Note: Descriptions are shown in the official language in which they were submitted.
DOWNIIOLE ELECTROMAGNETIC TELEMETRY SYSTEM UTILIZING
ELECTRICALLY INSULATING MATERIAL AND RELATED METHODS
FIELD OF THE INVENTION
The present invention relates generally to electromagnetic telemetry and, more
.. specifically, to a downhole telemetry system in which electrically
insulating material is
placed around one or more portions of a well string in order to extend the
range of the
telemetry system, increase the telemetry rate, and/or reduce downhole power
requirements.
BACKGROUND
o Electromagnetic telemetry systems are used in downhole operations to
transmit
and receive electromagnetic signals for a variety of purposes. An
electromagnetic
telemetry transmitter launches an electrical signal into drill pipe either by
impressing a
potential difference across a section of drill collar connected to the drill
pipe or by
launching a current on the drill string by way of a toroid that is placed
around a section of
Is the drill string.
However, when an electromagnetic transmitter is within casing, signal losses
can
be excessive as the current on the pipe jumps to the casing, thus launching
part of the
signal to the casing, but also shorting part of the signal along the casing.
Furthermore,
and especially when there is direct contact between any part of the pipe and
the casing,
20 motion of the drill string can cause intermittent contact and, thus,
introduce a very
significant noise into the telemetry signal. Moreover, as the signal travels
up or down the
pipe and/or casing, it is attenuated substantially as current leaks into the
formation
surrounding the borehole. As a result, the signal received at the surface or
downhole
receiver can be attenuated to the point where the signal to noise ratio is not
high enough
25 to allow for reliable communication, even at a data rate of a few bits
per second.
In view of the foregoing, there is a need in the art for a cost effective
method by
which to extend the range of the telemetry system and/or to prevent short
circuits through
the mud and into the easing or directly into the casing.
SUMMARY
In one aspect, there is provided a method for utilizing an electromagnetic
telemetry system in a downhole well, the method comprising: providing a well
string
comprising one or more tubulars attached to a bottom hole assembly, the bottom
hole
CA 2890618 2017-10-12 1
assembly comprising at least one of an electrical current launching device or
a receiver;
applying electrically insulating material around one or more portions of the
well string,
wherein applying the electrically insulating material around the one or more
portions of
the well string comprises: determining a length of an electrically conductive
portion of
the formation along the well; and positioning an insulation sleeve around the
one or more
portions of the well string based upon the determined length, the insulation
sleeve being
comprised of is electrically insulating swellable material; deploying the
bottom hole
assembly into the well; conducting an electromagnetic telemetry operation
using the
bottom hole assembly; and utilizing the electrically insulating material to
reduce at least
io one of: short circuits from the current launching device to casing; or
current leakage from
the well string into the casing or formation along the well.
In another aspect, there is provided an electromagnetic telemetry system for
use in
a downhole well, the system comprising: a well string comprising one or more
tubulars
attached to a bottom hole assembly, the bottom hole assembly comprising at
least one of
Is an electrical current launching device or a receiver; and electrically
insulating material
positioned around one or more portions of the well string to reduce at least
one of: short
circuits from the current launching device to casing; or current leakage from
the well
string into the casing or formation along the well, wherein the electrically
insulating
material positioned around the one or more portions of the well string is an
insulation
20 sleeve comprised of electrically insulating swellable material and is
applied based upon a
determined length of an electrically conductive portion of the formation along
the well.
In a further aspect, there is provided a method for utilizing an
electromagnetic
telemetry system in a downhole well, the method comprising: applying
electrically
insulating material around one or more portions of a well string comprising at
least one of
25 an electrical current launching device or a receiver, wherein applying
the electrically
insulating material around the one or more portions of the well string
comprises:
determining a length of an electrically conductive portion of the formation
along the well;
and positioning an insulation sleeve around the one or more portions of the
well string
based upon the determined length, the insulation sleeve being comprised of
electrically
30 insulating swellable material; deploying the well string into the well;
and utilizing the
electrically insulating material to reduce at least one of: short circuits
from the current
launching device to casing; or current leakage from the well string into the
casing or
formation along the well.
la
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BRIEF DESCRIPTION OF THE DRAWINGS
FIGS. IA and 1B illustrate a drilling rig and an electromagnetic telemetry
system
according to one or more exemplary embodiments of the present invention; and
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FIGS. 2A, 2B and 2C arc graphs illustrating the signal improvement effects of
adding electrically insulating material above and/or below the current
launching device,
according to one or more exemplary embodiments of the present invention.
DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS
Illustrative embodiments and related methodologies of the present invention
are
described below as they might be employed in a downhole telemetry system in
which
electrically insulating material is placed around one or more portions of the
well string. In
the interest of clarity, not all features of an actual implementation or
methodology are
described in this specification. Also, the -exemplary" embodiments described
herein refer
to examples of the present invention. It will of course be appreciated that in
the
development of any such actual embodiment, numerous implementation-specific
decisions
must be made to achieve the developers' specific goals, such as compliance
with system-
related and business-related constraints, which will vary from one
implementation to
is another. Moreover, it will be appreciated that such a development effort
might be
complex and time-consuming, but would nevertheless be a routine undertaking
for those
of ordinary skill in the art having the benefit of this disclosure. Further
aspects and
advantages of the various embodiments and related methodologies of the
invention will
become apparent from consideration of the following description and drawings.
As described herein, exemplary embodiments of the present invention extend the
range of an electromagnetic telemetry system when the system is within a cased
or
uncased section of a well. To achieve this objective, electrically insulating
material is
applied to the well string immediately above and/or immediately below the
electrical
current launching device (gap sub assembly or toroid, for example) or
receiver. In other
embodiments, the electrically insulating material may also cover the current
launching
device or receiver. Accordingly, as the current launching device launches the
electrical
signal into the drill pipe, the electrically insulating material prevents the
current from
jumping to the casing either directly or through the drilling mud, thus
preventing or
reducing the severity of short circuits through the casing and/or electrical
current leakage
into the formation in situations where casing is not present around the
transmitter, thereby
improving the range and/or signal to noise ratio of the telemetry system,
and/or reducing
the power required by the system. Moreover, in those embodiments where a
downhole
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receiver is utilized, the electrically insulating material acts to reduce
current leakage from
the well string to the casing or formation during downlink operations.
In certain exemplary embodiments, the electrically insulating material is one
or
more sheets of material wrapped around the bottom hole assembly or drill pipe
using an
adhesive backing. In others, for example, electrically insulating swellable
material or a
variety of coatings may also be utilized. As a result, the range of the
electromagnetic
telemetry system within and without the cased section is increased by roughly
the same
amount of pipe that is electrically insulated.
Therefore, the data rate of the
electromagnetic telemetry system may also be increased without the need for
adding
repeaters.
FIGS. 1A and 1B illustrate a drilling rig 12 and an electromagnetic telemetry
system 10 according to one or more exemplary embodiments of the present
invention. As
understood in the art, electromagnetic telemetry system 10 generates and/or
receives
electromagnetic waves downhole. Electromagnetic telemetry system 10 includes a
bottom
is hole assembly 14, current launching device 16 (gap sub assembly, for
example) and
tubular section 18 (referred to in combination as a well string, for example),
all extending
down through casing 20 of well 22. The term "well string," as used herein, may
refer to a
variety of deployment strings such as, for example, drill string, coiled
tubing, production
tubing, etc. In the exemplary embodiment of FIGS. 1A and 1B, the well string
is a drill
string.
In addition, electromagnetic telemetry system 10 includes a receiver 24
electrically
coupled to a ground reference 26, and may also have one or more repeaters (not
shown)
along tubular 18 as necessary. In general, electromagnetic telemetry system 10
communicates by launching a low frequency current (between about 1 and 30 Hz,
for
example) along tubular 18. Signals associated with the current are then
detected at the
surface by receiver 24 where a potential difference is measured between
drilling rig 12 and
ground 26. In this exemplary embodiment, electromagnetic telemetry system 10
may
operate in, for example, a phase modulated carrier mode, pulse position
modulation mode
or orthogonal frequency-division multiplexing mode, or a number of other
modulation
.. modes, as will be understood by those ordinarily skilled in the art having
the benefit of this
disclosure.
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In order to produce the current transmitted by electromagnetic telemetry
system
10, electrical current launching device 16 is provided adjacent bottom hole
assembly 14
(or may form part of bottom hole assembly 14). In a first exemplary
embodiment,
electrical current launching device 16 is provided as an electrical break
between bottom
hole assembly 14 and tubular 18 which effectively turns the well string into a
large
antenna. In the exemplary embodiment of FIG. 1A, a gap sub assembly serves as
the
electrical break or antenna. An electrical potential difference is thereby
created between
bottom hole assembly 14 and tubular 18, thus creating the transmitted current.
As
understood in the art, the gap sub assembly is an electrical isolation joint
designed to
io withstand the high torsional, bending, tensile and compression loads of
electromagnetic
telemetry system 10. However, in other embodiments, electrical current
launching device
16 may instead be a toroid assembly, as understood in the art. These and other
aspects of
electromagnetic telemetry system 10 will be readily understood by those
ordinarily skilled
in the art having the benefit of this disclosure.
Still referring to FIGS. lA and 1B, tubular 18 has been lowered through blow
out
preventer 28 down into well 22, and through casing 20. As previously
mentioned, in this
exemplary embodiment, tubular 18 is drill pipe forming part of a drill string;
however, in
other embodiments, tubular 18 may be, for example, coiled or production tubing
utilized
for some other operation. Nevertheless, tubular 18 extends down to current
launching
device 16 which is coupled to bottom hole assembly 14. A drill bit 30 is
positioned at the
distal end of bottom hole assembly 14. Drill bit 30 may be rotated by a
variety of methods
including, for example, tubular 18 or a mud motor. In this exemplary
embodiment,
bottom hole assembly 14 comprises a CPU (not shown) and electromagnetic
telemetry
transmitter 32 that includes electronics necessary to sense, detect and
transmit
electromagnetic signals via current launching device 16, in addition to
handling other
operations of bottom hole assembly 14, as understood in the art.
In certain exemplary embodiments of electromagnetic telemetry system 10, an
electrically insulating material 34 is applied around one or more portions of
a drill string
(tubular 18 or bottom hole assembly 14) above and/or below current launching
device 16.
In one embodiment, the electrically insulating material 34 need not be a
perfect insulator;
rather, the resistivity of electrically insulating material 34 is no less than
two orders of
magnitude higher than that of the fluid (drilling mud, for example) used
during the
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downholc operation. Moreover, in certain embodiments, it is also not necessary
that
electrically insulating material 34 be without break along tubular 18 or
bottom hole
assembly 14. Nevertheless, electrically insulating material 34 may be a
variety of
materials, such as, for example, a swellable material, injection-molded
coating, bands,
sleeves, stabilizers, high oxygen fuel spray coating, anodized layers, etc.
The swellable
material may be, for example, such materials as used in the Swell TechnologyTm
Systems,
commercially available through the Assignee of the present invention,
Halliburton Energy
Services, Co. or Houston, Texas. In addition, the swellable material may be
selected
based upon the mud type (oil or water based, for example) such that, once
contact has
io been made with the drilling mud, the swellable material swells onto
bottom hole assembly
14 and/or tubular 18 and adheres to it.
As previously described, electrically insulating material 34 is applied to one
or
more portions of the well string (i.e., tubular 18 and bottom hole assembly
14) above
and/or below the current launching device 16. In one embodiment, electrically
insulating
is material 34 is applied immediately above and/or below current launching
device 16, as
shown in FIGS. lA and 1B. However, in other embodiments, electrically
insulating
material 34 may also be placed all along tubular 18 as desired. In certain
exemplary
embodiments, electrically insulating material 34 may be applied as a tape that
is wrapped
around one or more portions of bottom hole assembly 14 as it is tripped into
well 22. The
20 electrically insulating tape may be adhered along the well string by
wetting it with the
same fluid (drilling mud, for example) that will be utilized to cause it to
swell. However,
in other embodiments, an adhesive backing may also be utilized on the tape to
adhere it to
the well string. Exemplary insulating tapes may be, for example, swellable
materials,
adhesive-backed rubber, silicone rubber, Teflon, polyester films, polyimide
tapes, polymer
25 sheets (polyethylene, for example). In certain embodiments, however, the
use of
polyethylene would be limited to about 115 C since a typical melting point for
a
polyethylene plastic is around 120 C. Moreover, the tape may be one to several
feet wide
and a fraction of an inch thick (1/8 inch, for example).
In an alternate embodiment, electrically insulating material 34 may be formed
into
30 a sleeve having an inner diameter somewhat larger than that of the box-
pin outer diameter
of bottom hole assembly 14 or tubular 18. In one example, the electrically
insulating
sleeve would be applied along the well string as it is tripped into well 22.
The electrically
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insulating sleeve may be held in place during deployment in a variety of ways
such as, for
example, by applying clamps or tape to hold the electrically insulating sleeve
in place until
the swellable material begins to swell. In the alternative, the electrically
insulating sleeve
may be snug enough around the well string portion to hold itself in place
until swelling
begins. In addition, portions of the electrically insulating sleeve may be
wetted with
drilling mud, thus causing that portion of the sleeve to swell and adhere to
the well string.
Nevertheless, after deployment, as the electrically insulating sleeve comes
into the contact
with the drilling fluid, the swellable material is then activated to swell
against the surface
of bottom hole assembly 14 or tubular 18, thus adhering to it. The swellable
material may
be selected, for example, based upon the type of drilling mud utilized, as
will be
understood by those ordinarily skilled in the art having the benefit of this
disclosure.
Moreover, still referring to FIGS. lA and 1B, electrically insulating material
34
may also be applied to one or more sections of tubular 18 using any of the
methods
described herein. Such an embodiment will minimize current loss during
transmission
is along tubular 18. In prior art telemetry systems, the current traveling
up the well string
and casing tends to migrate off the well string/casing and go to ground, thus
resulting in
signal loss. However, through use of this alternate embodiment of the present
invention
whereby one or more portions of tubular 18 are insulated above current
launching device
16, the amount of current going to ground along tubular 18 is then reduced,
which
increases the amount of current traveling back up the well string and reaching
the surface,
thus resulting in a larger amplitude signal. In certain embodiments,
electrically insulating
material 34 may be utilized along bottom hole assembly 14 only, tubular 18
only, or in
combination along both bottom hole assembly 14 and tubular 18.
Additionally, in yet another alternative embodiment, an electrically resistive
fluid
may be pumped into well 22 to assist in electrically isolating electromagnetic
telemetry
system from casing 22. Such fluid may be drill mud and or fluid additives
added to the
fluid. In another embodiment, the electrically resistive fluid may be utilized
without
electrically insulating material 34, as will be understood by those ordinarily
skilled in the
art having the benefit of this disclosure.
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Although not shown in FIGS. 1A and 1B, exemplary embodiments of present
invention may also be utilized in downlink telemetry systems which may only
utilize a
downhole receiver. As understood in the art, electromagnetic telemetry system
10 may
comprise a receiver in place of current launching device 16 which is used to
receive
signals transmitted from the surface via tubular 18. Such an embodiment may or
may not
include electromagnetic telemetry transmitter 32. In such embodiments, the
receiver may
be, for example, a gap sub assembly or toroid as previously described.
However, unlike
the previous embodiments described herein, the receiver will instead receive
and decode
the signal in order to perform some operation within bottom hole assembly 14.
In such
embodiments, placement of electrically insulating material 34 around one or
more portions
of tubular 18 will reduce and/or eliminate current leakage from tubular 18
into casing 20
or the open hole formation, as will be understood by those ordinarily skilled
in the art
having the benefit of this disclosure.
Now with reference to the graphs of FIGS. 2A-2C, the signal improvement
effects
is of adding electrically insulating material 34 above and/or below current
launching device
16 will now be described. The graphs plot the current on tubular 18 and casing
20 along
various depths of well 22 wherein various lengths of electrically insulating
material 34
have been applied. FIG. 2A is a plot of the current on tubular 18 and casing
20 in a 2,800
foot well with 2,500 feet of drill pipe, 2,500 feet of casing, a 1 inch gap
sub assembly, at a
depth of 1400 feet and using .25 ohm meter mud. As can be seen, the current
very rapidly
bleeds off of the pipe into casing 20 in such a way that a significant portion
of the current
is no longer available as a signal, but instead has been effectively shorted
out by casing 20.
FIG. 2B is a plot of the current on tubular 18 and casing 20 in the same well
as
FIG. 2A, but with 400 feet of electrically insulating material 34 along bottom
hole
assembly 14 below the 1 inch gap sub assembly. The mud resistivity is again
.25 ohm
meters. As illustrated, current still quickly bleeds to casing 20 as soon as
there is no
electrically insulating material 34, but the overall signal level is
significantly improved.
FIG. 2C is yet another plot of the current along the well, but with 400 feet
of insulation
above and 400 feet of insulation below a 1 inch gap sub assembly. The mud
resistivity is
again .25 ohm meters. As before, the current quickly leaks to casing 20 where
the
electrically insulating material 34 ends, but the overall signal level is
again improved.
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Chart 1 below is a summary of these and other signal levels that may be
observed at the
surface.
Voltage V dB R mud Insulation
my c dBm Ohm m Inches/feet
to inf
0.21972 73.1624 0.25 1"
0.33617 69.4688 0.25 100 feet below gap
0.61561 64.2139 0.25 400 feet below gap
1.3439 57.433 0.25 800 feet centered
on gap
0.33688 69.4505 2.5 1"
0.43331 67.2641 2.5 100 feet below gap
0.71538 62.9092 2.5 400 feet below gap
1.4828 56.5782 2.5 800 feet centered
on gap
Chart I.
As shown, the signal level in millivolts appears in the first column, the
signal level
expressed as decibel millivolts appears in the second column, the mud
resistivity appears in
the third column, and a summary of the insulation appears in the fourth
column. Although
io the foregoing examples address embodiments utilizing transmitters, the same
types of
gains in signal to noise ratio will be present in embodiments utilizing
downhole receivers,
as will be understood by those ordinarily skilled in the art having the
benefit of this
disclosure.
In view of the foregoing, electrically insulating material 34 may be applied
to the
well string in a variety of ways. For example, electrically insulating
material 34 may be
applied to one or more portions of the well string as the well string is being
made up. In
the alternative, one or more portions of the well string may be insulated
before the well
string is made up. Moreover, exemplary embodiments of the present invention
may be
utilized in open and cased wells. In cased sections of the well, electrical
insulating
material 34 reduces or prevents short circuits from current launching device
16 into casing
20. In open sections of the well, electrical insulating material 34 reduces or
prevents
current leakage from the well string into the formation. Accordingly, the up
hole or down
hole telemetry range of electromagnetic telemetry system 10 is increased by a
distance
roughly equal to the length of insulation applied and downhole power
requirements are
reduced. Therefore, electromagnetic telemetry is efficiently provided while
drilling (or
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performing other operations) with the telemetry transmitter inside and outside
the casing.
In addition, in those embodiments of the present invention utilized inside
cased
wells, the portion of the well string below current launching device 16 (or
the receiver)
may be insulated. However, in those embodiments utilized along portions of
wells that are
open to the formation, portions of the well string above current launching
device 16 (or
the receiver) may be insulated. In the latter embodiment, the length of one or
more
electrically conductive portions of the formation along the open well may be
determined,
and the length of electrically insulating material 34 is determined based upon
the length of
the conductive formation. As understood in the art, the location of the
electrically
io conductive formations may be determined based upon, for example,
resistivity logs of
other wells near the well under construction, as will be understood by those
ordinarily
skilled in the art having the benefit of this disclosure. Based upon the
logged data, as well
as the planned well trajectory and how far the bit will be beyond the
conductive formation
at a given time (in those embodiments utilized in a drill string), those same
skilled persons
can readily determine the length of electrically conductive material necessary
to be applied
above current launching device 16 (or the receiver). For example, if the well
is a vertical
well and the bit run is planned to extend to a depth of 12,000 feet, the
electromagnetic
transmitter is 200 feet above the drill bit, and a very conductive formation
extends from
10,000 to 11,000 feet, then 1,800 feet of electrically insulating material 34
may be
positioned above the current launching device 16 so that once current
launching device 16
passed the bottom of the conductive formation (i.e. once it was beyond a depth
of 11,000
feet), there would always be electrically insulating material 34 between
tubular 18 and the
formation. Nevertheless, in either embodiment, one or more portions of the
well string
above and/or below current launching device 16 or the receiver (not shown) may
also be
insulated.
An exemplary methodology of the present invention provides a method for
utilizing an electromagnetic telemetry system in a downhole well, the method
comprising
providing a well string comprising one or more tubulars attached to a bottom
hole
assembly, the bottom hole assembly comprising at least one of an electrical
current
launching device or a receiver; applying electrically insulating material
around one or more
portions of the well string; deploying the bottom hole assembly into the well;
conducting
an electromagnetic telemetry operation using the bottom hole assembly; and
utilizing the
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electrically insulating material to reduce at least one of short circuits from
the current
launching device to casing or current leakage from the well string into the
casing or
formation along the well. The conducted electromagnetic telemetry operation
may be, for
example, transmitting and/or receiving electromagnetic signals along the
system. Another
method further comprises applying the electrically insulating material around
one or more
portions of the well string immediately above or below the current launching
device or
receiver. In another method, applying the electrically insulating material
around the one
or more portions of the well string comprises wrapping the one or more
portions of the
well string with one or more sheets of electrically insulating material.
In yet another, applying the electrically insulating material around the one
or more
portions of the well string comprises positioning an insulation sleeve around
the one or
more portions of the well string, the insulation sleeve being comprised of
electrically
insulating swellable material. In another, applying the electrically
insulating material
around the one or more portions of the well string comprises applying at least
one of: an
is electrically insulating swellable material; an electrically insulating
injection-molded
coating; an electrically insulating spray coating; or an electrically
insulating anodized layer.
In yet another, applying the electrically insulating material around the one
or more
portions of the well string comprises: determining a length of an electrically
conductive
portion of the formation along the well; and applying the electrically
insulating material
based upon the determined length.
An exemplary embodiment of the present invention provides an electromagnetic
telemetry system for use in a downhole well, the system comprising a well
string
comprising one or more tubulars attached to a bottom hole assembly, the bottom
hole
assembly comprising at least one of an electrical current launching device or
a receiver;
and electrically insulating material positioned around one or more portions of
the well
string to reduce at least one of short circuits from the current launching
device to casing;
or current leakage from the well string into the casing or formation along the
well. In
another embodiment, the electrically insulating material is positioned
immediately above or
below the current launching device or receiver. In yet another, the electrical
current
launching device is a gap sub assembly or a toroid. In another, the receiver
is a gap sub
assembly or a toroid. In another, the electrically insulating material is one
or more sheets
of electrically insulating material. In yet another, the electrically
insulating material is an
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insulation sleeve. In another, the electrically insulating material is at
least one of: an
electrically insulating swellable material; an electrically insulating
injection-molded
coating; an electrically insulating spray coating; or an electrically
insulating anodized layer.
Yet another exemplary methodology of the present invention provides a method
for utilizing an electromagnetic telemetry system in a downhole well, the
method
comprising: applying electrically insulating material around one or more
portions of a well
string comprising at least one of an electrical current launching device or a
receiver;
deploying the well string into the well; and utilizing the electrically
insulating material to
reduce at least one of short circuits from the current launching device to
casing or current
to leakage from the well string into the casing formation along the well.
Another method
further comprises applying the electrically insulating material around one or
more portions
of the well string immediately above or below the current launching device or
receiver. In
another, applying the electrically insulating material around the one or more
portions of
the well string comprises applying at least one of an electrically insulating
swellable
is material; an electrically insulating injection-molded coating; an
electrically insulating spray
coating; or an electrically insulating anodized layer. In yet another,
applying the
electrically insulating material around the one or more portions of the well
string
comprises determining a length of an electrically conductive portion of the
formation
along the well; and applying the electrically insulating material based upon
the determined
20 length.
The foregoing disclosure may repeat reference numerals and/or letters in the
various examples. This repetition is for the purpose of simplicity and clarity
and does not
in itself dictate a relationship between the various embodiments and/or
configurations
discussed. Further, spatially relative terms, such as "beneath," "below,"
"lower,"
25 "above," "upper" and the like, may be used herein for ease of
description to describe one
element or feature's relationship to another element(s) or feature(s) as
illustrated in the
figures. The spatially relative terms are intended to encompass different
orientations of
the apparatus in use or operation in addition to the orientation depicted in
the figures. For
example, if the apparatus in the figures is turned over, elements described as
being
30 "below" or "beneath" other elements or features would then be oriented
"above" the other
elements or features. Thus, the exemplary term "below" can encompass both an
orientation of above and below. The apparatus may be otherwise oriented
(rotated 90
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degrees or at other orientations) and the spatially relative descriptors used
herein may
likewise be interpreted accordingly.
Although various embodiments and methodologies have been shown and
described, the invention is not limited to such embodiments and methodologies
and will be
understood to include all modifications and variations as would be apparent to
one
ordinarily skilled in the art having the benefit of this disclosure. For
example, one or more
repeaters may also form part of the telemetry systems described herein and, in
such cases,
the same inventive principles would be applicable, as will be understood by
those same
ordinarily skilled persons. Therefore, it should be understood that the
invention is not
intended to be limited to the particular forms disclosed. Rather, the
intention is to cover
all modifications, equivalents and alternatives falling within the spirit and
scope of the
invention as defined by the appended claims.
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