Note: Descriptions are shown in the official language in which they were submitted.
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METHOD AND APPARATUS FOR INITIALIZATION OF A WELLBORE SURVEY
TOOL VIA A REMOTE REFERENCE SOURCE
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation-in-part of U.S. Pat. Appl.
No.
12/555,737, filed September 8, 2009 and incorporated in its entirety by
reference herein,
which claims the benefit of priority from U.S. Provisional Appl. Nos.
61/180,779 filed May
22, 2009 and 61/186,748 filed June 12, 2009, both of which are incorporated in
their entirety
by reference herein. This application also claims the benefit of priority from
U.S. Provisional
Appl. No. 61/450,073 filed March 7, 2011, which is incorporated in its
entirety by reference
herein.
BACKGROUND
Field
[0002] The present application relates generally to methods and
apparatus for
initialization of a wellbore survey tool.
Description of the Related Art
[0003] There are typically two types of surveying by which wellbore
survey tools
conduct surveys (e.g., gyroscopic- or gyro-based surveys) of wellbores. The
first type is
static surveying, in which measurements of the Earth's rotation are taken at
discrete depth
intervals along the well trajectory. These measurements can be used to
determine the
orientation of the survey tool with respect to a reference vector, such as the
vector defined by
the horizontal component of the Earth's rate in the direction of the axis of
the Earth's
rotation; a process also referred to herein as gyro-compassing. The second
type is continuous
surveying, in which the gyroscopic or gyro measurements are used to determine
the change in
orientation of the survey tool as it traverses the well trajectory. This
process uses the gyro
measurements of turn rate with respect to a known start position. The start
position may be
derived, for example, by conducting a static survey prior to entering the
continuous survey
mode (which may also be referred to as an autonomous or autonomous/continuous
survey
mode).
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[0004] Under certain circumstances, static surveying generally becomes
less
accurate than in other circumstances. For example, when operating at high
latitudes on the
Earth's surface the static survey process becomes less accurate than at low
latitudes. At
relatively high latitudes, the reference vector to which the survey tool
aligns itself during the
gyro-compassing procedure, the horizontal component of Earth's rate (OH)' is
small
compared to the value in equatorial and mid-latitude regions, as indicated by
the following
equation:
OH =OcosL, (Eq. 1)
where Q = Earth's rate and L = latitude. Generally, a satisfactory directional
survey can be
achieved using gyro-compassing at latitudes of up to about 60 degrees.
However, the
accuracy can degrade rapidly thereafter as the cosine of latitude reduces more
rapidly and the
magnitude of Oõ thus becomes much smaller. Figure 1 schematically illustrates
the
horizontal component OH of the Earth's rate for changing latitude. As shown,
at zero
latitude OH is at its maximum value and is equal to the Earth's rate ( Q ). OH
successively
decreases to OH = Q cos L, and OH = Q cos L2 for increasing latitudes L1 and
L2,
respectively, and f2H is zero at 90 degrees of latitude (i.e., at the North
Pole). There is a
significant amount of oil and gas exploration at relatively high latitudes
(e.g., latitudes in
excess of 70 degrees). At these latitudes, the accuracy of well surveys based
on gyro-
compassing can be degraded. Similar degradations in survey accuracy can also
occur when
using magnetic survey tools instead of, or in addition to, gyro-based survey
tools. As such,
survey accuracy may similarly decrease at locations close to the Earth's
magnetic poles when
using magnetic survey tools.
[0005] In addition, the accuracy of gyro-compassing can be degraded
when
conducted from a moving platform (e.g., an offshore platform), as compared to
being
conducted from a relatively static platform. For example, during operation
from a moving
platform, the survey tool will be subjected to platform rotational motion in
addition to the
Earth's rotation. Under such conditions, tool orientation with respect to the
horizontal
Earth's rate vector (H) may be difficult to determine with the precision that
is possible on a
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stationary platform since the directional reference, defined by OH is
effectively corrupted by
the platform motion.
SUMMARY
[0006] In certain embodiments, a method is provided for determining an
orientation of a wellbore survey tool at a first position with respect to a
reference direction.
The method comprises receiving at least one first signal indicative of an
orientation of a
directional reference system with respect to the reference direction. The
directional reference
system is positioned at a second position spaced from the first position. The
method further
comprises receiving at least one second signal indicative of a relative
orientation of the
wellbore survey tool with respect to the directional reference system. The
method further
comprises determining the orientation of the wellbore survey tool at the first
position in
response at least in part to the at least one first signal and the at least
one second signal.
[0007] In certain embodiments, a system for determining an orientation
of a
wellbore survey tool is provided. The system comprises one or more computer
processors.
The system further comprise one or more inputs configured to receive data
indicative of an
orientation of a directional reference system with respect to a reference
direction and data
indicative of a relative orientation of the wellbore survey tool with respect
to the directional
reference system. The direction reference system is positioned at a first
position relative to a
wellbore entrance and a wellbore survey tool is mounted at a second position
relative to the
wellbore entrance spaced away from the first position. The system further
comprises a
wellbore initialization module executing in the one or more computer
processors and
configured to, in response at least in part to the received data, calculate an
orientation of the
survey tool.
[0008] In certain embodiments, a system for use in determining an
orientation of a
wellbore survey tool is provided. The system comprises at least one
directional reference
system configured to provide data indicative of an orientation of the at least
one directional
reference system with respect to a reference direction. The system further
comprise an
optical component mounted at a predetermined orientation with respect to the
directional
reference system and configured to transmit light along a line extending
between the
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directional reference system and a first reflecting surface mounted at a
predetermined
orientation with respect to the wellbore survey tool.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] Figure 1 schematically illustrates the horizontal component of
the Earth's
rate for changing latitude.
[0010] Figure 2 schematically illustrates an example apparatus for
initializing a
wellbore survey tool in accordance with certain embodiments described herein.
[0011] Figure 3 schematically illustrates apparatus according to
certain
embodiments described herein in a first location in which a relatively clear
communication
path between GPS antennae of the apparatus and GPS satellites, and in a second
location in
which the GPS antennae are at least partially shielded from communication with
GPS
satellites by a derrick.
[0012] Figure 4 schematically illustrates another example apparatus in
accordance
with certain embodiments described herein.
[0013] Figure 5 schematically illustrates a top view of an apparatus
including an
integrated GPS/AHRS unit in accordance with certain embodiments described
herein.
[0014] Figures 6A-6C schematically illustrate top, front and right side
views,
respectively, of an apparatus including a tool positioning element in
accordance with certain
embodiments herein.
[0015] Figure 6D schematically illustrates a partial perspective view
of an
apparatus including a tool positioning element during positioning of a survey
tool in
accordance with certain embodiments described herein.
[0016] Figure 7 schematically illustrates an example wellbore survey
tool on
which a directional reference system is directly mounted in accordance with
certain
embodiments described herein.
[0017] Figure 8 is a flow diagram illustrating an example wellbore
survey tool
initialization process in accordance with certain embodiments described
herein.
[0018] Figure 9 is a flowchart of an example method of initializing a
wellbore
survey tool in accordance with certain embodiments described herein.
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[0019] Figure 10 is a flowchart of an example method of initializing a
wellbore
survey tool utilizing an angular rate matching procedure in accordance with
certain
embodiments described herein.
[0020] Figure 11 schematically illustrates an example apparatus for
moving a
wellbore survey tool in accordance with certain embodiments described herein.
[0021] Figure 12 is a flowchart of an example method for determining an
orientation of a wellbore survey tool at a first position with respect to a
reference direction in
accordance with certain embodiments described herein.
[0022] Figure 13 illustrates an example survey tool initialization
configuration
including a survey tool and a reference system and also illustrates a
corresponding
initialization process, according to certain embodiments described herein.
[0023] Figure 14 illustrates an example survey tool mounted vertically
and having
a mirror attached to the tool, according to certain embodiments described
herein.
[0024] Figure 15 illustrates an example survey tool mounted
horizontally in a v-
block mount, according to certain embodiments described herein.
[0025] Figure 16 illustrates an example survey tool initialization
configuration in
which a reference system is mounted on a platform along with one or more
optical sighting
instruments, according to certain embodiments described herein.
[0026] Figures 17A and 17B illustrate example initialization
configurations in
which a reference system is mounted on a platform along with one or more
optical sighting
instruments and a survey tool, according to certain embodiments described
herein.
[0027] Figure 18 illustrates an example initialization configuration in
which an
autocollimation device is mounted at a predetermined orientation with respect
to a reference
system and is used to determine the initial orientation of the survey tool.
[0028] Figure 19 illustrates an example survey tool initialization
configuration in
which a sleeve is affixed to a survey tool, according to certain embodiments
described herein.
[0029] Figure 20 illustrates another example survey tool initialization
configuration in which a sleeve is affixed to a survey tool and the
tool/sleeve assembly are
keyed into a clamping mechanism, according to certain embodiments described
herein.
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[0030] Figure 21 shows an example rig having a survey tool and
reference system
mounted thereon, according to certain embodiments described herein.
[0031] Figures 22 and 23 shows further example initialization
configurations
including inertial attitude and heading reference systems (AHRS), according to
certain
embodiments described herein.
DETAILED DESCRIPTION
[0032] Embodiments described herein provide systems and methods which
generally allow precision well surveys to be conducted at high latitude
locations, from a
moving surface (e.g., an off-shore moving platform), or both.
A. Overview
[0033] While underground, gyro survey tools generally rely upon gyro-
compassing to conduct a static survey and/or to initiate a period of
continuous surveying to
determine the orientation of the survey tool with respect to a reference
vector (e.g., the vector
defined by the horizontal component of the Earth's rate). However, at the
surface, there are
other procedures which may be adopted. For example, land surveying techniques
can be used
to define a reference direction (which may also be referred to as a "benchmark
direction") to
which the tool can be aligned. This process may be referred to as fore-
sighting.
[0034] Alternatively, measurements from a directional reference system,
such as a
satellite navigation system, may be used to determine the orientation (e.g.,
the attitude) of a
survey tool with respect to a known geographic reference frame. The Global
Positioning
System (GPS) or the equivalent system developed by the former Soviet Union,
the Global
Navigation Satellite System (GLONASS), may be used, for example. Systems exist
which
use measurements of the differences in carrier wave phase between two or more
receiving
antennae spaced a known distance apart to determine the attitude of the body
or vehicle on
which the antennae are mounted. Examples of such systems are described, for
example, in
U.S. Patent No. 5,534,875, entitled "Attitude Determining System for Use with
Global
Positioning System", which is incorporated in its entirety by reference
herein. These systems
provide world-wide measurement of position, velocity and attitude on and above
the surface
of the Earth and are substantially immune to magnetic deviations and
anomalies.
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[0035] Using such systems in accordance with certain embodiments
described
herein, the initial orientation (e.g., attitude) of a survey tool may thus be
defined accurately
while above ground (e.g., on the surface) and data indicative of the initial
orientation (e.g.,
attitude data) can then be transferred to the tool. In certain circumstances,
the survey tool
may then be switched to continuous survey mode prior to being positioned for
insertion into
the wellbore and/or prior to insertion into the wellbore. For example, the
initial orientation of
the tool may be measured prior to pick-up of the survey tool (e.g., from
horizontal to vertical
with respect to the wellbore) to position the survey tool into the wellbore.
In certain
embodiments, this initial measurement may be made while the tool is positioned
generally
horizontally with respect to the wellbore (e.g., laying on a surface in the
vicinity of the
wellbore), for example. The survey tool may be switched to continuous mode
such that its
subsequent orientation (e.g., heading, trajectory, attitude, azimuth, etc.)
can be measured with
respect to the initial orientation. The survey tool may then be lifted from
the horizontal
position to another position, such as a vertical position. A continuous survey
of the wellbore
may then be conducted as the survey tool traverses the well trajectory.
[0036] Both land surveying techniques and methods using satellite
navigation
techniques for determining an initial orientation of the survey tool are
susceptible to human
errors under certain conditions. For example, the tool may be picked up
relatively rapidly
and one or more of the sensors keeping track of the orientation of the tool
(e.g., in continuous
survey mode) may become saturated or otherwise reach their rate limits. In
addition, the tool
may be dropped in some cases. Certain embodiments described herein address
such
problems by linking a survey/GPS reference with an inertial system in the
survey tool through
a semi-automated or automated process that can operate both at high latitude
and on a
moving surface (e.g., a moving off-shore drilling rig). For example, some
embodiments
enable the movement of a wellbore tool in a controlled manner (e.g., at a
controlled rate) with
respect to the wellbore (e.g., through an automated or semi-automated process)
and while the
tool is in continuous mode after determining an initial orientation (e.g.,
using a GPS system).
[0037] In general, a wellbore survey tool (e.g., a gyro survey tool)
may be
operated under at least the following categories of conditions:
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(1) Operation from a fixed, non-moving platform at limited borehole
inclination. In such
conditions, for example, one approach is to use a two axis (xy) gyro system to
conduct static gyro-compassing surveys. In addition, continuous surveys may be
initiated (e.g., using gyro-compassing) and conducted over the whole, or
sections, of
the wellbore.
(2) Operation in high inclination boreholes from a fixed platform. Under these
conditions, for example, one approach is to use a three axis (xyz) gyro system
to
conduct static gyro-compassing surveys. In addition, continuous surveys may be
initiated (e.g., using gyro-compassing) and conducted over the whole, or
sections, of
the wellbore.
(3) Operation at high latitude from a fixed platform. Here, continuous surveys
may be
used as the survey tool passes along the wellbore. The survey may be initiated
(e.g.,
an initial orientation may be determined), at the surface using techniques
described
herein (e.g., using satellite navigation such as GPS) in accordance with
embodiments
herein. In certain embodiments, satellite navigation techniques may be used in
conjunction with an inertial navigation system (INS) (e.g., a joint GPS/INS
system, or
a stand alone inertial navigation system) which can address issues such as
satellite
signal non-availability or shielding described herein.
(4) Operation on or from a moving surface (e.g., on or from an off-shore
drilling rig). In
such conditions, and in accordance with embodiments described herein,
continuous
surveys may be used throughout the wellbore. The survey may be initiated
(e.g., an
initial orientation may be determined) at the surface using satellite
navigation. In
certain embodiments, satellite navigation techniques may be used in
conjunction with
an inertial navigation system (INS) (e.g., a joint GPS/INS system, or a stand
alone
inertial navigation system) which can address issues such as satellite signal
non-
availability or shielding as described herein, and to aid transfer of
satellite reference
data to the survey tool. Angular matching techniques described herein may also
be
used to improve the accuracy of the survey.
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[0038] In certain embodiments, an apparatus (e.g., a rigid
platform structure) is
configured to be attached to a wellbore surveying tool and to be moved between
multiple
positions on a drilling rig. The apparatus can be configured to allow for
accurate
initialization of the survey measurement system within the wellbore survey
tool. The
apparatus may be configured to enable the transfer of relatively precise
orientation (e.g.,
attitude and/or azimuth) data to a directional survey system in the wellbore
survey tool for
drilling operations, such as drilling operations at high latitude locations on
the Earth, or when
operating off-shore from a moving drilling rig.
[0039] Certain embodiments described herein provide a
relatively precise
determination of the orientation of a wellbore survey tool (e.g., attitude,
azimuth and/or
heading reference) at the surface which does not use gyro-compassing. In
certain
embodiments, this orientation information may be transferred to an inertial
system in the
survey tool. This technique can be performed by devices that generally operate
independently of the instrumentation and equipment within the survey tool.
This independent
orientation determination may be performed, for example, based on established
land
surveying methods (e.g., fore-sighting) or the use of satellite based
information (e.g., using
GPS technology), and/or using inertial navigation systems (e.g., using an
attitude and heading
reference system (AHRS) unit). Once the orientation (e.g., attitude and/or
azimuth) data is
transmitted to the survey tool, a continuous survey procedure can be initiated
which involves
the integration of gyro measurements as the survey tool is placed in a bore-
hole and as it
traverses the well path. This continuous surveying process is generally
initiated or initialized
by the orientation data (e.g., attitude, azimuth, and/or heading data) derived
at the surface.
[0040] To enable these functions while avoiding potential
problems that can occur
when surveying underground bore-holes, apparatus (e.g., platform structures)
as described
herein can be moved to a drilling rig generally anywhere in the world where it
can be set up
to accommodate the various items of equipment used to perform the orientation
determination (e.g., attitude, azimuth and/or heading reference
determination). These
apparatus may comprise rigid platform structures, be of relatively low weight,
and may be
capable of being mounted generally rigidly on the drilling rig at a
location(s) alongside or
close to the well head.
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[0041] The apparatus described herein can include fixturing (e.g., one
or more
mounts) to allow both independent surface reference equipment (e.g., a
directional reference
system such as a GPS receiver with two or more antennae) and the survey tool
to be mounted
(e.g., relatively rigidly) on or within the apparatus. In certain embodiments,
the apparatus can
be levelled and the orientation of the survey tool can be aligned relatively
precisely to a
reference direction defined on the platform by the surface reference equipment
(e.g., defined
by the relative positioning of two or more antennae in the case of a GPS
reference). In one
embodiment, a GPS receiver is capable of determining the direction of the line
joining two
antennae of the GPS receiver with respect to true north. In this situation,
the azimuth angle
defined by the GPS (e.g., the angle of the line joining the two antennae with
respect to true
north) can be transferred to the survey tool. Inclination and tool-face angle
of the survey tool
can additionally be determined based on measurements provided by the survey
tool (e.g., by
one or more accelerometers within the survey tool). The initial orientation
(e.g., azimuth,
inclination and tool-face angles) can be thereby determined and used to
initialize the
subsequent integration process (e.g., during continuous surveying) that can be
implemented
within the tool for keeping track of bore-hole direction as the tool moves
along its trajectory.
In general, the orientation information can be made available independent or
regardless of the
latitude of the drilling platform.
B. Initialization of the Survey Tool at High Latitudes
[0042] Figure 2 schematically illustrates an example apparatus 10 for
initializing
a wellbore survey tool 30 in accordance with certain embodiments described
herein. In
certain embodiments, the apparatus 10 comprises a base portion 12 and a first
mounting
portion 14 mechanically coupled to the base portion 12. The first mounting
portion 14 of
certain embodiments is adapted to be mechanically coupled to at least one
directional
reference system 16. The at least one directional reference system 16 can be
configured to
provide data indicative of an orientation (e.g., attitude and/or azimuth) of
the at least one
directional reference system 16 with respect to a reference direction 18. The
reference
direction 18 may be north (e.g., true or rotational north or magnetic north).
In certain
embodiments, the apparatus 10 further comprises a second mounting portion 20
mechanically
coupled to the base portion 12. The second mounting portion 20 may be
configured to be
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mechanically coupled to the wellbore survey tool 30 such that the wellbore
survey tool 30 has
a predetermined orientation with respect to the at least one directional
reference system 16.
For example, as shown in Figure 2, the survey tool 30 may be substantially
parallel to the
directional reference system 16. In other embodiments, the survey tool 30 may
be oriented at
some predetermined angle relative to the directional reference system 16, or
may be oriented
in some other predetermined fashion with respect to the directional reference
system 16.
[0043] As shown in Figure 2, the base portion 12 may comprise a
substantially
rigid, generally rectangular platform structure including a generally planar
surface 13. In
other embodiments, the base portion 12 may have a different shape (e.g.,
circular, ovular,
trapezoidal, etc.), may be somewhat flexible, and/or may include one or more
inclined
surfaces, declined surfaces, stepped portions, etc.
[0044] In certain embodiments, the base portion 12 comprises carbon
fiber. In
other configurations, the base portion 12 may comprise another material such
as steel, other
metal, or a polymer or plastic material. In certain embodiments, the first
mounting portion 14
comprises an area of the base portion 12 on which the directional reference
system 16 can be
mounted. In some embodiments, the first mounting portion 14 comprises one or
more
fixtures (e.g., mounting faces or blocks) or cut-outs into which the
directional reference
system 16 may be fitted. In various embodiments, the directional reference
system 16 is
releasably secured to the first mounting portion 14. For example, the first
mounting portion
14 may include one or more straps, clamps, snaps, latches, threaded posts or
sockets, etc., for
mounting the directional reference system 16. In addition, the directional
reference system
16 may include one or more mounting features which are configured to be
coupled to
corresponding mating features on the first mounting portion 14. In other
embodiments, the
directional reference system 16 and the first mounting portion 14 may be
generally
permanently coupled (e.g., welded or glued together). In certain
configurations, the first
mounting portion 14 comprises or forms a part of a shelf structure which is
mounted on or
above the base portion 12.
[0045] The first mounting portion 14 may also include one or more ports
(not
shown) (e.g., electrical ports) for operatively coupling the directional
reference system 16 to
the apparatus 10. For example, the ports may enable electrical communication
between the
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directional reference system 16 and the apparatus 10 or components thereof. In
certain other
embodiments, the directional reference system 16 is not in direct
communication with or
otherwise operatively coupled to the apparatus 10 but is in communication with
one or more
systems or subsystems physically separate from the apparatus 10. Such systems
or
subsystems may themselves be in communication with the apparatus 10 or
components
thereof
[0046] In certain embodiments, the at least one directional reference
system 16
comprises at least one signal receiver of a global positioning system (GPS).
For example, the
at least one signal receiver may comprise a first antenna 22 and a second
antenna 24 spaced
apart from the first antenna 22. In certain such embodiments, the first
antenna 22 and the
second antenna 24 define a line 26 from the first antenna 22 to the second
antenna 24. In
certain embodiments more than two antennae may be used. In certain
embodiments, the at
least one signal receiver further comprises a processor (not shown) configured
to receive
signals from the first and second antennae 22, 24 and to determine an
orientation of the line
26 with respect to the reference direction 18. For example, the processor may
be configured
to determine an attitude or azimuth of the directional reference system 16
with respect to the
reference direction 18. In certain embodiments, the attitude or azimuth
determination is
relatively precise. For example, the determination can be within about 0.2
degrees in some
embodiments. In other embodiments the determination may be more or less
precise. In
certain embodiments, the first mounting portion 14 comprises a first antenna
mount 28 to be
mechanically coupled to the first antenna 22 and a second antenna mount 29 to
be
mechanically coupled to the second antenna 24.
[0047] In certain other embodiments, the at least one signal receiver
may be a
non-GPS signal receiver. For example, the at least one signal receiver may be
a signal
receiver of another satellite navigation system (e.g., GLONASS), or some non-
satellite based
navigation or positioning system. As shown, the directional reference system
16, the
components thereof, and the base portion 12 may form one physically integral
unit (e.g., the
generally rectangular unit of Figure 2). In certain other embodiments, the
directional
reference system 16 comprises one or more physically separate units, each
independently
mounted on the base portion 12. For example, in one embodiment, the first
antenna 22 forms
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a first unit to be mounted to the first antenna mount 28 and the second
antenna 24 forms a
second unit to be mounted to the second antennae mount 29 and physically
separate from the
first unit.
[0048] In some embodiments, surveying methods (e.g., optical sighting
methods
such as fore-sighting) may be used an alternative method of defining
determining or defining
the orientation of the platform or a line on the platform with respect to the
reference direction
18. In such embodiments, a directional reference system 16 may not be employed
and
another device, such as a sighting or other surveying device, for example, may
be used to
determine the orientation (e.g., the direction 19 of the apparatus 10) of the
platform or a line
thereon (e.g., a line corresponding to the direction 19 of the apparatus 10)
with respect to the
reference direction 18. Land-surveying techniques (e.g., fore-sighting) may
thus be used to
determine an initial orientation (e.g., attitude and/or azimuth) of the
apparatus 10 or a portion
thereof with respect to the reference direction 18. In certain embodiments,
the orientation
may be determined by optically sighting to a reference object or point at a
known location
with respect to the location of the apparatus 10 (e.g., an oil rig location).
The first mounting
portion 14 of such embodiments may be configured to receive and accommodate
the
surveying device (e.g., a sighting device). The first mounting portion 14 may
comprise
features described above with respect to Figure 2, for example (e.g., one or
more cut-outs,
clamps, snaps, latches, threaded posts or sockets, etc.), but such features
are generally
configured to mount the surveying device instead of the directional reference
system 16.
Data indicative of the initial orientation of the platform (e.g., the
direction 19 of the platform
with respect to the reference direction 18) may then be transmitted to the
survey tool 30. In
one embodiment, the data may be manually entered by an operator into a
computing system
in communication with the survey tool 30 and then be transmitted to the tool
30 (e.g.,
wirelessly). Because the survey tool 30 of certain embodiments is mounted in a
predetermined orientation with respect to the apparatus 10 (e.g., parallel
with the apparatus
10), the orientation of the survey tool 30 can be determined in accordance
with embodiments
described herein.
[0049] The second mounting portion 20 of certain embodiments comprises
an
area of the base portion 12 on which the survey tool 30 is mounted. For
example, the second
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mounting portion 20 may comprise the area or surface 21 of the base portion
12. In some
embodiments, the second mounting portion 20 comprises one or more fixtures or
cut-outs
into which the survey tool 30 may be fitted. In various embodiments, the
survey tool 30 is
releasably secured to the second mounting portion 20. In certain embodiments,
the second
mounting portion 20 comprises one or more mounting faces or blocks. For
example, the
mounting faces may be similar to the mounting faces 46 and can extend from the
base portion
12 and be positioned on the apparatus 10 such that the survey tool 30 abuts
against one or
more surfaces of the mounting faces, thereby securing and/or limiting the
movement of the
survey tool 30 along the base portion 12 in one or more directions. The
mounting faces may
comprise blocks (e.g., rectangular, cylindrical, triangular, etc. shaped
blocks), sheets, and the
like. In certain embodiments, the first mounting portion 14, the third
mounting portion 44
(Figure 4), and/or the fourth mounting portion 53 (Figure 4) can comprise
mounting faces
similar to the mounting faces 46 of the second mounting portion 20 and which
are configured
to secure and/or limit the movement of the directional reference system 16,
the inertial
navigation system 42, and the computing system 52, respectively. The apparatus
10 of Figure
4 includes mounting faces 46 on one side of the survey tool 30. Other
configurations are
possible. For example, in one embodiment, there are mounting faces 46 on the
opposite side
of the survey tool 30 and/or on each end of the survey tool 30.
100501 In various embodiments, the second mounting portion 20 may
include one
or more straps, clamps, snaps, latches, threaded posts or sockets, etc., for
mounting the
survey tool 30. In addition, the survey tool 30 may include one or more mating
features
configured to be coupled to corresponding mating features on the second
mounting portion
20. In some embodiments, the second mounting portion 20 comprises one or more
securing
elements (e.g., straps, clamps, etc.) positioned along the casing of the
survey tool 30 when the
survey tool 30 is mounted. In certain embodiments, the securing elements are
positioned
along one or both of the long sides of the casing of the survey tool 30, at
one or both of the
two ends of the casing of survey tool 30, or a combination thereof. In various
other
embodiments, the securing elements are positioned along only one side, along
one or more of
the ends of the casing of the survey tool 30, or beneath or above the casing
of the survey tool
30. In certain embodiments, the second mounting portion 20 comprises or forms
a part of a
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shelf structure which is mounted on or above the base portion 12. For example,
in one
embodiment, the first mounting portion 14 and the second mounting portion 20
each
comprise separate shelf structures and form a multi-leveled shelf structure on
or over the base
portion 12.
[0051] The second mounting portion 20 may also include one or more
ports (e.g.,
electrical ports) for operatively coupling the survey tool 30 to the apparatus
10. For example,
the ports may enable electrical communication between the survey tool 30 and
the apparatus
or components thereof. In certain other embodiments, the survey tool 30 is not
in direct
communication or otherwise operatively coupled to the apparatus 10, but is in
communication with one or more systems or subsystems physically separate from
the
apparatus 10. Such systems or subsystems may themselves be in communication
with the
apparatus 10 or components thereof.
[0052] The survey tool 30 of certain embodiments can comprises various
sensors
and computing hardware such that it can make use of various measured
quantities such as one
or more of acceleration, magnetic field, and angular rate to determine the
orientation of the
survey tool 30 and of the wellbore with respect to a reference vector such as
the Earth's
gravitational field, magnetic field, or rotation vector. In certain
embodiments, the survey tool
30 is a dedicated survey instrument while, in other embodiments, the survey
tool 30 is a
measurement while drilling (MWD) or logging while drilling (LWD)
instrumentation pack
which may be coupled to a rotary steerable drilling tool, for example.
[0053] Because the line 26 between the two antennae 22, 24 may be
generally
aligned with a direction 19 of the apparatus 10, or the orientation of the
line 26 with respect
to the apparatus 10 may otherwise be known, the line 26 may define, correspond
to, or be
used as the orientation (e.g., direction 19) of the apparatus 10 with respect
to the reference
direction 18. In Figure 2, for example, the line 26 is shown rotated with
respect to the
reference direction 18 (e.g., true north) by angle A. The angle A may define
or be
characterized as the angle (e.g., azimuth angle) of the apparatus 10 with
respect to the
reference direction 18. Moreover, because the survey tool 30 can be aligned
with respect to
the line 26, the angle A can therefore also correspond to the direction (e.g.,
azimuth direction)
of the survey tool 30 with respect to the reference direction 18. The angle A
can thus be
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transmitted (e.g., as electronic data) to the survey tool 30 for the
initialization of the survey
tool 30.
[0054] Loss of satellite telemetry to and/or detected by the
directional reference
system 16 can arise in some conditions. Such loss can occur, for example, due
to shielding of
one or more of the GPS antennae from one or more of the satellites by a
derrick or other
equipment on a rig. In addition, relatively unfavorable positioning of the
satellites that are in
view of the platform can lead to a loss of precision in the orientation (e.g.,
attitude and/or
azimuth) determination process. This loss of precision may be referred to as
the geometric
dilution of precision, for example. Figure 3 schematically illustrates the
apparatus 10
according to certain embodiments described herein in a first location 32 on a
drilling rig 35
having a relatively clear communication path between the antennae 22, 24 and
the GPS
satellites 36, 38, and in a second location 34 at which one or more of the
antennae 22, 24 are
shielded from communication with one or more GPS satellites 36, 38 by the
derrick 31. As
illustrated by the dotted lines, the apparatus 10 to which the survey tool 30
is to be mounted
for initialization is in clear view of the satellites 36, 38 in the first
location 32 when spaced
from the derrick 31 by a first distance 40. As such, a relatively clear
communication path
may exist between the antennae 22, 24 and the satellites 36, 38. On the other
hand, when
located directly under the derrick 31 in the second position 34, the derrick
31 may block or
otherwise interfere with communications from the satellites 36, 38 to the
antennae 22, 24,
and there may no longer be a relatively clear communication path between the
antennae 22,
24 and the satellites 36, 38. As such, satellite telemetry to and/or detected
by the directional
reference system 16 may be interrupted. In the example configuration of Figure
3,
communications from the satellites 36, 38 to the antennae may be similarly
interrupted when
the apparatus 10 is in other positions, such as when the apparatus 10 is
positioned to the left
of the derrick 31. The distance 40 may generally be selected so as to ensure a
relatively clear
communication path between the antennae 22, 24 and the satellites 36, 38. For
example, the
distance 40 may range from 5 to 10 meters in certain embodiments. In other
embodiments,
the distance 40 can be less than 5 meters or greater than 10 meters.
[0055] It can be beneficial to have the capability to move the
apparatus 10 (e.g.,
along the surface of a rig) between the first location 32 where the effect of
signal shielding is
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small (e.g., where the apparatus 10 is spaced apart from the drilling derrick
31) and the
second location 34, where the survey tool 30 may be inserted into the wellbore
but where the
satellite telemetry may be compromised. In certain embodiments, an orientation
of the
directional reference system 16 and/or survey tool 30 may be accurately
obtained at the first
location 32 without substantial obstruction or other interference from the
derrick 31, or from
other sources. In addition, it is desirable to be able to keep track of the
relative orientation of
the apparatus 10 or components thereof as it moves from the first location 32
to the second
location 34. As such, deviations from the at the first location 32 may be
tracked while the
apparatus 10 is moved to the second location 34, thereby maintaining an up-to-
date
orientation (e.g., attitude, azimuth, and/or heading) of the apparatus and
components thereof
during movement. As described herein, an inertial navigation system may be
used for such
purposes.
[0056] Figure 4 schematically illustrates an example apparatus 10 in
accordance
with certain embodiments described herein. The apparatus 10 of certain
embodiments
includes a third mounting portion 44 mechanically coupled to the base portion
12. The third
mounting portion 44 is configured to be mechanically coupled to at least one
inertial
navigation system 42. In certain embodiments, the third mounting portion 44
comprises an
area of the base portion 12 on which the inertial navigation system 42 is
mounted. In some
embodiments, the third mounting portion 44 comprises one or more fixtures or
cut-outs into
which the inertial navigation system 42 may be fitted. In various embodiments,
the inertial
navigation system 42 is releasably secured to the third mounting portion 44.
For example,
the third mounting portion 44 may include one or more straps, clamps, snaps,
latches, or
threads, etc. for mounting the inertial navigation system 42. In addition, the
inertial
navigation system 42 may include one or more mating features configured to be
coupled to
corresponding mating features on the third mounting portion 44. In other
embodiments, the
inertial navigation system 42 and the third mounting portion 44 may be
generally
permanently coupled (e.g., welded or glued together). In certain embodiments,
the third
mounting portion 44 comprises or forms a part of a shelf structure which is
mounted on or
above the base portion 12. For example, in one embodiment, the third mounting
portion 44
and one or more of the first mounting portion 14 and the second mounting
portion 20 may
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each comprise separate shelves and form a multi-leveled shelf structure on or
over the base
portion 12.
[0057] The third mounting portion 44 may also include one or more ports
(e.g.,
electrical ports) for operatively coupling the inertial navigation system 42
to the apparatus 10.
For example, the ports may enable electrical communication between the
inertial navigation
system 42 and the apparatus 10 or components thereof. In certain other
embodiments, the
inertial navigation system 42 is not in direct communication or otherwise
operatively coupled
to the apparatus 10, but is in communication with one or more systems or
subsystems
physically separate from the apparatus 10. Such systems or subsystems may
themselves be in
communication with the apparatus 10 or components thereof.
[0058] The inertial navigation system 42 generally provides the
capability of
maintaining the heading or orientation information obtained at the first
location 32 while the
apparatus 10 is moved from the first location 32 (e.g., on a rig from the
first location 32 to the
second location 34). The inertial navigation system 42 may comprise an
attitude and heading
reference system (AHRS), for example, and may be used to keep track of the
orientation of
the apparatus 10 and components thereon (e.g., attitude and/or azimuth) during
movement of
the apparatus 10 (e.g., from the first location 32 to the second location 34
of Figure 3). For
example, the inertial navigation system 42 may keep track of the orientation
(e.g., attitude,
azimuth, and/or heading) during movement of the apparatus 10 should the
performance of the
directional reference system 16 become compromised (e.g., the antennae of a
GPS system are
obscured from the satellite by the derrick 31 on a rig) or cannot be used to
determine the
orientation of the apparatus at the well head of the wellbore. In other
embodiments, other
types of inertial navigation systems, such as a full inertial navigation
system (INS) may be
used. In some embodiments, the directional reference system 16 or components
thereof and
the inertial navigation system 42 may be integrated into a single unit (e.g.,
a GPS/AHRS
unit).
[0059] Figure 5 schematically illustrates a top view of an apparatus 10
including
an integrated GPS/AHRS unit 43 in accordance with certain embodiments
described herein.
Referring again to Figure 4, the inertial navigation system 42 may comprise a
processor and
one or more motion sensors (e.g., accelerometers) positioned within the
GPS/AHRS unit 43
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and may be configured to generally continuously calculate the position,
orientation, and/or
velocity of the apparatus 10 as it is moved.
[0060] As shown in Figure 4, the second mounting portion 20 of certain
embodiments may comprise one or more mounting faces 46 which are described in
detail
above with respect to Figure 2.
[0061] The apparatus 10 further comprises at least one leveler 48
configured to
level the apparatus 10 with respect to the Earth (e.g., to be substantially
perpendicular to the
direction of gravity). The at least one leveler 48 may comprise a set of one
or more
adjustable supports, for example. Various adjustment mechanisms are possible.
For example,
in one embodiment, the leveler 48 comprised a retractable portion (e.g., a
threaded rod)
which can be used to lengthen or shorten the leveler 48 (e.g., by extending
from and
retracting into the base portion 12). In another embodiment, the leveler
comprises an
expandable portion (e.g., a balloon or other fillable member) which can be
inflated and
deflated to adjust the length of the leveler to level the apparatus 10 with
respect to the Earth.
The apparatus 10 of Figure 4 comprises three levelers 48 (one of which is not
shown) shaped
as cylindrical support posts. One leveler 48 is attached to the underside of
one corner of the
base portion 12, one leveler 48 is attached to the underside of a neighboring
corner of the
base portion 12, and one leveler 48 (not shown) is attached to the center of a
side between
two other corners of the base portion 12. In some embodiments, the at least
one leveler 48
comprises an elongate leg portion attached to the base portion 12 and a foot
portion which
contacts the surface beneath the apparatus 100. The foot portion of certain
embodiments is
generally widened with respect to the leg portion and may be attached to the
bottom of the leg
portion. In one embodiment, there are four levelers 48, each attached to the
underside of one
of the four corners of the base portion 12. In another embodiment, the
levelers 48 comprise a
set of elongate members each attached to and extending laterally from a side
of the base
portion 12, and extending downwards to make contact with the surface beneath
the apparatus
10. In yet other embodiments, the at least one leveler comprises one or more
rails extending
along the underside of the base portion 12. In other embodiments, there may be
one leveler
48, two levelers 48, or more than three levelers 48 and/or the levelers 48 may
be shaped or
configured differently (e.g., as rectangular posts, blocks, hemispherical
protrusions, etc.).
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[0062] In addition, the apparatus 10 may further comprise at least one
level
detector 50 configured to generate a signal indicative of the level or tilt of
the apparatus 10
with respect to the Earth. In certain such embodiments, the at least one
leveler 48 is
configured to level the apparatus 10 with respect to the Earth in response to
the signal from
the at least one level detector 50. For example, the level detector 50 may
comprise a bubble-
type level detector, or some other type of level detector. In certain
embodiments, the
apparatus 10 may include one or more supports which are not adjustable. In
certain other
embodiments (e.g., where the apparatus 100 does not include a leveler 48), the
signal from
the at least one level detector 50 may be used to adjust computations, such as
computations
regarding the orientation of the apparatus 10, components thereof (e.g., the
directional
reference system 16), or the survey tool 30. For example, the signal may be
used to
compensate for any level differences between the apparatus 10 and the Earth in
such
computations. In general, the at least one level detector 50, in conjunction
with the at least
one leveler 48 can be configured to detect tilt of the apparatus 10 and
physically level the
apparatus 10 in response to such tilt.
[0063] In certain embodiments, the apparatus 10 further comprises at
least one
member (not shown) movably coupled to a portion of the apparatus 10 and
configured to
allow the apparatus 10 to move along a surface beneath the apparatus 10. The
surface may be
the Earth's surface, a rig surface, etc. In certain embodiments, the at least
one member
comprises at least one wheel configured to rotate about at least one axis. In
other
embodiments, the at least one member may comprise a tread, ski, or other
mechanism
configured to allow for movement of the apparatus 10 along the surface. For
example, in one
embodiment the apparatus 10 comprises four with each wheel positioned near a
corresponding one of the four corners of the base portion 12. The at least one
member may
be extendable/retractable such that it can be extended towards the surface
(e.g., away from
the base portion 12) for use and can be retracted away from the surface (e.g.,
towards the base
portion 12) when the at least one member is not in use. For example, in one
embodiment, the
at least one member comprises a set of wheels which can be extended from a
first position in
which the wheels are not in contact with the surface to a second position in
which the wheels
are in contact with the surface for moving the apparatus 10 along the surface.
The wheels can
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then be raised from the second position back to the first position, such as
when the apparatus
has reached the desired destination. The raising of the wheels can allow for
relatively
improved stability of the apparatus 10 on the surface in certain embodiments
(e.g., while
survey tool is being initialized). In other embodiments, the at least one
member is not
retractable and is in continuous contact with the surface. In various
configurations, generally
any number of members (e.g., 1, 2, 3, 4, 5, or more) may be employed.
[0064] In certain embodiments, the apparatus 10 further comprises a
computing
system 52. In certain embodiments, the computer may be in communication with
the
directional reference system 16 (e.g., as indicated by arrow 47), the inertial
navigation system
42 (e.g., as indicated by arrow 45), and/or the survey tool 30 (e.g., as
indicated by arrow 49).
For example, the computing system 52 may receive data indicative of the
orientation of the
apparatus 10 with respect to the reference direction 18 from the directional
reference system
16. The computing system 52 may also receive information from the inertial
navigation
system 42, such as information regarding the position, orientation, and/or
velocity of the
apparatus 10 as it moves along the surface beneath the apparatus 10. The
computing system
52 may further be configured to process the information from the directional
reference system
16 and/or the inertial navigation system 42 to determine an initial
orientation of the survey
tool 30. The computing system 52 may further be configured to transmit such
information to
the survey tool 30 in some embodiments. In other embodiments, the computing
system 52
may transmit the data from the directional reference system 16 and/or the
inertial navigation
42 directly to the survey tool 30 for at least some of the processing instead
of performing the
processing of the data itself. In some embodiments, there is no computing
system 52, and the
survey tool 30 receives the data directly from the directional reference
system 16 and the
inertial navigation system 42 and processes the data itself.
[0065] The apparatus 10 may further comprise a fourth mounting portion
53. The
fourth mounting portion 53 comprises an area of the base portion 12 on which
the computing
system 52 is mounted. In some embodiments, the fourth mounting portion 53
comprises one
or more cut-outs or fixtures onto which the computing system 52 may be fitted.
In various
embodiments, the computing system 52 is releasably secured to the fourth
mounting portion
53. For example, the fourth mounting portion 53 may include one or more
straps, clamps,
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snaps, latches, or threads, etc. for mounting the computing system 52. In
addition, the
computing system 52 may include one or more mating features configured to be
coupled to
corresponding mating features on the fourth mounting portion 53. In other
embodiments, the
computing system 52 and the fourth mounting portion 53 may be generally
permanently
coupled (e.g., welded or glued together). In certain embodiments, the fourth
mounting
portion 53 comprises or forms a part of a shelf structure which is mounted on
or above the
base portion 12. For example, in one embodiment, the fourth mounting portion
53 and one or
more of the first mounting portion 14, the second mounting portion 20, and the
third
mounting portion 44 may each comprise separate shelves and form a multi-
leveled shelf
structure on or over the base portion 12.
[0066] The fourth mounting portion 53 may also include one or more
ports (e.g.,
electrical ports) for operatively coupling the computing system 52 to the
apparatus 10. For
example, the ports may enable electrical communication between the computing
system 52
and the apparatus 10 or components thereof
[0067] In certain embodiments, the apparatus 10 further comprises a
tool
positioning element 56. Figures 6A-6C schematically illustrate top, front and
right side
views, respectively, of an apparatus 10 including a tool positioning element
56. The tool
positioning element 56 can be configured to controllably move the wellbore
survey tool 30
between a first position relative to the apparatus 10 and a second position
relative to the
apparatus 10. In certain embodiments, the first position is horizontal with
respect to the base
portion 12 and the second position is vertical with respect to the base
portion 12. In other
embodiments, the survey tool 30 may be positioned at an angle relative to the
base portion 12
in one or more of the first and second positions. hi certain embodiments, the
tool positioning
element 56 comprises a motorized system such as a motor drive 60. The tool
positioning
element 56 may be configured to rotate the surface 21 of the second mounting
portion 20 to
which the survey tool 30 can be coupled and which can be rotated (e.g., using
the motorized
drive 60 or another motorized system) with respect to the base portion 12 from
horizontal to
vertical so as to move the survey tool 30 between the first position and the
second position.
In other embodiments, the tool positioning element 56 comprises a pulley
system (e.g., a
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motorized pulley system) for lifting and lowering the survey tool 30 between
the first position
and second position, or some other mechanism for moving the survey tool 30.
[0068] Figure 6D schematically illustrates a partial perspective view
of an
apparatus 10 including a tool positioning element 56 during positioning of a
survey tool 30 in
accordance with certain embodiments described herein. The drive motor 60 of
the apparatus
of Figure 6D is visible through the base portion 12 for the purposes of
illustration. As
indicated by the directional arrow 25, the tool positioning element 56 is
movable between a
first (e.g., horizontal) position and a second (e.g., vertical position). The
tool positioning
element 56 may, in certain embodiments, controllably move or rotate the survey
tool 30 in
inclination while it is attached or otherwise coupled to the apparatus 10. The
survey tool 30
is shown in Figure 6D during movement of the survey tool 30 by the positioning
element 56
between the first and second positions such that the survey tool 30 is
currently positioned at
an angle B with respect to surface 13 of the apparatus 10. As shown, the drive
motor 60 of
the positioning element 56 is configured to controllably move the surface 21
to which the
survey tool 30 can be generally rigidly attached about the axis 66 between the
first and
second position.
[0069] In one example scenario, the tool positioning element moves the
survey
tool 30 is mounted to the apparatus 10 in a generally vertical orientation,
while the surface 21
is positioned by the tool positioning element 56 in a generally vertical
orientation with
respect to the surface 13 of the base portion 12. The surface 21 and survey
tool 30 mounted
thereon are then rotated by the positioning element 56 such that the surface
21 and survey
tool 30 are generally horizontal or flush with respect to the surface 13 of
the base portion 12.
The survey tool 30 may be initialized using the initialization process
described herein while
in the horizontal position. The survey tool 30 may then be rotated back to the
vertical
position by the tool positioning element 56 and then disconnected or un-
mounted from the
apparatus 10 at which point the survey tool 30 may be supported by a wire line
58, for
example and lowered into the well bore.
[0070] In other embodiments, the survey tool 30 is not rotated to
horizontal, but is
rotated to some other angle with respect to the apparatus 10 (e.g., 15
degrees, 30 degrees, 45
degrees, 60 degrees, etc.). In addition, the survey tool 30 may not be rotated
to a complete
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vertical position, but to some other angle with respect to the apparatus 10.
In other
embodiments, the apparatus 10 does not include a positioning element 56. In
such
embodiments, the survey tool 30 may be mounted generally in the orientation
(e.g., vertical
with respect to the surface 13 of the apparatus 10) in which the apparatus 10
will be deployed
to the well bore. In addition, the positioning element 56 may be positioned or
mounted
differently on the apparatus 10. For example, the motor drive 60 and
corresponding axis 66
are shown positioned generally in the middle cut-out portion 23 in Figure 6D.
As such, when
the survey tool 30 is positioned in the vertical position, half of the survey
tool 30 is
positioned substantially above the base portion 12 and the other half of the
survey tool 30 is
positioned above the base portion 12. In other embodiments, the corresponding
motor drive
60 axis 66 may be positioned differently, such as generally at one end of the
cut-out portion
23. In some such cases, the positioning element 56 may rotate the survey tool
30 generally
from a horizontal position to a vertical position in which a survey tool 30 or
a substantial
portion thereof is rotated under the base portion 12. In other such cases, the
positioning
element may rotate the survey tool 30 generally from a horizontal position to
a vertical
position in which a survey tool 30 or a substantial portion thereof is rotated
above the base
portion 12.
[0071] It is desirable to move (e.g., rotate) the tool at a relatively
low rate (e.g.,
within the rate limits of the gyroscopes on the survey tool 30). Certain
embodiments
advantageously avoid turning of the survey tool 30 undesirably high turn rates
which exceed
the maximum rates which can be measured by one or more rotation sensors (e.g.,
gyroscopes)
of the survey tool 30. Under such undesirable conditions, the orientation data
(e.g.,
directional reference data) stored in the survey tool 30 can be lost and
subsequent orientation
(e.g., attitude and/or azimuth) processing will be in error. By controllably
moving the survey
tool 30 (e.g., using the drive motor 60 about the axis 66), the tool
positioning element 56
may, in certain embodiments, avoid saturation of sensors of the survey tool 30
and thereby
allow the survey tool 30 to continue to keep track of its rotation as it is
moved.
100721 In an example use scenario, the apparatus 10 can be location at
a position
at which the directional reference system 16 is operational and the reference
direction 18 may
be determined using the directional reference system 16 (e.g., a GPS signal
receiver). The
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apparatus 10 may then be moved physically to the well head of the wellbore
(e.g., using the at
least one member movably coupled to a portion of the apparatus 10) with the
orientation or
directional reference being maintained, monitored, or detected by the inertial
navigation
system 42 (e.g., an AHRS unit) while the apparatus 10 is moved. In certain
embodiments,
this movement occurs over a relatively short period of time (e.g., on the
order of several
minutes). Once positioned at the well head, the survey tool 30 may be placed
into a
designated position (e.g., to the second mounting portion 20) and clamped to
the apparatus
10. The orientation data (e.g., attitude, azimuth and/or heading data) may
then be transmitted
from the inertial navigation system 42 (e.g., an AHRS) to the wellbore survey
tool 30 to
initialize the survey tool 30. For example, the orientation data may be
transmitted to an
inertial system within the survey tool 30 via the computing system 52 or,
alternatively,
directly to the wellbore survey tool 30. In certain other embodiments, the
survey tool 30 is
mounted on to the apparatus 10 while the apparatus 10 is moved from the first
position to the
second position.
[0073] Figure 7 schematically illustrates an embodiment in which the
directional
reference system 16 is mounted directly on the wellbore survey tool 30 in
accordance with
certain embodiments described herein. The directional reference system 16
comprises at
least one signal receiver of a global positioning system (GPS) which can
include a first
antenna 22 and a second antenna 24 spaced apart and defining a line 26 from
the first antenna
22 to the second antenna 24. In certain embodiments, the survey tool 30
comprises a
processor 54 configured to receive signals from the first and second antennae
22, 24 and to
determine an orientation of the line 26 with respect to the reference
direction in response to
the signals. Because a processor 54 of the survey tool 30 may be used instead
of a dedicated
processor of the directional reference system 16, hardware costs may thereby
be reduced. In
addition, because the directional reference system 16 may be directly mounted
on the survey
tool 30, there may be less calibration inaccuracy due to possible
misalignments in the
orientation of the directional reference system 16 with respect to the survey
tool 30. In other
embodiments, the directional reference system 16 comprises a processor which
is used to
determine the orientation and a processor of the survey tool 30 is not used.
For example, the
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processor 53 may be configured to determine an orientation (e.g., attitude
and/or azimuth) of
the directional reference system with respect to the reference direction.
[0074] Where the directional reference system 16 (e.g., a GPS signal
receiver
comprising the two or more antennae 22, 24) is mounted on or within the survey
tool 30
itself, as illustrated in Figure 7, the survey tool 30 itself can be mounted
relatively rigidly on
the drilling rig (e.g., in a horizontal or other non-vertical orientation) to
conduct the
initialization process (e.g., initial attitude and heading determination). For
example, the
orientation (e.g., attitude) determination may be made using measurements of
the phase
difference in the satellite carrier signals (e.g., between the antennae 22,
24). Such a
determination may be made by computation by the processor 54 within the survey
tool 30, for
example. This information may again be used to define the initial attitude of
the survey tool
30 prior to engaging or initializing a continuous survey mode. The attitude
data (e.g., data
derived from GPS data from the directional reference system 16) can form the
initial
conditions for the gyro measurement integration process, which allows for
tracking of the
attitude of the survey tool 30 after the initialization.
[0075] In certain embodiments, the apparatus 10 further comprises at
least one of
the at least one directional reference system 16 and the at least one inertial
navigation system
42. In certain embodiments in which the apparatus comprises the at least one
directional
reference system 16, the apparatus 10 further comprises a mounting portion
(e.g., one or more
portions of the base portion 12, the first mounting portion 14, the second
mounting portion
20, the third mounting portion 44, and the fourth mounting portion 53)
mechanically coupled
to the at least one directional reference system 16 and configured to be
mechanically coupled
to the wellbore survey tool 30 while the wellbore survey tool 30 is outside a
wellbore such
that the wellbore survey tool 30 has a predetermined orientation with respect
to the at least
one directional reference system 16 while the wellbore survey tool 30 is
outside the wellbore.
The mounting portion may be further configured to be mechanically decoupled
from the
wellbore survey tool 30 while the wellbore survey tool 30 is within the
wellbore. The
apparatus 10 may further comprise a support structure configured to allow the
apparatus to
move along a surface beneath the apparatus while the wellbore survey tool 30
is transported
outside the wellbore. For example, in certain embodiments, the support
structure may
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comprise one or more of the base portion 12, the at least one member movably
coupled to a
portion of the apparatus 10, the at least one leveler 48, or portions thereof,
as described
herein.
[0076] Embodiments described herein may further be used to provide a
relatively
long term attitude reference on the drilling rig. As discussed, after
initialization of the survey
tool 30 according to embodiments described herein, the survey tool 30 may be
deployed into
the wellbore and used to conduct a survey (e.g., in continuous survey mode).
In certain cases,
the survey tool 30 may have been initialized accurately according to
embodiments described
herein prior to deployment, but calibration errors may accumulate during
operation, thereby
causing "drift." Such calibration errors may be acceptable under certain
circumstances (e.g.,
where the drift of less than about 10%). However, relatively large calibration
errors can be
problematic and it can be desirable to measure such errors. In certain
embodiments, after
withdrawal of the survey tool 30 from the wellbore, the survey tool 30
orientation (e.g.,
attitude) determined by the survey tool 30 can be compared to a reference
orientation (e.g.,
attitude) determined by the apparatus 10 to can provide a post-survey check on
the calibration
or amount of drift of the survey tool 30. For example, the survey tool 30 may
be mounted to
the apparatus 10 following its withdrawal from the wellbore and readings of
the orientation
(e.g., attitude) of the survey tool 30 from the survey tool 30 may be compared
to readings of
the orientation (e.g., attitude) from the directional reference system 16. In
certain other
embodiments, the orientation readings from the survey tool 30 may be compared
to readings
from the orientation of the inertial navigation system 42, or from an
integrated device such as
the GPS/AHRS 43 of Figure 5. Differences in orientation determined from such a
comparison may correspond to calibration errors or "drift." This general
process may be
described as a quality control (QC) check on the 'health' of the survey tool
30, for example.
[0077] Figure 8 is a flow diagram illustrating an example wellbore
survey tool 30
initialization process 100 in accordance with certain embodiments described
herein. While
the flow diagram 100 is described herein by reference to the apparatus 10
schematically
illustrated by Figures 2-6, other apparatus described herein may also be used
(e.g., the
apparatus 400 of Figure 11). At operational block 102, the survey tool 30 can
be suspended
above the base portion of the apparatus 10, such as by a wire-line, for
example. The
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apparatus 10 may then be leveled at operational block 104 by adjusting one or
more of the at
least one levelers 48 (e.g., an adjustable support), for example.
[0078] At operational block 106, the directional reference system 16
(e.g., GPS
receiver, integrated GPS/AHRS) and/or inertial navigation system 42 may be
initiated and
may generate one or more signals indicative of the orientation (e.g., the
attitude, azimuth,
and/or heading) of the apparatus 10. At operational block 108, the apparatus
10 may be
moved to the well head of the wellbore. This movement of the apparatus 10 may
be
performed in situations where the apparatus 10 has initially been positioned
away from the
wellbore, to avoid interference from a derrick, for example. The survey tool
30 may be
lowered and attached to the apparatus 10 (e.g., clamped to the second mounting
portion 20) at
operational block 110. The survey tool 30 may be rotated to the horizontal
(e.g., with respect
to the base portion 12 of the apparatus 10) at operational block 112 and power
may be
supplied to the survey tool 30 at operational block 114.
[0079] At operational block 116, the orientation (e.g., attitude,
azimuth, and/or
heading) data from the directional reference system 16, inertial navigation
system 42, or both,
may be transferred to the survey tool 30. In some embodiments, an angular rate
matching
process (e.g., using an angular rate matching filter) as described below is
employed. The tool
may be switched to continuous survey mode at operational block 118, and moved
(e.g.,
rotated using the tool positioning element 56) to vertical (e.g., with respect
to the apparatus
10) at a controlled rate at operational block 120. The survey tool 30 can be
detached from the
apparatus 10 while still being supported (e.g., by a wire-line) at operational
block 122 and
raised above the apparatus 10 at operational block 124. The survey tool 30 may
be lowered
into the top of the wellbore at operational block 126 and continuous surveying
may be
enabled at operational block 128.
[0080] Figure 9 is a flowchart of an example method 200 of initializing
a
wellbore survey tool 30 in accordance with certain embodiments described
herein. At
operational block 202, the method 200 includes positioning a wellbore survey
tool 30 at a
predetermined orientation relative to a directional reference system 16. For
example, the
wellbore survey tool 30 may be positioned substantially parallel to the
directional reference
system 16 in certain embodiments. While the method 200 is described herein by
reference to
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the apparatus 10 described with respect to Figures 2-7, other apparatus
described herein may
be used (e.g., the apparatus 400 of Figure 11).
[0081] At operational block 204, the method 200 of certain embodiments
further
comprises generating a first signal indicative of an orientation of the
directional reference
system 16 with respect to a reference direction 18. For example, the first
signal may be
generated by the directional reference system 16, and the reference direction
may be north.
The method 200 may further comprise determining an initial orientation of the
wellbore
survey tool 30 with respect to the reference direction 18 in response to the
first signal at
operational block 206. For example, a computing system 52 of the apparatus 10
may receive
the first signal from the directional reference system 16 and determine the
orientation of the
directional reference system 16 with respect to the reference direction 18 in
response to the
first signal. In certain embodiments, because the wellbore survey tool 30 is
positioned at a
predetermined orientation (e.g., parallel) relative to the directional
reference system 16, the
computing system 52 can also determine the initial orientation of the survey
tool 30 with
respect to the reference direction 18.
[0082] At operational block 208, the method 200 further comprises
moving the
wellbore survey tool 30 from a first position to a second position after
determining the initial
orientation of the wellbore survey tool 30. For example, the wellbore survey
tool 30 may be
substantially horizontal with respect to the Earth when in the first position
and the wellbore
survey tool 30 may be substantially vertical with respect to the Earth when in
the second
position. The tool positioning element 56, (e.g., a motorized system) can be
used to
controllably move the survey tool from the first position to the second
position, as described
herein.
[0083] In some embodiments, the method 200 may further comprise moving
the
wellbore survey tool 30 from a first location 32 to a second location 34
(Figure 3) after
generating the first signal. The first location 32 may be farther from the
wellbore than the
second location 34. As described herein, the directional reference system 16
may be able to
accurately determine the orientation of the directional reference system 16
with respect to the
reference direction 18 at the first location 32. For example, the directional
reference system
16 may comprise a signal receiver of a satellite navigation system which can
communicate
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with satellites of the satellite navigation system free from shielding or
other interference from
the derrick 31 at the first location 32, but not at the second location 34.
The wellbore survey
tool 30 may have a first orientation with respect to the reference direction
18 when at the first
location 32 and a second orientation with respect to the reference direction
18 when at the
second location 34. For example, the orientation of the apparatus 10, and thus
of the
directional reference system 16 and the survey tool 30 coupled to the
apparatus 10, may
change in angle with respect to the reference direction 18 as the apparatus 10
moves from the
first location 32 to the second location 34.
100841 The method 200 may further comprise generating a second signal
indicative of a change in orientation between the first orientation and the
second orientation.
For example, the computing system 52 may receive the second signal from the
inertial
navigation system 42. In certain embodiments, the determining the initial
orientation in the
operational block 206 comprises determining the initial orientation of the
wellbore survey
tool 30 with respect to the reference direction 18 in response to the first
signal and in
response to the second signal. For example, the computing system 52 may
determine the first
orientation of the directional reference system 16 and thus the survey tool 30
at the first
location in response to the first signal. The computing system 52 may then
determine the
change in orientation of the survey tool between the first orientation and the
second
orientation in response to the second signal. The computing system 52 may
further process
the first and second signals (e.g., add the change in orientation to the
initial orientation) to
determine the initial orientation of the survey tool 30 at the second
location.
C. Example Attitude Computation in the Survey Tool
100851 In certain circumstances, the initial orientation data (e.g.,
reference attitude
data determined in accordance with embodiments described herein) form the
initial
conditions for the gyro measurement integration process which can keep track
of survey tool
30 attitude while a continuous survey mode of operation is maintained. During
continuous
periods of operation (e.g., during continuous survey mode), the survey tool 30
may keep track
of attitude (tool face, inclination and azimuth) using the integrated outputs
of the gyroscopes.
Tracking of the attitude may involve solving the following equations to
provide estimates of
tool-face ( a ), inclination ( I) and azimuth (A) angles:
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a = a0 + fet dt ; (Eq. 2)
I = Io + ydt ; and (Eq. 3)
A = A0 + f.=Adt , (Eq. 4)
where a0, 10 and Ao are the initial values of tool face, inclination and
azimuth, and a,
and A are the estimated rates of change of a, 1 and A which may be expressed
as function
of the gyro measurements (denoted Gx, Gy and G,) as follows:
õ cos A
= Gõ +(Gx sin a + Gy cos a )cot / ______
sin/ ; (Eq. 5)
= ¨Gx cos a + G sin a + Q11 sin A; and
(Eq. 6)
sina + G cosa)
A = x +S-2õ cosAcoti¨S2,
sin/ (Eq. 7)
where S2, and f2, represent the horizontal and vertical components of Earth's
rate. The
initial value of the azimuth angle can be derived directly from the GPS
attitude estimation
process. An initial value of inclination may also be derived using the GPS
measurements, or
using survey tool 30 accelerometer measurements (As, Ay, and Aõ) and the
following
equation:
.x 2 4. A y2
arctan ________________________________________________ (Eq. 8)
Aõ
[0086] The initial value of inclination may also be determined using a
combination of both satellite and accelerometer estimates. Tool-face angle is
initialized
using accelerometer measurements as follows:
a0 = arctan Ax
[¨ Al=
D. Example Alternative Method of Computing Attitude
[0087] In accordance with certain embodiments described herein, the use
of
direction cosines allows the tool orientation to be tracked generally at any
attitude, such as
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when the tool is at or near vertical as occurs during tool pick-up and initial
descent in the
wellbore. This allows the methods of keeping track of tool-face angle and
azimuth discussed
in the previous section, which may be relatively imprecise, to be avoided. The
use of the
quaternion attitude representation can provide an alternative in this
situation.
[0088] The
attitude of an alignment structure (e.g., the directional reference
system 16) on the apparatus 10, such as on a platform (P) of the apparatus 10
with respect to
the local geographic reference frame (R) (e.g., the reference direction 18),
which may be
determined from the GPS measurements, may be expressed in term of the
direction cosine
matrix C. . The reference frame R can be generally defined by the directions
of true north
and the local vertical. In certain other configurations, other Earth fixed
reference frames may
be used. The platform (P) may comprise or form a part of the base portion 12,
for example.
Given knowledge of the mounting orientation of the survey tool (7) 30 with
respect to the
alignment structure (e.g., the directional reference system 16), which may
also be expressed
as a direction cosine matrix, , the
attitude of the survey tool 30 with respect to the
geographic reference frame (R) is given by the product of these matrices, as
follows:
CTR = C.: = C7I: (Eq. 9)
[0089] After
switching to continuous survey mode, the survey tool 30 can keep
track of tool attitude as it traverses the wellbore by solving the equation
below. Expressing
C = C7R and the initial value derived from the GPS measurements as CO3
C = Co + fèdt, (Eq. 10)
where
= C = [co x] (Eq. 11)
G x H
CO = G ¨ CT = 0 (Eq. 12)
G _
_ v _
[0090]
Attitude information expressed in terms of tool-face, inclination and
azimuth may be computed, from the elements of the direction cosine matrix:
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_ _
c11 C12 C13
c= C21 C22 C23 /
_C31 C32 C33 _
which may also be expressed as function of these angles as follows:
_
cos Acos I sin a + sin Acos a cos Acos I cos a ¨ sin A sin a cos A sin I-
C = sin a cos I sin a ¨ cos Acos a sin A cos I cos a + cos A sin a sin A sin /
¨ sin /sin a ¨ sin / cos a cos I
- - (Eq. 13)
[0091] In certain embodiments, the tool-face, inclination and azimuth
angles may
be extracted using the following equations:
a = arctan[ ¨ c31 =
¨ C32 _ (Eq. 14)
_ Vc231 __ 32 + C 2 _
I = arctan ; and (Eq. 15)
C33
A = arctan[c231. (Eq. 16)
c13
[0092] For example, using the above equation for inclination for the
situation
where inclination approaches 900, c33 approaches zero and / may become
indeterminate. In
this case, inclination may be expressed as follows:
/ = arccos[c33]. (Eq. 17)
[0093] For the situation where / passes through zero, the equations in
a and A
generally become indeterminate because both the numerator and the denominator
approach
zero substantially simultaneously. Under such conditions, alternative
solutions for a and A
can be based upon other elements of the direction cosine matrix. For example,
a and A can
be determined as follows:
e11 +c22 = sin(a + A) = (c o s I + 1) ; (Eq. 18)
C21 ¨c12 = cos(a + A) = (c o s I + 1) , (Eq. 19)
and the following expression for the sum of azimuth and tool face may be
written:
C
a + A = arctan ell 22 . (Eq. 20)
C21 ¨C12
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This quantity corresponds to the so-called gyro tool-face angle that is
currently computed
while the tool is at or near vertical.
[0094] Separate solutions for a and A may not be obtained when I= 0
because
both generally become measures of angle about parallel axes (about the
vertical), i.e. a degree
of rotational freedom is lost. Either a or A may be selected arbitrarily to
satisfy some other
condition while the unspecified angle is chosen to satisfy the above equation.
To avoid
'jumps' in the values of a or A between successive calculations when I is in
the region of
zero, one approach would be to 'freeze' one angle, a for instance, at its
current value and to
calculate A in accordance with the above equation. At the next iteration, A
would be frozen
and a determined. The process of updating a or A alone at successive
iterations could
generally continue until I is no longer close to zero.
E. Example Attitude Matching Filter for the Transfer of Orientation Data
(e.g., Attitude
and Heading Reference Data) to the Survey Tool
[0095] In certain embodiments, orientation (e.g., attitude) data
extracted from
satellite navigation techniques (e.g., using the directional reference system
16) can be
combined with inertial system data (e.g., from the inertial navigation system
42). For
example, a least-squares or Kalman filtering process can be used determine a
relatively
accurate estimate (e.g., a best estimate) of survey tool 30 orientation (e.g.,
attitude) prior to
engaging/initializing the continuous survey mode. Data which may be determined
while the
survey tool 30 is at the surface includes:
[0096] (1) satellite based estimates of azimuth and inclination (e.g.,
using the
directional reference system 16);
[0097] (2) estimates of inclination and high-side tool-face angle of
the survey tool
30 using accelerometers of the survey tool 30;
[0098] (3) estimates of azimuth, inclination and tool-face angle of the
survey tool
30 using sensors gyroscopes of the survey tool 30;
[0099] An example filtering process is provided herein. Embodiments
described
herein include a Kalman filter formulation that may be used to initialize the
continuous
survey process while the survey tool 30 is at the surface. In certain
embodiments, it may be
assumed that the survey tool 30 provides measurement of acceleration along,
and turn rate
about, the three principal axes of the tool, denoted x, y and z. While
continuous estimates of
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survey tool 30 orientation can be derived from the gyro measurements by a
process of
integration, it may further be assumed that the accelerometer measurements can
provide a
separate and independent estimate of survey tool orientation with respect to
the local vertical.
Further, a satellite attitude determination process (e.g., using the
directional reference system
16) provides estimates of survey tool 30 azimuth during this period. Gyro,
accelerometer and
GPS based attitude estimates can be combined using a Kalman filter as
described below. In
addition to providing initial estimates of tool orientation (e.g., attitude),
the filtering process
may also be used to form estimates of any residual gyro biases and mass
unbalance.
System equations
101001 During periods where the survey tool 30 is in
continuous mode, the tool
keeps track of attitude (e.g., tool face, inclination and azimuth) using the
integrated outputs of
the gyroscopes. This may be achieved by solving the following equations to
provide
estimates of tool face (a), inclination (I) and azimuth (A) angles directly.
For example,
these values may be expressed as follows:
a = ao + dt ; (eq. 21)
/ = /0 + y dt ; and (eq. 22)
A = Ao + dt , (eq. 23)
where ao, I 0 and Ao are the initial values of tool face, inclination and
azimuth (e.g.,
approximate values derived based on a relatively coarse gyro-compassing
procedure available
at high latitude, or in the presence of platform rotational motion), and
õ cos A
= G. +0, sin a + Gy cos a)cot / _____________________________ (eq. 24)
sill
= ¨Gxcosa + G sin a + S2, sin A
;and (eq. 25)
(Gx sin a + GyCOS a)
A= ___________________________________ +S.2õ cosAcot/¨Qv
sin/ (eq. 26)
where Gx , Gy and Gz are measurements of angular rate about the x, y and z
axes of the
survey tool.
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System error equations
[0101] System error equations may be expressed as follows:
= (Gx cos a - Gy sin a)cot / = Aa
x sin a + G cosa) S2õ cos Acot /
__________________________ = A/ + ________ Al ; (eq. 27)
sin 2 I sin/
sin A
________________ AA + sin a cot I = AGx + cos a cot I = AG y + AG z
sin I
Ai = x sin a + G cos a). Aa + C2, cos A = AA
; and (eq. 28)
- cos a = AG õ + sin a = AG y
X cos a - Gy sin a)
AA = _______________________ = A a
sin I
x sin a + G cos a )cot / õ cos A
_____________________________ = Al _______ Al ; (eq. 29)
sin/ sin 2 I
sin a cos a = AG
- S2, sin A cot = AA ________ = AG , __
sin/ sin/
[0102] The system error equations may further be expressed in matrix
form as:
5c= F=x+G=w, (eq. 30)
where x = Al AA AG, AG y AG zr (eq. 31)
and represents the system error states, w is a 3 element vector representing
the gyro
measurement noise, G is the system noise matrix and the error matrix F can be
given by:
-(G sina + Gy cosa)+ C2, cosAcos/ Qõ sin A
0, cosa ¨ G, sina)cot/ ______________________________________ sinacot/
cosacot/ 1
sin2 I sin/
(G sin a + Gy cosa) 0 C2, cosA ¨cosa sina
0 (eq. 32)
F = (G cosa¨ Gy sin a) (G sin a + G y cosa)cos/ ¨
Q,. cosA sin a cosa
sinAcot/ 0
sin/ sin2 / sin/ sin/
0 0 0 0 0 0
0 0 0 0 0 0
0 0 0 0 0 0_
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Filter measurement equations
[0103] Three accelerometers in the survey system (e.g., the survey tool
30) can
provide independent measurement of tool face and inclination angles, as shown
by the
following equations:
(
= arctan A' ; and (eq. 33)
A
( ____________________
4,2 + Ay2
7 = arctan ____________________________________________ (eq. 34)
and it can be assumed for the purposes of this example filter formulation that
an estimate of
survey tool 30 azimuth (-A) is provided by the satellite attitude
determination process (e.g.,
using the directional reference system 16).
[0104] The differences between the two estimates of tool-face,
inclination and
azimuth can form the measurement difference inputs (z) to a Kalman filter, as
follows:
_
a¨a
z= - . (eq. 35)
A¨A_
[0105] The measurement differences (z) may also be expressed in terms
of the
error states ( x ) as follows:
z=H=x+I=v, (eq. 36)
1 0 0 0 0 0
where H= 0 1 0 0 0 0 , (eq. 37)
0 0 1 0 0 0
v may be a 3 element vector that represents the accelerometer measurement and
GPS azimuth
measurement noise, and I is a measurement noise matrix.
Kalman filter equations
Discrete system and measurement equations
[0106] While the system may be described mathematically in the
continuous
differential equation form given above, the measurements are in practice
provided at discrete
intervals of time. To address with this, and to provide a computationally
efficient filtering
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algorithm, the continuous equations can be expressed in the form of difference
equations as
shown below:
Xk+1=xk +Ak =Wk = (eq. 38)
k
where OA = exp[F = (ti ¨ tk
(eq. 39)
with measurements expressed as:
zA+1 = Hk+1 = xk+I + vk+1, (eq. 40)
and where x = error state at time tk,
W k= system noise at time tk,
Ok= state transition matrix from time tk to time tk-F1,
Ak = system noise matrix at time tic,
;1_1= measurement difference at time tk-F1,
vk+1= measurement noise at time tk_Fi, and
H k+I measurement matrix calculated at time tk+1.
[0107] The noise can be zero mean, but now discrete, and can
be characterized by
the covariance matrices Q
k and Rk respectively.
Prediction step
[0108] A relatively accurate estimate (e.g., a best
estimate) of the error state at
time tk is denoted below by xkik . Since the system noise wk of certain
embodiments has
zero mean, the best prediction of the state at time tk4-1 can be expressed as:
Xk+11k = (I)k = Xkl k (eq. 41)
while the expected value of the covariance at time tk_FI predicted at time tk,
can be given by:
4_, T
Pk+Ilk = (13k = Pklk = "1-1, Ak = Q k = Ak . (eq. 42)
Measurement update
[0109] The arrival of a new set of measurements zk+i at time
tk+i can be used to
update the prediction to generate a relatively accurate estimate (e.g., a best
estimate) of the
state at this time. For example, a relatively accurate (e.g., best) estimate
of the state at time
tk_Fi can be expressed as:
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Xk+1/k+1 = Xk+11k-K [H
k+1 k+1x k+11k ¨ z k+1]) (eq. 43)
[0110] and its covariance by:
P =Pk+1I k ¨Kk+1 Hk+1 Pk+1Ik (eq. 44)
k+11k+1
[0111] where the Kalman gain matrix can be given by:
K
1-1
P H T[H P H k 1T d-Rk+1 =
k+1 = k+11k k+1 k+1 k+11 k +- (eq. 45)
State correction
[0112] Following each measurement update, the states can be
corrected using
current estimates (e.g., best estimates) of the errors. In this situation, the
predicted state
errors become zero:
xk+11k = 0. (eq. 46)
F. Initialization of the Survey Tool on a Moving Surface
[0113] In certain circumstances, the apparatus 10 may be
positioned on a moving
surface. For example, the apparatus 10 may be on an off-shore drilling rig or
platform. The
continuous survey mode will generally operate properly on the Earth under such
conditions,
provided some means of initializing the integration process involved, other
than gyro-
compassing, can be established. For example, given some independent means of
keeping
track of the substantially instantaneous attitude of a moving platform, and
the dynamic
transfer of that information to the survey tool to initialize the continuous
survey process, the
potential exists to remove the survey uncertainties associated with platform
motion. It can
therefore be beneficial to maintain a dynamic orientation (e.g., reference
attitude) on the
moving surface (e.g., a rig) which can be initialized at a particular moment.
For example, the
orientation (e.g., reference attitude or azimuth) of the survey tool 30 with
respect to the
reference direction 18 can be determined and/or transferred to the survey tool
30 generally
immediately before the tool is placed in continuous survey mode (e.g., upon
insertion of the
survey tool 30 into the wellbore) in accordance with certain embodiments. In
certain
embodiments, the directional reference system 16 and/or the inertial
navigation system 42
may be used to conduct the determination, transfer the information regarding
the orientation
to the survey tool 30, or both, as described herein (e.g., with respect to
Figure 6).
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[0114] In some other embodiments, the motion of the drilling rig or
platform may
be advantageously used to initialize the survey tool 30. For example, an
angular rate
measurement matching procedure may be used to determine the relative
orientation (e.g.,
attitude and/or azimuth) between two orthogonal sets of axes on the platform
structure (e.g.,
between a set of axes defined by the inertial navigation system 42 and a set
of axes defined
by the survey tool 30). Such a procedure may account for relative differences
between the
orientation of the survey tool 30 and the apparatus 10. In general, as
described herein,
initialization of the survey tool 30 using the apparatus 10 can be achieved
accurately where
the wellbore survey tool 30 is mounted in some predetermined orientation with
respect to the
apparatus 10 or components thereof (e.g., the directional reference system
16). Thus, the
accuracy of the determination of the orientation of the survey tool 30 may be
improved when
the alignment of the survey tool 30 (e.g., attitude) with respect to the
apparatus 10 is
relatively accurate and/or precise. Using the angular rate matching process
described herein,
residual misalignments between the survey tool 30 and the apparatus 10 may be
determined
such that actual mounting alignment accuracy of the survey tool 30 on the
apparatus 10
becomes less critical.
[0115] Examples of a generally similar angular rate matching procedure
used to
produce precision alignment in attitude and corresponding systems for aligning
a weapons
system on a sea-borne vessel are described in U.S. Patent No. 3,803,387,
entitled "Alignment
Error Detection System," which is hereby incorporated in its entirety by
reference herein. By
comparing the sets of angular rate measurements (e.g., from the inertial
navigation system 42
and the survey tool 30), it is possible to deduce the relative orientation of
the two sets of axes
(e.g., o the apparatus 10 and the survey tool 30). The orientation of the
apparatus 10 (which
may be referred to as the platform reference frame) may be defined by the
orientation of the
inertial navigation system 42, an integrated device 43 (e.g., an integrated
GPS/AHRS unit), or
the directional reference system 16.
[0116] In an offshore drilling or platform, for example, the rocking
motion of the
rig is generally sufficient to provide angular motion sufficient to allow the
attitude
determination. Accurate knowledge of the inertial navigation system 42
reference orientation
with respect to the geographic reference frame (e.g., the reference direction
18), combined
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with knowledge of the relative orientation (e.g., attitude and/or azimuth)
between the survey
tool 30 and the inertial navigation system 42 according to an angular rate
matching
procedure, can allow for accurate determination of the orientation (e.g.,
attitude and/or
azimuth) of the survey tool 30 with respect to the geographic reference frame
(e.g., the
reference direction 18). Advantageously, utilizing the angular rate matching
procedure, the
initial orientation of the survey tool 30 can be accurately obtained in
situations where the tool
30 is physically misaligned with respect to the platform reference system
(e.g., due to
operator error in mounting the tool, misalignment due to imprecision in the
manufacturing/assembly of the platform, etc.). In certain embodiments, the
directional
reference system 16, or an integrated unit comprising a directional reference
system 16 and
an inertial navigation system 42 (e.g., GPS/INS unit 43), is used instead of
or in addition to
the inertial navigation system 42 in the angular rate matching procedure.
[0117] Figure 10 is a flowchart of an example method 300 of
initializing a
wellbore survey tool 30 utilizing an angular rate matching procedure. While
the method 300
is described herein by reference to the apparatus 10 described with respect to
Figures 2-8,
other apparatus described herein can also be used (e.g., the apparatus 400 of
Figure 10). At
operational block 302, the method 300 comprises receiving a first signal
indicative of an
orientation of a directional reference system 16 with respect to a reference
direction 18. For
example, the orientation of the directional reference system 16 may be
calculated by a
processor of the directional reference system 16 in response to signals
received by the first
antenna 22 and the second antenna 24 as described herein. The first signal may
be generated
by the directional reference system 16 and transmitted for processing (e.g.,
to the computing
system 52 or directly to the wellbore survey tool 30). In certain embodiments,
the method
300 further comprises positioning the wellbore survey tool 30 such that the
wellbore survey
tool 30 has a predetermined orientation with respect to the directional
reference system 16.
For example, the wellbore survey tool 30 may be positioned substantially
parallel with the
directional reference system 16 on the apparatus 10 (e.g., using a tool
positioning element as
described herein).
[0118] The method 300 further comprises receiving a second signal
indicative of
the rate of angular motion of the directional reference system 16 at
operational block 304.
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For example, in certain embodiments, one or more sensors (e.g., one or more
gyroscopes) of
the inertial navigation system 42 measure the rate of angular motion of the
inertial navigation
system 42 and generate the second signal indicative of the same. The inertial
navigation
system 42 may then transmit the second signal for processing (e.g., to the
computing system
52 or directly to the wellbore survey tool 30). In certain other embodiments,
the rate of
angular motion is measured directly by the directional reference system 16. In
one
embodiment, apparatus 10 comprises an integrated system, such as the
integrated GPS/AHRS
unit 43. In such an embodiment, because the directional reference system 16 is
integrated
with the inertial navigation system 42, the GPS/AHRS unit 43 generates the
second signal.
[0119] At operational block 306, the method 300 comprises receiving a
third
signal indicative of the rate of angular motion of a wellbore survey tool 30.
For example, one
or more sensors of the survey tool 30 (e.g., one or more gyroscopes) may
measure the rate of
angular motion of the survey tool 30 and generate the third signal. The third
signal may then
be transmitted for processing (e.g., to the computing system 52 or directly to
the wellbore
survey tool 30).
[0120] The method 300 can further comprise determining a relative
orientation of
the directional reference system 16 and the wellbore survey tool 30 in
response to the second
signal and the third signal at operational block 308. For example, the
relative orientation can
be determined using an angular rate matching procedure described herein. At
operational
block 310, the method 300 of certain embodiments comprises determining an
orientation of
the wellbore survey tool 30 with respect to the reference direction 18 in
response to the first
signal and the relative orientation. Given the orientation of the directional
reference system
16 with respect to the reference direction 18, as indicated by the first
signal, and given the
relative orientation of the survey tool 30 to the directional reference system
16, as indicated
by the angular rate matching procedure, such a determination can be made.
[0121] In certain embodiments, the second signal may be indicative of
the rate of
angular motion of the inertial navigation system 42, or of generally the
entire apparatus 10 or
components thereof (e.g., the base portion 12), instead of, or in addition to
the directional
reference system 16. For example, in one embodiment, the second signal is
generated by the
inertial navigation system 42 and is directly indicative of the orientation of
the inertial
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navigation system 42 with respect to the reference direction 18. For example,
the inertial
navigation system 42 may be oriented in substantially the same orientation on
the apparatus
with respect to the survey tool 30 as the directional navigation system 16 is
oriented with
respect to the survey tool 30 and is therefore at least indirectly indicative
of the orientation of
the directional reference system 16 with respect to the reference direction
18.
G. Example Angular Rate Matching Filter for the Transfer of Orientation
Data (e.g.,
Attitude and Heading Reference Data) to the Survey Tool on a Moving Platform
[0122] As described, in some embodiments, the apparatus 10 includes an
integrated unit, such as a GPS/AHRS reference system 43 generally including
the
functionality of both a directional reference system 16 and an inertial
navigation system 42.
On a moving apparatus 10 (e.g., a moving platform or board), the azimuth
difference between
the survey tool 30) GPS/AHRS reference system 43 and the survey tool 30 may be
determined by comparing angular rate measurements provided by the two systems,
provided
that the drilling rig exhibits some rocking motion. For example, the
measurements may be
processed using a Kalman filter based on an error model of an inertial system
in the survey
tool 30. One form of the measurement equation is expressed below. In certain
other
embodiments, as described herein, separate directional reference system 16 and
inertial
navigation system 42 are used. Such embodiments are also compatible with the
example
described herein. For example, in one embodiment, the directional reference
system 16 and
the inertial navigation system 42 comprise separate units but are
substantially aligned with
respect to each other on the apparatus 10.
[0123] The measurements of turn rate provided by the GPS/AHRS reference
system 43 and survey tool 30 system can be assumed to be generated in local co-
ordinate
frames denoted a and b respectively. In certain embodiments, the rates sensed
by a triad of
strap-down gyroscopes mounted at each location with their sensitive axes
aligned with these
reference frames may be expressed as co' and cob. The measurements provided by
the
gyroscopes in the reference and aligning systems are resolved into a common
reference
frame, the a-frame for example, before comparison takes place.
[0124] Hence, the reference measurements may be expressed as:
z = , (eq. 47)
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assuming the errors in the measurements are negligible. The estimates of these
measurements generated by the survey tool 30 system are denoted by the ^
notation.
ba c,t) b
(eq. 48)
[0125] The gyroscope outputs ( ci)b ) may be written as the sum of the
true rate
( cob ) and the error in the measurement ( 8cob ) while the estimated
direction cosine matrix
may be expressed as the product of a skew symmetric error matrix, [./ ¨9 x],
and the true
matrix Cba as follows:
= ¨ xrba [cob + &ob]. (eq. 49)
[0126] Expanding the right hand side of this equation and ignoring
error product
terms gives:
= cbacob 9 x bez co b ba gco b (eq. 50)
[0127] The measurement differences may then be written as:
(eq. 51)
_[cba coblx ba job
[0128] The measurement differences (evzk ) at time tk may be expressed
in terms of
the error states ( bkk ) as follows:
eeZk= HIcaX1,4-Vk) (eq. 52)
where Hk is the Kalman filter measurement matrix which can be expressed as
follows:
0 cox ¨ C11 C12 C13
Hk= ¨00 0 Wx C21 C22 C23 , (eq. 53)
co
_ ¨ cox 0 c31 c32 c33
Y
where cox , oy and co, are the components of the vector qcob, c11,c12,..= etc.
are the
elements of direction cosine matrix cbi and vk is the measurement noise
vector. This
represents the noise on the measurements and model-mismatch introduced through
any
flexure of the platform structure that may be present.
[0129] A Kalman filter may be constructed using the measurement
equation and a
system equation of the form described above in relation to the attitude
matching filter. The
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filter provides estimates of the relative orientation of the platform
reference (e.g., the
GPS/AHRS reference system 43) and the survey tool 30.
H. Alternative Embodiments
[0130] Figure 11 schematically illustrates an example apparatus 400 for
moving a
wellbore survey tool. The apparatus 400 of Figure 11 is configured to
transport the survey
tool 30 along a surface beneath the apparatus 400. In certain embodiments, the
apparatus 400
is configured to be mechanically coupled to at least one directional reference
system 416
(e.g., on the apparatus 400 itself or on a platform configured to be removably
coupled to the
apparatus 400). In this way, certain embodiments advantageously decouple the
transportation
functionality from the orientation-determination functionality.
[0131] The apparatus 400 of certain embodiments comprises at least one
support
402 and a base portion 403 mechanically coupled to the at least one support
402. The
apparatus 400 can further comprise a tool receiving portion 404 mechanically
coupled to the
base portion 403 and configured to receive a wellbore survey tool 406. The
apparatus 400
may also comprise at least one member movably coupled to a portion of the
apparatus 400
and configured to allow the apparatus to move along a surface beneath the
apparatus 400.
The apparatus 400 can further comprise a tool positioning element 408
configured to
controllably move the wellbore survey tool 406 between a first position
relative to the
apparatus and a second position relative to the apparatus 400.
[0132] As shown in Figure 11, the base portion 403 may comprise a
substantially
rigid, generally rectangular platform structure including a generally planar
surface 405. In
other embodiments, the base portion 12 may have a different shape (e.g.,
circular, ovular,
trapezoidal, etc.), may be somewhat flexible, and/or may include one or more
inclined
surfaces, declined surfaces, stepped portions, etc. The base portion 403 may
be similar to the
base portion 12 of the apparatus 10 described above (e.g., with respect to
Figure 2 and Figure
4), for example.
[0133] The at least one support 402 may comprise one or more posts. The
apparatus 400 of Figure 11 comprises three supports 402. In other embodiments,
there may
be more or less supports 402 and/or the supports 402 may be shaped differently
(e.g., as
rectangular posts, blocks, hemispherical protrusions, etc.). In various
embodiments, the at
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least one support may be similar to the at least one leveler 48 of the
apparatus 10 described
above (e.g., with respect to Figure 4).
[0134] The tool receiving portion 404 of certain embodiments comprises
an area
of the base portion 403 on which the well survey tool 406 is mounted. In
various
embodiments, the survey tool 406 can be releasably secured to the tool
receiving portion 404.
In certain embodiments, the tool receiving portion 403 is similar to the
second mounting
portion 20 of the apparatus 10 described above (e.g., with respect to Figure
2).
[0135] The surface beneath the apparatus 400 may be the Earth's
surface, a rig
surface, etc. In certain embodiments, the at least one member comprises a
wheel, tread, ski,
or other mechanism configured to allow for movement of the apparatus 400 along
the
surface. In some embodiments, for example, the at least one member of the
apparatus 400 is
similar to the at least one member of the apparatus 10 described above (e.g.,
with respect to
Figure 4).
[0136] The tool positioning element 408 can be configured to
controllably move
the wellbore survey tool 406 between a first position relative to the
apparatus 400 and a
second position relative to the apparatus 400. In certain embodiments, the
first position is
horizontal with respect to the base portion 403 and the second position is
vertical with respect
to the base portion 403. The tool positioning element 408 may be similar to
the tool
positioning element 56 of the apparatus 10 described above (e.g., with respect
to Figures 6A-
6C) in certain embodiments.
[0137] The apparatus 400 may further comprise a mounting portion 414
mechanically coupled to the base portion 403 and configured to receive at
least one
directional reference system 416. The at least one directional reference
system 416 can be
configured to provide data (e.g., attitude or azimuth) indicative of an
orientation of the at
least one directional reference system 416 with respect to a reference
direction. In certain
embodiments, the mounting portion 414 is similar to the first mounting portion
14 of the
apparatus 10 described above (e.g., with respect to Figure 2).
[0138] The directional reference system 416 may be similar to the
directional
reference system 16 described above (e.g., with respect to Figure 2). For
example, the at least
one directional reference system 416 comprises at least one signal receiver of
a global
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positioning system (GPS). For example, the directional reference system 16 may
comprise a
first antenna 418 and a second antenna 420 spaced apart from the first antenna
and defining a
line 422 from the first antenna 418 to the second antenna 420. In certain
embodiments, the at
least one signal receiver further comprises a processor (not shown) configured
to receive
signals from the first and second antennae 418, 420 and to determine an
orientation of the
line 422 (e.g., attitude or azimuth) with respect to the reference direction
424.
[0139] In certain embodiments, the tool receiving portion 408 is
configured to
receive the wellbore survey tool 406 such that the wellbore survey tool 406
has a
predetermined orientation with respect to the at least one directional
reference system 416.
This general configuration may be similar the one described above (e.g., with
respect to
Figure 2) for the apparatus 10, the wellbore survey tool 30, and the
directional reference
system 16, for example. In addition, the survey tool 406 of certain
embodiments may be
similar to the survey tool 30 described above (e.g., with respect to Figure
2).
[0140] The apparatus 400 of certain embodiments may further include one
or
more of components described herein, such as an inertial navigation system
and/or computing
system similar to the inertial navigation system 42 and computing system 52 of
the apparatus
described above (e.g., with respect to Figure 4).
I. Remote Reference Source
[0141] Certain embodiments described above include methods and
apparatus for
initializing a wellbore survey system using an external directional reference
system such as a
satellite navigation system (GPS/GLONASS). One of the methods described
generally
involves mounting both the satellite reference system (e.g., comprising 2 or
more antennae,
receivers and processor) and the survey tool on a stable platform in a known
orientation with
respect to one another and transferring attitude data from the reference
system to the tool.
Thereafter, the tool is switched to a continuous survey mode allowing its
orientation to be
tracked during pick-up of the tool and positioning at the entrance to the
well, and throughout
the subsequent survey of the well.
[0142] In certain cases, screening of the GPS antennae may occur (e.g.,
by the
derrick or other objects). Thus, it can be advantageous to mount the GPS well
away from the
derrick and so have a sufficient number of satellites in view. However, it can
also be
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desirable to mount the survey tool in close proximity to the well head/Kelly
bushing (e.g.,
near to the entrance to the wellbore) so as to avoid having to transport the
tool to this location
after initialization. Survey errors can propagate throughout the period of
tool surface
handling ¨ therefore it is often desirable to keep this to a minimum duration.
Further, there is
a possibility of exceeding the dynamic range of the sensors in the tool, e.g.
of saturating the
gyroscopes by exceeding maximum allowable input rate. If this occurs, the
attitude reference
stored in the tool at initialization will be lost and the procedure of
aligning the tool to the
GPS reference will need to be repeated. Thus, there can be a tension between
these two
design goals: performing initialization using GPS measurements on the rig and
positioning
the tool close to the well head/Kelly bushing tool to minimize the surface
handling
requirement.
[0143] To address the competing design goals described above, certain
methods
described herein involve mounting the GPS equipment and the survey tool remote
from one
another during the initialization process. For example, the GPS equipment can
be mounted
well away from the derrick (e.g., in order to maximize the number of
satellites in view) and
the tool may be located close to the entrance to the well (e.g., in order to
minimize or
otherwise reduce the movement of the tool prior to running into the well
and/or the time
taken in any physical transfer of the tool between two locations). In certain
embodiments, the
initial orientation of the wellbore survey tool is determined with respect to
a chosen reference
frame (e.g., the local vertical geographic frame expressed as an azimuth
angle, an inclination,
and a high-side orientation of the wellbore survey tool). In certain
embodiments described
herein, the directional reference system and the wellbore survey tool are not
mechanically
coupled to one another and are mounted on respective surfaces that are not
mechanically
coupled to one another.
[0144] Figure 12 is a flowchart of an example method 500 for
determining an
orientation of a wellbore survey tool at a first position with respect to a
reference direction in
accordance with certain embodiments described herein. In an operational block
510, the
method 500 comprises receiving information (e.g., at least one first signal)
indicative of an
orientation of a directional reference system with respect to the reference
direction. The
directional reference system is positioned at a second position spaced from
the first position.
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In an operational block 512, the method 500 further comprises receiving
information (e.g., at
least one second signal) indicative of a relative orientation of the wellbore
survey tool with
respect to the directional reference system. In an operational block 514, the
method 500
further comprises determining the orientation of the wellbore survey tool at
the first position
in response at least in part to the received information (e.g., the at least
one first signal and
the at least one second signal).
[0145] In certain embodiments, the at least one first signal and the at
least one
second signal are received by a computer system comprising one or more
computer
processors (e.g., one or more computer microprocessors). For example, the one
or more
computer processors can comprise one or more processors of the wellbore survey
tool, the
directional reference system, or one or more processors that are dedicated to
determining the
orientation of the wellbore survey tool. Additional information, such as
parameter values
(e.g., distance between two reference points on the wellbore survey tool,
distance between
two reference points on the directional reference system, distance between the
wellbore
survey tool and the directional reference system, and horizontal and vertical
components of
these distances) that are directly or indirectly representative of one or more
dimensions or
geometric relationships of or between the wellbore survey tool and the
directional reference
system (e.g., angle between lines linking reference points and axes of tool
and GPS reference
directions) may also be used in determining the orientation of the wellbore
survey tool, and
such parameter values are received by the one or more processors which are
used to calculate
the orientation of the wellbore survey tool. In certain embodiments, the one
or more
computer processors comprise one or more inputs to receive data (e.g.,
information or one or
more signals) indicative of (e.g., to be used to compute) the orientation of
the directional
reference system with respect to the reference direction and indicative of the
relative
orientation of the wellbore survey tool with respect to the directional
reference system.
[0146] In certain embodiments, the computer system further comprises a
memory
subsystem adapted to store information (e.g., one or more signals or parameter
values) to be
used in the determination of the orientation of the wellbore survey tool. The
computer
system can comprise hardware, software, or a combination of both hardware and
software. In
certain embodiments, the computer system comprises a standard personal
computer. In
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certain embodiments, the computer system comprises appropriate interfaces
(e.g., modems)
to receive and transmit signals as needed. The computer system can comprise
standard
communication components (e.g., keyboard, mouse, toggle switches) for
receiving user input,
and can comprise standard communication components (e.g., image display
screen,
alphanumeric meters, printers) for displaying and/or recording operation
parameters,
orientation and/or location coordinates, or other information used in
determining the
orientation or generated as a result of determining the orientation. In
certain embodiments,
the computer system is configured to read a computer-readable medium (e.g.,
read-only
memory, dynamic random-access memory, flash memory, hard disk drive, compact
disk,
digital video disk) which has instructions stored thereon which cause the
computer system to
perform a method for determining an orientation of the wellbore survey tool in
accordance
with certain embodiments described herein. In certain embodiments, at least
one signal of
the at least one first signal and the at least one second signal is received
from user input,
computer memory, or sensors or other components of the system configured to
provide
signals having the desired information.
[0147] Techniques are also described herein for transferring the
attitude reference
defined by the GPS to a location physically removed from it (e.g., the tool
location). In
certain embodiments, the wellbore survey tool is at a first position spaced a
first distance
from the wellbore entrance (e.g., spaced a first distance from the well
head/Kelly bushing)
and the directional reference system is at a second position spaced a second
distance from the
wellbore entrance (e.g., spaces a second distance from the well head/Kelly
bushing), with the
second distance being greater than the first distance. In certain embodiments,
the first
distance has a first horizontal component that is less than 10 feet, or the
second distance has a
second horizontal component that is greater than the first horizontal
component by at least
about 30 feet, or both. In certain embodiments, the first distance has a first
vertical
component that is less than about 20 feet.
[0148] In some cases, the horizontal separation distance between the
first position
and the second position could be as much as 50 feet, and the two positions
could be at
different levels on the rig (also up to 50 feet). In other configurations, the
horizontal and
vertical separation distances can vary. For example, in various
configurations, the horizontal
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and/or vertical separation distances may range from between about 10 and 1000
feet, may be
at least 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90,
95, 100, 1000 feet, or
may be some value greater than 1000 feet. For example, in certain such
embodiments, the
GPS equipment (or other directional reference system) and the survey tool are
separated by a
distance beyond a distance for which it is physically easy or straightforward
to have the GPS
equipment and the survey tool mechanically connected to one another. Moreover,
in some
cases, the survey tool and the GPS equipment are mounted during the
initialization process
such that they are not mechanically coupled to one another, are mounted on
respective
surfaces that are not mechanically coupled to one another, or both.
[0149] In certain embodiments, the information (e.g., the at least one
first signal)
indicative of an orientation of the directional reference system with respect
to the reference
direction is generated or provided by the directional reference system itself.
For example, the
directional reference system can generate one or more signals based on the
orientation of the
directional reference system, and can input the one or more signals to the one
or more
computer processors.
[0150] Furthermore, a number of methods are described herein generate
the
information (e.g., the at least one second signal) indicative of the relative
orientation of the
wellbore survey tool with respect to the directional reference system e.g.,
using either (i)
laser/optical sighting between the GPS reference equipment and the tool or
(ii) the
application of an inertial attitude reference system. In both cases, the
survey tool may be
mounted vertically, horizontally, or anywhere in between during the attitude
initialization
process. Provided the tool can be physically located close to the entrance to
the well at this
time, any need to move the tool over a significant distance following GPS
attitude
initialization is avoided or reduced and the time for attitude errors to
propagate before the
start of a wellbore survey is therefore reduced. If the tool can be held close
to vertical during
this process, the need to rotate the tool before insertion in the well is also
avoided or reduced.
Therefore, by holding the survey tool vertical close to the wellbore entrance
(e.g., the well
head/Kelly bushing) throughout the initialization process, attitude errors
which would grow
and contribute to the overall attitude error at the start of a survey may be
kept to a minimum
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or are otherwise significantly reduced. Techniques are described here which
address these
issues.
[0151] It is desirable to accurately determine, the full attitude of
the survey tool,
e.g., the azimuth, inclination and high side orientation with respect to the
chosen reference
frame (the local vertical geographic frame for example). It is therefore
desirable for the
attitude reference to be capable of defining fully the attitude of the tool
for initialization
purposes, particularly for operation on a moving offshore platform. It is
noted that whilst the
inclination and high side angles can be determined very accurately on a
stationary platform
using the measurements provided by the accelerometers installed in the tool,
this approach is
less reliable offshore, and may not produce accurate results.
[0152] However, for the purposes of illustrating and providing a clear
(flat page)
visualization of the techniques described below, single plane illustrations
are given, and
attention is focused on the determination of tool orientation with respect to
true north which
is used as the tool azimuth angle. In the event that the tool is mounted at,
or close to, the
local vertical, it is desirable to determine the direction of a lateral axis
of the tool (usually the
y-axis) with respect to north. The direction of the projection of this lateral
axis on the
horizontal plane, with respect to north, is commonly referred to as the gyro
tool face angle.
[0153] It is stressed that some or all of the methods described herein
may be
adapted and used to define the attitude of the survey tool completely, and
made to work
irrespective of the orientation of the survey tool. In such cases, the system
geometry will
become more complex and additional measurements may be taken and used to
extract full
attitude data.
1. Optical sighting procedures
[0154] In certain embodiments, one or more optical sighting procedures
are used
to generate information (e.g., the at least one second signal) indicative of
the relative
orientation of the wellbore survey tool 530 with respect to the directional
reference system
540. Figure 13 illustrates an example wellbore survey tool/ directional
reference system
arrangement and corresponding initialization process that may be implemented
when the
survey tool 530 is horizontal. A theodolite and a ranging device (not shown)
mounted on the
platform containing the satellite antennae provides measurements of the line
of sight to two
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points marked at a known spacing along the tool casing. Together with
measurements of the
ranges to each of these points, it is possible to define fully the triangle
formed by the location
of the theodolite and two known points on the casing of the tool 530. Given
this information,
the direction in which the tool is pointing with respect to north (the tool
azimuth) may be
calculated using the geometric relationships shown in Figure 13. For example,
the reference
azimuth (AR) can be determined using the directional reference system 540
(e.g., satellite
reference system), and angles 01 and 02 and distances R1 and R2 can be
measured. Angles a
and 3 can be computed, which are functions of measured distances R1 and R2 and
the
difference A0 between angles 01 and 02. The tool azimuth can then be computed
using AT =
AR - 01- CC 180 or AT = AR - 02+11
[0155] The accuracy of the process described may be limited by the
ability to site
on to the appropriate points on the survey tool casing, but may be enhanced by
taking
multiple measurements at known spacing along the casing. By this method some
redundancy
is introduced into the measurement data, and the measurements may then be
processed using
a least squares adjustment.
[0156] Whilst the procedure and calculation described in Figure 13 is
valid for the
situation where the tool is horizontal, the method can be extended to cases in
which the tool
is mounted in any orientation with respect to the reference frame. In such
cases, both the
geometrical arrangement and the calculations used to determine the orientation
of the tool
become more complex, but are within the capability of persons of ordinary
skill in the art
using the disclosure herein.
[0157] If the tool were to be mounted vertically, a similar process may
be
implemented. For example, the orientation of a mirror 532 attached to the tool
530 aligned
perpendicular to a known axis (e.g., the y-axis as depicted in Figure 14) may
be determined.
The angle measured with respect to a reference direction and the angle of the
reference
direction with respect to north may then be summed to determine the gyro tool
face angle.
According to this approach, it is desirable to accurately align and position
the mirror 532 with
respect to the axes of the survey tool 530. A method of achieving this
alignment is described
below.
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[0158] The tool 530 can be mounted horizontally in a v-shaped channel
or block
mount(s) 550 and a flat bar 552 can be positioned above the tool 530 as shown
in Figure 15.
The bar 552 may be leveled accurately using a level sensor 554 attached to the
bar 552. A
laser 556 can be positioned on the bar 552 with its beam pointing
perpendicular to it, e.g.,
aligned vertically. Using x and y accelerometer measurements, the tool high
side angle can
be determined, which corresponds to the angle between the y-axis of the tool
530 and the
laser beam direction. For example, the tool high side angle a can be expressed
using the x
accelerometer measurement (Az) and the y accelerometer measurement (Ay) as a =
tan-1(Ax/Ay). If the tool 530 is subsequently lifted to the vertical and the
direction of the laser
beam with respect to true north can be established, the gyro tool face angle
can be determined
by simply summing the high side angle, measured when the tool 530 was
horizontal, and the
beam angle. Thus, in certain embodiments, the tool highside angle is
determined while the
wellbore survey tool 530 is substantially horizontal (e.g., aligned with the
local horizontal
using the level sensor), and the wellbore survey tool 530 is then moved to be
substantially
vertical, and the orientation of the wellbore survey tool 530 at the first
position is determined
by calculating the gyro tool face angle (e.g., using accelerometer
measurements from the
wellbore survey tool 530) at least in part based on the determined tool
highside angle.
[0159] A similar result may be achieved by replacing the laser 556 with
a mirror
attached to the bar 552 described above. A method of determining the gyro tool
face angle is
described next with respect to Figures 16-18.
[0160] According to such a method, the satellite antennae 542 of the
directional
reference system 540 are mounted on a platform as described previously. Also
mounted on
this platform can be a laser light source 544 coupled with an optical sight
and a mirror 546
which can be both rotated and moved along the axis of the platform as depicted
in Figure 16.
A motor driven screw mechanism may be used to achieve linear motion of the
mirror 546
along the reference axis 548, and a further motor can be incorporated to
rotate the tool 530 to
the desired angle. The laser beam can be directed or transmitted along a first
line extending
between the directional reference system 540 and the centre of the reflecting
surface of the
mirror 532 attached to the survey tool 530, or at a flat surface machined on
the casing of the
tool 530. The mirror 532 or flat surface on the casing of the tool 530 is at a
predetermined
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orientation with respect to the tool 530, and reflects the incident light. In
certain
embodiments, the wellbore survey tool 530 at the first position is mounted
substantially
vertically with respect to the wellbore entrance. In certain embodiments, the
mirror 532 is
moved to change the direction the light is reflected by the mirror 532, and
since the mirror
532 is mechanically coupled to the wellbore survey tool 530, the mirror 532
and tool 530
maintain their relationship with one another while being moved.
[0161] The light reflected by the mirror 532 is transmitted along a
second line
extending between the mirror 532 and a movable mirror 546 on the reference
platform. The
movable mirror 546 is positioned to intersect the beam reflected from the tool
mounted
minor 532 and subsequently rotated in order to reflect or direct the beam back
along the axis
548 of the reference platform. The operator or other entity makes the
necessary linear and
angular adjustments to this mirror 546 to ensure that the returning beam from
the tool
mounted mirror 532 is directed at a target point alongside the laser source.
In certain
embodiments, the light reflected by the mirror 546 propagates along a third
line extending
between the mirror 546 and a portion of the directional reference system
(e.g., the light
source 544), such that the first line, the second line, and the third line
form a triangle.
[0162] The resulting triangle (denoted ABC) formed by the light path (A
to C to
B to A) is shown in Figure 17A. The geometry of this triangle can be fully
defined using the
measured angles which are shown in Figure 17A. Point 0 denotes the central
axis of the
survey tool 530, and the lateral axes of the tool Ox and Oy are also shown in
Figure 17A.
Other measured angles are the beam angle 0 with respect to the azimuth
reference, mirror
angle pm with respect to the azimuth reference, and the tool y-axis a with
respect to the tool
mirror axis (corresponding to the measured highside angle). Given knowledge of
the
reference azimuth axis AB direction with respect to north (defined by the
satellite system and
corresponding to the reference azimuth angle To), the internal angles of the
triangle ABC and
the orientation of the tool axis Oy with respect to the axis of the mirror 532
attached to the
tool 530, the orientation of the tool axis Oy with respect to north (the gyro
tool face angle)
can be determined.
[0163] An example sequence of calculations used to establish this
angle, using the
angles shown in Figure 17B, is now described. The azimuth reference direction
wo is defined
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by the directional reference system 540, is the direction of line AB with
respect to north. The
direction of line BC with respect to north, defined by azimuth reference wo
and mirror angle
Pm is given by wi = + 2 pm. The direction of line CO with respect to north,
defined by xv
and measured angle 0, is given by Nr2 = y + 180 - pm + 0/2 = No + 180 + pm +
0/2. The
direction of tool axis (Oy) with respect to north (gyro toolface angle),
defmed by kv2 and
measured highside angle a, is given by 11'3 = 1112 + a - 360 = 11Jo + pm + 0/2
+ a - 180.
[0164] Additional geometric measurements may be provided to aid the
process
defined in Figure 17B. For example, the distance between the laser source and
the movable
mirror (AB) may be measured and used in the computational process to determine
tool
orientation (shown in Figure 17A). The availability of additional measurement
data such as
this may be used to advantage to check the accuracy of the computational
process and
provide quality control, through a least squares adjustment process for
example.
[0165] In alternative embodiments and as illustrated in Figure 18, the
gyro tool
face angle and/or other parameters can be determined using a mirror 532
attached to the tool
530 (e.g., at the highside point), and an autocollimating head 549 attached to
the directional
reference system 540 (e.g., a GPS unit or fixture). The autocollimating head
549 and the
mirror 532 can then be aligned via a visual sighting, or a light beam, for
example. In such an
arrangement, it may be desirable that the mirror 532 be locked in the "gyro
tool face" plane,
but able to be tilted in the inclination plane to allow any differences in
height to be
accommodated. During the autocollimation process, a beam of light can be sent
out through
the head 549 and the reflection can be detected coming back onto the eyepiece.
In other
embodiments, alignment can be determined by detecting that the image of the
end of the
autocollimating head 549 is in the mirror reflection (e.g., when looking
through the
eyepiece), indicating that the mirror 532 and head 549 are lined up or
substantially lined up
with each other.
[0166] A further alterative scheme for establishing the instantaneous
gyro tool
face angle of a survey tool on a moving platform is described next. The
following method
relies on the accurate surveying of the orientations of two mounting locations
on the rig, one
for the satellite reference antennae and one for the survey tool, each with
respect to a defined
platform reference frame. Given that the survey tool is clamped in the defined
reference
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location, and that its orientation relative to the satellite reference system
is known to an
acceptable level of accuracy, the satellite reference can be transferred to
the survey tool and
the survey process initiated. In the following description, it is assumed
throughout that the
rig structure is substantially rigid and that the relative orientations of the
mounting locations
are therefore substantially unchanging.
[0167] The
transformations between the various coordinate frames are denoted by
direction cosine matrices, viz.
CR
[0168] G =
coordinate transformation from the local geographic reference (G),
defined by the directions of true north, east and the local vertical, and the
satellite reference
frame (R) ¨ established using the satellite system.
CR
[0169] P =
coordinate transformation from the platform reference (P) and the
satellite reference frame (R) ¨ determined using standard land surveying
procedures
CT
[0170] P =
coordinate transformation from the platform reference (P) and the
survey tool frame (T) ¨ determined in part using land surveying procedures
(orientation of x
and y tool axes). The orientation of the tool about its longitudinal (z) axis
is more difficult to
control, particularly if the oil platform on which the initialization process
is taking place is
moving. To overcome this concern, the following method can be used.
[0171] The
high side of the tool 530 can be established to a relatively high degree
of accuracy using the tool accelerometer measurements provided that the tool
530 is
substantially stationary. Thus, one example method includes determining the
tool highside
on land (as part of the tool calibration process) and affixing (e.g.,
clamping) a sleeve 560 to
the tool casing with reference structures, e.g., clearly defined protrusions
562, in a known
position(s) with respect to the x and y axes of the instrument assembly within
the tool ¨ as
schematically illustrated in Figure 19. This sleeve assembly 560 then remains
attached to the
tool 530 while it is shipped to the offshore platform. The assembly 570 in
which the survey
tool 530 is to be mounted (e.g., clamped) on the platform can be designed to
allow the tool
protrusions 562 to key into a corresponding mechanism on the platform to lock
the tool 530
in a predetermined orientation about its z-axis, as illustrated in Figure 20.
Thus, in certain
embodiments, the wellbore survey tool 530 is mounted at a predetermined
orientation with
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respect to the directional reference system 540 using corresponding keying
structures affixed
to a mount that is located at the first position.
[0172] Other methods of achieving the same or similar result involve
the
substantially rigid attachment of a cross-over piece to one end of the survey
tool, to which a
key way can be machined; either a protrusion or an indentation in the cross-
over, for
example.
CT
[0173] The attitude of the survey tool with respect to the geographic
frame ( 6)
may then be calculated using the following matrix equation:
rT cR reP c7
G G R
CP CR
where R is equal to the transpose of the matrix P.
[0174] One object of this particular scheme is to initialize the survey
tool 530
while positioned above the well in the derrick, although the method is
generally applicable
for any tool orientation; vertical to horizontal on the rig. The tool 530 may
be fully made up
prior to the start of the initialization process, ready to be inserted into
the wellbore, and
clamped in position at its two ends (e.g., at the ends of tool section
containing the instrument
assembly). Land surveying techniques may be used to establish the position of
the end
supports, thus defining the tool orientation about its lateral (x and y) axes
with respect to the
platform reference axis set. The sleeve assembly 560 attached to the casing of
the tool prior
to shipment offshore and the clamping assembly 570 on the rig can be used to
define the tool
orientation about the z-axis.
[0175] Figure 21 shows the example locations of the directional
reference system
540 and the survey tool 530 in which the initialization process is to take
place. The survey
tool 530 can be held by tool initialization support 580 (including clamping
assembly 570) of
the derrick 590 and spaced away from the directional reference system 540.
2. Methods involving the use of an additional inertial reference
system
[0176] Certain alternative methods for initializing a gyro survey tool
530 are
described next. According to some embodiments, these alternative methods are
not reliant on
and/or may not involve optical measurements and lasers. As described more
fully below,
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values received from an inertial reference system can be used to determine the
orientation of
the wellbore survey tool 530 at the first position.
[0177] Figure 22 shows a reference platform containing the directional
reference
system 540 (e.g., GPS system) comprising satellite antennae 542 (two or more)
and a survey
tool 530 located at a location remote from the directional reference system
540. The method
shown here involves the application of an inertial attitude and heading
reference system
(AHRS) unit 600 to store the azimuth reference set up using the directional
reference system
540. This result can be achieved by initially mounting the AHRS unit 600 on
the reference
platform of the directional reference system 540. Having transferred the
satellite reference to
the AHRS unit 600, it can be detached from the platform and physically moved
or carried to
the entrance to the well where it can be affixed (e.g., clamped) to a platform
to which the tool
530 is also attached. Assuming that the AHRS unit 600 and the tool 530 are
accurately
aligned relative to one another, or their relative orientation is known to
sufficient accuracy,
the azimuth defined by the AHRS unit 600 may be transferred to the survey tool
530.
[0178] For example, the reference azimuth (AR) can be determined using
the
directional reference system 540 and can be transferred to the AHRS unit 600.
While the
AHRS unit 600 is carried to the wellbore entrance, the AHRS unit 600 maintains
the attitude
reference throughout. The AHRS unit 600 can then be attached to mounting
blocks to which
the survey tool 530 is also attached, and the attitude reference from the AHRS
unit 600 can
then be transferred to the survey tool 530. The survey tool 530 can then be
switched to
continuous survey mode and rotated to vertical above the wellbore entrance.
Thus, in certain
embodiments, before the orientation of the wellbore survey tool 530 is
determined, the
inertial reference system (e.g., AHRS unit 600) is moved from a first mounting
position in
which the inertial reference system is mounted at a predetermined orientation
with respect to
the directional reference system 540 to a second mounting position in which
the inertial
reference system is mounted at a predetermined orientation with respect to the
wellbore
survey tool 530.
[0179] The accuracy of the method involving the physical transfer of
the AHRS
unit 600 to the tool location can depend to some degree on the accuracy with
which the
AHRS unit 600 can be aligned mechanically in its respective mounting
locations; firstly to
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the satellite antennae structure of the directional reference system 540 and
subsequently to the
survey tool 530. This alignment can be more challenging with the tool
vertical, since the
length of the baseline which controls the accuracy of this alignment may only
be a few
centimeters (the diameter of the tool) compared to meters (the length of the
tool) in the case
where the tool 530 is horizontal. However, the method described earlier of
setting up a key
way during tool assembly to define the orientation of the tool when affixed or
clamped in
place on the rig may be used (ref. Figures 19 and 20).
[0180] In certain cases, a significant advantage of this method,
compared to the
optical sighting methods described above, is a reduced dependency on the
degree of rigidity
of the rig structure. For example, the mounting arrangement over the
relatively short
distances between the AHRS unit 600 and the satellite antennae structure of
the directional
reference system 540, and between the AHRS unit 600 and the tool 530, are
relevant to such
a method.
[0181] A further option, which according to certain embodiments does
not
involve the physical transport of the AHRS unit 600 between the reference site
of the
directional reference system 540 and the location of the tool 530, is shown in
Figure 23. In
this case, angular rate measurements generated by the AHRS unit 600 and the
gyroscopes in
the survey tool 530 are compared and used to determine the relative
orientation of the tool
530 and the AHRS unit 600 in a process referred to as inertial measurement
matching. The
time taken to perform this operation, and the accuracy to which it can be
accomplished, can
be a function of the motion of the rig or drilling platform on which the
system is located.
Given knowledge of the reference orientation (generated using the satellite
system) to which
the AHRS unit 600 is physically aligned and the relative orientation to the
tool 530, as
described above, the orientation of the tool 530 with respect to true north
can be calculated.
This information is then used to initialize the survey tool 530 before
engaging continuous
survey mode.
[0182] For example, the reference azimuth (AR) can be determined using
the
directional reference system 540 and can be transferred to the AHRS unit 600.
A comparison
of the angular rate measured by the AHRS unit 600 and measured by the survey
tool 530 can
be performed by the processor 610, which can then determine the relative
attitude (AA)
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between the AHRS unit 600 and the tool 530. The tool azimuth can then be
expressed as AT
= AR ¨ AA. The tool 530 can then be switched to continuous survey mode and
rotated to
vertical above the wellbore.
[0183] Both methods involving the use of the AHRS unit 600 may be
implemented with the survey tool 530 either vertical or horizontal, or
anywhere in between.
[0184] In an alternative configuration, when the tool 530 is vertical
or
substantially vertical, a large spinning wheel (spinning vertically) is set in
a full gravity
weighted gimbal system. The gimbal system may have a window on the top of the
box to see
the gyro tool face angle, for example. One example usage of such a
configuration is to attach
the directional reference system 540 (e.g., GPS unit or fixture) and spin up
in the reference
position and then detach and move to the rig floor where it gets attached to
the tool 530 (e.g.,
to a tool reference plate). Then the tool 530 can be turned in the gyro tool
face plane until the
AHRS unit 600 is back at its reference position, and the survey tool
initialisation can be
performed.
[0185] Although certain preferred embodiments and examples are
discussed
above, it is understood that the inventive subject matter extends beyond the
specifically
disclosed embodiments to other alternative embodiments and/or uses of the
invention and
obvious modifications and equivalents thereof. It is intended that the scope
of the inventions
disclosed herein should not be limited by the particular disclosed
embodiments. Thus, for
example, in any method or process disclosed herein, the acts or operations
making up the
method/process may be performed in any suitable sequence and are not
necessarily limited to
any particular disclosed sequence. Various aspects and advantages of the
embodiments have
been described where appropriate. It is to be understood that not necessarily
all such aspects
or advantages may be achieved in accordance with any particular embodiment.
Thus, for
example, it should be recognized that the various embodiments may be carried
out in a
manner that achieves or optimizes one advantage or group of advantages as
taught herein
without necessarily achieving other aspects or advantages as may be taught or
suggested
herein.
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