Note: Descriptions are shown in the official language in which they were submitted.
CA 02865736 2014-09-30
SYSTEM AND METHOD FOR DOWNHOLE POWER GENERATION
USING A DIRECT DRIVE PERMANENT MAGNET MACHINE
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] The present application claims the benefit of U.S. Provisional
Application No.
61/884,394, filed September 30, 2013, entitled "Downhole Tool With Direct
Drive
Permanent Magnet Machine," which is incorporated herein by reference in its
entirety for
all purposes.
BACKGROUND
[0002] In the drilling of oil and gas wells, various downhole tools are
typically included in
the drill string. The downhole tools may provide, for example, control of
drilling operations,
measurement of borehole and/or formation properties, and/or communication
between
downhole and surface systems. Many such downhole tools are powered by
electrical
energy. The electrical energy that powers downhole tools may be generated at
the
surface and conducted downhole. Alternatively, the electrical energy powering
a
downhole tool may be generated downhole.
SUMMARY
[0003] A system and method for generation of electrical energy in a wellbore
are
disclosed herein. In one embodiment, a downhole tool for use in a wellbore
includes a
housing and a power generation system disposed within the housing. The power
generation system includes a power section and an axial flux generator. The
power
section is configured to convert flow of drilling fluid through the downhole
tool to rotation.
The axial flux generator is coupled to the power section. The axial flux
generator is
configured to produce magnetic flux that extends parallel to an axis of the
rotation, and to
generate electrical energy responsive to the rotation.
[0004] In another embodiment, a method for generating power in a downhole tool
used
in a wellbore includes pumping drilling fluid into a drill string disposed in
the wellbore.
Movement of the drilling fluid through a power section disposed in the drill
string is
converted into rotation of a shaft in the power section. A rotor of an axial
flux generator
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coupled to the shaft is rotated by the rotation of the shaft. Electrical
energy is generated in
the axial flux generator, via the magnetic flux, responsive to the rotating of
the rotor.
[0005] In a further embodiment, a system for generating electrical energy
downhole
includes an axial flux permanent magnet machine and a power section. The axial
flux
permanent magnet machine includes a plurality of disks arranged in a stack
wherein a
face of one of the disks is adjacent to a face of another of the disks. At
least one of the
disks is a stator that includes a plurality of wire coils, and at least one of
the disks is a
rotor that includes a plurality of permanent magnets arranged in
correspondence with the
wire coils of an adjacent stator. The power section is configured to rotate
the rotor of the
axial flux permanent magnet machine responsive to flow of drilling fluid
through the power
section. Rotation of the rotor by the power section generates
BRIEF DESCRIPTION OF THE DRAWINGS
[0006] For a detailed description of exemplary embodiments of the invention,
reference
will now be made to the figures of the accompanying drawings. The figures are
not
necessarily to scale, and certain features and certain views of the figures
may be shown
exaggerated in scale or in schematic form, and some details of conventional
elements
may not be shown in the interest of clarity and conciseness.
[0007] Figure 1 shows a drilling system that includes downhole power
generation in
accordance with principles disclosed herein;
[0008] Figure 2 shows a schematic diagram of a downhole power generation
system in
accordance with principles disclosed herein;
[0009] Figure 3 shows views of an exemplary axial flux permanent magnet
machine in
accordance with principles disclosed herein;
[0010] Figure 4 shows a schematic diagram of a downhole power generation
system
arranged to allow fluid flow through a generator in accordance with principles
disclosed
herein;
[0011] Figure 5 shows a schematic diagram of a downhole power generation
system
that integrates a generator and a power system bearing assembly in accordance
with
principles disclosed herein; and
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[0012] Figure 6 shows a schematic diagram of a downhole tool using an axial
flux
permanent magnet machine as both a generator and a motor in accordance with
principles disclosed herein.
NOTATION AND NOMENCLATURE
[0013] Certain terms are used throughout the following description and claims
to refer to
particular system components. In the following discussion and in the claims,
the terms
"including" and "comprising" are used 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
device couples
to a second device, that connection may be through direct engagement of the
devices or
through an indirect connection via other devices and connections. The
recitation "based
on" is intended to mean "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.
DETAILED DESCRIPTION
[0014] In the drawings and description that follow, like parts are typically
marked
throughout the specification and drawings with the same reference numerals.
The present
disclosure is susceptible to embodiments of different forms. Specific
embodiments are
described in detail and are shown in the drawings, with the understanding that
the present
disclosure is to be considered an exemplification of the principles of the
disclosure, and is
not intended to limit the disclosure to that illustrated and described herein.
It is to be fully
recognized that the different teachings and components of the embodiments
discussed
below may be employed separately or in any suitable combination to produce
desired
results.
[0016] Conventional downhole power generation generally employs an alternator
driven
by a turbine through a gearbox. Impellers of the turbine convert the flow of
drilling fluid
into rotation. The gearbox turns the alternator and adapts the rotation rate
of the turbine
for use by the alternator. For example, the gearbox may provide an increased
rate of
rotation to the alternator with respect to the turbine where the turbine
rotation rate is too
low to generate adequate power via the alternator. The alternator is
conventionally a
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radial flux machine in which magnetic flux extends radially with respect to
the alternator's
axis of rotation. The radial flux machine is generally cylindrical in shape,
and a radial flux
alternator of a downhole power generation system may occupy a substantial
portion of
the length of a downhole tool.
[0016] Embodiments of the downhole power generation system disclosed herein
provide a reduction in both area and complexity relative to conventional
systems. Rather
than the radial flux machines used in conventional systems, embodiments of the
present
disclosure generate power downhole using an axial flux machine. In an axial
flux
machine, magnetic flux extends axially with respect to the machine's axis of
rotation (i.e.,
parallel to the machine's axis of rotation). The axial flux machine is disk
shaped, and can
produce sufficient electrical energy to power a downhole tool at a
substantially lower
rotation rate than is required using a radial flux generation system.
Consequently, the
axial flux machine can be directly driven by a turbine rather than driven via
a gearbox. As
a result, embodiments of the downhole power generation system disclosed herein
Occupy
a substantially smaller lengthwise portion of a downhole tool than a
conventional
downhole power generation system.
[0017] In some embodiments of the downhole power generation system disclosed
herein, the axial flux machine generates direct current (DC) electrical
energy. In such
embodiments, the complexity of the power generation system is further reduced
by
eliminating the need for complex rectification circuitry.
[0018] In some downhole tools, the axial flux machine may be used as a motor
as well
as a generator. In such tools, the axial flux machine may be used to drive
various
mechanisms the affect tool operation.
[0019] Figure 1 shows a drilling system 100 that includes downhole power
generation in
accordance with principles disclosed herein. In the drilling system 100, a
drilling platform
102 supports a derrick 104 having a traveling block 106 for raising and
lowering a drill
string 108. A kelly 110 supports the drill string 108 as it is lowered through
a rotary table
112. In some embodiments, a top drive is used to rotate the drill string 108
in place of the
kelly 110 and the rotary table 112. A drill bit 114 is driven by a downhole
motor and/or
rotation of the drill string 108. As drill bit 114 rotates, it creates a
borehole 116 that
passes through various subsurface formations. A pump 120 circulates drilling
fluid
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through a feed pipe 122 to kelly 110, downhole through the interior of drill
string 108,
through orifices in drill bit 114, back to the surface via the annulus around
drill string 108,
and into a retention pit 124. The drilling fluid transports cuttings from the
borehole into
the pit 124 and aids in maintaining the borehole integrity.
[0020] The drill string 108 is made up of various components, including drill
pipe 118,
drill bit 114, and other downhole tools. The drill pipe 118 may be standard
drill pipe or
wired drill pipe. The drill string 108 includes a downhole tool 126 that is
operated via
electrical energy. The electrical energy powering the downhole tool 126 is
generated
downhole by the power generation system 128. The power generation system 128
may
be disposed within the downhole tool 126 or elsewhere in the drill string 108.
[0021] The power generation system 128 includes a direct drive permanent
magnet
machine that generates electrical energy from rotation induced by the flow of
drilling fluid
through the drill string 108. The direct drive permanent magnet machine
includes an axial
flux machine that can generate power at the relatively low rotation rate
induced by the
flow of drilling fluid.
[0022] While the system 100 is illustrated with reference to an onshore well
and drilling
system, embodiments of the system 100 are also applicable to power generation
and
control in offshore wells. In such embodiments, the drill string 108 may
extend from a
surface platform through a riser assembly, a subsea blowout preventer, and a
subsea
wellhead into the subsea formations.
[0023] Figure 2 shows a schematic diagram of the downhole power generation
system
128 in accordance with principles disclosed herein. The downhole power
generation
system 128 includes a power section 202 and an axial flux generator 204
disposed in a
bore formed by the interior surface of housing 200. Housing 200 may be
generally
cylindrical in shape. The power section 202 may include a turbine, a
progressive cavity
pump, or other device that converts the flow of drilling fluid 206, pumped
through the drill
string 108 from the surface, into rotation.
[0024] The power section 202 is coupled to the axial flux generator 204, and
provides
rotation to the axial flux generator 204. The axial flux generator 204 may
include an axial
flux permanent magnet machine disposed in a housing 212. The housing 212 may
be
dimensioned to allow flow of drilling fluid 206 around the axial flux
generator 204 to the
CA 02865736 2014-09-30
power section 202. In other embodiments, the axial flux generator 204 may be
disposed
downstream of the power section 202. The axial flux generator 204 converts the
rotary
energy provided by the power section 202 into electrical energy. Because the
axial flux
generator is directly coupled to the power section 202, rather than coupled
through a
gearbox as in conventional systems, the rotation rate of the axial flux
generator 204 may
be relatively low. In various embodiments, the electrical energy produced by
the axial flux
generator 204 may include direct current or alternating current.
[0025] The electrical energy generated by the axial flux generator 204 is
conducted to a
regulator 208. The regulator 208 can adjust the voltage and/or current of the
electrical
energy produced by the axial flux generator 204 to ensure that the voltage
and/or current
provided to devices powered by the electrical energy is within a predetermined
operational range. For example, the regulator 208 may include a buck/boost
switching
power converter that produces a predetermined output voltage from the
electrical energy
provided by the axial flux generator 204. Voltage and/or current output by the
regulator
208 is provided to electronics 210 or other electrical devices in the downhole
tool 126 or
elsewhere in the drill string 108.
[0026] Figure 3 shows views of an illustrative axial flux permanent magnet
machine 300
in accordance with principles disclosed herein. The axial flux permanent
magnet machine
300 is suitable for use in the axial flux generator 204. The axial flux
permanent magnet
machine 300 includes a plurality of disks 302, 304, and shaft 306. Disks 302
may be
stators and disk 304 may be a rotor. Disk 302 includes a plurality of coils
308, and disk
304 includes a plurality of permanent magnets arranged in correspondence to
the coils
308. The magnets may be arranged with alternating north-south orientation. The
magnets
of the disk 304 and the coils 308 of the disks 302 face one another when the
disks are
stacked as shown in Figure 3. The coils 308 may be wound parallel to the disk
302.
[0027] The shaft 306 is coupled to a shaft of the power section 202, and
rotation
generated in the power section causes the disk 304 to rotate via the shaft
306, while the
disks 302 remain stationary relative to the disk 304. Rotation of the disk 304
produces
changes in magnetic flux as the magnets of the disk 304 move past the coils
308. The
changes in magnetic flux induce current flow in the coils 308. Conductors
connected to
the coils transfer the generated electrical energy to the regulator 208. The
relatively large
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number of magnets and coils operating in concert allow the axial flux
permanent magnet
machine 300 to generate substantially more electrical energy at a low rotation
rate than
would be provided by a conventional downhole energy generation system at the
same
rate of rotation. Thus, the axial flux generator 204 can be directly connected
to the power
section 202, rather than connected through a gearbox that increases the rate
of rotation
provided to the generator 204.
[0028] Because the axial flux permanent magnet machine 300 is disk-shaped, the
lengthwise area occupied by the axial flux generator 204 may substantially
smaller than
for an equivalent radial flux generator. Accordingly, the size of the downhole
power
generation system 128 is reduced relative to conventional power generation
systems.
The reduction in size may allow for inclusion of additional sensors/subsystems
in the
downhole tool 126, and/or allow for reduction in length of the tool 126.
[0029] Embodiments of the axial flux permanent magnet machine 300 may include
any
number of rotors 304 and corresponding stators 302, where increasing the
number of
rotors and stators stacked may produce a correspondent increase in electrical
current
generated. A variety of differently configured axial flux permanent magnet
machines may
be applied in the axial flux generator 204. For example, an axial flux
permanent magnet
machine that generates direct current rather than alternating current may be
included in
the axial flux generator 204 to alleviate the need for rectifiers. Some
embodiments of an
axial flux permanent magnet machine included in the axial flux generator 204
may include
a stator disposed between rotors.
[0030] Figure 4 shows a schematic diagram of a downhole power generation
system
128 arranged to allow fluid flow through the axial flux generator in
accordance with
principles disclosed herein. The power generation system 128 of Figure 4
includes a
power section 402 and an axial flux generator 404 disposed in a bore formed by
the
interior surface of housing 400. Housing 400 and the power section 402 may be
as
described with reference to the housing 200 and the power section 402
disclosed with
respect to Figure 2.
[0031] The power section 402 is coupled to the axial flux generator 404, and
provides
rotation to the axial flux generator 404. The axial flux generator 404
includes an axial flux
permanent magnet machine. A shaft or other rotatable structure of the power
section 402
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is coupled to a shaft 406 of the permanent magnet machine, and induces
rotation of the
shaft 406. The shaft 406 includes a bore 408. Drilling fluid 206, pumped
through the drill
string 108 from the surface, passes through the bore 408 into the power
section 402, and
causes the power section to induce rotation in the axial flux generator 404.
Thus, in the
downhole power generation system 128 of Figure 4, drilling fluid flows through
the axial
flux generator 404 in addition to or in lieu of flowing around the axial flux
generator 404.
[0032] Figure 5 shows a schematic diagram of a downhole power generation
system
128 that integrates the generator and the power system bearing assembly in
accordance
with principles disclosed herein. The power generation system 128 of Figure 5
includes a
power section 502 and an axial flux generator 504 disposed in a bore formed by
the
interior surface of housing 500. Housing 500 and the power section 502 may be
substantially as described with reference to the housing 200 and the power
section 402
disclosed with respect to Figure 2.
[0033] As explained above, an axial flux permanent magnet machine may be
formed as
a relatively thin disk. The power generation system 128 of Figure 5 takes
advantage of
the disk shape of the axial flux generator 504 by incorporating the axial flux
generator 504
in a bearing assembly 506 of the power section 502. The bearing assembly 506
may
include roller bearings that facilitate rotation of a shaft of the power
section 502 induced
by the flow of drilling fluid 206. The rotor(s) of the axial flux generator
504 may be directly
or indirectly coupled to the shaft of the power section 502 in the bearing
assembly. By
incorporating the axial flux generator 504 in the bearing assembly 506 of the
power
section 502, the length of the power generation system 128 is further reduced,
allowing
for a reduction in the length of downhole tools in which the power generation
system 128
is to be applied.
[0034] In addition to generating electrical energy, an axial flux permanent
magnet
machine may operate as motor. As described with reference to the axial flux
permanent
magnet machine 300, generation of electrical energy is induced by rotation of
the shaft
306, which in turn, rotates the rotor 304. The axial flux permanent magnet
machine 300
may function as a motor by driving current through the coils 308. The current
induces
magnetic fields that cause the rotor 304 to rotate, and in turn rotate the
shaft 306.
Accordingly, in some embodiments of the downhole tool 126, an axial flux
permanent
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magnet machine may be applied as a motor to provide mechanical actuation
and/or as a
generator to generate electrical energy. For example, an axial flux permanent
magnet
machine may operate as a generator during intervals when mechanical actuation
is not
needed, and at other times operate as a motor to open valves when needed,
activate a
tool, etc.
[00351 Figure 6 shows a schematic diagram of the downhole tool 126 applying an
axial
flux permanent magnet machine as both a generator and a motor in accordance
with
principles disclosed herein. The downhole tool 126 of Figure 6 includes a
valve 604
disposed in a bore 610. The valve 604 may be opened to allow fluid (e.g.,
drilling fluid
206) to flow through the bore 610. Fluid flow is inhibited when valve 604 is
positioned
against valve seats 612.
[0036] The downhole tool 126 also includes an axial flux permanent magnet
machine
602, a power section 202, and motor/generator control circuitry 608. The
motor/generator
control circuitry 608 controls the operation of the axial flux permanent
magnet machine
602 by configuring the axial flux permanent magnet machine 602 to operate as
either a
motor or a generator. Accordingly, the motor/generator control circuitry 608
may include
switches to route electrical energy produced by the axial flux permanent
magnet machine
602 to an energy storage system (e.g., a battery), and drive circuitry to
drive current to the
axial flux permanent magnet machine 602 for operation as a motor.
[0037] The axial flux permanent magnet machine 602 is coupled to the valve 604
via a
shaft 606. The axial flux permanent magnet machine 602 may operate as a motor
to
rotate the shaft. Rotation of the shaft 606 in one direction may cause the
valve 604 to
open, and rotation of the shaft 606 in the opposite direction may cause the
valve 604 to
close. For example, at least a portion of the shaft 606 may be threaded such
that rotation
of the shaft causes the valve 604 to move.
[0038] When the valve 604 is open, fluid flowing through the power section 202
may
induce rotation in the power section 202, and the motor/generator control
circuitry 608
may configure the axial flux permanent magnet machine 602 to operate as a
generator.
Accordingly, the power section 202 may induce rotation in the axial flux
permanent
magnet machine 602 thereby causing the axial flux permanent magnet machine 602
to
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generate electrical energy that can be stored for use by other devices or
subsequent
motor application of the axial flux permanent magnet machine 602.
[0039] The above discussion is meant to be illustrative of various embodiments
of the
present invention. Numerous variations and modifications will become apparent
to those
skilled in the art once the above disclosure is fully appreciated, It is
intended that the
following claims be interpreted to embrace all such variations and
modifications.
