U.S. patent application number 14/191371 was filed with the patent office on 2014-10-02 for closed-loop geosteering device and method.
This patent application is currently assigned to Schlumberger Technology Corporation. The applicant listed for this patent is Schlumberger Technology Corporation. Invention is credited to Edward Richards, Junichi Sugiura.
Application Number | 20140291024 14/191371 |
Document ID | / |
Family ID | 51619711 |
Filed Date | 2014-10-02 |
United States Patent
Application |
20140291024 |
Kind Code |
A1 |
Sugiura; Junichi ; et
al. |
October 2, 2014 |
Closed-Loop Geosteering Device and Method
Abstract
A closed-loop method for geosteering a subterranean borehole
includes rotating a roll-stabilized control unit in the borehole,
obtaining formation evaluation sensor measurements via sensors
located in the control unit, and processing downhole the sensor
measurements to obtain a corrective steering tool setting that may
be applied to a steering tool to control a direction of drilling. A
logging while drilling method includes obtaining sensor
measurements via sensors located on a rotating roll-stabilized
control unit and processing the sensor measurements to obtain an
LWD image. A downhole tool includes a downhole tool body and a
roll-stabilized control unit. The roll-stabilized control unit is
deployed in a through bore of the tool body such that it is free to
rotate with respect to the tool body. A tool face sensor and a
partially shielded gamma ray sensor are deployed in the
roll-stabilized control unit.
Inventors: |
Sugiura; Junichi; (Bristol,
GB) ; Richards; Edward; (Warwickshire, GB) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Schlumberger Technology Corporation |
Sugar land |
TX |
US |
|
|
Assignee: |
Schlumberger Technology
Corporation
Sugar land
TX
|
Family ID: |
51619711 |
Appl. No.: |
14/191371 |
Filed: |
February 26, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61806400 |
Mar 29, 2013 |
|
|
|
Current U.S.
Class: |
175/45 |
Current CPC
Class: |
E21B 7/04 20130101; E21B
44/005 20130101 |
Class at
Publication: |
175/45 |
International
Class: |
E21B 44/00 20060101
E21B044/00; E21B 7/04 20060101 E21B007/04 |
Claims
1. A closed-loop method for geosteering a subterranean borehole,
the method comprising: (a) causing a bottom hole assembly to drill
a subterranean borehole, the bottom hole assembly including a
steering tool having a roll-stabilized control unit, the roll
stabilized control unit including at least one formation evaluation
sensor and a tool face sensor deployed therein; (b) causing the
roll-stabilized unit to rotate with respect to the borehole while
drilling in (a); (c) causing the formation evaluation sensor and
the tool face sensor to obtain corresponding sensor measurements
while rotating in (b); (d) processing the sensor measurements
obtained in (c) to compute a borehole image parameter; (e)
processing the borehole image parameter to obtain a corrective
steering tool setting; and (f) applying the corrective steering
tool setting to the steering tool to change a direction of
drilling.
2. The method of claim 1, further comprising: (g) continuously
repeating (c), (d), (e), and (f) while drilling in (a).
3. The method of claim 1, wherein the formation evaluation sensor
comprises a gamma ray sensor deployed in the roll-stabilized
control unit.
4. The method of claim 3, wherein the gamma ray sensor comprises a
substantially cylindrical scintillator deployed co-axially in a
semi-cylindrical shield.
5. The method of claim 3, wherein the gamma ray sensor comprises a
substantially cylindrical scintillator deployed in a cylindrical
shield, the scintillator being axially offset from the cylindrical
shield.
6. The method of claim 3, wherein the gamma ray sensor comprises a
substantially cylindrical scintillator deployed in the
roll-stabilized control unit and a partially cylindrical shield is
deployed about the roll-stabilized control unit on an inner surface
of a rotary steerable tool body.
7. The method of claim 1, wherein the borehole image parameter is
at least one of a difference or a ratio between high side gamma ray
counts and low side gamma ray counts, a relative dip angle between
the borehole and a formation boundary of interest, and an azimuthal
width and intensity of a gamma ray peak or trough.
8. The method of claim 1, wherein (d) further comprises processing
the sensor measurements obtained in (c) and a rate of penetration
in (a) to compute the borehole image parameter.
9. The method of claim 1, wherein (e) further comprises processing
the borehole image parameter and a borehole azimuth measurement to
obtain the corrective steering tool setting.
10. The method of claim 1, further comprising: (g) receiving a
borehole azimuth measurement; (h) processing the borehole azimuth
measurement to obtain a second corrective steering tool setting,
the second steering tool setting operative to change a borehole
azimuth; and (i) applying second corrective steering tool setting
to the steering tool to change a direction of drilling.
11. The method of claim 1, wherein (e) comprises processing the
borehole image parameter in combination with a target image
parameter to obtain a corrective steering tool setting.
12. The method of claim 11, further comprising: (g) causing a
surface system to execute an outer control loop to obtain the
target image parameter; and (h) downlinking the target image
parameter from the surface system to a downhole processor for
processing in (e).
13. A downhole tool comprising: a downhole tool body; a
roll-stabilized control unit deployed in a through bore of the
downhole tool body, the roll-stabilized control unit being free to
rotate with respect to the downhole tool body; a tool face sensor
deployed in the roll-stabilized control unit; and a partially
shielded gamma ray sensor deployed in the roll-stabilized control
unit, the gamma ray sensor including a scintillator crystal and a
substantially cylindrical shield that subtends an angle less than
360 degrees.
14. The downhole tool of claim 13, wherein the tool is a rotary
steerable tool and the downhole tool body is a rotary steerable
tool body;
15. The downhole tool of claim 13, wherein the tool is a logging
while drilling tool and the downhole tool body is a logging while
drilling tool body;
16. The downhole tool of claim 13, wherein the downhole tool body
is configured to be connected with a drill string such that the
tool body is rotationally coupled with the drill string.
17. The downhole tool of claim 13, wherein the scintillator is
substantially cylindrical and deployed co-axially in a
semi-cylindrical shield with both the scintillator and the shield
being deployed in the roll-stabilized control unit.
18. The downhole tool of claim 13, wherein the scintillator is
substantially cylindrical and deployed in a cylindrical shield, the
scintillator being axially offset from the cylindrical shield with
both the scintillator and the shield being deployed in the
roll-stabilized control unit.
19. The downhole tool of claim 13, wherein the scintillator is
substantially cylindrical and deployed in the roll-stabilized
control unit and the shield is partially cylindrical and deployed
about the roll-stabilized control unit on an inner surface of a
rotary steerable tool body.
20. A logging while drilling method comprising: (a) deploying a
logging while drilling tool in a subterranean borehole, the logging
while drilling tool including a roll-stabilized control unit
deployed in a tool body, the roll stabilized control unit including
at least one formation evaluation sensor and a tool face sensor
deployed therein; (b) causing the logging while drilling tool body
to be rotationally stationary with respect to the borehole; (c)
causing the roll-stabilized control unit to rotate with respect to
the borehole; (d) causing the formation evaluation sensor and the
tool face sensor to obtain corresponding sensor measurements while
rotating in (c); (e) processing the corresponding formation
evaluation sensor measurements and the tool face measurements
obtained in (d) to obtain an image.
Description
RELATED APPLICATIONS
[0001] None.
FIELD OF THE INVENTION
[0002] The disclosed subject matter relates generally to an
apparatus and method for geosteering a subterranean borehole. More
particularly, the disclosed embodiments relate to an apparatus and
method for a closed-loop geosteering operation.
BACKGROUND
[0003] The use of on-site and remote geosteering methods is well
known in the downhole drilling arts. During such geosteering
operations, drilling typically proceeds according to a
predetermined well plan (e.g., derived using geometric
considerations in combination with a three dimensional model of the
subterranean formations). Real-time geological measurements, for
example, measurement while drilling (MWD), logging while drilling
(LWD), and/or mud logging measurements, are made while drilling.
Data obtained from these measurements are then used to make "on the
fly" adjustments to the direction of drilling, for example, to
maintain the drill bit at a desired location in a payzone.
[0004] In conventional geosteering operations, steering decisions
are made at the surface, e.g., at the rig site or at a remote
location. LWD data (or other downhole data) are compressed downhole
and then transmitted to the surface while drilling (e.g., via
conventional telemetry techniques). The transmitted data is then
processed at the surface in combination with a model of the
subterranean formations to determine a subsequent drilling
direction (or a correction to the current drilling direction).
Changes to the predetermined (preplanned) drilling direction (e.g.,
in the form of a corrected well path) are then transmitted from the
surface to a downhole steering tool (e.g., via conventional
downlinking techniques).
[0005] While such geosteering methods are commercially utilized,
there remains room for improvement. For example, the viability of
prior art geosteering methods is often limited by the bandwidth and
accuracy of the communication channel between the bottom hole
assembly (BHA) and the surface. This limitation can cause
geosteering methods to be slow and somewhat unresponsive (e.g., due
to the time lag associated with transmitting LWD measurements to
the surface and then transmitting steering instructions or a
corrected well plan from the surface to the BHA). Moreover,
telemetry errors and/or the reduced accuracy that results from data
compression can lead to further errors when computing the corrected
well path. These and other limitations of prior art techniques lead
to a need for improved geosteering methods.
SUMMARY
[0006] A closed-loop method for geosteering a subterranean borehole
is disclosed. A subterranean borehole is drilled using a bottom
hole assembly including a steering tool having a roll-stabilized
control unit. The roll stabilized control unit includes at least
one formation evaluation sensor and a tool face sensor deployed
therein. The roll-stabilized control unit may be rotated with
respect to the borehole while drilling. Corresponding formation
evaluation sensor measurements and tool face sensor measurements
are obtained while rotating the roll-stabilized control unit and
are processed to compute a borehole image parameter. The borehole
image parameter is processed to obtain a corrective steering tool
setting which is applied to the steering tool to change a direction
of drilling. The method may be executed continuously while drilling
so as implement closed-loop control of the direction of
drilling.
[0007] A logging while drilling method includes deploying a logging
while drilling tool in a subterranean borehole. The tool includes a
roll-stabilized control unit deployed in a tool body, the roll
stabilized control unit including at least one formation evaluation
sensor and a tool face sensor deployed therein. The logging while
drilling tool body is held rotationally stationary with respect to
the borehole while the roll-stabilized control unit is rotated with
respect to the borehole. Corresponding formation evaluation sensor
measurements and tool face sensor measurements are obtained while
rotating the roll-stabilized control unit. The sensor measurements
are then processed to obtain a logging while drilling image.
[0008] A downhole tool includes a downhole tool body and a
roll-stabilized control unit. The roll-stabilized control unit is
deployed in a through bore of the tool body such that it is free to
rotate with respect to the tool body. A tool face sensor and a
partially shielded gamma ray sensor are deployed in the
roll-stabilized control unit. The gamma ray sensor may include a
scintillator crystal and a substantially cylindrical shield that
subtends an angle less than 360 degrees. The downhole tool may
include, for example, a rotary steerable drilling tool or a logging
while drilling tool.
[0009] Disclosed embodiments may provide several technical
advantages. For example, in providing a closed-loop methodology,
the disclosed embodiments tends to advantageously improve the
timeliness and accuracy of geosteering operations as well as
further improve borehole placement in the subterranean geology
(e.g., in a predetermined payzone) while also reducing borehole
tortuosity. Deployment of logging while drilling sensors in a
roll-stabilized control unit may advantageously enable borehole
images to be obtained when the drill string is stationary
(non-rotating) in the borehole or during slide drilling operation.
Moreover, the deployment of LWD sensors in a roll stabilized unit
may reduce image blurring owing to stick slip and torsional
vibrations of the drill string.
[0010] This summary is provided to introduce a selection of
concepts that are further described below in the detailed
description. This summary is not intended to identify key or
essential features of the claimed subject matter, nor is it
intended to be used as an aid in limiting the scope of the claimed
subject matter.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] For a more complete understanding of the disclosed subject
matter, and the advantages thereof, reference is now made to the
following descriptions taken in conjunction with the accompanying
drawings, in which:
[0012] FIG. 1 depicts an example drilling rig on which disclosed
embodiments may be utilized.
[0013] FIG. 2 depicts a flow chart of one disclosed method
embodiment.
[0014] FIG. 3 depicts a portion of a steering tool having a
roll-stabilized control unit (in hidden lines) deployed in the
throughbore of a drill collar.
[0015] FIGS. 4A and 4B (collectively FIG. 4) depict a first
embodiment of an integrated gamma ray sensor deployed in the
roll-stabilized control unit of FIG. 3 in cutaway perspective (FIG.
4A) and circular cross-sectional (FIG. 4B) views.
[0016] FIGS. 5A and 5B (collectively FIG. 5) depict a second
embodiment of an integrated gamma ray sensor deployed in the
roll-stabilized control unit of FIG. 3 in cutaway perspective (FIG.
5A) and circular cross-sectional (FIG. 5B) views.
[0017] FIGS. 6A and 6B (collectively FIG. 6) depict a third
embodiment of an integrated gamma ray sensor deployed in the
roll-stabilized control unit of FIG. 3 in cutaway perspective (FIG.
6A) and circular cross-sectional (FIG. 6B) views.
[0018] FIG. 7 depicts a flow chart of another disclosed method
embodiment.
[0019] FIG. 8 depicts a hypothetical eight-sector gamma image in
which the borehole crosses a formation of interest (an active
bed).
[0020] FIG. 9 depicts a flow chart of yet another disclosed method
embodiment.
[0021] FIG. 10 depicts a hypothetical eight-sector gamma image in
which an active bed drops down away from the borehole.
DETAILED DESCRIPTION
[0022] FIG. 1 depicts a drilling rig 10 suitable for using various
method and system embodiments disclosed herein. A semisubmersible
drilling platform 12 is positioned over an oil or gas formation
(not shown) disposed below the sea floor 16. A subsea conduit 18
extends from deck 20 of platform 12 to a wellhead installation 22.
The platform may include a derrick and a hoisting apparatus for
raising and lowering a drill string 30, which, as shown, extends
into borehole 40 and includes a bottom hole assembly (BHA) 50. The
BHA 50 includes a drill bit 32 and a steering tool 60 including a
roll-stabilized control unit (not shown on FIG. 1). The
roll-stabilized control unit further includes at least one
formation evaluation (FE) sensor (e.g., an azimuthal gamma sensor)
and a tool face sensor. These sensors are depicted schematically in
FIGS. 1 at 62 and 64. The BHA 50 may further include substantially
any other suitable downhole tools such as a downhole drilling
motor, a downhole telemetry system, a reaming tool, and the like.
The disclosed embodiments are not limited in these regards.
[0023] It will be understood that substantially any suitable
steering tool 60 having a roll stabilized control unit (e.g., a
roll-stabilized sensor housing) may be used. For example, certain
of the PowerDrive.RTM. rotary steerable systems (available from
Schlumberger) make use of a roll stabilized control unit. The
PowerDrive.RTM. Archer.RTM. makes use of an internal
roll-stabilized control unit as well as a lower steering section
joined at a swivel with an upper section. The swivel is actively
tilted via pistons so as to change the angle of the lower section
with respect to the upper section and maintain a desired drilling
direction as the bottom hole assembly rotates in the borehole.
Accelerometer, magnetometer, and rate gyro sensor sets may be
deployed in the roll-stabilized control unit such that they remain
substantially stationary (in a bias phase) or rotate slowly with
respect to the borehole (in a neutral phase). To drill a desired
curvature, the bias phase and neutral phase may be alternated
during drilling at a predetermined ratio (referred to as the
steering ratio).
[0024] It will be understood by those of ordinary skill in the art
that the deployment depicted on FIG. 1 is merely an example for the
purposes of describing the disclosed embodiments set forth herein.
It will be further understood that the disclosed embodiments are
not limited to use with a semisubmersible platform 12 as
illustrated on FIG. 1. These embodiments are equally well suited
for use with any kind of subterranean drilling operation, either
offshore or onshore.
[0025] FIG. 2 depicts a flow chart of one closed-loop method
embodiment 100 for controlling the direction of drilling a
subterranean borehole. A subterranean borehole is drilled at 102,
for example, via rotating a drill string, pumping drilling fluid
through a downhole mud motor, and/or the like. The drill string
includes a steering tool including a roll-stabilized control unit
including at least one formation evaluation (FE) sensor. While
drilling at 102 the steering tool may be actuated so as to control
the direction of drilling. The roll-stabilized control unit is
rotated with respect to the borehole at 104 thereby causing the FE
sensor to also rotate with respect to the borehole. At 106 FE
measurements are made using the FE sensor while rotating in 104.
The FE measurements may include, for example, a plurality of gamma
ray measurements and corresponding tool face measurements. The FE
measurements may be processed downhole at 108 (e.g., using a
downhole processor located in the steering tool or elsewhere in the
drill string) to obtain a borehole image parameter that may be
further processed downhole to obtain a corrective steering tool
setting at 110. The steering tool setting may then be applied to
the steering tool at 112 to control the direction of drilling
(e.g., to control/change the borehole inclination). Steps 106, 108,
110, and 112 may be continuously repeated downhole so as to
maintain a desired drilling direction (e.g. a fixed distance above
or below a formation boundary).
[0026] FIG. 3 depicts a portion of a downhole tool 200 (e.g., a
steering tool or a logging while drilling tool) having a
roll-stabilized control unit 210 (in hidden lines) deployed in the
through bore 232 of a drill collar 230. In use the drill collar 230
is coupled with a drill string and rotates at the collar rotation
speed or the bit rotation speed depending upon whether it is
deployed above or below a mud motor. The roll-stabilized control
unit 210 may be configured to rotate with respect to the drill
collar 230 such that it may be substantially geostationary
(nonrotating with respect to the borehole) or rotated at some
predetermined angular velocity with respect to the borehole. For
example, the roll-stabilized control unit 210 may be configured to
rotate at some absolute rotation rate with respect to the borehole
(in the earth's reference frame) in the neutral phase.
Alternatively, the roll-stabilized control unit may be configured
to rotate at some relative rotation rate with respect to the collar
rotation rate (such as a fixed number of revolutions per minute
less than the collar rotation rate). In such embodiments,
azimuthally resolved FE measurements may be obtained while in the
neutral phase (i.e., when the roll-stabilized control unit rotates
with respect to the borehole).
[0027] It will be understood that the disclosed embodiments are not
limited to steering tool embodiments having a roll-stabilized unit.
The disclosed embodiments may also include a roll-stabilized unit
deployed in a measurement while drilling (MWD) or logging while
drilling (LWD) tool with the MWD and/or LWD sensors deployed in the
roll-stabilized unit. Such an MWD and/or LWD tool may be utilized,
for example, to obtain azimuthally resolved sensor data and/or LWD
images. Moreover, a downhole steering tool connected via a common
communication bus in the BHA may control the steering direction
based on the azimuthal FE image constructed at the roll-stabilized
MWD/LWD unit.
[0028] Deployment of MWD and/or LWD sensors in a roll-stabilized
unit may advantageously enable borehole imaging data to be obtained
when the drill string is not rotating (e.g., when the drill bit is
off bottom and circulating drilling fluid or when drilling in
sliding mode). For example, various downhole sensors may be
utilized to determine the current state of the drill string/bit.
These sensors may include, for example, weight on bit sensors,
accelerometers, and the like. U.S. Patent Publication 2013/0341091,
which is fully incorporated by reference herein, discloses downhole
methods for processing sensor data to determining whether or not
the drill string is rotating and on or off bottom. In certain
embodiments disclosed herein the roll-stabilized control unit may
be programmed to rotate when the drill string is not rotating and
the FE sensors may be programmed to obtain sensor data to obtain
LWD images. Such embodiments may advantageously be utilized to
produce LWD images without rotating the drill string, for example,
in slide drilling applications, coiled tubing steering operations,
when the drill bit is off bottom, and/or when the LWD tool is
located above a mud motor. Deployment of the LWD sensors in a
roll-stabilized control unit may further reduce image blurring and
smearing owing to stick slip and torsional vibrations of the drill
string. Moreover such embodiments may enable LWD imaging tools to
be located further up the drill string so as to preserve valuable
real-estate close to the bit
[0029] Suitable roll-stabilized housings are disclosed, for
example, in U.S. Pat. Nos. 5,265,682 and 6,816,788, and GB
2,426,265. U.S. Pat. No. 5,265,682 discloses an apparatus in which
impellers and mud flow are used to stabilize the housing. U.S. Pat.
No. 6,816,788 uses an electrical motor to stabilize the housing.
Notwithstanding, the disclosed embodiments are not limited to any
particular drive mechanism for controlling the roll-stabilized
unit.
[0030] In the disclosed embodiments, the steering tool 200 further
includes an FE sensor deployed in the roll-stabilized unit 210. The
FE sensor may include, for example, an integrated gamma ray sensor
capable of providing real-time azimuthal gamma ray data while
drilling. FIGS. 4-6 depict three embodiments in which a
roll-stabilized unit includes an integrated gamma ray sensor. The
roll-stabilized unit 210 typically further includes a tool face
sensor deployed therein (e.g., including an accelerometer set).
[0031] FIGS. 4A and 4B depict a first embodiment of an integrated
gamma ray sensor 220 deployed in the roll-stabilized control unit
of FIG. 3. Sensor 220 includes a substantially cylindrical
scintillator rod 222 deployed in a semi-cylindrical shield 224 in
the roll-stabilized control unit 210. In the depicted embodiment,
the scintillator rod 222 and the shield 224 are substantially
co-axial. The shield 224 may be fabricated from substantially any
suitable high density material such as tungsten. The
semi-cylindrical shield provides a 180-degree azimuthal window 226
in which gamma rays may be detected in the formation.
[0032] FIGS. 5A and 5B depict a second embodiment of an integrated
gamma ray sensor 240 deployed in the roll-stabilized control unit
of FIG. 3. Sensor 240 includes a substantially cylindrical
scintillator rod 242 axially offset in a substantially cylindrical
shield 244 in the roll-stabilized control unit 210. As with sensor
220, the shield 244 may be fabricated from substantially any
suitable high density material such as tungsten. Radially
offsetting the scintillator rod 242 in the shield 244 tends to
provide a narrower azimuthal window in which gamma rays may be
detected in the formation (e.g., about 45-90 degrees in the
depicted embodiment) and may therefore provide improved azimuthal
resolution.
[0033] FIGS. 6A and 6B depict a third embodiment of an integrated
gamma ray sensor 250 deployed in the roll-stabilized control unit
of FIG. 3. Sensor 250 includes a substantially cylindrical
scintillator rod 252 deployed in the roll-stabilized control unit
210. In the depicted embodiment, a partially cylindrical shield 254
is deployed on an inner surface of the drill collar 230 and rotates
with the drill collar 230 such that the shield 254 and window 255
rotate with respect to the control unit 210. Again, the shield 254
may be fabricated from substantially any suitable high density
material such as tungsten. The partially cylindrical shield
provides an azimuthal window (e.g., 90 degree) in which gamma rays
may be detected in the formation.
[0034] It will be understood that each of the embodiments disclosed
on FIGS. 4-6 may be used to detect natural gamma rays or induced
gamma rays. Those of ordinary skill in the art will readily
appreciate that induced gamma rays may be used when making
formation density and/or porosity logging measurements. In order to
induce gamma rays the steering tool may further include a
radioactive source deployed, for example, in the roll-stabilized
control unit 210 or the drill collar 230.
[0035] It will be further understood that the steering tool
embodiments depicted on FIGS. 4-6 may be utilized in the
closed-loop geosteering method 100. For example, in the embodiments
depicted on FIGS. 4 and 5, rotation of the roll-stabilized unit 210
with respect to the borehole enables azimuthally resolved gamma ray
data to be acquired at 106. In the embodiment depicted on FIG. 6,
rotation of the drill collar 230 with respect to the
roll-stabilized unit 210 enables azimuthally resolved gamma ray
data to be acquired at 106 (as the shield rotates about the
housing). Using the embodiments depicted on FIGS. 4 and 5, logging
while drilling images may be acquired while the steering tool is in
the neutral phase (and the control unit is rotating with respect to
the borehole). Using the embodiments depicted on FIG. 6, logging
while drilling images may be acquired while the steering tool is in
the bias phase (and in the neutral phase so long there is relative
rotation between the collar 230 and the control unit 210 in the
neutral phase).
[0036] The FE measurements may be acquired and correlated with
corresponding tool face measurements while drilling. The
measurements may then be distributed in azimuth (tool face) using
substantially any known methodologies, for example, conventional
binning, windowing, or probability distribution algorithms. U.S.
Pat. No. 5,473,158 discloses a conventional binning algorithm. U.S.
Pat. No. 7,027,926 discloses a technique for constructing a
borehole image in which sensor data is convolved with a
one-dimensional window function. U.S. Pat. No. 7,558,675 discloses
an image constructing technique in which sensor data is
probabilistically distributed in either one or two dimensions. Each
of these patents (the '158, '926, and '675 patents) is incorporated
by reference in its entirety herein.
[0037] With reference again to FIG. 2, the FE measurements may be
processed downhole at 108 to obtain a borehole image parameter that
may be evaluated downhole at 110 to control the direction of
drilling. For example, the borehole image parameter may be compared
with a predetermined value to obtain an error value which is in
turn further processed downhole to obtain a corrective steering
tool setting. Application of the corrective steering tool setting
thus changes the direction of drilling. In one common geosteering
operation, the intent is to drill a borehole a substantially fixed
distance above or below a particular subterranean formation. For
example, the borehole may be routed through an approximately
horizontal oil-bearing reservoir (e.g., having an inclination in
the range from about 80 to about 100 degrees). In such operations,
the corrective steering tool setting is intended to build
(increase) inclination, maintain the current inclination, or drop
(decrease) inclination in response to the FE sensor
measurements.
[0038] FIG. 7 depicts a flow chart of another closed-loop method
embodiment 120 for controlling the direction of drilling a
subterranean borehole. Method 120 is similar to method 100 in that
a subterranean borehole is drilled at 102, for example, via
rotating a drill string, pumping drilling fluid through a downhole
mud motor, or the like. As with method 100, the drill string
includes a steering tool including a roll-stabilized control unit
including at least one formation evaluation (FE) sensor. The
roll-stabilized control unit is rotated with respect to the
borehole at 104 thereby causing the FE sensor to also rotate with
respect to the borehole. At 106 FE measurements are made using the
FE sensor while rotating in 104. The FE measurements may be
processed downhole at 108 to obtain a borehole image parameter
which may be further processed downhole at 122 to obtain a first
corrective steering tool setting operative to change the borehole
inclination (i.e., to build, drop, or hold inclination).
[0039] Method 120 further includes measuring the borehole azimuth
at 124, e.g., using survey sensors such as accelerometers,
magnetometers, and/or gyroscopic sensors deployed in the steering
tool or elsewhere in the drill string. The measured borehole
azimuth may be processed downhole at 126 to obtain a second
corrective steering tool setting intended to control the borehole
azimuth (i.e., to turn left or turn right). The measured azimuth
may be processed, for example, in combination with a desired
azimuth to obtain an azimuth error, which may be further processed
downhole to obtain the second corrective steering tool setting. The
first and second corrective steering tool settings may then be
applied to the steering tool 128 to control the direction of
drilling. It will be understood that the first and second
corrective steering tool settings may be applied simultaneously (to
change the inclination and azimuth simultaneously) or incrementally
(so as to first change one and then the other of the inclination
and azimuth). Steps 106, 108, 122, 124, 126, and 128 may be
continuously repeated downhole so as to maintain a desired drilling
direction (e.g. a fixed distance above or below a formation
boundary).
[0040] Substantially any suitable borehole image parameter may be
utilized in methods 100 and 120 (FIGS. 2 and 7). For example, the
borehole image parameter may include (i) a difference or a ratio
between high side gamma ray counts and low side gamma ray counts,
(ii) a relative dip angle between the borehole and a formation (or
formation boundary) of interest, and (iii) the azimuthal width and
the intensity of a gamma ray peak or trough. The difference or
ratio between high side gamma ray counts and low side gamma ray
counts and the azimuthal width of a gamma ray peak or trough may be
indicative of the distance between the borehole and a target
formation while the relative dip angle between the borehole and a
formation of interest is indicative of the relative direction of
the borehole with respect to the formation of interest.
[0041] Using one of the gamma ray sensors depicted on FIGS. 4-6,
the difference or ratio between high side and low side gamma ray
counts may be utilized to sense bed boundaries above or below the
tool. When the difference or ratio is outside a predetermined range
of values (e.g., indicative of an approaching bed boundary), the
direction of drilling may be appropriately changed so as to stay in
the desired formation. For example, a ratio of high side to low
side gamma ray counts above a first predetermined threshold may be
taken to be indicative of an approaching bed boundary above the
steering tool. The corrective steering tool setting may thus be
selected to change the direction of drilling downward (in the
direction of decreasing inclination) when the count ratio is above
the first threshold. Likewise, a ratio of high side to low side
counts below a second predetermined threshold may be taken to be
indicative of an approaching bed boundary below the steering tool.
The corrective steering tool setting may thus be selected to change
the direction of drilling upward (in the direction of increasing
inclination) when the count ratio is below the second threshold.
Alternatively, a ratio between the high side measurement and a
non-azimuthal measurement (made for example via summing or
averaging the FE sensor measurements over all tool face angles)
and/or a ratio between the low side measurement and a non-azimuthal
measurement may be used to determine the location of an approaching
bed boundary.
[0042] The azimuthally resolved FE measurements may also be
processed to obtain a formation dip angle. The formation dip angle
represents the relative angle between the borehole and a formation
(or formation boundary) of interest. FIG. 8 depicts a hypothetical
eight-sector gamma image in which the borehole crosses a formation
of interest (an active bed). A formation dip angle may be computed
from the image data using techniques known to those of ordinary
skill in the art. The formation dip angle may then be further
processed to obtain the corrective steering tool setting.
[0043] FIG. 9 depicts a flow chart of yet another method embodiment
140 for controlling the direction of drilling a subterranean
borehole. Method 140 is similar to method 100 in that a
subterranean borehole is drilled at 102, for example, via rotating
a drill string, pumping drilling fluid through a downhole mud
motor, or the like. As with method 100, the drill string includes a
steering tool including a roll-stabilized control unit including at
least one formation evaluation (FE) sensor. The roll-stabilized
control unit is rotated with respect to the borehole at 104 thereby
causing the FE sensor to also rotate with respect to the borehole.
At 106 FE measurements are made using the FE sensor while rotating
in 104. The rate of penetration (ROP) while drilling in 102 is
received at 142. The ROP may be obtained, for example, from surface
measurements via conventional downlinking techniques.
Alternatively, the ROP may be computed downhole, for example, as
disclosed in U.S. Pat. Nos. 7,058,512 and 7,916,041 and U.S. Patent
Publication 2013/0341091 each of which is fully incorporated by
reference herein. At 144 the ROP may be processed in combination
with the FE measurements obtained at 106 to obtain a borehole image
parameter such as a formation dip angle. The borehole image
parameter may be further processed at 146 to obtain a corrective
steering tool setting which may be applied to the steering tool at
148 to change the direction of drilling. Steps 106, 142, 144, 146,
and 148 may be continuously repeated downhole so as to maintain a
desired drilling direction (e.g. a fixed distance above or below a
formation boundary).
[0044] FIG. 10 depicts a hypothetical eight-sector gamma image in
which an active bed 302 drops down away from the borehole 304. Note
that the width and intensity of the stripe (the band of high gamma
counts) 306 decreases as the distance to the active formation
increases (and conversely the width and intensity increases as the
distance decreases). As such the azimuthal width and the intensity
of the gamma data may be computed and processed to obtain the
corrective steering tool parameter. For example, in an operation in
which the borehole is intended to remain a fixed distance above an
active formation, a reduced azimuthal width and intensity (as
observed in FIG. 8) may be indicative of an increasing distance
between the borehole and the active bed. The corrective steering
tool setting may thus be selected to change the direction of
drilling downward. Alternatively, an increased azimuthal width and
intensity may be indicative of a decreasing distance between the
borehole and the active bed. The corrective steering tool setting
may thus be selected to change the direction of drilling
upward.
[0045] It will be understood that the above described method
embodiments may be advantageously operated in a closed-loop manner
for both up/down (inclination) control and turn right/turn left
(azimuth) control of the drilling operation. Such closed-loop
operations enable the drilling direction to be controlled
independently of any surface communications. However, the disclosed
embodiments may also be executed as part of a cascaded loop control
system. For example, a set point (target value) to the formation
characteristics (e.g. Gamma counts) and/or azimuth may be
downlinked from the surface on occasion. In such embodiments, a
surface system may execute an outer loop automated control defined,
for example, by a 3-D petro-physical model and/or defined by a 3-D
well trajectory. Cascaded loop control systems are disclosed in
U.S. Patent Publication 2010/0175922, which is fully incorporated
by reference herein.
[0046] The methods described herein are configured for downhole
implementation via one or more controllers/processors deployed
downhole (e.g., in the steering tool). A suitable controller may
include, for example, a programmable processor, such as a
microprocessor or a microcontroller and processor-readable or
computer-readable program code embodying logic, including FPGA
(field-programmable gate array). A suitable processor may be
utilized, for example, to execute the method embodiments described
above with respect to FIGS. 2, 7, and 9. A suitable controller may
also optionally include other controllable components, such as
sensors (e.g., a depth sensor), data storage devices, power
supplies, timers, and the like. The controller may also be disposed
to be in electronic communication with the FE sensor and the tool
face sensor (e.g., to receive corresponding sensor measurements). A
typical controller may further optionally include volatile or
non-volatile memory or a data storage device.
[0047] The controller may also optionally communicate with other
instruments in the drill string, such as telemetry systems that
communicate with the surface or an EM (electro-magnetic) short hop
that enables two-way communication across a downhole motor. A
surface controller may optionally run a closed loop control with a
supervisory function, which communicates with a downhole
closed-loop system to change the set point (target value) to the
downhole control system. It will be appreciated that the controller
is not necessarily located in the rotary steerable tool, but may be
disposed elsewhere in the drill string in electronic communication
therewith. Moreover, one skilled in the art will readily recognize
that the multiple functions described above may be distributed
among a number of electronic devices (controllers).
[0048] Moreover, it will be understood that the aspects and
features of the disclosed embodiments may be embodied as logic that
may be processed by, for example, by the above described
controller. Similarly the logic may be embodied on software
suitable to be executed by a processor, as is also well known in
the art. The disclosed embodiments are not limited in this regard.
The software, firmware, and/or processing device may be included,
for example, in the downhole steering tool or elsewhere in the
drill string. Electronic information such as logic, software, or
measured or processed data may be stored in memory (volatile or
non-volatile), or on conventional electronic data storage devices
such as are well known in the art.
[0049] While the disclosed embodiments depict a steering tool
having a roll-stabilized unit it will be understood that the
disclosed embodiments are not limited only to steering tool
embodiments. For example, the roll-stabilized unit may be deployed
in an measurement while drilling (MWD) or logging while drilling
(LWD) device. A downhole steering tool connected via a common
communication bus in the BHA may control the steering direction
based on the azimuthal FE image contructed at the roll-stabilized
MWD/LWD unit.
[0050] Although a closed-loop geosteering device and method and
advantages thereof have been described in detail, it should be
understood that various changes, substitutions and alterations may
be made herein without departing from the spirit and scope of the
disclosure as defined by the appended claims.
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