U.S. patent application number 15/772574 was filed with the patent office on 2018-11-08 for magnetic coupling for downhole applications.
The applicant listed for this patent is Halliburton Energy Services, Inc.. Invention is credited to Mukul M. Agnihotri, Satish Rajagopalan.
Application Number | 20180320482 15/772574 |
Document ID | / |
Family ID | 58797692 |
Filed Date | 2018-11-08 |
United States Patent
Application |
20180320482 |
Kind Code |
A1 |
Agnihotri; Mukul M. ; et
al. |
November 8, 2018 |
Magnetic Coupling for Downhole Applications
Abstract
The present disclosure relates to a magnetic coupling of a
downhole tool that includes a first annular array of magnetic
sections, a second annular array of magnetic sections coupled to
the first annular array by a magnetic field that transfers
rotational motion from the first annular array to the second
annular array, and a barrier disposed between the first annular
array and the second annular array, the barrier including an
erosion-resistant layer. The present disclosure also relates to a
method of bootstrapping a magnetic coupling of a downhole tool. The
method includes supplying electrical current from a battery to an
electromagnetic coil in the magnetic coupling, transferring
rotational motion from the magnetic coupling to an alternating
current (AC) source and supplying electrical current from the AC
source to the electromagnetic coil.
Inventors: |
Agnihotri; Mukul M.;
(Spring, TX) ; Rajagopalan; Satish; (Tomball,
TX) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Halliburton Energy Services, Inc. |
Houston |
TX |
US |
|
|
Family ID: |
58797692 |
Appl. No.: |
15/772574 |
Filed: |
December 4, 2015 |
PCT Filed: |
December 4, 2015 |
PCT NO: |
PCT/US2015/064041 |
371 Date: |
May 1, 2018 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
E21B 41/0085 20130101;
E21B 17/03 20130101; E21B 17/028 20130101 |
International
Class: |
E21B 41/00 20060101
E21B041/00 |
Claims
1. A magnetic coupling of a downhole tool comprising: a first
annular array of magnetic sections; a second annular array of
magnetic sections coupled to the first annular array by a magnetic
field that transfers rotational motion from the first annular array
to the second annular array; and a barrier disposed between the
first annular array and the second annular array, the barrier
including an erosion-resistant layer.
2. The magnetic coupling of claim 1, wherein: the first annular
array has a first outer diameter; the second annular array has a
second outer diameter approximately equal to the first outer
diameter; the first annular array and the second annular array are
configured to rotate about a common axis of rotation; and the
magnetic field is oriented approximately parallel to the common
axis of rotation.
3. The magnetic coupling of claim 1, wherein: the first annular
array has an inner diameter; the second annular array has an outer
diameter smaller than the inner diameter; the second annular array
is disposed within the inner diameter of the first annular array;
the first annular array and the second annular array are configured
to rotate about a common axis of rotation; and the magnetic field
is oriented approximately perpendicular to the common axis of
rotation.
4. The magnetic coupling of claim 1, wherein the erosion-resistant
layer includes a layer of titanium.
5. The magnetic coupling of claim 1, wherein the second annular
array comprises a plurality of permanent magnets.
6. The magnetic coupling of claim 5, wherein a magnet among the
plurality of permanent magnets is a samarium cobalt magnet.
7. The magnetic coupling of claim 1, wherein the second annular
array comprises a plurality of electromagnetic coils.
8. The magnetic coupling of claim 7, further comprising a bootstrap
circuit for energizing the plurality of electromagnetic coils, the
bootstrap circuit comprising: a battery; and a first diode coupled
to the battery, the first diode permitting the battery to supply
electrical current to the plurality of electromagnetic coils.
9. The magnetic coupling of claim 8, the bootstrap circuit further
comprising: a current source coupled to the second annular array,
the current source configured to transform rotation of the second
annular array into electrical current; and a second diode coupled
to the current source, the second diode permitting the current
source to supply electrical current to the plurality of
electromagnetic coils.
10. A drilling system comprising: a drill string; a magnetic
coupling located within the drill string, the magnetic coupling
including: a first annular array of magnetic sections; a second
annular array of magnetic sections coupled to the first annular
array by a magnetic field that transfers rotational motion from the
first annular array to the second annular array; a barrier disposed
between the first annular array and the second annular array, the
barrier having an erosion-resistant layer; a motor coupled to the
first annular array; and a load coupled to the second annular
array.
11. The drilling system of claim 10, wherein: the first annular
array has a first outer diameter; the second annular array has a
second outer diameter approximately equal to the first outer
diameter; the first annular array and the second annular array are
configured to rotate about a common axis of rotation; and the
magnetic field is oriented approximately parallel to the common
axis of rotation.
12. The drilling system of claim 10 wherein: the first annular
array has an inner diameter; the second annular array has an outer
diameter smaller than the inner diameter; the second annular array
is disposed within the inner diameter of the first annular array;
the first annular array and the second annular array are configured
to rotate about a common axis of rotation; and the magnetic field
is oriented approximately perpendicular to the common axis of
rotation.
13. The drilling system of claim 10, wherein the erosion-resistant
layer includes a layer of titanium.
14. The drilling system of claim 10, wherein the second annular
array comprises a plurality of permanent magnets.
15. The drilling system of claim 10, wherein a magnet among the
plurality of permanent magnets is a samarium cobalt magnet.
16. The drilling system of claim 10, wherein the second annular
array comprises a plurality of electromagnetic coils.
17. The drilling system of claim 16, further comprising a bootstrap
circuit for energizing the plurality of electromagnetic coils, the
bootstrap circuit comprising: a battery; and a first diode coupled
to the battery, the first diode permitting the battery to supply
electrical current to the plurality of electromagnetic coils.
18. The drilling system of claim 17, the bootstrap circuit further
comprising: a current source coupled to the plurality of
electromagnetic coils; and a second diode coupled to the current
source, the second diode permitting the current source to supply
current to the plurality of electromagnetic coils.
19. The drilling system of claim 10, wherein the load is a
generator.
20. A method of bootstrapping a magnetic coupling of a downhole
tool, comprising: rotating a first annular array of magnetic
sections in a magnetic coupling; supplying current from a battery
to an electromagnetic coil located within a second annular array of
magnetic sections in the magnetic coupling; coupling the first
annular array to the second annular array using a magnetic field
produced by the electromagnetic coil; transferring rotational
motion from the first annular array to the second annular array
using the magnetic field; transferring rotational motion from the
second annular array to an alternating current (AC) source
configured to transform rotational motion into electrical current;
and supplying electrical current from the AC source to the
electromagnetic coil.
21. The method of claim 20, wherein the magnetic coupling includes
a barrier disposed between the first annular array and the second
annular array, the barrier including an erosion-resistant
layer.
22. The method of claim 20, wherein: the first annular array has a
first outer diameter; the second annular array has a second outer
diameter approximately equal to the first outer diameter; the first
annular array and the second annular array are configured to rotate
about a common axis of rotation; and the magnetic field is oriented
approximately parallel to the axis of rotation.
23. The method of claim 20, wherein: the first annular array has an
inner diameter; the second annular array has an outer diameter
smaller than the inner diameter; the second annular array is
disposed within the inner diameter of the first annular array; the
first annular array and the second annular array are configured to
rotate about a common axis of rotation; and the magnetic field is
oriented approximately perpendicular to the axis of rotation.
Description
TECHNICAL FIELD
[0001] The present disclosure relates generally to drilling tools
and, more particularly, to magnetic coupling for downhole
applications.
BACKGROUND
[0002] Natural resources, such as oil and gas, often reside in
various forms within a subterranean geological formation that may
be located onshore or offshore. These natural resources can be
recovered by drilling a wellbore that penetrates the formation.
[0003] A variety of fluids are used in both drilling and completing
the wellbore. For example, during the drilling of the wellbore, a
portion of the drill string may be immersed in a drilling fluid
used to cool the drill bit, lubricate the rotating drill string to
prevent it from sticking to the walls of the wellbore, prevent
blowouts by serving as a hydrostatic head to the entrance into the
wellbore of formation fluids, and remove drill cuttings from the
wellbore, among other uses. Other portions of the drill string may
be immersed in oil, in air, or in other suitable media.
[0004] The drill string used in such drilling operations may
include a variety of components. Some components may capture energy
from the flow of drilling fluid through the drill string. For
example, the drill string may include a turbine that produces
rotational motion. Other components may make use of such rotational
motion. For example the drill string may include a pump driven by a
swash plate, an actuator such as a ball screw, or a generator that
produces electrical current used to operate other equipment within
the drill string. Such other equipment may include sensors,
telemetry components, measurement while drilling (MWD) tools,
logging-while-drilling (LWD) tools, or other components.
BRIEF DESCRIPTION OF THE DRAWINGS
[0005] For a more complete understanding of the present invention
and its features and advantages, reference is now made to the
following description, taken in conjunction with the accompanying
drawings, in which:
[0006] FIG. 1 is an elevation view of an exemplary drilling
system;
[0007] FIG. 2 is a section view of a portion of an exemplary drill
string containing a magnetic coupling;
[0008] FIG. 3 is a perspective view of an exemplary axial magnetic
coupling;
[0009] FIG. 4 is an elevation section view of an exemplary radial
magnetic coupling;
[0010] FIG. 5 is a plan section view of an exemplary radial
magnetic coupling;
[0011] FIG. 6 is a circuit diagram of an exemplary bootstrap
circuit for energizing electromagnetic coils in a magnetic
coupling; and
[0012] FIG. 7 is a flow chart of an exemplary method for
bootstrapping a magnetic coupling.
DETAILED DESCRIPTION
[0013] The present disclosure describes magnetic couplings used to
transfer mechanical power from a prime mover such as a turbine or
other source of rotational motion to a load that includes equipment
that can make use of that motion, such as a generator. The turbine
is driven by the flow of drilling fluid. A barrier is interposed
between the drive side of the magnetic coupling and the follower
side of the magnetic coupling to prevent the drilling fluid, which
is electrically conductive, from interfering with the operation of
the load. The magnetic coupling includes a pair of Halbach arrays,
each of which includes a series of magnetic sections arranged to
enhance the magnetic field in the space between the two arrays
while diminishing or eliminating the field on the opposite side of
each array. As a result, the amount of torque that is transmitted
by the magnetic coupling is greater than the torque transmitted by
a coupling using conventional magnetic arrays. The magnetic
coupling may use electromagnetic coils in the place of some
permanent magnets, allowing the strength of the magnetic coupling
to be tuned to meet varying operational requirements. Additionally,
the power used to energize the electromagnetic coils in the
magnetic coupling may be supplied by the load driven by the
coupling, once the coupling begins to turn.
[0014] Embodiments of the present disclosure and its advantages are
best understood by referring to FIGS. 1 through 7, where like
numbers are used to indicate like and corresponding parts.
[0015] FIG. 1 is an elevation view of an exemplary drilling system.
Drilling system 100 includes well surface or well site 106. Various
types of drilling equipment such as a rotary table, drilling fluid
pumps and drilling fluid tanks (not expressly shown) are located at
well surface or well site 106. For example, well site 106 may
include drilling rig 102 that has various characteristics and
features associated with a "land drilling rig." However, drilling
systems incorporating teachings of the present disclosure may be
satisfactorily used with drilling equipment located on offshore
platforms, drill ships, semi-submersibles and drilling barges (not
expressly shown). Well site 106 and drilling rig 102 are located
above subterranean region 107.
[0016] Drilling system 100 also includes drill string 103
associated with drill bit 101 that may be used to form a wide
variety of wellbores or bore holes such as wellbore 114. A portion
of wellbore 114 that is closer to well surface 106 is referred to
as uphole, and a portion of wellbore 114 that is further from well
surface 106 is referred to as downhole. Wellbore 114 may be defined
in part by casing string 110 that extends from well surface 106 to
a selected downhole location. Portions of wellbore 114 that do not
include casing string 110 are described as open hole.
[0017] Various drilling fluids are used during the drilling of
wellbores. The drilling fluid serves many purposes, including
cooling the drill bit, lubricating the rotating drill string to
prevent it from sticking to the walls of the wellbore, preventing
blowouts by serving as a hydrostatic head to the entrance into the
wellbore of formation fluids, and removing drill cuttings from the
wellbore. Typically the drilling fluid is circulated downward
through drill string 103 and drill bit 101 and then moves upward
through the wellbore towards the surface through annulus 108. In
open hole embodiments, annulus 108 is defined in part by outside
diameter 112 of drill string 103 and inside diameter 118 of
wellbore 114. In embodiments using casing string 110, annulus 108
is defined by outside diameter 112 of drill string 103 and inside
diameter 111 of casing string 110. Other circulation pathways are
possible, however. Drilling fluid typically includes a base fluid,
for example water or salt water, mixed with other materials or
additives. As a result, drilling fluid is often electrically
conductive.
[0018] Drill string 103 may include a wide variety of components
configured to form wellbore 114. For example, components 122a,
122b, and 122c of drill string 103 may include, but are not limited
to, drill bits (e.g., drill bit 101), coring bits, drill collars,
rotary steering tools, directional drilling tools, downhole
drilling motors, turbines, magnetic couplings, generators, reamers,
hole enlargers, stabilizers, sensors, logging-while-drilling tools,
or telemetry subs. The number and types of components 122 included
in drill string 103 depend on anticipated downhole drilling
conditions and the type of wellbore that will be formed by drill
string 103 and rotary drill bit 101. Drill string 103 may also
include one or more electrically powered components, such as
sensors, logging-while-drilling (LWD) tools, controllers, telemetry
subs, communication components, well logging instruments, and
downhole tools associated with directional drilling of a
wellbore.
[0019] Drill string 103 may also include components to provide the
electrical current required to operate components of the drill
string, such as component 122c discussed above. For example,
component 122a may include a turbine or other type of motor
immersed in the drilling fluid within drill string 103. The turbine
is configured to transform the flow of the drilling fluid through
drill string 103 into rotational motion of a drive shaft. Component
122b may include a generator configured to transform the rotational
motion of the drive shaft into electrical current for use by other
components, such as component 122c. Although this disclosure
describes specific components 122a, 122b, and 122c, any suitable
components of a drill string may be used. Furthermore, although
this disclosure discusses a particular arrangement of components
122a, 122b, and 122c, components of drill string 103 may be
arranged in any suitable positions within drill string 103.
[0020] Because drilling fluid is often electrically conductive,
immersion of the generator in the drilling fluid may interfere with
the operation of the generator. Therefore, the generator is
contained within a load-enclosure portion of drill string 103 that
contains oil, air, or other suitable non-conductive media, and is
separated from the drilling fluid by a barrier such as a static
seal that does not rotate relative to drill string 103 and is not
penetrated by the drive shaft. A magnetic coupling, as shown in
further detail in FIGS. 2-6, is used to transfer rotational motion
across the barrier, from the portion of the drive shaft connected
to the turbine and immersed in the drilling fluid to the portion of
the drive shaft connected to the generator and immersed in the
non-conductive media. The load enclosure allows drilling fluid to
flow towards the downhole end of drill string 103. For example, the
load enclosure may be narrower than the inner diameter of drill
string 103, allowing drilling fluid to flow downhole between the
load enclosure and the inner diameter of drill string 103.
[0021] Drill bit 101 typically includes one or more blades 126
located on exterior portions of rotary bit body 124 of drill bit
101. Blades 126 are any suitable type of projections extending
outwardly from rotary bit body 124. Drill bit 101 rotates with
respect to bit rotational axis 104 in a direction defined by
directional arrow 105. Blades 126 include one or more cutting
elements 128 located on exterior portions of each blade 126. Blades
126 may also include one or more depth of cut controllers (not
expressly shown) configured to control the depth of cut of cutting
elements 128. Blades 126 may further include one or more gage pads
(not expressly shown) located on blades 126. Drill bit 101 may have
many different designs, configurations, and/or dimensions according
to the particular application of drill bit 101.
[0022] Drilling system 100 may include additional or different
features, and the features of drilling system 100 may be arranged
as shown in FIG. 1, or in another suitable configuration.
[0023] FIG. 2 is a section view of a portion 200 of an exemplary
drill string containing a magnetic coupling. Drill string 103
includes one or more segments of drill pipe 116 whose inner
diameter defines throat 208. Turbine 202 is located within throat
208. Turbine 202 may be a motor or any apparatus that produces
rotational motion. For example, turbine 202 as illustrated in FIG.
2 is an axial flow turbine including an impeller located in throat
208 of drill pipe 116 and configured to capture the kinetic energy
of drilling fluid flow to produce rotational motion. Turbine 202
has several blades 204 distributed around the periphery and angled
relative to the axis of drill pipe 116. Although turbine 202 is
illustrated in FIG. 2 as an axial flow turbine, turbine 202 may
include a transverse-flow turbine in which fluid flow through the
turbine is substantially perpendicular to the rotational axis of
the impeller. Turbine 202 is coupled to drive shaft 210, which runs
parallel to axis 226 of throat 208. Drive shaft 210 is coupled to
drive array 222 of magnetic coupling 220.
[0024] Magnetic coupling 220 includes drive array 222 and follower
array 224, separated by barrier 230. Each of drive array 222 and
follower array 224 includes an annular array of magnetic sections,
which may include permanent magnets or electromagnetic coils,
arranged in a Halbach array. In a Halbach array, sections of the
array that produce a magnetic flux oriented normal to the surface
of the array alternate with sections that produce a magnetic flux
oriented transverse to the surface of the array. As a result of
this arrangement of magnetic fluxes, the magnetic field between
drive array 222 and follower array 224 is stronger than using only
array sections that produce fluxes normal to the surface. As a
result, magnetic coupling 220 is capable of transferring higher
levels of torque.
[0025] As illustrated in FIG. 2, magnetic coupling 220 is an axial
coupling, in which the two arrays are of substantially similar
diameter. Specifically, drive array 222 includes an annular array
of diameter 221, with the magnetic sections arranged in a circle
about axis of rotation 226. Follower array 224 also includes an
annular array of diameter 221, with the magnetic sections arranged
in a circle about axis of rotation 226. Drive array 222 and
follower array 224 are coupled by magnetic field 228, which
penetrates barrier 230. The arrangement of magnetic sections and
magnetic fields in drive array 222 and follower array 224 is
described in more detail in connection with FIG. 3 below.
[0026] Follower array 224 is coupled to follower shaft 240.
Follower shaft 240 is coupled to load 250, for example an
electrical generator.
[0027] Load enclosure 252 encloses follower array 224, follower
shaft 240, and load 250. Barrier 230, located between drive array
222 and follower array 224, separates drilling fluid in throat 208
from oil, air, or other suitable non-conductive media within load
enclosure 252. Magnetic field 228 between drive array 222 and
follower array 224 penetrates barrier 230 to couple the two arrays.
Barrier 230 may be coupled to the interior surface of drill pipe
116 by stays 232, so that barrier 230 does not rotate with drive
array 222 or follower array 224. Barrier 230 may be composed of a
variety of materials in one or more layers. For example, Barrier
230 may include one or more layers of ceramic, polymers or
thermoplastics such as polyether ether ketone (PEEK), composites
such as fiberglass, or other suitable materials. In some
embodiments, the surface of barrier 230 in contact with drilling
fluid includes a layer of titanium, which is resistant to erosion
from the flow of drilling fluid. The layer of titanium included in
barrier 230 may be very thin to limit the strength of eddy currents
that are induced in the titanium layer by the changing magnetic
flux produced by the motion of drive array 222 and follower array
224 relative to barrier 230.
[0028] Although turbine 202 is illustrated in FIG. 2 as being
located uphole from magnetic coupling 220 and load 250, these
components of portion 200 may be located in any suitable
arrangement. For example, turbine 202 may be located downhole from
magnetic coupling 220 and load 250. As another example, turbine 202
may be located outside the outer diameter of drive array 222.
[0029] In operation, drilling fluid flows through throat 208 in the
direction indicated by arrow 205. As it flows, the drilling fluid
contacts blades 204 of turbine 202. Because blades 204 are angled
with respect to the flow of drilling fluid, the drilling fluid
pushes against blades 204 and causes turbine 202 to spin, producing
rotational motion. This rotational motion is transferred to drive
array 222 by drive shaft 210. Because drive array 222 is
magnetically coupled to follower array 224 of magnetic coupling 220
by magnetic field 228, the rotational motion of drive array 222 is
transferred to follower array 224 across barrier 230. Follower
array 224 is coupled to load 250 through follower shaft 240. As a
result, the rotational motion produced by turbine 202 is
transmitted to load 250.
[0030] Load 250, located within load enclosure 252, utilizes the
rotational motion of follower shaft 240. In some embodiments, load
250 may be a generator that transforms the rotational motion of
follower shaft 240 into electrical current. For example, load 250
may be a permanent magnet alternating current generator, a
transverse flux generator, a radial flux generator, an axial flux
generator, a direct current generator, an alternator, or any other
suitable type of generator. In some embodiments, load 250 may be a
pump that transforms the rotational motion of follower shaft 240
into reciprocal motion of one or more pistons through the use of a
swash plate. In some embodiments, load 250 may include an actuator
that transforms the rotational motion of follower shaft 240 into
linear motion, for example through the use of a ball screw.
Although the present disclosure discusses particular examples of
load 250, any suitable load that makes use of rotational motion of
follower shaft 240 may be used.
[0031] After drilling fluid passes turbine 202, it continues
through throat 208 and around barrier 230 into fluid passage 234.
For example, fluid passage 234 may be an annulus between barrier
230 and drill pipe 116. From fluid passage 234, drilling fluid
continues downhole toward drill bit 101, as discussed in connection
with FIG. 1.
[0032] In embodiments that include electromagnetic coils, the
current supplied to the electromagnetic coils may be tuned to vary
the amount of magnetic flux produced by each coil. In some
embodiments, the current supplied to the electromagnetic coils is
lower when follower array 224 and follower shaft 240 are turning
than when follower array 224 and follower shaft 240 are not
turning. For example, when drive shaft 210 first begins to rotate,
for example when turbine 202 is started, a large torque is
typically required to cause follower shaft 240 to begin rotating to
drive load 250. Under such circumstances, the power supplied to the
electromagnetic coils may be approximately 75% to 80% of the
maximum power P.sub.mx that can be provided to the electromagnetic
coils, allowing magnetic coupling 220 to transfer a large torque
without slipping. However, in normal operation, drive shaft 210 and
follower shaft 240 typically spin rapidly to drive load 250, but
only a low amount of torque is required to keep follower shaft 240
spinning at the desired high speed. As a result, the power supplied
to the electromagnetic coils may be reduced to approximately 40-50%
of P.sub.mx, saving electric power. In addition, in some
embodiments, reducing the power to the electromagnetic coils allows
magnetic coupling 220 to disengage when the torque applied to
magnetic coupling 220 is too high, protecting valuable components
on the far side of magnetic coupling 220. For example, some
embodiments of load 250 have a maximum rotational speed at which
they can safely operate. For example, in embodiments in which load
250 is an electric generator, the generator may be damaged if
operated at speeds higher than approximately 4000 revolutions per
minute (RPM). If drive shaft 210 approaches an unsafe rotational
speed, the amount of torque required to accelerate follower shaft
240 increases, exceeding the amount of torque that can be
transmitted by magnetic coupling 220 when supplied approximately
40-50% of P.sub.mx. As a result, magnetic coupling 220 may transmit
rotational motion when driven at a safe operational speed, but
disengage if driven at a higher, unsafe speed.
[0033] FIG. 3 is a perspective view of an exemplary axial magnetic
coupling 220. As described above in connection with FIG. 2, axial
magnetic coupling 220 includes drive array 222 and follower array
224, which are of approximately the same diameter, separated by
barrier 230. Drive array 222 includes an annular array of sections
310a through 310h, each of which includes a permanent magnet or
electromagnetic coil that produces a magnetic flux in a particular
direction. Similarly, follower array 224 includes an annular array
of sections 320a through 320h, each of which includes a permanent
magnet or electromagnetic coil that produces a magnetic flux in a
particular direction. Together, drive array 222 and follower array
224 produce a magnetic field oriented substantially parallel to
their common axis of rotation 226. The magnetic field penetrates
barrier 230 and couples drive array 222 to follower array 224.
[0034] Arrows 330 indicate the orientation of the magnetic flux
produced by each particular section 310a through 310h or 320a
through 320h. As illustrated, sections 310a through 310h are
arranged in a Halbach array, in which the sections alternate
between sections in which the magnetic flux is oriented normal to
the downhole surface of magnetic coupling 220, such as sections
310b and 310d, and sections in which the magnetic flux is oriented
transverse to such downhole surface, such as sections 310a and
310c. In addition, as illustrated, the orientation of the magnetic
flux in successive sections rotates in a consistent direction as
one proceeds around the annular array. For example, section 310b of
drive array 222 produces a magnetic flux oriented uphole and
substantially parallel to axis 226 of magnetic coupling 220, while
section 310d produces a magnetic flux oriented downhole and
substantially parallel to axis 226 of magnetic coupling 220. In the
alternating sections, for example, section 310a of drive array 222
produces a magnetic flux oriented transverse to axis 226, in a
clockwise direction when viewed from the uphole surface of drive
array 222, while section 310c of drive array 222 produces a
magnetic flux oriented transverse to axis 226, in a
counter-clockwise direction when viewed from the uphole surface of
drive array 222. This arrangement of magnetized sections with
rotating orientations increases the strength of the magnetic field
on one side of the array while decreasing or eliminating the
magnetic field on the other side of the array. In the embodiment
illustrated, the magnetic field of drive array 222 is enhanced on
the downhole face of drive array 222, which faces follower array
224.
[0035] Sections 320a through 320h of follower array 224 are also
arranged in a Halbach array, but in follower array 224 the
direction in which the orientation of the magnetic flux in
successive sections rotates is opposite to that in drive array 222.
For example, in section 320b, the magnetic flux is oriented uphole
and substantially parallel to axis 226 of magnetic coupling 220, as
it is in the corresponding section 310b of drive array 222. By
contrast, in section 320c, the magnetic flux is oriented transverse
to axis 226, in a clockwise direction when viewed from the uphole
surface of follower array 224, which is in the opposite direction
from that of corresponding section 310c of drive array 222. As a
result, the magnetic field of follower array 224 is enhanced on the
uphole face of follower array 224, which faces drive array 222.
[0036] As a result of the enhancement of the magnetic fields on the
facing surfaces of drive array 222 and follower array 224, the
maximum amount of torque transmitted through magnetic coupling 220
is increased. For example, in embodiments in which the magnetic
field is substantially eliminated on the non-facing sides of each
array, the maximum amount of torque transmitted through magnetic
coupling 220 may be approximately doubled.
[0037] In some embodiments, sections 310a through 310h of drive
array 222 and sections 320a through 320h of follower array 224
include permanent magnets. Because the temperature within wellbore
114 can be high, the permanent magnets may include a material with
a high magnetic coercivity, but whose magnetic flux density changes
very little or not at all with increases in temperature. In
particular, the permanent magnets may have a high temperature
coefficient of residual flux (Br) and intrinsic coercivity (Hcl)
such as a Br and/or Hcl greater than -0.05%/C and -0.25%/C
respectively. These materials exhibit little change to temperature,
which makes them suitable for downhole applications. For example,
the permanent magnets in drive array 222 or follower array 224 may
include samarium cobalt.
[0038] In some embodiments drive array 222 or follower array 224
include electromagnetic coils, which produce the desired magnetic
flux when energized. For example, in the embodiment illustrated in
FIG. 3, follower array 224 includes electromagnetic coils in
sections 320a through 320h. Such electromagnetic coils may include
cores that include steel or other ferrous materials to increase the
magnetic flux produced by the coils.
[0039] In some embodiments, follower array 224 may include a slip
ring (not shown) that includes conductive material located on a
surface of follower array 224. For example, a slip ring may be
located on downhole surface 350 of follower array 224. The slip
ring may be in electrical contact with a brush (not shown) that
provides electrical current to energize electromagnetic coils in
sections 320a through 320h of follower array 224. A second slip
ring and brush may be used to provide a return path for the
electrical current. In such embodiments, the slip rings and brushes
cannot be immersed in a conductive fluid, such as drilling fluid,
because the conductive fluid would create a short circuit between
the brushes and prevent current from reaching and energizing the
electromagnetic coils. As a result, such embodiments include
barrier 230 to prevent drilling fluid from coming into contact with
the slip rings and brushes.
[0040] Although FIG. 3 illustrates an axial magnetic coupling that
include a particular number of sections 310a through 310h of drive
array 222 and sections 320a through 320h of follower array 224, any
suitable number of sections may be used. For example, in some
embodiments, drive array 222 and follower array 224 may each
include sixteen sections. Furthermore, although barrier 230 is
illustrated in FIGS. 2 and 3 as enclosing follower array 224,
follower shaft 240, and load 250, barrier 230 may be arranged in
any suitable fashion. For example, in some embodiments, barrier 230
encloses drive array 222 and drive shaft 210.
[0041] Although FIGS. 2 and 3 illustrate magnetic coupling 220 as
an axial magnetic coupling, in which drive array 222 and follower
array 224 are of substantially similar diameter and magnetic field
228 between drive array 222 and follower array 224 is substantially
parallel to the arrays' axis of rotation 226, any suitable
arrangement of arrays 222 and 224 and field 228 may be used. For
example, in some embodiments, magnetic coupling 220 is a radial
magnetic coupling, in which follower array 224 is of substantially
smaller diameter and is placed within the inner diameter of drive
array 222. Alternatively, drive array 222 may be of substantially
smaller diameter and is placed within the inner diameter of
follower array 224. FIGS. 4-5, discussed in more detail below,
illustrate an exemplary radial magnetic coupling.
[0042] FIG. 4 is an elevation section view of an exemplary radial
magnetic coupling 400 that may be used in place of axial magnetic
coupling 220. Radial magnetic coupling 400 includes drive array 422
and follower array 424 separated by barrier 230. Unlike in the
arrays in axial magnetic coupling 220, which have a substantially
similar diameter, the arrays in radial magnetic coupling 400 are of
unequal size, with one located within the other. For example, drive
array 422 in radial magnetic coupling 400 may have an inner
diameter larger than the outer diameter of follower array 424.
Furthermore, follower array 424 may be located within the inner
diameter of drive array 422, with drive array 422 and follower
array 424 sharing a common axis of rotation 226. Although FIG. 4
illustrates drive array 422 having the larger diameter and follower
array 424 as located within the inner diameter of drive array 422,
any other suitable radial arrangement of the arrays may be used.
For example, follower array 424 may have an inner diameter larger
than the outer diameter of drive array 422, and drive array 422 may
be located within the inner diameter of follower array 424.
[0043] As with axial magnetic coupling 220, drive array 422
includes an annular array of sections, each of which includes a
permanent magnet or electromagnetic coil that produces a magnetic
flux in a particular direction to form a Halbach array. Similarly,
follower array 424 includes an annular array of sections, each of
which includes a permanent magnet or electromagnetic coil that
produces a magnetic flux in a particular direction to form a
Halbach array. The arrangement of magnets or electromagnetic coils
in drive array 422 and follower array 424 described in more detail
in connection with FIG. 5 below
[0044] In some embodiments, drive array 422 and follower array 224
include permanent magnets. Because the temperature within wellbore
114 can be high, the permanent magnets may include materials with a
high magnetic coercivity, but whose magnetic flux density changes
very little or not at all with increases in temperature. In
particular, the permanent magnets may have a high temperature
coefficient of residual flux (Br) and intrinsic coercivity (Hcl)
such as a Br and/or Hcl greater than -0.05%/C and -0.25%/C
respectively. These materials exhibit little change to temperature,
which makes them suitable for downhole applications. For example,
the permanent magnets in drive array 422 or follower array 424 may
include samarium cobalt.
[0045] In some embodiments drive array 422 or follower array 424
include electromagnetic coils, which produce the desired magnetic
flux when energized. For example, in the embodiment illustrated in
FIG. 4, follower array 424 may include electromagnetic coils in
sections 420a through 420h. Such electromagnetic coils may include
cores that include steel or other ferrous materials to increase the
magnetic flux produced by the coils.
[0046] In some embodiments, follower array 424 includes a slip ring
(not shown) that includes conductive material located on a surface
of follower array 424. For example, a slip ring may be located on
downhole surface 450 of follower array 424. The slip ring may be in
electrical contact with a brush (not shown) that provides
electrical current to energize electromagnetic coils in sections
420a through 420h of follower array 424. A second slip ring and
brush may be used to provide a return path for the electrical
current. In such embodiments, the slip rings and brushes cannot be
immersed in a conductive fluid, such as drilling fluid, because the
conductive fluid would create a short circuit between the brushes
and prevent current from reaching and energizing the
electromagnetic coils. As a result, such embodiments include
barrier 230 to prevent drilling fluid from coming into contact with
the slip rings and brushes.
[0047] Although barrier 230 is illustrated in FIG. 4 as enclosing
follower array 424 and follower shaft 240, barrier 230 may be
arranged in any suitable fashion. For example, in some embodiments,
barrier 230 encloses drive array 422 and drive shaft 210.
[0048] FIG. 5 is a plan section view of exemplary radial magnetic
coupling 400, cut along line A in FIG. 4.
[0049] Drive array 422 includes an annular array of sections 510a
through 510h, each of which includes a permanent magnet or
electromagnetic coil that produces a magnetic flux in a particular
direction. Similarly, follower array 424 includes an annular array
of sections 520a through 520h, each of which includes a permanent
magnet or electromagnetic coil that produces a magnetic flux in a
particular direction. Together, drive array 422 and follower array
424 produce a magnetic field oriented substantially perpendicular
to their common axis of rotation 226. The magnetic field penetrates
barrier 230 and couples drive array 422 to follower array 424.
[0050] Arrows 530 indicate the orientation of the magnetic flux
produced by each particular section 510a through 510h or 520a
through 520h. As illustrated, sections 510a through 510h are
arranged in a Halbach array, in which the sections alternate
between sections in which the magnetic flux is oriented normal to
the inner surface of drive array 422, such as sections 510b and
510d, and sections in which the magnetic flux is oriented
transverse to such inner surface, such as sections 510a and 510c.
In addition, as illustrated, the orientation of the magnetic flux
in successive sections rotates in a consistent direction as one
proceeds around the annular array. For example, sections 510b and
510f of drive array 422 each produce a magnetic flux oriented
inward toward axis 226, while sections 510d and 510h each produce a
magnetic flux oriented outward away from axis 226. In the
alternating sections, for example, sections 510a and 510e of drive
array 422 each produce a magnetic flux oriented transverse to axis
226, in a counter-clockwise direction when viewed from the uphole
surface of drive array 422, while sections 510c and 510g of drive
array 422 each produce a magnetic flux oriented transverse to axis
226, in a clockwise direction when viewed from the uphole surface
of drive array 422. This arrangement of magnetized sections with
rotating orientations increases the strength of the magnetic field
on one side of the array while decreasing or eliminating the
magnetic field on the other side of the array. In the embodiment
illustrated, the magnetic field of drive array 422 is enhanced on
the inner surface of drive array 422, which faces the outer surface
of follower array 424.
[0051] Sections 520a through 520h of follower array 224 are also
arranged in a Halbach array, but here the direction in which the
orientation of the magnetic flux in successive sections rotates is
opposite to that in drive array 222. For example, in sections 520b
and 520f, the magnetic flux is oriented inward toward axis 226, as
it is in the corresponding sections 510b and 520f of drive array
422. By contrast, in section 520c, the magnetic flux is oriented
transverse to axis 226, in a counter-clockwise direction when
viewed from the uphole surface of follower array 424, which is in
the opposite direction from that of corresponding section 510c of
drive array 422. As a result, the magnetic field of follower array
224 is enhanced on the outer surface of follower array 424, which
faces the inner surface of drive array 422.
[0052] In normal operation, the electrical current required to
energize electromagnetic coils in a magnetic coupling may be
provided by load which is driven by the coupling. For example, load
250, discussed in connection with FIG. 2, may include an electrical
generator. The generator may provide current to energize
electromagnetic coils in follower array 224, discussed in
connection with FIGS. 2 and 3. However, before magnetic coupling
220, discussed in connection with FIGS. 2 and 3, begins to turn,
the generator may produce no electrical current. As a result, a
separate power source is used to initially energize the
electromagnetic coils until a normal operating speed is
reached.
[0053] FIG. 6 is a circuit diagram of an exemplary bootstrap
circuit for energizing electromagnetic coils in a magnetic
coupling. For example, bootstrap circuit 600 may be used to
energize electromagnetic coils in follower array 224, discussed in
connection with FIGS. 2 and 3, or in follower array 424, discussed
in connection with FIGS. 4 and 5. In the embodiment illustrated in
FIG. 6, electromagnetic coils are present in follower array 424 of
magnetic coupling 400. Circuit 600 allows a battery to initially
energize the electromagnetic coils in follower array 424 before
magnetic coupling 400 begins to turn, then allow a separate power
source, such as a generator or alternator powered by the motion of
follower array 424, to sustain the electromagnetic coils during
normal operation.
[0054] Circuit 600 includes battery 610, which is electrically
coupled to direct current to direct current (DC/DC) converter 620
through switch 612. The positive terminal of DC/DC converter 620 is
electrically coupled to magnetic coupling 400 through node 622,
diode 630, and node 626. The negative terminal of DC/DC converter
620 is electrically coupled to magnetic coupling 400 through node
624.
[0055] Circuit 600 also includes alternating current (AC) source
640. In some embodiments, AC source 640 is coupled through follower
shaft 240 (not shown) to follower array 424, discussed in
connection with FIGS. 4 and 5. For example, load 250, discussed in
connection with FIG. 2, may include AC source 640. Current source
640 transforms the rotational motion of follower shaft 240 into
electrical current. In some embodiments, AC source 640 is a
generator, as discussed in connection with load 250 in FIG. 2. AC
source 640 is electrically coupled to AC/DC converter 650, which in
turn is electrically coupled to DC/DC converter 660. The positive
terminal of DC/DC converter 620 is electrically coupled to magnetic
coupling 400 through node 662, diode 670, and node 626. The
negative terminal of DC/DC converter 660 is electrically coupled to
magnetic coupling 400 through node 664.
[0056] In operation, battery 610 supplies initial power to the
electromagnetic coils in follower array 424 before magnetic
coupling 400 begins to turn. When drive array 422 first begins to
turn, switch 612 is closed, permitting current to flow from battery
610 to power electronics such as direct current to direct current
(DC/DC) converter 620. DC/DC converter 620 produces a voltage
V.sub.batt at node 622 relative to node 624. As a result, current
flows from node 622 through diode 630 to node 626, through one or
more electromagnetic coils in follower array 424, energizing the
coils, through node 624 and back to DC/DC converter 620. As a
result of the current flow through the coils, follower array 424
magnetically couples to drive array 422 and thereby begins to turn
in conjunction with drive array 422, turning follower shaft 240
(not shown).
[0057] When follower shaft 240 is turning, it supplies rotational
motion to load 250, which may include AC source 640. AC source 640
transforms the rotational motion of follower shaft 240 into
electrical current. AC source 640 supplies an alternating current
to AC/DC converter 650. AC/DC converter 650 in turn supplies a
direct current to DC/DC converter 660. DC/DC converter 660 produces
a voltage V.sub.gen at node 662 relative to node 664. When AC
source 640 is spinning sufficiently rapidly, DC/DC converter 660
may supply sufficient current that V.sub.gen exceeds V.sub.batt. As
a result, current flows from node 662 through diode 670 to node
626, through one or more electromagnetic coils in follower array
424, energizing the coils, through node 664 and back to DC/DC
converter 660. At this point, current from battery 610 is no longer
used to energize the coils, and switch 612 may be opened.
[0058] Although FIG. 6 illustrates circuit 600 including a radial
magnetic coupling, any suitable magnetic coupling may be used. For
example, an axial magnetic coupling such as magnetic coupling 220,
discussed in connection with FIGS. 2 and 3, may be used in place of
magnetic coupling 400.
[0059] FIG. 7 is a flow chart of an exemplary method 700 for
bootstrapping a magnetic coupling.
[0060] Method 700 may begin at step 710, in which current is
supplied from a battery to an electromagnetic coil in a magnetic
coupling. For example, as discussed above in connection with FIG.
6, when switch 612 is closed, battery 610 provides current to an
electromagnetic coil in follower array 424 of magnetic coupling 400
through DC/DC converter 620, diode 630, and nodes 622, 624, and
626.
[0061] In step 720, the drive array and follower arrays in the
magnetic coupling are coupled using the electromagnetic coil. As a
result of the current flow supplied in step 710, the
electromagnetic coil in the magnetic coupling is energized and
produces a magnetic field. For example, the electromagnetic coil in
follower array 424 produces a field as described above in
connection with FIGS. 5 and 6. This magnetic field (in conjunction
with the field produced by magnetic sections in drive array 422)
couples drive array 422 and follower array 424.
[0062] In step 730, rotational motion is transferred to an AC
source using the magnetic coupling. For example, rotational motion
from turbine 202, discussed with reference to FIG. 2, may be
transferred to load 250 using drive shaft 210, magnetic coupling
400, and follower shaft 240. As discussed above in connection with
FIG. 6, load 250 may include AC source 640, which transforms that
rotational motion into electrical current.
[0063] In step 740, current is supplied from the AC source to the
electromagnetic coil. For example, as discussed above in connection
with FIG. 6, AC source 640 provides current to the electromagnetic
coil in follower array 424 through AC/DC converter 650, DC/DC
converter 660, diode 670, and nodes 662, 664, and 666.
[0064] In step 750, the battery stops supplying current to the
electromagnetic coil. For example, as discussed above in connection
with FIG. 6, once follower shaft 240 is spinning sufficiently
rapidly, AC source 640 supplies sufficient current to energize the
electromagnetic coils in follower array 424. As a result, battery
610 is disconnected by opening switch 612.
[0065] Modifications, additions, or omissions may be made to method
700 without departing from the scope of the present disclosure. For
example, the order of the steps may be performed in a different
manner than that described and some steps may be performed at the
same time. Additionally, each individual step may include
additional steps without departing from the scope of the present
disclosure.
[0066] Embodiments disclosed herein include:
[0067] A. A magnetic coupling of a downhole tool that includes (a)
a first annular array of magnetic sections; (b) a second annular
array of magnetic sections coupled to the first annular array by a
magnetic field that transfers rotational motion from the first
annular array to the second annular array, and (c) a barrier
disposed between the first annular array and the second annular
array, the barrier including an erosion-resistant layer.
[0068] B. A drilling system that includes (a) a drill string; and
(b) a magnetic coupling located within the drill string, in which
the magnetic coupling includes (c) a first annular array of
magnetic sections, (d) a second annular array of magnetic sections
coupled to the first annular array by a magnetic field that
transfers rotational motion from the first annular array to the
second annular array, and (e) a barrier disposed between the first
annular array and the second annular array, the barrier having an
erosion-resistant layer; (f) a motor coupled to the first annular
array; and (g) a load coupled to the second annular array.
[0069] C. A method of bootstrapping a magnetic coupling of a
downhole tool that includes (a) rotating a first annular array of
magnetic sections in a magnetic coupling; (b) supplying current
from a battery to an electromagnetic coil located within a second
annular array of magnetic sections in the magnetic coupling; (c)
coupling the first annular array to the second annular array using
a magnetic field produced by the electromagnetic coil; (d)
transferring rotational motion from the first annular array to the
second annular array using the magnetic field; (e) transferring
rotational motion from the second annular array to an alternating
current (AC) source configured to transform rotational motion into
electrical current; and (f) supplying electrical current from the
AC source to the electromagnetic coil.
[0070] Each of embodiments A, B, and C may have one or more of the
following additional elements in any combination. Element 1: the
first annular array has a first outer diameter; the second annular
array has a second outer diameter approximately equal to the first
outer diameter; the first annular array and the second annular
array are configured to rotate about a common axis of rotation; and
the magnetic field is oriented approximately parallel to the common
axis of rotation. Element 2: the first annular array has an inner
diameter; the second annular array has an outer diameter smaller
than the inner diameter; the second annular array is disposed
within the inner diameter of the first annular array; the first
annular array and the second annular array are configured to rotate
about a common axis of rotation; and the magnetic field is oriented
approximately perpendicular to the common axis of rotation. Element
3: wherein the erosion-resistant layer includes a layer of
titanium. Element 4: wherein the second annular array comprises a
plurality of permanent magnets. Element 5: wherein a magnet among
the plurality of permanent magnets is a samarium cobalt magnet.
Element 6: wherein the second annular array comprises a plurality
of electromagnetic coils. Element 7: further comprising a bootstrap
circuit for energizing the plurality of electromagnetic coils, the
bootstrap circuit including (a) a battery; and (b) a first diode
coupled to the battery, the first diode permitting the battery to
supply electrical current to the plurality of electromagnetic
coils. Element 8: the bootstrap circuit further including (c) a
current source coupled to the second annular array, the current
source configured to transform rotation of the second annular array
into electrical current; and (d) a second diode coupled to the
current source, the second diode permitting the current source to
supply electrical current to the plurality of electromagnetic
coils. Element 9: wherein the magnetic coupling includes a barrier
disposed between the first annular array and the second annular
array, the barrier including an erosion-resistant layer.
[0071] Although the present disclosure and its advantages have been
described in detail, it should be understood that various changes,
substitutions and alterations can be made herein without departing
from the spirit and scope of the disclosure as defined by the
following claims.
* * * * *