Note: Descriptions are shown in the official language in which they were submitted.
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DOWNHOLE SIGNAL COMMUNICATION AND MEASUREMENT THROUGH A
METAL TUBULAR
This is a divisional of Canadian Patent
Application Serial No. 2,346,546 filed May 7, 2001.
1. BACKGROUND OF THE INVENTION
1.1 Field of the Invention
This invention relates generally to investigation
of subsurface earth formations, systems and methods for
transmitting and/or receiving a signal through a metallic
tubular, and, more particularly, to a device for receiving a
run-in tool.
1.2 Description of Related Art
Resistivity and gamma-ray logging are the two
formation evaluation measurements run most often in well
logging. Such measurements are used to locate and evaluate
the properties of potential hydrocarbon bearing zones in
subsurface formations. In many wells, they are the only two
measurements performed, particularly in low cost wells and
in surface and intermediate sections of more expensive
wells.
These logging techniques are realized in different
ways. A well tool, comprising a number of transmitting and
detecting devices for measuring various parameters, can be
lowered into a borehole on the end of a cable, or wireline.
The cable, which is attached to some sort of mobile
processing center at the surface, is the means by which
parameter data is sent up to the surface. With this type of
wireline logging, it becomes possible to measure borehole
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and formation parameters as a function of depth, i.e., while
the tool is being pulled uphole.
Some wells may not be logged because wireline
logging is too expensive, when rig time is included in the
total cost. Conditioning the well for wireline logging,
rigging up the wireline tools, and the time to run the
wireline tools in and out require rig time. Horizontal or
deviated wells also present increased cost and difficulty
for the use of wireline tools.
An alternative to wireline logging techniques is
the collection of data on downhole conditions during the
drilling process. By collecting and processing such
information during the drilling process, the driller can
modify or correct key steps of the operation to optimize
performance. Schemes for collecting data of downhole
conditions and movement of the drilling assembly during the
drilling operation are known as Measurement While Drilling
(MWD) techniques. Similar techniques focusing more on
measurement of formation parameters than on movement of the
drilling assembly are know as Logging While Drilling (LWD).
As with wireline logging, the use of LWD and MWD tools may
not be justified due to the cost of the equipment and the
associated service since the tools are in the hole for the
entire time it takes to drill the section.
Logging While Tripping (LWT) presents a cost-
effective alternative to LWD and MWD techniques. In LWT, a
small diameter "run-in" tool is sent downhole through the
drill pipe, at the end of a bit run, just before the drill
pipe is pulled. The run-in tool is used to measure the
downhole physical quantities as the drill string is
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extracted or tripped out of the hole. Measured data is
recorded into tool memory versus time during the trip out.
At the surface, a second set of equipment records bit depth
versus time for the trip out, and this allows the
measurements to be placed on depth.
U.S. Pat. No. 5,589,825 describes a LWT technique
incorporating a logging tool adapted for movement through a
drillstring and into a drilling sub. The `825 patent
describes a sub incorporating a window mechanism to permit
signal communication between a housed logging tool and the
wellbore. The window mechanism is operable between an open
and closed position. A disadvantage of the proposed
apparatus is that the open-window mechanism directly exposes
the logging tool to the rugose and abrasive borehole
environment, where formation cuttings are likely to damage
the logging tool and jam the window mechanism. Downhole
conditions progressively become more hostile at greater
depths. At depths of 5,000 to 8,000 meters, bottom hole
temperatures of 260 C and pressures of 170 Mpa are often
encountered. This exacerbates degradation of external or
exposed logging tool components. Thus, an open-window
structure is impractical for use in a downhole environment.
UK Patent Application GB 2337546A describes a
composite structure incorporated within a drill collar to
permit the passage of electromagnetic energy for use in
measurements during the drilling operation. The `546
application describes a drill collar having voids or
recesses with embedded composite covers. A disadvantage of
the apparatus proposed by the 1546 application is the use of
composite materials as an integral part of the drill collar.
Fatigue loading (i.e., the bending and rotating of the drill
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pipe) becomes an issue in drilling operations. When the
drill pipe is subjected to bending or torsion, the shapes of
the voids or recesses change, resulting in stress failure
and poor sealing. The differences in material properties
between the metal and composite covers are difficult to
manage properly where the composite and metal are required
to act mechanically as one piece, such as described in the
1546 application. Thus, the increased propensity for
failure under the extreme stresses and loading encountered
during drilling operations makes implementation of the
described structure impractical.
U.S. Pats. Nos. 5,988,300 and 5,944,124 describe a
composite tube structure.adapted for use in a drillstring.
The 1300 and '124 patents describe a piecewise structure
including a composite tube assembled with end-fittings and
an outer wrapping connecting the tube with the end-fittings.
In addition to high manufacturing costs, another
disadvantage of this structure is that the multi-part
assembly is more prone to failure under the extreme stresses
encountered during drilling operations.
U.S. Pat. No. 5,939,885 describes a well logging
apparatus including a mounting member equipped with coil
antennas and housed within a slotted drill collar. However,
the apparatus is not designed for LWT operations. U.S.
Pats. Nos. 4,041,780 and 4,047,430 describe a logging
instrument that is pumped down into a drill pipe for
obtaining logging samples. However, the system proposed by
the 1780 and 1430 patents requires the withdrawal of the
entire drill string (for removal of the drill bit) before
any logging may be commenced. Thus, implementation of the
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}
described system is impractical and not cost effective for
many operations.
U.S. Pat. No. 5,560,437 describes a telemetry
method and apparatus for obtaining measurements of downhole
parameters. The 1437 patent describes a logging probe that
is ejected into the drill string. The logging probe
includes a sensor at one end that is positioned through an
aperture in a special drill bit at the end of the drill
string. As such, the sensor has direct access to the drill
bore. A disadvantage of the apparatus proposed by the 1437
patent is the sensor's direct exposure to the damaging
conditions encountered downhole. The use of a small probe
protruding through a small aperture is also impractical for
resistivity logging.
U.S. Pat. No. 4,914,637 describes a downhole tool
adapted for deployment from the surface through the drill
string to a desired location in the conduit. A modulator on
the tool transmits gathered signal data to the surface.
U.S. Pat. No. 5,050,675 (assigned to the present assignee)
describes a perforating apparatus incorporating an inductive
coupler configuration for signal communication between the
surface and the downhole tool. U.S. Pat. No. 5,455,573
describes an inductive coupling device for coaxially
arranged downhole tools. Downhole techniques have also been
proposed utilizing slotted tubes. U.S. Pat. No. 5,372,208
describes the use of slotted tube sections as part of a
drill string to sample ground water during drilling.
However, none of these proposed systems relate to through-
tubing measurement or signal transfer.
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It is desirable to obtain a simplified and
reliable LWT system and methods for locating and evaluating
the properties of potential hydrocarbon bearing zones in
subsurface formations. Thus, there remains a need for an
improved LWT system and methods for transmitting and/or
receiving a signal through an earth formation. There also
remains a need for a technique to measure the
characteristics of a subsurface formation with the use of a
versatile apparatus capable of providing LWT, LWD or
wireline measurements. Yet another remaining need is that
of effective techniques for sealing apertures on the surface
of tubular members used for downhole operations.
2. S'[JM+tARY OF THE INVENTION
Systems and methods are provided utilizing an
improved downhole tubular having an elongated body with
tubular walls and a central bore adapted to receive a run-in
tool. The tubular has at least one slot formed in its wall
to provide for continuous passage of a signal (e.g.,
electromagnetic energy) that is generated or received
respectively by a source or sensor mounted on the run-in
tool. The tubular also includes a pressure barrier within
the central bore to maintain hydraulic integrity between the
interior and exterior of the tubular at the slotted station.
The tubular and run-in tool combinations provide systems and
methods for downhole signal communication and formation
measurement through a metallic tubular. A technique for
measuring a formation characteristic utilizing a run-in tool
adapted with a multi-mode end segment is provided.
Techniques are also provided for effectively sealing
openings on the surface of tubular members.
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The invention provides a downhole tubular
comprising an elongated body with tubular walls and a
central bore, the body including at least one slot formed
therein such that the slot fully penetrates the tubular
wall; and means to provide a pressure barrier between the
interior and exterior of the tubular wall, the means located
within the central bore in alignment with the at least one
slot.
According to another aspect the invention provides
a downhole tubular, comprising: an elongated body with a
tubular wall and a central bore, the body including at least
one opening formed therein such that the opening penetrates
the tubular wall to provide a continuous channel for the
passage of a signal; the body adapted to connect with
another tubular to form a drill string segment; the body
adapted to house a run-in tool within the central bore when
said tool is disposed therein; and means to provide a
pressure barrier between the interior and exterior of the
tubular wall, the means located within the central bore in
alignment with the at least one opening.
The invention also provides a system for receiving
a run-in tool. The system comprising a sub havinci an
elongated body with tubular walls and a central bore, the
sub being adapted to form a portion of a length of drill
string. The sub including at least one station having at
least one slot formed therein such that the slot fully
penetrates the tubular wall to provide a continuous channel
for the passage of a signal. The run-in tool beirig adapted
for transit through the drill string and into the central
bore of the sub. The system also including means for
receiving the run-in tool within the sub.
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The invention also provides a system for receiving
a run-in tool. The system comprising a sub having an
elongated body with tubular walls and a central bore, the
sub being adapted to form a portion of a length of drill
string. The sub including at least one inductive coupling
means disposed thereon. The sub including at least one
signal source or sensor disposed thereon. The run-in tool
including at least one inductive coupling means disposed
thereon and being adapted for transit through the drill
string and into the central bore of the sub. The system
also including means for receiving the run-in tool within
the sub.
The invention also provides a method for
transmitting and/or receiving a signal through an earth
formation. The method comprising drilling a borehole
through the earth formation with a drill string, the drill
string including a sub having an elongated body with tubular
walls and including at least one station having at least one
slot formed therein, each at least one slot fully
penetrating the tubular wall to provide a continuous channel
for the passage of a signal; engaging a run-in tool within
the sub, the run-in tool being adapted with signal
transmitting means and/or signal receiving means; locating
the run-in tool within the sub such that at least one signal
transmitting or receiving means is aligned with at least one
slotted station on the sub; and transmitting or receiving a
signal through the formation, respectively via the
transmitting or receiving means.
The invention also provides a method for measuring
a characteristic of an earth formation surrounding a
borehole. The method comprising adapting a downhole tool
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with at least one signal transmitting means and at least one
signal receiving means; adapting the downhole tool with end
means capable of accepting a fishing head or a cable
connection; and with the fishing head on the tool, engaging
the tool within a drill string to measure the formation
characteristic utilizing the transmitting and receiving
means; or with the cable connection on the tool, connecting
a cable to the tool and suspending the tool within the
borehole to measure the formation characteristic utilizing
the transmitting and receiving means.
The invention also provides a method for sealing
an opening on the surface of a tubular, the tubular having
an elongated body with tubular walls and a central bore,
comprising: a) placing an insert within the opening, the
insert being tormed in the shape of the opening; b) applying
a bonding material to the insert and/or opening to bond the
insert within the opening; and c) placing a cylindrical
sleeve within the central bore or around the outer surface
of the tubular in alignment with the opening.
The invention also provides a method for sealing a
fully penetrating opening on the surface of a tubular, the
tubular having an elongated body with tubular walls and a
central bore, comprising: a) placing an insert within the
opening, the insert being formed in the shape of the
opening, and b) placing retainer means within the tubular to
support the insert against the opening, wherein the retainer
means comprises a sleeve positioned coaxially within the
central bore of the tubular.
The invention also provides a method for sealing a
fully penetrating opening on a tubular, the tubular having
an elongated body with tubular walls and a central bore,
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comprising: a) configuring an insert with a geometry that
restrains the insert within the opening when pressure is
applied against the insert from within the tubular bore;
b) fitting the insert within the opening; and c) placing
.5 retainer means within the tubular to retain the insert
within the opening wherein the retainer means comprises a
sleeve.
The invention also provides a method for sealing a
fully penetrating opening on a tubular, the tubular having
an elongated body with tubular walls and a central bore,
comprising the steps of: a) using an insert configured to
accept an o-ring; b) placing the insert within the opening
with an o-ring disposed between said insert and a surface of
said opening; and c) placing retainer means within the
tubular to retain the insert within the opening, wherein the
retainer means comprises a sleeve.
3. BRIEF DESCRIPTION OF THE DRAWINGS
Other aspects and advantages of the invention will
become apparent upon reading the following detailed
description and upon reference to the drawings in which:
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Figure 1 is a schematic diagram of a run-in tool
in accord with the invention.
Figure 2a is a cross-sectional view of a run-in
tool showing an antenna with associated wiring and passages
in accord with the invention.
Figure 2b is a schematic diagram of a shield
structure surrounding an antenna on the run-in tool in
accord with the invention.
Figure 3 is a schematic diagram of a tubular
member with slotted stations in accord with the invention.
Figures 4a and 4b are schematic diagrams of a run-
in tool engaged within a tubular member in accord with the
invention.
Figure 5 graphically illustrates the relationship
between the slot dimensions of a tubular segment of the
invention and the attenuation of passing electromagnetic
energy.
Figure 6 is a schematic diagram of a run-in tool
with a centralizer configuration in accord with the
invention.
Figure 7a is a cross-sectional view of a tubular
member with a pressure barrier configuration in accord with
the invention.
Figure 7b is a cross-sectional view of a three-
slotted tubular member of Figure 7a along line A-A.
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Figure 8a is a cross-sectional view of a tubular
member with another pressure barrier configuration in accord
with the invention.
Figure 8b is a cross-sectional view of a three-
slotted tubular member of Figure 8a along line B-]3.
Figure 9a is a cross-sectional view of a run-in
tool positioned in alignment with a pressure barrier
configuration in accord with the invention.
Figure 9b is a top view of the run-in tool and
pressure barrier configuration of Figure 9a.
Figure 10 is a cross-sectional view of a pressure
barrier and tubular member configuration in accord with the
invention.
Figure 11 is a cross-sectional view of a slotted
tubular member with an insert, seal, and retaining sleeve in
accord with the invention.
Figures 12a and 12b are cross-sectional views and
cut-away perspectives of a slotted tubular station with a
tapered slot and a corresponding tapered insert in accord
with the invention.
Figure 13a is a schematic diagram of a run-in tool
and antenna eccentered within a tubular member in accord
with the invention.
Figures 13b and 13c are schematic diagrams of a
run-in tool and antenna surrounded by a focusing shield and
respectively showing the shield's effect on the magnetic and
electric fields in accord with the invention.
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Figure 14 is a top view of a shielding structure
formed within the bore of the tubular member in accord with
the invention.
Figure 15 is a schematic diagram of a shielding
structure formed by a cavity within the run-in tool in
accord with the invention.
Figure 16 is a schematic diagram of a run-in tool
including a modulator engaged within a tubular mernber in
accord with the invention.
Figure 17 is a schematic diagram of the run-in
tool configuration of Figure 16 as used for real-time
wireless communication with a remote downhole tool in accord
with invention.
Figure 18 is a schematic diagram of a run-in tool
configuration for porosity measurements utilizing magnetic
nuclear resonance techniques in accord with the invention.
Figures 19a and 19b are schematic diagrams of run-
in tool antenna configurations within tubular members in
accord with the invention.
Figure 20 shows schematic diagrams of a tubular
member and run-in tool configuration with inductive couplers
in accord with the invention.
Figure 21 shows a top view and a schematic diagram
and of an eccentered run-in tool and tubular member with
inductive couplers in accord with the invention.
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Figures 22a and 22b are schematic diagrams of an
inductive coupler configuration within a run-in tool and
tubular member in accord with the invention.
Figure 23 is a cross-sectional view of an
inductive coupler and shield configuration mounted within a
tubular member in accord with the invention.
Figure 24 is a schematic diagram of a simplified
inductive coupler circuit in accord with the invention.
Figure 25 is a flow chart illustrating a method
for transmitting and/or receiving a signal through an earth
formation in accord with the invention.
Figure 26 is a flow chart illustrating a method
for measuring a characteristic of an earth formation
surrounding a borehole in accord with the invention.
Figure 27 is a flow chart illustrating a method
for sealing an opening on the surface of a tubular member in
accord with the invention.
Figure 28 is a flow chart illustrating a method
for sealing a fully penetrating opening on a surface of a
tubular member in accord with the invention.
4. DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS
In the interest of clarity, not all features of
actual implementation are described in this specification.
It will be appreciated that although the development of any
such actual implementation might be complex and time-
consuming, it would nevertheless be a routine undertaking
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for those of ordinary skill in the art having the benefit of
this disclosure.
The apparatus of the invention consists of two
main assets, a run-in tool (RIT) and a drill collar.
Henceforth, the drill collar will be referred to as the sub.
4.1 RIT
Figure 1 shows an embodiment of the RIT 10 of the
invention. The RIT 10 is an elongated, small-diameter,
metal mandrel that may contain one or more antennas 12,
sources, sensors [sensor/detector are interchangeable terms
as used herein], magnets, a gamma-ray detector/generator
assembly, neutron-generating/detecting assembly, various
electronics, batteries, a downhole processor, a clock, a
read-out port, and recording memory (not shown).
The RIT 10 does not have the mechanical
requirements of a drill collar. Thus, its mechanical
constraints are greatly reduced. The RIT 10 has a landing
mechanism (stinger) 14 on the bottom end and a fishing head
16 on the top. The fishing head 16 allows for the RIT 10 to
be captured and retrieved from within a sub with the use of
a conventional extraction tool such as the one described in
U.S. Pat. No. 5,278,550 (assigned to the present assignee).
An advantage of the fishable RIT 10 assembly is a reduction
of Lost-In-Hole costs.
As shown in Figure 2a, each antenna 12 on the RIT
10 consists of multi-turnwire loops encased in fiberglass-
epoxy 18 mounted in a groove in the RIT 10 pressure housing
and sealed with rubber over-molding 20. A feed-through 22
provides a passage for the antenna 12 wiring, leading to an
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inner bore 24 within the RIT 10. Each antenna 12 may be
activated to receive or transmit an electromagnetic (EM)
signal as known in the art.
The antennas 12 radiate an azimuthal electric
field. Each antenna 12 is preferably surrounded by a
stainless-steel shield 26 (similar to those described in
U.S. Pat. No. 4,949,045, assigned to the present assignee)
that has one or more axial slots 28 arrayed around the
shield 26 circumference. Figure 2b shows the axial slots 28
distributed around the circumference of the shield 26. The
shields 26 are short-circuited at the axial ends into the
metal mandrel body of the RIT 10. These shields 26 permit
transverse electric (TE) radiation to propagate through
while blocking transverse magnetic (TM) and transverse
electromagnetic (TEM) radiation. The shields 26 also
protect the antennas 12 from external damage. The RIT 10
electronics and sensor architecture resembles that described
in U.S. Pat. No. 4,899,112 (assigned to the present
assignee).
4.2 Sub
Figure 3 shows an embodiment of a sub 30 of the
invention. The sub 30 has an elongated body with tubular
walls and a central bore 32. The sub 30 contains neither
electronics nor sensors and is fully metallic, preferably
formed from stainless steel. It is part of the normal
bottom hole assembly (BHA), and it is in the hole with the
drill string for the duration of the bit run. The sub 30
has normal threaded oilfield connections (pin and box) at
each end (not shown).
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The sub 30 includes one or more stations 36 with
one or more axial slots 38 placed along the tubular wall.
Each elongated axial slot 38 fully penetrates the tubular
wall of the sub 30 and is preferably formed with fully
rounded ends. Stress modeling has shown that rather long
slots 38 may be formed in the sub 30 walls while still
maintaining the structural integrity of the sub 30. Stress
relief grooves 40 may be added to the OD of the sub 30, in
regions away from the slot(s) 38, to minimize the bending
moment on the slot(s) 38.
Each slot 38 provides a continuous channel for
electromagnetic energy to pass through the sub 30. The
slots 38 block TM radiation but allow the passage of TE
radiation, albeit with some attenuation. The degree of
attenuation of TE fields by the sub 30 depends on factors
such as frequency, the number of slots, slot width, slot
length, collar OD and ID, and the location and dimensions of
the RIT 10 antenna. For example, Figure 5 shows the sub 10
attenuation measured at 400 kHz with a 25-turn 1.75-inch
diameter coil centered in 3.55-inch ID, 6.75-inch OD subs 30
with one or two slots 38 of different lengths and widths.
As evident from Figure 5, adding more slots 38 and making
the slots longer or wider decreases the attenuation.
However, with only one or two 0.5-inch wide 6-8 inch long
slots 38, the sub 30 attenuation is already -15 dB, which is
sufficiently low for many applications.
In operation, the RIT 10 is pumped down and/or
lowered through the drillstring on cable at the end of the
bit run and engaged inside the sub 30. The RIT 1.0 is
received by a landing "shoe" 42 within the central bore 32
of the sub 30, as shown in Figure 4a. Figure 4b, shows how
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the RIT 10 is located in the sub 30 so that each antenna 12,
source, or sensor is aligned with a slot 38 in the sub 30.
The landing shoe 42 preferably also has a latching action to
prevent any axial motion of the RIT 10 once it is engaged
inside the sub 30.
Turning to Figure 6, an embodiment of the
invention includes a centralizer 44, which serves to keep
the RIT 10 centered and stable within the sub 30, lowering
shock levels and reducing the effects of tool motion on the
measurement. One or more centralizers 44 may be mounted
within the central bore 32 to constrain the RIT 10 and keep
it from hitting the ID of the sub 30. One or more spring-
blades 46 may also be mounted to extend from the centralizer
44 to provide positioning stability for the RIT 10. The
spring-blades 46 are compressed against the RIT 10 when it
is engaged within the sub 30. Bolts 48 with 0-ring seals 50
may be used to hold the centralizer(s) 44 in the sub 30
while preserving the pressure barrier between the ID and the
OD of the sub 30.
Alternatively, the centralizer 44 may be mounted
on the RIT 10 rather than on the sub 30 (See Figure 16). In
this case, the centralizer 44 may be configured to remain in
a retracted mode during the trip down, and to open when the
RIT 10 lands in the sub 30. It will be understood that
other centralizer 44 configurations may be implemented with
the invention as known in the art.
The RIT 10 and sub 30 have EM properties similar
to a coaxial cable, with the RIT 10 acting as the inner
conductor, and the sub 30 acting as the outer conductor of a
coaxial cable. If the drilling mud is conductivE:, then the
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"coax" is lossy. If the drilling mud is oil based, the
"coax" will have little attenuation. Parasitic antenna 12
coupling may take place inside of the sub 30 between
receiver-receiver or transmitter-receiver. As described
above, the shields 26 surrounding the antennas 12 are
grounded to the mandrel of the RIT 10 to minimize capacitive
and TEM coupling between them. Electrically balancing the
antennas 12 also provides for TEM coupling rejection. The
centralizers 44 may also be used as a means of contact to
provide radio-frequency (rf) short-circuits between the RIT
10 and the sub 30 to prevent parasitic coupling. For
example, small wheels with sharp teeth may be mounted on the
centralizers 44 to ensure a hard short between the RIT 10
and the sub 30 (not shown).
4.3 Pressure Barrier
Since each slot 38 fully penetrates the wall of
the sub 30, an insulating pressure barrier is used to
maintain the differential pressure between the inside and
the outside of the sub 30 and to maintain hydraulic
integrity. There are a variety of methods for establishing
a pressure barrier between the sub 30 ID and OD at the
slotted station 36.
Turning to Figure 7a, an embodiment of a sub 30
with a pressure barrier of the invention is shown. A
cylindrical sleeve 52 is positioned within the central bore
32 of the sub 30 in alignment with the slot(s) 38. The
sleeve 52 is formed of a material that provides transparency
to EM energy. Useable materials include the class of
polyetherketones described in U.S. Pat. No. 4,320,224, or
other suitable resins. Victrex USA, Inc. of West: Chester,
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PA manufactures one type called PEEK. Another usable
compound is known as PEK. Cytec Fiberite, Greene Tweed, and
BASF market other suitable thermoplastic resin materials.
Another useable material is Tetragonal Phase Zirconia
ceramic (TZP), manufactured by Coors Ceramics, of Golden,
Colorado. It will be appreciated by those skilled in the
art that these and other materials may be combined to form a
useable sleeve 52.
PEK and PEEK can withstand substantial pressure
loading and have been used for harsh downhole conditions.
Ceramics can withstand substantially higher loads, but they
are not particularly tolerant to shock. Compositions of
wound PEEK or PEK and glass, carbon, or KEVLAR may also be
used to enhance the strength of the sleeve 52.
A retainer 54 and spacer 56 are included within
the central bore 32 to support the sleeve 52 and provide for
displacement and alignment with the slots 38. The sleeve 52
is positioned between the retainer 54 and spacer 56, which
are formed as hollow cylinders to fit coaxially within the
central bore 32. Both are preferably made of stainless
steel. The retainer 54 is connected to the sleeve 52 at one
end, with the sleeve 52 fitting coaxially inside the
retainer 54. As the differential pressure increases within
the ID of the sub 30 during operation, the sleeve 52 takes
the loading, isolating the sub 30 from the pressure in the
slotted region. Hydraulic integrity is maintained at the
junction between the sleeve 52 and retainer 54 by an 0-ring
seal 53. A fitted "key" 55 is used to engage the sleeve 52
to the retainer 54, preventing one from rotating relative to
the other (See Figure 7a blow-up). An index pin 57 is
fitted through the sub 30 and engaged to the free end of the
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retainer 54 to prevent the retainer from rotating within the
bore 32 of the sub 30. 0-rings 59 are also placed within
grooves on the OD of the retainer 54 to provide a hydraulic
seal between the retainer 54 and the sub 30.
In operation, the internal sleeve 52 will likely
undergo axial thermal expansion due to high downhole
temperatures. Thus, it is preferable for the sleeve 52 to
be capable of axial movement as it undergoes these changes
in order to prevent buckling. The spacer 56 consists of an
inner cylinder 60 within an outer cylinder 62. A spring 64
at one end of the OD of the inner cylinder 60 provides an
axial force against the outer cylinder 62 (analogous to an
automotive shock absorber). The outer cylinder 62 is
connected to the sleeve 52 using the key 55 and 0-ring seal
53 at the junction as described above and shown in the blow-
up in Figure 7a. The spring-loaded spacer 56 accounts for
differential thermal expansion of the components. The sub
30 embodiment of Figure 7a is shown connected to other
tubular members by threaded oilfield connections 70.
For purposes of illustration, a sub 30 with only
one slot 38 is shown in Figure 7a. Other embodiments may
include several sleeves 52 interconnected in the described
manner to provide individual pressure barriers over multiple
slotted stations 36 (not shown). With this configuration,
only two 0-ring 53 seals to the ID of the sub 30 are used
over the entire slotted array section. This minimizes the
risk involved with dragging the 0-rings 53 over the slots 38
during assembly or repair. Figure 7b shows a cross-section
of the sub 30 (along line A-A of Figure 7a) with a three-
slot 38 configuration.
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Figure 8a shows another embodiment of a sub 30
with a pressure barrier of the invention. In this
embodiment, the spring-loaded spacer 56 maintains the outer
cylinder 62 abutted against the sleeve 52 and 0-rings 68 are
placed within grooves on the OD of the sleeve 52, preferably
at both ends of the slot 38. The retainer 54 rests at one
end against a shoulder or tab 58 formed on the wall of the
central bore 32. Figure 8b shows a cross-section of the sub
30 (along line B-B of Figure 8a) with a three-slot 38
configuration.
In another embodiment of a pressure barrier of the
invention, a sleeve 52 made out of PEEK or PEK, or glass,
carbon, or KEVLAR filled versions of these materials, may be
bonded to a metal insert (not shown), where the insert
contains 0-rings to seal against the sub 30 as described
above. The metal insert could be mounted within the sub 30
as described above or with the use of fastener means or
locking pins (not shown). The sleeve material may also be
molded or wrapped onto the supporting insert. The fibers in
the wrapped material can also be aligned to provide
additional strength.
Figure 9a shows another embodiment of a pressure
barrier of the invention. In this embodiment, the
cylindrical sleeve 52 is held in alignment with the slot(s)
38 by a metal retainer 72. The retainer 72 may be formed as
a single piece with an appropriate slot 74 cut into it for
signal passage as shown, or as independent pieces supporting
the sleeve 52 at the top and bottom (not shown). The
retainer 72 may be constrained from axial movement or
rotation within the sub 30 by any of several means known in
the art, including an index-pin mechanism or a keyed-jam-nut
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type arrangement (not shown). The slot 38 may also be
filled with a protective insert as will be further described
below. In operation, a RIT 10 is positioned within the sub
30 such that the antenna 12 is aligned with the slot(s) 38.
As shown in Figure 9b, the retainer 72 is formed
such that it extends into and reduces the ID of the sub 30
to constrain the RIT 10. Mudflow occurs through several
channels or openings 76 in the retainer 72 and through the
annulus 78 between the RIT 10 and the retainer 72. The
retainer 72 in effect acts as a centralizer to stabilize the
RIT 10 and to keep it from hitting the ID of the sub 30,
lowering shock levels and increasing reliability.
Figure 10 shows another embodiment of a pressure
barrier of the invention. A sub 30 may be formed with a
shop joint 80 so that the sleeve 52 can be inserted within
the central bore 32. The sleeve 52 is formed as described
above and provides a hydraulic seal using 0-rings 82 within
grooves at both ends on the OD of the sleeve 52. The sleeve
52 is restrained from axial movement within the central bore
32 by a lip 84 formed on one end of the two-piece sub 30 and
by the end of the matching sub 30 joint. Since the sleeve
52 sits flush within a recess 86 in the ID of the sub 30,
this configuration offers unrestricted passage to a large
diameter RIT 10. This configuration also provides easy
access to the sleeve 52 and slot(s) 38 for maintenance and
inspection.
Turning to Figure 11, another embodiment of a
pressure barrier of the invention is shown. The slot 38 in
the sub 30 is three-stepped, preferably with fully rounded
ends. One of the steps provides a bearing shoulder 90 for
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an insert 92, and the other two surfaces form the geometry
for an 0-ring groove 94 in conjunction with the insert 92.
A modified 0-ring seal consists of an 0-ring 96 stretched
around the insert 92 at the appropriate step, with metal
elements 98 placed on opposite sides of the 0-ring 96. The
metal elements 98 are preferably in the form of closed
loops.
The sleeve 52 may be fitted within the sub 30 with
one or more 0-rings (not shown) to improve hydraulic
integrity as described above. As shown in Figure 11, the
sleeve 52 may also have a slot 100 penetrating its wall to
provide an unobstructed channel for any incoming or outgoing
signal. The sleeve 52 may have a matching slot 100 for
every slot 38 in the sub 30.
The insert 92 and sleeve 52 are preferably made of
the dielectric materials described above to permit the
passage of EM energy. However, if the sleeve 52 is
configured with a slot 100, the sleeve 52 may be formed from
any suitable material.
If the sleeve 52 is configured with a slot 100,
the internal pressure of the sub 30 may push the insert 92
outward. The bearing shoulder 52 takes this load. As the
internal pressure increases, the 0-ring 96 pushes the metal
elements 98 against an extrusion gap, which effectively
closes off the gap. As a result, there is no room for
extrusion of the 0-ring 96. Since the metal is much harder
than the 0-ring material, it does not extrude at all. The
modified geometry therefore creates a scenario where a soft
element (the 0-ring) provides the seal and a hard element
(the metal loop) prevents extrusion, which is the ideal seal
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situation. In the event of pressure reversal, the sleeve 52
captures the insert 92 in the slot 38, preventing the insert
92 from being dislodged.
Other pressure barrier configurations may be
implemented with the invention. One approach is the use of
several individual sleeves 52 connected together by other
retaining structures and restrained by a pressure-
differential seal or a jam-nut arrangement (not shown).
Another approach is the use of a long sleeve 52 to span
multiple slotted stations 38 (not shown). Still another
approach is the use of a sleeve 52 affixed to the OD of the
sub 30 over the slotted region, or a combination of an
interior and exterior sleeve 52 (not shown).
4.4 Slot Inserts
While the slotted stations of the invention are
effective with fully open and unblocked slots 38, the
operational life of the assembly may be extended by
preventing debris and fluids from entering and eroding the
slots 38 and the insulating sleeve 52. The slots 38 could
be filled with rubber, an epoxy-fiberglass compound, or
another suitable filler material to keep fluids and debris
out while permitting signal passage.
An embodiment of a sub 30 with a tapered slot 38
is shown in Figure 12a. The slot 38 is tapered such that
the outer opening wi is narrower than the inner opening W2,
as shown in Figure 12b. A tapered wedge 88 of insulating
material (e.g., fiberglass epoxy) is inserted within the
tapered slot 38. The wedge 88 may be bonded into the sub 30
with rubber. The rubber layer surrounds the wedge 88 and
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bonds it into the sub 30. An annulus of rubber may also be
molded on the interior and/or exterior surface of the sub 30
to seal the wedge 88 within the slot 38.
4.5 Focusing Shield Structures
Measurements of the attenuation of the TE
radiation from a simple coil-wound antenna 12 through a
single slot 38 of reasonable dimensions show that the TE
field is notably attenuated. This attenuation can be
reduced, however, by using shielding around the antenna 12
to focus the EM fields into the slot 38.
Turning to Figure 13a, an antenna 12 consisting of
25 turns of wire on a 1.75-inch diameter bobbin was mounted
on a 1-inch diameter metal RIT 10 and positioned fully
eccentered radially inside the bore of a 3.55-inch ID, 6.75-
inch OD sub 30 against the slot 38 and centered vertically
on the slot 38. The measured attenuation of the TE field
between 25 kHz - 2 MHz was a nearly constant 16.5 dB.
Turning to Figure 13b, the same measurement was
performed with the antenna 12 inside a thin shield 102
formed of a metallic tube with a 0.5-inch wide, 6-inch long
slot 104 aligned with the slot 38 in the sub 30 (not shown).
The antenna 12 was fully surrounded by the shield 102 except
for the open slot 104 and placed inside the sub 30.
The attenuation with this assembly in the same sub
30 was 11.8 dB, a reduction of the attenuation of nearly 5
dB. Figures 13b and 13c respectively show how the shield
102 affects the magnetic and electric fields. The
attenuation due to this shield 102 alone is minimal.
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Figure 14 shows another embodiment of a shielding
structure of the invention. In this embodiment, the central
bore 32 of the sub 30 is configured with a bracket structure
106 that serves as a focusing shield by surrounding the
antenna 12 when the RIT 10 is engaged within the sub 30.
Figure 15 shows another embodiment of a shielding
structure of the invention. The mandrel of the RIT 10 has a
machined pocket or cavity 108 in its body. A coil antenna
12 wound on a bobbin 110 made of dielectric material is
mounted within the cavity 108. A ferrite rod may replace
the dielectric bobbin 110. With this configuration, the
body of the RIT 10 itself serves as a focusing shield. The
hydraulic integrity of the RIT 10 is maintained by potting
the antenna 12 with fiberglass-epoxy, rubber, or another
suitable substance. The attenuation of a coil antenna 12
having 200 turns on a 0.875-inch diameter bobbin was
measured for this assembly mounted the same way as described
above in the same sub 30. The measured attenuation was only
-7 dB. It will be appreciated by those skilled in the art
that other types of sources/sensors may be housed within the
cavity 108 of the RIT 10.
4.6 RIT / Sub Configurations
Figure 16 shows another embodiment of the
invention. A sub 30 of the invention is connected to
another tubular 111 forming a section of a drillstring. The
RIT 10 includes an antenna 12, a stinger 14 at the lower
end, and a fishing head 16 at the top end. The stinger 14
is received by the landing shoe 42 on the sub 30, which
serves to align the antenna 12 with the slotted station 36.
As above, the RIT 10 of this embodiment includes various
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electronics, batteries, a downhole processor, a clock, a
read-out port, memory, etc. (not shown) in a pressure
housing. The RIT 10 may also incorporate various types of
sources/sensors as known in the art.
4.6.1 RIT with Modulator
The RIT 10 of Figure 16 is also equipped with a
modulator 116 for signal communication with the surface. As
known in the art, a useable modulator 116 consists of a
rotary valve that operates on a continuous pressure wave in
the mud column. By changing the phase of the signal
(frequency modulation) and detecting these changes, a signal
can be transmitted between the surface and the RIT 10. With
this configuration, one can send the RIT 10 through the
drillstring to obtain measurement data (e.g., resistivity or
gamma-ray counts) of formation characteristics and to
communicate such data to the surface in real-time.
Alternatively, all or some of the measurement data may be
stored downhole in the RIT 10 memory for later retrieval.
The modulator 116 may also be used to verify that the RIT 10
is correctly positioned in the sub 30, and that measurements
are functioning properly. It will be appreciated by those
skilled in the art that a modulator 116 assembly may be
incorporated with all of the RIT/sub implementations of the
invention.
Figure 17 shows another embodiment of the
invention. The subs 30 and RITs 10 of the invention may be
used to communicate data and/or instructions between the
surface and a remote tool 112 located along the drill
string. For purposes of illustration, the tool 112 is shown
with a bit box 113 at the bottom portion of a drive shaft
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114. The drive shaft 114 is connected to a drilling motor
115 via an internal transmission assembly (not shown) and a
bearing section 117. The tool 112 also has an antenna 12
mounted on the bit box 113. The motor 115 rotates the shaft
114, which rotates the bit box 113, thus rotating the
antenna 12 during drilling.
With the configuration of Figure 17, the RIT 10
may be engaged within the sub 30 at the surface or sent
through the drill string when the sub 30 is at a desired
downhole position. Once engaged, a wireless communication
link may be established between the antenna 12 on the RIT 10
and the antenna 12 on the tool 112, with the signal passing
through the slotted station 36. In this manner, real-time
wireless communication between the surface and the downhole
tool 112 may be established. It will be appreciated by
those skilled in the art that other types of sensors and/or
signal transmitting/receiving devices may be mounted on
various types of remote tools 112 for communication with
corresponding devices mounted on the RIT 10.
4.6.2 Nuclear Magnetic Resonance Sensing
It is known that when an asseaLbly of magnetic
moments such as those of hydrogen nuclei are exposed to a
static magnetic field they tend to align along the direction
of the magnetic field, resulting in bulk magnetization. By
measuring the amount of time for the hydrogen nuclei to
realign their spin axes, a rapid nondestructive
determination of porosity, movable fluid, and permeability
of earth formations is obtained. See A. Timur, Pulsed
Nuclear Magnetic Resonance Studies of Porosity, Movable
Fluid, and Permeability of Sandstones, JOURNAL OF PETROLEUM
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TECHNOLOGY, June 1969, p. 775. U.S. Pat. No. 4,717,876
describes a nuclear magnetic resonance well logging
instrument employing these techniques.
A determination of formation porosity from
magnetic resonance may be obtained with a non-magnetic sub
30 of the invention as shown in Figure 18. The sub 30 can
be formed of the typical high-strength non-magnetic steel
used in the industry. The RIT 10 contains the electronics,
batteries, CPU, memory, etc., as described above. Opposing
permanent magnets 118 contained in the RIT 10 provide the
magnetic field. A rf coil 120 is mounted between the
magnets 118 for generating a magnetic field in the same
region to excite nuclei of the formation vicinity. The
design of the rf coil 120 is similar to the antennas 12
described above in being a multi-turn loop antenna with a
central tube for through wires and mechanical strength. The
permanent magnets 118 and rf coil 120 are preferably housed
in a non-magnetic section of the sub 30 that has axial slots
38 with a pressure barrier (not shown) of the invention.
With a non-magnetic sub 30, the static magnetic
fields B0 from the permanent magnets 118 penetrate into the
surrounding formation to excite the nuclei within the
surrounding formation. The coil 120 in the RIT 10 provides
a rf magnetic field 31, which is perpendicular to B0 outside
of the sub 30. The rf coil 120 is positioned in alignment
with the axial slot(s) 38 in the sub 30.
A magnetic resonance measurement while tripping
may be more complicated in comparison to propagation
resistivity measurements due to various factors, including:
an inherently lower signal-to-noise ratio, permanent magnet
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form factors, rf coil efficiency, high Q antenna tuning,
high power demands, and a slower logging speed.
4.6.3 Gamma-Ray Measurement
It is known that gamma ray transport measurements
through a formation can be used to determine its
characteristics such as density. The interaction of gamma
rays by Compton scattering is dependent only upon the number
density of the scattering electrons. This in turn is
directly proportional to the bulk density of the formation.
Conventional logging tools have been implemented with
detectors and a source of gamma rays whose primary mode of
interaction is Compton scattering. See U.S. Pat. No.
5,250,806, assigned to the present assignee. Gamma ray
formation measurements have also been implemented in LWT
technology. See Logging while tripping cuts time to run
gamma ray, OIL & GAS JOURNAL, June 1996, pp. 65-66. The
present invention may be used to obtain gamma-ray
measurements as known in the art, providing advantages over
known implementations.
The subs 30 of the invention provide the
structural integrity required for drilling operations while
also providing a low-density channel for the passage of
gamma rays. Turning to Figure 4b, this configuration is used
to illustrate a gamma-ray implementation of the invention.
In this implementation, a RIT 10 is equipped with a gamma-
ray source and gamma-ray detectors (not shown) of the type
known in the art and described in the 1806 patent. The
antennas 12 of Figure 4b would be replaced with a gamma-ray
source and gamma-ray detectors (not shown).
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Two gamma-ray detectors are typically used in this
type of measurement. The gamma-ray detectors are placed on
the RIT 10 at appropriate spacings from the source as known
in the art. The slotted stations 36 are also appropriately
placed to match the source and detector positions of the RIT
10. Calibration of the measurement may be required to
account for the rays transmitted along the inside of the sub
30. The gamma-ray detectors may also be appropriately
housed within the RIT 10 to shield them from direct
radiation from the source as known in the art.
Turning to Figure 14, this configuration is used
to illustrate another gamma-ray implementation of the
invention. With the RIT 10 equipped with the described
gamma-ray assembly and eccentered toward the slots 38, this
configuration will capture the scattered gamma rays more
efficiently and provide less transmission loss.
4.6.4 Resistivity Measurement
The invention may be used to measure formation
resistivity using electromagnetic propagation techniques as
known in the art, including those described in U.S. Pats.
Nos. 5,594,343 and 4,899,112 (both assigned to the present
assignee). Figures 19a and 19b show twc> RIT 10 / sub 30
configurations of the invention. A pair of centrally
located receiver antennas Rx are used to measure the phase
shift and attenuation of EM waves. Look-up tables may be
used to determine phase shift resistivity and attenuation
resistivity. Transmitter antennas Tx are placed above and
below the receiver antennas Rx, either in the configuration
shown in Figure 19a, which has two symmetrically placed
transmitter antennas Tx, or in the configuration shown in
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Figure 19b, which has several transmitter antennas Tx above
and below the receiver antennas Rx. The architecture of
Figure 19a can be used to make a borehole compensated phase-
shift and attenuation resistivity measurement, while the
multiple Tx spacings of Figure 19b can measure borehole
compensated phase-shift and attenuation with multiple depths
of investigation. It will be appreciated by those skilled
in the art that other source/sensor configurations and
algorithms or models may be used to make formation
measurements and determine the formation characteristics.
4.7 inductively-Coupled RIT / Sub
Turning to Figure 20, other embodiments of a sub
30 and RIT 10 of the invention are shown. The sub 30
contains one or more integral antennas 12 mounted on the OD
of the elongated body for transmitting and/or receiving
electromagnetic energy. The antennas 12 are embedded in
fiberglass epoxy, with a rubber over-molding as described
above. The sub 30 also has one or more inductive couplers
122 distributed along its tubular wall.
The RIT 10 has a small-diameter pressure housing
such as the one described above, which contains electronics,
batteries, downhole processor, clocks, read-out port,
recording memory, etc., and one or more inductive couplers
122 mounted along its body.
As shown in Figure 21, the RIT 10 is eccentered
inside the sub 30 so that the inductive coupler(s) 122 in
the RIT 10 and the inductive coupler(s) 122 in the sub 30
are in close proximity. The couplers 120 consist of
windings formed around a ferrite body as known in the art.
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Feed-throughs 124 connect the antenna 12 wires to the
inductive coupler 122 located in a small pocket 126 in the
sub 30. A metal shield 128 with vertical slots covers each
antenna 12 to protect it from mechanical damage and provide
the desired electromagnetic filtering properties as
previously described. Correctly positioning the RIT 10
inside the sub 30 improves the efficiency of the inductive
coupling. Positioning is accomplished using a stinger and
landing shoe (See Figure 4a) to eccenter the RIT 10 within
the sub 30. It will be appreciated by those skilled in the
art that other eccentering systems may be used to implement
the invention.
As shown in Figure 22a, the inductive couplers 122
have "U" shaped cores made of ferrite. The ferrite core and
windings are potted in fiberglass-epoxy, over molded with
rubber 131, and mounted within a coupler package 130 formed
of metal. The coupler package 130 may be formed of
stainless steel or a non-magnetic metal. Standard 0-ring
seals 132 placed around the inductive coupler package 130
provide a hydraulic seal. The inductive: couplers 122 in the
RIT 10 may also be potted in fiberglass-epoxy and over
molded with rubber 131. A thin cylindrical shield made of
PEEK or PEK may also be placed on the OL) of the sub 38 to
protect and secure the coupler package 130 (not shown).
In operation, there will be a gap between the
inductive couplers 122 in the RIT 10 and the sub 30, so the
coupling will not be 100% efficient. To improve the
coupling efficiency, and to lessen the effects of mis-
alignment of the pole faces, it is desirable for the pole
faces to have as large a surface area as possible.
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Figure 22b shows a 3.75-inch long by 1-inch wide
slot 38 in the sub 30. The pole face for this inductive
coupler 122 is 1.1-inches long by 0.75-inch wide, giving an
overlap area of 0.825 square inches. This configuration
maintains a high coupling efficiency and reduces the effects
due to the following: movement of the RIT 10 during drilling
or tripping, variations in the gap between the inductive
couplers 122, and variations in the angle of the RIT 10 with
respect to the sub 30. Another advantage of a long slot 38
design is that it provides space for the pressure feed-
throughs 124 in the inductive coupler package 130.
Antenna tuning elements (capacitors) may also be
placed in this package 130 if needed. It will be
appreciated by those skilled in the art that other aperture
configurations may be formed in the walls of the sub 30 to
achieve the desired inductive coupling, such as the circular
holes shown in Figure 20.
Since the pressure inside the sub 30 will be 1-2
Kpsi higher than outside the sub 30 in most cases, the
inductive coupler package 130 should be mechanically held in
place. Turning to Figure 23, the antenria shield 128 can be
used to retain the inductive coupler package 130 in place.
The shield 128 having slots over the antenna 12 as described
above, but solid elsewhere. The solid portion retains the
inductive coupler package 130 and takes the load from the
differential pressure drop. Tabs may also be placed on the
outside of the inductive coupler package 130 to keep it from
moving inward (not shown). The shield 128 may also be
threaded on its ID, with the threads engaging matching
"dogs" on the sub 30 (not shown).
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Figure 24 shows a simple circuit model for an
embodiment of the inductive coupler and transmitter antenna
of the invention. On the RIT 10 side, the current is I1, and
the voltage is V,. On the sub 30 side, the current is 12 and
the voltage is V2. The mutual inductance is M, and the self-
inductance of each half is L. This inductive coupler is
symmetric with the same number of turns on each half. With
the direction of 12 defined in Figure 24, the voltage and
currents are related by V1=j wLI1 +j wMI2 and V2=j o)MI l+j wLIZ .
The antenna impedance is primarily inductive (LA) with a
small resistive part (RA), ZA=RA+jcoLA. Typically the
inductive impedance is about 100 0, while the resistive
impedance is about 10 0. A tuning capacitor (C) may be used
to cancel the antenna inductance, giving a RIT side
impedance Z2= RA+jwLA-j /(OC - RA. The ratio of the current
delivered to the antenna to the current driving the
inductive coupler is I2/Il =-jmM/ (jmL + RA +jwLA - j/wC) .
The inductive coupler has many turns and a high permeability
core, so L>> LA and c)L > RA. To good approximation,
12/Il -M/L (the sign being relative to the direction of
current flow in Figure 24).
4.8 Implementations of the Invention
As described above, the RIT 10 may be equipped
with internal data storage means such as conventional memory
and other forms of the kind well known in the art or
subsequently developed. These storage means may be used to
communicate data and/or instructions between the surface and
the downhole RIT 10. Received signal data may be stored
downhole within the storage means and subsequently retrieved
when the RIT 10 is returned to the surface. As known in the
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art, a computer (or other recording means) at the surface
keeps track of time versus downhole position of the sub so
that stored data can be correlated with a downhole location.
Alternatively, the signal data and/or instructions may be
communicated in real-time between the surface and the RIT 10
by LWD/MWD telemetry as known in the art.
Figure 25 illustrates a flow diagram of a method
300 for transmitting and/or receiving a signal through an
earth formation in accord with the invention. The method
comprises drilling a borehole through the earth formation
with a drill string, the drill string iricluding a sub having
an elongated body with tubular walls and including at least
one station having at least one slot formed therein, each at
least one slot fully penetrating the tubular wall to provide
a continuous channel for the passage of electromagnetic
energy 305; engaging a run-in tool within the sub, the run-
in tool being adapted with signal transmitting means and/or
signal receiving means 310; locating the run-in tool within
the sub such that at least one signal transmitting or
receiving means is aligned with at least one slotted station
on the sub 315; and transmitting or receiving a signal
through the formation, respectively via the transmitting or
receiving means 320.
Figure 26 illustrates a flow diagram of a method
400 for measuring a characteristic of an earth formation
surrounding a borehole in accord with the invention. The
' method comprises adapting a downhole tool with at least one
signal transmitting means and at least one signal receiving
means 405; adapting the downhole tool with end means capable
of accepting a fishing head or a cable connection 410; and
with the fishing head on the tool, engaging the tool within
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a drill string to measure the formation characteristic,
utilizing the transmitting and receiving means, as the drill
string traverses the borehole; with the cable connection on
the tool, connecting a cable to the tool and suspending the
tool within the borehole to measure the formation
characteristic utilizing the transmitting and receiving
means 420.
The method 400 of Figure 26 may be implemented
with the run-in tools 10 and subs 30 of the invention. The
run-in tool may be configured with an end segment or cap
(not shown) adapted to receive the previously described
fishing head or a cable connection. With the fishing head
connected to the run-in tool, the tool may be used in accord
with the disclosed implementations. With the cable
connection, the run-in tool may be used as a memory-mode
wireline tool.
It will be understood that the following methods
for sealing an opening or slot on the surface of a tubular
are based on the disclosed pressure barriers and slot
inserts of the invention.
Figure 27 illustrates a flow diagram of a method
500 for sealing an opening on the surface of a tubular,
wherein the tubular has an elongated body with tubular walls
and a central bore. The method comprises placing an insert
within the opening, the insert being formed in the shape of
the opening 505; and applying a bonding material to the
insert and/or opening to bond the insert within the opening
510.
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Figure 28 illustrates a flow diagram of a method
600 for sealing a fully penetrating opening on the surface
of a tubular having an elongated body with tubular walls and
a central bore. The method comprises placing an insert
within the opening, the insert being formed in the shape of
the opening 605, and placing retainer means within the
tubular to support the insert against the opening 610.
While the methods and apparatus of this invention
have been described as specific embodiments, it will be
apparent to those skilled in the art that variations may be
applied to the structures and in the steps or in the
sequence of steps of the methods described herein without
departing from the concept and scope of the invention. For
example, the invention may be implemented in a configuration
wherein one RIT/sub unit is equipped to measure a
combination of formation characteristics, including
resistivity, porosity and density. All such similar
variations apparent to those skilled in the art are deemed
to be within this concept and scope of the invention as
defined by the appended claims.
38
