WIDE BANDWIDTH DRILL PIPE STRUCTURE FOR ACOUSTIC TELEMETRY
BACKGROUND
[0001] During drilling operations for extraction of hydrocarbons, a variety of
communication and transmission techniques have been attempted to provide real time data
from the vicinity of the bit to the surface during drilling. The use of measurement-whiledrilling
(MWD) and logging-while-drilling (LWD), with real time data transmission,
provides substantial benefits during a drilling operation. For example, monitoring of
downhole conditions (e.g., temperature, pressure, resistivity, density, and electromagnetic
fields) allows for an immediate response to potential well control problems and improves
mud programs.
[0002] Mud-pulse and electromagnetic telemetries are most commonly used for
transmitting downhole data to the surface with a typical 3-10 bits/sec data rate. Acoustic
telemetry may provide higher transmission capabilities at 40-80 bits/sec data rates with drill
pipe as a transmission line.
[0003] While acoustic telemetry may provide fast data rate benefits not possible in mudpulse
and electromagnetic telemetries, the existing acoustic telemetry technique suffers from
signal reflection or transmission loss at each acoustic impedance mismatched interface
because existing drillpipe structures lead to formation of frequency stopbands and passbands.
In particular, when transmitting acoustic signals within one of the frequency passbands, high
data error and low signal-to-noise ratio may result in the loss of the acoustic signals or in the
limited transmission range. The frequency stopbands and passbands may drift by thermal
induced variations of the pipe length and surrounding acoustic impedance variation, such as
the varied mud density. This may limit available acoustic transmission channels and induce
signal transmission reliability issues.
BRIEF DESCRIPTION OF THE DRAWINGS
[0004] FIG. 1 is a diagram showing acoustic transmission and reflection on a drill pipe in a
downhole environment.
[0005] FIG. 2 is a plot showing frequency versus amplitude of acoustic transmissions with
passbands and stopbands.
[0006] FIG. 3 is a diagram showing an example of acoustic impedance matched drill pipe
sections and a drill pipe joint section structure.
[0007] FIG. 4 is a plot showing an example of acoustic wavelength versus frequency in
accordance with the example of FIG. 3.
[0008] FIG. 5 is a plot showing an example of anti-phase acoustic waves that reduce or
eliminate reflected acoustic waves.
[0009] FIG. 6 is a plot showing an acoustic frequency versus wave vector of a typical
periodic drillstring acoustic band-gap.
[0010] FIG. 7 is a plot showing an acoustic frequency versus wave vector of an example of
a non-periodic drillstring acoustic band-gap.
[0011] FIG. 8 is a diagram showing an example of a drilling rig system in accordance with
various examples.
[0012] FIG. 9 is a flowchart showing an example of a method for acoustic signal
transmission.
DETAILED DESCRIPTION
[0013] To address some of the challenges described above, as well as others, apparatus,
systems, and methods for acoustic impedance matching drill pipe are described. The
described examples may reduce or eliminate acoustic impedance induced reflection at pipe
joint sections and reduce or eliminate acoustic frequency stopbands. Drill pipe acoustic
signals may be transmitted from the downhole environment to a different depth (e.g.,
geological formation surface) through a transmission medium (e.g., drillstring) having only
one passband without conventional stopbands. Thus, transmission of downhole acoustic
signals may then have more reliable acoustic data transmissions within a wide frequency
band without suffering from stopbands or passband variations.
[0014] FIG. 1 is a diagram showing acoustic transmission and reflection on a drill pipe in a
downhole environment. The propagating acoustic wave could be produced by
electromagnetic device with a modulated frequency. An acoustic wave may be longitudinal
compressive wave, shear wave, even Stoneley surface waves. A wellbore 100 is shown
having a casing or liner 101 that lines the wellbore. A drillstring 103 has been inserted into
the wellbore. The drillstring 103 includes a plurality of sections 110-1 12 of drill pipe that are
joined at drill pipe joint section structures 120, 121.
[0015] Acoustic telemetry utilizes acoustic waves to transmit sensing data (e.g.,
temperature, pressure, electromagnetic field, resistivity) from LWD/MWD tools (not shown),
through the drillstring 103. A forward acoustic signal 130-132 may be transmitted from the
downhole environment such that it propagates through the drillstring 103. If the drill pipe
joint section structures 1 0, 1 1 have impedances differences, a portion of the transmitted
acoustic wave 132 may be successfully transmitted through the drillstring 103 but would be
lost or attenuated from the original transmission due to acoustic wave reflections 140, 141.
[0016] The acoustic wave reflections 140, 141 are a result of the drill pipe joint section
structures 120, 121 having a different impedance of joint section (Z^) than the impedance of
the pipe section (Z ) . Both Z and å may be defined by a product of phase velocity (u) and
mass density (p) of the pipe sections 110-1 12 or drill pipe joint section structures 120, 121.
This may be represented by Z=u r .
[0017] When the drillstring 103 has a periodic Z -Z2modulated string, the reflected
acoustic waves 140, 141 may be in-phase and constructive. The acoustic band structure is
dependent upon the total length of the drilling pipe and joint section, which may result in
multiple frequency passbands separated by frequency regions referred to as stopbands. FIG. 2
is a plot showing frequency ( ) versus amplitude of acoustic transmissions with passbands
201-207 and stopbands 210-215 resulting from the reflected acoustic waves. The acoustic
signal will be strongly attenuated at stopband points, 210, 2 11, 212, 213, 214, 215, while
acoustic signals can be transmitted at 201, 202, 203, 204, etc., namely, acoustic passband.
[0018] An acoustic signal transmission from the downhole environment has a specific
frequency passband for the transmission channel. Signal loss may occur if the specific
passband has drifted either by mechanical or by thermal strain. The acoustic signal
transmission may be attenuated below a usable threshold if the passband has drifted from a
tolerated range, Dw, of the specific frequency passband. For example, the downhole geologic
thermal gradient is about 25°C/km, the thermal expansion of the drilling pipes will expand its
length at different well depth, and make stopband and passband drifting to low-frequency
side. This drifting effect may be significant whenever the downhole temperature is more than
120°C or 4,000 meters depth.
[0019] Reducing or eliminating acoustic impedance-induced reflection at each drill pipe
joint and/or eliminating frequency stopbands may be accomplished by a number of methods.
These methods may be used separately or together in any combination. For example, a
method for reducing or eliminating acoustic impedance induced reflections at each pipe joint
connection uses acoustic impedance matched drill pipe joint section structures 120, 121
across a selected band of frequencies. A method for reducing or eliminating acoustic
frequency stopbands may use non-periodic drillstring pipe sections 110-1 12 or an anti-phase
structure design. A method to further reduce or eliminate acoustic impedance interfaces along
the drillstring 103 may include material property matching of the pipe sections 110-1 12 and
the joint section structure 120, 121. Such methods are discussed subsequently in greater
detail.
[0020] FIG. 3 is a diagram showing an example of acoustic impedance matched drill pipe
sections and a drill pipe joint section structure. In the following discussions, the impedance of
each of the drill pipe sections 310, 311 is represented by Z . The impedance of the drill pipe
joint section structure 320 is represented by Z^. An outside diameter of narrower portions of
the drill pipe sections 310, 311 as well as the drill pipe joint section structure 320 is
represented by f. A wall thickness of the pipe sections 310, 3 11 and the drill pipe joint
section structure 320 is represented by h. A connection section length is represented by D.
The wavelength of acoustic signals to be transmitted over the drillstring is represented by l.
[0021] A drillstring may be constructed by a plurality of acoustic impedance matched drill
pipe joint section structures 320, across a selected band of frequencies, coupling drill pipe
sections 310, 311, as shown in FIG. 3. The joint section structure and pipe material's related
acoustic impedance related reflection amplitude (Z2-Zi)/(Zi+Z2) is close to the diameter
difference (f2- fi)/(fi+f2) related reflection amplitude while propagating in anti-phase.
[0022] The method for reducing or eliminating acoustic impedance induced reflections at
each pipe joint connection employs an acoustic impedance matched drill pipe joint section
structure 320 having an acoustic impedance that is matched to the adjacent, coupled drill pipe
sections 310, 311. The structure 320 is connected between the first and second drill pipe
sections 310, 311 by threaded connections 330, 33 1. The threaded connections may be an
internal threaded connection 330 on one side of the structure 320 and an external threaded
connection 33 1 on the other side of the structure 320. In another example, both sides 330, 33 1
may be externally or internally threaded.
[0023] Acoustic wave reflections from the pipe joint section structure may result from
multiple mechanisms. For example, one mechanism may be the acoustic impedance
difference between the drill pipe sections 310, 311 and the drill pipe joint section structure
320 (i.e., Zi¹å2). Another mechanism may be the diameter difference between the drill pipe
sections 310, 311 and the drill pipe joint section structure 320 (i.e., fi¹f2). In both
mechanisms, a partial acoustic wave is reflected with a reflection coefficient, R(z), calculated
by:
R(z)=(Z2-Z1)/(Z1+Z2)e i 6,+' z
), [1]
(f f2-f )/(f +f2) [2]
where both reflected acoustic waves may have different phases for downward propagations.
The reflected signal amplitude is enhanced under an in-phase condition but strongly
suppressed by an anti-phase condition. In a very simple case, the phase change occurs at a
specific acoustic impedance ratio as indicated by i>å and 0i>02. To reduce the reflection
coefficients, as shown in Eqs.(l-2), the acoustic impedances and the diameter difference are:
¾-Z *0, [3]
A = 1- 2« , [4]
[0024] FIG. 3 illustrates a drill pipe joint section structure that approximately satisfies these
conditions. To keep the mechanical structure as a smooth assembly, the wall thickness h of
the drill pipe joint section structure has a limited deviation Ah from the pipe section out
diameter f,where the middle section of the structure 320 is tapered smoothly. A way to avoid
potential reflection is to set the deviation Ah of the wall thickness, as compared to the drill
pipe sections, to be much less than the acoustic wavelength, namely, Ah«A. The connection
section length is also set to be much less than acoustic wavelength, namely, D«A.
[0025] For conventional carbon steel or stainless steel, the phase velocity is about 6000
meters/second and the corresponding acoustic wavelength is a function of the excitation
frequency. FIG. 4 is a plot showing acoustic wavelength (in meters) versus frequency (in
Hertz) in accordance with the example of FIG. 3. This figure shows that the acoustic
wavelength is greater than 1 meter (m) for a frequency of less than 6 kHz. Selection for
Ah«A and D«A may be Ah/A<0.\% and DIA less than 1%, respectively. The wavelength of
a high-frequency acoustic wave may be approximately 0.2 m at 30 kHz as an upper limit for
the drill pipe joint section structure 320 to be an effective non-acoustic impedance structure.
[0026] The method to reduce or eliminate acoustic frequency stopbands may be
accomplished using an anti-phase structure for the drillstring or non-periodic drillstring pipe
sections in the drillstring. Both examples are described subsequently.
[0027] Passband and stopband drift-induced transmission instability may be reduced or
eliminated by suppressing reflected acoustic waves by two reflection waves (i.e., R(z), R(^))
having anti-phase condition and being equal in amplitude. This may be represented by:
R(Z) = -R ( ), and «=0,1, 2, 3,... [6]
[0028] FIG. 5 is a plot showing anti-phase acoustic waves that reduce or eliminate reflected
acoustic waves. The acoustic waves 500, 501 reflected from a pipe joint section structure
have different phases. For example, the top wave has a phase < 0 while the bottom wave has
a phase > 0. The anti-phase condition may be represented by:
[0029] When the acoustic impedance and diameter related reflected wave amplitudes are
nearly equal but in a phase difference of (2«-1)p, the reflected waves from the drill pipe joint
section structure experience a destructive interference as represented by:
wi=w2, Ai A2, A 2
¾ p [8]
[0030] Such an anti-phase joint section structure may reduce or eliminate the reflected
acoustic waves. Thus, anti-phase pipe joint section structure design has an intrinsic nature for
eliminating acoustic wave downward propagation and maximizing acoustic signal
transmission.
[0031] When there is no reflected acoustic waves from each pipe joint section structure due
to acoustic impedance matching, the drillstring is not able to form stopbands and passbands.
While this may be good enough for low-loss acoustic wave transmissions from downhole
bottom to the surface, the acoustic impedance matching and anti-phase designs may be valid
only in a certain range of downhole temperatures. The varying temperature along the
wellbore may not satisfy such impedance matching conditions because thermal expansion
differences in drill pipe sections and drill pipe joint section structure materials. Whenever
such an ideal match is lost, weakly reflective acoustic waves from different pipe joint
sections still may form the passband and stopband frequencies. Building the drillstring in a
non-periodic sequence, as described subsequently, may reduce or eliminate the multiple
passbands and stopbands.
[0032] Typical drillstrings are made up of a plurality of drill pipe sections (A) having a
length represented by L and drill pipe joint section structures (B) having a length represented
by LB. A typical drill string having a periodic structure and, thus, experiencing acoustic
frequency stopbands, may be represented by -ABABABAB. ..AB-. FIG. 6 illustrates the
acoustic band-gap results of a periodic drillstring.
[0033] FIG. 6 is a plot showing an acoustic frequency (w) versus wave vector (k) of typical
periodic drillstring acoustic band-gap. If the total length of the pipe section (A) and joint
section structure (B) is L=LA (pipe)+ LB (joint section), the acoustic wave vector is
represented by p/L. The periodic modulated acoustic dispersion curves have frequencydependent
passbands 601, 602 and stopbands 605 as shown. It is clear that no acoustic waves
can transmit in a stopband such that an acoustic transmission channel has to be chosen at a
specific frequency range and consider the transmission band thermal drift effect. It may be
difficult to determine this drift effect at different downhole depths due to the mechanical and
thermal strains that may be involved.
[0034] In a non-periodic drillstring example, at least three different lengths of pipe
sections/joint section structures may be used. For example, pipe A may have a length of LA,
pipe B may have a length of LB, and pipe C may have a length of Lc, where LA¹L ¹LC. AS an
example, such drill pipe lengths may include lengths from 30ft, 60ft, and 90ft from
commercial available selections. The drill pipe joint section structure may be one of these
pipes (e.g., A, B, C) or some other length. Such a non-periodic example may be constructed
into a drillstring as -ABCCBBAA. ..CBA-, wherein the arranged sequence of the drill pipes
is a random order arranged without an average modulation length. The illustrated order of
pipe sections and drill pipe joint section structures is for purposes of illustration only as any
random order may be used. While three different lengths of pipe are discussed, any number
of pipe lengths may be used (e.g., L , LB, LC, LD) that may be represented by Lk.
[0035] When using a random sequence to building a drillstring, there is no periodic
modulation that can be used to predict a specific pipe length at a specific location. As
illustrated in FIG. 7, a benefit of this non-periodic modulated pipe building sequence is that
the drillstring acts as an acoustic waveguide with a broad passband, where its acoustic
frequency is continuous from long-wavelength at k~ to k=nla, where a is an average lattice
constant of the pipe material. In this way, such a drillstring becomes a broadband acoustic
channel and enables signal transmission from downhole to the surface without suffering from
potential signal loss due to temperature related stopband drift.
[0036] The method to further reduce or eliminate acoustic impedance interfaces along the
drillstring by material property matching the acoustic properties of the pipe sections and the
joint section structure may provide a transmission medium having only one passband without
intervening stopbands. This method may be accomplished in multiple ways. In one example,
the material used for the drill pipe sections may be chosen to be exactly the same as the
material used for the drill pipe joint section structure.
[0037] In another example, the density and phase velocity of the material for the drill pipe
joint section structure may be reduced to effectively compensate for the diameter difference
( 2- i> ) between the two pipe sections. In this example, the product of the phase velocity
(ui) and density (pi) of the drill pipe section material is made equal to the produce of the
phase velocity (u2) and density (p2) of the drill pipe joint section structure material are
approximately equal as represented by:
ui·ri u2·r2 [5]
[0038] FIG. 8 is a diagram showing an example of a drilling rig system in accordance with
various examples. Thus, the system 864 may include portions of a downhole tool 824, as part
of a downhole drilling operation.
[0039] The system 864 may form a portion of a drilling rig 802 located at the surface 804
of a well 806. The drilling rig 802 may provide support for the drillstring 808. The drill string
808 may operate to penetrate a rotary table 810 for drilling a borehole 812 through subsurface
geological formations 814. The drillstring 808 may include a plurality of drill pipe sections
818 connected by drill pipe joint section structures 819, as discussed previously. A bottom
hole assembly 820 may be located at the lower portion of the drillstring 808.
[0040] The bottom hole assembly 820 may include drill collars 822, a downhole tool 824,
and a drill bit 826. The drill bit 826 may operate to create a borehole 812 by penetrating the
surface 804 and subsurface formations 814. The downhole tool 824 may comprise any of a
number of different types of tools including measuring while drilling (MWD) tools, logging
while drilling (LWD) tools, and others.
[0041] During drilling operations, the drillstring 808 may be rotated by the rotary table 810.
In addition to, or alternatively, the bottom hole assembly 820 may also be rotated by a motor
(e.g., a mud motor) that is located downhole. The drill collars 822 may be used to add weight
to the drill bit 826. The drill collars 822 may also operate to stiffen the bottom hole assembly
820, allowing the bottom hole assembly 820 to transfer the added weight to the drill bit 826,
and in turn, to assist the drill bit 826 in penetrating the surface 804 and subsurface formations
814.
[0042] During drilling operations, a mud pump 832 may pump drilling fluid (sometimes
known by those of ordinary skill in the art as "drilling mud") from a mud pit 834 through a
hose 836 into the drill pipe 818 and down to the drill bit 826. The drilling fluid can flow out
from the drill bit 826 and be returned to the surface 804 through an annular area 840 between
the drill pipe 818 and the sides of the borehole 812. The drilling fluid may then be returned to
the mud pit 834, where such fluid is filtered. In some examples, the drilling fluid can be used
to cool the drill bit 826, as well as to provide lubrication for the drill bit 826 during drilling
operations. Additionally, the drilling fluid may be used to remove subsurface formation 814
cuttings created by operating the drill bit 826.
[0043] In some examples, a system 864 can include a display 896, computation logic,
perhaps as part of a surface logging facility 892, or a computer workstation 854, to receive
signals from transducers, receivers, and other instrumentation to determine properties of the
formation 814 and to transform acoustic data that has been received through acoustic
telemetry through the drillstring 808 as discussed previously. Data may be transmitted from
the downhole tool 824 through an acoustic telemetry method during LWD/MWD operations.
[0044] The processor/controllers/memory discussed herein can be characterized as
"modules". Such modules may include hardware circuitry, and/or a processor and/or memory
circuits, software program modules and objects, and/or firmware, and combinations thereof,
as appropriate for particular implementations of various examples.
[0045] FIG. 9 is a flowchart showing an example of a method for acoustic signal
transmission. The method uses a drillstring as a low-loss acoustic transmission line for
acoustic signal telemetry.
[0046] In block 900, an acoustic signal is transmitted over the drillstring from the
downhole environment (e.g., downhole tool) to a different level (e.g., surface). This
transmission is performed over the drillstring that has been constructed to reduce or eliminate
acoustic impedance reflections and acoustic frequency stopbands. One or more of the above
methods of construction of the drillstring may be used. In block 901, the acoustic signal is
received at the different level and demodulated.
[0047] The acoustic impedance matching and non-periodic drillstring examples may
improve acoustic telemetry downhole transmissions. One or more of the examples may be
used in applications such as improving seismic while drilling, short hop, and LWD/MWD.
[0048] Example 1 is a drillstring comprising: a plurality of drill pipe sections; and at least
one drill pipe joint section structure configured to couple adjacent drill pipe sections of the
plurality of drill pipe sections, wherein the drill pipe sections and the drill pipe joint section
structure are acoustically impedance matched across a selected band of frequencies.
[0049] In Example 2, the subject matter of Example 1 can further include wherein the
plurality of drill pipe sections each include a length of one of L or LB and the drill pipe joint
section structure comprises length of Lc, wherein L A ¹ LB ¹ L .
[0050] In Example 3, the subject matter of Examples 1-2 can further include wherein the
drillstring further comprises a plurality of drill pipe joint section structures each configured to
couple adjacent drill pipe sections such that the drillstring comprises a non-periodic sequence
of drill pipe section lengths and drill pipe joint section structure lengths.
[0051] In Example 4, the subject matter of Examples 1-3 can further include wherein the
drill pipe joint section structure comprises external threaded connections and/or internal
threaded connections for coupling to the adjacent drill pipe sections.
[0052] In Example 5, the subject matter of Examples 1-4 can further include wherein the
drill pipe sections have an outside diameter represented by fi, a wall thickness represented by
h, a connection length represented by D, and an impedance represented by Z , further wherein
the drill pipe joint section structure has an outside diameter represented by få, a wall
thickness deviation, as compared to the drill pipe sections, represented by Ah, and an
impedance represented by Z2, wherein Z -Z.2 «0, =fi-f ..
[0053] In Example 6, the subject matter of Examples 1-5 can further include wherein a
signal transmitted on the drillstring using an acoustic method has a wavelength of l, wherein
Ah«A and D«A.
[0054] In Example 7, the subject matter of Examples 1-6 can further include wherein the
plurality of drill pipe sections and the drill pipe joint section structure comprise materials
having substantially similar acoustic properties.
[0055] In Example 8, the subject matter of Examples 1-7 can further include, wherein the
plurality of drill pipe sections and the drill pipe joint section structure comprise the same
materials.
[0056] In Example 9, the subject matter of Examples 1-8 can further include wherein the
drill pipe joint section structure is configured to suppress reflected acoustic wave with an
anti-phase design between the acoustic impedance mismatch and pipe/joint section diameter
mismatch.
[0057] In Example 10, the subject matter of Examples 1-9 can further include wherein the
plurality of drill pipe sections have a phase velocity of ui and a density of pi, the drill pipe
joint section structure has a phase velocity of ¾ and a density of /¾, and Zi vi-p Z v2-pi)-
[0058] Example 11 is a method for building a drillstring, the method comprising: coupling
adjacent drill pipe sections together through a drill pipe joint section structure wherein the
drill pipe joint section structure and the drill pipe sections are acoustically impedance
matched across a selected band of frequencies.
[0059] In Example 1 , the subject matter of Example 11 can further include coupling
different lengths of adjacent drill pipe sections through a drill pipe joint section structure in a
non-periodic structure, wherein the drill pipe sections and drill pipe joint sections include
lengths of at least L , LB, or Lc, wherein LA ¹ LB ¹ L .
[0060] In Example 13, the subject matter of Examples 11-12 can further include coupling
different lengths of adjacent drill pipe sections through a drill pipe joint section structure in a
random structure sequence, wherein the drill pipe sections include different lengths of several
pipes which have different lengths, wherein L A ¹ L B ¹ L C¹ L D ¹ L k.
[0061] In Example 14, the subject matter of Examples 11- 13 can further include wherein
coupling the adjacent drill pipe sections together through the drill pipe joint section structure
comprises coupling drill pipe sections and drill pipe joint section structures having
substantially similar material properties.
[0062] In Example 15, the subject matter of Examples 11- 14 can further include, wherein
coupling the adjacent drill pipe sections together through the drill pipe joint section structure
comprises coupling drill pipe sections and drill pipe joint section structures comprising the
same material.
[0063] Example 16 is a method for acoustic communication over a drillstring, the method
comprising: transmitting a signal from a downhole environment over the drillstring using an
acoustic telemetry method, wherein the drillstring comprises a plurality of drill pipe sections
and at least one drill pipe joint section structure configured to couple adjacent drill pipe
sections of the plurality of drill pipe sections, wherein the drill pipe sections and the drill pipe
joint section structure are acoustically impedance matched across a selected band of
frequencies.
[0064] In Example 17, the subject matter of Example 16 can further include: receiving the
signal on a surface of a geological formation; and demodulating the signal.
[0065] Example 18 is a drilling system comprising: a drilling rig located on a surface of a
geological formation; and a drillstring supported by the drilling rig and configured to drill
through the geological formation, the drillstring comprising a plurality of drill pipe sections,
adjacent drill pipe sections joined by a drill pipe joint section structure, wherein the drill pipe
sections and the drill pipe joint section structures are acoustically impedance matched across
a selected band of frequencies.
[0066] In Example 19, the subject matter of Example 18 can further include wherein the
plurality of drill pipe sections comprise a plurality of different lengths and the drillstring
further comprises a non-periodic sequence of drill pipe section lengths and drill pipe joint
section structure lengths.
[0067] In Example 20, the subject matter of Examples 18-19 can further include wherein
the plurality of drill pipe sections and the drill pipe joint section structure comprise the same
materials.
[0068] In Example 1, the subject matter of Examples 18-20 can further include, wherein
the drill string further comprises a downhole tool configured to transmit acoustic telemetry
over the drillstring during LWD/MWD operations.
[0069] In the foregoing Detailed Description, it can be seen that various features are
grouped together in a single example for the purpose of streamlining the disclosure. This
method of disclosure is not to be interpreted as reflecting an intention that the claimed
examples require more features than are expressly recited in each claim. Rather, as the
following claims reflect, inventive subject matter lies in less than all features of a single
disclosed example. Thus the following claims are hereby incorporated into the Detailed
Description, with each claim standing on its own as a separate example.

Claims
What is claimed is:
1. A drillstring comprising:
a plurality of drill pipe sections; and
at least one drill pipe joint section structure configured to couple adjacent drill pipe
sections of the plurality of drill pipe sections, wherein the drill pipe sections
and the drill pipe joint section structure are acoustically impedance matched
across a selected band of frequencies.
2. The drillstring of claim 1, wherein the plurality of drill pipe sections each include a
length of one of LA or LBand the drill pipe joint section structure comprises length of
Lc, wherein LA ¹ LB ¹ L .
3. The drillstring of claim 2, wherein the drillstring further comprises a plurality of drill
pipe joint section structures each configured to couple adjacent drill pipe sections
such that the drillstring comprises a non-periodic sequence of drill pipe section
lengths and drill pipe joint section structure lengths.
4. The drillstring of claim 1, wherein the drill pipe joint section structure comprises
external threaded connections and/or internal threaded connections for coupling to the
adjacent drill pipe sections.
5. The drillstring of claim 1, wherein the drill pipe sections have an outside diameter
represented by fi, a wall thickness represented by h, a connection length represented
by D, and an impedance represented by Z , further wherein the drill pipe joint section
structure has an outside diameter represented by få, a wall thickness deviation, as
compared to the drill pipe sections, represented by Ah, and an impedance represented
by å2, wherein Z -Z 2«0, A =fi- f2~ .
6. The drillstring of claim 5, wherein a signal transmitted on the drillstring using an
acoustic method has a wavelength of l, wherein Ah«A and D«A.
7. The drillstrmg of claim 1, wherein the plurality of drill pipe sections and the drill pipe
joint section structure comprise materials having substantially similar acoustic
properties.
8. The drillstring of claim 1, wherein the plurality of drill pipe sections and the drill pipe
joint section structure comprise the same materials.
9. The drillstring of claim 1, wherein the drill pipe joint section structure is configured to
suppress reflected acoustic wave with an anti-phase design between the acoustic
impedance mismatch and pipe/joint section diameter mismatch.
10. The drillstring of claim 1, wherein the plurality of drill pipe sections have a phase
velocity of i and a density of pi, the drill pipe joint section structure has a phase
velocity of and a density of ¾, and Zi( pi ~ 2 v pi)-
11. A method for building a drillstring, the method comprising:
coupling adjacent drill pipe sections together through a drill pipe joint section
structure wherein the drill pipe joint section structure and the drill pipe
sections are acoustically impedance matched across a selected band of
frequencies.
The method of claim 11, further comprising coupling different lengths of adjacent
drill pipe sections through a drill pipe joint section structure in a non-periodic
structure, wherein the drill pipe sections and drill pipe joint sections include lengths of
at least LA, LB , or L , wherein LA ¹ LB ¹ L .
13. The method of claim 11, further comprising coupling different lengths of adjacent drill
pipe sections through a drill pipe joint section structure in a random structure
sequence, wherein the drill pipe sections include different lengths of several pipes
which have different lengths, wherein L ¹ LB ¹ L ¹ LD ¹ L .
14. The method of claim 11, wherein coupling the adjacent drill pipe sections together
through the drill pipe joint section structure comprises coupling drill pipe sections and
drill pipe joint section structures having substantially similar material properties.
15. The method of claim 11, wherein coupling the adjacent drill pipe sections together
through the drill pipe joint section structure comprises coupling drill pipe sections and
drill pipe joint section structures comprising the same material.
16. A method for acoustic communication over a drillstring, the method comprising:
transmitting a signal from a downhole environment over the drillstring using an
acoustic telemetry method, wherein the drillstring comprises a plurality of drill
pipe sections and at least one drill pipe joint section structure configured to
couple adjacent drill pipe sections of the plurality of drill pipe sections,
wherein the drill pipe sections and the drill pipe joint section structure are
acoustically impedance matched across a selected band of frequencies.
17. The method of claim 16, further comprising:
receiving the signal on a surface of a geological formation; and
demodulating the signal.
18. A drilling system comprising:
a drilling rig located on a surface of a geological formation; and
a drillstring supported by the drilling rig and configured to drill through the geological
formation, the drillstring comprising a plurality of drill pipe sections, adjacent
drill pipe sections joined by a drill pipe joint section structure, wherein the
drill pipe sections and the drill pipe joint section structures are acoustically
impedance matched across a selected band of frequencies.
19. The drilling system of claim 18, wherein the plurality of drill pipe sections comprise a
plurality of different lengths and the drillstring further comprises a non-periodic
sequence of drill pipe section lengths and drill pipe joint section structure lengths.
20. The drilling system of claim 18, wherein the plurality of drill pipe sections and the
drill pipe joint section structure comprise the same materials.
21. The drilling system of claim 18, wherein the drill string further comprises a downhole
tool configured to transmit acoustic telemetry over the drillstring during LWD/MWD
operations.