U.S. patent application number 14/574286 was filed with the patent office on 2015-10-29 for multi-cylinder hydraulically-driven pump system.
This patent application is currently assigned to NATIONAL OILWELL VARCO, L.P.. The applicant listed for this patent is National Oilwell Varco, L.P.. Invention is credited to Lei Cheng, Robert Benjamin Donnally.
Application Number | 20150308420 14/574286 |
Document ID | / |
Family ID | 52302384 |
Filed Date | 2015-10-29 |
United States Patent
Application |
20150308420 |
Kind Code |
A1 |
Donnally; Robert Benjamin ;
et al. |
October 29, 2015 |
Multi-Cylinder Hydraulically-Driven Pump System
Abstract
A hydraulically-driven pumping unit for pumping a working fluid
includes a pair of double-acting hydraulic piston-cylinder (HPC)
assemblies, each having a central axis, a hydraulic cylinder, a
piston, and a rod coupled to the piston for axial movement relative
to the first hydraulic cylinder. The pumping unit also includes a
hydraulic fluid source and an exhaust path for hydraulic fluid. The
two hydraulic cylinders are coupled to the hydraulic fluid source
and the exhaust path such that the movements of the two pistons are
synchronized. The two HPC assemblies are configured for
phase-shifted operation such that when pumping unit is
reciprocating the two pistons and rods, the a first pair of the
pistons and rods always has a different combination of axial
position and direction of travel than does a other pair of the
pistons and rods. During phase-shifted operation, at least one of
the two rods is moving to extend further beyond the corresponding
hydraulic cylinder at all times.
Inventors: |
Donnally; Robert Benjamin;
(Houston, TX) ; Cheng; Lei; (Shanghai,
CN) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
National Oilwell Varco, L.P. |
Houston |
TX |
US |
|
|
Assignee: |
NATIONAL OILWELL VARCO,
L.P.
Houston
TX
|
Family ID: |
52302384 |
Appl. No.: |
14/574286 |
Filed: |
December 17, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61984829 |
Apr 27, 2014 |
|
|
|
Current U.S.
Class: |
417/404 |
Current CPC
Class: |
F04B 47/00 20130101;
F04B 5/02 20130101; F04B 47/02 20130101; F04B 47/06 20130101; F04B
49/22 20130101; F04B 9/113 20130101; F04B 9/105 20130101 |
International
Class: |
F04B 9/113 20060101
F04B009/113 |
Claims
1. A hydraulically-driven pumping unit for pumping a working fluid,
the pumping unit comprising: a first double-acting hydraulic
piston-cylinder (HPC) assembly comprising a first central axis, a
first hydraulic cylinder, a first piston, and a first rod coupled
to the first piston for axial movement relative to the first
hydraulic cylinder; a second double-acting hydraulic
piston-cylinder (HPC) assembly comprising a second central axis, a
second hydraulic cylinder, a second piston, and a second rod
coupled to the second piston for axial movement relative to the
second hydraulic cylinder; a hydraulic fluid source; and an exhaust
path for hydraulic fluid; wherein the first and second hydraulic
cylinders are coupled to the hydraulic fluid source and the exhaust
path such that movements of the first and second pistons are
synchronized; wherein the first and second HPC assemblies are
configured for phase-shifted operation such that when pumping unit
is reciprocating the two pistons and rods, the second piston and
rod always have a different combination of axial position and
direction of travel than do the first piston and rod, and such that
at least one of the two rods is moving to extend further beyond the
corresponding hydraulic cylinder at all times.
2. The hydraulically-driven pumping unit of claim 1: wherein the
first piston defines a first extension-chamber and a first
retraction-chamber in the first hydraulic cylinder; wherein the
second piston defines a second extension-chamber and a second
retraction-chamber in the second hydraulic cylinder; wherein the
first piston is configured to move axially within the first
hydraulic cylinder to a first far-extended position, to a first
retracted position, and to a first extended position disposed
between the first far-extended position and the first retracted
position; wherein the second piston is configured to move axially
within the second hydraulic cylinder to a second far-extended
position, to a second retracted position, and to a second extended
position disposed between the first far-extended position and the
first retracted position; wherein the pumping unit is configured
with at least these following operational states for the first HPC
assembly: a first state in which the first extension-chamber is in
fluid communication with the hydraulic fluid source; and a second
state in which the first extension-chamber is in fluid
communication with the exhaust path; wherein the pumping unit is
configured with at least these following operational states for the
second HPC assembly: a third state in which the second
extension-chamber is in fluid communication with the hydraulic
fluid source; a fourth state in which hydraulic fluid is exhausted
from the second extension-chamber is in fluid communication with
the exhaust path; wherein the pumping unit is configured to perform
a first transition, transitioning the second HPC assembly from the
fourth state to the third state when the first piston reaches the
first extended position while the first rod moves to extend further
beyond the first hydraulic cylinder, or when the second piston
reaches the second retracted position while the second rod
retracts; wherein the pumping unit is configured to perform a
second transition, transitioning the first HPC assembly from first
state to the second state when the first piston reaches the first
far-extended position while the first rod moves to extend further
beyond the first hydraulic cylinder; wherein the pumping unit is
configured to perform a third transition, transitioning the first
HPC assembly from the second state to first state when the second
piston reaches the second extended position while the second rod
moves to extend further beyond the second hydraulic cylinder, or
when the first piston reaches the first retracted position while
the first rod retracts; and wherein the pumping unit is configured
to perform a fourth transition, transitioning the second HPC
assembly from the third state to the fourth state when the second
piston reaches the second far-extended position while the second
rod moves to extend further beyond the second hydraulic
cylinder.
3. The hydraulically-driven pumping unit of claim 2 further
comprising a rod-end fluid circuit configured to provide fluid
communication between the first retraction-chamber in the first
hydraulic cylinder and a second retraction-chamber in the second
hydraulic cylinder; wherein the rod-end fluid circuit is
fluidically-isolated from the hydraulic fluid source in at least
one mode of operation.
4. The hydraulically-driven pumping unit of claim 2: wherein the
first HPC assembly is in the first state during the first
transition; wherein the second HPC assembly is in the third state
during the second transition; wherein the second HPC assembly is in
the third state during the third transition; and wherein the first
HPC assembly is in the first state during the fourth
transition.
5. The hydraulically-driven pumping unit of claim 2: wherein the
first state and the second state are mutually exclusive; and
wherein the third state and the fourth state are mutually
exclusive.
6. The hydraulically-driven pumping unit of claim 5 further
comprising: a first control valve fluidically coupled between the
first extension-chamber and the hydraulic fluid source and
configured to activate and deactivate the first state; and a second
control valve fluidically coupled between the second
extension-chamber and the hydraulic fluid source and configured to
activate and deactivate the third state.
7. The hydraulically-driven pumping unit of claim 6 further
comprising: a first exhaust valve fluidically coupled between the
first extension-chamber and the exhaust path and configured to
activate and deactivate the second state; and a second exhaust
valve fluidically coupled between the second extension-chamber and
the exhaust path and configured to activate and deactivate the
fourth state.
8. The hydraulically-driven pumping unit of claim 6 wherein the
first control valve is also fluidically coupled between the first
extension-chamber and the exhaust path and is further configured to
activate and deactivate the second state; and wherein the second
control valve is also fluidically coupled between the second
extension-chamber and the exhaust path and is further configured to
activate and deactivate the fourth state.
9. The hydraulically-driven pumping unit of claim 1 further
comprising: a first pump driven by the first rod of the first HPC
assembly and having a first discharge port; a second pump driven by
the second rod of the second HPC assembly and having a second
discharge port; and a discharge manifold coupled for fluid
communication with the first and second discharge ports. wherein
the first and second pump are configured to receive and to pump a
working fluid through the discharge manifold.
10. The hydraulically-driven pumping unit of claim 2: wherein the
pumping unit is configured with the following operational states: a
fifth state in which the first extension-chamber chamber of the
first HPC assembly is not in fluid communication with the hydraulic
fluid source and is not in fluid communication with the exhaust
path; and a sixth state in which the second extension-chamber of
the second HPC assembly is not in fluid communication with the
hydraulic fluid source and is not in fluid communication with the
exhaust path; wherein the first HPC assembly is in the fifth state
between the first state and the second state during the second
transition; and wherein the second HPC assembly is in the sixth
state between the third state and the fourth state during the
fourth transition.
11. A method for operating a fluid-driven pumping unit, the method
comprising: supplying a flow rate of a driving fluid during an
operation period; dividing the flow rate of the driving fluid
between members of a plurality of double-acting hydraulic
piston-cylinder (HPC) assemblies, each assembly having a movable
rod; operating at least two of the HPC assemblies using
synchronized, phase-shifted cycles, wherein the corresponding two
movable rods extend and retract periodically, such that the two
rods always have a different combination of axial position and
direction of travel and such that at least one of the two rods is
extending at all times; providing a plurality of pumps configured
to deliver a working fluid, each pump driven by a rod of the
plurality of rods; and pumping a working fluid using the plurality
of pumps.
12. The method of claim 11 further including: interconnecting the
plurality of HPC assemblies so the extension of a first actuator
causes the refraction of a second actuator and the extension of the
second actuator causes retraction of the first actuator.
13. The method of claim 12 further including: operating the HPC
assemblies such that the pistons perform smooth reversals, not
reaching the maximum extent of their strokes.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims benefit of U.S. provisional patent
application Ser. No. 61/984829 filed Apr. 27, 2014, and entitled
"Multi-Cylinder Hydraulically-Driven Pump System," which is hereby
incorporated herein by reference in its entirety for all
purposes.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
[0002] Not applicable.
BACKGROUND
[0003] This disclosure relates generally to reciprocating pumps.
More particularly, it relates to reciprocating drilling fluid pumps
used for drilling wells in the oilfield industry.
[0004] When forming an oil or gas well, a bottom hole assembly
(BHA), including a drill bit, is coupled to a length of drill pipe
to form a drill string. The drill string is then positioned
adjacent the earth or inserted downhole, where drilling commences.
During drilling, a drilling fluid, or "mud," is circulated down
through the drill string to lubricate and cool the drill bit as
well as to provide a vehicle for removal of drill cuttings from the
borehole. After exiting the bit, the mud returns to the surface
through the annulus formed between the drill string and the
surrounding borehole wall.
[0005] Instrumentation for taking various downhole measurements and
communication devices are commonly mounted within the drill string.
Many such instrumentation and communication devices operate by
sending and receiving pressure pulses through the annular column of
drilling mud maintained in the borehole.
[0006] Reciprocating mud pumps are commonly used to deliver the mud
through the drill string during drilling operations. Reciprocating
pumps include one or more piston-cylinder assemblies having a
piston slidably enclosed in a cylinder. The cylinder is
hydraulically coupled to a suction valve and a discharge valve to
control the flow of a working fluid (e.g., the mud) into and out
from the cylinder. Many conventional mud pumps are single-acting
triplex pumps having three piston-cylinder assemblies driven by a
"power end" having a large rotating crankshaft and a mechanical
gear drive.
[0007] While pressurizing and delivering the drilling mud,
conventional reciprocating pumps impart unwanted pressure
pulsations into the fluid. These pulsations may disturb the
downhole instrumentation and communication devices by degrading the
accuracy of measurements taken by the instrumentation and hampering
communications between downhole devices and control systems at the
surface. Over time, the pulsations may also cause fatigue damage to
the drill string pipe and other downhole components.
[0008] The conventional triplex mud pumps are heavy and require a
change in the cylinder diameter to make a significant change to the
discharge pressure. The change may be accomplished by adding or
removing an annular liner during maintenance. This type of
modification is required to make the best use of the pump power end
capacity while obtaining as close as practical to the optimum flow
and pressure required for maximum down-hole drilling performance.
For example, to achieve a higher pressure, a smaller diameter liner
is used; however, this alteration reduces the flow capacity of the
pump. When, instead, the situation requires a higher flow rate and
a higher pressure capacity, the installation of a larger pump may
be necessitated, and the size and weight of the power section
increases substantially.
[0009] Accordingly, there is a need for improved designs and
improved methods for reciprocating pumps to address the pulsation
and size challenges of current designs.
BRIEF SUMMARY OF THE DISCLOSURE
[0010] These and other needs in the art are addressed in one
embodiment by a hydraulically-driven pumping unit. In an
embodiment, the hydraulically-driven pumping unit for pumping a
working fluid includes a first double-acting hydraulic
piston-cylinder (HPC) assembly having a first central axis, a first
hydraulic cylinder, and a first piston, and a first rod coupled to
the piston for axial movement relative to the first hydraulic
cylinder. In addition, the pumping unit includes a second
double-acting hydraulic piston-cylinder (HPC) assembly having a
second central axis, a second hydraulic cylinder, and a second
piston, and a second rod coupled to the piston for axial movement
relative to the second hydraulic cylinder. Further, the pumping
unit includes a hydraulic fluid source. Still further, the pumping
unit includes an exhaust path for hydraulic fluid. In this
embodiment, the first and second hydraulic cylinders are coupled to
the hydraulic fluid source and the exhaust path such that the first
and second HPC assemblies are synchronized. Also in this
embodiment, the first and second HPC assemblies are configured for
phase-shifted operation such that when pumping unit is
reciprocating the two pistons and rods, the second first piston and
rod always have a different combination of axial position and
direction of travel than do the first piston and rod, and such that
at least one of the two rods is moving to extend further beyond the
corresponding hydraulic cylinder at all times.
[0011] Also disclosed is method for operating a fluid-driven
pumping unit. In an embodiment, the method includes supplying a
flow rate of a driving fluid during an operation period; dividing
the flow rate of the driving fluid between members of a plurality
of double-acting hydraulic piston-cylinder (HPC) assemblies, each
assembly having a movable rod; and operating at least two of the
HPC assemblies using synchronized, phase-shifted cycles, wherein
the corresponding two movable rods extend and retract periodically,
such that the two rods always have a different combination of axial
position and direction of travel and such that at least one of the
two rods is extending at all times. In this embodiment, the method
also includes providing a plurality of pumps configured to deliver
a working fluid, each pump driven by a rod of the plurality of
rods; and pumping a working fluid using the plurality of pumps.
[0012] Thus, embodiments described herein include a combination of
features and characteristics intended to address various
shortcomings associated with certain prior devices, systems, and
methods. The various features and characteristics described above,
as well as others, will be readily apparent to those of ordinary
skill in the art upon reading the following detailed description,
and by referring to the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] For a detailed description of the disclosed embodiments of
the disclosure, reference will now be made to the accompanying
drawings in which:
[0014] FIG. 1 is side view of a hydraulically-driven pumping unit
having multiple pumping piston-cylinder assemblies coupled to
multiple hydraulic piston-cylinder assemblies in accordance with
the principles disclosed herein;
[0015] FIG. 2 is an end view of the hydraulically-driven pumping
unit of FIG. 1 in accordance with the principles disclosed
herein;
[0016] FIG. 3 is a top view in partial cross-section showing the
hydraulically-driven pumping unit of FIG. 1 along section A-A of
FIG. 1 in accordance with the principles disclosed herein;
[0017] FIG. 4 is a schematic diagram of the hydraulically-driven
pumping unit of FIG. 1 in accordance with the principles disclosed
herein;
[0018] FIG. 5 is a tabulated diagram disclosing various
transitional events related to the operation of the hydraulic
piston-cylinder assemblies of the pumping unit of FIG. 1 in
accordance with the principles disclosed herein; and
[0019] FIG. 6 is a diagram illustrating a method to operate a
fluid-driven pumping unit having multiple pumping piston-cylinder
assemblies in accordance with the principles disclosed herein.
NOTATION AND NOMENCLATURE
[0020] The following description is exemplary of embodiments of the
disclosure. These embodiments are not to be interpreted or
otherwise used as limiting the scope of the disclosure, including
the claims. One skilled in the art will understand that the
following description has broad application, and the discussion of
any embodiment is meant only to be exemplary of that embodiment,
and is not intended to suggest in any way that the scope of the
disclosure, including the claims, is limited to that
embodiment.
[0021] The drawing figures are not necessarily to scale. Certain
features and components disclosed herein may be shown exaggerated
in scale or in somewhat schematic form, and some details of
conventional elements may not be shown in the interest of clarity
and conciseness. In some of the figures, in order to improve
clarity and conciseness of the figure, one or more components or
aspects of a component may be omitted or may not have reference
numerals identifying the features or components that are identified
elsewhere. In addition, like or identical reference numerals may be
used to identify common or similar elements.
[0022] The terms "including" and "comprising" are used herein,
including in the claims, in an open-ended fashion, and thus should
be interpreted to mean "including, but not limited to . . . ."
Also, the term "couple" or "couples" is intended to mean either an
indirect or direct connection. Thus, if a first component couples
or is coupled to a second component, the connection between the
components may be through a direct engagement of the two
components, or through an indirect connection that is accomplished
via other intermediate components, devices and/or connections. In
addition, if the connection transfers electrical power or signals,
whether analog or digital, the coupling may comprise wires or a
mode of wireless electromagnetic transmission, for example, radio
frequency, microwave, optical, or another mode. So too, the
coupling may comprise a magnetic coupling or any other mode of
transfer known in the art, or the coupling may comprise a
combination of any of these modes. The recitation "based on" means
"based at least in part on." Therefore, if X is based on Y, X may
be based on Y and any number of other factors. The terms
"fluidically coupled" and "coupled for fluid communication" are
used interchangeably.
[0023] In addition, as used herein, including in the claims, the
terms "axial" and "axially" generally mean along or parallel to a
given axis (e.g., central axis of a body or a port), while the
terms "radial" and "radially" generally mean perpendicular to the
axis. For instance, an axial distance refers to a distance measured
along or parallel to the axis, and a radial distance means a
distance measured perpendicular to the axis.
[0024] Furthermore, as used herein, including in the claims, the
following terms are defined:
[0025] The term "open-state-exclusivity" means that the operations
of a supply valve and the operation of an exhaust valve, each
fluidically coupled to a same fluid transfer device (e.g., a
chamber of a hydraulic piston-cylinder assembly), are coordinated
so that the two valves may be simultaneously closed to restrict
fluid communication with the transfer device but will not be
simultaneously open . That is to say, at most, only one of the
supply valve and the exhaust valve will be open at any given
time
[0026] The term "open-state-assurance" means that the operations of
a plurality of supply valves, each coupled to a same fluid source,
are coordinated so that at least one of the supply valves will be
open at given time while the system containing the valves is
operating. Not all the supply valves will be simultaneously closed,
and during operation at least a portion of the flow rate from the
fluid source is always supplied to at least one of the fluid
recipients.
DETAILED DESCRIPTION OF THE DISCLOSED EMBODIMENTS
[0027] This specification discloses a reciprocating,
hydraulically-driven fluid pumping unit having two or more
hydraulic piston-cylinder assemblies as the "power end" for two or
more pumping piston-cylinder assemblies. The power to weight ratio
of a hydraulic piston-cylinder assembly is beneficially higher than
the power to weight ratio of a power end for various pumps having a
rotating crankshaft driven by a mechanical gear drive.
Consequently, the flow and pressure characteristics of the
disclosed pump can be altered with engineering or economic
advantages. As an example, the stroke length of the disclosed pump
can easily be built longer for reduced suction and discharge valve
cycling. Building a traditional mud pump with increased stroke
length reaches a practical limit much more quickly because the
weight and size of the crankshaft drive system grows exponentially
with stroke length increase. As another example, larger diameter
pistons and liners may be used for the working fluid than used with
conventional pumps. This can allow slower piston travel speeds for
reduced liner and seal wear.
[0028] In at least one embodiment disclosed herein, two hydraulic
piston-cylinder assemblies are configured to drive two pumping
piston-cylinder assemblies. In at least one mode of operation, the
two hydraulic piston-cylinder assemblies are coordinated, and the
total flow of hydraulic fluid driving the two assemblies is
constant. Therefore, in such embodiments, the speeds and
accelerations of the two pistons within the two assemblies "mirror"
each other. When one piston is accelerating the other piston is
decelerating. When one piston is traveling forward full speed, the
other piston is full speed in the reverse direction. This mode of
operation is accomplished by having the total flow of hydraulic
fluid directed through one valve, or multiple valves coordinated as
one, to feed both hydraulic piston-cylinder assemblies. The
valve(s) directs the full flow to either the first assembly or the
second assembly or to a combination of the two assemblies. During
operation, the flow of hydraulic fluid is always directed onto the
at least one of the hydraulic piston-cylinder assemblies.
[0029] Also disclosed herein is a hydraulic fluid control system
and a technique for sequencing the operation of the two or more
hydraulic piston-cylinder assemblies coupled to the two or more
pumping piston-cylinder assemblies. In various embodiments, the
result is a smoother discharge flow for the working fluid, e.g.,
drilling mud as compared to the discharge flow from a conventional
pump. A smoother flow of a fluid is generally characterized by a
steadier flow rate, by fewer or reduced pressure pulsations, or a
combination of these results.
[0030] FIG. 1 and FIG. 2 show a side view and an end view,
respectively, of a hydraulically-driven pumping unit 100 having
multiple hydraulic piston-cylinder assemblies configured to drive
multiple pumping piston-cylinder assemblies. In particular, for the
embodiment shown, pumping unit 100 includes two double-acting
hydraulic piston-cylinder assemblies 120, which will be
distinguished as assembly 120A and assembly 120B in the figures and
in the text when advantageous, and two reciprocating pumping
piston-cylinder assemblies 140, which are each driven by an
assembly 120.
[0031] Each assembly 120 is aligned with and coupled to an assembly
140 by means of a cylinder union 138. The assemblies 120, 140 are
further coupled to a mounting plate 105. Hydraulically-driven
pumping unit 100 also includes a fluid accumulator 260,
specifically a hydraulic accumulator 260, in fluid communication
with the two assemblies 120. Pumping unit 100 further includes a
working fluid reservoir 160 to contain water, drilling mud, or
another suitable fluid to be pressurized and discharged by pumping
piston-cylinder assemblies 140. Pumping unit 100 further includes a
variable displacement hydraulic pump 170 mechanically coupled to an
electric motor 172 and coupled for fluid communication between a
hydraulic reservoir 250 and the two piston-cylinder assemblies 120.
Driven by electric motor 172, pump 170 supplies hydraulic fluid
from reservoir 250 to piston-cylinder assemblies 120. In this
embodiment, pump 170 is an axial piston swash plate-type pump, with
variable volume control. In this embodiment, electric motor 172 is
a single speed A/C motor. Other embodiments may use other types of
hydraulic pumps and other types of motors. For example, other
embodiments of pump 170 may be coupled to a variable speed A/C
motor coupled to a variable frequency drive (VFD) or may be coupled
to a variable speed D/C motor having an appropriate electrical
drive to control rotational speed and maintain a selected pumping
flow rate or delivery pressure with the help of a flow meter or
pressure transducer.
[0032] Pump 170 is an example of a source for pressurized hydraulic
fluid for pumping unit 100 configured to supply a flow rate at an
operating pressure. In other embodiments, another suitable source
for pressurized hydraulic fluid may be used. In general, the flow
rate from the source for pressurized hydraulic fluid may be set or
established by making adjustments to the source for pressurized
hydraulic fluid or by selecting another source for pressurized
hydraulic fluid, one configured to provide a different discharge
rate for the anticipated operating conditions. A hydraulic fluid
control system 200 is coupled between hydraulic pump 170 and
piston-cylinder assemblies 120 to govern the flow of hydraulic
fluid therebetween, synchronizing the reciprocating motions of the
two assemblies 120A, 120B in phase-shifted cycles, which will be
explained below.
[0033] FIG. 3 presents a sectional view of hydraulically-driven
pumping unit 100 along section A-A of FIG. 1 to illustrate various
features of the two double-acting hydraulic piston-cylinder
assemblies 120, the two pumping piston-cylinder assemblies 140, and
the cylinder union 138. The various components or features of the
two hydraulic piston-cylinder assemblies 120A, 120B will likewise
be distinguished by the suffix letters "A" and "B" in the figures
and the text when advantageous. So too, various references to these
same components or features will exclude any suffix letter "A," "B"
when potentially associated with either assembly 120A, 120B. Thus,
for example, the reference numeral 125 may refer to either or to
both reference numerals 125A, 125B, as used elsewhere in the text
and in the figures.
[0034] Each double-acting hydraulic piston-cylinder assembly 120
includes a hydraulic cylinder 125 having a central axis 128, a
first or cap-end 126, and a second or rod-end 127 positioned
opposite cap-end 126 and coupled to cylinder union 138. Each
assembly 120 also includes a piston 130 slidably disposed within
cylinder 125 and a rod 134 coupled to piston 130. The rod 134
extends beyond rod-end 127, through cylinder union 138, and into a
coupled pumping piston-cylinder assembly 140. Piston 130 will also
be called power piston 130.
[0035] Referring to FIG. 3 and FIG. 4, within the first hydraulic
piston-cylinder assembly 120A, the movable power piston 130A
separates hydraulic cylinder 125A, or simply "cylinder A," into two
chambers having variable volumes. More specifically, an
extension-chamber 135A extends between cap-end 126A and piston
130A, and a refraction-chamber 136A extends between piston 130A and
rod-end 127A. A cap-end port P1 is located adjacent cap-end 126A
for fluid communication with chamber 135A. A rod-end port P2 is
located adjacent rod-end 127A for fluid communication with chamber
136A. In the example of FIG. 3, two cap-end ports P1 and two
rod-end ports P2 are shown. Likewise, in the second hydraulic
piston-cylinder assembly 120B, a power piston 130B separates a
hydraulic cylinder 125B, or simply "cylinder B," into two chambers
having variable volumes, namely extension-chamber 135B and
retraction-chamber 136B, with fluid communication provided by a
cap-end port Q1 and a rod-end port Q2, respectively.
[0036] Each pumping piston-cylinder assembly 140 includes cylinder
145 having a central axis 148, a cap-end 146, a rod-end 147
positioned opposite cap-end 146 and coupled to cylinder union 138.
Each assembly 140 also includes a piston 150 slidably disposed
within cylinder 145 and coupled to the rod 134 that extends from
the aligned and corresponding hydraulic piston-cylinder assembly
120. Piston 150 will also be called a pumping piston 150. The
movable pumping piston 150 defines a variable-volume pumping
chamber 155 proximal the cap-end 146 of cylinder 145. Proximal the
cap-end 146 of cylinder 145, an inlet port 156 is coupled to a
one-way check valve 157 to perform as a suction valve, and a
discharge port 158 is coupled to a one-way check valve 159 to
perform as a discharge valve. Ports 156, 158 provide fluid
communication for pumping chamber 155 in cylinder 145. The inlet
port 156 of each pumping piston-cylinder assembly 140 is coupled to
the working fluid reservoir 160. The discharge port 158 of each
pumping piston-cylinder assembly 140 is coupled to a discharge
manifold 165 having an outlet port166 to supply working fluid to a
process or a destination external to pumping unit 100. In the
example embodiment, pumping system 100 is a component of a drilling
mud recirculation system (not shown), and the manifold 165 is
capable of supplying drilling mud to a well drilling operation. As
configured, each pumping piston-cylinder assembly 140 may also be
called single-acting pumping unit. Acting together, the two pumping
piston-cylinder assemblies 140 may be called a single-acting duplex
pump.
[0037] As best shown in FIG. 3, cylinder union 138 couples to the
first hydraulic piston-cylinder assembly 120A at its rod-end 127A
and couples to the first of the pumping piston-cylinder assemblies
140 at rod-end 147 with central axes 128, 148 co-linearly aligned.
Cylinder union 138 also couples to the second hydraulic
piston-cylinder assembly 120B at its rod-end 127B and couples to
the second pumping piston-cylinder assembly 140 at its rod-end 147
with the corresponding central axes 128, 148 co-linearly aligned.
Thus, cylinder union 138 also laterally couples the first pair of
aligned assemblies 120A, 140 with the second pair of aligned
assemblies 120B, 140 for improved integrity and rigidity of pumping
unit 100.
[0038] Fluid or hydraulic accumulator 260 includes a pressurized,
contained gas held in an expandable and contractible chamber and a
transfer fluid in an adjacent, second chamber, which is also
expandable and contractible. At least in this embodiment, the total
volume of the accumulator 260 is fixed, and the transfer fluid is
hydraulic fluid. The second chamber of accumulator 260 couples to
ports P2, Q2 for simultaneous fluid communication with chambers
136A, 136B. A rod-end fluid circuit 265 is defined by at least
accumulator 260, chambers 136A, 136B, ports P2, Q2, and tubing
coupling these components. At least during some portions of routine
operation, the rod-end fluid circuit 265 is separate and does not
communicate with the fluid circuit that includes pump 170, and the
rod-end fluid circuit 265 is separate and does not communicate with
the fluid circuit that includes gear pump 220. Thus, rod-end fluid
circuit 265 is fluidically-isolated from a hydraulic fluid source
in at least one mode of operation. However, in some embodiments,
make-up fluid is introduced to the rod-end fluid circuit 265. In
some embodiments, the rod-end fluid circuit 265 is
fluidically-isolated from pump 170.
[0039] At least in this embodiment, the contained gas within
hydraulic accumulator 260 has a pre-charged pressure that is less
than the operating pressure of pump 170, greater than the pressure
required to start and to continue moving the first power piston
130A when the port P1 is in fluid communication with a hydraulic
reservoir 250, and greater than the pressure required to start and
to continue moving the second power piston 130B when the port Q1 is
in fluid communication with the hydraulic reservoir 250. In various
instances, the pre-charged pressure of the contained gas within
hydraulic accumulator 260 is set to a value that allows power
pistons 130A, 130B to travel at speeds within a selected range of
speeds and greater than a minimum speed associated with the pistons
130A, 130B.
[0040] In the schematic of FIG. 4, the hydraulic fluid control
system 200 is designated by a polygon drawn with dash-dot lines.
When advantageous in the figures and in the text, components of
control system 200 will be distinguished by a suffix letter "A" or
"B," depending on the piston-cylinder assembly 120A, 120B served by
the component. So too, various references to these same features
may exclude any suffix letters "A" or "B" when potentially
associated with either assembly 120A, 120B.
[0041] Fluid control system 200 includes a supply valve 205 and an
exhaust valve 210 for each hydraulic cylinder 125. In the example
embodiment, valves 205, 210 are "normally closed," spring-return
poppet valves having a hydraulically-driven control mechanism. The
selection of the open position or the closed position of each valve
205, 210 is governed by a solenoid-operated two-position three-way
valve 215, which are supplied with pressurized hydraulic fluid from
reservoir 250 by a gear pump 220. Pilot lines for hydraulic fluid,
indicated by dashed lines in FIG. 4, extend from gear pump 220 to
the valves 215 and from each valve 215 to the corresponding valve
205, 210. The embodiment of FIG. 4 has two supply valves 205, two
exhaust valves 210, and four of the solenoid-operated valves 215.
Any of the valves 205, 210, 215 may be called a "control valve."
Each valve 215 has an energizing position 215p configured to
transfer pressure from gear pump 220 to the control mechanism of
the coupled valve 205, 210 in order to open the respective valve
205, 210. Each valve 215 also has an exhaust position 215x
configured to relieve pressure from the control mechanism of the
coupled valve 205, 210, allowing the respective internal spring to
close the valve 205, 210. When a supply valve 205 is open, it is
configured to pass pressurized hydraulic fluid from pump 170 to a
coupled chamber 135A, 135B in a corresponding cylinder 125A, 125B.
When an exhaust valve 210 is open, it is configured to pass
pressurized hydraulic fluid from a coupled chamber 135A, 135B to an
exhaust path 218 that includes reservoir 250; passing the fluid to
path 218 reduces the pressure inside the corresponding
extension-chamber 135A, 135B.
[0042] Referring to FIG. 3 and FIG. 4, at least one position sensor
230 is coupled to each hydraulic piston-cylinder assembly 120.
Therefore, this exemplary embodiment includes two sensors 230, one
for piston 130A and one for piston 130B. In this embodiment, each
position sensor 230 is a linear displacement transducer (LDT)
configured to give position data or signals describing each power
piston 130 as it extends or retracts axially within cylinder 125.
The velocity and acceleration of the respective piston 130 can be
determined based on the response of the LDT position sensor 230.
For example, in some embodiments, the LDT's (i.e., the position
sensors 230) integrate position data to provide the velocity or
acceleration of the piston 130 as well as position. In various
other embodiments, a computational processor external to the LDT's
integrates position data to provide the velocity or acceleration of
the piston 130.
[0043] Referring now to cylinder 125A in FIG. 4 as an example, at
least three specific axial locations or positions 231A, 232A, 233A
along cylinder 125A are defined in relation to the travel of piston
130A between cylinder ends 126A, 127A and in relation to the amount
of extension of rod 134A beyond the cylinder's rod-end 127A. The
positions 231A, 232A, 233A are associated or indicated by the
position sensor 230 of cylinder 125A. For convenience, the
positions 231A, 232A, 233A will be discussed in terms of the piston
130A, but these positions could equally be described in terms of an
exterior portion of the rod 134A. An extended position 231A is
generally proximal the rod-end 127A, and a far-extended position
232A is closer to rod-end 127A, lying between extended position
231A and rod-end 127A. When piston 130A is at far-extended position
232A, chamber 136A still has more than its minimum volume, meaning
that piston 130A could still travel closer to rod-end 127A after
reaching far-extended position 232A. Thus, when piston 130A reaches
position 232A in cylinder 125A, piston 130A and the coupled rod
134A are near but not at full extension. The location of position
232A is selected to allow time for supply valve 205A to close and
exhaust valve 210A to open before piston 130 reaches its full
extension, i.e., its maximum stroke length. This arrangement causes
piston 130 to change direction without stopping abruptly adjacent
rod-end 127A. In at least some embodiments, pumping system 100 is
configured so that piston 130A and the coupled rod 134A change
direction without reaching their full extension during an
operational cycle to cause the change of direction to proceed more
smoothly. This event may be called a "smooth reversal." In a smooth
reversal the piston does not reaching the maximum extent of its
stroke, but rather changes direction before reaching the maximum
extent of its stroke.
[0044] The other position of piston 130A to be associated or
indicated by position sensor 230 is proximal the first or cap-end
126A of cylinder 125A and will be called the retracted position
233A. When piston 130A reaches position 233A in cylinder 125A,
piston 130A and the coupled rod 134A are near but not at full
refraction," meaning sufficient room still exists in the shrinking
chamber 135A to allow time for exhaust valve 210A to close and
supply valve 205A to open before piston 130A must change
directions. In at least some embodiments, pumping system 100 is
configured so that piston 130A and the coupled rod 134A change
direction without reaching their full retraction during an
operational cycle to cause the change of direction to proceed more
smoothly. This event is another example of a smooth reversal. Thus,
a smooth reversal for piston 130A may occur near either end 126A,
127A of cylinder 125A. The ability of piston 130A to perform a
smooth reversal when changing direction is based on the selected
locations established for one or more of the positions 231A, 232A,
233A, 231B, 232B, 233B, the response time of one or more of the
several valves that supply hydraulic fluid, and the momentum of the
piston. Piston 130B in hydraulic piston-cylinder assembly 120B may
also perform smooth reversals for some embodiments. Positions 231A,
232A, 233A correspond to the variable size of chambers 135A, 136A
during various stages of operation of piston-cylinder assembly
120A.
[0045] Continuing to reference FIG. 4, the locations designated as
positions 231A, 232A, 233A are axially adjustable along a hydraulic
cylinder 125A to test or tune the performance of
hydraulically-driven pumping unit 100. For example, in some
embodiments that implement position sensor 230 as an LDT, the
positions 231A, 232A, 233A are adjustable within the circuitry or
logic of control circuit 225. In some instances, these adjustments
are made in response to input from a human user. As a further
example, control circuit 225 may dynamically adjust the location of
any of the positions 231A, 232A, 233A during operation of pumping
unit 100 in response to system performance based on status data
relating to any of the position sensors 230, the solenoid operated
valves 215, the supply valves 205, the exhaust valves 210, or
another component of pumping unit 100, for example. In some
embodiments, additional instrumentation may be added to allow
control circuit 225 to monitor the status data of the particular
component or components of pumping unit 100. Adjusting the location
of any of the positions 231A, 232A, 233A influences the timing of
when valves 205A, 210A open and close and may influence other
events related to the components of pumping unit 100. The same
method is applicable to positions 231B, 232B, 233B along hydraulic
cylinder 125B.
[0046] It is contemplated that the distance between the extended
position 231A and the rod-end 127A (i.e., the position of full
extension at rod-end 127) will be approximately 20% of the stroke
length of the hydraulic piston-cylinder assembly 120A. In other
embodiments, the distance between the extended position 231A and
the rod-end 127A may range between 15% and 25% of the stroke
length, while a different value or values may be used in still
other embodiments.
[0047] It is contemplated that the distance between the retracted
position 233A and the cap-end 126A (i.e., the position of full
retraction at cap-end 126A) will be approximately 10% of the stroke
length of the hydraulic piston-cylinder assembly 120A. In other
embodiments, the distance between the retracted position 233A and
the cap-end 126A may range between 5% and 15% of the stroke length,
while a different value or values may be used in still other
embodiments. In at least some embodiments, the distance between the
far-extended position 232A and rod-end 127A is set to a distance
corresponding in the same range as described for the distance
between retracted position 233A and cap-end 126A.
[0048] Still referring to FIG. 4, the other position sensor 230
coupled to piston-cylinder assembly 120B also has at least three
specific locations or positions along the respective cylinder 125B
associated with the travel of piston 130B between cylinder ends
126B, 127B. An extended position 231B, a far-extended position
232B, and a retracted position 233B for position sensor 230 are
defined and established similar to the positions 231A, 232A, 233A
along the corresponding cylinder 125A. Positions 231B, 232B, 233B
correspond to the variable size of chambers 135B, 136B during
various stages of operation of piston-cylinder assembly 120B.
[0049] Fluid control system 200 also includes a control circuit 225
electrically coupled to the four solenoid-operated valves 215 and
to the two position sensors 230 on the two hydraulic
piston-cylinder assemblies 120. Control circuit 225 electrically
drives the positions of the various solenoid-operated valves 215
between the energizing position 215p and the exhaust position 215x
based on signals from position sensors 230, as will be explained.
Thereby, control circuit 225 governs the open or closed state of
each supply valve 205 and each exhaust valve 210.
[0050] Control circuit 225 is configured so that during normal
operation, the supply valve 205 and the exhaust valve 210 coupled
to any one hydraulic cylinder 125 are not both open at the same
time. For example, supply valve 205A and exhaust valve 210A, which
are both coupled to chamber 135A on hydraulic cylinder 125A, are
controlled by control circuit 225 so that valves 205A, 210A are not
both open at the same time. For instance, during operation, if
supply valve 205A is open at a point in time when the corresponding
position sensor 230 indicates that exhaust valve 210A should be
open, control circuit 225 first closes valve 205A before opening
valve 210A. Similarly, in other instances, control circuit 225
first closes valve 210A before opening valve 205A. Therefore,
control circuit 225 implements open-state-exclusivity to coordinate
the operation of supply valve 205A and exhaust valve 210A for
extension-chamber 135A to allow valves 205A, 210A to communicate
alternately but not simultaneously with port P1 and chamber 135A.
The open-state-exclusivity of the valve pair 205A, 210A prevents
hydraulic fluid supplied by pump 170 from by-passing cylinder 125A
and going directly to reservoir 250. Control circuit 225 governs
the valve pair 205B, 210B for extension-chamber 135B in a similar
manner to operate hydraulic cylinder 125B, applying
open-state-exclusivity to the valve pair 205B, 210B. In this
manner, open-state-exclusivity is applied to each hydraulic
piston-cylinder assembly 120 to control the flow of hydraulic fluid
entering and exiting the corresponding cylinder 125.
[0051] Control circuit 225 is further configured so that during
normal operation the supply valve 205 for at least one cylinder 125
is open at all times. Thus, in the example embodiment, valves 205A,
205B are not both closed at the same time. As implemented, in
various instances of the operation cycle, valve 205B opens before
valve 205A closes, and in various other instances of the operation
cycle, valve 205A opens before valve 205B closes. Therefore,
control circuit 225 implements open-state-assurance to cause at
least a portion of the flow rate of hydraulic fluid from pump 170
to be always supplied to one or both of the cylinders 125A, 125B of
the hydraulic piston-cylinder assemblies 120A, 120B,
respectively.
[0052] In an exemplary embodiment, during operation of the
hydraulic piston-cylinder assemblies 120A, 120B, the application of
open-state-exclusivity and open-state-assurance together causes all
or substantially all the flow rate of hydraulic fluid from pump 170
to be always supplied to one or both cylinders 125A, 125B without a
portion by-passing a cylinder 125A, 125B and moving directly to
reservoir 250. Thus, the flow rate established for pump 170 is
fully utilized and none is wasted. During non-routine situations
that result in an unacceptably high pressure in the supply line
extending from pump 170, a pressure relief safety valve (PRV) 222
releases some hydraulic fluid.
[0053] In some embodiments, control circuit 225 comprises and
utilizes electrical relays, wiring arrangements, or pilot line
arrangements for valves 215 to govern the operation of pumping unit
100 in accordance with the principles disclosed herein. In various
other embodiments, control circuit 225 includes an electronic
control unit such as a programmable logic controller (PLC), a
computer, or another suitable computational processor to govern the
operation of pumping unit 100. In various embodiments, control
circuit 225 includes or is coupled to a non-transitory
computer-readable storage device or a graphical user interface for
input and output of data and commands. In various embodiments,
control circuit 225 and the non-transitory computer-readable
storage device transfer machine readable code or instructions to
establish or to adjust the operation of pumping unit 100. Various
components of control circuit 225 may be remotely located away from
the other components of pumping system 100.
[0054] Operation of an Embodiment of a Multi-Cylinder
Hydraulically-Driven Pumping Unit
[0055] Various aspects of the operation of the hydraulically-driven
pumping unit 100 will be explained with reference to FIG. 4. This
discussion gives an example of the operation that may occur in
various circumstances. During operation, the reciprocal motion of
power piston 130A in hydraulic piston-cylinder assembly 120A drives
a reciprocal motion of pumping piston 150 in the coupled pumping
piston-cylinder assembly 140 shown in the top right corner of FIG.
4.
[0056] Similarly, the reciprocal motion within hydraulic
piston-cylinder assembly 120B drives a reciprocal motion within the
coupled pumping piston-cylinder assembly 140 shown in the lower
right corner of FIG. 4. The operation of assemblies 120A, 120B are
coordinated to provide smoother flow of working fluid, e.g.
drilling mud, from the pumping piston-cylinder assemblies 140 and
manifold 165. Pump 170 is configured to supply hydraulic fluid at a
selected or established flow rate and an operating pressure to the
group of piston-cylinder assemblies 120, directly powering or
driving the pistons 130 and rods 134 within the various assemblies
120 as they periodically extend during the synchronized,
phase-shifted cycles governed by fluid control system 200, which
will be described below. In some operational conditions, the flow
rate from pump 170 is substantially constant. The rod-end fluid
circuit 265, including accumulator 260, powers or drives the return
stroke, i.e., the retraction, of the pistons 130 and rods 134.
[0057] The hydraulic piston-cylinder assembly 120A and the
hydraulic piston-cylinder assembly 120B shown in the embodiment of
FIG. 4 are synchronized and configured for phase-shifted operation
such that when pumping unit 100 is reciprocating the two pistons
130A, 130B and rods 134A, 134AB, the second first piston 130B and
rod 134B always have a different combination of axial position and
direction of travel than do the first piston 130A and rod 134A, and
such that at least one of the two rods 134A, 134B is moving to
extend further beyond the corresponding hydraulic cylinder 125A,
125B at all times.
[0058] In order to cause the pistons and rods of the hydraulic
piston-cylinder assemblies 120A, 120B to reciprocate in
synchronized, phase-shifted cycles, hydraulic fluid control system
200 applies a plurality of operational states related to assembly
120A and assembly 120B. Some of the operational states overlap with
other operational states during the operation of pumping unit
100.
[0059] In an operational State lA (one-A), control system 200
places the extension-chamber 135A of assembly 120A in fluid
communication with pump 170, allowing rod 130A to extend. The State
1A is achieved by placing supply valve 205A in its open position
while exhaust valve 210A is in its closed position, insuring
open-state-exclusivity for supply valve 205A in relationship to
exhaust valve 210A. Thus, the supply valve 205A is a control valve
that is fluidically coupled between the extension-chamber 135A and
the hydraulic fluid source, i.e. pump 170, and is configured to
activate and deactivate the State 1A.
[0060] In an operational State 2A, control system 200 places the
extension-chamber 135A in fluid communication with exhaust path
218, including hydraulic reservoir 250, allowing rod 130A to
retract. The State 2A is achieved by placing supply valve 205A in
its closed position and then placing exhaust valve 210A in its open
position. Thus, exhaust valve 210A, being fluidically coupled
between the extension-chamber 136A and the exhaust path 218, is
configured to activate and deactivate State 2A.
[0061] In an operational State 1B, control system 200 places the
extension-chamber 135B of assembly 120B in fluid communication with
pump 170, allowing rod 130B to extend. The State 1B is achieved by
placing supply valve 205B in its open position while exhaust valve
210B is in its closed position, insuring open-state-exclusivity for
supply valve 205B in relationship to exhaust valve 210B. Thus,
supply valve 205B is a control valve that is fluidically coupled
between the extension-chamber 135B and the hydraulic fluid source
and is configured to activate and deactivate the State 1B. The
State 1A and State 1B may be individually activated or deactivated.
In some instances, the State 1A and State 1B may overlap, meaning
the State 1B may be active during at least a portion of the time
that the State 1A is active, in keeping with the concept of
open-state-assurance. Thus for a period of time, hydraulic fluid
may be supplied simultaneously to both supply valves 205A, 205B to
exert an extension force on both rods 130A, 130B
simultaneously.
[0062] In an operational State 2B, control system 200 places the
extension-chamber 135B in fluid communication with exhaust path
218, including hydraulic reservoir 250, allowing rod 130B to
retract. The State 2B is achieved by placing supply valve 205B in
its closed position and then placing exhaust valve 210B in its open
position. Thus, exhaust valve 210B, being fluidically coupled
between the extension-chamber 136B and the exhaust path 218, is
configured to activate and deactivate State 2B.
[0063] Additional operational states can be defined to help
describe the operation of the pumping unit 100. For example, in a
State 3A the first extension-chamber chamber of the first HPC
assembly is not in fluid communication with the hydraulic fluid
source and is not in fluid communication with the exhaust path. In
a State 3B the second extension-chamber of the second HPC assembly
is not in fluid communication with the hydraulic fluid source and
is not in fluid communication with the exhaust path.
[0064] Referring to FIG. 5, the coordinated operation of hydraulic
piston-cylinder assemblies 120A, 120B may also be described in
terms of transitional events governed by fluid control system 200.
FIG. 5 tabulates the locations of power pistons 130A, 130B during
four transitional events (Transitions 1, 2, 3, 4) in which the open
and closed positions of the fours valves 205A, 205B, 210A, 210B are
periodically selected in accordance with open-state-exclusivity and
open-state-assurance as previously defined. The four states of
operation previously described will be evidenced by the positions
of the four valves 205A, 205B, 210A, 210B. Prior to a first
transitional event, or Transition 1 (one), supply valve 205A is
open, exhaust valve 210A is closed, supply valve 205B is closed,
and exhaust valve 210B is open. Therefore, prior to Transition 1,
piston 130A and rod 134A in cylinder 125A extend while piston 130B
and rod 134B in cylinder 125B retract. The extension of piston 130A
and rod 134A is driven by hydraulic fluid from pump 170. The
retraction of piston 130B and rod 134B is driven by piston 130A
pushing fluid from chamber 136A toward accumulator 260 and chamber
136B.
[0065] At Transition 1, rod 134A has reached the extended position
231A, which is indicated by a signal from the corresponding
position sensor 230. Exhaust valve 210B is initially open (State 2B
is active), and rod 134B has reached the refracted position 233B,
which is indicated by a signal from the corresponding position
sensor 230, and rod 134B is near but not at full retraction, being
proximal cap-end 126B of cylinder 125B. The signal corresponding to
position 231A generated by position sensor 230 of cylinder 125A
directs control system 200 to close exhaust valve 210B (deactivate
State 2B) and then to open supply valve 205B (activate State 1B)
for cylinder 125B, in accordance with open-state-exclusivity for
these two valves. The signal corresponding to position 233B
confirms that rod 134B has retracted sufficiently. Supply valve
205A remains open (State lA is active), and exhaust valve 210A
remains closed (State 2A is inactive).
[0066] As a result of Transition 1, rod 134A continues to extend,
and rod 134B reverses direction and begins to extend. Because both
supply valves 205A, 205B are open (State lA and State 1B are
simultaneously active), and share the constant flow from fluid from
pump 170, in some embodiments, the average extension speed of the
two rods 134A, 134B after Transition 1 may be approximately one
half the previous extension speed of rod 134A while rod 134B was
retracting. In other embodiments, depending on the combined
characteristics and the loading of the hydraulic piston-cylinder
assemblies 120A, 120B, 140, the speed of the two rods 134A, 134B
after Transition 1 may vary in a different manner. Because both
pairs of pistons 130 and rods 134 are extending, the volumes of
chambers 136A, 136B are simultaneously reducing in volume.
Therefore, accumulator 260 receives and accumulates fluid from both
chambers 136A, 136B.
[0067] Assuming, for convenience of discussion, an embodiment in
which the pressure drop between pump 170 and chamber 135A equals
the pressure drop between pump 170 and chamber 135B, both chambers
135A, 135B and both pistons 130A, 130B receive an equal portion of
the hydraulic fluid flow rate and experience the same pressure
coming from pump 170 following Transition 1. In this assumed
situation, both pistons 130A, 130B exert generally the same force
on the respectively coupled pumping piston-cylinder assembly 140,
and the flow rates of working fluid leaving the two discharge ports
158 are therefore generally equal, following Transition 1 and prior
to the second transitional event.
[0068] At a second transitional event, or Transition 2, rod 134A
has reached the far-extended position 232A, which is indicated by a
signal from the corresponding position sensor 230, and rod 134A is
near but not at full extension, being proximal rod-end 127A of
cylinder 125A. Rod 134B is between the retracted position 233B and
extended position 231B, moving toward rod-end 127B of cylinder
125B. The signal corresponding to position 232A of cylinder 125A
directs control system 200 to close supply valve 205A (deactivate
State 1A) and then to open exhaust valve 210A (activate State 2A)
for cylinder 125A, in accordance with open-state-exclusivity for
these two valves. Supply valve 205B remains open (State lB is
active) in accordance with open-state-assurance for supply valves
205A, 205B, and exhaust valve 210B remains closed (State 2B is
inactive).
[0069] As a result of Transition 2, rod 134A reverses direction and
begins to retract, receiving fluid from accumulator 260 and from
chamber 135B as rod 134B continues to extend. The extension speed
of rod 134B is approximately twice as fast as it was following
Transition 1 because supply valve 205B feeds all hydraulic fluid
from pump 170 to chamber 135B.
[0070] A third transitional event, or Transition 3, is the inverse
or the "mirror" of Transition 1 with the events for assemblies
120A, 120B swapped. At Transition 3, rod 134B has reached its
extended position 231B. Rod 134A has reached the retracted position
233A and is near but not at full retraction. The signal
corresponding to position 231B of cylinder 125B directs control
system 200 to close the exhaust valve 210A (deactivate State 2A)
and then to open the supply valve 205A (activate State 1A) for
cylinder 125A, in accordance with open-state-exclusivity for these
two valves. The signal corresponding to position 233A confirms that
rod 134A has retracted sufficiently. Supply valve 205B remains open
(State 1B is active), and exhaust valve 210B remains closed (State
2B is inactive).
[0071] At Transition 3, rod 134B continues to extend, and rod 134A
reverses direction and begins to extend. Because both supply valves
205A, 205B are open (State lA and State lB are simultaneously
active), in some embodiments, the extension speed of each rod 134A,
134B after Transition 3 may be approximately one half the previous
extension speed of rod 134B while rod 134A was retracting. In other
embodiments, depending on the combined characteristics and the
loading of the hydraulic piston-cylinder assemblies 120A, 120B,
140, the speed of the two rods 134A, 134B after Transition 3 may
vary in a different manner. Accumulator 260 receives and
accumulates fluid from both chambers 136A, 136B, which are
shrinking in volume at this stage of the operation.
[0072] A fourth transitional event, or Transition 4, is the inverse
or the "mirror" of Transition 2. At Transition 4, rod 134B has
reached its far-extended position 232B and is near but not at full
extension. Rod 134A is between the retracted position 233A and
extended position 231A, moving toward rod-end 127A of cylinder
125A. The signal corresponding to position 232B of cylinder 125B
directs control system 200 to close supply valve 205B (deactivate
State 1B) and then to open exhaust valve 210B (activate State 2B)
for cylinder 125B, in accordance with open-state-exclusivity for
these two valves. Supply valve 205A remains open (State 1A is
active) in accordance with open-state-assurance for supply valves
205A, 205B, and exhaust valve 210A remains closed (State 2A is
inactive).
[0073] As a result of Transition 4, rod 134B reverses direction and
begins to retract, receiving fluid from accumulator 260 and from
chamber 136A as rod 134A continues to extend. The extension speed
of rod 134A is approximately twice as fast as it was following
Transition 3 because supply valve 205A feeds all hydraulic fluid
from pump 170 to chamber 135A.
[0074] In at least one embodiment, Transition 1, Transition 2,
Transition 3, and Transition 4 occur in sequence, as numbered. The
inverse or mirrored relationship between Transition 1 and
Transition 3 as well as the inverse or mirrored relationship
between Transition 2 and Transition 4 cause the two pairs of
pistons 130 and rods 134 within the assemblies 120A, 120B to
reciprocate in synchronized, phase-shifted cycles governed by fluid
control system 200. Thus, as previously stated, the hydraulic
piston-cylinder assemblies 120A, 120B are directly powered by pump
170 during their extension strokes. Assemblies 120A, 120B are
powered during their return strokes by rod-end fluid circuit 265
(FIG. 4), i.e., by fluid coming from the opposite assembly 120 or
coming from accumulator 260, exchanged through ports P2, Q2.
[0075] As stated, the signals of sensors 230 corresponding to
positions 233A, 233B confirm that rods 134A, 134B retract
sufficiently. The information these signals provide is used to
control the amount of fluid in the rod-end fluid circuit 265.
Occasionally, make-up fluid is added to the rod-end circuit 265 to
compensate for leakage. In some embodiments, the monitoring and
adjusting of the amount of fluid in circuit 265 is accomplished
automatically by hydraulic fluid control system 200 with the aid of
one or more additional valves (not shown) and a pump, for example
pump 170, gear pump 220, or an additional hydraulic pump. In some
other embodiments, a change to the amount of fluid in circuit 265
is accomplished manually during maintenance. The signal data from
sensors 230 that is monitored by control system 200 is available to
guide the maintenance operation, the data being presented in any
suitable manner, for example using a graphical user interface
coupled to control system 200.
[0076] In the operation scenario explained, the average retraction
speeds of the pistons 130 are faster than the average extension
speeds of the pistons 130. For example, the retraction of piston
130A is completed during and between Transition 2 and Transition 3,
but the extension of piston 130A starts during Transition 3 and
continues until the subsequent Transition 2. As similar analysis is
true of piston 130A for this embodiment. For some embodiments, the
higher retraction speed may be due to the over-pressurizing of the
accumulator 260 of circuit 265 (FIG. 4) that occurs during the
brief time when both pistons extend at the same time, e.g.
following Transition 1 and following Transition 3. A short time
later, when one of the pistons begins to retract during Transition
2 or Transition 4, the now-retracting piston 130 receives an
initial burst of fluid from the accumulator 265 as well as the
steady flow of hydraulic fluid that continues to come from the
other piston 130 that is still extending. As retraction continues,
the retraction speed may reduce below its initial magnitude.
[0077] In at least some embodiments, the first HPC assembly is in
the State 3A between the State 1A and the State 2A during the
Transition 2. In at least some embodiments, the second HPC assembly
is in the State 3B between the State 1B and the State 2B during the
Transition 4.
[0078] FIG. 6 presents a method 400 for operating a fluid-driven
pumping unit in accordance with the principles described herein. At
block 402, method 400 includes supplying a flow rate of a driving
fluid during an operation period. Hydraulic fluid is an example of
a driving fluid. Supplying a flow rate of the driving fluid is
accomplished in the example previously described by a source for
pressurized hydraulic fluid such as, for example, pump 170. At
block 404, method 400 includes dividing the flow rate of the
driving fluid between members of a plurality of double-acting
hydraulic piston-cylinder (HPC) assemblies, each assembly having a
movable rod. The synchronized, phase-shifted cycles are implemented
by a fluid control system. At block 406, method 400 includes
operating at least two of the HPC assemblies using synchronized,
phase-shifted cycles, wherein the corresponding two movable rods
extend and retract periodically, such that the two rods always have
a different combination of axial position and direction of travel
and such that at least one of the two rods is extending at all
times. In the example of pumping system 100, two double-acting
hydraulic piston-cylinder assemblies 120 drive the two pumping
piston-cylinder assemblies 140 to discharge a working fluid, such
as drilling mud, through the outlet port 166 of manifold 165. At
block 408, method 400 includes providing a plurality of pumps
configured to deliver a working fluid, each pump driven by a rod of
the plurality of rods. At block 410, method 400 includes pumping a
working fluid using the plurality of pumps. At block 412, method
400 includes interconnecting the plurality of HPC assemblies so the
extension of a first actuator causes the retraction of a second
actuator and the extension of the second actuator causes retraction
of the first actuator. In pumping system 100, for example, rod-end
fluid circuit 265 serves to accomplish the step described in block
408.
[0079] The steps or actions depicted in FIG. 6 or otherwise
described for method 400 may be performed in the order shown or in
a different order, and two or more of the actions may be performed
in parallel, rather than serially. The actions of method 400 may be
performed by control circuit 225, which in some embodiments
includes a computational processor. Various embodiments of method
400 may include additional steps based on any of the concepts
presented in this written description, including the figures. For
example, open-state-exclusivity or open-state-assurance, as
previously defined, may be applied to the operation of the
fluid-driven pumping unit.
[0080] Embodiments consistent with the present disclosure have been
presented. In addition, numerous modifications and variations are
possible, such as those stated here.
[0081] In addition to being useful for supplying a working fluid to
a process or a destination, in various embodiments, the disclosed
hydraulically-driven pumping unit is suited for extracting or
recovering a fluid from an above ground or underground reservoir,
such as extracting hydrocarbons from an operating oil well.
[0082] Although in the earlier discussion the sensing of various
locations of pistons 130 within hydraulic cylinders 125 is
accomplished using an LDT position sensor 230 coupled to each
cylinder 125 or, similarly, coupled to each piston 130, in some
other embodiments the position sensor 230 is implemented with
another suitable technology. For example, three proximity sensors
may instead be used for each cylinder 125. One proximity sensor is
placed at each position 231A, 232A, 233A for cylinder 125A, and one
proximity sensor is placed at each position 231B, 232B, 233B for
cylinder 125B. The proximity sensors detect the presence or
movement of piston 130A, 130B or another recognized, movable
feature. In some embodiments, the proximity sensors are mounted in
a configuration that allows them to be selectively moved in an
axial direction along a hydraulic cylinder 125A, 125B to simplify
testing or tuning of the performance of hydraulically-driven
pumping unit 100. Depending on space constraints or other
considerations, in other embodiments, proximity sensors acting as
position sensors 230 are mounted on each pumping piston-cylinder
assembly 140 and detect the presence or movement of pumping pistons
150 or another recognized, movable feature, such as a selected
locations adjacent the paths of travel of the rods 134A, 134B
outside cylinder 125A, 125B. The presence or movement of pumping
pistons 150 are then correlated to the movement of the coupled
piston 130A, 130B. Any suitable type of proximity sensor may be
used. For example, proximity sensors that operate based on sensing
changes in capacitance or proximity sensors that transmit and
receive acoustic signals, or sensors that rely on electrical
inductance or physical contact with the moving piston may be used
in various embodiments. Thus various position sensor(s) 230 that
utilize a mechanical phenomenon, an electrical phenomenon, or
another suitable phenomenon may be used to detect the localized
presence, i.e., the position, of piston 130 along cylinder 125.
[0083] In some embodiments, fewer than three positions 231A, 232A,
233A along hydraulic cylinder 125A are instrumented by position
sensor 230, and the presence or movement of piston 130A at some of
the positions 231A, 232A, 233A is determined by timing circuitry or
logic in control circuit 225, possibly in conjunction with status
data from a valve or another component of pumping unit 100. For
example, the determination of the presence of piston 130A at
position 232A may be implemented by a timing delay triggered by the
opening of second supply valve 205B and/or by the status of the
solenoid operated valve 215 that supplies pressurized hydraulic
fluid to valve 205B. A similar technique is applicable to position
232B along hydraulic cylinder 125B, and a similar technique may be
applicable to another position 231A, 233A, 231B, 233B.
[0084] Although the described embodiment includes two of the
hydraulic piston-cylinder assemblies 120, some other embodiments
include three or more double-acting hydraulic piston-cylinder
assemblies 120 coupled to three or more pumping piston-cylinder
assemblies 140, and include one or more rod-end fluid circuits 265.
The operation of each hydraulic piston-cylinder assembly 120 is
controlled by open-state-exclusivity so that the assembly's supply
valve and exhaust valve are not simultaneously in an open position
or open state. The operation of the three or more assemblies 120 is
coordinated according to open-state-assurance so that the supply
valve for at least one of the assemblies is open at any given
time.
[0085] In various embodiments, the separate supply valve 205 and
exhaust valve 210 for each cylinder 125 is replaced by a
two-position three-way control valve having "pressurizing position"
to place the corresponding port P1, Q1 in fluid communication with
the source for pressurized hydraulic fluid, e.g., pump 170, and a
"discharge position" to place the same port P1, Q1 in fluid
communication with the hydraulic reservoir 250. For example, an
alternative embodiment of pumping unit 100 of FIG. 1 would have two
such control valves. Each of the two-position three-way control
valves may be coupled to a solenoid operated two-position three-way
valve 215 or may have an integrated control mechanism that may be
fluid-operated or electrically-operated.
[0086] In various embodiments, a pumping piston-cylinder assembly
140 may be a double-acting piston-cylinder assembly having two
pumping chambers 155, one pumping chamber on either side of the
enclosed piston 150, and having an inlet port 156 and a discharge
port 158 for each of the two pumping chambers 155. The two pumping
chambers 155 in a single assembly 140 configures the assembly 140
to pump fluid when piston 150 moves in either direction, providing
higher capacity of fluid delivery or potentially providing a
smother flow of fluid to manifold 165.
[0087] While exemplary embodiments have been shown and described,
modifications thereof can be made by one skilled in the art without
departing from the scope or teachings herein. The embodiments
described herein are exemplary only and are not limiting. Many
variations and modifications of the systems, apparatus, and
processes described herein are possible and are within the scope of
the disclosure. Accordingly, the scope of protection is not limited
to the embodiments described herein, but is only limited by the
claims that follow, the scope of which shall include all
equivalents of the subject matter of the claims. The inclusion of
any particular method step or action within the written description
or a figure does not necessarily indicate that the particular step
or action is necessary to the method. Unless expressly stated
otherwise, the steps in a method claim may be performed in any
order. The recitation of identifiers such as (a), (b), (c) or (1),
(2), (3) before steps in a method claim are not intended to and do
not specify a particular order to the steps, but rather are used to
simplify subsequent reference to such steps.
* * * * *