U.S. patent application number 13/769017 was filed with the patent office on 2014-08-21 for rod-pumping system.
This patent application is currently assigned to ICI ARTIFICIAL LIFT INC.. The applicant listed for this patent is ICI ARTIFICIAL LIFT INC.. Invention is credited to Lee D. Basset, Nicholas Donohoe.
Application Number | 20140234122 13/769017 |
Document ID | / |
Family ID | 51351311 |
Filed Date | 2014-08-21 |
United States Patent
Application |
20140234122 |
Kind Code |
A1 |
Donohoe; Nicholas ; et
al. |
August 21, 2014 |
ROD-PUMPING SYSTEM
Abstract
A rod-pumping system is provided. In one embodiment, the system
includes a downhole pump positioned in a well and coupled to a well
string, such as a sucker-rod string. The system also includes a
first hydraulic actuator arranged with respect to the well string
so as to enable the first hydraulic actuator to move the well
string within the well. The first hydraulic actuator is connected
in fluid communication with a second hydraulic actuator. A control
pump is connected to both the first and second hydraulic actuators
to enable the control pump to alternate between pumping control
fluid to the first hydraulic actuator to cause the well string to
move in a first direction within the well and pumping control fluid
to the second hydraulic actuator to cause the well string to move
in an opposite, second direction within the well. Additional
systems, devices, and methods are also disclosed.
Inventors: |
Donohoe; Nicholas;
(Edmonton, CA) ; Basset; Lee D.; (Lloydminster,
CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
ICI ARTIFICIAL LIFT INC. |
Houston |
TX |
US |
|
|
Assignee: |
ICI ARTIFICIAL LIFT INC.
Houston
TX
|
Family ID: |
51351311 |
Appl. No.: |
13/769017 |
Filed: |
February 15, 2013 |
Current U.S.
Class: |
417/53 ;
417/57 |
Current CPC
Class: |
F04B 47/026 20130101;
F04B 23/023 20130101; F04B 9/105 20130101; F04B 9/1053 20130101;
F04B 47/04 20130101; F04B 47/145 20130101; F04B 23/04 20130101;
F04B 47/02 20130101 |
Class at
Publication: |
417/53 ;
417/57 |
International
Class: |
F04B 19/00 20060101
F04B019/00 |
Claims
1. A rod-pumping system comprising: a downhole pump positioned in a
well; a well string coupled to the downhole pump; a first hydraulic
actuator arranged with the well string so as to enable the first
hydraulic actuator to move the well string within the well; a
second hydraulic actuator connected in fluid communication with the
first hydraulic actuator; and a control pump connected to the first
hydraulic actuator and to the second hydraulic actuator in a manner
that enables the control pump, during operation, to alternate
between pumping control fluid to the first hydraulic actuator to
cause the well string to move in a first direction within the well
and pumping control fluid to the second hydraulic actuator to cause
the well string to move in an opposite, second direction within the
well.
2. The rod-pumping system of claim 1, wherein the control pump is
connected to a rod end of the first hydraulic actuator.
3. The rod-pumping system of claim 1, wherein the second hydraulic
actuator is connected to at least one accumulator set to
counterbalance the full load of the first hydraulic actuator.
4. The rod-pumping system of claim 3, wherein the connection of the
control pump to the first and second hydraulic actuators enables
the control pump to offset hydraulic balance between the first and
second hydraulic actuators.
5. The rod-pumping system of claim 1, comprising sensors to
facilitate detection of piston positions in the first and second
hydraulic actuators.
6. The rod-pumping system of claim 5, wherein the sensors include
proximity switches that facilitate detection of the position of a
piston of the first hydraulic actuator and a linear transducer that
facilitates detection of the position of a piston of the second
hydraulic actuator.
7. The rod-pumping system of claim 5, comprising a controller
configured to receive input from the sensors that facilitate
detection of the piston positions and to synchronize the first and
second hydraulic cylinders.
8. The rod-pumping system of claim 1, comprising an auxiliary pump
that enables the introduction of fresh control fluid to a hydraulic
circuit that includes the first hydraulic actuator and the second
hydraulic actuator.
9. The rod-pumping system of claim 1, wherein the first hydraulic
actuator is a double-acting hydraulic cylinder.
10. The rod-pumping system of claim 1, wherein the first hydraulic
actuator is coupled to a wellhead installed at the well.
11. The rod-pumping system of claim 1, wherein the well string
includes a sucker-rod string that is coupled to a rod clamp that
engages the first hydraulic actuator.
12. A rod-pumping system comprising: a slave cylinder mounted on or
adjacent to wellhead equipment installed at a well; a master
cylinder connected in fluid communication with the slave cylinder,
wherein the master cylinder is counterbalanced with fluid from at
least one accumulator and is able to absorb the full load of the
slave cylinder; and a closed-loop hydraulic circuit including a
pump connected in fluid communication with the slave cylinder and
with the master cylinder to enable the pump to drive a piston in
the slave cylinder and a piston in the master cylinder to
reciprocate a well string within the well.
13. The rod-pumping system of claim 12, comprising an additional
pump that enables hydraulic fluid to be pumped into the closed-loop
hydraulic circuit to replace used hydraulic fluid flushed from the
closed-loop hydraulic circuit.
14. The rod-pumping system of claim 13, comprising a prime mover
coupled to drive both the pump and the additional pump.
15. The rod-pumping system of claim 12, comprising: position
sensors on the slave cylinder and the master cylinder; and a
controller configured to synchronize the slave cylinder and the
master cylinder based on input from the position sensors.
16. The rod-pumping system of claim 12, comprising a downhole pump
coupled to the well string.
17. A method comprising: lowering a well string that is positioned
in a well and is coupled to a downhole pump within the well by
pumping control fluid to a first linear actuator; and raising the
well string by pumping control fluid to a second linear actuator
that is connected to the first linear actuator.
18. The method of claim 17, wherein pumping control fluid to the
first linear actuator includes pumping control fluid to a rod end
of the first linear actuator.
19. The method of claim 17, comprising: determining the positions
of pistons within the first linear actuator and the second linear
actuator; and synchronizing the first linear actuator and the
second linear actuator based on the determined positions of the
pistons.
20. The method of claim 17, comprising alternating flow of control
fluid between the first linear actuator and the second linear
actuator by reversing flow of a bidirectional pump connected to the
first linear actuator and the second linear actuator.
21. The method of claim 17, comprising: continually flushing
control fluid from a hydraulic or pneumatic circuit including the
first and second linear actuators and replacing the flushed control
fluid with fresh control fluid during operation of the first and
second linear actuators; and maintaining synchronization between
the first and second linear actuators during operation.
Description
BACKGROUND
[0001] This section is intended to introduce the reader to various
aspects of art that may be related to various aspects of the
presently described embodiments. This discussion is believed to be
helpful in providing the reader with background information to
facilitate a better understanding of the various aspects of the
present embodiments. Accordingly, it should be understood that
these statements are to be read in this light, and not as
admissions of prior art.
[0002] In order to meet consumer and industrial demand for natural
resources, companies often invest significant amounts of time and
money in finding and extracting oil, natural gas, and other
subterranean resources from the earth. Particularly, once a desired
subterranean resource such as oil or natural gas is discovered,
drilling and production systems are often employed to access and
extract the resource. These systems may be located onshore or
offshore depending on the location of a desired resource. Further,
such systems generally include a wellhead assembly mounted on a
well through which the resource is accessed or extracted. These
wellhead assemblies may include a wide variety of components, such
as various casings, valves, pumps, fluid conduits, and the like,
that control drilling or extraction operations.
[0003] In some instances, resources accessed via wells are able to
flow to the surface by themselves. This is typically the case with
gas wells, as the accessed gas has a lower density than air. This
can also be the case for oil wells if the pressure of the oil is
sufficiently high to overcome gravity. But often accessed oil does
not have sufficient pressure to flow to the surface and the oil
must be lifted to the surface through one of various methods known
as artificial lift. Artificial lift can also be used to raise other
resources through wells to the surface, or for removing water or
other liquids from gas wells. One form of artificial lift uses a
pump that is placed downhole in the well and is operated by a
reciprocating rod string extending through the well from the
downhole pump to the surface. Such systems are commonly referred to
as rod-pumping or sucker-rod systems.
SUMMARY
[0004] Certain aspects of some embodiments disclosed herein are set
forth below. It should be understood that these aspects are
presented merely to provide the reader with a brief summary of
certain forms the invention might take and that these aspects are
not intended to limit the scope of the invention. Indeed, the
invention may encompass a variety of aspects that may not be set
forth below.
[0005] Embodiments of the present disclosure generally relate to a
rod-pumping system for lifting fluids from a well. The rod-pumping
system of one embodiment includes a pair of hydraulic actuators,
such as hydraulic cylinders; a rod string moved by one of the
hydraulic actuators and coupled to a downhole pump; and a control
pump. The hydraulic actuators are connected in series, and the
control pump is connected to pump fluid to one end of each
hydraulic actuator such that alternating the flow direction from
the control pump controls operation of the hydraulic actuators and
operates the downhole pump via the rod string. In some embodiments,
sensors are used to detect the positions of pistons in the
actuators and a controller synchronizes the pistons to facilitate
proper operation.
[0006] Various refinements of the features noted above may exist in
relation to various aspects of the present embodiments. Further
features may also be incorporated in these various aspects as well.
These refinements and additional features may exist individually or
in any combination. For instance, various features discussed below
in relation to one or more of the illustrated embodiments may be
incorporated into any of the above-described aspects of the present
disclosure alone or in any combination. Again, the brief summary
presented above is intended only to familiarize the reader with
certain aspects and contexts of some embodiments without limitation
to the claimed subject matter.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] These and other features, aspects, and advantages of certain
embodiments will become better understood when the following
detailed description is read with reference to the accompanying
drawings in which like characters represent like parts throughout
the drawings, wherein:
[0008] FIG. 1 generally depicts a production system having an
artificial lift system to draw fluid from a well to the surface in
accordance with one embodiment of the present disclosure;
[0009] FIG. 2 is a block diagram of various components of the
artificial lift system of FIG. 1 in accordance with one
embodiment;
[0010] FIG. 3 generally depicts a hydraulic actuator of the
artificial lift system of FIG. 2 mounted on wellhead equipment in
accordance with one embodiment;
[0011] FIG. 4 is a cross-section generally depicting certain
components of the hydraulic actuator of FIG. 3 in accordance with
one embodiment;
[0012] FIG. 5 generally depicts the hydraulic actuator of FIG. 3
with a piston rod of the actuator extended from its housing;
and
[0013] FIG. 6 schematically depicts certain hydraulic components
and control components of the production system of FIG. 1 in
accordance with one embodiment of the present disclosure.
DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS
[0014] One or more specific embodiments of the present disclosure
will be described below. In an effort to provide a concise
description of these embodiments, all features of an actual
implementation may not be described in the specification. It should
be appreciated that in the development of any such actual
implementation, as in any engineering or design project, numerous
implementation-specific decisions must be made to achieve the
developers' specific goals, such as compliance with system-related
and business-related constraints, which may vary from one
implementation to another. Moreover, it should be appreciated that
such a development effort might be complex and time consuming, but
would nevertheless be a routine undertaking of design, fabrication,
and manufacture for those of ordinary skill having the benefit of
this disclosure.
[0015] When introducing elements of various embodiments, 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. Moreover, any use of "top," "bottom," "above," "below,"
other directional terms, and variations of these terms is made for
convenience, but does not require any particular orientation of the
components.
[0016] Turning now to the present figures, a system 10 is
illustrated in FIG. 1 in accordance with one embodiment. Notably,
the system 10 is a production system that facilitates extraction of
a resource, such as oil, from a reservoir 12 through a well 14.
Wellhead equipment 16 is installed on the well (e.g., attached to
the top of casing and tubing strings in the well). In one
embodiment, the wellhead equipment 16 includes a casing head, a
tubing head, and a stuffing box. But the components of the wellhead
equipment 16 can differ between different applications, and such
equipment could include various casing heads, tubing heads,
stuffing boxes, pumping tees, and pressure gauges, to name only a
few possibilities.
[0017] The system 10 also includes an artificial lift system 18. In
one embodiment generally depicted in FIG. 2, the artificial lift
system 18 is a rod-pumping system including a sucker-rod string 22
coupled to a downhole pump 24 in the well 14. The downhole pump 24
can be of any suitable design, such as one in which the downhole
pump 24 includes a stationary valve and a traveling valve
(connected to the sucker-rod string 22) that cooperate to lift
fluid from a reservoir to the surface. The sucker-rod string 22
extends through the well 14 and is also coupled to a linear
actuator, such as slave cylinder 26 in FIG. 2. This linear actuator
enables movement of the sucker-rod string 22 back-and-forth within
the well 14 to operate the downhole pump 24 and raise fluid (e.g.,
oil, gas condensate, or water) from the reservoir 12 to the
surface. In other embodiments, the sucker-rod string 22 could be
replaced by some other structure (e.g., a coiled tubing string)
connected to the downhole pump 24 and moved by the linear actuator
to lift fluids from the reservoir 12. As used herein, the term
"well string" means any device or structure that extends through a
well and enables a linear actuator (e.g., slave cylinder 26) to
operate a downhole pump. The term encompasses, but is not limited
to, both sucker-rod string and coiled tubing.
[0018] As depicted in FIG. 2, the artificial lift system 18
includes an additional linear actuator in the form of master
cylinder 28. The master cylinder 28 cooperates with the slave
cylinder 26 in controlling movement of the sucker-rod string 22, as
discussed in greater detail below. Although here described as
cylinders 26 and 28, it will be appreciated that the linear
actuators could be provided in any suitable form (including
non-cylindrical shapes, for instance) and may also be referred to
as rams, jacks, or the like. In some embodiments, the artificial
lift system 18 is a hydraulic system with hydraulic linear
actuators. But while the examples provided below refer to such a
hydraulic system, it is noted that in other embodiments the
artificial lift system 18 can instead be a pneumatic system with
pneumatic linear actuators that are operated with a gaseous control
fluid, such as compressed air.
[0019] The artificial lift system 18 depicted in FIG. 2 also
includes a pumping system 30. This pumping system 30 includes a
primary pump 32 and an auxiliary pump 34. As will be described in
greater detail below, the primary pump 32 is connected in fluid
communication with both of the hydraulic actuators (i.e., slave
cylinder 26 and master cylinder 28 in the depicted embodiment) to
control movement of pistons inside these actuators. Thus, primary
pump 32 is also referred to herein as control pump 32. In one
embodiment, the control pump 32 is a bidirectional pump capable of
pumping hydraulic control fluid (e.g., hydraulic oil)
back-and-forth between the slave cylinder 26 and the master
cylinder 28 by reversing the flow direction. If additional control
fluid is needed, the control pump 32 can draw such fluid from a
fluid tank 38. The control pump 32 is driven by a prime mover 36,
such as a diesel engine. But any suitable prime mover 36 could be
used, such as a propane engine, a natural gas engine (which could
include an engine run on casing head gas produced at the well 14),
or an electric motor.
[0020] The auxiliary pump 34 is connected to provide fresh control
fluid (i.e., new or reconditioned control fluid) to at least some
portions of the hydraulic circuit that includes the slave cylinder
26 and the master cylinder 28. The auxiliary pump 34 can also, but
need not, draw control fluid from the fluid tank 38 and be driven
by the prime mover 36 independent of the control pump 32. (It is
noted that taking a slip stream off of the control pump circuit to
feed the auxiliary pump 34, while possible, would reduce system
speed.) In one embodiment, control fluid is flushed from various
portions of the hydraulic circuit (e.g., with one or more flushing
valves) and replaced by fresh control fluid pumped from the fluid
tank 38 by the control pump 32 and the auxiliary pump 34. The
flushed control fluid can be routed through a conditioning system
40, such as through one or more filters to remove any contaminants
in the control fluid and through a cooler that lowers the
temperature of the control fluid to reduce wear on components of
the artificial lift system 18. Control fluid reconditioned by the
conditioning system 40 can be returned to the fluid tank 38 to be
reused in the pumping system 30.
[0021] The pumping system 30 also includes a controller 42. The
controller 42 processes inputs from various sensors 44 to control
operation of other components of the pumping system 30 (e.g., the
control pump 32, the auxiliary pump 34, the prime mover 36, any
flushing valves, and the cooler of the conditioning system 40) and,
by extension, operation of the slave cylinder 26 and the master
cylinder 28. In some embodiments, the sensors 44 include proximity
switches and a linear position transducer that allow the
determination of positions of pistons within the slave cylinder 26
and the master cylinder 28. The sensors could also, for example,
include a temperature sensor to monitor temperatures of control
fluid or components in the artificial lift system 18, pressure
sensors to detect hydraulic pressures at various locations within
the system 18, or a level sensor to detect the amount of control
fluid available in the fluid tank 38. The controller 42 in one
embodiment is a programmable logic controller that is programmed to
provide the control functionality described herein. But in other
embodiments, the controller 42 could be any circuit-based device
(with or without software) suitable for controlling operation of
the artificial lift system 18, such as a processor-based device
that executes instructions (firmware or software) stored in a
suitable memory of the device.
[0022] The depicted pumping system 30 also includes a skid 46 to
facilitate transport of various system components. For example, in
one embodiment the primary pump 32, the auxiliary pump 34, the
prime mover 36, the fluid tank 38, the conditioning system 40, the
controller 42, and some sensors 44 are provided on the skid 46,
allowing an operator to more easily move all of these components to
a desired location. Other components, such as the master cylinder
28, can also be mounted on the skid 46.
[0023] As noted above, the slave cylinder 26 engages the sucker-rod
string 22 to operate the downhole pump 24 and lift fluid up the
well 14 to the surface. The slave cylinder 26 can be attached to
wellhead equipment to receive the sucker-rod string 22 and operate
the downhole pump 24. One example of such an arrangement is
depicted in FIGS. 3-5. In this embodiment, the slave cylinder 26 is
positioned over a polished rod 50 of the sucker-rod string 22 and
is connected, via a pedestal stand 52, to a tubing head 54 of the
wellhead equipment 16. Although not depicted in the present figure,
the tubing head 54 can be coupled to other wellhead equipment 16,
such as a casing head, above the well 14. The tubing head 54
includes a flow conduit 56 for conveying fluid lifted from the well
14, as well as a test conduit 58. While the slave cylinder 26 is
depicted as being connected to the tubing head 54 by the pedestal
stand 52 in FIG. 3, the slave cylinder 26 can be connected to the
wellhead equipment 16 in any suitable manner (e.g., connected in
other ways or to other components of the wellhead equipment 16).
Indeed, in some embodiments the slave cylinder 26 is not connected
to the wellhead equipment 16 at all, and is instead positioned
adjacent the wellhead equipment 16. In one example of such an
embodiment, a slave cylinder 26 is mounted adjacent to, but
separated from, the wellhead equipment 16 and interacts with the
sucker-rod string 22 via cables and a bridle.
[0024] The wellhead equipment 16 also includes a stuffing box 60
attached to the tubing head 54. As will be recognized by those
knowledgeable in the art, the stuffing box 60 includes packing that
allows the polished rod 50 to move up-and-down through the stuffing
box 60 while inhibiting leaking. The polished rod 50 is connected
to a series of sucker rods to form the sucker-rod string 22 that
extends through the well 14 to the downhole pump 24. Movement of
the polished rod 50 causes corresponding movement of the sucker
rods to operate the downhole pump 24. In other embodiments, the
stuffing box 60 is omitted and the slave cylinder 26 itself
isolates wellbore fluids from the external environment.
[0025] The slave cylinder 26 includes a housing 66 in which a
piston rod 68 is disposed. The piston rod 68 of the depicted
embodiment is hollow (see FIG. 4) and a connecting rod 70 is
disposed within the bore of the piston rod 68. The connecting rod
70 is coupled to the polished rod 50 as part of the sucker-rod
string 22. A rod clamp 72 is coupled to the connecting rod 70 and
is positioned at the end of the piston rod 68 to allow the
sucker-rod string 22 to be suspended in the well 14. In other
embodiments, the connecting rod 70 is omitted and the polished rod
50 of the sucker-rod string 22 engages the slave cylinder 26 (e.g.,
via a rod clamp 72 attached to the polished rod 50 itself). By
applying appropriate pressure, the piston rod 68 can be extended or
retracted with respect to the housing 66. For instance, in the
present embodiment hydraulic control fluid can be provided into the
housing 66 through a connection 78 at the cap end of slave cylinder
26 to cause the piston rod 68 to extend from the housing 66, and
through a connection 80 at the rod end of the slave cylinder 26 to
cause the piston rod 68 to retract into the housing 66. For
convenience, the slave cylinder 26 can include a fluid conduit 82
and a connection 84 coupled to the connection 80, allowing a fluid
supply hose or pipe to be connected to the more-accessible (i.e.,
closer to the ground) connection 84. Although not depicted in the
present figure, in one embodiment the primary pump 32 is connected
directly to the connection 84 via a hose or pipe and the master
cylinder 28 is connected to the slave cylinder 26 via the
connection 78. Also, the rod clamp 72 in some embodiments rests on
the piston rod 68 such that the sucker-rod string 22 is lifted by
extension of the piston rod 68 from the housing 66 but is lowered
by gravity when the piston rod 68 retracts. In other embodiments,
the rod clamp 72 can be attached to the piston rod 68 such that the
sucker-rod string 22 is driven by the piston rod 68 in both
directions. In either of these instances, movement of the piston
rod 68 can be said to cause reciprocal movement of the sucker-rod
string 22.
[0026] As depicted in FIG. 4, the hollow piston rod 68 may be
mounted about a hollow tube 90 in the housing 66. The tube 90
provides a bearing surface for the hollow piston rod 68 and
isolates the working pressures in the slave cylinder 26 from the
connecting rod 70 and other components in the well 14. The piston
rod 68 may be extended or retracted by manipulating pressure
against the piston head 92. In the embodiment depicted in FIGS.
3-5, the slave cylinder 26 is a double-acting cylinder.
Specifically, pressurized hydraulic control fluid can be directed
into the chamber 96 (e.g., via connection 78) to cause the piston
head 92 to move and the piston rod 68 to extend from the housing
66, as depicted in FIG. 5. Conversely, such control fluid can be
directed into the chamber 98 (e.g., via connection 80) to move the
piston head 92 in an opposite direction and to retract the piston
rod 68 to the position depicted in FIG. 3. Although not depicted in
the present figures for the sake of clarity, it will be appreciated
that the slave cylinder 26 will generally include additional
components, such as various seals that inhibit leakage from the
housing 66 or between the chambers 96 and 98.
[0027] As noted above, the connecting rod 70 is positioned with
respect to the piston rod 68 and is coupled to the sucker-rod
string 22 to enable the movement of the piston rod 68 to operate
the downhole pump 24. In the embodiment depicted in FIG. 4, the
connecting rod 70 is coupled to the polished rod 50 of the
sucker-rod string 22 with a connector 102. But the connecting rod
70 (or, in the absence of the connecting rod 70, the slave cylinder
26) could engage the polished rod 50 in any suitable manner that
allows the slave cylinder 26 to operate the downhole pump 24.
[0028] In at least some embodiments, the slave cylinder 26 includes
one or more sensors to detect the position of the piston head 92
within the housing 66. Any suitable sensor could be used, such as a
proximity switch or a linear transducer. In one embodiment depicted
in FIGS. 3 and 5, sensors are provided on an external guide 108 and
include proximity sensors or switches 110 and 112. As one example,
the external guide 108 can be a length of pipe (e.g., PVC pipe)
with proximity switches 110 and 112 mounted on its exterior. A
trigger 114, such as a piece of metal in the case of inductive
proximity switches, is connected to a support 116. The support 116
moves with the piston rod 68, causing the trigger 114 to move
between the proximity switches 110 and 112. As the piston rod 68
extends from the housing 66 toward the position depicted in FIG. 5,
the trigger 114 is drawn upwardly through the guide 108 toward
proximity switch 110. Once the proximity switch 110 is activated by
the trigger 114, an output signal is sent to the controller 42 to
cause the piston rod 68 to begin to retract back into the housing
66 (toward the position depicted in FIG. 3). While the piston rod
68 retracts, the trigger 114 travels through the guide 108 toward
the proximity switch 112. Once this switch 112 is activated, an
output signal is sent to the controller 42 to cause the piston rod
68 to reverse direction again. In this manner, the proximity
switches 110 and 112 facilitate reciprocal motion of the piston rod
68 between the extended and retracted positions and of the
sucker-rod string 22 within the well 14. In another embodiment, the
position of the master cylinder 28 (e.g., as determined by a linear
position transducer 138 (FIG. 6)) is used to control operation of
the system and output from the switches 110 and 112 can be compared
to the detected position of the master cylinder 28 to verify proper
operation of the system.
[0029] Certain operational aspects of the rod-pumping system
described above may be better understood with reference to FIG. 6,
which is a schematic diagram generally depicting hydraulic
connections between certain hydraulic components of the system 18
and control of these hydraulic components by the controller 42 in
accordance with one embodiment. In this diagram, the master
cylinder 28 includes a floating piston 120 having a piston rod
between piston heads 122 and 124. As noted above with respect to
the slave cylinder 26, it will be appreciated that the master
cylinder 28 will generally include other components that are not
depicted in the present figure, including seals that inhibit
leaking from, or between different portions of the cylinder 28. The
piston rod of piston 120 is positioned through a wall or bulkhead
126 of the master cylinder 28 with the piston heads 122 and 124
disposed on opposite sides of the bulkhead. This generally divides
the interior of the master cylinder 28 into four isolated chambers,
referred to herein as chambers 128, 130, 132, and 134.
[0030] The master cylinder 28 is arranged in series with the slave
cylinder 26, with the chamber 128 connected in fluid communication
with the chamber 96 on the cap end of the slave cylinder 26.
Primary pump 32 is connected in fluid communication with both the
chamber 130 and the chamber 98 on the rod end of the slave cylinder
26. Pressurized hydraulic fluid in the chambers 128 and 130 may be
manipulated to act on the piston head 122 and move the piston 120
within the master cylinder 28. The master cylinder 28 in FIG. 6 is
assisted by one or more accumulators 136 connected to the chamber
134. As will be appreciated, the accumulators 136 are energy
storage devices that apply pressure to hydraulic fluid in the
accumulators. Any suitable accumulators 136 may be used, but in at
least some embodiments the accumulators 136 are compressed gas
accumulators (e.g., nitrogen accumulators). Pressure stored in the
accumulators 136 is transmitted via hydraulic fluid in the chamber
134 to the piston head 124. Chamber 132 in FIG. 6 is connected in
fluid communication with the fluid tank 38 so as to not inhibit
movement of the piston 120 in response to hydraulic pressures
within chambers 128, 130, and 134. Specifically, chamber 132 is
connected to draw fluid from the fluid tank 38 when chamber 132
expands and to expel the fluid back to the fluid tank 38 when the
chamber 132 contracts.
[0031] The system depicted in FIG. 6 is a proportional,
intelligent, closed-loop hydraulic system in which feedback from
various sensors (e.g., proximity switches 110 and 112, a position
transducer 138, and other sensors 144) is used by the controller 42
to adjust operation of the system. During operation, primary pump
32 alternates pumping of pressurized control fluid between the
chamber 130 of the master cylinder 28 and chamber 98 at the rod end
of the slave cylinder 26. Particularly, pumping of the control
fluid into the chamber 130 by the primary pump 32 causes the piston
120 to move to the left in FIG. 6, and movement in this direction
is assisted by the pressure stored in the accumulators 136
(transmitted via fluid in chamber 134). Movement of the piston 120
in this manner reduces the volume of chamber 128, causing
pressurized control fluid to flow from chamber 128 toward chamber
96 at the cap end of the slave cylinder 26. This in turn causes the
piston head 92 to move toward the rod end of the slave cylinder 26
and extends the piston rod 68 from the housing 66 of the slave
cylinder 26 to raise the sucker-rod string 22 in the well. Such
motion can be generally referred to as an upstroke. Conversely, the
primary pump 32 can pump fluid into the chamber 98 of the rod end
of the slave cylinder 26 to move the piston head 92 away from the
rod end and retract the piston rod 68. This movement causes the
sucker-rod string to be lowered further into the well and may be
referred to as a downstroke. The movement of the piston head 92
during the downstroke causes control fluid to flow from the chamber
96 toward the chamber 128, causing the master cylinder piston 120
to move to the right in FIG. 6. This also causes pressurized fluid
from chamber 134 to be pushed into the accumulators 136, thereby
storing energy for the next upstroke.
[0032] In one embodiment, the one or more accumulators 136 are set
(e.g., pre-charged) to counterbalance the full load of the slave
cylinder 26 during operation. That is, the force on the master
cylinder piston 120 caused by the one or more accumulators 136
meets or exceeds the load on the slave cylinder piston due to
gravity (which includes loading by the components borne by the
piston rod 68, such as the sucker-rod string 22 and any portion of
the downhole pump 24 connected to move with the sucker-rod string
22). This fully counterbalanced arrangement is in contrast to
systems in which the load on the slave cylinder is only partially
counterbalanced. In such partially counterbalanced systems,
upstrokes rely on pressure from control pumps to provide sufficient
force to overcome gravitational loading on pistons of slave
cylinders coupled to a rod string and the systems rely on gravity
to retract the slave cylinder piston and push the master cylinder
piston back toward accumulators. But having the primary pump 32
control one side of the slave cylinder 26, as described above,
reduces or eliminates the reliance on gravity to retract the slave
cylinder piston, allowing the counterbalance pressure from the
accumulators 136 to be set at or above the load on the slave
cylinder piston.
[0033] In one embodiment, the biasing force from the accumulators
136 balances the full load on the piston of slave cylinder 26, and
the primary pump 32 is used to offset this hydraulic balance
between the cylinders to provide directional control and speed
control of the piston rod 68 (and, by extension, of the sucker-rod
string 22). As one line from the primary pump 32 is connected to
the rod end of the slave cylinder 26 (rather than the pump having
direct control over the reciprocating of the master cylinder 28 by
being directly connected to both sides of its piston), the pistons
of the two cylinders move in consort based on differential
pressures. Such an arrangement allows the use of a differential
cylinder (e.g., slave cylinder 26) in a closed-loop system without
venting to atmosphere. This is in contrast to other arrangements
that rely on gravity to reset the piston of a slave cylinder and in
which the rod end of the slave cylinder is vented to atmosphere so
as to not inhibit movement of the piston. By not venting the rod
end of the slave cylinder 26 to atmosphere, the present arrangement
avoids large pressure differentials across seals provided on piston
head 92 to isolate the chambers 96 and 98 (such pressure
differentials could contribute to premature seal failure) and
reduces the likelihood of rust and contamination of the rod end
components of the slave cylinder 26, like piston rod 68.
[0034] In at least some embodiments, the master cylinder 28 is
constructed proportionally to the slave cylinder 26 to have larger
piston heads and a shorter stroke. The connection of the primary
pump 32 to both the slave cylinder 26 and the master cylinder 28 in
the manner depicted in FIG. 6 also allows the cylinder pistons to
be controlled by applying pressure to less surface area on the
piston heads of the cylinder pistons. Particularly, the piston rod
68 may be retracted and the master cylinder piston 120 pushed
toward the accumulators by pumping fluid into chamber 98 to act on
the effective area of the piston head 92 about the piston rod 68
rather than pumping fluid into chamber 128 to act on the greater
surface area of the piston head 122. By controlling operation via a
smaller piston head area, the present arrangement increases system
efficiency and allows the use of a smaller control pump 32, smaller
flow from the control pump 32, and less horsepower to achieve a
given amount of lift.
[0035] During normal operation of the hydraulic system depicted in
FIG. 6, the pistons of the slave cylinder 26 and the master
cylinder 28 are synchronized. That is, movement of the piston 120
to the left in FIG. 6 causes the piston head 92 (and its piston rod
68) to move up in the slave cylinder 26 with a desired stroke
length, and movement of the piston head 92 down causes the piston
120 to return to the right. But this synchronous movement relies on
proper amounts of control fluid in the system, and particularly
within the portion of the hydraulic circuit between the piston
heads 92 and 122 (including chambers 96 and 128). If too little
control fluid is provided in this portion of the hydraulic circuit
compared to the rest of the circuit, pressure from the chambers 98
and 130 (as well as the slave cylinder load and the accumulator
pressure) will cause the piston heads 92 and 122 to be too close
together. And if too much control fluid is provided in this
portion, the pressure in the chambers 96 and 128 will cause the
piston heads 92 and 122 to be too far apart. In either of these
cases, one of the piston heads 92 or 122 would bottom out (i.e.,
the piston would reach the end of its stroke) before the other has
moved a desired amount. In such a condition, the slave cylinder 26
and the master cylinder 28 can be considered to be out-of-sync.
[0036] To facilitate proper operation, the controller 42 receives
inputs from various sensors and controls the pumping system
components to synchronize the cylinders 26 and 28. Sensors (e.g.,
proximity switches 110 and 112, and linear position transducer 138)
facilitate determination of the positions of the cylinder pistons.
Based on this information, the controller 42 can synchronize the
cylinders 26 and 28. More specifically, at startup, the controller
42 determines whether the cylinders are synchronized. If they are
not, the controller 42 automatically synchronizes the cylinders
before starting normal operation of the system. That is, the
controller 42 operates the pumps 32 and 34, the flushing valves, or
both to vary the amount of fluid in the various chambers and,
consequently, to adjust the distance between the piston heads 92
and 122 in the circuit such that the pistons of both cylinders 26
and 28 can travel their intended stroke lengths during operation.
As one example, such synchronization can be achieved by pumping
control fluid with the primary pump 32 into chamber 98 to retract
the piston rod 68 and then varying the amount of fluid in chamber
128 (to properly space the piston head 122 with respect to the
piston head 92) by either pumping additional fluid into the chamber
128 with the auxiliary pump 34 or by flushing fluid from chamber
128. Such synchronization of the cylinders 26 and 28 can also be
based on other inputs, such as feedback from other sensors 144
(e.g., pressure sensors in the hydraulic circuit, temperature
sensors, and a level sensor in the fluid tank 38 (FIG. 2)). The
controller 42 could also control other components of the system,
such as the prime mover 36.
[0037] In some embodiments, the controller 42 provides additional
control functionality. For instance, the controller 42 can vary
operation of the hydraulic system based on temperature detected by
one or more temperature sensors. On a cold startup, the controller
42 may operate the system at a reduced speed (e.g., operate the
primary pump at a set percentage of maximum flow) until a desired
system temperature is achieved. This may reduce cavitation of the
pumps and damage to seals and filter elements in the system. And
during operation, the controller 42 can cause operation of the
system to be slowed if the detected temperature exceeds a first
threshold temperature and stopped if the detected temperature
exceeds a second, higher threshold. It is noted that continued
operation at a reduced speed allows hydraulic fluid to be passed
through a cooler of the conditioning system 40, which may allow the
system to cool faster than if the system were simply stopped.
[0038] Additionally, the controller 42 may provide an emergency
alarm or shut-off function to stop undesirable operation of the
system, which may include motion of the piston 120 outside of a
desired range. By way of example, the master cylinder 28 and the
slave cylinder 26 may be configured such that the maximum volume of
the chamber 128 exceeds that of chamber 96 to which it is
hydraulically connected. Movement of the piston head 122 to the
left in FIG. 6 causes control fluid to flow from the chamber 128 to
the chamber 96. But once chamber 96 is filled to its maximum volume
(which may be determined by the controller 42 based on proximity
switch 110 detecting, via trigger 114 (FIG. 5), that piston head 92
is at the end of the slave cylinder 26), additional movement of the
piston head 122 in the same direction could damage the cylinders
(e.g., by causing pressures within these chambers to exceed the
rated maximum of the cylinders). In at least some embodiments, the
controller 42 can operate a valve to flush fluid from the portion
of the hydraulic circuit including chambers 96 and 128 if it
detects (e.g., via a pressure sensor) that the pressure in that
portion of the hydraulic circuit is too high.
[0039] Further, in some embodiments the controller 42 monitors the
position of the piston 120 (via transducer 138) to facilitate
synchronization and ensure the piston 120 is not traveling too
close to the end of the master cylinder 28 at chamber 128. The
controller 42 can be programmed with one or more threshold
distances based on the allowable maximum travel of the piston 120.
For example, if the distance from the end of the master cylinder 28
and the piston head 122 falls below a first, set threshold the
controller 42 can trigger an alarm to alert an operator that the
piston 120 is moving to a distance from the end of the cylinder
that is near a minimum allowable distance. In addition to or
instead of triggering an alarm, the controller 42 can automatically
activate the auxiliary pump 34 to pump additional control fluid
into the chamber 128 to try to push the piston 120 to the right in
FIG. 6 and synchronize the system such that the detected distance
between the piston head 122 and the end of the master cylinder 28
is maintained above the first threshold. In the event the
controller 42 is unable to synchronize the system and the distance
from the end of the master cylinder 28 and the piston head 122
falls below a second, set threshold (e.g., set to the minimum
allowable distance), the controller 42 can deactivate the system to
allow servicing.
[0040] Closed-loop hydraulic systems typically have sections of
dead fluid (i.e., control fluid that cannot be removed from a
hydraulic circuit for cooling or filtration). Additionally,
synchronization between master and slave cylinders is maintained by
trying to minimize fluid loss across seals of the system, and dead
fluid resulting from trying to minimize fluid losses can lead to
damage as the fluid degrades or is contaminated. But in some
embodiments of the present technique, and as generally noted above,
control fluid can be continually flushed from the different
portions of the hydraulic circuit and replaced by fresh control
fluid. The flushed fluid can be conditioned (e.g., filtered and
cooled) via conditioning system 40 and returned to the hydraulic
circuit or to the fluid tank 38. During such flushing and
refilling, the controller 42 monitors the positions of the pistons
of the cylinders 26 and 28 and can automatically keep or put the
system back in synchronization by controlling the operation of the
primary pump 32 and the auxiliary pump 34 to replace the flushed
control fluid with a corresponding amount of fresh control fluid.
In some embodiments, the auxiliary pump 34 operates independently
from the primary pump 32 and pulls control fluid directly from the
fluid tank 38, which has fluid that will be generally cooler and
cleaner than fluid that could be drawn from the primary pump 32.
For instance, in the embodiment depicted in FIG. 6, control fluid
pumped between chamber 98 and chamber 130 to operate the cylinders
26 and 28 can be flushed from the hydraulic circuit and replaced
with fluid drawn from the fluid tank 38 by the primary pump 32.
Further, control fluid used in the portion of the circuit including
chambers 96 and 128 can be flushed and replaced with fluid drawn
from the tank 38 by the auxiliary pump 34. Control fluid in chamber
134 and the accumulators 136 can also be flushed and replaced with
fluid drawn from the tank 38 by the auxiliary pump 34.
[0041] While the aspects of the present disclosure may be
susceptible to various modifications and alternative forms,
specific embodiments have been shown by way of example in the
drawings and have been described in detail herein. But it should be
understood that the invention is not intended to be limited to the
particular forms disclosed. Rather, the invention is to cover all
modifications, equivalents, and alternatives falling within the
spirit and scope of the invention as defined by the following
appended claims.
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