U.S. patent number 3,906,435 [Application Number 05/396,400] was granted by the patent office on 1975-09-16 for oil well telemetering system with torsional transducer.
This patent grant is currently assigned to American Petroscience Corporation. Invention is credited to Arthur E. Lamel, William D. Squire, Harper J. Whitehouse.
United States Patent |
3,906,435 |
Lamel , et al. |
September 16, 1975 |
Oil well telemetering system with torsional transducer
Abstract
Zero order torsional acoustic waves are the preferred means for
acoustic communication in well drilling systems. Electroacoustic
transducers for such systems which operate at base band must be of
a size comparable with a length of drill pipe. The use of
cross-field magnetostrictive transducers is preferred as these
transducers can be made an integral part of the drill string since
they are rugged and self-supporting. When waves are launched from
the well platform or received there the transducer may be made an
integral part of the kelly. If the waves are either generated or
modulated down-hole near the bit, the transducers can be made an
integral part of the drill string or collars. In either case,
efficient transduction of zero order torsional waves is assured by
the use of crossed magnetic fields, e.g., circumferential and
longitudinal, one of which may be a bias field, and of which either
or both may be used as signal fields; the latter case particularly
for use as a modulator.
Inventors: |
Lamel; Arthur E. (Arcadia,
CA), Squire; William D. (San Diego, CA), Whitehouse;
Harper J. (San Diego, CA) |
Assignee: |
American Petroscience
Corporation (Bakersfield, CA)
|
Family
ID: |
26810741 |
Appl.
No.: |
05/396,400 |
Filed: |
September 12, 1973 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
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113147 |
Feb 8, 1971 |
3790930 |
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Current U.S.
Class: |
367/81;
175/50 |
Current CPC
Class: |
G01H
1/10 (20130101); E21B 47/16 (20130101) |
Current International
Class: |
E21B
47/12 (20060101); E21B 47/16 (20060101); G01H
1/00 (20060101); G01H 1/10 (20060101); G01v
001/40 () |
Field of
Search: |
;181/15RM,15AG
;340/18LD,18NC,17,11,15.5SW ;175/40,50 ;73/7.1C ;310/26,DIG.1 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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865,963 |
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Apr 1961 |
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GB |
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830,463 |
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Mar 1960 |
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GB |
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Other References
Rust et al., "Linearmagnetostrictive . . . Kreuzfelles," 1952, pp.
132-135, Acustica, Vol. 2..
|
Primary Examiner: Wilbur; Maynard R.
Assistant Examiner: Moskowitz; N.
Attorney, Agent or Firm: Lilly; Forrest J.
Parent Case Text
RELATED APPLICATION
This application is a division of our parent application, Ser. No.
113,147, filed Feb. 8, 1971, now U.S. Pat. No. 3,790,930 and
entitled "Telemetering System for Oil Wells."
Claims
What is claimed is:
1. In an acoustic communication system for use in well drilling
equipment, the combination of:
a drill string inclusive of a drill pipe, said drill string being
adapted to the propagation along its length of zero order torsional
acoustic waves within its substance, and
an electroacoustic transducer for transducing between an electrical
signal and zero order torsional acoustic waves propagating along
the length of said drill string within the substance of said drill
pipe, said transducer embodying a member connected into and
functioning mechanically and acoustically as part of said drill
string,
said transducer member including a field-strain element adapted to
experience a torsional mechanical strain in the presence of a
magnetic field, and, conversely, a magnetic field in the present of
a torsional mechanical strain, and
signal field means magnetically coupled to said field-strain
element, all in such manner and arrangement as to transduce between
a magnetic signal field and zero order torsional acoustic waves
within the substance of said field-strain element and said drill
pipe.
2. In an acoustic communication system for use in well drilling
equipment, the combination of:
a drill string inclusive of a drill pipe, said drill string being
adapted to the propagation along its length of zero order torsional
acoustic waves within its substance, and
an electroacoustic transducer for transducing between an electrical
signal and zero order torsional acoustic waves propagating along
the length of said drill string within the substance of said drill
pipe, said transducer including a member connected into and
functioning mechanically and acoustically as part of said drill
string,
said transducer member including a magnetostrictive element
provided with a magnetic bias field and adapted to experience a
torsional mechanical strain in the presence of a magnetic field,
and, conversely, a magnetic field in the presence of a torsional
mechanical strain, and
signal field means magnetically coupled to said magnetostrictive
element, all in such manner and arrangement as to transduce between
a magnetic signal field and zero order torsional acoustic waves
within the substance of said magnetostrictive element and said
drill pipe.
3. The system according to claim 2, wherein:
said transducer member includes at least in part a tubular body
coupled into said drill string,
said tubular body comprising also, at least in part, said
magnetostrictive element,
in an arrangement wherein said signal field is orthogonal to said
magnetic bias field, one of said fields being directed
longitudinally of said tubular body within the substance of said
magnetostrictive element and the other of said fields being
directed circumferentially of said tubular body within the
substance of said magnetostrictive element.
4. The system according to claim 3, wherein:
said signal field is directed circumferentially of said tubular
body within the substance of said magnetostrictive element, and
said bias field is established longitudinally of said tubular body
within the substance of said magnetostrictive element.
5. The system according to claim 4, wherein:
said signal field means comprises electrical conductors extending
lengthwise of said body in inductively coupled relation to said
magnetostrictive element, to transduce between an electrical signal
in said conductors and a circumferential magnetic signal field and
thereby a zero order torsional strain in said magnetostrictive
element.
6. The system according to claim 4, wherein:
said signal field means comprises conductors extending
longitudinally both internally and externally of said tubular body,
connected in such manner to transduce between an electrical signal
in said conductors and a circumferential magnetic signal field and
thereby zero order torsional strain in said magnetostrictive
element.
7. The system according to claim 6, wherein:
said conductors comprise an internal tubular conductor fixed within
said tubular body, external conductors fixed to the outside of said
body, means electrically connecting said internal and external
conductors at one end, and electrical terminals electrically
connected to the other ends of said internal and external
conductors for connecting to external circuitry.
8. The system according to claim 6, wherein:
said conductors comprise an internal tubular conductor fixed within
said tubular body, an external tubular conductor fixed to the
outside of said body, means electrically connecting said internal
and external conductors at one end, and electrical terminals
electrically connected to the other ends of said internal and
external conductors for connecting to circuitry external to said
element.
9. A system according to claim 3, including:
a mechanical coupling on at least one end of said tubular body for
coupling said body in the well bore drill string.
10. The system according to claim 3, wherein:
said tubular body has a longitudinal passage for the flow of
drilling mud, and
said tubular body is adapted to constitute a load bearing part of
said drill string.
11. A system according to claim 10, wherein:
said tubular body embodies also a kelly for the drill string and
has a non-circular external transverse cross-section.
12. A system according to claim 10, including:
a mechanical coupling on at least one end of said tubular body for
mechanically coupling said tubular body in the well bore drill
string,
a swivel rotatable on the end of said tubular body remote from said
mechanical coupling, conductor windings for at least one of said
fields on said tubular body, and means on said swivel and body for
electrically coupling said transducer field conductors to external
circuitry.
13. A system according to claim 10, wherein:
said tubular body provides a section of drill pipe for use as an
integral part of said drill string, and said body has a circular
external cross-section concentric with said drill pipe.
14. A system according to claim 3, wherein:
said bias field is provided by permanent magnetic means.
15. A system according to claim 3, wherein:
said bias field is afforded by magnetic remanence in said
magnetostrictive element.
16. A system according to claim 14, wherein:
said permanent magnetic means comprises permanent magnets disposed
in magnetically coupled relation to said magnetostrictive element
to induce in it a magnetic bias field.
17. A system according to claim 3, including:
bias field conductor means disposed in inductively coupled relation
to said magnetostrictive element for producing said magnetic bias
field, said bias field conductor means being energizable by an
electrical current to establish a bias field in said
magnetostrictive element.
18. A system according to claim 17, wherein:
said bias field conductor means is energized concurrently with said
signal field.
19. A system according to claim 17, wherein:
said bias field conductor means is energized with direct current
(D.C.).
20. A system according to claim 17, wherein:
said bias field conductor means is energized with a fluctuating
current with a direct current (D.C.) component.
21. A system according to claim 3, wherein:
said signal field is directed longitudinally of said tubular body
within the substance of said magnetostrictive element, and
said bias field means establishes a magnetic bias field directed
circumferentially of said tubular body within the substance of said
magnetostrictive element.
22. A system according to claim 21, wherein:
said signal field means comprises electrical conductors
circumferentially encircling said body in inductively coupled
relation to said magnetostrictive element to transduce between an
electrical signal in said conductors and a longitudinal magnetic
signal field and thereby a zero order torsional strain in said
magnetostrictive element.
23. A transducer according to claim 22, wherein:
said conductors comprise a coil encircling said body.
24. A system according to claim 21, wherein:
longitudinal slots are incorporated in at least a portion of said
member to reduce circumferential eddy currents.
25. A system according to claim 21, wherein:
tubular bodies of large magnetic reluctance are juxtaposed to ends
of the magnetostrictive part of said transducer to reduce coupling
of the magnetic signal field and thereby to reduce circumferential
eddy currents in parts of said transducer-drill string combination
other than said magnetostrictive part.
26. A system according to claim 25, wherein:
said large reluctance bodies are slotted longitudinally to reduce
circumferential eddy currents in said bodies.
27. A system according to claim 24, wherein:
said longitudinal slots are sealed to prevent leakage of the
drilling mud from within said tubular body.
28. A system according to claim 3, wherein:
an acoustic termination is juxtaposed to one end of said body to
provide a terminating acoustic impedance for efficient
transduction.
29. A system according to claim 28, wherein:
said termination is a reflecting termination that reflects acoustic
energy.
30. A system according to claim 29, wherein:
said termination is a torque reaction stub.
31. A system according to claim 28, wherein:
said termination is an absorbing termination that absorbs acoustic
energy.
32. A system according to claim 28, wherein:
said termination is both a reflecting and absorbing
termination.
33. A system according to claim 1, wherein:
said signal field means comprises electrical conductors disposed in
inductively coupled relation to said field-strain element, and
adapted to transduce between an electrical signal in said
conductors and a magnetic signal field and thereby a zero order
torsional strain in said field-strain element.
34. A system according to claim 3, wherein:
said tubular body is composed at least in part of an electrically
conductive material and said signal field means comprises the
electrically conducting part of said body in combination with
external conductors forming an electric circuit to transduce
between an electrical signal in said circuit and a circumferential
magnetic field and thereby zero order torsional strain in said
magnetostrictive element.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to the art of transmitting
telemetric and control information through a hollow well bore drill
string or other pipe. More particularly, the invention relates to
an improved acoustic communication method and system for the
purpose described wherein the information carrier is provided by
torsional acoustic waves preferably of zero order.
2. Description of the Prior Art
When drilling a well bore, it is desirable, if not essential, to
monitor selected drilling parameters in the vicinity of the drill
bit for the purpose of providing the drilling operator with
sufficient information to properly control the drilling operation.
Among the drilling parameters which provide valuable information to
the drilling operator are temperature, formation pressure,
formation porosity, and others. In slant drilling operations, such
as off-shore drilling of multiple wells from a single platform or
island, an additional drilling parameter which provides extremely
valuable, if not essential information to the drilling operator, is
drill string orientation.
The prior art relating to well drilling is replete with a vast
assortment of acoustic communication techniques for transmitting
information through a drill string. Simply stated, such
communication techniques involve propagation through the drill
string from one position or station to another of modulated
acoustic waves containing the information to be transmitted, and
demodulation of the modulated waves at another position or station
along the drill string to recover the transmitted information. In
the present disclosure, the station from which the modulated
acoustic waves propagate is referred to as a signal-transmitting
station. The position at which the modulated waves are demodulated
to recover the transmitted information is referred to as a
signal-receiving station.
The prior acoustic communication systems for transmitting
information through a drill string are deficient in that they
utilize relatively inefficient modes of acoustic wave propagation
and thus achieve, at best, only marginal information transmission.
In this regard, it is significant to note that most published
patents in the field use such descriptors as vibrations, sound,
acoustic waves, and the like, to describe the acoustic information
carrier, and do not specifically define the exact mode of acoustic
wave propagation. Those patents which do describe a specific form
of acoustic wave propagation utilize either longitudinal or
flexural vibration modes. These latter vibration modes, however,
are ill suited for use in transmitting information through a drill
string owing to the large transmission losses which occur as a
result of acoustic coupling of the drill string to the drilling
fluid and the wall of the well bore.
Because of these large transmission losses, the patented drill
string communication systems are at best capable of operation only
in a manner wherein the acoustic waves are modulated and launched
upwardly through the drill string from a signal-transmitting
station at the lower end of the string to a signal receiving
station at the surface. This manner of operation requires
installation of the acoustic wave transducer and its electronic
driving circuitry within the lower end of the drill string.
Accordingly, the transducer and circuitry must be designed to fit
the envelope of the drill string and to survive the hostile
environment existing within the lower end of the well bore during
drilling. In addition, servicing and replacement of the transducer
and its circuitry requires removal of the entire drill string from,
and subsequent lowering of the entire drill string into, the well
bore.
Our parent U.S. Pat. No. 3,790,930, of which this is a division,
discloses an improved acoustic communication method and system of
the class described whose primary application involves transmission
of telemetric and control information through a drill string
suspended within a well bore from a surface drilling platform.
According to the disclosure in said patent, modulated acoustic
waves containing the information to be transmitted are propagated
through the drill string from the signal transmitting station to
the signal receiving station, and the modulated waves arriving at
the receiving station are demodulated to recover the transmitted
information. It is significant to note here that the generic
invention contemplates within its scope two different methods of
establishing the modulated acoustic waves within the drill string.
According to one method, acoustic waves are first established in
the drill string and these waves are modulated at the signal
transmitting station by exciting an acoustic wave modulator in the
drill string with a modulating signal representing the information
to be transmitted. According to the other method, modulated
acoustic waves containing the information to be transmitted are
generated in the drill string at the signal transmitting station by
exciting an acoustic wave generator or transducer in the drill
string with a driving signal which is modulated to represent the
information to be transmitted. Accordingly, it will be understood
that within the context of the present disclosure, terms such as
"modulate," "modulation," cover both modulation of existing
acoustic waves in the drill string and generation or launching of
modulated acoustic waves into the drill string for the purpose of
establishing in the drill string modulated acoustic waves containg
the information to be transmitted.
Telemetric signals transmitted through the drill string may
represent selected drilling parameters in the vicinity of the drill
bit, such as temperature, formation pressure, formation porosity,
drill string orientation, and others. In this case, modulation
occurs at a subsurface signal-transmitting station adjacent the
lower end of the drill string with telemetric signals from sensors
responsive to the selected drilling parameters to be monitored.
Control signals transmitted through the drill string may be
utilized to operate, from a station on the drilling platform,
devices within the well bore, such as signal transmitters located
at sub-surface stations along the drill string.
One important aspect of the invention is concerned with the form of
acoustic waves which are employed to transmit information.
According to this aspect, the preferred waves are first of all
torsional acoustic waves. Such torsional acoustic waves are
superior to all other acoustic waves, such as longitudinal and
flexural, for information transmission through a drill string in
that they couple less acoustic energy into the drilling fluid and
wall of the well bore and thus permit efficient signal transmission
through a greater length of drill string. In its broader scope, the
invention contemplates the use of any torsional acoustic waves
which may be launched through a drill string and modulated to
transmit information through the string as broadly referred to
hereinabove. However, the preferred waves are torsional acoustic
waves of zero order, that is, torsional acoustic waves
characterized by pure rotation of the drill string about its
central axis. Such zero order torsional waves are non-dispersive,
i.e., the velocity of the waves is independent of their frequency,
while most other acoustic wave forms are dispersive. Non-dispersive
wave propagation through a drill string is highly desirable, and
often essential to rapid signal transmission through the string for
the reason that dispersion smears the information signals modulated
on the waves.
Another important aspect of the invention as disclosed in the
aforesaid parent patent involves the direction or torsional wave
propagation through the drill string. According to this aspect of
the generic invention, the torsional acoustic waves may be launched
downwardly through the drill string from the surface or upwardly
through the drill string from the lower end of the string. In the
preferred practice of the invention involving transmission of
telemetric signals representing selected drilling parameters, the
torsional acoustic waves are launched downwardly through the drill
string top-side, e.g., from the surface drilling platform to a
subsurface signal-transmitting station at the lower end of the
drill string. The waves arriving at the lower transmitting station
are modulated with the telemetric signals to be monitored and
returned back through the drill string to a signal receiving
station at the drilling platform where the modulated waves are
demodulated to recover the tramsmitted signals. This method of wave
propagation is permitted because of the above-described reduction
in acoustic transmission losses which results from the use of
torsional acoustic waves, particularly torsional waves of zero
order whose frequencies lie within the base band of the drill
string acoustic transmission characteristics. Such a propataion
method is preferred for the reason that the torsional wave
generator, comprising a transducer and its electronic driving
circuitry, may be located out of the well bore at the drilling
platform. The torsional wave generator is thereby isolated from the
hostile environment in the well bore and is readily accessible for
repair and servicing without removal of the drill string. Also, the
drill string envelope imposes no constraint on the size and
arrangement of the generator. However, it is considered to be
within the scope of the invention to launch the torsional waves
upwardly through the drill string from a subsurface
signal-transmitting station.
In those applications involving transmission of control signals
through the drill string from a signal-transmitting station at the
drilling platform to a subsurface signal-receiving station along
the drill string, the torsional waves are preferably launched
downwardly through the drill string from the surface. Here again,
however, it is considered to be within the scope of the invention
to launch waves upwardly through the drill string from its lower
end, modulate the waves at the surface signal-transmitting station
with the control signals to be transmitted, and return the
modulated waves back downwardly through the drill string to the
subsurface signal-receiving station.
A further important aspect of the invention is concerned with the
actual generation of the torsional acoustic waves within the drill
string. According to this aspect, the invention contemplates two
different methods of acoustic wave generation. One method involves
utilization of the torsional acoustic waves which are inherently
produced in a rotating drill string during a drilling operation. In
this regard, it is well-known that a drill string cutting bit, in
the process of cutting into an earth formation, generates large
quantities of noise which are transmitted along the drill string.
Since the cutting motion is primarily a turning or twisting motion,
a large component of this noise is torsional in character, i.e.,
consists of torsional acoustic waves. Such torsional waves are
composed of relatively broadband components and narrow spectral
lines or frequency bands generated by the teeth of a cutting bit
and the gears in the mechanical drill string drive. The rotation
generated torsional waves can be modulated at the bottom of the
drill string in a manner to effectively transmit upwardly through
the string selected torsional wave components representing
information signals. These signals may be detected at the surface
to recover the transmitted information. The specific process is
further disclosed and claimed in a continuing application to be
filed later.
The preferred method of acoustic wave generation contemplated by
the invention involves the use of a transducer, preferably a
cross-field magnetostrictive transducer, energized by an electrical
driving signal of the proper frequencies to drive the drill string
in torsional acoustic oscillation in a manner to produce in the
string torsional acoustic waves preferably torsional waves of zero
order.
In this latter regard, a further important aspect of the invention
is concerned with a novel crossed-field magnetostrictive transducer
for the present drill string communication system. This transducer
may be utilized as a torsional acoustic wave generator for the
drill string, an acoustic signal transmitter, and/or an acoustic
signal receiver. A major advantage of the transducer resides in its
self-supporting construction which permits the transducer to form a
load bearing part of the drill string. One transducer disclosed
herein, for example, is embodied directly in the drilling kelly.
Another advantage of our transducer resides in its ability to drive
the drill string in its base band of torsional acoustic
transmission. In this band, the acoustic attenuation or acoustic
transmission losses produced by the drill string are minimized.
This reduction of the acoustic transmission losses in the drill
string, along with the earlier mentioned reduction in transmission
losses resulting from the use of torsional waves, enable operation
of the present communication system in its preferred operating
manner, referred to earlier. It will be recalled that in this
preferred operating manner, the torsional acoustic waves are
launched downwardly through the drill string from the surface,
modulated at the subsurface signal-transmitting station with the
telemetric signals to be monitored, and then returned back to the
surface signal-receiving station.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 illustrates well bore drilling apparatus embodying a drill
string communication system according to the invention;
FIG. 2 is an enlarged detail of the rotary table kelly and hoist of
the drilling apparatus;
FIG. 3 is an enlarged longitudinal section through the drilling
kelly illustrating a magnetostrictive transducer embodied in the
kelly;
FIG. 4 is a further enlarged section taken on line 4--4 in FIG.
3;
FIG. 5 is an enlarged section taken on line 5--5 in FIG. 4;
FIG. 6 is an enlarged section taken on line 6--6 in FIG. 3;
FIG. 7 is an enlarged section through an inertial modulator
embodied in the communication system;
FIG. 8 is a section taken on line 8--8 in FIG. 7;
FIG. 9 is a section taken on line 9--9 in FIG. 7;
FIG. 10 is a diagrammatic illustration of the drill string
communication system;
FIGS. 11-13 are diagrams of the well bore transducer modulator
electronics of the communication system;
FIG. 13A is a diagram of the acoustic transmission characteristics
of a drill string;
FIG. 14 is a diagram of the top side transducer electronics of the
communication system;
FIG. 15 is a diagram of the top side transducer electronics of a
modified drill string communication system having separate acoustic
wave launching and receiving transducers;
FIG. 16 illustrates a modified crossed-field magnetostrictive
transducer according to the invention;
FIG. 17 is a section taken on line 17--17 in FIG. 16;
FIG. 18 is a section taken on line 18--18 in FIG. 16;
FIG. 19 diagrammatically illustrates a modified drill string
communication system according to the invention, wherein modulated
torsional acoustic waves are launched upwardly from the lower end
of the drill string;
FIG. 20 is a diagram of the surface receiving electronics of the
communication system of FIG. 19;
FIG. 21 illustrates a further modified crossed-field
magnetostrictive transducer according to the invention;
FIG. 22 is an enlarged section taken on line 22--22 in FIG. 21 with
the field coil omitted for clarity; and
FIG. 23 illustrates a further modified magnetostrictive transducer
according to the invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Turning now to FIGS. 1-14, there is illustrated a communication
system 10 according to the invention for transmitting information
through a subsurface pipe 12 from a signal-transmitting station 14
to a signal-receiving station 16 through an intervening length 17
of the pipe which is capable of sustaining torsional acoustic
oscillations. The communication system includes wave generating
means 18 for inducing in the pipe 12 torsional acoustic waves,
means 20 at the signal-transmitting station 14 for modulating the
waves with a modulating signal representing the information to be
transmitted, and receiving means 24 at the signal-receiving station
16 for demodulating the modulated waves to recover the transmitted
information. The particular embodiment of the invention selected
for illustration represents the primary application of the
communication system. In this case, the pipe 12 is a drill string
suspended within a well bore 26 from a surface drilling platform
28. The communication system is utilized to transmit signals along
the drill string between the transmitting and receiving stations.
These transmitted signals may be either control signals for
operating, from the drilling platform, a device within the well
bore, or telemetric signals representing selected drilling
parameters to be monitored at the platform.
The drilling platform 28 is conventional and hence need not be
described in elaborate detail. Suffice it to say that the platform
has a derrick 30 mounted on a floor 32 and supporting a hoist 34.
Hoist 34 includes a traveling block 36 supported by a cable 38 and
carrying a swivel 40. This swivel provides a rotatable connection
between the traveling block and the drilling kelly 42 at the upper
end of the drill string 12. Kelly 42 extends downwardly through a
rotary table 44 on the derrick floor 32 and through the well casing
46 and a blow-out preventer 48 sealed to the wall of the well bore
as at 49. The upper end of the drill string 12 proper is connected
to the lower end of the kelly. The hoist 34 and rotary table 44 are
powered by a draw works 50. A drilling fluid circulation pump 52
delivers drilling fluid or mud under pressure from a mud pit 54 or
other fluid reservoir to the swivel 40 through a mud hose 56. The
mud flows downwardly through the kelly 42 and the drill string 12
and finally returns to the surface through the well bore, about the
outside of the drill string, and then through blow-out preventer
48. The mud flows from the blow-out preventer back to the reservoir
through a return line 58.
Drill string 12 is composed of individual drill pipe sections 60 of
usually uniform length joined end to end by couplings 62 which are
commonly referred to as tool joints. In some cases the drill string
may contain additional sections, known as drill collars. Each drill
string section 60 normally has a length of approximately 30 feet.
Drill collar 63 and a drill bit or cutter 64 are coupled to the
lower end of the drill string.
In operation of the illustrated drilling rig, the rotary table 44
is driven in rotation by the draw works 50 to drive the kelly 42
and hence the drill string 12, in its rotary drilling motion. The
hoist 34 is operated to support a portion of the drill string
weight, such as to maintain the proper drilling pressure on the
cutter 64. The mud pump 52 is operated to provide continuous
circulation of drilling mud through the well bore to lubricate the
cutter and remove debris from the well bore.
The particular acoustic communication system 10 of the invention
which has been selected for illustration in FIGS. 1-14 is designed
for monitoring selected drilling parameters in the vicinity of the
drill bit in order to provide the drilling operator with sufficient
information to effectively control the drilling operation. As noted
earlier, typical drilling parameters which provide valuable
information to the drilling operator are temperature, formation
pressure, formation porosity, drill string orientation, and others.
In this case, the signal transmitting station 14 is located at the
lower end of the drill string 12, and the signal-receiving station
16 is located at the drilling platform 28. Sensors 65 are shown
mounted within the drill collar 63 to sense the drilling parameters
to be monitored. These sensors are connected to the modulating
means 20 and provide signals representing the monitored drilling
parameters. The modulating means processes the sensor output
signals to provide a modulating or telemetric signal containing
information representing all of the monitored drilling parameters
and modules the acoustic waves induced in the drill string 12 by
the wave generating means 18 with the telemetric signal. The
modulated waves travel up the string to the surface
signal-receiving station 16 where the waves are demodulated by the
receiving means 24 to recover the transmitted drilling parameter
information.
In certain of its aspects the generic invention disclosed in parent
U.S. Pat. No. 3,790,930 contemplates the use of any acoustic waves
capable of modulation by the telemetric signal to be transmitted
and capable of propagation through the drill string 12 with
sufficiently small acoustic loss and dispersion over the length of
the drill string to provide efficient signal reception at the
signal receiving station 16. In this regard, it is significant to
recall that torsional acoustic waves, however, are superior to all
other acoustic wave forms, such as longitudinal and flexural for
acoustic signal transmission through a drill string, since
torsional waves couple less acoustic energy into the drilling fluid
and the wall of the well bore. According to the preferred practice
of the invention, especially for depths of which communication
becomes difficult, or otherwise impossible, the torsional waves
used for signal transmission are torsional acoustic waves of zero
order. Such waves are characterized by pure rotation of each
transverse section of the drill string within an advancing wave
front about the longitudinal axis of the string. The major
advantage of such zero order torsional waves resides in the fact
that they are non-dispersive. Most other acoustic modes of
propagation are dispersive. Non-dispersive torsional wave
propagation is desirable, and essential to rapid efficient signal
transmission through a drill string, since dispersion smears the
transmitted signal along the string and renders difficult recovery
of the signal at the signal receiving station.
The frequency of the torsional waves is also an important factor in
efficient signal transmission through the drill string 12 in that
the couplings 62 which join the drill string pipe sections 60
acoustically load the string and the mud about the string
attenuates higher frequencies of acoustic oscillation. The jointed
string thus tends to pass lower acoustic frequencies with less
attenuation than higher frequencies, due to the frequency dependent
attenuation of the mud, while the couplings 62 introduce zeros of
transmission as shown in FIG. 13A. According to the preferred
practice of the invention, the frequency of the torsional acoustic
waves employed for signal transmission is selected to effect wave
propagation through the drill string in its base band of
transmission. This is the band from zero frequency to the first
zero of transmission, f.sub.o. In this band, the mud produces
minimum attenuation of the waves and thus permits maximum signal
transmission through the string. However, in its broader scope, the
invention contemplates acoustic wave propagation through the drill
string in its higher pass bands so long as suitable signal
reception is possible at the signal receiving station. As will
appear from the later description, operation of the present drill
string communication system in the base band is permitted by a
unique crossed-field magnetostrictive transducer of the invention
capable of inducing in the string torsional acoustic waves of the
relatively low frequency required for such base band operation. The
preferred torsional wave launching means for launching the
torsional acoustic waves through the drill string 12 is a torsional
acoustic wave generator including a crossed-field magnetostrictive
transducer. An important feature of the invention in this regard
resides in novel crossed-field magnetostrictive transducer
configurations which may be utilized to launch the waves through
the drill string as well as to modulate the waves and receive the
modulated waves. A unique feature of these transducers is their
rugged self-supporting construction which permits the transducers
to form an integral load supporting element of the rotating drill
string system. The drill string communication system in FIGS. 1-14,
for example, employs a crossed-field magnetostrictive transducer
which is embodied in and forms a load bearing part of the kelly 42.
It should be noted that by employing a bias field coincident with
rather than crossed with the signal field, a transducer for
launching or receiving longitudinal acoustic waves results, with
the same attributes as just mentioned, and is also considered
within the scope of the invention. An alternative method of
acoustic wave generation contemplated by the invention involves
utilization of the torsional waves or torsional noise inherently
produced in a rotating drill string.
The earlier discussed reduction in acoustic transmission losses
resulting from utilization, in the present drill string
communication system, of torsional acoustic waves, particularly
zero order torsional waves within the base band frequency range of
the drill string 12, together with the self-supporting construction
of the present magnetostrictive transducers permits various types
of acoustic wave communication through the drill string. When
monitoring drilling parameters, such as those mentioned earlier,
the preferred method of communication involves launching the waves
downwardly through the drill string from the surface to the
subsurface signal-transmitting station 14. The waves are modulated
at this station with the telemetric signal representing the
drilling parameters to be monitored and returned upwardly through
the drill string to the surface signal receiving station 16. A
primary advantage of this communication method resides in the fact
that the torsional wave generating transducer may be located out of
the well bore. The transducer is then isolated from the hostile
environment in the well bore, is readily accessible for servicing
and repair without removal of the drill string, and is free of the
design constraints imposed by the drill string envelope.
The drill string communication system illustrated in FIGS. 1-14
employs this preferred method of acoustic communication. Referring
now in greater detail to this communication system, the means 18
for inducing torsional acoustic waves in the drill string 12
comprises a torsional acoustic wave generator which is embodied in
the drilling kelly 42 and which includes a lower crossed-field
magnetostrictive transducer 66 according to the invention, and an
upper torque reaction stub 70, as shown in FIG. 3. The transducer
and torque reaction stub have tubular bodies 72, 76, respectively,
rigidly joined end to end in any convenient way. These tubular
bodies have a uniform, non-circular, usually square, cross section
matching that of a conventional drilling kelly and together
constitute the drilling kelly 42.
The lower end of the kelly 42, that is, the lower end of transducer
body 72, is coupled to the upper end of the drill string 12 by a
tool joint 78. Swivel 40 is rotatably coupled to an extension 79 at
the upper end of the kelly, that is, to the upper end of the upper
reaction stub body 76. As shown in FIGS. 1-14, this swivel has an
inverted cup-like housing 80 receiving the upper end of the stub
body extension 79. The housing is attached to the extension by a
pair of combined radial and thrust bearings 82. A seal ring 84
provides a liquid tight seal between the housing and extension. The
kelly 42 is thus restrained against longitudinal movement but is
free to rotate relative to the swivel housing 80. At the upper end
of the housing is a lifting bail 86 by which the housing and hence
the kelly 42 and drill string 12, are suspended from the travelling
block 36 of hoist 34.
The mud hose 56 connects to the swivel housing 80 and opens to the
interior housing chamber 88 above the seal 84. Extending centrally
through the kelly 42 is a mud passage 90 through which drilling mud
entering the chamber 88 through the mud hose 56 flows to the
central mud passage in the drill string 12.
As noted above, the torsional wave transducer 66 is a crossed-field
magnetostrictive transducer. Transducers of this general class are
known in the art. Such a transducer requires an elongated element
of body of magnetostrictive material and means for establishing two
magnetic fields within the body. One field is an axial field whose
field lines extend longitudinally through the body. The other field
is a transverse field whose field lines extend circumferentially
through the body. One field is commonly referred to as a bias field
and the other as a signal field. Either field may serve as the bias
field and the other field as the signal field. The interaction of
the bias and signal fields produces a torsional strain in the body
which may be caused to fluctuate in such a way as to induce
torsional oscillations in the body by varying, at the proper
frequency, either or both the bias and signal fields. In this mode,
the transducer is either a torsional wave generator or modulator,
i.e., signal transmitter. The transducer is also capable of
operating in an acoustic signal receiving mode. Thus a torsional
strain within the transducer body with only one of the transducer
fields present induces in the other field conductors a voltage, at
the conductor terminals, proportional to the rate of strain. The
communication system of FIGS. 1-14 employs the magnetostrictive
transducer 66 as both a torsional wave generator and a signal
receiver.
In such a crossed-field magnetostrictive transducer, the fields in
the longitudinal and circumferential directions may be established
in various ways. For example, the field in the circumferential
direction may be established by passing a current longitudinally
through the transducer body or through a conductor within the body.
The field in the longitudinal direction may be established by
passing a current through a coil surrounding the body.
Alternatively, either field may be established by constructing the
transducer body of a magnetically remanent magnetostrictive
material which is permanently magnetized in the proper direction.
The field in the longitudinal direction may also be established by
permanent magnets along the transducer.
Suitable materials for the body of a transducer designed for such
remanent operation are iron-cobalt alloys, such as 50--50 iron
cobalt, or ternary iron-cobalt alloys, such as 2V Permandure
containing approximately 49% iron, 49% cobalt and 2% vanadium, or
nickel-cobalt alloys such as Ni204 containing approximately 4%
cobalt and 96% nickel. Also suitable are iron-nickel-cobalt alloys,
including multi-element alloys based on the iron-nickel-cobalt
complex as are many alloys consisting of one of the magnetic
elements iron-nickel-cobalt in combination with non-magnetic
elements such as an alloy consisting of approximately 12% aluminum
and 88% iron. For non-remanent transducer operation, the transducer
body may be constructed of nickel or any of the magnetostrictive
alloys of nickel and iron commonly called permalloys, such as
50--50 nickel iron, or some of the more complex alloys such as
NiSpan C, containing nickel, iron, titanium, and chromium.
It is significant to note here that in the present drill string
communication applications, the mechanical properties of the
transducer body also enter into the selection of the
magnetostrictive material for the body. Foremost among these
mechanical properties are machinability, tensile strength, effect
of tensile stress on the magnetostrictive characteristics,
electrical conductivity, and others.
The crossed-field magnetostrictive transducer 66 embodied in the
well drilling apparatus of FIGS. 1-14 is designed for remanent
operation. To this end the transducer body 72 has a major central
portion 72P constructed of a magnetically remanent magnetostrictive
material. In this instance the material is biased with a remanent
field in the longitudinal direction.
Fixed to and extending the full length of the kelly mud passage 90
is a sleeve 94 of copper or the like which provides an inner
signal-field conductor of the transducer. Fixed within channels 96
in the four sides of and extending the full length of the kelly 42
are strips 98 of copper or the like which provide outer
signal-field conductors of the transducer. These outer conductors
are electrically insulated from the transducer body 72 by
electrical insulation 100. The lower ends of the inner and outer
conductors 94, 98 are electrically connected at 102. The upper ends
of the conductors are electrically connected to the leads of a
cable 104 through collector rings 106 surrounding the upper end of
the kelly 42 and collector brushes 108 carried by the swivel
housing 80. The upper collector ring is assured good electrical
contact to the inner conductor by means of copper rivets 107. The
lower collector ring is in direct electrical contact with the outer
conductors.
As will be explained in more detail presently, a driving signal is
applied to the transducer signal-field conductors 94, 98, through
the cable 104. This driving signal produces in the conductors a
fluctuating current which induces in the transducer body 72P a
circumferential magnetic signal field that interacts with the
longitudinal remanent bias field of the body to produce an
alternating torsional strain in the body. Such alternating
torsional strain, in turn, propagates as a torsional wave
downwardly through the drill string 12 to the subsurface signal
transmitting station 14. The torsional waves are modulated at the
signal transmitting station with a telemetric signal representing
the drilling parameters to be monitored and returned upwardly
through the drill string to the surface, in the manner to be
explained presently. These modulated waves are received by the
transducer 66 and then demodulated to recover the transmitted
signal.
It will be recalled from the earlier description that the
invention, in its broader aspects, contemplates any torsional
acoustic waves capable of propagation through the drill string 12
and capable of modulation by the telemetric signal to be monitored
to achieve effective signal transmission from the subsurface signal
transmitting station 14 to the surface signal receiving station
16.
It will be further recalled, however, that the preferred waves are
torsional acoustic waves of zero order and of the proper frequency
to effect wave propagation through the drill string 12 in its base
band. In this latter regard, attention is directed to FIG. 13A.
This figure depicts the relationship between a quantity T,
representing the relative transmission of torsional acoustic wave
propagation through a drill string, and the frequency f of the
torsional waves expressed in units of the quantity f.sub.o. This
latter quantity is the torsional wave frequency at which the
transmission quantity T first becomes zero. The frequency quantity
f.sub.o is related to the velocity c of torsional wave propagation
through the drill string and a distance d, (the effective acoustic
distance between the drill string couplings 62) by the following
equation. ##EQU1##
As indicated in FIG. 13A, the base band of torsional wave propation
through the drill string 12 occurs in the region between f = 0 and
f = f.sub.o. From this it will be understood that propagation of
the torsional acoustic waves of the invention through the drill
string 12 is accomplished by exciting the transducer 66 with a
driving signal having frequency components such that if f is the
frequency of a component, then ##EQU2##
For a standard drill string composed of 30 foot pipe sections and
conventional tool joint couplings 62, f.sub.o is on the order of 80
Hz.
Returning again to the torsional wave transducer 66, the transducer
body 72 will be recalled to have a torque reaction stub 70 which
provides an acoustic reaction termination at the upper end of the
transducer. While this upper reaction stub or termination may
conceivably be designed to serve as an absorbing termination, the
particular termination shown is assumed to be a reflecting
termination.
The theory of reflecting terminations is well understood and hence
need not be explained in great detail. Suffice it to say that the
correct length of a reflecting termination depends on the nature of
the reflections occurring at the upper end of the termination. For
example, if the upper end of the termination is open, with no
acoustic connection to any structure, the end constitutes a node
for torque and an antinode for torsional displacement. In this
case, the optimum termination length is an odd number of quarter
wave lengths of the acoustic waves to be reflected. On the other
hand, if the end of the termination is acoustically rigid, that is,
anchored to a very large mass with an acoustic impedance large
relative to that of the transducer and termination, the end of the
termination is an antinode for torque and a node for torsional
displacement. In this case, the optimum termination length is an
even number of quarter wave lengths of the acoustic waves to be
reflected. For intermediate cases, the termination must have an
intermediate length determined by the acoustic conditions at the
end of the termination. Obviously, the torque reaction stub or
termination 70 represents such an intermediate case and must be
dimensioned accordingly.
It will be understood from the description to this point that the
transducer 66 is excited with a driving signal of the proper
frequencies to launch torsional acoustic waves of zero order
downwardly through the drill string 12 in the base band of the
drill string. The manner in which this driving signal is generated
will be explained presently. Suffice it to say here that the
driving signal is applied to the transducer through the cable 104,
collector brushes 108, collector rings 106 and the upper rivets
107. The waves are modulated at the subsurface signal transmitting
station 14 by the modulating means 20 and returned to the signal
receiving station 14, to provide at the receiving station modulated
waves containing information representing the drilling parameters
to be monitored.
It will be immediately evident to those versed in the art that a
variety of acoustic wave modulating means 20 may be employed in the
present drill string communication system. FIGS. 7-9 illustrate an
inertial modulator for the system. This inertial modulator has a
central tube or pipe 110. Surrounding the upper end of the
modulator pipe 110 is a relatively massive inertial cylinder 118.
Inertial cylinder 118 is rotatably supported on and restrained
against movement along the pipe 110 by combined radial and thrust
bearings 120. Seals 122 seal the ends of cylinder to the pipe.
Between its ends, the inertial cylinder 118 is internally enlarged
to define an annular chamber 124 between the cylinder and the pipe
110. This chamber is filled with a magnetic fluid 126, such as a
mixture of oil and powdered iron. Contained in four uniformly
spaced longitudinal slots 128 in the portion of the modulator pipe
110 within the chamber 124 is a drive coil 130. As shown best in
FIG. 8, the conductors of the drive coil extend lengthwise of the
slots 128. Moreover, as indicated by the + and - signs in the
figure, the drive coil is wound in such a way that when a voltage
is impressed across the coil, current flows in one direction
through the conductors in two diametrically opposed slots and in
the opposite direction through the conductors in the remaining two
diametrically opposed slots.
It will now be understood that the modulator structure described
thus far constitutes, in effect, an electromagnetic clutch. Thus,
when the drive coil 130 is deenergized, the pipe 110 and inertial
cylinder 118 are capable of relatively free relative rotation.
Energizing of the drive coil produces a magnetic coupling between
the pipe and cylinder which resists relative rotation of the pipe
and cylinder with a torque proportional to the current flow through
the drive coil.
Surrounding and fixed to the modulator pipe 110 below the inertial
cylinder 118 is an annular circuit housing 132 containing the
driving circuit 134 for the modulator drive coil 130. The drive
coil is connected to the output of the circuit through leads 135.
Modulator driving circuit 134 will be described shortly.
Between the modulator 20 and the drill collar 63 is a lower
reactance termination 136. This reactance termination comprises a
section of drill pipe or a pipe collar of the proper mass and
length to constitute a reflecting termination for the torsional
acoustic waves launched downwardly through the drill string 12 by
the topside transducer 66. The earlier discussion relative to the
topside reflecting termination 70 applies with equal force to the
termination 136. The modulator pipe 110 and lower termination are
connected end to end in the drill string 12 by conventional tool
joints. In this regard, it will be observed that the latter pipe
and termination transmit drilling torque to the drilling cutter 64
and support the weight of the drill string below and thus must be
designed to have sufficient torsional and tensile strength to
withstand these loads. Extending through the pipes are mud passages
which form a continuation of the drill string mud passage.
As noted earlier, it is desirable or necessary during a drilling
operation to monitor several different drilling parameters in the
vicinity of the drilling cutter 64. Some of these parameters were
listed in the earlier description and thus need not be repeated
here. Suffice it to say that the sensors 65 are selected and
arranged within the drill collar 63 to be responsive to the
particular drilling parameters to be monitored. In this regard, it
is significant to note that sensors for this purpose are well-known
and available on the commerical market. Accordingly, it is
unnecessary to describe the senors except to say that each sensor
produces an electrical output representing its respective drilling
parameter. The several sensors 65 are electrically connected
through leads 146 to the input of the modulator driving circuit
134.
The modulator driving circuit 134 will be explained presently.
Suffice it to say here that the circuit effectively combines the
several outputs from the drilling parameter sensors 65 and produces
a telemetric signal containing information representing all the
drilling parameters. This telemetric signal is processed to produce
a corresponding modulator driving signal which is applied to the
modulator drive coil 130 and produces a corresponding fluctuating
magnetic coupling between the inner pipe 110 and outer inertial
cylinder 118 of the modulator 20. As a consequence the torsional
acoustic waves propagating downwardly through the drill string 12
and the modulator pipe 110 to the lower reaction termination 136
and then reflected from the termination unwardly through the pipe
and drill string are modulated to contain information representing
the drilling parameters being monitored. Thus, an increase in the
magnitude of the modulator driving signal produces a corresponding
increase in the magnetic coupling between the modulator pipe and
inertial cylinder, thereby increasing the effective torsional mass
of the pipe and retarding the phase as well as altering the
amplitude of the waves when traveling through the modulator.
Similarly, a decrease in the magnitude of the driving signal
produces a corresponding reduction in the magnetic coupling between
the modulator pipe and inertial cylinder, thereby reducing the
effective torsional mass or movement of the pipe and advancing the
phase as well as altering the amplitude of the waves then traveling
through the modulator.
The modulated waves travel upwardly through the drill string 12 to
the surface signal receiving station 16. These modulated waves
produce a corresponding fluctuating torsional strain in the
magnetostrictive body 72 of the transducer 66, thereby inducing in
the transducer field conductors 94, 98 a fluctuating voltage
containing information representing the transmitted telemetric
signal. As explained below, the voltage signal from the transducer
is processed by a combined transducer driving-receiving circuit at
the surface to recover the transmitted information representing the
drilling parameters being monitored.
A variety of torsional acoustic modulators, other than the inertial
modulator described above, may be employed in the present drill
string acoustic communication system. By way of example, a
crossed-field magnetostrictive transducer similar to the top side
transducer 66 may be employed as a modulator. In this regard,
attention is directed to FIGS. 16-18 illustrating a modified
magnetostrictive transducer 66b according to the invention which
may be utilized as a modulator. This same transducer configuration
may be utilized to launch modulated torsional acoustic waves
through the drill string, as will be described in connection with
the communication system of FIGS. 19 and 20.
Turning now to FIG. 11 there is illustrated the general arrangement
of the modulator driving circuit 134 which is contained in the
modulator circuit housing 132. As noted, this circuit converts the
outputs from the drilling parameter sensors 65 to a coded driving
signal for the modulator 20. This driving circuit includes a power
source (not shown), such as a battery, an encoder 148 and modulator
driving circuitry 150. The encoder is connected to the drilling
parameter sensors 65 to receive the several sensor outputs and
processes these outputs to produce a telemetric signal containing
information representing all of the sensor outputs. This telemetric
signal is applied to the driving circuit 150 which processes the
signal in such a way as to produce a modulated driving signal for
the modulator drive coil 130.
The driving circuit 134 may utilize various signal processing
techniques for converting the outputs from the drilling parameter
sensors 65 to a suitable driving signal for the inertial modulator
20 or for a crossed-field magnetostrictive transducer when employed
as a modulator. FIGS. 12 and 13 illustrate possible signal
processing techniques for this purpose. These illustrated signal
processing techniques are well-known and understood so that an
elaborate description of the same is unnecessary.
Suffice it to say that FIG. 12 is a binary phase coded system
wherein the encoder 148 is a binary digital encoder for converting
the analog outputs from the sensors 65 to a binary digital signal
containing information representing the outputs of all the sensors.
The modulator driving circuit 150 is a power amplifier which
amplifies this binary digital signal to the proper strength for
driving the modulator 20. FIG. 13 is a frequency shift keyed system
suitable for use with a magnetostrictive transducer as will be
explained presently in connection with communication system 10b
(FIGS. 19 and 20). In this case, the encoder 148 is a digital
encoder which converts the outputs of the sensors 65 to a digital
frequency shift keying signal containing information representing
all of the sensor outputs. The modulator driving circuit 150
includes a frequency shift keyer 150a which converts the encoder
output to a frequency shifted transducer driving signal and a power
amplifier 150b for amplifying the signal to the proper strength for
driving the transducer.
Considering now the system of FIG. 10, there is connected to the
topside transducer 66 a driving and receiving electronic system,
comprising means 154 (FIG. 14) for separating the driving signal to
and the information signal from the transducer. The means 154 shown
in FIG. 14 is a hybrid juction having one branch connected to the
transducer field conductors 94, 98. A second branch of the hybrid
is connected to a transducer driving circuit 156 including a high
power drive source 158. Connected to the third branch of the hybrid
is a transducer receiving circuit 160 including an amplifier 162,
phase detector 164, digital decoder 166, and an output display or
recorder 168. The reference input of the phase detector 164 is
connected to the source 158 through an attenuator 170.
The operation of transducer 66 and driving and receiving circuit
152 will be immediately evident to those versed in the art. Thus,
the hybrid junction 154 feeds the high power driving signal from
the source 158 to the transducer field conductors 94, 98 to drive
the transducer to launch the earlier described torsional acoustic
waves downwardly through the drill string 12. At the subsurface
signal transmitting means station 14, these waves are modulated to
contain the information representing the telemetric signal to be
transmitted and are returned upwardly through drill string 12.
These modulated waves produce a fluctuating torsional strain in the
transducer body 72 and thereby a corresponding fluctuating voltage
signal in the transducer field conductors 94, 98. The hybrid
junction 154 feeds this voltage signal to the receiving circuit
160. This signal is amplified by amplifier 162 and its phase is
compared to the phase of the transducer driving signal in the phase
detector 164 to provide an output representing the telemetric
signal. The digital decoder 166 reduces the output of the phase
detector to discrete output signals representing the various
monitored drilling parameters. These output signals are then
displayed or recorded as drilling parameter information by the
display or recorder 168.
In some applications it may be desirable or essential to employ
separate transducers at the surface for launching the torsional
acoustic waves downwardly through the drill string 12 to the
subsurface signal transmitting station 14 and receiving the
modulated waves returning to the surface. FIG. 15 illustrates such
a dual tranducer communication system 10a. In this system, the
single transducer 66 in FIGS. 1-14 is replaced by launch and
receive transducers 66L, 66R coupled end to end at the upper end of
the drill string. The launch transducer has a driving circuit 170
comprising a low power source 172 connected through a power
amplifier 174 to the field conductors 94, 98 of the transducer. The
receiving transducer has a receiving circuit 176 connected to the
field conductors 94, 98 of the transducer. This circuit includes a
blanking circuit 178, phase detector 180, digital decoder 182, and
output display or recorder 184. A pulse keyer 186 is connected to
the amplifier 174 and blanking circuit 178, phase detector 180 is
connected through an attenuator 188 to the source 172.
The operation of communication system 10a (FIG. 15) is similar to
that of communication system 10, except that the driving and
receiving circuits 170, 176 are activated alternatively by the
pulse keyer 186. During the intermittent transducer driving modes
of the system 10a, the pulse keyer conditions the launch amplifier
174 to feed an amplified signal to the launch transducer 66L and
conditions the blanking circuit 178 to block the output of the
receiver transducer 66R. Under these conditions the launch
transducer 66L is driven by the amplified driving signal from the
source 172 to launch torsional acoustic waves downwardly through
the drill string 12. During the intervening transducer receiving
modes of the system, the pulse keyer 186 conditions the launch
amplifier 174 to block signal transmission to the launch transducer
66L and conditions the blanking circuit 178 to pass the output of
the receiver transducer 66R. Under these conditions, the
fluctuation voltage signal induced in the receiving transducer 66R
by the returning modulated waves is fed to the receiving circuit
176 to produce a display or recording of the drilling parameter
information being monitored.
The present drill string communication systems described to this
point employ the preferred mode of wave propagation from the
surface to the subsurface signal transmitting station and return of
the modulated acoustic waves to the surface. The reasons why this
mode of propagation can be employed and its advantages were
explained earlier and need not be repeated here. In some
applications, it may be desirable or necessary to employ the
alternate mode of wave propagation referred to earlier, i.e.,
launching of the modulated waves directly from the subsurface
signal transmitting station 14. FIGS. 19 and 20 diagrammatically
illustrate a drill string communication system 10b which employs
this alternate propagation mode.
Communication system 10b is identical to system 10 except for the
replacement of the modulator 20 by the crossed-field
magnetostrictive transducer 66b of FIGS. 16-18 and modification of
the transducer driving and receiving electronics. Turning first to
FIGS. 16-18, it will be seen that the subsurface transducer 66b is
similar to the topside transducer 66 and differs from the latter in
that transducer 66b is inverted and includes a circuit housing 190
surrounding the lower end of the transducer body 72. Within this
housing is the electronic circuitry 192 for processing the outputs
of the drilling parameter sensors 65 to produce a modulated
transducer driving signal containing information representing the
drilling parameters being monitored. Also the outer transducer
field conductor 98 is a copper sleeve, rather than bars fitting in
slots in the transducer body as in the topside transducer 66.
Transducer 66b may employ such an outer conductor sleeve, of
course, since it is not required to couple to the driving torque of
the rotary table 44, as with the topside transducer.
During operation of the drill string communication system 10b of
FIGS. 19, 20, the lower well bore transducer 66b is driven by the
modulated driving signal from its driving circuitry 192 to launch
upwardly through the drill string 12 modulated torsional acoustic
waves containing information representing the drilling parameters
being monitored. These modulated waves induce in the field
conductors 94, 98 of the topside transducer 66 a fluctuating
voltage which is processed to recover the drilling parameter
information.
The electronic driver 192 for the lower well bore transducer 66b
may embody circuitry similar to that of FIG. 13, described earlier,
for converting the output signals from the drilling parameter
sensors 65 to a modulated transducer driving signal. In the case of
transducer 66b, however, it will be understood that the driving
circuitry will include a power source capable of producing the
energy required to induce in the drill string the desired acoustic
torsional waves. Such a power source may comprise a battery
connected to a charging generator driven by mud flow through the
drill string. FIG. 20 illustrates the receiving circuit 198 for the
topside transducer 66. The operation of this receiving circuit will
be obvious to those versed in the frequency shift keying
systems.
At this point, it is significant to recall that the well bore
transducer 66b of FIGS. 16-18 may be employed as a modulator in a
communication system which utilizes the preferred mode of wave
propagation discussed in connection with FIGS. 1-14. In this
regard, it will be understood that the communication system 10b of
FIGS. 19, 20 may be operated in this preferred propagation mode by
utilizing the well bore transducer 66b as a modulator only and
replacing the topside receiving circuit 198 with a combined
transducer driving-receiving circuit such as shown at 152 of FIGS.
10 and 14 for operating the topside transducer 66 to launch
torsional waves downwardly through the drill string and receive the
returning modulated waves.
The communication systems described to this point are designed
primarily for relatively continuous monitoring of selected drilling
parameters. It should be noted in this regard that in some drilling
applications it may be possible to communicate effectively through
the drill string 12 while drilling is actually in progress, i.e.,
while the string is being driven by the rotary table 44. In other
cases, effective communication may require cessation of the
drilling operation and release of the rotary table gripping jaws
from the drill string.
FIGS. 21 and 22 illustrate a modified crossed-field
magnetostrictive transducer 300 which may be employed in the
invention. In this transducer, the longitudinal field is
established by current flow through a coil 302 about the transducer
body 304 rather than by magnetic remanence in the body. The
circumferential field is established by current flow through
longitudinal conductors 305 on the body. Alternatively, the
circumferential field may be established by the use of a remanent
transducer body which has a permanent field in the circumferential
direction. As noted earlier, either the longitudinal field or the
circumferential field of the transducer may be employed as the bias
field and the remaining field as the signal field, or both fields
may be used as signal fields. The transducer of FIG. 23, is like
that of FIGS. 21 and 22, except that the longitudinal field is
established by permanent magnets 307.
In relatively large transducers, such as are required for the
present drill string communication applications, however, the
inductance of the longitudinal field coil 302 and the corresponding
time constant of the coil circuit may be so large that the
frequency response of the transducer may be too low. In this case,
it is necessary to use the longitudinal field of the coil as a bias
field and the circumferential field of the longitudinal transducer
conductors as the signal field. Moreover, when the longitudinal
field of the coil 302 is employed as the signal field, the
transducer body 304 must be longitudinally slotted at 306 to
prevent the signal field from inducing circumferential eddy
currents in the body. When used in a drill string communication
system, the body slot is sealed against mud leakage in any
convenient way. This slot preferably extends only the length of the
central magnetostrictive portion of the body to preserve the
strength of its joints. In this case, high reluctance buffer
sections 308 may be placed between the slotted body portion and
tool joints to permit the longitudinal field to leak out to prevent
eddy currents in the drill string and torque reaction stub. These
buffer sections may be longitudinally slotted for the same reason
as the body. When the circumferential field is employed as the
signal field, the body slot is not required since the eddy circuits
flow lengthwise of the transducer body and become negligible due to
the long path length through the body.
The discussion to this point has been concerned with transducer
operation only in a mode wherein the bias field is constant and the
signal field is varied to launch torsional acoustic waves through
the drill string 12 and modulate acoustic waves with drilling
parameter information. However, the invention contemplates within
its scope modulation of both fields. The transducer then becomes a
multiplier wherein the instantaneous torque produced in the
transducer body is the product of the bias and signal field
amplitudes. This multiplier operating mode is particularly useful
when the transducer is used as a modulator.
Those versed in the art will understand at this point that the
drill string in the various disclosed inventive embodiments
constitutes an acoustic transmission line and that the various
elements in the drill string, such as tool joints, acoustic wave
generator and modulator, and the like, constitute perturbations in
the string at which occur a complex action of partial reflection
and partial transmission of the acoustic waves traveling through
the drill string. However, it can be demonstrated by well-known
mathematical transmission line analysis techniques that during
operation of the present well bore communication system, the
several acoustic wave reflections and transmissions result in
transmsission from the signal transmitting station to the signal
receiving station of net or resultant modulated acoustic waves
containing information representing the signal impressed on the
modulator or transducer at the transmitting station and hence also
representing the drilling parameter or other information to be
transmitted. These net or resultant modulated acoustic waves are
demodulated at the signal receiving station in the manner
heretofore explained to recover the transmitted information.
From the foregoing description, it will be understood that various
changes in the detailed construction and arrangement of the parts
constituting the telemetering system for oil wells of the present
invention may occur to those skilled in the art without departing
from the spirit and scope of the present invention. Accordingly, it
is to be understood that the foregoing description is considered to
be illustrative of, rather than limitative upon, the invention as
defined by the appended claims.
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