U.S. patent application number 14/370899 was filed with the patent office on 2015-01-01 for wireless acoustic communications method and apparatus.
The applicant listed for this patent is The Technology Partnership Plc. Invention is credited to Edward Bean, Fernando Rodriguez Llorente, Tim Palmer, David Martin Pooley, David Tegerdine.
Application Number | 20150003202 14/370899 |
Document ID | / |
Family ID | 45755730 |
Filed Date | 2015-01-01 |
United States Patent
Application |
20150003202 |
Kind Code |
A1 |
Palmer; Tim ; et
al. |
January 1, 2015 |
WIRELESS ACOUSTIC COMMUNICATIONS METHOD AND APPARATUS
Abstract
A method and apparatus for generating, propagating, encoding,
decoding, modulating and detecting acoustic signals in a well
borehole that comprises a signal generator (10) located at a first
location for generating an acoustic source signal; a medium for the
propagation the acoustic source signal to a second location and the
propagation of the reflections and partial reflections of acoustic
signals as it propagates through the medium; an apparatus to remove
a detectable amount of energy from propagated acoustic signals; a
controllable signal modulator (11) for attenuating the transmitted
acoustic source signal; and a receiver (12) for receiving the
modulated acoustic signals reflected, partially reflected or both
by at least one reflector respectively located at one or more other
locations.
Inventors: |
Palmer; Tim; (Royston,
GB) ; Tegerdine; David; (Royston, GB) ; Bean;
Edward; (Royston, GB) ; Llorente; Fernando
Rodriguez; (Royston, GB) ; Pooley; David Martin;
(Stapleford, GB) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
The Technology Partnership Plc |
Royston, Hertfordshire |
|
GB |
|
|
Family ID: |
45755730 |
Appl. No.: |
14/370899 |
Filed: |
January 4, 2013 |
PCT Filed: |
January 4, 2013 |
PCT NO: |
PCT/GB2013/050004 |
371 Date: |
July 7, 2014 |
Current U.S.
Class: |
367/82 |
Current CPC
Class: |
E21B 47/18 20130101;
E21B 47/14 20130101; E21B 47/16 20130101; G01V 1/44 20130101; E21B
47/20 20200501; G01V 1/223 20130101 |
Class at
Publication: |
367/82 |
International
Class: |
E21B 47/16 20060101
E21B047/16 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 5, 2012 |
GB |
1200093.1 |
Claims
1. A communication system for a well borehole, the system
comprising: a controllable signal modulator for damping an acoustic
signal in the well thereby removing a detectable amount of energy
from the acoustic signal; a receiver for receiving the damped
acoustic signal and detecting the amount of removed energy; and an
acoustic propagation medium for propagating the acoustic signal,
modulated by a controllable signal modulator located at a first
location, to a second location; wherein the receiver is arranged to
detect the acoustic signal, and wherein the controllable signal
modulator comprises a plurality of conductive coils moveable
relative to a plurality of magnets.
2. A system according to claim 1, the system further comprising: a
signal generator located at a third location for generating an
acoustic source signal.
3. A system according to claim 1, wherein the acoustic propagation
medium comprises a pipe disposed in the borehole.
4. A system according to claim 2, wherein the third location is a
location at the top of the borehole.
5. A system according to any of claim 1, wherein the first location
is within the borehole.
6. A system according to claim 5, wherein the first location is at
the end of a pipe disposed in the borehole or at a pipe joint.
7. A system according to claim 1, wherein the receiver is located
at the first location.
8.-9. (canceled)
10. A system according to claim 1, wherein the conductive coils and
the magnets are coupled to a pipe.
11. A system according to claim 9, claim 7, wherein the magnets
have poles arranged symmetrically along the axis of the
borehole.
12. A system according to claim 1, wherein the magnets are aligned
with the conductive coils such that, in use, magnetic flux through
the coil is optimised.
13. A system according to claim 1, wherein the conductive coils are
selectively connected to vary the amount of damping.
14. A system according to claim 1, wherein the controllable signal
modulator is located within a pipe.
15. A system according to claim 1, wherein the acoustic signal is
transmitted at two or more frequencies.
16. A system according to claim 1, wherein the acoustic signal is
continuous.
17. A method of communicating in a well borehole, the method
comprising the steps of: damping an acoustic signal in the borehole
thereby removing a detectable amount of energy from the propagated
acoustic signal in the well; receiving the damped acoustic signal
to detect the amount of removed energy; and propagating the
acoustic signal from a first location, wherein the signal modulator
modulates the acoustic signal, to a second location, wherein the
receiver is arranged to detect the acoustic signal, and wherein the
controllable signal modulator comprises a plurality of conductive
coils moveable relative to a plurality of magnets.
18. A method according to claim 17, the method further comprising
the steps of: generating at a third location an acoustic source
signal.
19. A method according to claim 17, wherein the acoustic
propagation medium comprises a pipe disposed in the borehole.
20. A method according to claim 18, wherein the third location is a
location at the top of the borehole.
21. A method according to claim 17, wherein the first location is
within the borehole.
22. A method according to claim 17, wherein the first location is
at the end of a pipe disposed in the borehole or at a pipe
joint.
23. A method according to claim 17, wherein the receiver is located
at the first location.
24.-25. (canceled)
26. A method according to claim 17, wherein the conductive coils
and the magnets are coupled to a pipe.
27.-32. (canceled)
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] The present application is a national phase entry under 35
U.S.C. .sctn.371 of International Application No. PCT/GB2013/050004
filed Jan. 4, 2013, published in English, which claims priority
from Great Britain Patent Application No. 1200093.1 filed Jan. 5,
2012, all of which are hereby incorporated herein by reference.
[0002] This invention relates to a method and apparatus for
transmitting information in a well borehole.
[0003] In general, a borehole comprises a jointed steel pipe called
the production pipe that carries oil/gas from distances of several
kilometres from the reservoir to the surface. Around the production
pipe is an outer annulus that is normally filled with salt water or
some other fluid. The outer annulus is contained by a casing, which
is cemented in. The end of the production pipe is held in place by
a packer. A number of sensors to measure temperature, pressure and
other well parameters are placed along the borehole. Communicating
with these sensors and other devices placed down a well borehole is
a long standing problem for the oil and gas industry.
[0004] A variety of communication methods already exist, including
electromagnetic, acoustic and wired. Wired solutions suffer from
issues with the reliability and maintainability of the connection
between pipe joints, and it is normally not possible to retrofit
wired solutions. Generally, wireless solutions have the primary
disadvantage of having to generate communication signals at every
active point (i.e. node), which for down-hole components implies
the availability of a local source of energy powerful enough to
support the transmission of signals over the required communication
distance. As a consequence, the majority of wireless solutions
require batteries which are undesirable at the high temperatures
typically found down-hole and having limited lifetimes requiring a
need for well intervention to replace the batteries at expense to
the operator of the well. Most methods also utilise a number of
repeaters to send a signal, which further increases the maintenance
cost. Data rates of such communication methods do not necessarily
need to be high, as in certain situations even low data rates that
return some information are useful, which helps to reduce battery
consumption. Nevertheless higher data rates are always
desirable.
[0005] This invention is mainly but not exclusively concerned with
acoustic communication methods which use the production pipe as a
communication channel and low energy consumption acoustic modulator
apparatus that can be fitted or retrofitted to the production pipe.
Communication methods using acoustic approaches propose the usage
of the production pipe, the production fluid or the outer annulus
fluid as a transmission medium. These methods are practical from an
energy point of view due to the low acoustic attenuation of
longitudinal and quasi-longitudinal waves in steel pipes, even over
distances of several kilometres, and the low energy needed for
attenuating those waves. This invention therefore reduces the
number of repeaters needed to achieve long distance communications,
potentially eliminating the need for repeaters altogether. Other
type of pipes or borehole structures with good acoustic propagation
properties would be equally suitable for the methods and apparatus
covered by this invention, even if they are made of different
materials or have different functionalities in the well.
[0006] An acoustic signal propagates through the bore-hole
structure, tubing, fluid or casing in two directions, downward and
upwards. For horizontal completions the terms downwards and upwards
are to mean propagation towards the end of the well and propagation
towards the top of the well respectively. Because of their
different physical dimensions, the joints of jointed pipe present
acoustic impedance discontinuities to the propagation of acoustic
signals through the jointed pipe and will cause an acoustic signal
to suffer many partial reflections at the joints. All these
reflections contribute to the propagation of the acoustic signal in
both directions and define the acoustic characteristics of jointed
pipe structure.
[0007] The qualitative behaviour of this acoustic structure has
been recognised by Barnes and Kirkwood in "Passbands for
Transmission in an idealized drill string", J. Acoustic Soc. Am.
Volume 51, Issue 5B, pp. 1606-1608 (1972). Typically, transmission
over long distances is supported within only a small number of
narrow frequency pass bands in the acoustic spectrum. Those
frequency bands are the best candidate communication channels for
such a structure. The acoustic signals propagated on those bands
include the transmitter generated signal and its partial joint
reflections. Because the dimensions for joints in a typical
production pipe are very short in comparison to the wavelength of
sound, there is no easy way to distinguish between the transmitter
signal and its reflections after a short period of time and the
terms transmitter signal, propagated signal and reflected signals
refer to different aspect of the same signal as it propagates
through the borehole and are used to help clarify some aspects of
the invention.
[0008] U.S. Pat. No. 4,293,936 discloses an acoustic telemetry
method for transmitting signals over a string of standard drill
pipe positioned in a borehole during drilling operations. It makes
use of knowledge of the pass bands to ensure optimal transmission.
The method has repeaters that repeat only at certain
frequencies.
[0009] U.S. Pat. No. 0,086,336 discloses a semi passive two way
borehole communication method whereby the signal is only generated
at the top of the well, and is in some manner selectively reflected
back up the well by a controllable reflector. The transmission
medium is either considered to be the production fluid or the
production pipe. The reflector is detailed as a mechanical device
(a two position diaphragm reflector or a two position internal
volume control Helmholtz resonator, both of which operate by
changing the geometry of reflecting structure).
[0010] Acoustic communication concepts that are in existence
include those that operate during drilling, and those that are
permanently fixed down the hole. Both require the use of
repeaters.
[0011] A difference to the requirements of communication while
drilling is data rate. During drilling, a high data rate is
necessary to react quickly to changes. During down-hole operations,
the data rates can be lower as the general interest is in long term
monitoring of the well condition.
[0012] The present invention seeks to address the above identified
problems in bore-hole communications by utilising a low power
device at the down-hole site and a transmission method that
identifies and utilises low propagation attenuation acoustic
signals. Depending on the borehole length and build, this invention
could eliminate the need for batteries down-hole, maximise the life
of any batteries and reduce the number of devices deployed down the
well.
[0013] According to the present invention there is provided a
communication system for a well borehole, the system
comprising:
[0014] a controllable signal modulator for damping an acoustic
signal in the well thereby removing a detectable amount of energy
from the acoustic signal; and
[0015] a receiver for receiving the damped acoustic signal and
detecting the amount of removed energy.
[0016] A corresponding method is also provided.
[0017] The acoustic signal may be provided by a transmitter. The
transmitter and receivers may be positioned in the same location.
The modulator may be arranged to operate with preference to one
direction of acoustic propagation, causing different attenuation to
downward signals than to upward signal or vice versa. The acoustic
signal generator, the modulator and the receivers or any
combination of them may be positioned in the same location. In
another embodiment, a plurality of transmitter, modulator and
receivers could be used over the same bore-hole. In another
embodiment, a plurality of transmitter, modulator and receivers
could be used on the same well where the tubing has been split into
more than one branch.
[0018] The present solution is semi passive in that there is no
need to generate an acoustic signal down within the well, reducing
the amount of energy required by communication devices down-hole.
Instead, the signal can be generated at the first location, for
example at the well head (top of the borehole) where relatively
easy access to power is available. This signal is then modulated
before being reflected back up to the well head detector.
[0019] The present invention utilizes long propagation acoustic
modes present in the bore-hole structure. In one embodiment, a
longitudinal or quasi-longitudinal acoustic wave will be generated
(along with other wave modes, which are not of interest due to
their increased acoustic attenuation) at the well head. The signal
will then propagate down the well to the proposed wireless acoustic
modulator. This modulator will affect the signal by means of
attenuation, such that energy is removed from the acoustic wave.
The modulator will be able to appropriately modulate the acoustic
wave to enable communication. A percentage of the signal is
reflected from the device, the terminus of the well (the packer),
and each individual pipe joint such that some energy will propagate
back up towards the well head. At the well head, an acoustic
receiver will detect the acoustic wave and determine, over a
selected integration time, that the modulator device was either
`on` or `off` (or potentially other states in between) by examining
the characteristics of the returned acoustic wave. When the
modulator device is on the amount of acoustic energy that can be
sensed at another point of the bore-hole, like in the receiver, is
different than when the modulator is off. For modulators that
support more than two states, the amount of energy sensed will have
more than two levels. The detectable change in energy at the
receiver as the modulator changes state allows bits of information
to be transmitted between modulator and receivers.
[0020] The apparatus may be arranged to provide two way
communication (i.e. from the surface of the well to a location
along the tubing and vice versa) by modulating the time between the
transmission pulses, and introducing an acoustic sensor down-hole
to detect the time change and thereby retrieve a message.
Alternatively, the current generated within the acoustic modulator
could be used as a detector.
[0021] This solution improves on existing acoustic communication
concepts by acoustically modulating the signal using an innovative
electromagnetic device, as opposed to detecting the signal at the
bottom of the well and retransmitting or by just reflecting the
signal. Some of the advantages of this invention over prior art are
the following. Firstly, there are low power requirements for down
hole communication nodes, the acoustic modulator requires only a
low power switch(es) to effect the modulation that allows a message
to be transmitted between communication nodes.
[0022] Secondly, there are no high power electromechanical parts:
The solution uses acoustic-electromagnetic effects, and requires no
high power mechanically active parts down-hole. Furthermore, there
are a reduced number of down-hole components, reducing the cost of
installation and any maintenance as opposed to solutions which
require acoustic repeaters to be installed along the well, in many
circumstances, one down-hole device might be sufficient.
[0023] Examples of the present invention will now be described with
reference to the accompanying drawings, in which:
[0024] FIG. 1 shows an example of a communication apparatus
according to the invention;
[0025] FIG. 2 is a cross sectional view of an example
electromagnetic device for an acoustic modulator for the apparatus
of the invention;
[0026] FIG. 3 is a perspective view of the example electromagnetic
device of FIG. 2;
[0027] FIG. 4 is an example cross section of the electromagnetic
device of FIGS. 2 and 3;
[0028] FIG. 5 is an overall view of an embodiment of the invention
showing potential specific locations for certain components;
[0029] FIG. 6 shows some of the elements of the method of the
invention for an up-hole communication;
[0030] FIG. 7 is a block diagram showing the main steps of an
up-hole communication enabled by the invention;
[0031] FIG. 8 shows some of the elements of the method of the
invention for a down-hole communication; and
[0032] FIG. 9 is a block diagram showing the main steps of a
down-hole communication enabled by the invention.
[0033] Referring to FIG. 1, an apparatus according to the invention
comprises the following elements. An acoustic transmitter 10
positioned at location A in FIG. 1; an acoustic modulator 11
positioned at location B in FIG. 1, and
[0034] an acoustic receiver 12 positioned at location A in FIG.
1.
[0035] The acoustic transmitter 10 is arranged to broadcast a
longitudinal or quasi-longitudinal acoustic wave. The operational
frequencies of this acoustic wave are selected to suit the acoustic
characteristic of the pipe 13. The physical build of the
transmitter and the driving waveforms used to excite it are
designed to maximize the efficient generation of acoustic
propagating modes with long distance propagation in the borehole.
The acoustic transmitter is arranged to provide the following
functionality:
[0036] a. the generation of acoustic signals to enable downhole
communication nodes to transmit information using acoustic
modulators;
[0037] b. the generation of acoustic signals to enable top of the
well equipment to communicate with downhole devices;
[0038] c. the generation of acoustic signals to identify most
favourable propagation frequencies and waveforms for the borehole;
and
[0039] d. the generation of acoustic signals to detect and track
changes in the acoustic characteristics of the borehole.
[0040] The acoustic transmitter 10 can be built using different
electro-acoustic transduction principles, such as air coil
speakers, piezoelectric, magnetostriction, electromechanical shaker
and other electro-acoustic technologies. It will be appreciated
that the acoustic transmitter can be built with one or more than
one transducer, with one or more than one transducer technology,
with one or more than one transducer in one location and with more
than one transducer in more than one physical location.
[0041] An acoustic transmitter encoder 14 is provided. The acoustic
transmitter encoder 14 maps the logical information to transmit
into appropriate signals used to drive the acoustic transmitter. As
an example, an acoustic transmitter encoder 14 may map a bit of
information to be transmitted by a four element acoustic
transmitter array into four different waveforms that drive four
different transducers at four different locations. The acoustic
transmitter encoder may perform message encoding to facilitate the
error detection and error correction at the acoustic receiver
12.
[0042] An acoustic transmitter controller 15 is also provided. The
acoustic transmitter controller 15 operates the acoustic
transmitter 11 and encoder 14 and is an interface to other
equipment like a controlling computer system (not shown) that might
be used to generate the information to be transmitted.
[0043] The modulation of an acoustic wave is by means of an
acoustic-electromagnetic device 11. An example is depicted in FIGS.
2 to 4. The device has an outer series of conducting coils 1. These
coils 1 can either be connected together and switched as one, or
disconnected and switched independently. The modulator length can
be varied to optimize its performance. Elastically coupled to the
inside of the coils 1 is a series of ring (or cylindrical) magnets
2 with the North and South poles along the main axis of the
cylindrical production pipe 4. The coils 1 are positioned such that
they experience the maximum radial flux from the magnets 2. The
magnets will be separated by spacers 3. The modulator is fixed by a
device fixing 5 to the inner walls of the device (for simple
retrofitting) with optimum acoustic coupling. The device can be
coupled either along the entire length of the device, 5 or using
other conventional methods for retrofitting devices inside a well
bore that provide suitable acoustic coupling. The modulator can be
configured either to allow production fluid flow through the middle
of the device, or around its perimeter. A low power FET switch or
other device is used to short and open the coils 1 by the sensor or
device that is attached to it. The coils may be connected to ensure
the direction of the force from the coil/flux linkage is
maximised.
[0044] The acoustic modulator device 11 makes use of damping to
remove energy from the incoming acoustic wave. This damping of the
acoustic signal can be induced mechanically, electromagnetically or
by a combination of both of them.
[0045] In the case of mechanical damping, this is accomplished by
coupling the acoustic wave to a mechanical oscillator, therefore
transferring a portion of the acoustic energy from the pipe to the
mechanical oscillator. The energy transferred to the mechanical
oscillator is dissipated in a damper or transferred to a mechanical
oscillation mode that is not compatible with linear or quasi-linear
acoustic propagation through the pipe or by a combination of both
methods. In the first implementation, the mechanical oscillator is
selectively switched between two or more damping levels to modulate
the acoustic energy levels being propagated though the tubing. In
the second implementation, the mechanical oscillator is selectively
switched between two or more oscillation modes incompatible with
acoustic propagation through the pipe, subtracting different
amounts of energy from the pipe propagation mode and in this way
modulating the acoustic energy levels being propagated though the
tubing. A combination of both methods can be combined to modulate
the acoustic energy levels being propagated though the tubing.
[0046] In the case of electromagnetic damping, this is accomplished
by ensuring that the acoustic wave transfers some of its energy to
conducting coils which will then move relative to a series of
magnets. The relative motion between the conducting coils and the
magnets will cause a current to flow in the coils if electrically
shorted, which in turn sets up an opposing magnetic field which
will cause a retarding force, i.e. a force that is against the
direction of motion. it is this set of forces that couples the
acoustic wave propagating through the pipe and coils to the
magnets. If the coils themselves are not electrically shorted, then
a current will not be able to flow, disabling the coupling between
the acoustic waves in the pipe and the magnets. Thus, by switching
the coils between open and closed, the acoustic signal can be
effectively modulated.
[0047] In the case of combined mechanical and electromagnetic
damping, this is accomplished attaching the magnets to a mechanical
oscillator and coupling the acoustic wave to the mechanical
oscillator by means of electrically conductive coils attached to
the pipe. The controlled damping of energy and can be accomplishing
in a number of ways:
[0048] 1. by adding a controllable mechanical damper to the
mechanical oscillator;
[0049] 2. by adding a mechanical damper to the mechanical
oscillator and varying the strength of the coupling between the
acoustic wave and the mechanical oscillator;
[0050] 3. by adding a mechanical damper to the mechanical
oscillator and varying the strength of the coupling between the
acoustic wave and the mechanical oscillator by selecting the number
of coils switched to open and close circuit position;
[0051] 4. by adding a mechanical damper to the mechanical
oscillator and varying the strength of the coupling between the
acoustic wave and the mechanical oscillator by selecting the
electrical resistivity of coils by means of a controllable
resistance device;
[0052] 5. by adding a mechanical damper to the mechanical
oscillator and varying the strength of the coupling between the
acoustic wave and the mechanical oscillator by selecting the
electrical resistivity of coils by means of a controllable
resistance device, where the controllable resistance device is a
transistor, or a vacuum valve, or a variable resistor, or a switch
with more than one pole attached to fixed resistors, or a
combination of the pervious elements that provides a means to
change the level of resistivity of coil circuit, or a combination
of electrical circuit elements that provides a means to change the
level of resistivity of the coil circuit;
[0053] 6. any of the methods described above where a mechanical
oscillator mode not compatible with propagation is used instead of
the mechanical damper.
[0054] An acoustic receiver 12 is provided. The acoustic receiver
12 operation is based on an electro-acoustic transduction principle
with the sensor configured to convert acoustic signals into
electrical signals, like an air coil microphone. Other
implementations could be used based on other electro-acoustic
technologies like piezoelectric, magnetostriction,
electromechanical shaker and others. The acoustic receiver can be
built with one or more than one transducer, with one or more than
one transducer technology, with one or more than one transducer in
one location and with more than one transducer in more than one
physical location.
[0055] An acoustic receiver decoder 16 maps the acoustic receiver
signal into information that can be stored digitally. A number of
analogue electrical signals are generated by the acoustic receiver
12. These signals can be filtered and processed in the analogue
domain and converted to digital signals in an analogue to digital
converter. The signal can them be further filtered and processed in
the digital domain to extract the communication information. The
acoustic receiver decoder unit may perform message decoding, error
detection and error correction functions.
[0056] The apparatus of the invention and its method of operation
can be optimised on a well by well basis to ensure that the signal
transmitted at the top of the well is tuned to the transmission
medium. As the transmission medium might change over the life of
the well, this optimisation could take place periodically.
[0057] Adaptations to the invention include the following.
[0058] Different coil on/off combinations. When the coils 1 are
grouped with multiple switches for different sets, then with a
suitably sensitive detector and a strong enough input signal at the
top of the well, different groups and patterns can be switched such
that the waves are attenuated at different levels. This allows
transmission of more than one bit per pulse depending on the level
of attenuation.
[0059] Mounting acoustic modulator outside of the pipe. When the
acoustic modulator is not for a retrofit solution it could be built
in a special joint of pipe with the modulator onto the outside of
the production pipe. This implementation does not interfere with
the flow inside the production pipe.
[0060] Transmission on more than one frequency band. When two or
more different pass frequencies can be found to propagate for long
enough distances, it is possible to transmit acoustic pulses at the
found different frequencies simultaneous or close in time. This
enables the possibility of simultaneous or almost simultaneous
transmission to and from two different communication nodes with
acoustic modulators optimized to operate and different frequency
bands.
[0061] Continuous carrier wave. The transmitted wave could be a
continuous source rather than a pulse. The device would not then
have to wait for the travel time from the top of the well to the
device. The modulator could then switch faster, and the detector
method at the wellhead would have to distinguish between
overlapping signals to deduce the on and off states. This would
allow a higher data rate.
[0062] Use naturally occurring noise. The transmitted wave could be
naturally occurring noise in the borehole. The modulator attenuates
the noise propagating through the borehole and the receiver can
detect the changes in noise energy levels induced by the
modulator.
[0063] Referring to FIG. 5, it can be seen how a combined
transmitter and receiver unit 10, 12 can be attached to tubing 13
via a tubing hanger 20 at the head of a well. The modulator 11 in
this example is positioned within the tubing 13 at a location down
well.
[0064] Referring to FIG. 6, the main steps of up-hole communication
are shown, in which a parameter is detected by sensors, data from
the sensors encoded and modulated and provided to an acoustic
transducer for transmission. These are received by an acoustic
transducer, demodulated and decoded for processing.
[0065] FIG. 7 shows a little more detail of these key steps, with
the information being placed into a frame structure correction
encoded, mapped in a logical to physical format and then provided
to a modulator transducer for passage through the acoustic channel,
in this example in the form of pipe 13. This is received by a
demodulator transducer and followed by a physical to logical
mapping, error correction decoding, the provision of frame
structure and then an output of information.
[0066] FIG. 8 shows down hole communication in which data to be
encoded is provided to a modulator which applies it to an acoustic
carrier for transmission down the well via pipe 13. The acoustic
transducer at the other end receives the acoustic signal, following
which it is demodulated and decoded.
[0067] FIG. 9 shows the steps in more detail.
* * * * *