U.S. patent number 3,793,632 [Application Number 05/129,665] was granted by the patent office on 1974-02-19 for telemetry system for drill bore holes.
Invention is credited to William L. Still.
United States Patent |
3,793,632 |
Still |
February 19, 1974 |
TELEMETRY SYSTEM FOR DRILL BORE HOLES
Abstract
Apparatus and method for signaling within a drill bore hole
without disturbing an ongoing drilling operation. Repeater stations
are utilized at intervals along a drill string with the repeater
input and output being in different noninterfering first and second
modes. Furthermore, means are shown for causing successive repeater
transmitters of any given mode to produce only negative feedback
and hence to cause the overall system to be self-stabilizing.
Special means are also shown for selectively attenuating one or
both modes of transmission between repeater stations thereby
substantially eliminating undesired feedback in the cases where
self-stabilization cannot be guaranteed. Both active and passive
attenuators are discussed as well as two exemplary overall systems.
One exemplary system uses electric current for one mode and
magnetic flux for the other mode while the other exemplary system
utilizes different signal frequencies for the different
transmission modes.
Inventors: |
Still; William L.
(Purcellville, VA) |
Family
ID: |
22441032 |
Appl.
No.: |
05/129,665 |
Filed: |
March 31, 1971 |
Current U.S.
Class: |
367/182;
367/6 |
Current CPC
Class: |
E21B
47/13 (20200501) |
Current International
Class: |
E21B
47/12 (20060101); G01v 001/40 () |
Field of
Search: |
;340/18LD,18NC ;325/1,9
;250/199 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Wilbur; Maynard R.
Assistant Examiner: Birmiel; H. A.
Attorney, Agent or Firm: Cushman, Darby & Cushman
Claims
What is claimed is:
1. A data transmission system for use with a drill string having a
length comprising sections in a bore hole within the earth without
requiring electrical conductors running the full length of said
sections, said system comprising:
data input means for generating data signals,
transmitting means for transmitting said data signals along at
least one section length of said bore hole in a first mode of
energy transfer
at least first and second spaced apart repeater means located along
said bore hole at intervals of at least one of said section
lengths,
said first repeater means receiving said first mode from said
transmitting means and retransmitting said data signals at an
amplified energy level along at least one section length of said
bore hole in a second mode, said second mode of energy transfer
being non-interacting with said first mode,
said second repeater means receiving said second mode from said
first repeater means and retransmitting said data signals at an
amplified energy level along at least one section length of said
bore hole in said first mode, and
receiving means for receiving and detecting said data signals from
at least the last repeater means nearest thereto.
2. A data transmission system as in claim 1 wherein said repeater
means include means for inverting the phase of information
transmitted on any given mode each time that particular mode is
retransmitted.
3. A data transmission system as in claim 1 wherein said repeater
means are arranged to cause all retransmissions of said first mode
to be phase coherent with the first transmission of said first
mode, and all retransmissions of said second mode to be phase
coherent with the first transmissions of said second mode.
4. A data transmission system as in claim 3 wherein said repeater
means are arranged to cause the phase of said first mode to be
reversed on retransmission with respect to the phase of the next
earlier transmission of said first mode, and to cause the phase of
said second mode to be reversed on retransmission with respect to
the phase of the next earlier transmission of said second mode.
5. A data transmission system for use in a bore hole in the earth
comprising:
data input means for generating data signals,
transmitting means for transmitting said data signals in a first
mode of energy transfer,
at least first and second spaced apart repeater means,
said first repeater means receiving said first mode from said
transmitting means and transmitting said data signals on a second
mode, said second mode of energy transfer being non-interacting
with said first mode,
said second repeater means receiving said second mode from said
first repeater means and retransmitting said data signals on said
first mode, and
receiving means for receiving and detecting said data signals from
at least the last repeater means nearest thereto,
said transmitting means and said first and second repeater means
comprising means for transmitting energy through a drill string in
said bore hole and the surrounding earth as a transmission
medium.
6. A data transmission system as in claim 5 wherein said first and
second repeater means comprise amplification means for providing an
amplified output signal on the particular transmission mode
involved.
7. A data transmission system as in claim 6 wherein said first
energy transfer mode comprises a magnetic flux along said drill
string and said second energy transfer mode comprises an electric
current along said drill string and wherein said first and second
repeater means comprise means for generating said electric current
and said magnetic flux in response to received magnetic flux and
electric current respectively thereby transducing the first to the
second mode and vice versa respectively.
8. A data transmission system as in claim 7 including:
toroidal coils for transmitting and receiving the current or second
mode, and
solenoidal coils for transmitting and receiving the magnetic or
first mode,
said toroidal and solenoidal coils encompassing at least a portion
of said drill string.
9. A data transmission system as in claim 6 wherein said first
energy transfer mode and said second energy transfer mode comprise
signals at first and second frequencies and wherein said first and
second repeater means comprise means for generating said first and
said second frequency in response to receiving said second and said
first frequency respectively thereby transducing the first to the
second mode and vice versa respectively.
10. A data transmission system as in claim 9 wherein said repeater
means include means for reversing the phase of each frequency with
respect to its previous state each time it is retransmitted.
11. A data transmission system for use in a bore hole in the earth
comprising:
data input means for generating data signals,
transmitting means for transmitting said data signals in a first
mode of energy transfer,
at least first and second spaced apart repeater means,
said first repeater means receiving said first mode from said
transmitting means and retransmitting said data signals on a second
mode, said second mode of energy transfer being non-interacting
with said first mode,
said second repeater means receiving said second mode from said
first repeater means and retransmitting said data signals on said
first mode, and
receiving means for receiving and detecting said data signals from
at least the last repeater means nearest thereto,
said repeater means including means for inverting the phase of
information transmitted on any given mode each time that particular
mode is retransmitted, and
said transmitting means and said first and second repeater means
comprising means for transmitting energy through a drill string in
said bore hole and the surrounding earth as a transmission
medium.
12. A data transmission system as in claim 11 wherein said first
and second repeater means comprise amplification means for
providing an amplified output signal on the particular transmission
mode involved.
13. A data transmission system as in claim 12 wherein said first
energy transfer mode comprises a magnetic flux along said drill
string and said second energy transfer mode comprises an electric
current along said drill string and wherein said first and second
repeater means comprise means for generating said electric current
and said magnetic flux in response to received magnetic flux and
electric current respectively thereby transducing the first to the
second mode and vice versa respectively.
14. A data transmission system as in claim 13 including:
toroidal coils for transmitting and receiving the current or second
mode, and
solenoidal coils for transmitting and receiving the magnetic or
first mode,
said toroidal and solenoidal coils encompassing at least a portion
of said drill string.
15. A data transmission system for use in a bore hole in the earth
comprising:
data input means for generating data signals,
transmitting means for transmitting said data signals in a first
mode of energy transfer,
at least first and second spaced apart repeater means,
said first repeater means receiving said first mode from said
transmitting means and retransmitting said data signals on a second
mode, said second mode of energy transfer being non-interacting
with said first mode,
said second repeater means receiving said second mode from said
first repeater means and retransmitting said data signals on said
first mode,
receiving means for receiving and detecting said data signals from
at least the last repeater means nearest thereto, and
selective mode attenuators inserted in the transmission path at
locations occurring after a particular mode has been received and
prior to its retransmission on another mode for attenuation of said
particular mode.
16. A data transmission system as in claim 15 wherein said repeater
means include means for inverting the phase of information
transmitted on any given mode each time that particular mode is
retransmitted.
17. A data transmission system as in claim 16 for use in a bore
hole in the earth, said transmitting means and said first and
second repeater means comprising means for transmitting energy
through a drill string in said bore hole and the surrounding earth
as a transmission medium.
18. A data transmission system as in claim 17 wherein said first
and second repeater means comprise amplification means for
providing an amplified output for providing an amplified output
signal on the particular transmission mode involved.
19. A data transmission system as in claim 18 wherein said first
energy transfer mode comprise a magnetic flux along said drill
string and said second energy transfer mode comprises an electric
current along said drill string and wherein said first and second
repeater means comprise means for generating said electric current
and said magnetic flux in response to received magnetic flux and
electric current respectively thereby transducing the first to the
second mode and vice versa respectively.
20. A data transmission system as in claim 19 including:
toroidal coils for transmitting and receiving the current or second
mode, and
solenoidal coils for transmitting and receiving the magnetic or
first mode,
said toroidal and solenoidal coils encompassing at least a portion
of said drill string.
21. A data transmission system for use in a bore hole within the
earth comprising:
data input means for generating data signals,
transmitting means for transmitting said data signals along said
bore hole in a first mode of energy transfer,
at least first and second spaced apart repeater means located along
said bore hole,
said first repeater means receiving said first mode from said
transmitting means and retransmitting said data signals along said
bore hole on a second mode, said second mode of energy transfer
non-interacting with said first mode,
said second repeater means receiving said second mode from said
first repeater means and retransmitting said data signals on said
first mode,
receiving means for receiving and detecting said data signals from
at least the last repeater means nearest thereto, and
including means whereby said first mode is modulated at a first
frequency and said second mode is modulated at a second
frequency.
22. A data transmission system for use in a bore hole within the
earth comprising:
data input means for generating data signals,
transmitting means for transmitting said data signals along said
bore hole in a first mode of energy transfer,
at least first and second spaced apart repeater means located along
said bore hole,
said first repeater means receiving said first mode from said
transmitting means and retransmitting said data signals along said
bore hole on a second mode, said second mode of energy transfer
being non-interacting with said first mode,
said second repeater means receiving said second mode from said
first repeater means and retransmitting said data signals on said
first mode,
receiving means for receiving and detecting said data signals from
at least the last repeater means nearest thereto, and
wherein said transmitting means and said first and second repeater
means include means for causing electromagnetic energy to flow in
the drill string in said bore hole and in the surrounding
earth.
23. A data transmission system as in claim 22 wherein one of either
said first or second modes comprises a magnetic flux along said
drill string and the other of either said first or second modes
comprises an electric current along said drill string.
24. A data transmission system for use in a bore hole within the
earth comprising:
data input means for generating data signals,
transmitting means for transmitting said data signals along said
bore hole in a first mode of energy transfer,
at least first and second spaced apart repeater means located along
said bore hole,
said first repeater means receiving said first mode from said
transmitting means and retransmitting said data signals along said
bore hole on a second mode, said second mode of energy transfer
being non-interacting with said first mode,
said second repeater means receiving said second mode from said
first repeater means and retransmitting said data signals on said
first mode,
receiving means for receiving and detecting said data signals from
at least the last repeater means nearest thereto, and
wherein said transmitting means and said first and second repeater
means include means for causing acoustical energy to flow in a
drill string within said bore hole.
25. A data transmission system as in claim 24 wherein one of said
first and second modes is comprised of a torsional vibration along
said drill string, and the other of said first and second modes is
comprised of a longitudinal vibration along said drill string.
26. A data transmission system for use in a bore hole within the
earth comprising:
data input means for generating data signals,
transmitting means for transmitting said data signals along said
bore hole in a first mode of energy transfer,
at least first and second spaced apart repeater means located along
said bore hole,
said first repeater means recieving said first mode from said
transmitting means and retransmitting said data signals along said
bore hole on a second mode, said second mode of energy transfer
being non-interacting with said first mode,
said second repeater means receiving said second mode from said
first repeater means and retransmitting said data signals on said
first mode,
receiving means for receiving and detecting said data signals from
at least the last repeater means nearest thereto, and
wherein said repeater means are arranged to cause all
retransmissions of said first mode to be phase coherent with the
first transmission of said first mode, and all retransmissions of
said second mode to be phase coherent with the first transmissions
of said second mode,
wherein said first mode is modulated at a first frequency and said
second mode is modulated at a second frequency.
27. A data transmission system for use in a bore hole within the
earth comprising:
data input means for generating data signals,
transmitting means for transmitting said data signals along said
bore hole in a first mode of energy transfer,
at least first and second spaced apart repeater means located along
said bore hole,
said first repeater means receiving said first mode from said
transmitting means and retransmitting said data signals along said
bore hole on a second mode, said second mode of energy transfer
being non-interacting with said first mode,
said second repeater means receiving said second mode from said
first repeater means and retransmitting said data signals on said
first mode,
receiving means for receiving and detecting said data signals from
at least the last repeater means nearest thereto,
wherein said repeater means are arranged to cause all
retransmissions of said first mode to be phase coherent with the
first transmissions of said first mode, and all retransmissions of
said second mode to be phase coherent with the first transmissions
of said second mode, and
wherein said transmitting means and said first and second repeater
means cause electromagnetic energy to flow in a drill string in
said bore hole and in the surrounding earth.
28. A data transmission system as in claim 27 wherein one of said
first and second modes comprises a magnetic flux along said drill
string and the other of said first and second modes comprises an
electric circuit along said drill string.
29. A data transmission system for use in a bore hole within the
earth comprising:
data input means for generating data signals,
transmitting means for transmitting said data signals along said
bore hole in a first mode of energy transfer,
at least first and second spaced apart repeater means located along
said bore hole,
said first repeater means receiving said first mode from said
transmitting means and retransmitting said data signals along said
bore hole on a second mode, said second mode of energy transfer
being non-interacting with said first mode,
said second repeater means receiving said second mode from said
first repeater means and retransmitting said data signals on said
first mode,
receiving means for receiving and detecting said data signals from
at least the last repeater means nearest thereto,
wherein said repeater means are arranged to cause all
retransmissions of said first mode to be phase coherent with the
first transmission of said first mode, and all retransmissions of
said second mode to be phase coherent with the first transmissions
of said second mode, and
wherein said transmitting means and said first and second repeater
means cause acoustical energy to flow in a drill string within said
bore hole.
30. A data transmission system as in claim 29 wherein one of said
first and second modes is comprised of a torsional vibration along
said drill string and the other of said first and second modes is
comprised of a longitudinal vibration along said drill string.
31. A data transmission system for use in a bore hole within the
earth comprising:
data input means for generating data signals,
transmitting means for transmitting said data signals along said
bore hole in a first mode of energy transfer,
at least first and second spaced apart repeater means located along
said bore hole,
said first repeater means receiving said first mode from said
transmitting means and retransmitting said data signals along said
bore hole on a second mode, said second mode of energy transfer
being non-interacting with said first mode,
said second repeater means receiving said second mode from said
first repeater means and retransmitting said data signals on said
first mode,
receiving means for receiving and detecting said data signals from
at least the last repeater means nearest thereto,
wherein said repeater means are arranged to cause all
retransmissions of said first mode to be phase coherent with the
first transmission of said first mode, and all retransmissions of
said second mode to be phase coherent with the first transmissions
of said second mode,
wherein said repeater means are arranged to cause the phase of said
first mode to be reversed on retransmission with respect to the
phase of the next earlier transmission of said first mode, and to
cause the phase of said second mode to be reversed on
retransmission with respect to the phase of the next earlier
transmission of said second mode, and
wherein said first mode is modulated at a first frequency and said
second mode is modulated at a second frequency.
32. A data transmission system for use in a bore hole within the
earth comprising:
data input means for generating data signals,
transmitting means for transmitting said data signals along said
bore hole in a first mode of energy transfer,
at least first and second spaced apart repeater means located along
said bore hole,
said first repeater means receiving said first mode from said
transmitting means and retransmitting said data signals along said
bore hole on a second mode, said second mode of energy transfer
being non-interacting with said first mode,
said second repeater means receiving said second mode from said
first repeater means and retransmitting said data signals on said
first mode,
receiving means for receiving and detecting said data signals from
at least the last repeater means nearest thereto,
wherein said repeater means are arranged to cause all
retransmissions of said first mode to be phase coherent with the
first transmission of said first mode, and all retransmissions of
said second mode to be phase coherent with the first transmissions
of said second mode,
wherein said repeater means are arranged to cause the phase of said
first mode to be reversed on retransmission with respect to the
phase of the next earlier transmission of said first mode, and to
cause the phase of said second mode to be reversed on
retransmission with respect to the phase of the next earlier
transmission of said second mode, and
wherein said transmitting means and said first and second repeater
means cause electromagnetic energy to flow in a drill string in
said bore hole and in the surrounding earth.
33. A data transmission system as in claim 32 wherein one of either
said first or second modes comprises a magnetic flux along said
drill string and the other of either said first or second modes
comprises an electric current along said drill string.
34. A data transmission system for use in a bore hole within the
earth comprising:
data input means for generating data signals,
transmitting means for transmitting said data signals along said
bore hole in a first mode of energy transfer,
at least first and second spaced apart repeater means located along
said bore hole,
said first repeater means receiving said first mode from said
transmitting means and retransmitting said data signals along said
bore hole on a second mode, said second mode of energy transfer
being non-interacting with said first mode,
said second repeater means receiving said second mode from said
first repeater means and retransmitting said data signals on said
first mode,
receiving means for receiving and detecting said data signals from
at least the last repeater means nearest thereto,
wherein said repeater means are arranged to cause all
retransmissions of said first mode to be phase coherent with the
first transmission of said first mode, and all retransmissions of
said second mode to be phase coherent with the first transmissions
of said second mode,
wherein said repeater means are arranged to cause the phase of said
first mode to be reversed on retransmission with respect to the
phase of the next earlier transmission of said first mode, and to
cause the phase of said second mode to be reversed on
retransmission with respect to the phase of the next earlier
transmission of said second mode, and
wherein said transmitting means and said first and second repeater
means cause acoustical energy to flow in a drill string within said
bore hole.
35. A data transmission system as in claim 34 wherein one of said
first and second modes is comprised of a torsional vibration along
said drill string, and the other of either said first or second
modes is comprised of a longitudinal vibration along said drill
string.
36. A data transmission system for use in a bore hole within the
earth comprising:
data input means for generating data signals,
transmitting means for transmitting said data signals along said
bore hole in a first mode of energy tranfer,
at least first and second spaced apart repeater means located along
said bore hole,
said first repeater means receiving said first mode from said
transmitting means and retransmitting said data signals along said
bore hole on a second mode, said second mode of energy transfer
being non-interacting with said first mode,
said second repeater means receiving said second mode from said
first repeater means and retransmitting said data signals on said
first mode,
receiving means for receiving and detecting said data signals from
at least the last repeater means nearest thereto,
wherein said repeater means are arranged to cause all
retransmissions of said first mode to be phase coherent with the
first transmission of said first mode, and all retransmissions of
said second mode to be phase coherent with the first transmissions
of said second mode, and
wherein at least one of said first and second repeater means
contains a sensing device for detecting the existence of positive
feedback through the receiver of the next earlier repeater means
and a phase adjustment device for adjusting the phase of the output
of said at least one repeater means containing said sensing device
in such a manner that the feedback between said at least one
repeater means and the receiver of said next earlier repeater means
will be negative.
37. A data transmission system as in claim 36 wherein said first
mode is modulated at a first frequency and said second mode is
modulated at a second frequency.
38. Data transmission system as in claim 36 wherein said
transmitting means and said first and second repeater means cause
electromagnetic energy to flow in a drill string in said bore hole
and in the surrounding earth.
39. A data transmission system as in claim 38 wherein one of said
first and second modes comprises a magnetic flux along said drill
string and the other of either said first or second modes comprises
an electric current along said drill string.
40. A data transmission system as in claim 36 wherein said
transmitting means and said first and second repeater means cause
acoustical energy to flow in a drill string in said bore hole.
41. A data transmission system as in claim 40 wherein one of said
first and second modes is comprised of a torsional vibration along
said drill string and the other of said first and second modes is
comprised of a longitudinal vibration along said drill string.
Description
This invention generally relates to methods and apparatus for
signaling or information transmission within a drill hole. It is
applicable to any task which includes the requirement to transmit
information from any point within the drill hole to the surface;
from the drill hole to any point, or plurality of points, within
the drill hole; or between any plurality of points within the drill
hole. It is particularly applicable to the transmission of data
while drilling is in progress, from sensors located within the
drill hole, and attached to the drill string.
A number of techniques and devices have been proposed for achieving
the transfer of data from within the drill hole to the surface,
without the use of separate conducting cables. For example,
Silverman in U.S. Pat. No. 2,354,887 proposes the use of a toroid
which surrounds the drill pipe. Alternating current introduced into
winding of the toroid produces a magnetic flux in the core of the
toroid which, in turn, produces a current in the drill stem. The
drill stem acts as a one turn loop through the core of the toroid
with the earth acting as a return path to complete a current loop
between points on the drill stem above and below the toroid.
A variety of techniques are used at the surface to measure the
drill stem currents thus produced. One of these techniques includes
a second toroid surrounding the drill string at the surface. A
portion of the current introduced into the drill string also flows
through this second toroid and thereby produces a measureable
voltage at the output terminals of the second toroid as will be
apparent to those in the art.
In U.S. Pat. No. 2,411,696, Silverman proposes essentially the same
system except that he uses an intermediate repeater station also
attached to the drill stem. Here, he employs a second toroid to
receive the data transmitted from a first toroid on a modulated
carrier. He demodulates this data at the second toroid location and
uses the demodulated information to remodulate a second carrier
frequency which is then amplified and retransmitted, either through
a third toroid, or through another winding on the second
toroid.
In U.S. Pat. No. 3,079,549, Martin proposes a series of repeater
stations, operating on essentially the same frequency. In a form of
time duration frequency shift keying, all repeater stations receive
and retransmit using toroids on the drill stem, as in Silverman's
system. However, all repeater stations are only conditionally
stable oscillators, while the master station, which originates the
data transmission operates with stable oscllators. The presumption
is that the conditionally stable oscillators will tend to lock to
the frequency controlled by the master station and thus, in time
after stabilizing, the information will be relayed along the drill
stem.
These prior art systems suffer from the common failing of
inherently providing insufficient bandwidth for either high speed
data transfer, or for multi-channel operation, wherein data from a
number of sensors is to be transferred simultaneously. Furthermore,
extensions of the technique, based on these teachings, to establish
any major increase in data transmission rates, will soon meet
inherent limits established by the technique itself.
For instance, extensions of Silverman's teachings will require
higher frequencies to accommodate the increased data transmission
rates. They will also require a wider bandwidth with a resulting
requirement for, either more signaling power, or less attenuation.
The signaling power will soon reach practical limitations. Thus,
reduced attenuation of the signal will be the only recourse. This
implies reduced transmission distances and more repeaters, which,
in turn, requires additional frequencies, with attendant cross
modulation, frequency management, and supply problems.
On the other hand, extensions of Martin's technique will soon
encounter stability problems. His transmission channel is, at best,
only conditionally stable. Adequate time must be allowed for
settling, as all oscillators gradually lock into the signal
frequency. Thus, it is inherently limited to very slow rates of
data transmission.
This invention will provide a data transmission system for use in
drilling holes while drilling is in progress, without any necessity
for removing the drill string from the hole, or for stopping the
drilling in any manner. Furthermore, the system of this invention
will be capable of continuous data transmission at increased
rates.
Such capabilities of the system of this invention are achieved by
the use of repeater stations involving mode transfer transducers
which receive signal energy being transferred between these
repeater stations by one mode of energy transfer, amplify it, and
retransmit this signal energy by a second mode of energy transfer,
wherein the receiver of the repeater, while sensitive to the first
mode, is insensitive to the second. That is, the first and second
modes may be termed "orthogonal" in the sense that they are
independent modes substantially unaffected by each other.
In addition, where the selected type of transmission modes and/or
geologic conditions permit, the system of repeater stations in this
invention will be automatically self-stabilizing. This
self-stabilization result is achieved by having successive
transmissions on each mode reversed in phase from the just previous
phase condition on that particular mode. Thus any feedback between
nearest neighbor transducers of like modes (remembering that a
transducer of another mode will be located between nearest neighbor
transducers of a common mode) will be negative and, hence,
self-stabilizing.
Where the transmission modes selected and/or the geologic
conditions cannot insure that the feedback between transducers of
like modes will be negative, mode selective attenuators will be
provided at strategic locations to attenuate one specific mode and
not the other, and, thus insure that feedback between transducers
of like modes is attenuated to the point that the system can remain
stable regardless of the phase of the signal fed back by a
transducer transmitter of one mode to the transducer receiver of
the same mode.
This invention also provides special selective mode attenuators
which will attenuate one mode without interference with the other
mode being used. Additionally, to provide these attenuators in both
active and passive configurations.
In a first exemplary embodiment, the system of this invention
comprises mode transducer repeaters which are placed as integral
members of the drill string in alternating mode configurations at
separation distances predetermined by prior knowledge of the
general geology which is expected to be found within the drill
hole. In a second embodiment, only the first transducer of each
mode is an integral member of the drill string, while other
repeater transducers are attached to the drill string in
predetermined order, but are so configured that such attachment can
be transferred from the drill string to the wall of the drill hole
on command from the surface. This allows the drill to penetrate an
unknown geologic environment, with the location of the mode
transducer repeaters being determined by ongoing evaluation of the
signals received at the surface as the drilling progresses.
Thus, this invention relates to a high quality data transmission
system for operation in a drill bore hole while drilling is in
progress without the necessity of stopping the drilling action.
Essentially, it comprises using the drill system and/or the
surrounding drilling fluid and/or earth as the transmission medium.
It is improved over and therefore differs from other prior art
systems in that it uses repeater stations and, at least, two
noncoupling or orthogonal modes of transmitting signal energy. The
repeater stations are in the form of mode transfer transducers
which receive a signal transmitted on one mode, amplify the data
thus received, and retransmit it on a second mode of signal energy
transfer (to which the receiver of the first mode in the same
transducer is insensitive).
In its more general use, the term "mode of energy transfer" is used
to include any physical energy transfer mechanism capable of being
used to transmit data from one point to another. The preferred
exemplary method and apparatus will be discussed in detail later.
However, examples of non-interacting or orthogonal mode pairs would
includes:
1. A mode of electromagnetic energy, and a mode of acoustic
energy.
2. Acoustic energy, wherein one mode consists of lateral vibrations
introduced into the drill string, and torsional vibrations
introduced into the same drill string which, although not
completely decoupled, can exist as separate modes over a
considerable length of the drill string.
Many other energy transfer methods too numerous to mention also
exist as should now be apparent to those in the art. Any one of
these can be used to transfer the desired information signal over a
short distance where it may be detected, amplified and
retransmitted by another mode to which the detector of that same
transducer is insensitive.
For the sake of brevity only the preferred exemplary methods and
apparatus will be discussed in detail but, it must be remembered
that the teachings which make the exemplary method and apparatus
new and improved can be applied by analogy to the broader classes
of non-interacting modes of signal transmission in general.
In the exemplary method and apparatus discussed below the two
non-interferring or orthogonal modes are a lateral current mode and
a lateral magnetic mode. These modes have been selected because
they are easily excited, have fair to good propagation
characteristics, and simple rugged means exist whereby one mode can
be coupled to the other.
The exemplary lateral current mode is excited in the drill string
by use of a toroid through which the drill string passes. The
current is induced by the toroid into the drill string which acts
as a one turn winding with the earth providing the return path.
The exemplary lateral magnetic mode is induced by the use of a
solenoidal winding around the drill string, wherein the drill
string acts as part of the core for the magnetic flux with the
earth once again providing the return path for the magnetic flux
produced by the solenoid.
These two exemplary modes do not naturally couple one to the other
except in so far as secondary field distortions cause a minor
coupling. In addition they are truly orthogonal modes where, in the
current mode, the current flows in the pipe or drill string and the
magnetic field exists at right angles to it in a circumferential
pattern around the pipe. In the magnetic mode the exact reverse
occurs where the magnetic flux flows in the drill string pipe and
the current flows in a circumferential pattern around the pipe. The
recognition of these characteristics permit a particularly simple
and desirable configuration for the mode transfer transducers
utilized in the exemplary embodiment. By simple changes of
connections the same transducer unit can be used to perform a
number of functions. It can be a current receiver to magnetic
transmitter, or a magnetic receiver to current transmitter. It can
also be used as either a current or magnetic attenuator where the
need exists as will be explained more fully below.
A more complete understanding of this invention and appreciation of
its improvements and advantages may be obtained from the following
detailed description and accompanying drawings, of which:
FIG. 1 is a schematic depiction of an exemplary mode repeater
transducer suitable for use in this invention;
FIG. 2 is a diagrammatic view of an exemplary embodiment of this
invention actually in use in a drill hole and utilizing a plurality
of mode transducers such as shown in FIG. 1;
FIG. 3 is a graph showing relative signal strengths for the various
transmission modes along the length of the drill hole shown in FIG.
2;
FIG. 4 depicts an exemplary embodiment of a passive current mode
attenuator for use with this invention;
FIG. 5 is similar to FIG. 4 but in less detail and showing a
complete preferred current path;
FIG. 6 is a schematic depiction of an exemplary embodiment of an
active current mode attenuator;
FIG. 7 is a schematic depiction of an exemplary embodiment of a
combined active current and magnetic mode attenuator; and
FIG. 8 is a block diagram of a further exemplary embodiment of this
invention utilizing different signal frequencies as the different
transmission modes.
Referring to FIG. 1, a mode repeater transducer 10 is shown as
being mounted on a short piece of drill stem or sub 12. The
transducer comprises a toroidal transformer 14 surrounding the sub
12 in such a manner that a changing electrical current 16 (shown by
solid lines) flowing in the sub 2 and through the toroid 14 will
induce a voltage therein which is proportional to the current 16 at
the output terminals 18 of the toroid 14. The voltage at output
terminals 18 of the toroid 14 is applied to the input of amplifier
20 which then produces an output signal current at 22 proportional
to the voltage at terminals 18. This signal current is caused to
flow through solenoid winding 24 and return to one of the input
terminals 18 thereby providing a common reference, or ground point.
In flowing through the turns of solenoid 24, the current from
amplifier 20 produces a magnetic flux 26 (shown by a dotted line)
proportional to the current 16 and much stronger than, and
orthogonal (at right angles) to the circumferential magnetic flux
28 produced directly by the flow of current 16 in sub 12. The
changing flux 26 also produces a current 30 which flows
circumferentially around sub 2. This current 30 is proportional to,
but greatly amplified over, input current 16, but cannot couple
back into toroid 14 because its circumferential flow does not
encircle the core of toroid 14.
Amplification of the incoming current 16 has thus been achieved
without feedback into the input terminals 18 of amplifier 20. It
must be noted that if such amplification had been attempted without
the utilization of a non-coupling mode, there would have been
negligible amplification if the feedback had been negative (in such
a direction that the output tended to subtract from the input).
And, if the feedback were positive (in such a direction as to add
to the input signal) the system would have been unstable, by
breaking into oscillation. Accordingly, the use of two
non-interferring or noncoupling modes provides a substantially
improved transmission system.
It should now be apparent that if the input and output terminals of
amplifier 20 were reversed, then exactly the same teaching as
applied to the current amplifier, would show that the transducer 10
would act as a flux amplifier, taking flux 26 and amplifying it to
produce a much greater flux 28 flowing circumferentially around sub
2 and current 16 flowing laterally in the sub 2. In that flux 28 is
parallel to the windings of solenoid 24 cannot couple into the
input circuit of amplifier 20 and, again, amplification has been
achieved without feedback.
Diagrammatically, the toroid 14 is represented as a block with
lines running parallel to the drill stem to indicate the direction
of the windings and solenoid 24 is shown with lines running across
the drill string again to indicate the direction of windings.
Amplifier 20 is shown as a triangle pointed in the direction of
amplification and is a relatively standard symbol. Current flow 16
is shown by solid lines with the symbol of a generator to indicate
that the current comes from an external source when transducer 10
is used as a current amplifier. Flux 26 is shown by dotted lines.
Not shown in the diagram are the necessary details of switching
power sources or transformer taps for proper impedance matching.
These are details which can be supplied by any competent mechanic
in the art.
FIG. 2 gives a diagrammatic view of one of the preferred exemplary
configurations of the total system. Once again, conventional
details obviously necessary, but peripheral to the understanding of
the system, are omitted.
A plurality of mode repeater transducers A through G are mounted on
a drill string 50 which is inserted in a bore hole 52. The latter
designations are used to indicate differing connections on
identical mode repeater transducers and will be explained later.
For convenience, the term "mode repeater transducer" will hereafter
be referred to by the initials MRT.
MRT A is shown as connected to a data source 54. Since the purpose
of this invention is to provide a high quality data transmission
channel, the nature of the data source is peripheral to the heart
of the invention. The source could represent sensor data output as
an aid to drilling, or it could represent data from any or all of a
number of sensors for bore hole logging or any other source which
generates data to be transmitted to the surface. FIG. 2 shows the
amplifier input of MRT A connected to the data source 54 rather
than to the output of either the associated toroid or solenoid
windings. The amplifier output is connected to the input of the
solenoid winding 56 thus the initial mode launched along drill
string 50 is magnetic. The magnetic mode containing information
from data source 54 propagates along drill string 50 and attenuates
with distance as shown in FIG. 3. The plus sign above MRT A
indicates the initial time phase of this signal. The distance
between MRT A and MRT B is such that only moderate signal
attenuation occurs before the signal is picked up by the solenoid
coil 58 of MRT B. The MRT B configuration is such that it is
connected as a magnetic to current mode transducer as shown. The
plus sign indicates that the output current mode from MRT B is
still in the same time phase as the input magnetic flux.
The amplified current output of MRT B flows along the drill string
50 and attenuates in both directions as shown in FIG. 3. The
spacing between MRT B and MRT C is again such that only moderate
attenuation of the current from MRT B occurs prior to reaching MRT
C where it is detected, amplified and transferred back into a
magnetic mode. Thus in FIG. 2, MRT C is connected as a current to
magnetic flux transducer. The minus sign above MRT C now indicates
that it is so connected that its output is reversed in time phase
with respect to its input. MRT D is again so spaced that only
moderate attenuation occurs between MRT C and MRT D and the
connection as a magnetic to current mode transducer is the same for
MRT B. Its output is in phase with its input and, thus, out of
phase with the signal which exists at MRT B. The separation between
MRT D and MRT E is variable and increases as the drilling
progresses, but it is never allowed to become so great that more
than moderate attenuation occurs prior to adding another MRT.
An analysis of the history of the path between MRT E and the next
lower MRT will show alternating predominate forms of excitation.
The signal existing at MRT E prior to the installation of MRT D
would primarily comprise a magnetic flux from MRT C and residual
current from MRT B. While FIG. 2 shows MRT E with the toroid 60 and
solenoid 62 connected in series (with the output voltages adding),
prior to the installation of MRT D, these coils would have been
connected with the output voltages subtracting since the two
principle components would have been out of phase. The net result
would have again been additive voltages. It is obvious that, by
proper selection of output connections of the toroids 60 and
solenoid 62, the two signals can be made additive regardless of the
excitation fields entering MRT E. The output of the amplifier 64
from MRT E is fed to a conventional data receiving and demodulation
device 66.
Also shown in FIG. 2 is a special configuration involving two MRT's
F and G. These are so connected that they act as attenuators of
both magnetic flux and current. The details of this configuration
will be discussed later. It is only the function this performs
which is important at this point of the teaching.
In the past, the drill 68 has been used as part of the current or
magnetic path. From the standpoint of this invention it is a path
which, while usable, should preferably be excluded if possible. The
drill bit 68 is one of the major sources of noise entering the
system and, as such, any currents or flux entering the bit path
should be excluded. This is achieved by insertion of attenuators F
and G into the path as will be discussed in more detail below.
FIG. 3 represents the various field strengths along the profile of
the drill string 50. Here the solid lines are used to represent the
magnetic flux mode, while the dotted lines represent the current
mode. The displacement of points on these curves represents the
relative field strengths with the most distant displacement to the
right representing the stronger field; while the plus and minus
signs again represent time phase with respect to the initial
signal.
The solid lines crossing at the location of MRT B represent the
magnetic fields to which the input of MRT B is sensitive. It can be
seen that, while the input from MRT A is of a positive phase, that
which is fed back from MRT C is of a negative phase or of opposite
sign. Thus the feedback of the system is negative and the system is
self-stabilizing. The same fact can be observed for the current
inputs at MRT C which are again of opposite sign and, thus
self-stabilizing.
One familiar with the art of feed back systems will recognize that,
if this phasing arrangement were not observed, the system could
become unstable and oscillate. Thus, the proper phasing connections
of the various mode repeater transducers is an important
factor.
The system shown in FIG. 2 is the preferred exemplary configuration
where conductivity contrasts, between various layers within the
earth are not too great or the frequencies involved are not high
(e.g., below approximately 1,000 hertz). However, sharp changes
have been observed in the conductivity of the walls of bore holes.
Some changes are on the order of one hundred to one, and even
approaching one thousand to one, within very short distances. These
sharp changes can produce standing waves of reflected energy along
the bore hole. While it is true that the signal's phase must be
continuous and that no sharp changes can occur, phase changes
within bore holes have been measured which exceed 180.degree. at
higher frequencies, within distances which would be short with
respect to desirable separation distances between MRT units. These
phase changes raise the possibility of positive feedback which
would cause the line of repeaters to oscillate and thus negate the
proper functioning of the system.
In such cases where negative feedback cannot be assured, the next
preferred approach would be one in which positive feedback either
cannot occur or, at least, is unlikely to occur.
It will be observed by reference to FIGS. 2 and 3 that once either
mode has been coupled into its respective MRT, the residual flux or
current which eventually couples back as feedback serves no useful
purpose other than the stabilization thus achieved. In those cases
where this feedback could be detrimental, rather than beneficial,
the preferred solution of this invention is to block the entry of
feedback flux or current by use of strategically located magnetic
attenuators thus blocking magnetic flux fields and current
attenuators thus blocking feedback currents.
The simplest form of magnetic field attenuator would be the use of
a monel metal or a non-magnetic form of stainless steel or other
non-magnetic materials as a sub. This special sub section could be
inserted between joints of the drill string and centrally located
between MRT units to block the flow of magnetic flux along the
drill string. As an example: such a unit centrally located between
MRT B and MRT C in FIG. 2 would block any magnetic feedback between
MRT B and MRT C.
FIG. 4 represents an exemplary passive attenuator for use in the
current mode. However, it is not truly an attenuator. It will be
seen by the following discussion that it effectively blocks an
undesirable current path by establishing a more preferred current
path, the currents of which tend to cancel the currents which would
otherwise flow in the undesirable current path. It thus acts more
in the function of an imperfect switch than as an attenuator.
However, for ease of explanation and of visualizing its function it
will be referred to as an "attenuator".
In FIG. 4, the drill string 100 is shown surrounding by two toroids
23 and 24. Toroids 102 and 104 are connected in series in such a
manner that current induced in the drill string 100 by toroid 102
are opposed or cancelled by the currents induced in the drill
string 100 by toroid 104. Connected to the drill string 100 and
between toroid 102 and toroid 104 are one or more conductors 106
(two are shown) which pass around the outside of toroid 104 and
back through the center of toroid 104 adjacent to drill string 100
but insulated therefrom. Conductors 25 then connect to a conducting
shell 108 which shell surrounds the drill stem 100 and is insulated
therefrom by an insulating shell 110 which may, if desired, be the
same insulation as used to insulate conductors 106 from drill
string 100. It should be noted that the length of conducting shell
108 and insulator 110 while not critical should be as long as
practical consideration permits, and that insulator 110 should
extend as far beyond the termination of shell 108 as is reasonably
practical.
It will also be noted that since conductors 106 all terminate on
the drill string 100 at one end and conductive shell 108 on the
other end and all encircle toroid 104 one time in the same
direction. They constitute a one turn loop around toroid 104.
In FIG. 4, amplifier 112 is shown as forcing signal current through
toroids 102 and 104. Insofar as current induced in the drill string
100 by toroid 102 attempts to flow through toroid 104 it will tend
to be cancelled by the currents induced by toroid 104 in drill
string 100. However, the current path from the drill string 100 to
the surrounding electrode 108 is different. It can be seen that
currents induced in conducting loop 106 (which passes through
toroid 104 in the opposite direction from the drill string 100) are
now in the same direction as the currents which are induced in the
drill string 100 by toroid 102 and follow the current path through
loop 106 to electrode 108.
It can now be seen that by use of this attenuator scheme it is
possible to establish a preferred current path between the drill
string 100 and electrode 106 while tending to block the direct
current path along the drill string 100 and through both toroids
102 and 104. Although its use is obviously not limited to this
location, FIG. 4 shows the attenuator placed adjacent to drill bit
114. This has been done to illustrate two of the desirable features
of this device:
1. It tends to block current flow through the drill bit, which, due
to resistance and pressure variation, moving parts, and high fluid
turbulence can be expected to provide a major source of noise
modulation of currents flowing through this path.
2. It allows the location of the communication transmitter
(amplifier 112) to be as close to the drill bit as possible, and
yet it provides a substantial electrode area 108 which, while
physically above the trans-mitting toroids 23 and 24 is
electrically below them with respect to the current paths involved.
For practical considerations, there is an advantage in having the
freedom to locate the information transmitter at this point if so
desired.
FIG. 5 shows essentially the same as FIG. 4 except in less current
detail. It represents a complete preferred current path, wherein
the attenuator unit 150 is of the same configuration as described
in the discussion of FIG. 4. While attenuator 152 has not been
discussed, those skilled in the art will recognize that the same
discussion as that given for the unit 150 is generally applicable,
in that the preferred current path is once again established.
The mechanism and desirability of utilizing the output of the
toroidal unit 154 to drive the solenoid 156 by amplifier 158 has
been established. The preferred current path established by the use
of these two units is represented by dotted lines 160.
It will also be recognized by those skilled in the art, that the
same teachings as used in the discussion of FIGS. 4 and 5 would
apply if the device were to be used as an attenuator of magnetic
flux. All that would be necessary would be to replace toroids 102
and 104 by two solenoids connected in the same manner, and to
establish that coil 106 and electrode 108 be of material of high
magnetic permeability. However, such configuration would not be as
efficient for the magnetic mode. Insulator 110 cannot present any
degree of magnetic permeability contrast approaching the
resistivity contrast achievable between an electrical insulator and
the return path when used in the current modes.
FIG. 6 represents a sketch of an active attenuator which, according
to its design, may attenuate either electric current or magnetic
flux. While the drawing represents a current attenuator and the
discussion will pertain to such a current attenuator, it will be
recognized that the drawing and discussion will equally well
pertain to an active magnetic attenuator, if the word solenoid is
used to replace the word toroid, and the alternating current
induced in the drill string is referred to as alternating magnetic
flux.
Referring to FIG. 6, drill stem 200 is shown surrounding by two
toroids 202 and 204. As shown, toroids 202 and 204 are connected so
that a voltage applied to the ungrounded terminal of toroid 202
will cause a current to flow in toroid 202 which will induce a
current in stem 200, which, on flowing through toroid 204 will
produce a voltage of like sign at the ungrounded terminal of toroid
204. The ungrounded terminal of toroid 204 is then connected to the
input of amplifier 206, which is of the class of amplifiers known
as operational amplifiers. The characteristic of this type of
amplifier is such that its amplification, or gain, is so high that
it can be considered infinite with respect to the voltages being
amplified. Although such infinite amplification is never actually
achieved, the discussion is simplified if amplifier 206 is
considered to have phase inversion and infinite gain which is
common practice in dealing with such amplifiers.
Assume there is an electrical current 208 (indicated by dotted
arrows) in drill string 200. Current 208 will cause a voltage to
appear at the output of toroid 204. This voltage will be amplified
and inverted in amplifier 206 which will attempt to generate a
voltage at its output which is infinitely greater than, and of
opposite sign to, the initial voltage generated at the input by the
initial current 208. The infinite voltage from amplifier 206 into
toroid 202 will start to generate an infinite current 210 in
opposition to current 208, current 210 then becomes an input to be
again fed back as was current 208. Thus any current which attempts
to flow through toroids 202 and 204, including current caused by
the output of amplifier 206, will immediately be cancelled by an
equal and opposite current. Ideally, zero alternating current can
flow between toroids 202 and 204. Thus, the configuration shown
achieves the effect of being an infinite attenuator or insulator,
without in any manner jeopardizing the structural integrity of the
drill string 200.
Although the discussion refers to ideal components, and such can
never be achieved, excellent results can be obtained with far from
such ideal components and without infinite gain. In excess of 30
decibels (31.6 to 1) of attenuation has been achieved with
configurations such as those shown in FIG. 6. This was achieved
with little regard to leakage inductances, stray capacitances, core
saturations and nonlinearities which one skilled in the art of
transformer design would normally consider. Thus attenuations as
high as 100 or even 1000 to one should be easily achievable.
It will now be recognized that the sign conventions used were for
purposes of discussion. Any combination of coil connections and
inverting or non-inverting amplifiers can be used as long as the
net result is that the system attempts to generate a current in the
drill string 200 which is much greater and in opposite direction
than any current attempting to flow between toroids 202 and 204 on
drill string 200.
FIG. 7 is included to show how two of the MRT units discussed under
FIG. 1 could be connected to attenuate both electric current and
magnetic flux as should now be apparent from the drawing itself.
Obviously, either current or magnetic modes could be attenuated
independently and individually by disconnecting the amplifier
controlling the mode which one does not wish to attenuate.
Returning now to FIGS. 1, 2 and 3, on the basis of the teaching
concerning FIG. 6, it is now possible to establish that if the
gains of the MRT units A through D are made as high as practical
consideration permits, the system will have a high degree of noise
immunity.
Adjacent stations are so configured that they are connected by
alternate modes of transmission. The first station, such as, C,
receives on the same mode as D transmits, but in opposite phase.
The broad requirement of the attenuator is met, but only for
currents or electromagnetic flux which attempts to impress itself
on drill string 50 without having been properly introduced into the
data channel. Thus, the system will have an improved degree of
immunity to noise introduced along drill string 50.
Where two or more similar devices are discussed as working in
conjunction, such as the discussion concerning active attenuation
devices, these have been discussed as separate devices as a matter
of convenience. Accordingly, it is intended that if several such
devices should be combined on a single core to achieve the same
results, this would be within the scope of this invention.
While these teachings have pertained primarily to transmission from
a drill hole, they could equally well apply to transmission from
the surface into the drill hole, or they could have applied to a
two way transmission path, or to transmission between points within
the bore hole.
There may be times when one mode, for instance the current mode,
may be vastly preferred over the other. These teachings are not
changed if the two modes comprise two frequencies, or two
combinations of frequencies, as long as these two frequencies, or
combination of frequencies, possess certain inherent
characteristics. These characteristics would include:
1. The capability to transform the first frequency, or first group
of frequencies, which constitute the first mode, into the second
frequency, or second group of frequencies. This is to be achieved
by operations performed solely upon the constitutents of the first
mode after they have been received at the next MRT unit from the
just previous transmitting MRT unit.
2. The capability to transform the second frequency, or second
group of frequencies, constituting the second mode back into the
first frequency, or first group of frequencies, constituting the
first mode. This is to be achieved by operations performed solely
upon the constituents of the second mode after they have been
received at the next MRT unit from the just previous transmitting
MRT unit.
3. The entire operation of transformation from mode one to mode two
and back to mode one, to be achieved without loss of the time phase
reference of the original mode one transmitted. Of course this
includes the same characteristics for the mode two to mode one to
mode two transformation.
4. The phase of such transformations being either preset or
self-controlled, such that feedback between like modes between
adjacent MRT units will be negative and self-stabilizing.
5. The MRT receiver for each mode being insensitive to the other
transmitted mode from that MRT.
FIG. 8 presents a flow diagram of one such system, wherein mode one
consists of a single carrier frequency f, and mode two consists of
the second harmonic of the mode one frequency 2f. MRT unit 250
receives the mode one frequency f and, through frequency doubling
circuits well known to the art, extracts the second harmonic in
such a manner that the data imposed on mode one is not lost. This
second harmonic is then retransmitted as mode two 2f. The act of
frequency doubling preserves the phase information of f. MRT unit
252 receives 2f and, through a frequency divider, divides 2f by 2
and retransmits mode one as f. The act of division by two generates
a 180.degree. phase ambiguity. Thus f, as retransmitted by MRT 252
may provide either positive or negative feedback when received by
MRT unit 250. If the feedback is positive, the pair of MRT units
250 and 252 will go into uncontrolled signal build up and
oscillation. Thus, MRT unit 252 has a stability sensor 254 which
detects this uncontrolled build up, or oscillation, and, should
such a condition occur, generates a reset pulse to the frequency
divider in MRT 252. This reset pulse, indicated by arrow 256 causes
the divider to either advance or retard 180.degree. thus causing
the output of MRT 252 to generate the condition of f as the only
stable condition. The feedback, therefor, is either negative, or
automatically forced to become negative, and the line becomes
self-stabilizing.
Although only a few embodiments of this invention have been
described in detail, those skilled in the art will readily
appreciate that there are many ways to modify the disclosed system
without materially changing the desired functioning or results.
Accordingly, all such modifications are intended to be included
within the scope of this invention.
* * * * *