Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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CORE AND DRILL BITS WITH INTEGRATED OPTICAL ANALYZER
BACKGROUND
Formation coring is well known in the oil and gas industry. In brief, a coring
bit at the
end of a drill string cuts a columnar core from. the bottom of the borehole.
The core passes into
an inner barrel as it is cut. The inner barrel can then be lifted to transport
the core to the surface
for laboratory analysis. Characteristics such as formation permeability,
porosity, fluid
saturations, etc., can usually be determined accurately in this way. Such
information is
considered to be essential for many companies involved in the search for
petroleum, gas, and
mineral reserves. Such data may al.so be useful for construction site
evaluation and in quarrying
operations.
Inasmuch as possible, cores are preferably obtained in a continuous fashion to
preserve
the core sam.ples in as pristine a state as possible. Standard lengths for the
inner barrel (and hence
the core sam.ple) are 30 feet (9 meters), 60 feet (18 m.eters), and 90 feet
(27 meters). If anything
goes awry with the coring process, it could be many hours before the problem
is discovered.
Moreover, the failure to detect and correct such problems in a timely fashion
can necessitate days
of additional effort to replace the lost core sample material.
Another issue of concern is that many formations are poorly consolidated or
are subject
to degradation as the core samples are retrieved to the surface. Sandy soils
and gas hydrates are
just two examples of such formations. As a core sample is retrieved through a
borehole, the
sample experiences changes in pressure and temperature which can cause
hydrates to sublimate
and gases to expand. Such phenomena can destroy the fabric of the core sam.ple
before the core
sample reaches the surface, making porosity, permeability, and saturation
measurements
infeasible.
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BRIEF DESCRIPTION OF THE DRAWINGS
The following detailed description should be considered in conjunction with
the
accompanying drawings, in which:
Fig. 1 shows an illustrative drilling system;
Fig. 2 shows an illustrative coring bit cross-section;
Fig. 3 shows a throat of an illustrative coring bit;
Fig. 4A shows the principles of operation of an illustrative optical analyzer;
Fig. 4B shows the principles of operation of an alternative optical analyzer;
Fig. 5 shows the principles of operation of an illustrative MOE-based
detector;
Fig. 6 shows the principles of operation of an optical analyzer with dual
windows;
Fig. 7 shows an illustrative drill bit;
Fig. 8 shows an illustrative drill bit impact arrestor; and
Fig. 9 is a flow diagram for an illustrative coring method.
It is noted that the drawings and detailed description are directed to
specific illustrative
embodiments of the invention. It should be understood, however, that the
illustrated and
described embodiments are not intended to limit the disclosure, but on the
contrary, the intention
is to cover all modifications, equivalents and alternatives falling within the
scope of the
appended claims.
DETAILED DESCRIPTION
Accordingly, disclosed herein are core bits and drill bits having integrated
optical
analyzers. At least some disclosed drill bit embodiments include fixed cutting
teeth -that form a
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borehole through a formation as the bit rotates, and at least one impact
arrestor that rides in
grooves formed by the cutting teeth. An integrated optical analyzer
illuminates the formation
through a window in the impact arrestor and analyzes light reflected from. the
formation. Light
travels between the window and the optical analyzer via a transmission system.
that may employ
one or more optical fibers. The optical analyzer may employ multiple filters
including one or
more multivariate optical elements designed to measure spectral
characteristics of selected fluids
and/or rock types. Position and orientation sensors can be included to enable
the optical
measurements to be presented as an image I.og. At least some coring bit
embodi.m.ents cut a core
sample from the formation and perform optical analysis and imaging of the core
sample's surface
as it is acquired. Axially-spaced windows enable the coring rate to be
accurately measured and
compared to the bit's rate of motion to verify that the coring process is
proceeding satisfactorily.
These and other aspects of the disclosed tools and methods are best understood
in terms
of a suitable usage context. Accordingly, an illustrative drilling system 100
is shown in Fig. 1. A
drilling platform 102 is equipped with a derrick 104 that supports a hoist 106
for raising and
lowering a drill string 108. The hoist 106 suspends a top drive 110 that is
used to rotate the drill
string 108 and to I.ower the drill string 108 through a well head 112.
Sections of the drill string
108 are connected by threaded connectors 107. Connected to the lower end of
the drill string 108
is a drill bit 114. As the drill bit 114 rotates, the drill bit 114 creates a
borehole 120 that passes
through various formations 122. A pump 116 circulates drilling fluid through a
supply pipe 118
to the top drive 110, downhole through th.e interior of the drill string 108,
through orifices in the
drill bit 114, back to the surface via the annulus around the drill string
108, and into a retention
pit 124. The drilling fluid transports cuttings from the borehole into the pit
124 and aids in
maintaining the integrity of the borehole 120.
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The drill bit 114 is just one piece of a bottom-hole assembly that includes
one or more
drill collars (thick-walled steel pipe) to provide weight and rigidity to aid
the drilling process.
Some of these drill collars include togging instruments to gather measurements
of various
drilling paratneters such as position, orientation, weight-on-bit, borehole
diameter, etc. The tool
orientation ma:yr be specified in terms of a tooi face angle (a.k.a.
rotationai or azimuthal
orientation), an inclination angle (the slope), and a compass direction, each
of which can be
derived from measurements by magnetometers, inclinometers, andior
accelerometers, though_
other sensor types such as inertial sensors and gyroscopes may additionally or
alternatively be
used to detetmine position as well as orientation.. In one specific
embodiment, the tool includes a
3-axis fluxgate magnetometer and a 3-axis accelerometer. As is known in the
art, the
combination of those two sensor systems enables the measurement of the tool
face angle,
inclination angle, and compass direction. In some embodiments, the tool face
and hole
inclination angles are calculated from the accelerometer sensor output. The
magnetometer sensor
outputs are used to calculate the compass direction.
The drill. bit 114 may be a "coring bit" designed to obtain a core sample. (In
some
alternative embodiments discussed herein, the drill bit 114 m.ay be a fixed
cutter bit such as a
polycrystalline diamond compact (PDC) bit.) Fig. 2 is a side section view of a
tower portion of
an illustrative coring bit embodiment having a construction similar to that
described in U.S.
Patent No. 6,394,196 to Fanuei et al.., which is hereby incorporated herein by
reference in its
entirety. In the embodiment of Fig. 2, the drill bit 114 includes a cutter
assembly 202 attached to
an end of an outer tube 200. During operation, the outer tube 200 rotates,
turning the cutter
assembly 202 about a longitudinal axis 204 of the drill bit 114 and driving
the cutter assembly
202 forward along the axis 204, The drill bit 114 also includes an inner tube
206 mounted within
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the outer tube 200 for receiving a core sample cut by the cutter assembly 202.
The drill bit 114
also includes a split ring 208 disposed at a front end of the inner tube 206
for gripping and/or
grasping the core sample. During normai core drilling, a flow space between
the outer tube 200
and the inner tube 206 conveys drilling fluid through fluid channels in the
bit to a bottom of the
borehole. Alternative bit embodiments include nozzles and/or liquid jet
cutters to direct the
drilling fluid as it exits from the bit. As the drill bit 114 cuts an annular
space around the core
sample, the core sample enters the inner tube 206 as the bit moves forward
along the axis 204.
The drill bit 114 of Fig. 2 includes an optical analysis system 210 including
a window
212, an analyzer 216, and an optical transmission system 214 connected between
the window
212 and the analyzer 216. As indicated in Fig. 2, the window 212 is located on
an inner surface
of the core bit 202 such that the window 212 is proximate to a core sample
being acquired by the
drill bit 1.14. As described in more detail below, the optical transmission
system 214
communicates light from the analyzer 216 to the core sample, and communicates
reflected light
from the core sample to the analyzer 216. The analyzer 216 analyzes the
received reflected light
to determine at least one characteristic of the core sample and/or form an
image of the core
samp le.
Fig. 3 shows the throat of drill bit 114 as it acquires a core sample 300. In
Fig. 3, the core
sample 300 is entering the inner tube 206 of the drill bit 114 as it gets cut
from the floor of the
borehole. The window 212 is a distance 'D' frorn the core sam.ple being
acquired by the drill. bit
114. The distance D is expected to be, on average, no more than about 1/32 of
an inch (0.8
millimeter) such that the light from the window can readily penetrate the
drilling fluid and be
reflected from the core sample 300.
In the embodiment of Fig. 3, the optical transmission. system. 214 includes a
pair of
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optical fibers 302A and 302B. The optical fiber 302A conveys light 304 from
the analyzer 216
(see Fig. 2) to the core sample 300 via the window 212, and the optical fiber
302B conveys tight
reflected from the core sample 300 via window 212 to the analyzer 216.
Fig. 4A is a diagram depicting one embodiment of th.e optical analysis system
210. In the
embodiment of Fig. 4A, the analyzer 216 includes a light source 400, a
detector system 402, a
processor 404, and a telemetry system 406. The optical transmission system
21,4 includes the pair
of optical. fibers 302A and 302B shown in Fig. 3 and described above. The
light source 400
produces electromagnetic radiation in the form. of light. The light may be,
for example, infrared
(Ii) light having wavelengths between about 780 nanometers and approximately
1000
micrometers, visible tight having wavelengths between about 380 nanometers and
approximately
780 nanometers, and/or ultraviolet (UV) light having wavelengths between about
10 nanometers
and approximately 380 nanometers. Suitable light sources include electrically
heated filaments,
arc lamps, solid state LEDs, to name just a few. Other suitable light sources
are also weli known
and commercially available.
Light from light source 400 is directed into the optical fiber 302A as a light
beam 304.
The optical fiber 302A conveys the light beam. 304 from the analyzer 216 to
the window 212. As
described above, the window 212 is located on an inner surface of the core bit
202 (see Figs. 2
and 3) and proximate the core sample 300 being acquired by the drill bit 11.4.
The window 212 is
substantially tran.sparent to the light 304 exiting the optical fiber 302A,
and is preferably made of
a scratch resistant material that has a high resistance to friction and
abrasion. The window 212
may be formed of or include, for example, sapphire or diamond.
Some or all of the light beam 30.4 exiting the optical fiber 302A passes
through the
window 212 and strikes the core sample 300. A portion. of -the light 304
striking the core sample
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300 reflects from the core sample 300, passes through. the window 212, and
enters the optical
fiber 302B as the light 306. The optical fiber 302B conveys the light 306
reflected from the core
sample 300 to the anal.yzer 21.6,
As indicated in Fig. 4A, the detector system 402 receives the light 306
reflected from the
core sample 300. The detector system 402 produces an output signal dependent
upon a
characteristic of the received light 306. The output signal may be, for
example, an electrical
signal such as a voltage or current. !In some embodiments, the detector system
402 includes one
or more one multivariate optical elements (MOEs) to define the light
characteristic(s) that are
measured by the detector system. An embodiment of the detector system. 402
including multiple
MOEs is described with reference to Fig. 5 below.
The processor 404 also receives the output signal produced by the detector
system 402,
digitizes it, associates it with a tool face angle and/or a bit depth, and
combines it with other
measurements for that position to improve measurement quality. For additional
measurement
accuracy, the processor 404 also controls the light source 400 to regulate its
temperature and/or
intensity. The processor m.ay further use the measurements to detennine the
core's characteristics
in situ, including for example, rock type, hydrocarbon type, water
concentration, porosity, and/or
permeabilit2,,,,. The processor can further use the measurements to construct
an image of the core
sample's surface. As the drill bit 114 cuts the core sample 300, the window
212 follows a helical
path around the core sample, forming a two dimensional area over which the
processor can
acquire measurements to image the core.
At least some detector system embodiments emplo2,,,, one or more MOEs to
determine
whether the spectrum of the reflected light matches the spectral signature of
one or more known
materials. For example, one MOE may be designed to detect the spectral
signature of methane,
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while another MOE detects the spectral signature of a light hydrocarbon. Yet
other MOEs can be
used to detect, e.g., long-chain hydrocarbons, water, CO2, sulfur compounds,
shale, silicates, or
carbonates. The detector can determine intensities of light passing through an
MOE and reflected
from an :MOE to obtain a measure of how much of the given material is
illuminated by the light
beam 304. Additional details regarding MOE detectors and their usage can be
found in, e.g., U.S.
Patent No. 7,911,605 to Myrick et al. entitled "Multivariate Optical Elements
for Optical
Analysis System," and in U.S. Patent Application Publication No. 2010/0265509
by Jones et al.
entitled "In Situ Optical Computation Fluid Analysis System and Method,"
incorporated herein
by reference in their entirety. In addition to MOEs, the detector can employ
filters, dispersion
gratings, and/or prisms to measure the spectrum of the reflected light. Such
spectral
measurements can be used for calibration and performing analysis of those
materials for which
no MOE has been specifically included.
As previously mentioned, core samples are often obtained to measure formation
porosity,
permeability, and saturation. Porosity is a measure of how much fluid- or gas-
filled volume there
is per unit volume of rock. For example, 20% porosity means that 20% of the
volume is filled
with fluid or gas. Permeability is a measure of resistance to fluid flow,
i.e., how easily fluids or
gases can propagate through the formation. As a general rule (though not an
inviolate one), the
more porous the formation, the higher its permeability. Saturation is a
measure of what
percentage of the formation fluids is water as opposed to hydrocarbon liquids
or gases. To
measure these values, the MOEs can be designed to detect water and hydrocarbon
signatures, but
also to detect the spectral signatures of certain types of rock which are
known to be more porous
or permeable than other types. Accordingly, the processor analyzes the
detector output signals to
detect concentrations of the various fluid types as well as signs of a
spectral match to one of the
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known rock types. A neural network or other processing technique can then be
used to arrive at a
quantitative estimate of porosity, permeability, and/or saturation. Even where
quantitative
estimates are somewhat ambiguous, it should be possible to correlate the
opticai analyzer
measurem.ents with laboratory analysis of the retrieved core. Such a
correlation can then be
employed as a basis for estimating porosity, permeability, and saturation
measurements for those
portions of the core sample which have degraded during the retrieval process.
As previou.sl.y mentioned, the processor 404 m.ay also or alternatively use
the output
signal produced by the detector system 402 to form a surface image of the core
sample 300.
Again, as the drill bit 114 is acquiring the core sample 300, the window 212
is turning in a
helical path about an outer surface of the core sample 300. The intensity of
the light 306 reflected
from. the core sampl.e 300 and other spectrai m.easurements obtained by the
detector system 402
expectedly varies with the texture of the surface of the core sampl.e 300. The
processor 404 is
configured to track the movement of the drill bit 114 (both the rotational
motion about the axis
204 and the linear motion parallel to the axis 204), enabling the processor
404 to associate the
intensity measurements produced by the detector system. 402 with corresponding
positions on the
outer surface of the core sample 300. Displaying the intensity measurements as
pixels having
different levels of gray, or different colors, at positions on a screen
corresponding to their
positions on the outer surface of the core sample 300 will expectedly create
an image of the outer
surface of the core sample 300 on the screen.
in the embodi.m.ent of Fig. 4A., the telemetry system. 406 cotnmunicates
information by
sending and receiving data signals. The telemetry system 406 receives data
signals conveying
instructions or commands for the processor 404 to carry out, and sends data
signals conveying
data from the processor 404 indicative of the one or more characteristics of
the core sample 300
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determined by the processor 404. The data signals may be, for exainple, radio
signals conducted
via radio waves, electrical signals conveyed via one or more conductors,
optical signals
conveyed via one or more optical fibers, acoustic signals conveyed via the
tool body, or
pressure-pulse signal.s conveyed via the fluid flow.
Fig. 4B is a diagram depicting an alternative embodiment of the optical
analysis system
210 where the optical transmission system 214 includes a single optical fiber
302. In this
alternative embodiment the analyzer 216 further includes a beam splitter 420.
Some of the light
produced 'by the light source 400 passes through the beam splitter 420,
emerges from the 'beam
splitter 420, and enters the optical fiber 302 as the light 304. Some or all
of the light 304 exiting
the optical fiber 302 passes through the window 212 and strikes the core
sample 300. A portion
of the light 304 striking the core sample 300 reflects from the core sample
300, passes through
the window 212, and enters the optical fiber 302 as reflected light 306. The
optical fiber 302
conveys the light 306 reflected from the core sample 300 to the analyzer 216,
where the 'beam
splitter directs at least some of the reflected light 422 to the detector
system 402. The beam
splitter inherently induces some intensity losses to the tight bearn, but this
embodiment tnay be
preferred where the physical size of the optical transmission system 214 is a
key factor.
Fig. 5 is a diagram of an illustrative detector system 402. In the embodiment
of Fig. 5, the
detector system 402 includes a wheel 500 including multiple filters and/or
multivariate optical
elern.ents (MOEs) 502 disposed about a periphery of the wheel 500. During
operation of the
detector system 402, the wheel 500 mtates about an axis 504, 'bringing each
filter or MOE
successively into the path of the reflected light 306 or reflected light 422
reaching the detector
system. A light sensor 506 measures the intensity of the light passing through
(or alternatively,
reflected from) each filter or MOE in the wheel. The light sensor 506 rna.y
be, fig example,
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coupled to an analog-to-digital converter that produces a value included in
the output signal. The
processor 404 (see Fig. 4A) is configured to detennine which MOE 502 the light
306 (422) has
passed through, and processes the output signal accordingly.
Various forms of light sensors are contemplated including quantum-effect
photodetectors
(such as photodiodes, photoresistors, phototransistors, photovoltaic cells,
and photomultiplier
tubes) and theimal-effect photodectors (such as pyroelectric detectors, Golay
cells,
thermocouples, thermopiles, and thermistors). Most quantum-effect
photodetectors are
semiconductor based, e.g., silicon, lnGaA.s, PbS, and PbSe. One contemplated
tool embodiment
employs a combined detector made up of a silicon photodiode stacked above an
InGaAs
photodiode. In tools operating in only the visible and/or near infrared, both
quantum-effect
photodetectors and thermal-effect photodetectors are suitable. In tools
operating across wider
spectral ranges, thertnal-effect photodetectors are preferred.
The detector system 402 may also include a second light detector (not shown)
responsive
to light reflected from each of the MOEs 502 when the MOEs 502 pass through
the path of the
light 306 (422). The second light detector may be coupled to an analog-to-
digital converter that
produces a value included in the output signal
Fig. 6 is a diagram depicting an illustrative embodiment of the optical
analysis system
210 having two axially-separated windows 212A and 212B. That is, the windows
212A and
212B are spaced apart from_ one another along the longitudinal axis 204 of the
drill bit 114. in the
embodiment of Fig. 6, the optical analysis system 210 also includes a second
pair of optical
fibers 302C and 3021), and the analyzer 216 includes two detector systems 402A
and 402B.
A portion of the light produced by the light source 400 enters the optical
fiber 302A as
the light 304, and another portion of -the light produced by the light source
400 enters the optical_
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fiber 302C as light 600. The optical fiber 302A conveys the light 304 to the
window 212A, and
the optical fiber 302C conveys the light 600 to the window 212B. A portion of
the light 304
striking the core sample 300, reflecting from. the core sample 300, and
passing through the
window 212A enters the optical fiber 302B as the light 306. The optical fiber
302B conveys the
light 306 reflected from the core sample 300 to the detector system 402A.
Similarly, a portion of
the light 600 striking the core sample 300, reflecting from the core sample
300, and passing
through the window 212B enters the optical fiber 302D as the light 602. The
optical fiber 302D
conveys the light 306 reflected from the core sample 300 to the detector 402B.
The processor 404 receives the output signals produced by the detector systems
402A and
402B and determines from each an image of the core sample. For example, the
intensity of the
light 306 and the light 602 reflected from. the core sample 300 and reaching
the respective
detector systems 402A and 402B expectedly varies with the texture of the
surface of the core
sample 300. In the embodiment of Fig. 6, a specific region of texture would to
move past the
window 212A first, then past the window 212B. The axial offset between windows
is known,
and by determining the time offset required to align portions of the two
images, the processor
can determine to a high precision the rate at which the core sample is
entering into the inner
barrel.
This "coring rate" can be compared to the bit's rate of motion as measured by
inertial
sensors or other means. A rate mismatch can be readily detected and used to
quickly alert the
operators of a potential issue with the coring process. The operators can then
act to address the
issue and correct any problems before any substantial core losses occur. For
example, the
operators can vary the rotation rate and the weight-on-bit to restore smooth
core cutting, or
possibly retrieve the coring assembly to correct any mechanical issues.
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The focus of the foregoing discussion has been on coring bits with integrated
spectral
analyzers. However, the spectral analyzers need not be focused on the core
sample, but could
alternatively be focused on the floor of -the borehole to characterize the
fonnation as soon after it
has been exposed as possible. Such a configuration would also be applicable to
non-coring, fixed
cutter bits.
Accordingly, Fig. 7 is an isometric view of a fixed cutter drill bit 700 for
engaging and
removing adjacent portions of a d.ownhole formation at the bottom of a
borehole. (Certain
details, such as the bit box, the internal chain:her, and flow nozzles, are
omitted for clarity.)
Illustrative drill. bit 700 includes a steel body 702 having multiple 'blades
704. Multiple cutting
teeth 706 are disposed on cutting edges of each of the blades '704 to form the
borehole through
the formation as the drill bit 700 rotates. The Gutter inserts may be
polycrystalline diamond
compact (PDC) cutters seated in the blades 704. A.s the bit rotates, the
cutting teeth 706 create
grooves in the borehole floor. Positioned behind at least some of the teeth
are impact arrestors
708, i.e., stabilizing projections that ride in the grooves to reduce bit
vibration. More detail
regarding the design and use of impact arrestors is available in LS. Patent
No. 5,090,492 to
O'Han ion et al., incorporated h.erein by reference.
Advantageously, the average distance between the impact arrestors and the
formation can
be less than 132 inch (0.8 millimeter). In the illustrative bit 700, one of
these impact arrestors
708 is equipped with a diamond or sapphire window 212. In some embodiments,
the window is
slightly inset and positioned slightly towards th.e trailing edge of th.e
impact arrestor to provide
some protection against wear. An optical transmission system 214 communicates
light through
the blade between the window 212 and an optical analyzer. The optical analysis
system 210
operates as described above to d.etermine, at least one characteristic of the
formation at the
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bottom of the welibore and/or to form an image of a cylindrical portion of the
formation.
Some bit embodiments may locate the window in a junk slot and/or in a flow
nozzle to
measure the ch.aracteristics of -the drilling fluid before or after it
interacts with the formation. As
existing fixed cutter bit may- be retrofitted with an optical analysis system
210 by positioning the
system in the space fonnerly reserved for a flow nozzle.
Fig. 8 is a side elevation view of one embodiment of a representative one of
the impact
arrestors 708 of Fig. 7. In the embodiment of Fig. 8, the impact arrestor 708
is substantially
cylindrical and h.as threaded end 800 and a rounded end 802. Th.e threaded end
800 is installed in
a threaded hole in the corresponding blade 704 of Fig. 7. As the drill bit 700
of Fig. 7 turns, the
cutting teeth 706 rentove material from a fonnation 804 at a bottom of a
v,iellbore. The impact
arrestor 708 follows a preceding cutting tooth. 706. The rounded end 800 of
the impact arrestor
708 is adapted to follow a drilling slope formed in an exposed surface 806 of
the formation 804
by the corresponding cutting tooth 706, and to ride snuggly in a groove cut in
the exposed
surface 806 by the corresponding cutting tooth 706. The rounded end 802 of the
impact arrestor
708 has a wear resistant coating 808 on an. outer surface. The coating 808 may
be or include an
extremely hard materiai such. as tungsten carbide, natural diamonds, and/or
man-made
polycrystalline diamond such as polycrystalline diamond compact (PDC) or
thermally stable
diamond (TSD).
The illustrated impact arrestor 708 inciudc.s a conduit 810 extending through.
the impact
arrestor 708 from the threaded end 800 to th.e rounded end 802.. The wi.ndow
212 of the opticai
analysis system 210 is positioned at an end of the conduit 810 in the rounded
end 802. The drill
bit 700 of Fig. 7 has a conduit 812 that passes through the corresponding
blade 704 and aligns
with -the conduit 810 of the impact arrestor 708. The conduit 812 meets the
conduit 810 of the
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impact arrestor 708 at the threaded end 800 of the impact arrestor 708. The
optical fiber(s) 302 of
the optical transmission system 214 are positioned in the conduit 810 of the
impact an-estor 708
and extend through_ the impact arrestor 708 as indicated in Fig. 8.
During operation of the dril.l bit 700 of Fig. 7, some of the light produced
by the light
source 400 of Fig. 4B passes through the conduit 810 in the drill bit 700 and
enters the optical
fiber 302 as the light 304. Some or all of the tight 304 exiting the optical
fiber 302 passes
through the window 212 and strikes the exposed surface 806 of the formation
804. A portion_ of
the light 304 striking the exposed surface 806 reflects from the exposed
surface 806, passes
through the window 212, and enters the optical fiber 302 as reflected light
306. The optical fiber
302 conveys the tight 306 reflected from the formation 804 to the analyzer 216
(see Fig. 4B),
The optical analysis system 210 operates as described above to determine at
least one
characteristic of th.e formation 804 at the bottom of the well:bore. In other
embodiments, the
window 212 of the optical analysis system 210 may be positioned in the impact
arrestor 708 such.
that the window 212 is slightly above the exposed surface 806 of the formation
804, and the
optic,a1 analysis system 210 may analyze drilling fluid located between the
window 212 and the
exposed surface 806.
Fig. 9 is a flow chart of an illustrative method 900 for obtaining a core
sample. In a first
block 902 of the method 900, light is directed at the core sample as the core
sample is being
collected. At least a portion of -the light reflected fro_m the core sample is
received during a block
904. During a block 906, the received reflected light is analyzed to determine
at least one
characteristic of the core sample. The core sample ma2,,,, be, for example, a
sample of a subsurface
folination. The method 900 may also include directing a coring bit into the
earth, and actuating
the coring bit -to collect the core sample. Blocks 904 and 906 m.ay be carried
out at with two
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CA 02837656 2013-11-28
WO 2012/166138 PCT/US2011/038839
axially separated positions in the coring bit to obtain two different
measurements, and the two
different measurements may be conipared to deterinine a rate at which the core
sample is
entering a coring bit.
Numerous -variations and modifications wili become apparent to those skilled
in the art
once the above disclosure is fully appreciated. For example, the optical
transmission system is
described as having one or more optical fibers which could be replaced with
wayeguides or open
channels and an arrangement of mirrors and/or lenses to define the optical
path. As another
exatnple, the optical analysis system can be adapted to other types of drill
bits, such as roller
cone drill bits. (To examine the fotmation, the window can be located in a
gauge surface of one
of the legs for the roller cones. Drilling fluids can be examined by locating
the window in a flow
nozzle and/or a junk slot. A com.parison of uncontaminated and contaminated
fluids may be
perfortned.) :It is intended that the claims be interpreted to embrace all
such variations and
modifications.
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