Note: Descriptions are shown in the official language in which they were submitted.
CA 02799888 2012-12-20
LIFT SYSTEM
TECHNICAL FIELD
[0001] The present invention relates to lift systems, including hydraulic
lift
systems used in pump jack applications.
BACKGROUND
[0002] Hydraulic lift systems are used in a number of applications. One
type
of application is as a pump jack for operating a down-well pump. Hydraulic
lift
systems used in this type of application are an alternative to conventional
"donkey" or "rocking-arm" type pump jacks.
[0003] Typically, hydraulic lift systems which are used as pump jacks
suffer
from a number of problems. These problems may include complexity, low
efficiency and high power requirements. Often, the shortcomings of current
hydraulic lift systems makes them unsuitable for use as pump jacks other than
in
temporary production or tuning applications.
[0004] Accordingly, there is a need for improved lift systems.
SUMMARY
[0005] In an aspect of the present invention, there is provided a hydraulic
lift
system comprising; a source of pressurized hydraulic fluid; a plurality of
hydraulic
cylinders, each one of the cylinders having a piston therein with a piston rod
of
the piston extending from an end of each one of the hydraulic cylinders,
wherein
the piston rods are mechanically interconnected so that the piston rods and
the
pistons of each of the hydraulic cylinders are operable to move upwards and
downwards in unison with each other; a hydraulic fluid communication sub-
system operable to deliver fluid from the source of pressurized hydraulic
fluid to
at least a first cylinder of the plurality of hydraulic cylinders to drive the
pistons in
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CA 02799888-2012-12-20
an upward direction through an upstroke; the hydraulic fluid communication sub-
system also operable to deliver hydraulic fluid from the source of pressurized
hydraulic fluid to a second cylinder of the plurality of hydraulic cylinders
to drive
the pistons in a downward direction through a downstroke; the hydraulic fluid
communication sub-system also operable to deliver hydraulic fluid from the
first
cylinder to the second cylinder; a hydraulic fluid flow control sub-system
operable
to: (a) selectively direct hydraulic fluid from the source of pressurized
hydraulic
fluid to the first cylinder to drive the pistons in an upward direction to
provide an
upstroke; and (b) alternatively, selectively direct hydraulic fluid from the
source of
pressurized hydraulic fluid to the second cylinder to drive the pistons in a
downward direction to provide a downstroke; and (c) during the downstroke
direct hydraulic fluid from the first cylinder to the second cylinder to
assist the
second cylinder in driving the pistons in the downward direction during the
downstroke.
[0006] In another aspect of the present invention, there is provided a
method
of reciprocating a down-well pump in a shaft of a well, the method comprising:
a)
pumping a pressurized fluid into a lift chamber of a first hydraulic cylinder
to lift a
carriage coupled to the down-well pump and to a piston of the first hydraulic
cylinder; b) pumping a pressurized fluid into a lowering chamber of a second
hydraulic cylinder having a piston coupled to the carriage, to lower the
carriage;
c) connecting the lift chamber in fluid communication with the lowering
chamber
such that pressurized fluid is expelled from the lift chamber into the
lowering
chamber during the lowering.
[0007] In another aspect of the present invention, there is provided a lift
system comprising a pump for supplying a flow of pressurized driving fluid; at
least one upward driving cylinder having a movable piston rod; at least one
downward driving cylinder having a movable piston rod; the piston rods of the
upward driving cylinder and the downward driving cylinder being interconnected
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CA 02799888 2012-12-20
to each other such that the piston rods of both the upward driving cylinder
and
the downward driving cylinder are operable to move upwards and downwards in
unison with each other; a driving fluid communication sub-system operable to
deliver a flow of driving fluid supplied by the pump from the pump to the
upward
driving cylinder to drive the piston rods in an upward direction in an
upstroke; the
driving fluid communication sub-system also operable to deliver a flow of
driving
fluid supplied by the pump from the pump to the downward driving cylinder to
drive the piston rods in a downward direction in a downstroke; and the driving
fluid communication sub-system also operable to deliver a flow of driving
fluid in
the upward driving cylinder from the upward driving cylinder to the downward
driving cylinder during the downstroke; a fluid direction control sub-system
operable to: (a) in a first mode of operation to direct a flow of driving
fluid from
the pump to the upward driving cylinder to drive the pistons in an upward
direction to create an upstroke; (b) in a second mode of operation to direct a
flow
of driving fluid from the pump to the downward driving cylinder to drive the
pistons in a downward direction to create a downstroke; and (c) in the second
mode of operation, to also direct a flow of driving fluid from the upward
driving
cylinder to the downward driving cylinder during the downstroke, such that
during
the downstroke, the driving fluid is delivered from the upward driving
cylinder
to/towards the downward driving cylinder to assist the downward driving
cylinder
in driving the pistons in the downward direction during the downstroke.
[0008] In another
aspect of the present invention, there is provided a method
of moving a reciprocating mass upwards and downwards, the method comprising
a) providing a pump for supplying a flow of pressurized driving fluid; b)
providing
at least one upward driving cylinder having a movable piston rod
interconnected
to the reciprocating mass; c) providing at least one downward driving cylinder
having a movable piston rod interconnected to the reciprocating mass; the
piston
rods of the upward driving cylinder and the downward driving cylinder being
interconnected to each other such that the piston rods of both the upward
driving
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cylinder and the downward driving cylinder are operable to move upwards and
downwards in unison with each other; d) providing a driving fluid
communication
sub-system for delivering a flow of driving fluid supplied by the pump from
the
pump to the upward driving cylinder to drive the piston rods in an upward
direction in an upstroke and for delivering a flow of driving fluid supplied
by the
pump from the pump to the downward driving cylinder to drive the piston rods
in
a downward direction in a downstroke, the driving fluid communication sub-
system also for delivering a flow of driving fluid in the upward driving
cylinder
from the upward driving cylinder towards the downward driving cylinder during
the downstroke; e) providing a fluid direction control sub-system; f)
directing a
flow of driving fluid from the pump to the upward driving cylinder to drive
the
pistons in an upward direction to create an upstroke to thereby move the
reciprocating mass upwards; g) directing a flow of driving fluid from the pump
to
the downward driving cylinder to drive the pistons in a downward direction to
create a downstroke; and simultaneously also directing a flow of driving fluid
from
the upward driving cylinder to the downward driving cylinder during the
downstroke, such that during the downstroke, the driving fluid is delivered
from
the upward driving cylinder to the downward driving cylinder to assist the
downward driving cylinder in driving the pistons in the downward direction
during
the downstroke, to thereby move the reciprocating mass downwards.
[0009] In another
aspect of the present invention, there is provided a method
of operating a lift system, wherein lift system comprises: a pump for
supplying a
flow of pressurized driving fluid; at least one upward driving cylinder having
a
movable piston rod; at least one downward driving cylinder having a movable
piston rod; the piston rods of the upward driving cylinder and the downward
driving cylinder being interconnected to each other such that the piston rods
of
both the upward driving cylinder and the downward driving cylinder are
operable
to move upwards and downwards in unison with each other; a driving fluid
communication sub-system for delivering a flow of driving fluid supplied by
the
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pump from the pump to the upward driving cylinder to drive the piston rods in
an
upward direction in an upstroke and for delivering a flow of driving fluid
supplied
by the pump from the pump to the downward driving cylinder to drive the piston
rods in a downward direction in a downstroke, the driving fluid communication
sub-system also for delivering a flow of driving fluid in the upward driving
cylinder
from the upward driving cylinder towards the downward driving cylinder during
the downstroke; a fluid direction control sub-system operable to: (a) in a
first
mode of operation to direct a flow of driving fluid from the pump to the
upward
driving cylinder to drive the pistons in an upward direction to create an
upstroke;
(b) in a second mode of operation to direct a flow of driving fluid from the
pump to
the downward driving cylinder to drive the pistons in a downward direction to
create a downstroke; and (c) in the second mode of operation, to also direct a
flow of driving fluid from the upward driving cylinder to the downward driving
cylinder during the downstroke; and wherein the method comprises: a) directing
a flow of driving fluid from the pump to the upward driving cylinder to drive
the
pistons in an upward direction to create an upstroke; b) directing a flow of
driving
fluid from the pump to the downward driving cylinder to drive the pistons in a
downward direction to create a downstroke; and simultaneously also directing a
flow of driving fluid from the upward driving cylinder to the downward driving
cylinder during the downstroke, such that during the downstroke, the driving
fluid
is delivered from the upward driving cylinder to the downward driving cylinder
to
assist the downward driving cylinder in driving the pistons in the downward
direction during the downstroke.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] In the figures, which illustrate by way of example only, embodiments
of
this invention:
[0011] FIG. 1. is a schematic view of a lift system in exemplary of an
embodiment of the present invention;
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[0012] FIG. 2. is an enlarged front elevation view of a portion
of the lift system
=
of FIG. 1;
[0013] FIG. 3 is a schematic view of part of the lift system of
FIG. 1;
[0014] FIG. 4 is a schematic view of the lift system of FIG. 1
in a stationary
state;
[0015] FIG. 5 is a schematic view of forces acting on components
of the lift
system of FIG. 1 in the state of FIG. 4;
[0016] Fig. 6 is a schematic view of the lift system of FIG. 1
in a first state of
operation;
[0017] FIG. 7 is a schematic view of forces acting on components
of the lift
system of FIG. 1 in the state of FIG. 6;
[0018] FIG. 8 is a schematic view of the lift system of FIG. 1
in a second state
of operation;
[0019] FIG. 9 is a schematic view of forces acting on components
of the lift
system of FIG. 1 in the state of FIG. 8;
[0020] FIG. 10 is a schematic view of another lift system;
[0021] FIG. 11 is a schematic view of the lift system of FIG. 10
in a first state
of operation;
[0022] FIG. 12 is a schematic view of the lift system of FIG. 10
in a second
state of operation.
DETAILED DESCRIPTION
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[0023] FIG. 1 depicts an example lift system 100. Lift system 100 may be
installed at a wellhead 102 for extracting fluids, e.g. oil, natural gas
and/or
dewatering fluid from a reservoir 104.
[0024] Extraction of fluids from a reservoir 104 may be effected by
operation
of a down-well pump 106 at the bottom of a well shaft 108. Down-well pump 106
may be operated by up-and-down reciprocating motion of a sucker rod 110. It
should be noted that in some applications, the well shaft 108 may not be
oriented
entirely vertically, but may have horizontal components and/or portions to its
path.
[0025] With each downward stroke of sucker rod 110, down-well pump 106
may be moved downwardly and a one-way valve 112 opens, admitting fluid from
reservoir 104 into down-well pump 106. During this downstroke, one-way valve
114 at the bottom of well shaft 108 may be closed, preventing fluids from
escaping. During each upstroke of sucker rod 110, down-well pump 106 may be
drawn upwardly and one-way valve 112 may be closed. Thus, fluids drawn in
through one-way valve 112 during the downstroke can be raised. When one-way
valve 114 opens, fluids can enter well shaft 108 through one-way valve 114 and
passages 116. Successive upstrokes of down-well pump 106 form a column of
fluid in well shaft 108 above down-well pump 106. Once this column of fluid is
formed, each upstroke pushes a volume of fluid to the surface.
[0026] Sucker rod 110 may be actuated by a set of cylinders which may be
hydraulic cylinders 118a, 118b, 118c (collectively, cylinders 118). Hydraulic
cylinders 118 may be supported on a frame 120 mounted to well head 102 by
conventional means, e.g., by welding and/or using fasteners. Sucker rod 110
may be attached to cylinders 118 by a carriage 122, described in more detail
below. Cylinders 118 may be arranged above and in generally parallel
orientation with sucker rod 110. Cylinder 118c may be vertically oriented and
axially aligned with sucker rod 110 and cylinders 118a, 118b may be vertically
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oriented but transversely spaced equal distances to either side of cylinder
118c.
Cylinders 118a-c may also be transversely aligned with each other in a
transverse plane. That way, the forces acting up and down on carriage 122 by
the cylinders 118 in both the upstroke and downstrokes of the lift system 100
may not cause any moment or rotation of the carriage about the axis of the
sucker rod (ie. it will move the sucker rod up and down without any
significant
tendency to rotate the sucker rod).
[0027] Cylinders 118 may be powered by a fluid circuit 124. Fluid circuit
124
may comprise a reservoir 126 containing a driving fluid, such as hydraulic
fluid, a
source of pressurized driving fluid, such as pump 128 and a fluid
communication
sub-system comprising communication lines 130, 132, in fluid communication
with cylinders 118 by way of a fluid flow control subsystem 134 that may
comprise a plurality of valves as described below (also referred to herein as"
valve subsystem 134"). The driving fluid may for example be any suitable fluid
that is substantially incompressible, contains anti-wear additives or
constituents,
and has an ability to transfer heat from within fluid circuit 124 to reservoir
126.
By way of example, driving fluid within fluid circuit 124 may reach
temperatures
within the range of -40 C to 80 C Some example driving fluids include
SKYDROLTM airplane fluid, automatic transmission fluid, and other synthetic
and
semi-synthetic fluids.
[0028] In the depicted embodiment, line 130 may be a hose or pipe with an
internal diameter (ID) of 1 inch and line 132 may be a hose or pipe with an ID
of
1.25 inches. Fluid communication lines described herein may be, for example,
steel lines or steel braided hydraulic lines with appropriate pressure rating
and
resistance to environmental factors such as UV exposure, high temperature and
abrasion. Pump 128 may be a variable-displacement piston pump able to deliver
a flow rate of about 46 gallons of hydraulic fluid per minute at a pressure of
at
least 3000 psi. For example pump 128 may be a series 45 axial piston open
circuit pump made by Sauer Danfoss. The output flow rate of a variable-
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displacement piston pump may be adjustable by changing the pump's
displacement in each cycle. The flow rate of pump 128 determines the speed at
which lift system 100 performs each downstroke or upstroke. Thus,
conveniently, pump 128 may allow the operating speed, that is the speed and
frequency of strokes of lift system 100, to be changed. By way of example
only,
lines which carry peak system hydraulic pressure may be sized to create a
maximum fluid velocity of about 20 feet per second. Lines which carry low
hydraulic pressure under 500 psi, that is, lines which drain to reservoir 126,
may
be sized to create a maximum fluid velocity of about 4 feet per second. Lines
which carry counterbalance fluid may be sized to create a maximum fluid
velocity
of about 100 feet per second.
[0029] Pump 128 may be controlled for pressure-compensated operation.
That is, pump 128 may be controlled to operate so as to maintain a
substantially
constant pressure of driving fluid. Run in these conditions, pump 128 may
output
a substantially constant volumetric flow rate of driving fluid. The pressure
and
flow rate output by pump 128 may be linked. That is, increasing the pressure
produced by pump 128 may also result in an increased flow rate, while
decreasing the pressure may result in a decreased flow rate. Also, since the
forces acting upon the components of the lift system may be dynamic and vary
over time, it is possible that in order to maintain a substantially constant
rate of
flow of driving fluid throughout the fluid circuit 124, the pump pressure may
have
to be adjusted. For example, if varying amounts of friction are encountered
throughout the operation of the cylinders 118, the pressure setting of the
pump
may need to be adjusted. Further details of an example of suitable pump 128
for
use with hydraulic fluid and the manner in which it is controlled may be found
in a
brochure entitled "Series 45 Axial Piston Open Circuit Pumps Technical
Information", published 2011 by Sauer Danfoss and available at
http://vvww.sauer-
danfoss.com/Products/PistonPumpsandMotors/OpenCircuitAxialPistonPumps/in
dex.htm, the contents of which are hereby incorporated by reference.
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[0030] In other embodiments, pump 128 could be another type of pump
operable to deliver a suitable pressure and flow rate, such as a vane or gear
pump with means of creating variable displacement and pump controls or
external valves to regulate flow. Pump 128 may be configured to deliver a flow
rate of about 46 gallons per minute (GPM), however in other embodiments, pump
128 may be sized to deliver flow rates between 10-150 GPM at pressures
between 500-5000 psi. Pump 128 may be selected so that it can deliver a
substantially constant flow rate during operation. In some embodiments, pump
128 may deliver a varying flow rate during operation.
[0031] Cylinders 118 may be provided with a counterbalance subsystem that
can be used to offset some or all of the weight of the various components
acting
down. The counterbalance subsystem may comprise a counterbalance fluid
reservoir 136 holding a counterbalance fluid. Counterbalance fluid reservoir
136
may be in fluid communication with a lower chamber of cylinder 118c through
fluid communication line 138 and multi-way valve subsystem 134. The
counterbalance fluid may be a compressible gas, and the gas may be inert. For
example the counterbalance fluid may be nitrogen.
[0032] Turning to FIG. 2, lift system 100 is depicted in more detail.
Cylinders
118 may be oriented such that they are aligned with one another in a
transverse
plane when connected to carriage 122. Carriage 122 may be a generally flat
plate made from a suitably strong'material such as steel. Cylinders 118 may be
fixedly mounted to frame 120 by conventional attachment devices such as for
example bolts and/or welding and may be oriented with their rod ends
downwards. Cylinders 118 may contain pistons 140a, 140b and 140c
(collectively referred to as pistons 140). Piston rods 141a, 141b, 141c
(collectively referred to as piston rods 141) may be interconnected to or
integrally
formed with pistons 140 and may extend from pistons 140 and protrude from
ends of cylinders 118a, 118b, 118c, respectively, and can be commonly and
fixedly mounted to carriage 122. When any of pistons 140 moves within the
CA 02799888 2012-12-20
respective cylinder 118, piston rods 141 likewise move therewith. Pistons 140
may thus be mechanically coupled to one another by piston rods 141 and
carriage 122 and therefore pistons 140 can move together in unison during
operation. Carriage 122 may comprise upper and lower plates 143a,b mounted
to and held together by three rods 145, 147, 149. Sucker rod 110 may be
mounted to carriage 122 by one or more clamps 142 or other suitable attachment
mechanisms. Sucker rod 110 may also be provided with a rotator 144. Rotator
144 may rotate sucker rod 110 to promote even wearing of parts down well shaft
108, particularly in applications in which at least a portion of well shaft
108 is
horizontal. Further, down-well pump 106 may resist rotation, so that rotation
of
sucker rod 110 may serve to tighten threaded joints, which may help to prevent
disconnection of components by unthreading. Rod 149, clamp 142 and rotator
144 may be attached to one another by conventional fixation devices or
techniques, with rod 149 attached to plate 143a and rotator 144 attached to
plate
143b, so that collectively, rod 149, clamp 142 and rotator 144 are mounted to
and connect plates 143a,b. Frame 120 may be mounted to wellhead 102 by
conventional attachment devices, such as by a series of bolted and/or welded
flanges.
[0033] Down-well pump 106 may be operated by reciprocating motion of
pistons 140 and piston rods 141. During an upstroke, pistons 140, carriage
122,
rotator 144, sucker rod 110 and down-well pump 106, hereinafter referred to
collectively as the reciprocating masses, are drawn upwardly, as is down-well
pump 106. Conversely, during a downstroke, the reciprocating masses are
lowered. Therefore, as used herein, an upstroke or downstroke of lift system
100
means an upstroke or downstroke of the reciprocating masses. Also, the terms
upstroke and downstroke refer to the movements of the pistons 140 and piston
rods 141 in their cylinders 118.
[0034] By way of example only, cylinders 118 may be approximately 174
inches in length, and pistons 140 and piston rods 141 may be moved through a
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stroke approximately 168 inches in length. In some example embodiments, the
stroke of the reciprocating masses may be between 48 inches and 360 inches in
length and cylinders 118 may be slightly longer than the stroke to avoid
"bottoming out" of the piston at either end of the chambers. In other
embodiments, cylinders 118 may be longer if a longer stroke is desired.
[0035] Each of cylinders 118 may be a piston-type device. Each of cylinders
118a, 118b, 118c may have an upper (blind end) chamber 119a, 119b, 119c
(collectively, chambers 119) above the respective one of pistons 140 and a
bottom (rod end) chamber 121a, 121b, 121c (collectively, chambers 121) below
the respective one of pistons 140. Each of pistons 140 has a rod end face
partially defining the respective rod end chamber 121 and a blind end face
partially defining the respective blind end chamber 119.
[0036] Ports 125a, 125b, 125c allow for communication of fluid into or out
of
each of blind end chambers 119a, 119b,119c. Ports 125a, 125b are open to the
atmosphere, while port 125c is connected to line 138. Ports 127a, 127b, 127c
allow for communication of fluid into or out of each of blind end chambers
121.
Ports 127a, 127b are connected to lines 146a, 146b respectively. Port 127c is
connected to line 138.
[0037] The rod end inlet/outlet ports 127a, 127b of cylinders 118a, 118b,
respectively are connected by fluid communication lines 146a, 146b to valve
subsystem 134. Lines 146a, 146b may, by way of example only, be hoses or
pipes with an internal diameter ("ID") of 0.75 inches. Lines 146a and 146b may
merge into a common line that may have an ID of 1 inch which runs into valve
subsystem 134. The blind end inlet/outlet ports 125a, 125b of cylinders 118a,
118b may be open to atmosphere as the upper chambers in cylinders 118a,
118b are not filled with, and emptied of, driving fluid.
[0038] The rod end inlet/outlet 127c of cylinder 118c may be connected by
fluid communication line 138 to counterbalance reservoir 136. The blind end
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inlet/outlet 125c of cylinder 118c may be connected by fluid communication
line
148 to valve subsystem 134. In the depicted embodiment, each of lines 138 and
148 may be a hose or pipe with an ID of 1.25 inches.
[0039] Turning now to FIG. 3, example components of lift system 100 are
depicted schematically in detail.
[0040] In one embodiment, valve subsystem 134 may comprise a 4-port, 3-
state valve 150, check valve 152 and counterbalance valve 154. 3-state valve
150 may have a first port 151c connected to driving fluid pump 128 by way of
fluid communication line 130 to receive pressurized driving fluid. A second
port
151d of 3-state valve 150 may be connected to driving fluid reservoir 126 by
way
of fluid communication line 132 for draining driving fluid. Third and fourth
ports
151a, 151b of 3-state valve 150 may be connected to two different flow paths
through valve subsystem 134. While valve 150 is in a first state, lift system
100
is in a first mode of operation performing an upstroke. While valve 150 is in
a
second state, lift system 100 is in a second mode of operation performing a
downstroke. While valve 150 is in a third state, lift system 100 may be
stationary.
As will become apparent, valve subsystem 134 controls flow of driving fluid,
selectively directing pressurized fluid either to rod end chambers 121a,b of
cylinders 118a,b or to the blind end chamber 119c of cylinder 118c.
[0041] A first flow path through valve subsystem 134 connects one port 151a
of 3-state valve 150 to a first inlet/outlet 153a of valve subsystem 134 which
may
be in fluid communication with chambers 121a, 121b by way of lines 146a, 146b.
This flow path passes through a one-way check valve 158 in one direction, and
through a relief valve 156 in the other direction. Relief valve 156 may be
biased
closed to resist flow up to a certain pressure, which may be adjustable. In
some
embodiments, relief valve 156 and check valve 158 for example may be part of a
model CBEA counterbalance valve, manufactured by Sun Hydraulics
Corporation. Relief valve 156 may be provided with pilot lines 160, 162. Under
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CA 02799886 2012-12-20
certain conditions as will be explained below, if pressure in the blind end
chamber 119c of cylinder 118c exceeds the opening pressure of relief valve
156,
pilot line 162 cause relief valve 156 to smoothly open, diverting driving
fluid to
reservoir 126.
[0042] A second flow path through valve subsystem 134 connects one port
151b of 3-state valve 150 to a second inlet/outlet 153b of valve subsystem 134
which may be in fluid communication with chamber 119c by way of line 148.
[0043] A one-way cross-relief valve 152 lies between the first and second
flow
paths. The cross-relief valve may be biased closed by a pilot line 164. In
some
embodiments, cross-relief valve 152 may be a model COFA pilot-closed check
valve, manufactured by Sun Hydraulics Corporation. Alternatively, cross-relief
valve 152 may be biased closed by other means, such as electronically using a
solenoid or with a spring.
[0044] In some embodiments, the components of valve subsystem 134 may
be part of a single module, such as a model YDEC-LHN pressure sensitive
regenerative valve assembly, made by Sun Hydraulics Corporation.
[0045] Pump 128 may be in communication with driving fluid reservoir 126
and one of ports 151a, 151b of 3-state valve 150 to supply pressurized driving
fluid to cylinders 118 by way of valve subsystem 134. As will become apparent,
the upstroke lifting force of lift system 100 may be created by pressure in
the rod
ends 121a, 121b of cylinders 118a and 118b, which may be assisted during at
least part of the stroke by an upward counterbalance force acting on piston
140c.
Thus, cylinders 118a, 118b are upward driving cylinders. The total lifting
force
acting on pistons 140a, 1.40b is the product of the pressure in the rod-end
chambers during lifting and the total area of the rod-end sides of pistons
140a,
140b. Pump 128 may be therefore selected to develop sufficient pressure to
provide the desired lifting force and to provide a sufficient flow rate for
the
desired lifting rate.
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CA 02799888 2012-12-20
[0046] Similarly, the downstroke lowering force may be created by pressure
in
the blind end chamber 119c of cylinder 118c. Thus, cylinder 118c is a downward
driving cylinder.
[0047] Pump relief valve 166 may provide a bypass flow path from pump 128
to fluid reservoir 126 to prevent excessive pressure from developing in the
fluid
communication lines, for example, when pistons 140 reach the limit of their
travel. Pump relief valve 166 may be biased closed, for example by a spring.
If
pressure reaches a predetermined threshold, a pilot line may cause pump relief
valve 166 to open, draining excess fluid back to reservoir 126.
[0048] The rod end of cylinder 118c may be in fluid communication with a
counterbalance reservoir 136 by way of communication line 138.
Counterbalance reservoir 136 may have two chambers, one containing a first
counterbalance fluid and the other a second counterbalance fluid. In the
depicted embodiment, the first counterbalance fluid may be hydraulic fluid and
the second counterbalance fluid may be counterbalance fluid gas which may be
nitrogen most commonly at pressures in the range of 1200-2000 psi, depending
on the characteristics of the particular application, such as the size of down-
hole
pump 106, depth of well shaft 108 and other well characteristics. However, in
some example embodiments, the second counterbalance fluid may be at
pressures as low as 200 psi or as high as 3000 psi. The temperature of the
second counterbalance fluid is generally close to that of ambient air in the
environment in which system 100 is installed. Typically, the ambient
temperature
is between about -40 C and 50 C. The second counterbalance fluid may be
another suitable inert compressible fluid. A floating piston 170 separates the
two
chambers. During each downstroke of lift system 100, some of the first
counterbalance fluid from the lower chamber of cylinder 118c and line 138 may
be forced into reservoir 136, causing piston 170 to be displaced upwards to
thereby compress the second counterbalance fluid (e.g. nitrogen gas), storing
energy. During each upstroke, the compressed second counterbalance fluid,
CA 02799888 2012-12-20
which is pushing against piston 170, will force the first counterbalance fluid
out
of reservoir 136 and into the rod end of cylinder 140c, thereby assisting
lifting.
[0049] Counterbalance reservoir 136 may optionally have one or more
auxiliary tanks 172a, 172b, 172c, 172d (collectively, tanks 172) of second
counterbalance fluid to provide additional counterbalance fluid capacity. The
additional capacity provided by tanks 172a-d keeps the relative change in
volume of the second counterbalance fluid small for a given displacement of
driving fluid from chamber 121c. This likewise limits the relative change in
pressure of the second counterbalance fluid, so that the upward force
generated
by the second counterbalance fluid is approximately constant.
[0050] Controller 200 may be operable to control the operating modes or
operation / state of lift system 100. Controller 200 may be electronically
connected to pump 128 and to valve 150. Controller 200 may further includes a
user interface with one or more control inputs (not shown). Controller 200 may
also control any additional electrically operated valves in other embodiments.
[0051] Controller 200 may be, for example, a PLUS+1 MC050-10
programmable logic controller made by Sauer Danfoss. Controller 200 may also
be provided with a user interface comprising a screen, such as a DP600
graphical terminal made by Sauer Danfoss. Optionally, controller 200 may also
be provided with a network gateway to allow remote access to controller 200,
for
example, over the intemet. Such a network gateway may be, for example, a
PLUS+1 RG150 remote connectivity gateway made by Sauer Danfoss,
[0052] In the depicted embodiment, the respective components of valve sub-
system 134 and pump 128 and the operating state thereof may be controlled
either by a signal from controller 200, and/or by pressure at one or more
points of
lift system 100. Alternatively or additionally, the components may be
individually
controllable using electronic or mechanical controls at each respective
component.
16
CA 02799888 2012-12-20
[0053] Turning now to FIGS. 4-7, the operation of lift system 100 will now
be
described.
[0054] In FIG. 4, lift system 100 is depicted in an idle state. Driving
fluid is
present in both the rod end and blind end chambers of cylinder 118c and the
rod
end chambers of cylinders 118a, 118b. Pump 128 may be idle. If pump 128 is
running, valve 150 directs flow of driving fluid from pump 128 to reservoir
126. In
the idle state of system 100, cross-relief valve 152 and relief valve 156 are
biased to open at a line pressure of subtantially 0 psig. Thus, in the idle
state of
lift system 100, driving fluid may drain to reservoir 126 and driving fluid in
the
system may be maintained at a pressure of substantially 0 psig, with the
exception of the first counterbalance fluid that is in the rod end chamber of
cylinder 118c and/or counterbalance reservoir 136.
[0055] FIG. 4 depicts lift system 100 in an idle state after cylinders 118
have
been primed with hydraulic driving fluid, that is, after the rod end chamber
of
each cylinder and the blind end chamber of cylinder 118c have been loaded with
driving fluid at approximately 0 psig. Suitable procedures for priming
cylinders
118 will be readily apparent to skilled persons and accordingly are not
described
in detail herein. In some embodiments, it may not be necessary to prime
cylinders 118. Instead, air may be bled off from fluid circuit 124 over one or
more
strokes.
[0056] In the idle state of lift system 100, piston 140c sits in
equilibrium with
counterbalance reservoir 136. In particular, the weight of the reciprocating
masses pulls piston 140c down. The pressure of the second counterbalance
fluid in reservoir 136 tends to urge piston 170 downwards, pressurizing the
first
and second counterbalance fluids in counterbalance reservoir 136 and the first
counterbalance fluid in the rod end chamber 121c of cylinder 140c.
[0057] Other forces may act on lift system 100 in the upwards direction.
For
example, as previously described, sucker rod 110 may extend through a column
17
CA 02799888 2012-12-20
of oil in well shaft 1011 and may have some buoyancy in the column. Friction,
including friction acting on the reciprocating masses, may resist movement.
Other factors which may influence the forces acting on lift system 100 may
include reservoir pressure, oil viscosity, weight of the column of oil above
down-
well pump 106, orientation of well shaft 108, and the condition fluid circuit
124
including the presence of waxy deposits that may form in the fluid
communication
lines. The magnitudes of these other forces acting on system 100 may vary over
the course of a stroke.
[0058] The system will reach a stable equilibrium at the point when the
upward-acting forces exerted on piston 170 equal the downward-acting forces
exerted on piston 170 and when the upward force of first counterbalance fluid
acting on piston 140c equals the weight of the reciprocating masses. FIG. 5
depicts the forces acting on carriage 122 in the equilibrium point of system
100 in
its idle state. An upward force Fc acts on piston 140c, and the weight of the
reciprocating masses pulls downwardly. Other forces such as buoyancy may act
upwardly. For simplicity, weight is depicted net of other upward forces acting
on
the reciprocating masses, such as buoyancy and friction. That is, weight is
depicted net of upward-acting forces that are not exerted on the reciprocating
masses by pistons 140 (referred to herein as net weight). At equilibrium, F,
will
equal the net weight W of the reciprocating masses. If both faces of piston
170
have equal area, as in the depicted embodiment, this equilibrium point will
occur
when the pressure of the first counterbalance fluid within counterbalance
reservoir '136 is equal to the pressure of the second counterbalance fluid in
counterbalance reservoir 136.
[0059] The point at which system 100 will reach a stable equilibrium is
dependent on design of counterbalance reservoir 136. For example, the
dimensions of reservoir 136 and the faces of piston 170, and the quantity and
pressure of second counterbalance fluid in reservoir 136 and any auxiliary
tanks
172 in communication with reservoir 136 will determine both the equilibrium
18
CA 02799888 2012-12-20
position and the pressure of the first and second counterbalance fluids at
equilibrium, and at the upper and lower limits of the stroke of piston 140c.
[0060] Counterbalance reservoir may be designed so that the equilibrium
point is approximately in the middle of the stroke of piston 140c. The second
counterbalance fluid can be pressurized such that its minimum pressure,
occurring at the top of a stroke of system 100, is at least high enough that
the
upward force on piston 140c is equal to the downward force on piston 140c due
to unpressurized fluid in the blind end chamber of cylinder 118c. In alternate
embodiments, it may be desired to have an equilibrium point that is not mid-
stroke. In such embodiments, the equilibrium point could be moved up in the
stroke by putting more of the second counterbalance fluid in reservoir 136 and
tanks 172, that is, increasing the pressure of the second counterbalance fluid
in
reservoir 136 and tanks 172, or it could be moved down in the stroke by
removing some second counterbalance fluid from the reservoir and reducing
pressure in reservoir 136 and tanks 172, that is, reducing the pressure of
counterbalance fluid in reservoir 136 and tanks 172.
[0061] To begin cycling lift system 100 from an idle state, pump 128 may be
activated using a control module of controller 200. Cross relief valve 152 and
relief valve 156 can be first biased closed and 3-state valve 150 put in its
upstroke state.
[0062] In FIG. 6, system 100 is depicted during an upstroke. Three-state
valve 150 is in its first (upstroke) state. Pump 128 provides pressurized
driving
fluid, which travels through check valve 158 of valve subsystem 134 and to the
rod ends of cylinders 118a, 118b by way of lines 146a, 146b. Cross-relief
valve
152 is biased closed by pilot line 164. In alternate embodiments where cross-
relief valve 152 is not hydraulically piloted, it may instead be biased to
open
above a certain pressure, so that it is normally closed but may open to
relieve
excess pressure.
19
CA 02799868 2012-12-20
[0063] The pressurized fluid increases pressure in the rod end chambers of
cylinders 118a, 118b and urges pistons 140a, 140b upwards. The blind end
chambers of cylinders 118a and 118b are filled with air and are open to the
atmosphere. As pistons 140a, 140b are urged upwards, air is expelled from the
blind ends of cylinders 118a, 118b.
[0064] Piston 140c is likewise urged upwards by virtue of being
mechanically
coupled to pistons 140a, 140b by carriage 122.
[0065] Upward pressure is also exerted on piston 140 by the counterbalance
fluid, through piston 170 and the first counterbalance fluid in reservoir 136
and
the rod end chamber of cylinder 118c. As piston 140c progresses upwardly, the
second counterbalance fluid is allowed to expand and pressure in
counterbalance reservoir 136 decreases, as does the upward force exerted on
piston 140c.
[0066] Over the entire upstroke, on average, the effect of the
counterbalance
reservoir 136 offsets at least part of the weight of the reciprocating masses.
That
is, the counterbalance subsystem urges piston 140c upwards with a force equal
to a substantial portion of the weight of the reciprocating masses. In the
depicted
embodiment, the volume of second counterbalance fluid in counterbalance
reservoir 136 and auxiliary tanks 172 is large relative to the change in
volume
due to compression during a stroke of lift system 100. As will be appreciated,
the
change in pressure, and thus, the change in upward force on piston 140c over a
stroke may be relatively small. In some embodiments, the maximum second
counterbalance fluid pressure, occurring at the bottom of a stroke, may be no
more than 8%-15% higher than the minimum second counterbalance fluid
pressure, occurring at the top of a stroke.
[0067] As piston 140c travels upwards, first counterbalance fluid is
expelled
from the blind end of cylinder 118c and flows to valve subsystem 134 by way of
_
CA 02799888 2012-12-20
communication line 148. While 3-state valve 150 is in its first (upstroke)
state,
fluid is free to drain from communication line 148 to reservoir 126.
[0068] FIG. 7 depicts the forces acting on carriage 122 during an upstroke.
Forces Fa and Fb, act on pistons 140a, 140b respectively, and are
approximately
equal to the pressure in the rod end chambers 121a, 121b of cylinders 118a,
118b, multiplied by the areas of pistons 140a, 140b on their rod-end faces,
that
is, the areas of the pistons 140a, 140b, less the areas of the rods 141a, 141b
themselves. Another upward force Fa acts on piston 140c and is equal to the
pressure in chamber 121c, multiplied by the area of the rod-end face of piston
140c. The other forces acting on carriage 122, such as weight, buoyancy and
friction, are assumed to act in a net downward direction and are depicted as
Fa.
As the pistons 140 travel upwardly, the volume of the rod end chambers 121a,
121b increases at a rate equal to the linear speed of the pistons, multiplied
by
the total area of the rod-end faces of pistons 140a, 140b. Thus, pump 128
should be capable of providing fluid at sufficient pressure to generate the
desired
upward force and at a sufficient flow rate to maintain the desired rate of
piston
travel.
[0069] It is desirable that the pistons 140 will not "bottom out" at either
end of
the chambers during the upstroke or downstroke. Therefore the system may be
configured to alternate between the modes of operations (i.e. upstroke /
downstroke) before the pistons reach the end of the chambers.
[0070] However, possibly, pistons 140 may reach the limit of their travel
within
cylinders 118 while 3-state valve 150 is in its first (upstroke) state or
downstroke
state. If pump 128 continues to run, excess pressure may develop. In the event
of excess pressure, pump relief valve 166, which is normally closed, opens to
provide relief. Specifically, in response to excess pressure at the outlet of
pump
128, pilot line 174 causes pump relief valve 166 to open, allowing driving
fluid to
drain from the outlet of pump 128 back to driving fluid reservoir 126.
21
CA 02799888 2012-12-20
[0071] When an upstroke or downstroke is completed, lift system 100 may
transition to a stationary state. If lift system 100 is running continuously,
it may
only stay in the stationary state very briefly or only momentarily or not at
all.
Alternatively, lift system 100 may remain in a stationary state indefinitely
at the
end of an upstroke or downstroke.
[0072] FIG. 8 depicts a downstroke of system 100. During a downstroke, a
signal from controller 200 causes valve 150 to transition to its upstroke
state. In
this state, pressurized driving fluid flow from pump 128 flows from port 151b
through port 153b and to the blind end chamber 119c of cylinder 118c, urging
piston 140c downwards. Downward movement of piston 140c expels fluid from
chamber 121c and into reservoir 136, causing second counterbalance fluid in
reservoir 136 to be compressed. Thus, as piston 140c moves downwardly, it
does work on the second counterbalance fluid. The energy associated with
lowering the reciprocating masses is stored so that the energy can be used to
assist in raising the reciprocating masses during the upstroke as described
above.
[0073] Downward movement of piston 140c also urges pistons 140a and
140b downwards by virtue of their mechanical coupling at carriage 122.
Downward movement of pistons 140a, 140b causes driving fluid to be expelled
from the rod end chambers of cylinders 118a, 118b respectively. The expelled
driving fluid flows under pressure through communication lines 146a, 146b to
components of valve subsystem 134. The pressurized flow causes cross-relief
valve 152 to open, allowing pressurized fluid to flow from communication lines
146a, 146b to communication line 148 and then into the blind end of cylinder
118c by way of valve subsystem 134. Fluid expelled from cylinders 140a, 140b
is therefore used to supplement the flow of fluid from pump 128 to cylinder
140c,
In other words, driving fluid expelled from cylinders 118a, 118b is
regenerated
under pressure to cylinder 118c.
22
CA 02799888 2012-12-20
[0074] As will be apparent, driving fluid flowing to valve subsystem 134
from
lines 146a, 146b during a downstroke must pass through cross-relief valve 152
unless relief valve 156 is open. As previously described, relief valve 156 is
normally closed, however, if excess pressure occurs in valve subsystem 134,
pilot lines 160 and/or 162 may cause relief valve 156 to open, allowing excess
driving fluid to drain to reservoir 126 by way of 3-state valve 150. Driving
fluid
that is expelled from cylinders 118a, 118b during a downstroke therefore flows
into communication line 148 unless excess pressure develops, in which case, it
is drained to reservoir 126.
[0075] As depicted in FIG. 6, during the upstroke of lift system 100,
pressure
is substantially released from driving fluid in the blind end chamber of
cylinder
118c. Thus, the fluid in that chamber does not significantly resist the
upstroke of
pistons 140. In contrast, during the downstroke of pistons 140, driving fluid
in the
rod end chambers of cylinders 118a, 118b is maintained under pressure and
therefore resists the downstroke.
[0076] FIG. 9 depicts the forces acting on carriage 122 during a
downstroke.
Pressure in counterbalance reservoir 136 causes an upward force to be exerted
on piston 140c. As piston 140c progresses in a downward direction, second
counterbalance fluid in counterbalance reservoir 136 and any auxiliary tanks
172
is compressed, increasing its pressure and increasing the upward force from
the
first counterbalance fluid acting on piston 140c. The upward force acting on
piston 140c increases from a minimum at the top of the downstroke to a
maximum at the bottom of the downstroke, when the second counterbalance gas
is in its most highly compressed state.
[0077] On average, over the downstroke, the effect of the force produced by
the counterbalance fluids and counterbalance reservoir 136 balances at least a
substantial part of the weight of the reciprocating masses.
23
CA 02799888 2012-12-20
[0078] During the downstroke, a force F, acts in the downward direction
through piston 140c. Force Fc is equal to the pressure of driving fluid in the
upper/blind end chamber 119c of cylinder 118c, multiplied by the area of
piston
140c on its blind end face, less the upward force resulting from second
counterbalance fluid in lower chamber 121c, that is the pressure in chamber
121c, multiplied by the area of the rod end face of piston 140c. Forces Fa and
Fb
act in the upward direction against pistons 140a, 140b respectively and are
approximately equal to the products of the pressure in the rod end chambers of
cylinders 118a, 118b and the areas of pistons 140a and 140b on their rod end
faces. The other forces acting on carriage 122 and thus on the piston rods and
pistons that are connected to the carriage 122, such as weight, buoyancy and
friction, are depicted as Fo. Again, the upward force resulting from the first
counterbalance fluid acting in piston 140c offsets at least part of the weight
of the
reciprocating components.
[0079] If the pressure in the upper/blind end chamber of cylinder 118c is
equal to the pressure in the lower/rod end chambers of cylinders 118a, 118b,
the
area of the blind end face of piston 140c must be larger than the total area
of the
rod end faces of pistons 140a, 140b in order to yield a net downward force and
drive pistons 140 downwardly.
[0080] In the depicted embodiment, the area of the upper/blind end face of
piston 140c may be double the total area of the rod end faces of pistons 140a,
140b. With this ratio, if the driving fluid pressure in the lower/rod end
chambers
of cylinders 118a, 118b is equal to that in the upper/blind end chamber of
cylinder 118c, the downward force acting on piston 140c, less the upward
forces
acting on pistons 140a, 140b will be approximately equal to the upward force
acting on pistons 140a, 140b during an upstroke.
[0081] Therefore, if the pressures in the lower/rod end chambers of
cylinders
118a, 118b and the upper/blind end chamber of cylinder 118c are held
24
CA 02799888 2012-12-20
substantially equal throughout substantially the entire upstroke and
substantially
the entire downstroke, and if the net effect of the counterbalance, weight,
and
other down-well forces is on average the same over both upward and downward
strokes, the rates of the upstroke and downstroke will be substantially the
same.
If the area of the blind end face of piston 140c is substantially double the
total
area of the rod end faces of pistons 140a, 140b, the required flow rate of
driving
fluid in the downstroke will be approximately twice the flow rate that is
required in
the upstroke. Absent regeneration of driving fluid, a larger pump flow of
driving
fluid would be required for the downstroke than for the upstroke.
[0082] Regeneration of driving fluid from the rod end chambers of cylinders
118a, 118b to the blind end chamber of 118c by way of valve subsystem 134
allows the larger flow rate required for the downstroke to be obtained using a
relatively small pump sized to deliver the flow rate required for the
upstroke. This
may provide cost and/or energy efficiency benefits compared to a system which
uses a larger pump.
[0083] Following completion of a downstroke, lift system 100 may begin a
new
upstroke as depicted in FIGS. 6-7. Thus, lift system 100 may be operated in a
substantially continuous mode of operation alternating substantially
continuously
between an upstroke and a downstroke. Lift system 100 may also be operated in
a manner where the rate of movement of the pistons 140 on the upstroke is
different than the rate of movement on the downstroke. This may be achieved by
having controller 200 adjust the flow rate provided by pump 128 on the
upstroke
compared to the downstroke.
[0084] Alternatively, following the completion of any upstroke or
downstroke,
or even possibly during an upstroke or downstroke, lift system 100 may be
returned to the idle state depicted in FIGS. 4-5 and may remain in that state
indefinitely.
CA 02799e88 2012-12-20
[0085] FIG 10. depicts another example lift system 300. Lift system 300 may
have upward driving cylinders 318a, 318b and downward driving cylinder 318c,
like cylinders 118a, 118b, 118c, with pistons 340a, 340b, 340c (collectively,
pistons 340) therein. Piston rods 341a, 341b, 341c may extend from pistons
340a, 340b, 340c and protrude from cylinders 118 and may be mounted to a
carriage like carriage 122 to control a sucker rod, down-well pump and
possibly,
other reciprocating masses, such as referenced in the embodiment of FIGS. 1-
10.
[0086] System 300 may be equipped with a pump 328. The pump 328 can be
chosen to provide flow rates / pump pressures that are suitable for a
particular lift
system 300 and application. In the depicted embodiment, pump 328 may be like
pump 128, in particular, it may be a variable-displacement piston pump and may
be able to deliver a maximum and constant flow rate of about 46 gallons per
minute at a pressure of at least 3000 psi. For example, pump 328 may as
before, be a series 45 axial piston open circuit pump made by Sauer Danfoss.
Alternatively, pump 328 could be another type of pump operable to deliver
suitable pressures and flow rates, such as a vane or gear pump. A piloted
relief
valve 366 can allow excess pressure from pump 328 to drain to reservoir 326.
Valve 366 may be biased closed up to a certain pressure, which may be
infinitely
variable between a certain maximum and minimum.
[0087] Pump 328 may be controlled for pressure-compensated operation.
That is, pump 328 can be controlled to operate so as to maintain a
substantially
constant pressure of driving fluid (which again may be hydraulic fluid). Run
in
these conditions, pump 328 may output a substantially constant volumetric flow
rate of driving fluid. The pressure and flow rate output by pump 328 may be
linked. That is, increasing the pressure produced by pump 328 may also result
in
an increased flow rate, while decreasing the pressure may result in a
decreased
flow rate of the driving fluid. Additionally, if the resistance to movement of
driving
fluid though out the driving fluid system changes over time in an upstroke or
26
CA 02799888 2012-12-20
downstroke, to maintain a substantially constant flow rate during the upstroke
or
downstroke it may be required to adjust the pressure setting for the pump
during
the upstroke and downstroke by a controller such as a controller 400.
[0088] System 300 may comprise a controller 400 to control the operation of
its components. Controller 400 may be, for example, a PLUS+1 MC050-10
programmable logic controller made by Sauer Danfoss. Controller 400 may also
be provided with a user interface comprising a screen, such as a DP600
graphical terminal made by Sauer Danfoss. Optionally, controller 400 may also
be provided with a network gateway to allow remote access to controller 400,
for
example, over the internet. Such a network gateway may be, for example, a
PLUS+1 RG150 remote connectivity gateway made by Sauer Danfoss.
[0089] Each one of cylinders 318 has a rod (lower) and blind (upper) end.
Each one of pistons 340 defines two chambers within the respective cylinder
318, with one lower chamber lying between the piston and the rod end of the
cylinder (rod end chambers 321a, 321b, 321c, respectively) and one upper
chamber lying between the piston and the blind end of the cylinder (blind end
chambers 319a, 319b, 319c, respectively). Each one of pistons 340 has a rod
end face partially defining the lower/rod end chamber and a blind end face
partially defining the upper/blind end chamber.
[0090] Each one of cylinders 318 has an inlet/outlet port 325 for its
upper/blind end chamber and an inlet/outlet port 327 for its lower/rod end
chamber. Ports 325a, 325b are open to the atmosphere. Port 325c is
connected to line 348 for supplying driving fluid to, or draining driving
fluid from,
upper/blind end chamber 319c. Ports 327a, 327b are connected to lines 346a,
346b for supplying driving fluid to or draining driving fluid from chambers
321a,
321b respectively. Port 327c is connected to line 338 to allow counterbalance
fluid to flow between chamber 321c and counterbalance fluid tanks 372a, 372b,
372c (collectively, tanks 372).
27
CA 02799888 2012-12-20
[0091] The rod end inlet/outlet ports 327a, 327b of cylinders 318a, 318b
are
connected by fluid communication lines 346a, 346b to valve subsystem 334. In
the depicted embodiment, lines 346a, 346b may be hoses or pipes and may
have for example have an internal diameter ("ID") of about 0.75 inches. Lines
346a and 346b merge into a common line that may be hoses or pipes that may
have an ID of about 1 inch which runs into tee 333 and then a port 380 of
valve
subsystem 334. The blind end inlet/outlet ports 325a, 325b, 325c of cylinders
318a, 318b may be open to atmosphere as the upper chambers in cylinders
318a, 318b are not filled with, and emptied of, driving fluid.
[0092] The rod end inlet/outlet of cylinder 318c may be connected by fluid
communication line 338 to, and in fluid communication with, counterbalance
fluid
tanks 372. The blind end inlet/outlet of cylinder 318c may be connected by
fluid
communication line 348 to port 382 of valve subsystem 334. In the depicted
embodiment, each of lines 338 and 348 may be a hose or pipe and may, for
example, have an ID of about 1.25 inches.
[0093] Valve subsystem 334 may comprise a two way pilot-operated valve
350 and a one-way pilot operated valve 352. Valve 350 may be, for example, a
model RSJC8 pilot operated, balanced piston sequence valve produced by Sun
Hydraulics Corporation. Valve 352 may be, for example, a model RPKC8 pilot
operated, balanced piston relief valve produced by Sun Hydraulics Corporation.
Valve 350 may be biased closed up to the pressure in line 360, which allows a
small amount of fluid to flow from line 358, at the pressure in line 358 to
line 362
and valve 354. Valve 350 may open when the pressure in pilot line 396 exceeds
the pressure in line 360, which biases valve 350 closed.
[0094] Valve 354 may be, for example, a model RBAP electro-proportional
relief valve produced by Sun Hydraulics Corporation. A small amount of fluid
is
allowed to flow through line 362 to an input and a pilot line of valve 354. A
solenoid may bias valve 354 closed up to a certain pressure differential
between
28
CA 02799888 2012-12-20
lines 364 and line 362 (the opening pressure). If this pressure difference
exceeds the opening pressure, valve 354 opens and a small amount of fluid
flows through line 364 to reservoir 326 by way of port 384. The opening of
valve
354 reduces the pressure in lines 360, 362, which in turn reduces the pressure
to
which valve 350 is biased closed. Thus, valve 354 may control valve 350. That
is, valve 350 will open if the pressure in line 358 reaches the opening
pressure of
valve 354.
[0095] A signal from controller 400 may control the opening pressure of
valve
354 by way of a solenoid. This likewise may control the pressure at which
valve
350 will open. Valve 354 may be infinitely variable between a certain minimum
and maximum. In the depicted embodiment, valve 354 is variable between a
minimum opening pressure of 0 psi and a maximum opening pressure of about
3000 psi. When valve 354 is set to open at 0 psi, valve 350 is effectively
opened.
When valve 354 is set to open at 3000 psi, it closes valve 350 to pressures
below
3000 psi. The path from port 384 to reservoir 326 may be designed to minimize
backpressure. As valve 354 operates based on the differential pressure between
lines 362 and 364, reducing backpressure in lines 364 will allow valves 350
and
354 to be opened in response to a lower input pressure at line 358.
[0096] Valve 352 may be operated in a similar way to valve 350. Valve 352
is
biased closed by pressure in line 374 and piloted by pressure in line 376.
Pressure in line 374 is controlled by electrically controlled valve 356. Valve
352
may open when the pressure in pilot line 376 exceeds the pressure in line 374,
which biases valve 352 closed. Valve 356 may be, for example, a model RBAP
electro-proportional relief valve produced by Sun Hydraulics Corporation.
[0097] Lines 374, 378 may permit a small amount of driving fluid to flow
from
line 370, at the fluid pressure in line 370. A small amount of fluid at this
pressure
is allowed to flow through line 374 to an input and a pilot line of valve 356.
A
solenoid biases valve 356 closed up to a certain pressure differential between
29
CA 02799888 2012-12-20
lines 378 and line 379 (the opening pressure). If this pressure difference
exceeds the opening pressure, valve 354 opens and a small amount of fluid
flows through line 380 to reservoir 326 by way of port 384. The opening of
valve
356 reduces the pressure in lines 370, 378, which in turn reduces the pressure
to
which valve 352 is biased closed. Thus, valve 356 may control valve 352. That
is, valve 352 will open if the pressure in line 370 reaches the opening
pressure of
valve 356.
[0098] A signal from controller 400 may control the opening pressure of
valve
356 by way of a solenoid. This may likewise control the pressure at which
valve
352 will open. Valve 356 may be infinitely variable between a certain minimum
and maximum. In the depicted embodiment, valve 356 is variable between a
minimum opening pressure of 0 psi and a maximum opening pressure of about
3000 psi. When valve 356 is set to open at 0 psi, valve 352 is effectively
opened.
When valve 356 is set to open at 3000 psi, it closes valve 352 to pressures
below
3000 psi.
[0099] Valve subsystem 334 may also have ports 388 and 390 for measuring
fluid pressure in lines 358, 370 respectively. Fluid cannot flow through ports
388,
390. Rather, ports 388 and 390 provide a pressure reading.
[00100] It should be noted that lines 360, 362, 374, 378 may be provided
with restrictors to limit the amount of driving fluid that can flow
therethrough.
[00101] Much like system 100, system 300 as illustrated has a
counterbalance subsystem. In system 300, rod end chamber 321c of cylinder
318c is filled with a pressurized counterbalance fluid. Rod end port 327c of
chamber 321c is in communication by way of line 338 with a counterbalance
fluid
reservoir comprising 3 tanks 372 of pressurized counterbalance fluid that may
be
a compressible inert gas. Nitrogen gas may be the counterbalance fluid.
However, in other embodiments, the counterbalance gas may be another
compressible inert gas. Cylinder 318c with piston 340c may be selected to
CA 02799888 2012-12-20
accommodate this configuration being designed with among other things
appropriate seals and be made from appropriate materials that allow the piston
340c to maintain driving fluid such as hydraulic fluid in the upper chamber
and
nitrogen gas in the lower chamber and may be able to sustain continued
operation for a prolonged period of time without encountering a significant
degree
of cylinder failure during operation. Pressurized counterbalance gas in
chamber
321c urges piston 340c upwards, offsetting the weight of the reciprocating
masses, in much the same way as the counterbalance of lift system 100
described above.
[00102] Counterbalance gas in chamber 321c and tanks 372 is typically
pressurized to between 1200 and 2000 psi and may be approximately at typical
environment temperatures in the range of about -40 C to 50 C. The amount of
pressure of the counterbalance gas is determined by the weight of the
reciprocating masses. For heavier reciprocating masses, counterbalance gas
will be more highly pressurized. In some embodiments, the pressure of the
counterbalance gas may be as low as 200 psi or as high as 3000 psi or possibly
higher.
[00103] In some embodiments, counterbalance fluid may be sufficiently
pressurized to offset about 60% of the weight of the reciprocating masses. It
has
been found that in some applications, this results in an equilibrium point
near the
middle of a stroke of system 300, which typically results in sufficient
efficiency
levels. The pressure of counterbalance fluid in chamber 321c and tanks 372
varies over each stroke of system 300, with a pressure minimum occurring at or
near the top of the stroke and a pressure maximum near the bottom of the
stroke. Of course, the amount of pressure variation depends on the total
volume
of counterbalance fluid in tanks 372 and chamber 321c ¨ the larger the volume
of
counterbalance fluid, the smaller the variation in pressure.
31
CA 02794888 2012-12-20
[00104] The operation of lift system 300 will now be described with
reference to FIGS. 11 ¨ 12.
[00105] To begin cycling lift system 300 from an idle state, pump 328 is
activated using controller 400.
[00106] In FIG. 11, system 300 is depicted during an upstroke. Valves 354
and 350 are in their closed state, that is, they are biased closed to a
pressure
exceeding the normal operating pressure expected at port 380. Pump 328
provides pressurized driving fluid, which travels through check valve 392 and
to
the rod ends of cylinders 318a, 318b by way of lines 346a, 346b.
[00107] The pressurized fluid increases pressure in the lower/rod end
chambers of cylinders 318a, 318b and urges pistons 340a, 340b upwards. The
upper/blind end chambers of cylinders 318a and 318b are filled with air and
are
open to the atmosphere. As pistons 340a, 340b are urged upwards, air is
expelled from the blind ends of cylinders 318a, 318b through ports 325a, 325b.
[00108] Piston 340c is likewise urged upwards by virtue of being
mechanically coupled to pistons 340a, 340b by a carriage which is connected to
the sucker rod etc.
[00109] Upward pressure is also exerted on piston 340c by the
counterbalance fluid in chamber 321c. Other upward forces may also act on the
system, such as buoyancy of the sucker rod in the well and friction in the
well
may also act against the direction of movement.
[00110] As piston 340c progresses upwardly, the counterbalance fluid is
allowed to expand and pressure in chamber 321c and tanks 372 decreases, as
does the upward force exerted on piston 340c.
[00111] Over the entire upstroke, on average, the effect of the pressurized
counterbalance fluid in chamber 321c may at least partially offset the weight
of
32
CA 02799888 2012-12-20
the reciprocating masses, less any other upward-acting forces. In the depicted
embodiment, the volume of counterbalance fluid in chamber 321c and auxiliary
tanks 372, may be large relative to the change in volume due to compression
during a stroke of lift system 300. As will be appreciated, the change in
pressure,
and thus, the change in upward force on piston 340c over a stroke may be
relatively small. In some embodiments, the peak counterbalance fluid pressure,
occurring at the bottom of a stroke, may be no more than 8%-15% greater than
the minimum pressure, occurring at the top of a stroke. For practical
purposes,
the upward force may be considered to be substantially constant over a stroke
in
either the up or down direction, and is equal to a portion of the weight of
the
reciprocating masses. In some embodiments, the upward force from
counterbalance fluid in chamber 321c is equal to approximately 60% of the
weight of the reciprocating masses. In other embodiments, counterbalance fluid
pressure may be tuned to produce a different average upward force. For
different applications, e.g. different wells, pumps designs or sucker rod
designs,
different counterbalance forces will yield the optimum efficiency. The desired
counterbalance force for a particular application may be, for example,
experimentally determined.
[00112] As piston 340c travels upwards, driving fluid is expelled from the
blind end of cylinder 318c and flows to valve subsystem 334 by way of
communication line 148. During the upstroke, controller 400 causes valves 352,
356 to be substantially open to 0 psi, which freely allows driving fluid to
drain
from communication line 348 to reservoir 326 by way of port 382, valve 352 and
port 386.
[00113] During an upstroke of system 300, the forces acting on the
carriage of system 300 vary substantially as described above with respect to
system 100, and as illustrated in FIG. 7.
33
CA 02799888 2012-12-20
[00114] It is desirable that the pistons 340 will not "bottom out" at
either end
of the chambers during the upstroke or downstroke, Therefore the system may
be configured to alternate between the modes of operations (i.e. upstroke /
downstroke) before the pistons reach the end of the chambers.
[00115] Possibly, however, pistons 340 may reach the limit of their travel
within cylinders 318 while valve subsystem 334 is in its first (upstroke)
state, that
is, while valves 350, 354 are closed to a predetermined opening pressure and
valves 352, 356 are substantially open. In that event, the volume of the rod
end
chambers of cylinders 318a, 318b can no longer increase. If pump 328
continues to run, excess pressure may develop at port 380 and in line 358. In
the event of excess pressure, valves 354 and 350, which are normally closed,
open to provide relief. Specifically, in response to excess pressure at port
380
and in line 358, valves 354 and 352 open, allowing driving fluid to drain to
reservoir 326 by way of ports 384 and 386, thereby relieving excess pressure.
[00116] FIG. 12 depicts a downstroke of system 300. During a downstroke,
a signal from controller 400 causes valves 350, 354 to be set to open to
substantially 0 psi. Pressurized driving fluid provided by pump 328 flows to
port
380 and through line 358, valve 350 and port 382 to the blind end chamber of
cylinder 318c, urging piston 340c downwards. Downward movement of piston
340c compresses counterbalance fluid in chamber 321c and tanks 372. Thus,
as piston 340c moves downwardly, it does work on the counterbalance fluid.
The energy associated with lowering the reciprocating masses is stored so that
the energy can be used to assist in raising of the reciprocating masses during
the
upstroke as described above.
[00117] Downward movement of piston 340c also urges pistons 340a and
340b downwards by virtue of their mechanical coupling. Downward movement of
pistons 340a, 340b causes driving fluid to be expelled from the rod end
chambers of cylinders 318a, 318b respectively. The expelled driving fluid
flows
34
CA 02799888 2012-12-20
under pressure through communication lines 346a, 346b to port 380 of valve
subsystem 334.
[00118] During the downstroke, valves 350, 354 are opened substantially to
0 psi. Pressurized driving fluid flows from lines 346a, 346b to port 380 and
through line 358, valve 350 and port 382 to the blind end chamber of cylinder
318c. Thus, fluid expelled from cylinders 340a, 340b is added to flow from
pump
328, effectively doubling the flow rate of fluid being supplied to chamber
319c. In
other words, fluid expelled from cylinders 340a, 340b is regenerated under
pressure to cylinder 340c. At the same time, controller 400 causes valves 352,
356 to close to approximately 3000 psi, preventing the driving fluid flowing
into
valve subsystem 334 at port 380 from flowing through valve 352 to port 386 and
reservoir 326.
[00119] If excess pressure occurs in valve subsystem 334, pilot lines 374,
378 may cause relief valves 356, 352 to open, allowing excess driving fluid to
drain to reservoir 326 by way of port 382. Driving fluid that is expelled from
cylinders 318a, 318b during a downstroke therefore flows into rod end chamber
319c of cylinder 340c unless excess pressure develops, in which case, at least
some of the fluid is drained to reservoir 326.
[00120] As in system 100, in system 300 during the downstroke of pistons
340, driving fluid in the lower/rod end chambers of cylinders 318a, 318b is
maintained under pressure and therefore resists the downstroke.
[00121] During the downstroke, counterbalance fluid in chamber 321c and
tanks 372 causes an upward force to be exerted on piston 340c. As piston 340c
progresses in a downward direction, counterbalance fluid in chamber 321c and
tanks 172 is compressed, increasing its pressure and increasing the upward
force on piston 340c. The upward force increases from a minimum at the top of
the downstroke to a maximum at the bottom of the downstroke, when the
counterbalance gas is in its most highly compressed state. On average, over
the
CA 02799888 2012-12-20
downstroke, the effect of the counterbalance fluid balances at least part of
the
weight of the reciprocating masses.
[00122] During the downstroke, the forces acting on the carriage of lift
system 300 vary substantially as illustrated in FIG. 9 and described above for
lift
system 100.
[00123] The area of the blind end face of piston 340c may be substantially
double the total area of the rod end faces of pistons 340a, 340b. With this
ratio,
if the driving fluid pressure in the rod end chambers of cylinders 318a, 318b
is
substantially equal to that in the blind end chamber of cylinder 318c, the
downward force acting on piston 340c, less the upward force acting on pistons
340a, 340b, will be approximately equal to the upward force acting on pistons
340a, 340b during an upstroke
[00124] Therefore, if the pressures in the rod end chambers 321a, 321b of
cylinders 318a, 318b and the blind end chamber 319c of cylinder 318c are held
equal throughout substantially the entire upstroke and substantially the
entire
downstroke, the rates of the upstroke and downstroke will be approximately the
same. As the area of the blind end face of piston 340c is double the total
area of
the rod end faces of pistons 340a, 340b, the required flow rate of driving
fluid in
the downstroke will be approximately twice the flow rate that is required in
the
upstroke. Absent regeneration of driving fluid, a larger pump or at least a
greater
flow rate by a pump would therefore be required for the downstroke than for
the
upstroke.
[00125] Regeneration of driving fluid from the rod end chambers of
cylinders 318a, 318b to the blind end chamber of 318c by way of regeneration
subsystem 334 allows the larger flow rate required for the downstroke to be
obtained using a relatively small pump sized to deliver the flow rate required
for
the upstroke. This may provide cost and/or energy efficiency benefits compared
to a system which uses a larger pump.
36
_
CA 02799888 2012-12-20
[00126] Following completion of a downstroke, lift system 300 may begin a
new upstroke as depicted in FIG. 11.
[00127] Conveniently, providing valves 366, 350/354, 352/356 that are
infinitely variable within a certain pressure range allows for the speed of
the
upstroke and downstroke of system 300 to be tuned within a certain interval.
By
varying the flow rate provided by pump 328 (with corresponding changes in
pump pressure) the upper pressure settings for the valve pairs 350/354 and
352/356 can be adjusted through controller 400 to accommodate lower or
increased pressures thus allowing for slower or faster speeds of travel of the
pistons 340a-c in the cylinders 318a-c.
[00128] As described above, the state of lift systems 100, 300 are
controlled by controllers 200, 400, respectively. Specifically, controller 200
controls the state of pump 128 and 3-state valve 150, thus controlling the
state of
lift system 100, and controller 400 controls the state of pump 328 and valves
354,
356, thereby controlling the state of lift system 300.
[00129] After the completion of a stroke, system 100 or system 300 may be
maintained in a stationary state. However, it will sometimes be desirable to
run
system 100 or system 300 substantially continuously. In such a case, system
100 or system 300 may be in a stationary state only very briefly, during the
transition from upstroke to downstroke or vice-versa.
[00130] Controllers 200, 400 may be interconnected with one or more
sensors to detect the position of pistons 140 or pistons 340, respectively. As
depicted in FIGS. 3, 4, 6, 8-9, controller 200 may be interconnected with a
linear
position sensor 202 located on cylinder 118b. Linear position sensor 202 may
be
for example an LK series transducer made by Rota Engineering. Sensor 202
may be able to detect the movement of the piston rod 141b and/or piston 140b
and output a signal indicative of the linear position of piston 140b within
cylinder
37
CA 027-99888 2012-12-20
118b. Sensor 202 may also output a signal indicative of the velocity of piston
140b.
[00131] When the signal from sensor 202 indicates that piston 140b is
approaching the top of an upstroke, controller 200 may respond to this signal
by
causing 3-state valve 150, and thus, lift system 100, to change from its
upstroke
state to its downstroke state. When the signal from sensor 202 indicates that
piston 140b is approaching the bottom of a downstroke, controller 200 may
respond by causing 3-state valve 150 and thus, lift system 100 to transition
from
its downstroke state to its upstroke state.
[00132] As depicted in FIGS. 10-12, controller 400 may be interconnected
with a linear position sensor 402, like linear position sensor 202, located on
cylinder 318b. Sensor 402 may output a signal indicative of the position of
piston
340b within cylinder 318b. Sensor 402 may also output a signal indicative of
the
velocity of piston 340b.
[00133] When the signal from sensor 402 indicates that piston 340b is
approaching the top of an upstroke, controller 400 may respond by
transitioning
lift system 300 to a downstroke state. Specifically, controller 400 may first
cause
the opening pressure of valves 354, 350 to gradually lower. This will cause
valve
350 to slowly open, allowing some driving fluid to flow from port 380, through
valves 350 and 352 to reservoir 326. The flow rate of driving fluid into
chambers
321a, 321b will therefore decrease until it reaches zero at the very peak of
the
upstroke, when valve 350 is fully open. The upward velocity of pistons 340
will
likewise decrease until it reaches zero at the top of the upstroke.
[00134] At the top of the upstroke, pistons 340 may be above the
equilibrium point at which the counterbalance fluid in chamber 321c is
sufficient
to support the reciprocating masses. As a result, when valve 350 is fully
open,
pistons 340 may momentarily begin to fall, as pressure will be momentarily
released from chambers 321a, 321b. Sensor 402 may be configured to indicate
38
CA 02799888 2012-12-20
that piston 340b is beginning to fall, and in response, controller 400 will
cause
valves 356, 352 to gradually close, diverting flow from pump 328 and from
chambers 321a, 321b to port 382 and out to chamber 319c. Once valves 356,
352 are fully closed, pistons 340 will be driven downwardly at their full
downstroke speed. Thus, at the top of an upstroke, pistons 340 gradually
decelerate, briefly stop moving, and then gradually accelerate downwards=to
the
downstroke speed.
[00135] When the signal from sensor 402 indicates that piston 340b is
approaching the bottom of a downstroke, controller 400 may respond by
transitioning lift system 300 back to an upstroke state. Specifically,
controller
400 may first cause the opening pressure of valves 352, 356 to gradually
lower.
This will cause valve 352 to slowly open, allowing some driving fluid to flow
from
port 380, through valves 350 and 352 to reservoir 326. The flow rate of
driving
fluid into chamber 319c will therefore decrease until it reaches zero at the
very
bottom of the downstroke, when valve 352 is fully open. At the same time,
controller 400 may cause the opening pressure of valves 354, 350 to gradually
increase, effectively slowly closing those valves. The gradual closing of
valve
350 may have a braking effect, decelerating the reciprocating masses. The
downward velocity of pistons 340 may therefore decrease until it reaches zero
at
the bottom of the downstroke.
[00136] At the bottom of the downstroke, pistons 340 may be below the
equilibrium point at which the counterbalance fluid in chamber 321c is
sufficient
to support the reciprocating masses. As a result, when valve 352 is fully
open,
pistons 340 may momentarily begin to rebound upwardly, as pressure may be
momentarily released from chambers 319c. Sensor 402 may be configured to
indicate that piston 340b is beginning to rise. Controller 400 may cause
valves
354, 350 to gradually close, directing flow from pump 328 into chambers 321a,
321b. Pistons 340 may therefore gradually accelerate upwardly. Once valves
356, 352 are fully closed, pistons 340 may be driven upwardly at their full
39
CA 02799888 2012-12-20
upstroke speed. Thus, at the bottom of a downstroke, pistons 340 gradually
decelerate, briefly stop moving, and then gradually accelerate upwards to the
upstroke speed.
[00137] Alternatively, if desired, controller 400 may cause system 300 to
transition to an idle state. In such a case, controller 400 may be set to
cause
valves 352, 356 to open, allowing driving fluid pressure to drain from the
system.
Controller 400 may cause valves 350, 354 to gradually open, so that the system
gradually returns to equilibrium in its idle state awaiting the beginning of
the next
stroke. Pump 328 may also be powered down while system 300 is in its idle
state.
[00138] It may sometimes be desired to hold the reciprocating masses
stationary in a position other than the equilibrium position. This may be
effected
by, for example, manual override at the user interface of controller 400. In
response, controller 400 may cause valves 352, 356 to open, allowing driving
fluid to drain to reservoir 326. Meanwhile, valves 350, 354 may be held closed
by biasing valve 354 closed up to a high pressure. As check valve 392 prevents
fluid from flowing back to pump 328, driving fluid may therefore be held under
pressure in chambers 321a, 321b, holding pistons 340 in position.
[00139] Sensors 202, 204 and 402, 404 thus enable controllers 200 and
400 to control the period and transition between the upward and downward
strokes of system 100 and system 300, respectively. As desired, systems 100,
300 may be run continuously, with substantially no delay between successive
strokes, or they may be run intermittently.
[00140] Alternatively or additionally, position sensors may be provided on
cylinders 118a, 118c, 318a, 318c, pistons 140, 340, or other components of
lift
systems 100, 300. Sensors may also be provided on any of the valves of valve
system 134 or valve subsystem 334, to detect the presence of excess pressure.
CA 02799888 2012-12-20
Excess or a predetermined pressure may indicate, for example, that the end of
a
stroke is near or has been reached.
[00141] Signals from sensors 202, 204 and 402, 404 may also be used to
control the speed of the strokes of lift systems 100, 300. For example,
controller
200 or controller 400 may measure the elapsed time between the beginning and
end of each stroke. If the elapsed time is higher than desired, controller 200
or
controller 400 may then output a signal to pump 128 or pump 328, respectively,
to increase the flow rate, increasing the stroke speed. Conversely, if the
elapsed
time is lower than desired, controller 200 or controller 400 may then output a
signal to pump 128 or pump 328, respectively, to decrease the flow rate,
decreasing the stroke speed. Also, through speed measurement sensors the
controller may be able to monitor the speed of movement in approximately real
time and make appropriate adjustments to the speed of movement of the pistons
during the strokes.
[00142] In some applications, it may be desired to have the upstroke and
downstroke occur at substantially constant, but different speeds. For example,
in
heavy oil pumping applications, it may be desired to perform downstrokes
slowly, to allow oil to flow into the down-well pump. When it is desired to
run the
stokes at different rates, an entry may be made at the user interface of
controller
400, in response to which controller 400 sends signals to cause pump 328 to
run
at a first flow rate and pressure during one stroke and at a second flow rate
and
pressure during the other stroke.
[00143] As described above, in different applications, lift systems 100
and
300 may be operated with varying quantities of counterbalance fluid. As will
be
appreciated, for a given lift system, increasing the amount of counterbalance
fluid
will shift the equilibrium point upwards in the stroke. That is, the point at
which
the counterbalance fluid is sufficient to support the reciprocating masses
without
41
CA 02799888 2012-12-20
assistance from driving fluid in chambers 121a, 121b or 321a, 321b will be
shifted upwards by adding counterbalance fluid.
[00144] Of course, if the amount of counterbalance fluid is altered, the
pressure of the counterbalance fluid, and therefore, the upward force exerted
on
piston 140c or 340c at different points in the stroke will likewise be
altered. Any
efficiency benefit to be gained from the counterbalance is therefore dependent
on
appropriate tuning of counterbalance fluid pressures, that is, selection of an
appropriate quantity / pressure of counterbalance fluid.
[00145] The appropriate amount / pressure of counterbalance fluid will vary
from application to application and from well to well and may be influenced by
factors such as weight of the reciprocating masses, sizes of various
components
of the lift system, depth of the well, fluid column height and composition
within
the well, sucker rod construction, and numerous other factors. Accordingly,
the
optimum counterbalance tuning will typically need to be experimentally
determined for each well, and may need to be periodically adjusted over the
life
cycle of the well.
[00146] In some embodiments, the most efficient counterbalance
configuration will be the configuration that results in the lift system
expending
approximately equal amounts of energy and producing approximately equal peak
forces during the upstroke and the downstroke. This may be determined by
estimating an appropriate quantity of counterbalance fluid (measured, e.g. by
pressure of counterbalance fluid at a particular point in a stroke), and
cycling lift
system 100 or 300 while measuring with some kind of suitable electrical power
/
current sensor the power consumed by pump 128 or pump 328. The information
of power consumption may be provided to the controller so that an operator or
the controller can make suitable adjustments. If the power consumed by pump
128 or pump 328 is higher during a downstroke than during an upstroke, it will
tend to indicate excess pressure of counterbalance fluid. In such a case,
42
CA 02799888 2012-12-20
counterbalance fluid should be released from the system and the experiment
repeated. Conversely, if the power consumed by pump 128 or pump 328 is
higher during an upstroke, it will tend to indicate insufficient
counterbalance fluid
pressure, meaning that fluid should be added to the system. In general, once
the
power is consistent through both strokes, the counterbalance will be correctly
tuned. Of course, as well conditions may change over time, this counterbalance
tuning process should be repeated periodically to maintain desired efficiency
levels.
[00147] Lift systems 100, 300 may be configured in a range of sizes for
driving different loads. Dimensions for 3 example systems are set out in table
1,
below. The three systems, designated "standard", "heavy" and "super lift", are
intended for loads of increasing size. Of course, the dimensions contained in
table 1 are by way of example only and other embodiments could be configured
in a range of different sizes for other applications.
43
CA 02799888 2012-12-20
Std Heavy
Super Lift
Peak operating pressure 3000 psi 3000 psi 3000
psi
Piston 140a-b/340a-b diameter 2.5 in 2.5 in 3.5 in
Rod 141a-b/341a-b diameter 2 in 1.5 in 2 in
Total lifting area of pistons 140a-b/340a-b 3.53 in 6.28 in
12.96 in2
Estimated lift capacity of pistons 140a-b/340a-b 10,603 lb
18,850 lb 388771b
Piston 140c/340cdiameter 3 in 4 in 5.75
in
Rod 141c/341c diameter 1.25 in 1.5 in 1.5 in
Total lifting area of piston 140c/340c 5.84 in 10.80 in 24.20 in
Lowering area of piston 140c/340c 7.07 in2 12.57 in2
25.97 in2
Estimated lift capacity of piston 140c/340c 17,524 lb
32,398 lb 72,600 lb
Estimated total lift capacity of pistons 140/340 28,127 lb
51,248 lb 111,477 lb
Table 1
[00148] Variations of the illustrated embodiments are contemplated. By way
of example only, instead of having the three cylinders 118a, 118b and 118c or
318a, 318b, 318c being horizontally aligned, with the downward driving and /
counter balance cylinder being located between the two upward driving
cylinders,
the following are example variations:
44
CA 02799888 2012-12-20
[00149] In one variation, the orientation of cylinders 118/318 may be
reversed, with piston rods 141/341 extending upwardly from cylinders 118/318
to
a carriage above cylinders 118/318.
[00150] In another variation, system 300 may be provided with one or more
pressure relief lines between rod end chambers 321a,b and/or blind end
chamber 319c and reservoir 326. By way of example, the pressure relief lines
may run from fluid communication lines 346a,b to reservoir 326. Each pressure
relief line may pass through one or more relief valves, which may be normally
biased closed up to a high fluid pressure (for example, 3000 psi) and which
may
be electrically or hydraulically controlled to open in the event of excess
pressure
developing in rod end chambers 321a,b and or blind end chamber 319c. With
the pressure relief valves closed, fluid may be prevented from draining
through
the pressure relief lines to reservoir 326. When the pressure relief valves
open in
the event of excess pressure, fluid may drain to reservoir 326, relieving the
excess pressure. One or more pressure relief valves may thus be provided that
if the pressure gets too high, allow for pressure to be relieved in the rod
end
chambers 321a,b and lines 346a, 346b during the downstroke when pistons
340a, 340b are providing regeneration hydraulic fluid for blind end chamber
319c
of cylinder 318c.
[00151] When introducing elements of the present invention or the
embodiments thereof, the articles "a," "an," "the," and "said" are intended to
mean
that there are one or more of the elements. The terms "comprising,"
''including,"
and "having" are intended to be inclusive and mean that there may be
additional
elements other than the listed elements.
[00152] Of course, the above described embodiments are intended to be
illustrative only and in no way limiting. The described embodiments of
carrying
out the invention are susceptible to many modifications of form, arrangement
of
CA 02799888 2012-12-20
parts, details, and order of operation. The invention, therefore, is intended
to
encompass all such modifications within its scope.
46
