Note: Descriptions are shown in the official language in which they were submitted.
CA 02450391 2006-06-09
79350-95
LOGGING WHILE TRIPPING WITH A MODIFIED TUBULAR
BACKGROUND OF THE INVENTION
Field of the Invention
This invention relates generally to investigation of subsurface earth
formations, and, more
particularly, to techniques for transmitting and/or receiving a signal through
a metallic tubular
using a run-in tool adapted for disposal within and extraction from the
metallic tubular.
Embodiments of the invention are particularly suited for iinplementation with
retrievable and re-
seatable MWD apparatus.
Description of Related Art
Resistivity and gamma-ray logging are the two fonnation 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 fonnations. In many wells,
they are the only
two measurements perfoi-med, particularly in low cost wells and in surface and
intermediate
sections of nzore expensive wells.
These logging teclmiques 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 wliich parameter data
is sent up to the
surface. With this type of wireline logging, it becomes possible to measure
borehole and
fonnation parazneters as a function of depth, i.e., while the tool is being
pulled uphole.
Sonie 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 otirt require rig time.
Horizontal or deviated
wells also present increased cost and difficulty for the use of wireline
tools.
1
CA 02450391 2003-11-24
24.0806-CIP2
Other wells present a challenge for wireline conveyance. Wells with extremely
rugose,
washed out, collapsed, or deviated boreholes can hinder or prevent the well
tool from traveling
through the borehole. These tough logging conditions (TLC) are typically
handled by conveying
the tool into the borehole on drilipipe. The instruments are mounted on
drilipipe and tripped
down into the open hole section. The wireline is protected inside the
drillpipe in the open hole
section of the well but lies between the drillpipe and the casing running to
the surface, where it is
prone to damage. Another disadvantage of this technique is that wireline power
and
communication are required while pushing the tool into the open hole section
in order to avoid
breaking the tool if an obstruction is encountered. Because of the danger of
tool and wireline
damage, logging is slow.
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 do'vnhole 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 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 drilistring and into a drilling sub. The '825 patent
describes a sub
incorporating a window mechanism to permit signal communication between a
housed logging
2
CA 02450391 2003-11-24
24.0806-CIP2
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 these situations.
UK Patent Application GB 2337546A describes a composite structure incorporated
within a drill collar to permit the passage of electromagnetic energy (EM) 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 '546 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 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 '546
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. Pat. Nos. 5,988,300 and 5,944,124 describe a composite tube structure
adapted for
use in a drillstring. The '300 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. Pat. Nos. 4,041,780 and 4,047,430
describe a logging
3
CA 02450391 2003-11-24
24.0806-CIP2
instrument that is pumped down into a drill pipe for obtaining logging
samples. However, the
system proposed by the '780 and '430 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 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 '437 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 sucli, the
sensor has direct access to
the drill bore. Disadvantages of the apparatus proposed by the '437 patent are
the sensor's direct
exposure to the damaging conditions encountered downhole and the requirement
of an
unobstructed path in the drillstring for the probe to travel, which is
incompatible with drilistrings
containing a mud-pulse telemetry tool or a mud motor. 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.
U.S. Pat. No.
6,288,548 describes a while-drilling logging technique using a measurement
sonde disposed
within a drill collar implemented with slots.
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
techniques to
measure the characteristics of a subsurface formation in combination with
retrievable and re-
seatable apparatus used to make measurements from within the drill collar.
4
CA 02450391 2006-06-09
79350-95
SiJbMARY OF THE INVENTION
The invention provides a system for receiving a
run-in tool, comprising: a sub having an elongated body with
tubular walls and an inner bore, the sub adapted to form a
portion of a length of drill string; the sub including at
least one slot formed therein such that the slot fully
penetrates the tubular wall to provide a channel for the
passage of a signal; the sub including means to provide a
pressure barrier between the interior and exterior of the
tubular wall at the at least one slot, said barrier means
located within the sub bore; a retrievable measurement-
while-drilling apparatus having an upper engagement means,
the retrievable apparatus being positioned in the drill
string below the sub; a run-in tool having upper and lower
ends and adapted for transit through the drill string and
into the sub bore; and the run-in tool having means to
engage with other apparatus at said upper and lower ends;
wherein said lower engagement means on said run-in tool are
adapted for selective release from said retrieval apparatus,
said lower engagement means comprising a selectively
releasable connection engageable with the retrievable
apparatus to allow retrieval of the run-in tool together
with the retrievable apparatus or selective release of the
run-in tool from the retrievable apparatus.
The invention provides a method for disposing a
run-in tool within a sub in a length of drill string,
comprising: (a) adapting a run-in tool having upper and
lower ends for transit through the drill string and into a
sub having an elongated body with tubular walls and an inner
bore forming a part of said drill string, the sub including
5
CA 02450391 2006-06-09
79350-95
at least one slot fully penetrating its wall to provide a
channel for the passage of a signal and barrier means within
its bore to provide a pressure barrier between the interior
and exterior of the wall at the at least one slot, said run-
in tool adapted with selectively releasable means to engage
with other apparatus at said upper and lower ends, and
determining the distance between at least one slot on said
sub and a measurement point on said apparatus disposed
within the bore of said drill string; (b) disposing the
drill string with the sub within a subsurface formation,
said drill string having an apparatus disposed within its
inner bore and positioned near said sub; and (c) disposing
the run-in tool within the drill string for engagement with
said apparatus disposed within the inner bore of said drill
string. ,
The invention provides a method for disposing a
run-in tool within a sub in a length of drill string. The
method comprises: adapting a run-in tool having upper and
lower ends for transit through the drill string and into a
sub having an elongated body with tubular walls and an inner
bore forming a part of the drill string, the sub including
at least one slot fully penetrating its wall to provide a
channel for the passage of a signal and barrier means within
its bore to provide a pressure barrier between the interior
and exterior of the wall at the at least one slot, the run-
in tool having a signal source or sensor disposed thereon
and adapted with selectively releasable
5a
CA 02450391 2003-11-24
24.0806-CIP2
means to engage with other apparatus at the upper and lower ends; adapting the
run-in tool or an
apparatus disposed within the bore of the drill string such that the signal
source or sensor on the
run-in tool is positioned near the at least one slot when the tool is disposed
within the sub and
engaged with the apparatus; disposing the drill string, along with the sub and
the apparatus
disposed within its inner bore, within a subsurface formation; and disposing
the run-in tool
within the drill string for engagement with the apparatus.
The invention provides a system for receiving a run-in tool. The system
comprises a first
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; an elongated run-in tool having
upper and lower ends
and adapted for transit through the drill string and into the sub bore; the
run-in tool adapted with
connecting means at the upper end to connect with other apparatus for removal
of said tool from
the first sub bore; a segment of the run-in tool having an oversized diameter
compared to other
segments of said tool; the first sub adapted with means to catch and hold the
run-in tool by the
oversized segment such that a predetermined length of the run-in tool extends
into the sub bore
and the run-in tool is restricted from further axial displacement into the
bore; and the catch and
hold means adapted to permit the passage of fluid through the bore while
holding the run-in tool
by the oversized segment.
The invention also provides a method for disposing a run-in tool within a sub
in a length
of drill string. The method comprises adapting an elongated run-in tool such
that a segment of
the tool includes an oversized diameter compared to other segments of the
tool, the tool having
upper and lower ends and adapted for transit through the drill string;
disposing the run-in tool
through the drill string for engagement in the bore of a first sub forming
part of the drill string;
catching the run-in tool by the oversized segment with catch and hold means
disposed in the first
sub, the catch and hold means permitting a predetermined length of the tool to
extend into the
sub bore; and with the catch and hold means, restricting the run-in tool from
further axial
displacement into the bore such that a source or sensor on the tool is
positioned near a slot in the
wall of the drill string when the tool is engaged within the catch and hold
means on the first sub.
6
CA 02450391 2003-11-24
24.0806-CIP2
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:
FIG. 1 is a schematic diagram of a run-in tool in accord with the invention.
FIG. 2a is a cross-sectional view of a run-in tool showing an antenna with
associated
wiring and passages in accord with the invention.
FIG. 2b is a schematic diagram of a shield structure surrounding an antenna on
the run-in
tool in accord with the invention.
FIG. 3 is a schematic diagram of a tubular member with slotted stations in
accord with the
invention.
FIGS. 4a and 4b are schematic diagrams of a run-in tool engaged within a
tubular member
in accord with the invention.
FIG. 5 graphically illustrates the relationship between the slot dimensions of
a tubular
segment of the invention and the attenuation of passing electromagnetic
energy.
FIG. 6 is a schematic diagram of a run-in tool with a centralizer
configuration in accord
with the invention.
FIG. 7a is a cross-sectional view of a tubular member with a pressure barrier
configuration in accord with the invention.
FIG. 7b is a cross-sectional view of a three-slotted tubular member of FIG. 7a
along line
A-A.
FIG. 8a is a cross-sectional view of a tubular member with another pressure
barrier
configuration in accord with the invention.
FIG. 8b is a cross-sectional view of a three-slotted tubular member of FIG. 8a
along line
B-B.
FIG. 9a is a cross-sectional view of a run-in tool positioned in alignment
with a pressure
barrier configuration in accord with the invention.
FIG. 9b is a top view of the run-in tool and pressure barrier configuration of
FIG. 9a.
FIG. 10 is a cross-sectional view of a pressure barrier and tubular member
configuration
in accord with the invention.
7
CA 02450391 2003-11-24
24.0806-CIP2
FIG. 11 is a cross-sectional view of a slotted tubular member with an insert,
seal, and
retaining sleeve in accord with the invention.
FIGS. 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.
FIG. 13a is a schematic diagram of a run-in tool and antenna eccentered within
a tubular
member in accord with the invention.
FIGS. 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.
FIG. 14 is a top view of a shielding structure formed within the bore of the
tubular
member in accord with the invention.
FIG. 15 is a schematic diagram of a shielding structure forined by a cavity
within the run-
in tool in accord with the invention.
FIG. 16 is a schematic diagram of a run-in tool including a modulator engaged
within a
tubular member in accord with the invention.
FIG. 17 is a schematic diagram of the run-in tool configuration of FIG. 16 as
used for
real-time wireless communication with a remote downhole tool in accord with
invention.
FIG. 18 is a schematic diagram of a run-in tool configuration for porosity
measurements
utilizing magnetic nuclear resonance techniques in accord with the invention.
FIGS. 19a and 19b are schematic diagrams of run-in tool antenna configurations
within
tubular members in accord with the invention.
FIG. 20 shows schematic diagrams of a tubular member and run-in tool
configuration
with inductive couplers in accord with the invention.
FIG. 21 shows a top view and a schematic diagram of an eccentered run-in tool
and
tubular member with inductive couplers in accord with the invention.
FIGS. 22a and 22b are schematic diagrams of an inductive coupler configuration
within a
run-in tool and tubular member in accord with the invention.
FIG. 23 is a cross-sectional view of an inductive coupler and shield
configuration
mounted within a tubular member in accord with the invention.
8
CA 02450391 2003-11-24
24.0806-CIP2
FIG. 24 is a schematic diagram of a simplified inductive coupler circuit in
accord with the
invention.
FIG. 25 is a flow chart illustrating a method for transmitting and/or
receiving a signal
through an earth formation in accord with the invention.
FIG. 26 is a flow chart illustrating a method for measuring a characteristic
of an earth
formation surrounding a borehole in accord with the invention.
FIG. 27 is a flow chart illustrating a method for sealing an opening on the
surface of a
tubular member in accord with the invention.
FIG. 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.
FIG. 29 shows a run-in tool within a slotted tubular member in combination
with an
independent MWD apparatus housed within a drill collar segment in accord with
the invention.
FIG. 30 shows an expanded view of the junction between the run-in tool and
apparatus of
FIG. 29.
FIG. 31 shows a run-in tool engaged within a tubular member adapted with a
catch-and-
hold centralizer in combination with a slotted tubular forming a drill string
in accord with the
invention.
DETAILED DESCRIPTION
The apparatus of the invention consists of two main assets, a run-in tool
(RIT) and a
tubular sleeve or drill collar. Henceforth, the tubular will be referred to as
a sub.
RIT. FIG. 1 shows an embodiment of the RIT 10 of the invention. The RIT 10 is
an
elongated, small-diameter, metallic support or 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
9
CA 02450391 2003-11-24
24.0806-CIP2
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. The RIT 10
may also be
implemented with one or more articulated or "knuckle" joints as known in the
art (see FIG. 29).
As shown in FIG. 2a, one antenna 12 configuration on the RIT 10 consists of
multi-turn
wire 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 inner bore 24 within the RIT 10. Each antenna 12 may
be activated to
receive or transmit an 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. FIG. 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
metallic 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).
SUB. FIG. 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 preferably fully metallic, preferably formed from stainless
steel. It may form
part of the normal bottom hole assembly (BHA), and it may be placed in the
hole with the drill
string for the duration of the bit run. One embodiment of the sub 30 has
normal threaded oilfield
connections (pin and box) at each end (not shown). The sub 30 may also be
coupled to coiled
tubing or to other tubular seginents for conveyance into the wellbore in TLC
operations.
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.
CA 02450391 2003-11-24
24.0806-CIP2
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 EM 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, FIG. 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
FIG. 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, one embodiment of 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 10 is
received by a landing "shoe" 42 within the central bore 32 of the sub 30, as
shown in FIG. 4a.
FIG. 4b shows how 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 FIG. 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 FIG. 16). In this case, the centralizer 44 may be configured to remain in
a retracted mode
11
CA 02450391 2003-11-24
24.0806-CIP2
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 "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).
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 FIG. 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, 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. U.S. Pat. No.
6,300,762 (assigned to
the present assignee) describes a class of polyaryletherketone-based materials
that may be used to
implement the invention. 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
12
CA 02450391 2003-11-24
24.0806-CIP2
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 FIG. 7a blow-up). An index pin 57 is fitted through the sub
30 and engaged to
the free end of the 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 FIG.
7a. The spring-
loaded spacer 56 accounts for differential thermal expansion of the
components. The sub 30
embodiment of FIG. 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 FIG.
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
13
CA 02450391 2003-11-24
24.0806-CIP2
during assembly or repair. FIG. 7b shows a cross-section of the sub 30 (along
line A-A of FIG.
7a) with a three-slot 38 configuration.
FIG. 8a shows another embodiment of a sub 30 with a pressure barrier of the
invention.
In this embodiment, the spring-loaded spacer 62 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. FIG. 8b shows a cross-section of the sub 30
(along line B-B of
FIG. 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.
FIG. 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 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 FIG. 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.
14
CA 02450391 2003-11-24
24.0806-CIP2
FIG. 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 FIG. 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 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 FIG. 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 90 takes this load. As the
interna.l 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
CA 02450391 2003-11-24
24.0806-CIP2
metal loop) prevents extrusion, which is the ideal seal 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 (discussed below).
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 FIG. 12a. The
slot 38 is
tapered such that the outer opening Wl is narrower than the inner opening W2,
as shown in FIG.
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 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.
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 FIG. 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 FIG. 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
16
CA 02450391 2003-11-24
24.0806-CIP2
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 saine sub 30 was 11.8 dB, a
reduction of the
attenuation of nearly 5 dB. FIGS. 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.
FIG. 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.
FIG. 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.
RIT / Sub Configurations. FIG. 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
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.
RIT with Modulator. The RIT 10 of FIG. 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
17
CA 02450391 2003-11-24
24.0806-CIP2
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
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.
FIG. 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 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 FIG. 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.
Nuclear Magnetic Resonance Sensing. It is known that when an assembly 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
18
CA 02450391 2003-11-24
24.0806-CIP2
Permeability of Sandstones, JOURNAL OF PETROLEUM 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 FIG. 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 Bo from the pennanent
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 BI, which
is perpendicular to
Bo 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 ineasurement 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 form factors, rf coil
efficiency, high Q
antenna tuning, high power demands, and a slower logging speed.
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-
19
CA 02450391 2003-11-24
24.0806-CIP2
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
FIG. 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 '806 patent. The
antennas 12 of
FIG. 4b would be replaced with a gamma-ray source and gamma-ray detectors (not
shown).
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 FIG. 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.
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. Pat. Nos. 5,594,343 and 4,899,112 (both assigned to the present
assignee). FIGS. 19a and
19b show two 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 FIG. 19a, which has two symmetrically placed transmitter antennas Tx,
or in the
configuration shown in FIG. 19b, which has several transmitter antennas Tx
above and below the
receiver antennas Rx. The architecture of FIG. 19a can be used to make a
borehole compensated
phase-shift and attenuation resistivity measurement, while the multiple Tx
spacings of FIG. 19b
can measure borehole compensated phase-shift and attenuation with multiple
depths of
CA 02450391 2003-11-24
24.0806-CIP2
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.
Inductively-Coupled RIT / Sub. Turning to FIG. 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 FIG. 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. 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
FIG. 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 FIG. 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
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 OD of the sub 38 to
protect and secure
the coupler package 130 (not shown).
21
CA 02450391 2003-11-24
24.0806-CIP2
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.
FIG. 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 FIG. 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
FIG. 23, the antenna 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).
FIG. 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 I.
On the sub 30 side, the current is I2 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 1Z defined in FIG. 24, the voltage
and currents are
related by V1 jcoLIi+jwMI2 and V2 jwMIj+jwLI2. The antenna impedance is
primarily inductive
(LA) with a small resistive part (RA), ZA=RA+ja)LA. Typically the inductive
impedance is about
22
CA 02450391 2003-11-24
24.0806-CIP2
100 S2, while the resistive impedance is about 10 Q. A tuning capacitor (C)
may be used to
cancel the antenna inductance, giving a RIT side impedance Z2= RA+j(eLA j/o)C -
RA. The ratio
of the current delivered to the antenna to the current driving the inductive
coupler is IZ/I1 =-
jcoM/(jWL + RA +jcoLA - j/wC). The inductive coupler has many turns and a high
permeability
core, so L>> LA and w L>>> RA. To good approximation, I2/I1= ~-M/L (the sign
being relative
to the direction of current flow in FIG. 24).
Implementations. 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 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
(including EMAG telemetry).
FIG. 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
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 electromagnetic energy 305; engaging a run-in tool
within the sub, the
run-in tool being adapted with sigmal 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.
FIG. 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
23
CA 02450391 2003-11-24
24.0806-CIP2
head or a cable connection 410; 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,
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 FIG. 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.
FIG. 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/oar
opening to bond the
insert within the opening 510.
FIG. 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.
The invention may also be implemented in combination with conventional
retrievable and
re-seatable MWD apparatus known in the art. One such apparatus is known as the
SLIMPULSE
(mark of Schlumberger) tool. These are retrievable MWD tools that are disposed
within the drill
collar and used to make various measurements while drilling. These apparatus
typically include
a fishing head at the upper end for retrieval from the drill collar without
having to pull out the
drill string. By incorporating a sub of the invention into the BHA, an RIT of
the invention can be
24
CA 02450391 2003-11-24
24.0806-CIP2
used in combination with these retrievable apparatus without compromising the
retrievability or
reseatability of such apparatus. FIG. 29 shows such an embodiment of the
invention.
FIG. 29 shows the slotted sub 30 interconnected within and forming part of the
drill string
136. The RIT 10 is shown disposed within the sub. This particular embodiment
of the RIT 10 is
equipped with selectively releasable engagement means at both its upper and
lower ends. A
fishing head 16 protrudes from the upper end. At the lower end, the RIT 10
includes an
"overshot tool" 138, which is used to engage with and connect to a fishing
head as known in the
art. One or more spacers 139 or extensions are also attached to the lower end
of the RIT to adjust
its length as described below. The spacers 139 are simple pieces of pipe of
various lengths with
male thread on one end and female on another as known in the art.
An independent retrievable apparatus 140 is also disposed within a collar 137
in the drill
string and connected to the lower end of the RIT 10. The apparatus 140 may
consist of any
conventional retrievable instrument (as described above) or other types of
downhole apparatus
designed for use within the drill collar as known in the art. The apparatus
140 is equipped with a
stinger at the lower end and mounted within a landing shoe 42 or sleeve
configured in the collar
137 similar to the embodiment shown in FIG. 16. At the upper end, the
apparatus 140 is
equipped with a fishing head 16, which engages with the overshot tool 138 at
the lower end of
the RIT 10. The apparatus 140 may be equipped with a modulator and sources or
sensors to
obtain desired measurements (not shown).
FIG. 30 shows a more detailed view of the embodiment of FIG. 29. The RTT 10 is
shown
equipped with a source or sensor 141 as described herein. The RIT is equipped
with the pressure
barrier means 142 of the invention to provide the desired sealing at the
slot(s) 38. The RIT 10
may also be equipped with one or more clamp-on centralizers 44 or drifts to
position and
maintain the RIT centered within the sub 30 once the RIT is seated in the sub.
The centralizers
44 are preferably positioned on the RIT so that they correspond in axial
location to the
constrictrions in the sub 30 having a slightly larger bore than the
centralizer. Those skilled in the
art will recognize that the centralizer(s) 44 may be affixed or mounted to the
RIT 10 in any
suitable manner.
In operation, the sub 30 is assembled above the collar adapted to house the
apparatus 140.
The apparatus 140 is then inserted into the collar 137 and fixed into its
orientation and landing
CA 02450391 2003-11-24
24.0806-CIP2
shoe 42. Axial alignment of RIT 10 within the sub 30 is ensured by a simple
calculation that
yields the proper distance between the RIT source/sensor 141 and apparatus 140
fishing head 16.
The axial distance between the fishing head 16 and the sub's slot array 38 is
determined prior to
tripping the BHA into the hole. The drill string, with the sub 30 in the BHA,
is then disposed
within the hole for drilling. Alternatively, the apparatus 140 :may also be
pumped down or
shuttled into the drill string on cable means after the drill collar is
disposed into the hole.
The RIT 10 is then adapted for transit through the drill string for engagement
within the
sub 30. The axial spacers 139 are attached to the lower end of the RIT 10 as
needed to make up
the proper amount of axial length to allow the source/sensor 141 to align with
the sub slot(s) 38
(determined from the measurement made during assenlbly of the BHA). An
overshot tool 138 is
placed below the spacer(s) 139. The overshot tool lands and engages with the
fishing head on the
apparatus. The overshot tool 138 may be configured with a sheareable pin
assembly adapted to
shear when a specific stress or tension is applied, such as when an upward
pull or downward
push is applied (not shown). The overshot 138 thus forms a selectively
releasable connection
between the RIT 10 and the apparatus 140. Innicor Subsurface Technologies Inc.
of Canada
manufactures a tool known as the CJC PULLING TOOL that :may be used to
implement the
overshot tool 138 of the invention. Further information regarding Innicor's
tools may be found at
http://www.innicor.com.
Once the desired depth has been reached via drilling, the RIT 10 is then
picked up with
cable means such as a standard wireline or slickline fishing assembly. The
overshot used on the
bottom of the fishing assembly and attached to the RIT upper fishing head 16
may also be
configured with a shearable pin assembly to form a selectively shearable
connection. The fishing
string and RIT are then run into the hole via the slickline or wireline (not
shown). The overshot
138 at the bottom end of the RIT 10 is then seated on the apparatus 140 and
the cable means is
used to shear the pin attaching the fishing string to the RIT - leaving the
RIT attached to the
fishing head of the apparatus. Properly seated, the RIT source/sensor 141 will
align axially with
the sub slot(s) 38 due to the axial spacers 139 between the overshot 138 and
RIT 10.
The cable means is then removed from the hole. The log is made as the BHA (and
RIT/sub system) is tripped out of the hole. The same cable means and fishing
assembly may also
be used to retrieve the RIT 10 and apparatus 140 if the BHA becomes stuck in
the hole. A steady
26
CA 02450391 2003-11-24
24.0806-CIP2
pull instead of a shearing motion will typically remove the apparatus 140 from
its landing shoe
without shearing the shearable pin in the overshot connecting the two devices.
The previously described process for combining the RIT 10 with an MWD
apparatus 140
is but one technique for implementing the invention. It will be appreciated by
those skilled in the
art that other overshot configurations/assemblies may be implemented with the
invention
depending on the conditions and requirements of the operation. Since the tool
string, including
the RIT, being run in the hole has at least two overshots 138 and both have
multiple
configurations, the possibilities are endless. For example, another process of
the invention
entails stopping the drilling operation to drop in the RIT on top of the MWD
apparatus, logging
the zone of interest, retrieving the RIT and continuing to drill with the
apparatus 140 still in the
hole.
Another embodiment of the invention combines the RIT 10 and slotted subs 30
for
implementation with downhole apparatus equipped with nuclear or radiation-
emitting sources,
which require special handling and entail strict environmental considerations.
One such
apparatus is described in U.S. Pat. No. 4,879,463. The '463 patent describes
an MWD apparatus
disposed in a drill collar forming part of a drill string and housing a gamma
ray source. The
source is disposed within the collar on a retrievable carrier so that if the
BHA becomes stuck or
some other failure occurs, the gamma ray source can be fished out and
retrieved from the well.
FIG. 31 shows another embodiment of the invention including such a gamma ray
source 146
disposed within the drill string 136.
The RIT 10 is equipped with a fishing head 16 at the upper end and includes an
oversized
diameter segment 148 in comparison to the rest of the RIT body. The oversized
segment 148 can
be formed on the RIT during manufacture, or a barrel can be mounted on the RIT
using fasteners
or any suitable means as known in the art. A "hanger sub" 150 is connected
into the drill string.
The sub 150 consists of a standard section of drill collar except that it
includes a catch and hold
centralizer 152 mounted within its inner bore. The centralizer 152 is similar
to conventional
centralizers and is large enough to allow an overshot tool 138 to pass through
unobstructed while
restricting passage of the oversized segment 148 on the RIT.
Thus the oversized segment 148 on the RIT provides a "hanging lip" that
engages with
the centralizer 152 to prevent the RIT from traveling deeper into the drill
string. FIG. 32 shows
27
CA 02450391 2003-11-24
24.0806-CIP2
a cross section of the centralizer 152. When the RIT is engaged within the
hanger sub 150, the
oversized segment 148 sits on the centralizer and channels 154 in the
centralizer still allow for
mudflow within the drill string 136.
With this embodiment, the RIT 10 can be landed in a sub above the nuclear or
radiation
emitting source 146 and still provide for retrievability of the source 146. If
retrieval of the source
146 becomes necessary, the RIT is extracted by its fishing head 16 and then
the fishing string is
disposed through the centralizer 152 to retrieve the source from the source
carrier 156. The
embodiment of FIG. 31 shows the RIT 10 extending into a slotted sub 30 of the
invention such
that the sources/sensors 141 are aligned with the sub slots 38 when the
oversized segment 148 is
engaged with the centralizer 152. In this embodiment, an intermediate sub 158
is positioned
between the hanger sub 152 and the slotted sub 30 in the drill string. A
simple calculation is
done to determine the appropriate sub 158 needed to ensure proper alignment of
the
source/sensor with the slots. In some embodiments the slotted sub 30 also
incorporates the
centralizer 152 (not shown). Other embodiments combine the centralizer 152 and
the source
carrier 156 in one slotted sub 30 so that only one additional sub is connected
into the drill string
to implement the invention (not show-n).
For the purposes of this specification it will be clearly understood that the
word
"comprising" means "including but not limited to", and that the word
"comprises" has a
corresponding meaning.
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 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 (e.g., resistivity, porosity and density).
28
