates multiple well system with regenerative assist power by a
single
prime mover or motor.
DETAILED DESCRIPTION OF THE INVENTION
[0013] 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
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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.
[0014] 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.
[0015] 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
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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.
[0016] 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 54 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 62.
The retainers 62 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,
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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.
[0017] 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.
[0018] 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.
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[0019] 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.
[0020] 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.
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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-
5 sectional area of the piston rod 30.
[0021] 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
10 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.
[0022] 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
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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.
[0023] 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.
[0024] 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
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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.
[0025] 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.
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[0026] 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).
[0027] 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-
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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.
[0028] 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).
[0029] 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
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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
5 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
10 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
15 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.
[0030] 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.
[0031] This system is preferably used for a cluster of wells which are within
150 ft.(50m) of
each other, and it allows a single hydraulic power unit 14 to operate up to
four different wells.
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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.
[0032] 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'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.
[0033] 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
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preferably close to each other, spaced apart no more than 150 Ft .(50m) to
allow the hydraulic
pump assist to function properly. The following are examples of a test well:
CYLINDER "A" ON UP STROKE CYLINDER "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.)
[0034] 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.
[0035] 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
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displacement of the pump.
[0036] 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.
[0037] 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.
100381 FIG. 11 is a schematic block diagram of variable stroke and speed pump
down
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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
Figure 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.
[0039] 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.
[0040] 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
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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
5 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
10 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.
[0041] FIGS. 13-15 illustrate a downhole pump 222 suspended on tubing 220 and
powered
15 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
20 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.
[0042] 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 ad 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.
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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.
[0043] 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.
[0044] 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
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will always stay synchronized, starting and ending their cycles substantially
together, no
matter which well is pumped-down.
[0045] 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.
[0046] 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.
[0047] 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)
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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 & 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 & 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
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40% 37.5 5.1 37.4
50% 40.1 0 40.1
70% 45.5 -10.8 45.5
[0048] 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.
[0049] 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.
[0050] 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
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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
5 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
10 speed and stroke length for the ram pump for Well 2.
[0051] 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
15 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
20 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.
[0052] 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
25 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
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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.
[0053] 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.
[0054] 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
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well to end and begins each stroke simultaneously with the paired well.
[0055] 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.
[0056] 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 scope of the invention as defined by the appended claims.
