Note: Descriptions are shown in the official language in which they were submitted.
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PROPAGATING WAVE EARTH FORMATION RESISTIVITY
MEASURING ARRANGEMENT
1. Field Of the Invention
The invention relates to measurement of geophysical
parameters in earth formations surrounding well bores and,
more particularly, to apparatus for measuring the resistivity
of earth formations in drilling operations.
2. Background Of the Invention
In oil and gas exploration in which well bores are drilled,
the well boring apparatus includes a drill collar to which a
drill bit is attached. A drilling fluid is pumped to the
drill bit through the drill collar. The drilling fluid
exiting from the drill bit is returned to the surface through
the space between the exterior of the drill collar and the
already drilled portion of well bore.
Resistivity measurements are generally performed in the well
bore to determine the characteristics of the surrounding
earth formations. These resistivity measurements may be
performed by measuring the conduction of electrical current
using an arrangement of electrodes within the well bore in a
wireline system or using an arrangement of electrodes mounted
on a drill collar in a measurement performed while drilling
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system. Low frequency induction coils on the drill collar
exterior may be used instead of the electrodes.
Alternatively, propagating wave resistivity measurements may
be performed utilizing transmitting and receiving loop
antennas operating at higher frequencies in the range from
400 KHz to 2 MHz. The electronic equipment associated with
the electrodes or the loop antennae is housed in a sonde
positioned within the drill collar. The sonde has a
generally tubular metallic housing and mountings in the
l0 housing for electronic equipment used in the measurements.
Where electrodes or low frequency loop antennae are used,
they are located in recesses on the surface of the drill
collar for measurements made while drilling. For the
propagating wave resistivity measurements in the 400 KHz to 2
MHz range, one or more pairs of transmitting and receiving
antennas may be wound on the exterior of a metal drill collar
since the 400 KHz to 2 MHz signals do not propagate through
the conductive drill collar.
An exemplary arrangement using antennas mounted on the
exterior surface of a drill collar and electronic equipment
in a sonde inside the drill collar is disclosed in U.S.
Patent 5,892,361 issued April 6, 1999. With the transmitting
and receiving antennae on the exterior of the drill collar,
the drilling fluid flows in the annulus between the sonde and
the interior surface of the drill collar and connections are
required between the electronic equipment associated with the
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antennae inside the sonde and the antennae on the drill
collar exterior. Such connections make it very difficult to
retrieve the propagating wave resistivity measuring apparatus
from the well bore. Alternatively, the electronic equipment
may be mounted in the drill collar itself as disclosed in
U.S. Patent 5,402,068 issued March 28, 1995. In the drill
collar mounting arrangement, the transmitting and receiving
antennae as well as the electronic equipment associated
therewith are a part of the drill collar and are not
l0 retrievable. The antennae may also be arranged to be
proximate to the interior of the drill collar on extensions
connected to the sonde so that the drilling fluid flows in
the space between the sonde and the antennae. With this
structure, it is also very difficult to retrieve the sonde
from the well bore.
3. Brief Summary of the Invention
The invention is directed to a propagating wave resistivity
measuring arrangement in a well bore. The measurement
arrangement is adapted to determine properties of earth
formations surrounding the well bore in which a sonde that
houses electronic equipment is positioned in one section of a
drill collar structure having plural sections that adjoins
the earth formation. The sonde houses devices for processing
of signals for the propagating wave resistivity measurements
and devices for communicating the results of the propagating
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wave resistivity measurements to the surface end of the well
bore.
According to the invention, one or more transmitting antennae
in the exterior of the sonde housing at first positions
generate interrogating signals for transmission to the earth
formation surrounding the drill collar and one or more
receiving antennae in the exterior of the sonde housing at
second positions spaced from first positions receive signals
corresponding to the interrogating signals from the earth
formation surrounding a first section of drill collar
structure. The drill collar passes the interrogating signals
from the transmitting antennae on the sonde into the earth
formation and passes signals responsive to the interrogating
signals from the earth formation to the receiving antennae on
the sonde.
According to one aspect of the invention, the exterior
surface of the sonde is smooth for laminar drilling fluid
flow in the annular passageway between the sonde and the
interior surface of the first section of the drill collar
structure. Each transmitting antenna is inserted into a
recess at a first position on the exterior surface of the
sonde and each receiving antenna is inserted into a recess at
a second position on the exterior surface of the sonde. The
recesses in which the antennae are inserted are filled with a
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non-conductive material that is substantially flush with the
smooth surface of the housing exterior.
According to another aspect of the invention, a lower end of
the sonde is supported in a predetermined position within the
drill collar structure on a support in a second section of
the drill collar structure located below the first section of
the drill collar. The support orients the sonde in a
predetermined longitudinal and rotational positions within
the drill collar structure.
According to yet another aspect of the invention, the first
section of the drill collar structure is made of a material
such as a fiber glass epoxy that is transparent to the
interrogating signals from the transmitting antennae and to
the signals from the earth formation corresponding to the
interrogating signals.
According to yet another aspect of the invention, the first
section of the drill collar structure is made of a conductive
material and includes slotted portions each positioned to
provide passage of the interrogating signals from a
transmitting antenna to the earth formation and passage of
signals from the earth formation corresponding to the
interrogating signals to a receiving antenna. The support in
the second section of the drill collar structure for the
sonde is adapted to position the sonde so that each
transmitting antenna radiates interrogating signals through
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the slots therein and each receiving antenna receives signals
from the earth formation corresponding to the interrogating
signals through the slots therein.
According to yet another aspect of the invention, the sonde
includes a device at an upper end that receives apparatus for
retrieving the sonde from the well bore such as a spear point
shaped top section which can be latched with a standard
overshot.
In one embodiment illustrative of the invention, a
sonde has one or more transmitting antennae in spaced
relationship with one or more receiving antennae. The
antennae are wound in recesses of a smooth exterior surface
of the sonde housing. The recesses are filled with a non-
conductive material to be flush with the smooth exterior
surface. The sonde is positioned within a non-conductive
section of a drill collar structure inserted in a well bore
with the lower end of the sonde supported in a predetermined
position by a second section of the drill collar structure.
Drilling fluid flows down the inside of the drill collar
around the smooth exterior surface of the sonde and then,
having exited through the drill bit, between the exterior
surface of the drill collar and the well bore. The upper end
of the sonde has a spear point structure for connection to a
wire line to the sonde from the well bore.
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In another embodiment illustrative of the invention, a sonde
has one or more transmitting antennae in spaced relation to
one or more receiving antennae along its length. Each
antenna is wound in a recess of a smooth exterior surface of
the sonde. The sonde is positioned in a metal section of a
drill collar structure inserted into a well bore. The
antenna recesses are filled to be flush with the smooth
exterior surface and the drill collar has slotted portions
positioned along the axis of the sonde aligned with the
antennae. The slots are filled with a material transparent
to the interrogating signals from the transmitting antennae
and to the signals from the earth formation corresponding to
the interrogating signals. Processing apparatus associated
with the antennae are housed within the sonde. Drilling fluid
is pumped down around the sonde within a wash pipe proximate
the interior surface of the drill collar and up to the
surface of the earth formation around the exterior of the
drill collar. The lower end of the sonde is supported in a
second section of the drill collar structure in a
predetermined position so that the interrogating signals from
the transmitting antennae pass through the slots to the
surrounding earth formation and the signals from the earth
formation corresponding to the interrogating signals pass
through the slots to the receiving antennae.
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The invention will be better understood from the following
more detailed description taken together with the
accompanying drawings and the claims.
4. Brief Description of the Drawinas
Fig. 1 shows a general diagram of a system for drilling and
measuring propagating wave resistivity in an earth formation
surrounding a well bore;
Fig. 2 illustrates an arrangement of a sonde in a drill
collar structure for propagating wave resistivity
measurements while drilling according to the prior art.
Fig. 3 depicts apparatus for propagating resistivity
measurement while drilling housed in a sonde within a non-
metallic drill collar structure according to one embodiment
of the invention;
Fig. 4 depicts apparatus for propagating wave resistivity
measurement while drilling housed in a sonde within a
metallic drill collar structure according to another
embodiment of the invention;
Fig. 5 shows the slot structure of the metallic drill collar
structure used in the embodiment of Fig. 4;
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Fig. 6 illustrates the arrangement of electronic equipment
housed in the sonde in the embodiments of Figs. 3 and 4;
Fig. 7 illustrates a structure that supports the sonde in the
drill collar structure of Figs. 3 and 4;
Fig. 8 illustrates an arrangement for retrieving the sonde of
the embodiments of Figs. 3 and 4 from the well bore of Fig.
1; and
Fig. 9 shows an alternative drill collar structure for the
embodiment of Fig. 4.
5. Detailed Description
Fig. 1 is a schematic diagram showing a well bore 1 being
drilled in an earth formation 50 using a drilling rig that
includes a derrick 3, a derrick floor 5, a drill string 7, a
drill collar 10 and a drill bit structure 28. In drilling, a
drilling fluid or "mud" is pumped down through the drill
collar 10 by a pump (not shown) and the drill bit structure
28 for drilling. After passing through the drill bit
structure, the drilling fluid is returned to the surface of
the earth formation 50 between the exterior of the drill
collar 10 and the well bore 1.
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During the drilling, the propagating wave resistivity of the
earth formation 50 surrounding the well bore is measured by
apparatus within the drill collar section 10. The measuring
apparatus includes spaced apart transmitting antennae
radiating interrogating signals in the frequency range of 400
KHz to 2 MHz into the earth formation, spaced apart receiving
antennae for receiving signals corresponding to the
interrogating signals and processing apparatus that processes
the received signals to determine the propagating wave
resistivity.
Fig. 2 shows a prior art arrangement of propagating wave
resistivity measurement apparatus in a tubular metal drill
collar 200. In Fig. 2, a sonde 210 having a tubular housing
230 is shown affixed to and centered in a drill collar 200.
Drilling fluid flows in the annular space between the
exterior of the sonde and the interior surface of the drill
collar. Since the annular space is interrupted by
connection/supports 218-1 through 218-4, the drilling fluid
flow is somewhat restricted. The metal drill collar 200 has
axially positioned circumferential recesses 212-l, 212-2,
212-3 and 212-4. A transmitting loop antenna 215-1 is wound
in the recess 212-1 and a transmitting loop antenna 215-4 is
wound in the recess 212-4. A receiving loop antenna 215-2 is
wound in the recess 212-2 and a receiving loop antenna 215-3
is wound in the recess 212-3.
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The transmitting loop antennae 215-1 receives timed signals
in the frequency range from 400 KHz to 2 MHz from a
transmitter within the housing of the sonde 210 through a
connection structure 218-1. The transmitting loop antenna
215-4 receives differently timed signals from another
transmitter in the sonde 210 through a connection structure
218-4. The transmitting loop antennae 215-1 and 215-4 operate
to transmit differently timed interrogating signals to the
surrounding earth formation. Signals responsive to the
interrogating signals that are returned from the earth
formation to the drill collar 210 are picked up by the
receiving antennae 215-2 and 215-3. The returned signals
from the receiving antennae are applied to a receiver in the
sonde through the connection structures 218-2 and 218-3 and
IS are processed by a processor in the sonde to generate
propagating wave resistivity data.
Since the metal drill collar is not transparent to the
interrogating and return signals in the frequency range of
400 KHz to 2 MHz, it is necessary to locate the antennae 212-
1 to 212-4 on the exterior of the drill collar. It is also
necessary to provide connections through the connection
structures 218-1 through 218-4 for interrogating signals
generated by transmitters within the sonde and for receiving
and processing return signals from earth formation in
receivers and processors in the sonde. Alternatively, a
sonde may not be used and the transmitter, receiver and
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processor associated with the transmitting antennae 215-1 and
215-4 and the receiving antennae 215-2 and 215-3 may be
mounted on the drill collar itself. In either arrangement,
however, the design is relatively complex and expensive and,
in addition, the propagating wave resistivity measurement
equipment is not retrievable independent of the drill collar.
Fig. 3 depicts a sonde in a non-conducting drill collar for a
propagating wave resistivity measurement according to one
embodiment of the invention. Referring to Fig. 3, there is
schematically shown a drill collar structure 300; a non-
conductive measuring section 302 of drill collar structure
300, a sonde 310 in the drill collar structure section 302,
recesses 312-1, 312-2, 312-3 and 312-4, loop antennae 315-1,
315-2, 315-3 and 315-4, a pony section 325 of the drill
collar structure 300, a landing sub section 328 of the drill
collar structure 300 and an attachment structure 335. The
transmitting and receiving antennae of the sonde 310 are
positioned in the measurement section 302, the landing sub
section 328 has a muleshoe device 344 and the pony section
325 connects the measuring section 302 and the landing sub
section 328. The drill collar measuring section 302 may be
made of any suitable non-conducting material such as
fiberglass reinforced epoxy. In order to protect the drill
collar section 302 from rapid wear, wear rings containing
tungsten carbide may be inserted or the drill collar section
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302 may be coated overall with a hard material such as a
ceramic.
A housing 330 of the sonde 310 in Fig. 3 may be made of
stainless steel or beryllium copper. The housing 330 has a
general shape of a right circular cylinder with a smooth
outer surface. Circumferential recesses 312-1 through 312-4
that are spaced along the axis of the sonde are formed in the
outer surface of the housing. A first transmitting loop
antenna 315-1 is wound in the recess 312-1 and a second
transmitting loop antenna 315-4 is wound in the recess 312-4.
A first receiving loop antenna 315-2 is wound in the recess
312-2 and a second receiving antenna 315-3 is wound in the
recess 312-3. After the antenna 315-1 through 315-4 are
wound, the recesses 312-1 through 312-4 are filled with a
material such as Viton rubber and the surfaces of the filled
recesses are made substantially flush with the smooth surface
of the housing 330. The lower end of the sonde is supported
on a support structure in a landing sub section 328 which is
connected to the section 302 by a pony section 325.
Fig. 7 is a schematic diagram showing one arrangement to
detachably support the sonde 310 on the drill collar 300 of
Fig. 3 so that the sonde can be lifted from the drill collar
and retrieved from the well bore. In Fig. 7, there is shown
the pony section 325 and the landing sub section 328. The
pony section 325 is threadedly attached to the measuring
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section 302 of the drill collar and the landing sub section
328 is threadedly attached to the pony section 325. The
interior surface of the landing sub section 328 has a
"muleshoe" sleeve 344 which detachably supports an orienting
sleeve 342 of the lower end of the sonde 310 so that the
sonde is longitudinally oriented. A muleshoe pin 346 of the
landing sub section fits into the orienting sleeve 342 of the
lower end of the sonde 310 to rotationally orient the sonde.
Since the sonde 310 is detachably supported by the landing
sub arrangement but is not affixed to the drill collar 300,
the sonde may be retrieved from the drill collar by lifting
it upward in the well bore using a wire line connection to
the attachment structure 335 shown in Fig. 3. The attachment
structure may be a spear point formed at the upper end of the
sonde 310 as shown in Fig. 8. The spear point end 537 of the
upper sonde portion shown in Fig. 8 is positioned in the
center of the drill collar 310 as determined by the sonde
support structure in the landing sub section 328. In
retrieving the sonde 310 from the drill collar 300, a
standard overshot device connected to a wire line is latched
onto the spear point and the sonde is raised in the well bore
1. It is to be understood that structures other than a
muleshoe and a spear point and overshoot device may be
employed to support the sonde and to retrieve the sonde from
the well bore.
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The drill collar 300 is made of a non-conductive material
that is transparent to the interrogating signals from the
transmitting antennae 315-1 and 315-4 and is also transparent
to the responsive return signals from the earth formation
surrounding the drill collar. The electronic equipment
associated with the transmitting and receiving antennae 315-1
through 315-4 is located within the sonde housing and is
directly coupled to the antennae. Accordingly, there is no
restriction to drilling fluid flow from the electromechanical
connections between the sonde and the adjacent drill collar.
Since the entire propagating wave resistivity system is
located in the sonde and the sonde is not affixed to the
drill collar, the sonde may be readily retrieved from the
well bore as disclosed with respect to Fig. 8.
Fig. 4 depicts another embodiment of the invention in which
the sonde is supported in a predetermined position within a
drill collar structure. Shown in Fig. 4 is a drill collar
400 having a metal drill collar measurement section 402, a
wash pipe 405 and a sonde 410. The sonde has recesses 412-l,
412-2, 412-3 and 412-4 into which loop antennae 415-1, 415-2,
415-3 and 415-4 are wound, a lower end orienting sleeve 442
and an upper end attachment section 435. The loop antennae
415-1, 415-2, 415-3 and 415-4 is positioned in the drill
collar structure measurement section 402 and has slotted
portions 421-1, 421-2, 421-3 and 421-4 aligned with the loop
antennae. A landing sub section 428 of the drill collar
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includes a structure for detachably supporting the lower end
of the sonde and a pony section 425 connects the measuring
section 402 and the landing sub section 428.
A housing 430 of the sonde 410 has a smooth exterior surface.
The circumferential recesses in the housing 430 are spaced
along the length of the sonde. A first transmitting loop
antenna 415-1 is wound in the recess 412-1 and a second
transmitting loop antenna 415-4 is wound in the recess 412-4.
A first receiving antenna 415-2 is wound in the recess 412-2
and a second receiving antenna 415-3 is wound in the recess
412-3. After winding of the antennae therein, the recesses
are filled with a non-conductive material such as Viton
rubber and the surfaces of the recesses are made
substantially flush with the smooth surface of the housing
430.
The lower end of the sonde is supported on a landing sub
section 428 which is arranged to position the sonde
longitudinally and rotationally. The supporting structure is
substantially the same as that described with respect to Fig.
7 in which an orienting sleeve 442 is detachably supported by
a muleshoe 444. The muleshoe 444 orients the sonde 410
longitudinally and a muleshoe pin 446 orients the sonde
rotationally. The top end of the sonde includes an
attachment unit 435 such as a spear point adapted to be
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connected to a wire from the derrick 3 for retrieving the
sonde from the well bore.
When the sonde 410 is in a supported position on the landing
sub section 428, the sonde is positioned so that the
transmitting loop antennae 415-1 and 415-4 are aligned with
slots of slotted portions 421-1 and 421-4, respectively, of
the measuring portion 402 of the drill collar structure and
the receiving loop antennae 415-2 and 415-3 are aligned with
slots of slotted portions 421-2 and 421-3, respectively, of
the measuring portion 402 of the drill collar structure.
Drilling fluid flowing around the sonde 410 in the drill
collar 400 is contained within a wash pipe 405 in the slotted
drill collar measuring section 402. The wash pipe 405 is
proximate the interior surface of the drill collar section
402. The exterior surface of the wash pipe 405 is sealed to
the interior surface of the drill collar at a point above the
uppermost set of slots by an O ring 439 or other sealing
device and at a point below the lowermost set of slots by an
O ring 440. It is to be understood that other sealing
arrangements may be used in Fig. 4. Each of the slots of
the slotted portions 421-1 through 421-4 is preferably filled
with a non-conductive material that is transparent to the
interrogating signals from the transmitting loop antennae
415-1 and 415-4 and to the return signals from the
surrounding earth formation. The sealing of the exterior of
the wash pipe to the interior of the drill collar prevents
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the highly pressurized drilling fluid flowing inside the wash
pipe 405 from exiting through the slotted portions of the
sonde.
Fig. 5 illustrates the slot structures in the drill collar
section 402 of Fig. 4. Referring to Fig. 5, in which a set
of slots of slotted portion 421-1 in the drill collar
structure section 402 is located at one end to be aligned
with the transmitting loop antenna 415-1 when lower end of
the sonde 410 is supported in the landing sub section 428 of
the drill collar structure. A set of slots of the slotted
portion 421-4 is located at the lower end of the drill collar
section 402 for alignment with the transmitting loop antenna
415-4. A set of slots of the slotted portion 421-2 in the
drill collar is located on the sonde 410 to be aligned with
the receiving antenna 415-2 and a set of slots of the slotted
portion 412-3 is located on the sonde for alignment with the
receiving antenna 415-3.
The drill collar structure section 402 of Fig. 4 may also be
constructed as shown in Fig. 9 to have fiber-glass epoxy
composite sections aligned with the transmitting antennae and
the receiving antennae wound on the sonde 410. Referring to
Fig. 9, the propagating resistivity measuring section 402 of
the drill collar structure 400 has generally cylindrical
metal sections 930-1, 930-2, 930-3, 930-4 and 930-5. A
generally cylindrical fiber-glass epoxy composite section
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923-1 is secured between the metal sections 930-1 and 930-2
and is aligned with the transmitting antenna 415-1 for
passage of interrogating signals therethrough to the
surrounding earth formation. Similarly, a cylindrical fiber-
s glass composite section 923-4 between the metal sections 930-
4 and 930-5 is aligned with the transmitting antenna 415-4
for passage of interrogating signals therethrough. A
cylindrical fiber-glass composite section 923-2 between metal
sections 930-2 and 930-3 aligned with the receiving antenna
415-2 allows passage of return signals from the earth
formation to the antenna 415-2. In like manner, a
cylindrical fiber-glass section 923-3 between metal sections
930-3 and 930-4 is aligned with receiving antenna 415-3 to
permit passage of return signals from the earth formation to
the antenna 415-3. The alternating metal and fiber-glass
composite sections of the same diameter of Fig. 9 may be
threadedly connected to form the drill collar structure
section 402. It is to be understood that other arrangements
of interrogating and return signal transparent materials may
be used to assure passage of these signals between the sonde
410 and the surrounding earth formation. For example, a
single fiber-glass composite section may be aligned with both
receiving antennae 414-2 and 415-3.
The electronic equipment associated with the transmitting and
receiving loop antennae 415-1 through 415-4 is located in the
sonde housing 430 and is connected directly to the antennae.
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As discussed with respect to the embodiment shown in Fig. 3,
the sonde 410 is readily detachable from the drilling collar
400. Accordingly, a wire from the derrick 3 may be lowered
into the well bore and connected to the sonde attachment unit
435 so that the sonde may be retrieved from its supported
position in the drill collar 400. As shown in Fig. 8 and
disclosed with respect to the embodiment of Fig. 3, the sonde
410 may have a spear point end 537 for connection with a wire
line so that the sonde may be lifted off the support
structure in the landing sub section 428 and retrieved from
the well bore.
Fig. 6 shows electronic equipment located inside the housing
330 of the sonde 310 of Fig. 3 or inside the housing 430 of
the sonde 410 of Fig. 4. The electronic equipment includes a
control 601, an upper transmitter 610 and a lower transmitter
615, an upper receiver 620 and a lower receiver 625, a
propagating wave resistivity signal processor 630 and a data
transmitting device 635 such as a mud pulser, an EM telemetry
device or other arrangement well known in the art. The
control 601 controls the operations of the transmitters, the
receivers and the signal processor. The upper transmitter
610 provides an interrogating signal in the range of 400 KHz
to 2 MHz and controls the timing of the operation of
transmitting antenna 315-1 or 415-1. The lower transmitter
615 provides an interrogating signal in the range of 400 KHz
to 2 MHz and controls the timing of the operation of the
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transmitting antenna 315-4 or 415-4. Upper and lower
receivers 620 and 625 receive signals from the earth
formation returned to antennae 315-2 and 315-3 or 415-2 and
415-3 in response to the interrogating signals. Signal
processor 630 processes the return signals from the receivers
to generate amplitude ratio and phase difference signals
corresponding to the propagating wave resistivity. The coded
signals corresponding to the propagating wave resistivity are
transmitted to the surface by the data transmitting device
635 so that coded signals are picked up at the top of the
well bore.
In operation, upper and lower transmitters 610 and 615
sequentially send interrogating signals to antennae 315-1 and
315-4 or 415-1 and 415-4. Receivers 620 and 625 operate to
receive return signals in response to each of the sequential
interrogating signals. The outputs of receivers 620 and 625
are processed in propagating wave resistivity signal
processor 630 as is well known in the art to determine
propagating wave resistivity of the earth formation
surrounding the drill collar responsive to the return
signals. The output of the propagating wave resistivity
processor 630 is applied to the data transmitter 635 and is
communicated to the top of the well bore.
While the invention has been described by way of particular
illustrative embodiments, it is to be understood that the
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invention is not limited to the above-described embodiments
but that various changes and modifications may be made by
those of ordinary skill in the art without departing from the
scope and spirit of the invention. Accordingly, the
foregoing embodiments should not be construed as limiting the
scope of the invention which is encompassed instead by the
following claims.
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