U.S. patent application number 10/878242 was filed with the patent office on 2005-12-29 for downhole transmission system comprising a coaxial capacitor.
Invention is credited to Bartholomew, David B., Hall, David R., Hall, H. Tracy JR., Johnson, Monte L., Pixton, David S., Rawle, Michael.
Application Number | 20050285706 10/878242 |
Document ID | / |
Family ID | 35505072 |
Filed Date | 2005-12-29 |
United States Patent
Application |
20050285706 |
Kind Code |
A1 |
Hall, David R. ; et
al. |
December 29, 2005 |
Downhole transmission system comprising a coaxial capacitor
Abstract
A transmission system in a downhole component comprises a
plurality of data transmission elements. A coaxial cable having an
inner conductor and an outer conductor is disposed within a passage
in the downhole component such that at least one capacitor is
disposed in the passage and having a first terminal coupled to the
inner conductor and a second terminal coupled to the outer
conductor. Preferably the transmission element comprises an
electrically conducting coil. Preferably, within the passage a
connector is adapted to electrically connect the inner conductor of
the coaxial cable and the lead wire. The coaxial capacitor may be
disposed between and in electrically communication with the
connector and the passage. In another embodiment a connector is
adapted to electrical connect a first and a second portion of the
inner conductor of the coaxial cable and a coaxial capacitor is in
electrical communication with the connector and the passage.
Inventors: |
Hall, David R.; (Provo,
UT) ; Pixton, David S.; (Lehi, UT) ; Johnson,
Monte L.; (Orem, UT) ; Bartholomew, David B.;
(Springville, UT) ; Hall, H. Tracy JR.; (Provo,
UT) ; Rawle, Michael; (Springville, UT) |
Correspondence
Address: |
David R. Hall
2185 S. Larsen Pkwy.
Provo
UT
84606
US
|
Family ID: |
35505072 |
Appl. No.: |
10/878242 |
Filed: |
June 28, 2004 |
Current U.S.
Class: |
336/132 |
Current CPC
Class: |
F16L 25/01 20130101;
H04B 5/0012 20130101; H01R 2103/00 20130101; H01R 13/005 20130101;
H01R 13/533 20130101; E21B 47/13 20200501; H04B 5/0018 20130101;
H01R 24/40 20130101; E21B 17/028 20130101 |
Class at
Publication: |
336/132 |
International
Class: |
H01F 021/06 |
Goverment Interests
[0001] This invention was made with government support under
contract number No. DE-FC26-01NT41229 awarded by the Department of
Energy. The government has certain rights in this invention.
Claims
What is claimed:
1. A transmission system in a downhole component, comprising: a
plurality of data transmission elements connected by a coaxial
cable; the coaxial cable having an inner conductor and an outer
conductor disposed within a passage in the downhole component; at
least one capacitor disposed in the passage and having a first
terminal coupled to the inner conductor and a second terminal
coupled to the outer conductor.
2. The transmission system of claim 1 wherein the transmission
elements comprises a lead wire extending from a coil.
3. The transmission system of claim 2 wherein the system further
comprises a connector adapted to electrically connect the inner
conductor of the coaxial cable and the lead wire.
4. The transmission system of claim 1 wherein the system further
comprises a connector adapted to electrically connect the first and
second portions of the inner conductor.
5. The transmission system of claim 1 wherein the capacitor
displaces a portion of dielectric material within the coaxial
cable.
6. A transmission system in a downhole component, comprising: a
plurality of data transmission elements wherein each data
transmission element comprises an electrically conducting coil, a
lead wire on at least one coil; a coaxial cable disposed within a
passage in the downhole component; and a connector adapted to
electrically connect an inner conductor of the coaxial cable and
the lead wire; and a coaxial capacitor disposed between and in
electrical communication with the connector and the passage.
7. The transmission system according to claim 6, wherein the
transmission element comprises an anti-rotation device coaxially
mounted on the lead wire for preventing the electrically conducting
coil to rotate about the axis of the lead wire.
8. The transmission system according to claim 6, wherein the data
transmission element comprises electrical contacts adapted to be in
electrical communication with an adjacent transmission element in
an adjacent downhole component.
9. The transmission system according to claim 6, wherein the data
transmission element comprises an inductive coupler adapted to be
in magnetic communication with an adjacent transmission element in
an adjacent downhole component.
10. The transmission system according to claim 9, wherein the
inductive coupler houses the electrically conducting coil in MCEI
material.
11. The transmission system according to claim 10, wherein the MCE
material is ferrite.
12. The transmission system according to claim 6, wherein the
passage is formed in the downhole component.
13. The transmission system according to claim 6, wherein the
passage is a metal tube.
14. The transmission system according to claim 6, wherein the
passage is an outer conductor of the coaxial cable.
15. The transmission system according to claim 6, wherein the
connector is comprised of a signal section.
16. The transmission system according to claim 6, wherein the
connector is comprised of at least two sections.
17. The transmission system according to claim 16, wherein the at
least two sections are separated by a spacer.
18. The transmission system according to claim 6, wherein the
connector is at least partially electrically insulated.
19. The transmission system according to claim 6, wherein the
capacitor comprises at least one electrically conducting spacer in
electrical communication with the passage.
20. The transmission system according to claim 6, wherein the
transmission system comprises a sealing assembly.
21. The transmission system according to claim 20, wherein the
sealing assembly is axial mounted around the lead wire.
22. A transmission system in a downhole component, comprising: a
plurality of data transmission elements; a coaxial cable, disposed
within a passage in the downhole component, comprising a first and
a second portion of an inner conductor; a connector adapted to
electrically connect the first and second portions of the inner
conductor wherein a coaxial capacitor is disposed between and in
electrical communication with the connector and the passage;
wherein the first portion is in electrical communication with a
first data transmission element, and the second portion is in
electrical communication with a second transmission element.
23. The transmission system according to claim 22, wherein the
transmission system comprises at least one inductor located on
either side of the coaxial capacitor.
24. The transmission system according to claim 22, wherein the
transmission element comprises an anti-rotation device coaxially
mounted on the lead wire for preventing an electrically conducting
coil to rotate about the axis of the lead wire.
25. The transmission system according to claim 22, wherein the data
transmission element comprises a direct electrical coupler.
26. The transmission system according to claim 22, wherein the data
transmission element comprises an inductive coupler.
27. The transmission system according to claim 26, wherein the
inductive coupler houses an electrically conducting coil in MCEI
material.
28. The transmission system according to claim 27, wherein the MCEI
material is ferrite.
29. The transmission system according to claim 22, wherein the
transmission system further comprises a sealing assembly mounted
axial around the lead wire.
30. The transmission system according to claim 22, wherein the
passage is formed in the downhole component.
31. The transmission system according to claim 22, wherein the
passage is a metal tube.
32. The transmission system according to claim 22, wherein the
passage is an outer conductor of the coaxial cable.
33. The transmission system according to claim 22, wherein the
connector is comprised of a signal section.
34. The transmission system according to claim 22, wherein the
connector is comprised of at least two sections.
35. The transmission system according to claim 34, wherein the at
least two sections are separated by a spacer.
36. The transmission system according to claim 22, wherein the
connector is at least partially electrically insulated.
37. The transmission system according to claim 22, wherein the
coaxial capacitor is axially mounted to the connector.
38. The transmission system according to claim 22, wherein the
capacitor comprises at least one electrically conducting spacer in
electrical communication with the passage.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0002] None
BACKGROUND
[0003] This invention relates to transmission systems in downhole
components, more specifically to transmission systems comprising
capacitors. U.S. Pat. No. 6,670,880, which is herein incorporated
by reference, discloses a downhole transmission system through a
string of downhole components. A first transmission element is
located in one end of each downhole component, which includes a
first magnetically-conductive, electrically-insulating trough, and
a first electrically conductive coil lying therein. A second data
transmission element is located in the other end, with a similar
arrangement comprising a second magnetically-conductive,
electrically-insulating trough and a second electrically conductive
coil. The transmission system further comprises an electrical
conductor in electrical communication with and running between each
first and second coil in the downhole component. The string of
downhole components is cooperatively arranged such that the
components are in magnetic communication with each other and
transmit signals through induction. Each downhole component
comprises electrical characteristics such as impedance, reactance,
capacitance and inductance.
[0004] Downhole tool strings may comprise components of different
lengths. Some components are tools and others may be pipes.
Depending on the function of the components, the length may vary.
Many of the electrical characteristics of the component are
dependent on the physical dimensions of the electrical conductor
connecting the transmission elements, such as length and diameter.
Impedance reflections may create noise between two conductors of
different impedances, which result in signal loss and
attenuation.
[0005] U.S. Pat. No. 2,414,719 assigned to Cloud, discloses a
conduit for transmitting both fluids and pulsating electrical
energy. The conduit comprises a plurality of pipe sections joined
at each end, an insulated conductor extending along the conduit,
and magnetic coupling means at a joint between two of the pipes for
transmitting the electrical energy across the joint. The conduit
further comprises a condenser and in one aspect a coil in the
magnetic coupling means. The condenser, coil, and insulated
conductor produce a circuit which passes only a selected band of
frequencies whereby extraneous noises will not be transmitted along
the conductor. FIGS. 8 and 9 of the '719 patent show a box
comprising a condenser attached to a terminal of a coil, while
another terminal connects the condenser to armored cable. The
armored cable is attached to the box by fasteners. In this
specification the term capacitor and condenser are considered
equivalent.
[0006] U.S. Pat. No. 6,587,054 discloses an electrical submersible
pump cable having an integral capacitor. The electrical submersible
pump cable has a primary conductor with an insulator surrounding
the primary conductor. A coaxial conductive layer surrounds the
insulator, wherein the insulator serves as a dielectric between the
primary conductor and the coaxial conductive layer. The coaxial
conductive layer and primary conductor enable the coupling of data
information onto and off of the cable.
[0007] U.S. Pat. No. 3,753,294 discloses a method and an apparatus,
wherein the distributed capacitance between a conductor and the
outer metallic armor of a cable is measured to enable a
determination of the instantaneous changes in position of a tool
supported by an elastic cable in a borehole. The correction
calculated from the capacitance measurement is used to correct
cable length measurements derived from a measure wheel which
engages and rotates with movement of the cable.
[0008] It should be noted that the term "magnetically-conducting,
electrically-insulating material" will be referred to in the rest
of the specification as MCEI material.
SUMMARY OF THE INVENTION
[0009] This invention is a transmission system for a string
downhole components, including drill pipe and tools that make up a
drill string. The transmission system comprises a plurality of data
transmission elements joined by one or more coaxial cables, each
having a dielectric material intermediate an inner conductor and an
outer conductor. The transmission system further comprises at least
one capacitor in communication with at least one of the coaxial
cables. The one or more coaxial cables are disposed within a
passage in the downhole component. At least one capacitor is also
disposed in at least one of the passages of the downhole component,
having a first terminal coupled to the inner conductor and a second
terminal coupled to the outer conductor the coaxial cable.
[0010] An embodiment of the present invention comprises a coaxial
capacitor.
[0011] In one embodiment of the present invention, the passage is
formed in at least a portion of a wall of the downhole
component.
[0012] In another embodiment of the present invention, the passage
is a metal conduit at least partially disposed within the passage
formed in at least a portion of the wall of the downhole
component.
[0013] In one embodiment of the present invention, the capacitor
displaces a portion of dielectric material of the coaxial
cable.
[0014] In another embodiment of the present invention, the
capacitor is disposed between the outside wall of the metal conduit
and inside wall of the passage formed in the wall of the downhole
component.
[0015] Each data transmission element comprises an electrically
conducting coil having a lead wire. A connector is adapted to
electrically connect the inner conductor and the lead wire. In
another embodiment, the capacitor is disposed between and in
electrical communication with the connector and the passage.
[0016] In a preferred embodiment of the invention, the transmission
system comprises an inductive coupler. The inductive coupler may
house the electrical conducting coil of magnetically-conducting,
electrically-insulating material. Preferably, the
magnetically-conducting- , electrically-insulating material is
ferrite or a laminate of conductor and insulators. In some
embodiments of the present invention the data transmission elements
comprise direct electrical couplers and in other embodiments of the
invention, the transmission elements comprise inductive couplers.
The transmission element comprises an anti-rotation device. The
transmission system may comprise a sealing assembly. Preferably the
sealing assembly is axially mounted around the lead wire.
[0017] In the preferred embodiment the downhole component forms a
part of a downhole tool string, or drill string. In other aspects
of the invention, the downhole tool string is part of a production
well. The downhole component may be a downhole tool, including a
drill pipe.
[0018] In an embodiment of the invention, the coaxial connector is
comprised of one or more sections comprising at least one
electrically conducting spacers in electrical communication with
the passage.
[0019] In another embodiment, the transmission system comprises
first and second transmission elements connected by a coaxial cable
comprising first and second portions of an inner conductor. The
first and second portions of the inner conductor are respectively
in electrical communication with first and second transmission
elements. A connector is adapted to electrically connect the first
and second portions of the inner conductor, and a coaxial capacitor
is disposed between and in electrical communication with the
connector and the passage.
[0020] It is believed that downhole components of different lengths
may produce different impedances, which result in impedance
reflections during signal transmission. It is believed that the
reflections result in signal loss and attenuation. It is believed
that the advantage of a coaxial capacitor in the transmission
system may help match impedances of downhole components of
different lengths.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] FIG. 1 is a schematic view of a downhole tool string.
[0022] FIG. 2 is a perspective cross section of an embodiment of
downhole components.
[0023] FIG. 3 is a perspective view of section of a transmission
element according to an embodiment of the present invention.
[0024] FIG. 4 is a schematic view an embodiment of a downhole
component according to an embodiment of the present invention.
[0025] FIG. 5 is a perspective cut-away of an embodiment of a
downhole component according to an embodiment of the present
invention.
[0026] FIG. 6 is a perspective cross section of an embodiment of a
capacitor assembly according to an embodiment of the present
invention.
[0027] FIG. 7 is a cross section of an embodiment of a capacitor
assembly according to an embodiment of the present invention.
[0028] FIG. 8 is a cross section of an embodiment of a capacitor
assembly according to an embodiment of the present invention.
[0029] FIG. 9 is a cross section of an embodiment of a capacitor
assembly according to an embodiment of the present invention.
[0030] FIG. 10 is an electrical schematic of an embodiment of a
downhole component according to an embodiment of the present
invention.
[0031] FIG. 11 is a cross section of an embodiment of a capacitor
assembly according to an embodiment of the present invention.
[0032] FIG. 12 is a cross section of an embodiment of a capacitor
assembly according to an embodiment of the present invention.
[0033] FIG. 13 is a cross section of an embodiment of a capacitor
assembly according to an embodiment of the present invention.
[0034] FIG. 14 is a cross section of an embodiment of a capacitor
assembly according to an embodiment of the present invention.
[0035] FIG. 15 is a cross section of an embodiment of a capacitor
assembly according to an embodiment of the present invention.
[0036] FIG. 16 is a cross section of an embodiment of a capacitor
assembly according to an embodiment of the present invention.
[0037] FIG. 17 is a perspective cross section of an embodiment of a
capacitor assembly according to an embodiment of the present
invention.
[0038] FIG. 18 is a cross section of an embodiment of a capacitor
assembly according to an embodiment of the present invention.
[0039] FIG. 19 is an orthogonal view of an embodiment of multiple
capacitors according to an embodiment of the present invention.
[0040] FIG. 20 is an orthogonal view of an embodiment of multiple
capacitors according to an embodiment of the present invention.
[0041] FIG. 21 is a perspective view of an embodiment of a
capacitor according to an embodiment of the present invention.
[0042] FIG. 22 is a perspective view of an embodiment of a
capacitor according to an embodiment of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0043] The disclosed description is meant to illustrate the present
invention and not limit its scope. Other embodiments of the present
invention are possible within scope and spirit of the claims.
[0044] FIG. 1 shows an embodiment of a downhole tool string 31
suspended in a well bore by a derrick 32. Surface equipment 33,
such as a computer, connects to a data swivel 34. The data swivel
34 is adapted to transmit data to and from an integrated
transmission network while the downhole tool string 31 is rotating.
The integrated transmission network comprises the transmission
systems of the individual components 35, 36, 57 of the downhole
tool string 31. Preferably the downhole component is a drill pipe
57 or a tool 35. Tools 35 may be located in the bottom hole
assembly 37 or along the length of the downhole tool string 31.
Examples of tools 35 on a bottom hole assembly 37 comprise sensors,
drill bits, motors, hammers, and steering elements. Examples of
tools 35 located along the downhole tool string 31 are links, jars,
seismic sources, seismic receivers, sensors, and other tools that
aid in the operations of the downhole tool string 31. Different
sensors are useful downhole such as pressure sensors, temperature
sensors, inclinometers, thermocouples, accelerometers, and imaging
devices. Preferably the downhole tool string 31 is a drill string.
In other embodiments the downhole tool string 31 is part of a
production well.
[0045] The downhole tool string 31 is made up of tool joint
components, as shown in FIG. 2. The components comprise data
transmission elements 38 located in the secondary shoulder 39 of
pin end 40 and in the secondary shoulder 41 of the box end 42 of
component 57. The transmission elements 38 comprise a segmented
circular trough of magnetically-conductive, electrically-insulating
material (shown in FIG. 3), which is disposed in an annular groove
formed in the secondary shoulders 39, 41. Alternatively, the
transmission elements may be a magnetizable element comprising a
multi-laminar body. The segments of the multi-laminar body are
separated by an electrical insulator and form a trough in which the
electrical conductor is disposed. The magnetizable element may be
constructed out of a highly permeable and ductile material
typically associated with the class of soft magnetic materials.
[0046] The annular groove may be formed by a metal ring 43, as
shown in FIG. 3. Preferably, the metal ring 43 is made of steel. In
other embodiment the metal ring 43 is made of stainless steel. The
data transmission elements 38 are connected by an electrical
conductor. In the preferred embodiment, the electrical conductor is
a coaxial cable 44.
[0047] The transmission elements 38 comprise an inductive coupler.
As shown in FIG. 3, the inductive coupler houses an electrically
conductive coil 45 embedded in the MCEI circular trough 46.
Preferably the MCEI trough 46 comprises is ferrite. In other
embodiments the MCEI trough 46 comprises soft iron, nickel iron
alloys, silicon iron alloys, cobalt iron alloys or mu-metals. The
coil 45 comprises at least one loop of insulated wire. The wire may
be made of copper and is insulated with varnish, enamel, or a
polymer. When the components of the downhole tool string 31 are
made up, or assembled into a string, the transmission elements 38
and 47 line up adjacent to each other and allow data transmission
between components 36 and 57. In other embodiments of the present
invention the transmission elements 38 comprises a direct
electrical coupler or a capacitive coupler. A threaded portion 48
located between the primary shoulder 49 and secondary shoulder 39
of the pin end 40 and a threaded portion 50 located between the
primary shoulder 51 and secondary shoulder 41 of the box end 42
provide a means of attachment for the downhole components 36 and
57.
[0048] FIG. 3 shows an embodiment of a connection between the
coaxial cable 44 and the electrical conducting coil 45. In the
preferred embodiment, a signal travels along the coaxial cable 44
of a downhole component 36. The signal passes from the coaxial
cable 44 to a lead wire 52 of the coil 45. The transmission element
38 comprises an anti-rotation device 53, which keeps the metal ring
43 from rotating about the axis of the lead wire 52. In the
preferred embodiment the lead wire 52 enters the metal ring 43
through a hole in the metal ring 43, where there is a void 54 of
the MCEI material 46. The coil 45 is housed in a channel 55 formed
by the segmented trough of MCEI material 46 and is grounded to the
metal ring 43 in the void 54 of the MCEI material 46. Preferably,
the grounded portion 56 of the coil 45 is brazed to the metal ring
43. In some embodiments of the present invention the coil 45 and
MCEI trough 46 are disposed in a groove formed in secondary
shoulders 39, 41 of both the pin end 40 and also in the box end 42
of the downhole component 36.
[0049] Preferably, the MCEI circular trough of 46 is held in place
within the circular trough, by an electrically-insulating filler
material. Preferably the filler material is selected from the group
consisting of epoxy, natural rubber, fiberglass, carbon fiber
composite, a polymer, polyurethane, silicon, a fluorinated polymer,
grease, polytetrafluoroethylene and perfluoroalkoxy, or a
combination thereof.
[0050] As the signal travels along the coil 45, a magnetic field
from the electrical current is produced in the MCEI material 46.
The magnetic field influences the MCEI material 46 in the adjacent
transmission element 47 in the adjacent downhole component 57. The
electrically conducting coils are arranged in a manner to allow the
magnetic fields to generate a magnetic transmission circuit. A
magnetic transmission circuit may be allowed by disposing one coil
in a clockwise direction in the segmented circular trough of
magnetically-conductive, electrically-insulating material and
disposing an adjacent coil in a counterclockwise direction in an
adjacent segmented circular trough of magnetically-conductive,
electrically-insulating material. The coil in the adjacent
transmission element 47 is influenced by the magnetic transmission
circuit to generate an electrical current and that signal is passed
to the coaxial cable 58 in the adjacent downhole component 57.
[0051] In the preferred embodiment as shown in FIG. 4, a passage 59
is formed in the component 36 for the coaxial cable 44 and lead
wire 52. The passage 59 runs from the secondary shoulder 39 to an
opening 60 in the inner diameter 61 of the downhole component 36.
Preferably the passage 59 is a drilled hole. In some aspects of the
invention, the passage 59 is a metal liner, such as conduit, which
coaxial cable 44 from fluids within the bore of the downhole
component 36. FIG. 4 shows an embodiment of the coaxial cable 44
disposed inside the downhole component 36. In the preferred
embodiment the inner diameter 61 of the downhole component 61
narrows at the ends of the component 36. The coaxial cable 44 exits
the passage 59 through the opening 60 in the region 63 where the
inner diameter 61 of the component 36 narrows. Preferably the
coaxial cable 44 comprises an inner conductor 64, a dielectric 65,
and an outer conductor 62. In some embodiments the outer conductor
62 in insulated. In the preferred embodiment the outer conductor 62
is in electrical communication with the passage 59. In this
embodiment the component 36 acts as ground for the coaxial cable
44. In another embodiment, the passage 59 is a metal tube
preferably made of conduit 159, which provides protection to the
outer conductor 62 of the coaxial cable 44 throughout the length of
the downhole component 36.
[0052] In the preferred embodiment, the transmission element 38
comprises a sealing assembly 66, which protects moisture or other
contamination from entering the passage 59. Preferably the sealing
assembly 66 is axial mounted around the lead wire 52. A sealing
assembly 66 is depicted in FIG. 5. The sealing assembly 66
comprises at least one ring 67 made of a polymer or rubber
surrounding the lead wire 62 of the coil 45. Preferably, the
sealing assembly 66 has at least four rings 67 and a sealing spacer
68 separating each of those rings 67. Also shown in FIG. 5 is the
capacitor assembly 69. In the preferred embodiment the capacitor
assembly 69 connects the coaxial cable 44 to the lead wire 52. In
other embodiments the capacitor assembly 69 connects a first
portion 70 and a second portion 71 of the coaxial cable 44.
[0053] FIG. 6 shows the preferred embodiment of the capacitor
assembly 69. Preferably, the connector 72 is comprised of at least
two sections. In other embodiments the connector 72 comprises a
single section. In the preferred embodiment the at least two
sections are separated by a coaxial spacer 73. Preferably, the
connector 72 is at least partially electrically insulated.
Preferably, the capacitor 74 comprises at least one electrically
conducting spacer 75 in electrically communication with the passage
59.
[0054] The first section 76 comprises a cable receptacle 77 for the
inner conductor 64 of the coaxial cable 44. The dielectric 65 and
the outer conductor 62 of the coaxial cable 44 surround the first
section 76 of the connector 72. The first section 76 of the
connector 72 comprises an insert 78 which fits in a middle
receptacle 79 of the second section 80 of the connector 72.
Preferably, a coaxial capacitor 74 is axial mounted around the
insert 78. A coaxial spacer 75 separates the capacitor 74 from the
second section 80 of the connector 72. The second section 80
comprises a lead wire receptacle 81. The dielectric 82 of the
capacitor 74 runs parallel to the insert 78 and the flow of the
electrical current. Preferably an electrically-conducting spacer 75
is soldered to the coaxial capacitor 74.
[0055] spring 83 may be soldered to the electrically conducting
spacer 75. Preferably the spring 83 is made of brass and is
soldered to the electrical conducting spacer 75 at two points to
provide a better electrical contact with the electrically
conducting spacer 75. The spring 83 physically contacts the outer
conductor 62 of the coaxial cable 44. Preferably, the first section
76 and second section 80 of the connector 72 comprises some
insulation 84. The second section 80 may be surrounded by an
insulating layer 85 (shown in FIG. 5), separating the second
section 80 from the outer conductor 62 of the coaxial cable 44. The
capacitor 74 needs to be adapted to withstand the harsh downhole
environment. The capacitor assembly 69 needs to withstand extreme
heat downhole, tension from the weight of the downhole tool string
31, and torque from rotating the downhole tool string 31. A coaxial
capacitor, Shoulder Feed-Thru #2463-000-X7UO-152P, is sold by
Tusonix, Tucson, Ariz. This capacitor has an operating temperature
of -55.degree. to 125.degree. C. A spring, Male Contact Band
#192048, is sold by AMP, Inc. Harrisburg, Pa.
[0056] In the preferred embodiment of the present invention, a
spring 83 provides the electrical communication between the
connector 72 and the outer conductor 62 of the coaxial cable 44.
The spring 83 is preferred due to the tolerance ranges in the
dimension of the passage 59, the coaxial cable 44, capacitor 74,
and connector 72. In another embodiment, the capacitor assembly 69
comprises a force fitted capacitor.
[0057] The impedance of a coaxial cable 44 is dependant on it's
length. A typical component 57 in a downhole tool string 31 is 25
to 90 feet long. More typically, a component 57 in a downhole tool
string 31 is 28 to 33 feet long. A matching length of coaxial cable
44 is needed to connect the transmission elements 38, 47 at both
ends of the component 57. Signal transmission from one component 57
of a certain impedance to another component 36 of a significantly
different impedance are believed to cause impedance reflections.
These reflections are believed to cause signal loss and
attenuation. Different lengths of coaxial cables between 28 to 33
feet are considered to be insignificant. However, some components
36 of a downhole tool string 31 may only be a couple of feet long
and the impedance difference between their respective coaxial
cables is significant. It is believed that a capacitor 74 may be
selected which may match the impedance of different lengths of
coaxial cable within a certain range of frequency. A preferred
ranged of frequency for the present invention is 4 MHz to 6.5 MHz,
although other frequencies could be used. It is believed that a
capacitor 74 may be selected which will match the impedance of
different lengths of coaxial cable with the frequency range of 4
MHz to 6.5 MHz and thereby reduce signal attention between downhole
components of different lengths. In the preferred embodiment, a
capacitor 74 is incorporated into the downhole components 36 that
fall outside of the typical component's length.
[0058] Changing other characteristics of the coaxial cable 44 may
also help to match the impedances of different lengths of coaxial
cables, such as changing the size of the diameter, the type of
dielectric, and the thickness of the dielectric. Wrapping a longer
coaxial cable in the inner diameter 61 of the downhole component 36
may also help to match the impedances of the different length
components. The impedance differences between the coaxial cable 44
and the coil 45 need to approximately match, although the coils 45
and coaxial cable 44 act as a circuit, so changing the electrical
characteristics of a coil 45 may change the impedance of the
overall downhole component 36. Changing the physical
characteristics of the coil 45 in the transmission element 38 may
help match the impedance of the components 36 of different lengths.
One embodiment of the present invention adds loops to the coil 45.
In another embodiment the diameter of the coil 45 is increased. In
another embodiment the diameter of the coil 45 in decreased.
[0059] The capacitor assembly 69 may be assembled to the lead wire
52 first. The transmission elements 38 are placed in the groove
formed in the secondary shoulder 39, so that the lead wire 52 may
be inserted into the passage 59. The downhole component 36 is
arranged such that the capacitor assembly 69 receives the inner
conductor 64 of the coaxial cable 44 when the transmission element
38 is positioned in the groove. Preferably, the capacitor assembly
69 is first secured to the coaxial cable 44. In this manufacturing
method, a good electrical connection between the first section 76
of the connector 72 and the inner conductor 64 of the coaxial cable
44 may be assured, before the coaxial cable 44 is secured in the
component 36. The lead wire 52 may then be received by the lead
wire receptacle 81 in the second section 80 of the connector 72
when the transmission element 38 is positioned within the groove of
the secondary shoulder 39.
[0060] FIG. 7 illustrates another embodiment of the capacitor
assembly 69. The first section 76 of the connector 72 comprises the
cable receptacle 77. The coaxial capacitor 74 is mounted around the
insert 78. The insert 78 is also received by the middle receptacle
79 of the second section 80. The capacitor 74 is in electrical
communication with both the insert 79 and the outer conductor 62 of
the coaxial cable 44.
[0061] FIG. 8 shows an embodiment of the capacitor assembly 69. The
connector 72 comprises a single section. The coaxial capacitor 74
makes a direct electrical connection between the connector 72 and
the outer conductor 62 of the coaxial cable 44. Also shown is the
dielectric 82 represented by a dotted line.
[0062] FIG. 9 shows a capacitor assembly 69 adapted to connect a
first portion 70 and a second portion 71 of the inner conductor 64
of the coaxial cable 44. The coaxial capacitor 74 may be spliced
into the coaxial cable 44 before the coaxial cable 44 is secured in
the downhole component 36. Preferably the coaxial capacitor 74 is
inserted into the coaxial cable 44 during the manufacturing of the
coaxial cable 44. The first portion 70 of the inner conductor 64 of
the coaxial cable 44 is inserted into a first cable receptacle 87
and the second portion 71 of the inner conductor 64 of the coaxial
cable 74 is inserted in a second cable receptacle 88. The brass
spring 83 provides electrical communication between the connector
72 and the outer conductor 62 of the coaxial cable 44.
[0063] FIG. 10 is an electrical schematic of the downhole component
36. The electrical characteristics of the preferred embodiment are
a series of inductance and capacitance in parallel. Inductor 89
represents the inductance provided by the transmission elements 38,
41. Inductor 90 represents the inductance of the coaxial cable.
Capacitor 91 represents the capacitance of the coaxial cable.
Capacitor 92 represents the capacitance provided by the coaxial
capacitor. Ground 93 represents ground.
[0064] FIG. 11 shows an embodiment of a capacitor 94 located in the
dielectric 65, which is in electrical communication with the outer
conductor 62 and the inner conductor 64. In this embodiment a
portion of the dielectric 65 is cut away to make space for the
capacitor 94. Preferably terminals 95 are made of wire and are
spliced into the outer conductor 62 and inner conductor 64. In some
embodiments of the present invention, the terminals 95 are soldered
to the outer conductor 62 and the inner conductor 64.
[0065] FIG. 12 shows an embodiment of a capacitor 94 also located
in the dielectric 65. The capacitor 94 is in electrical
communication with the outer conductor 62 of the coaxial cable 64
and a connector 72. Preferably, the connector 72 comprises a single
section, but in other embodiments it comprises at least two
sections 76, 80. The connector 72 has receptacles 96 for either a
lead wire 52 or a portion of the inner conductor 64 of the coaxial
cable 44.
[0066] FIG. 13 shows an embodiment of a connecting capacitor 96. In
this embodiment of the present invention, the connecting capacitor
96 comprises receptacles 97 for either a portion of the coaxial
cable 44 or a lead wire 52. A dielectric 98 separates the inner
plates 99 of the connecting capacitor 96 from the distal plates 100
in the capacitor 96. In this embodiment one terminal 101,
preferably made of a wire, connects the distal plates 100 to the
outer conductor 62 of the coaxial cable 44. In other embodiments,
the connecting capacitor 96 comprises at least one terminal 101.
FIG. 14 shows another embodiment of the connecting capacitor 96, a
dielectric 98 simply surrounds the inner conductor 64 of the
coaxial cable 44. The dielectric 98 is surrounded by distal plates
100 which are in electrical communication with the outer conductor
62 of the coaxial cable 44. Wire terminals 101 physically connects
the outer conductor 64 with the connecting capacitor 96.
[0067] FIG. 15 illustrates another embodiment of the capacitor
assembly 69. In this embodiment of the present invention, the
capacitor 74 makes a direct electrical connection with the passage
59. In another embodiment of this invention the capacitor 74 makes
a direct electrical connection with the metal tube. As shown in
FIG. 15, the outer conductor 62 and dielectric 65 end at the edge
102 of the first section 76 of the connector 72 and the inner
conductor 64 is received in the cable receptacle 77. In FIG. 15,
the lead wire receptacle 81 accepts the lead wire 52. The lead wire
52 is preferably further surrounded by electrical insulation 85. In
FIG. 16, the second section 80 of the connector 72 comprises a
cable receptacle 77 for connecting a first portion 70 and a second
portion 71 of the inner conductor 64 of the coaxial cable 44.
[0068] FIG. 17 shows another embodiment of the spring 103. The
spring 103 may be made of brass and soldered directly to the
coaxial capacitor 74. The soldered section 104 of the spring 103
extends distally away from the coaxial capacitor 74 and axially
towards the second section 80 of the connector 72. The spring 103
may make direct electrical contact with the passage 59, metal tube,
or outer conductor 62 of the coaxial cable 44.
[0069] In another embodiment of the present invention, in-line
inductors 105 are included on either side of the capacitor assembly
69, as shown in FIG. 18. There may be at least one inductor 105 on
either side of the capacitor assembly 69. In other embodiments,
there is only one in-line inductor 105 in the transmission system
of the downhole component 36. The in-line inductor 105 is not in
electrical communication with the outer conductor 62 of the coaxial
cable 44, the metal tube, or the passage 59. The inductor is not
grounded. The inductor assembly 106 comprises a first connector 107
receiving an inner conductor 70 of the coaxial cable 44 into a
cable receptacle 108. The first connector 107 also receives an
inductor insert 109, which brings the coaxial cable 44 into
electrical communication with the inductor 105. A second inductor
connector 110 connects the inductor 105 to a second portion 71 of
the inner conductor 64 of the coaxial cable 44. The second portion
71 of the inner conductor 64 of the coaxial cable 44 is received by
the capacitor assembly 69. It is believed that the inductors 105
may contribute to matching the impedances of different lengths of
coaxial cables 44.
[0070] Multiple capacitors may be disposed in the transmission
system in the downhole component 36. FIG. 19 shows two capacitor
assemblies 69. One capacitor assembly connects a first portion 70
and a second portion 71 of a coaxial cable 44. The other capacitor
assembly connects the second portion 71 of the coaxial cable 44 to
the lead wire 52 of the coil 45 in the transmission element 38.
Another embodiment of the present invention comprises more than one
capacitor assembly 69 disposed along the coaxial cable 44. In some
embodiments of the present invention, the capacitors may vary in
their capacitance, as shown in FIG. 20. The capacitance of
capacitors 111, 112, 113 is directly related to their physical
dimensions. The capacitor 111 has a thicker diameter than capacitor
112. Capacitor 113 is longer than both capacitors 111, 112. The
dimensions of the springs 83 in the capacitor assemblies 69 will
vary according to the dimensions of the capacitors 111, 112,
113.
[0071] In another embodiment of the present invention, the
capacitor assembly 69 is disposed between a first portion 114 and a
second portion 115 of a lead wire, as shown in FIG. 21. In other
embodiments the capacitor assembly 69 is part of the anti-rotation
device 53, as shown in FIG. 22. In this embodiment, the capacitor
assembly 69 comprises a first section 76 of the connector 72, which
comprises a lead wire receptacle 81. The capacitor 74 connects
directly to the anti-rotation device 53.
* * * * *