Note: Descriptions are shown in the official language in which they were submitted.
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CENTRALISING CORE ORIENTATION APPARATUS
Field of the Invention:
The present invention relates to orientation of a core sample extracted from a
bore hole.
Background of the Invention
Core sampling is one technique employed for geological surveying of the
ground. Such surveying may be used for example for exploration and/or mine
development. In core sampling a diamond drill is used to extract core samples
of the ground. The core samples may then be analysed to provide information
relating to the geological structure and composition of the ground from which
the core is extracted. In order to maximise the usefulness of this information
it
is necessary to have knowledge of the orientation of the core sample relative
to
the ground from which it is cut.
Summary of the Invention
One aspect of the invention provides a centralising core orientation apparatus
comprising:
a core orientation system; and,
a centralising system coupled to the core orientation system, the
centralising system operable to centralise the core orientation system within
a
conduit at a time when the core orientation system records orientation of a
core
to be extracted from the ground.
The centralising system may centralise the core orientation system within the
conduit at at least two points axially spaced by at least a portion of the
core
orientation system.
The centralising system may comprise first and second centralising tools,
wherein the first and second centralising tools are spaced apart by the
portion
of the core orientation system.
Each centralising tool may comprise:
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an expandable structure having a collapsed state wherein the tool has a
minimum diameter and an expanded state wherein the tool has an increased
diameter; and,
a locking system operable to unlock the expandable structure from the
collapsed state to the expanded state when the tool passes through a
restriction in a first direction and to lock the expandable structure in the
collapsed state when the tool passes in a reverse direction through the
restriction.
The expandable structure may comprise a plurality of links each link having
opposite first and second ends, and wherein the first and second ends are
spaced a maximum distance apart when the expandable structure is in the
collapsed state, and wherein the respective first and second ends are moved
toward each other and the link moves radially outward when the expandable
structure switches from the collapsed state to the expanded state.
Each link may be in the form of a length of resilient material.
In an alternate embodiment each link may comprises a plurality of link
elements
pivotally coupled together.
The expandable structure may comprise first and second components coupled
together wherein the components are moveable relative to each other when the
expandable structure switches between the collapsed and expanded states.
26
The first and second ends of the links may be coupled to the first and second
components respectively.
The first and second ends of the links may be pivotally coupled to the first
and
second components respectively.
The expandable structure may comprise a first bias device biasing the
expandable structure toward the expanded state.
The second component may be slideably coupled to the first component and
the first bias device acts to bias the second component towards the first
component.
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The locking system may comprise a stop mechanism having an engaged position
where the
stop mechanism engages the links to hold the expandable structure in the
collapsed state and a
disengaged position where the stop mechanism is disengaged from the links
enabling the
expandable structure to move to the expanded state.
The stop mechanism may be configured to move from the engaged position to the
disengaged
position when the system passes through in the first direction through the
restriction.
The stop mechanism may be moved from the engaged position to the disengaged
position by
physical contact of the locking system with the restriction.
The stop mechanism may comprise a piston which engages the links preventing
the links from
moving radially outward when the stop mechanism is in the engaged position,
and a bias device
which biases the piston toward the links.
The piston may be provided with a bearing surface which increases in outer
diameter in a
direction away from the first direction, and the stop mechanism comprises one
or more
elements configured to abut the restriction and the bearing surface when the
stop mechanism
passes through the restriction in the first direction wherein the piston moves
relative to the
elements and the elements move radially inward as the piston moves to enable
the stop
mechanism to pass through the restriction.
The elements may comprise a plurality of balls.
The core orientation system may comprise a core face position matching
apparatus and an
electronic bearing recording system coupled with the core face position
matching apparatus in a
known positional relationship, wherein the electronic bearing recording system
records a
bearing of a first reference point relative to a known bearing.
The electronic bearing recording system may comprise a down hole camera
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incorporating a compass wherein the camera takes a photo of the compass to
record a bearing of the first reference point.
In an alternative embodiment the electronic bearing recording system may
comprise a down hole survey tool wherein the survey tool digitally records a
bearing of the first reference point.
In a further embodiment the electronic bearing recording system may comprise
a nonmagnetic down hole gyroscope to record a rotational deviation of the
reference point to a known bearing.
In any embodiment the core face position matching apparatus may comprise a
marker adapted to place a mark on the core face.
The core face position matching apparatus may alternately or additionally
comprise a plurality of pins arranged to slide in an axial direction when the
pins
contact the core face to provide a plurality of profile points corresponding
to the
respective locations of contact with the core face.
In a further alternative the core face position matching apparatus may
comprise
a pad of mouldable material adapted for contacting the core face and
maintaining an impression of the core face.
A second aspect of the invention provides vertical hole core orientation
system
comprising a core face position matching apparatus and an electronic bearing
recording system coupled with the core face position matching apparatus in a
known positional relationship, wherein the electronic bearing recording system
records a bearing of a first reference point relative to a known bearing.
The vertical hole core orientation system may comprise a centralising system
coupled to the electronic bearing recording system core orientation system,
the
centralising system operable to centralise the electronic bearing recording
system within a conduit to record an in situ orientation of a core to be
extracted
from the ground.
A further aspect of the invention provides a centralising tool capable of
axial self
centralisation in a conduit, the tool comprising:
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an expandable structure having a collapsed state wherein the tool has a
minimum diameter and an expanded state wherein the tool is biased into a
configuration having an increased diameter wherein the tool contacts an inner
surface of the conduit at two or more radially spaced points;
a locking system operable to unlock the expandable structure from the
collapsed state to the expanded state when the tool passes through a
restriction in the conduit in a first direction, and to lock the expandable
structure
in the collapsed state when the tool passes in a reverse direction through the
restriction.
lo
Two of the two or more spaced apart points may be diametrically opposed.
The expandable structure may comprise a plurality of links each link having
opposite first and second ends, and wherein the first and second ends are
spaced a maximum distance apart when the expandable structure is in the
collapsed state, and wherein the respective first and second ends are moved
toward each other and the link moves radially outward when the expandable
structure switches from the collapsed state to the expanded state.
Brief Description of the Drawings
An embodiment of the present invention will now be described by way of
example only with reference to the accompanying drawings in which:
Figure 1 is a schematic representation of one embodiment of a centralising
core
orientation apparatus in accordance with the present invention.
Figure 2 is an enlarged view of a centralising system and a core face position
matching apparatus incorporated in the apparatus;
Figure 3 is a broken section view of the apparatus when in use in a core
drill;
Figure 4 is a perspective view of a centralising tool incorporated in the
centralising system;
Figure 5 is a cross section view of the centralising tool in an expanded
state;
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Figure 6 is a cross section view of the centralising tool in a collapsed
state;
Figures 7a and 7b are cross section views of the centralising system
progressively switching from the collapsed state shown in Figure 7a toward the
expanded state shown in Figure 7b;
Figures 8a ¨ 8c are cross section views showing in sequence the centralising
tool switching from the expanded state shown in Figure 8a to an intermediate
shown in Figure 8b, and the closed state shown in Figure 8c;
Figure 9 is a perspective view of a body of a core face position matching
apparatus incorporated in one embodiment of the centralising core orientation
apparatus; and,
Figure 10 depicts a method of using centralising core orientation apparatus.
Detailed Description of Preferred Embodiment
Figure 1 depicts an embodiment of a centralising core orientation apparatus
(hereinafter referred to in general as "the apparatus") 10 that may be used to
obtain information relating to the orientation of a core sample cut by the
core
drill. As will be apparent from the following description, the apparatus 10 is
operable to provide core orientation information irrespective of the
orientation of
the bore hole from which the core sample is extracted. More particularly,
embodiments of the apparatus 10 enable core orientation to be obtained from
vertical holes. By way of background, when a core sample is extracted from a
bore hole which is inclined to the vertical, the angle of rotation of the core
may
be recorded by use of a gravity reference system. Such a system may
comprise for example a ball that is able to run in an annular race. The ball
will
roll by action of gravity to the gravitational bottom of the bore hole when an
axis
of the race is inclined from the vertical. By recording the position of this
point
and referencing it to a reference point on the core, one is able to determine
the
rotation or bearing of the core. However for vertical bore holes, a
gravitational
system is unreliable. Embodiments of the present apparatus 10 enable core
orientation to be recorded for both vertical and non vertical bore holes.
The apparatus 10 comprises a core orientation system 12 and a centralising
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system 14 coupled to the core orientation system 12. The centralising system
14 is operable to centralise the core orientation system 12 within a conduit
such
as a bore hole 16 (shown in Figure 3) or a conduit such as a drill string 18
(see
Figure 7a). Indeed as described in greater detail below, the centralising
system
14 may also be operable to centralise the core orientation system 12 when
partially located in two different conduits such as both the bore hole 16 and
the
drill string 18, or a conduit with contiguous sections of different inner
diameter.
The core orientation system 12 is a distributed system comprising a core face
position matching apparatus 12a, and an electronic bearing recording system
12b. The centralising system 14 comprises two spaced apart centralising tools,
a down hole tool 14ad, and an up hole tool 14au, hereinafter referred to in
general as "centralising tools 14a". The tools 14a are axially spaced apart by
a
portion of the core orientation system 12, and in particular separated by the
electronic bearing recording system 12b. Each tool 14a is capable of axial
self
centralisation in a conduit. As explained in greater detail below each tool
has a
collapsed state where it has an outer diameter less than an inner diameter of
the conduit and is biased to an expanded stated where its outer diameter is
increased to contact the inner diameter of the conduit at two or more radially
spaced points. These points are usually, but not necessarily, evenly spaced
about the tool. In some arrangements two (or points in respective pairs of
points) may be diametrically opposed. The centralising system 14 operates to
locate the electronic bearing recording system 12b coaxial with the bore hole
16
at the time of recording bearing of the apparatus 12a and thus the bearing of
a
core face 20 (see Figure 3) of a core sample 22 to be drilled. Once the core
sample 22 has been extracted from the ground, its rotational position can be
matched with the core face position matching apparatus 12a. The rotational
position of the core face position matching apparatus 12a is referenced to or
keyed with the rotational position of a reference on the electronic bearing
recording system 12b. As will be explained below, due to the known rotational
position of the core face position matching apparatus 12a relative to the
reference on the electronic bearing recording system 12b and the recording of
the bearing of that reference by the electronic bearing recording system 12b
to
a known reference point such as North or true north, the rotational position
of
the core sample 22 can be determined.
The core face position matching apparatus 12a forms a lower most or down
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hole portion of the apparatus 10 and operates by physical contact with the
core
face 20. The core face position matching apparatus 12a is coupled to the down
hole centralising tool 14ad. The tool 14ad is coupled by a standard
orientation
bull plug 24 to a lower end of the electronic bearing recording system 12b. An
opposite end of the system 12b is attached to the up hole centralising tool
14au. One or more spacer rods 26 may be attached to an opposite end of the
up hole tool 14au. The spacer rods 26 do not form part of an embodiment of
the present invention and are used to space the apparatus 10 from a head
assembly (not shown) which latches to the drill string 18 and to suspend the
apparatus 10 from an end of the drill string 18.
Figures 4 ¨ 6 depict an embodiment of the centralising tool 14a. The
centralising tool 14a comprises an expandable structure 28 and a locking
system 30. The expandable structure 28 has a collapsed state shown in Figure
6, where the tool 14a has a minimum diameter and an expanded state shown in
Figures 4 and 5 where the tool 14a has an increased diameter. The locking
system 30 unlocks the expandable structure 28 from the collapsed state to the
expanded state when the tool 14a passes in a first direction D through a
restriction which in the present embodiment comprises the inside of a core bit
32 (see Figure 7a). The direction D corresponds with the down hole direction.
Conversely, the locking system 30 operates to lock the expandable structure 28
in the collapsed state when the tool 14a passes in a reverse direction, in
this
case an up hole direction U, through the core bit 32.
The expandable structure 28 comprises a plurality of links 34 each having
respective first and second ends 36 and 38. The ends 36 and 38 are pivotally
coupled via respective pivot pins 40 and 42 to two separate components of the
tool 14a, namely a centraliser collar 44 and a centraliser body 46. More
particularly, the end 36 is coupled by the pivot pin 40 to the collar 44,
while the
end 38 is coupled by pivot pin 42 to the body 46. The body 46 comprises an
axially extending portion 48 on which the collar 44 is slidably mounted. The
portion 48 threadingly engages an adapter 50 to which the core face position
matching apparatus 12a is connected. Each of the collar 44 and the adapter 50
are provided with respective shoulders 52 and 54 which seat respective ends of
a bias device in the form of a spring 56. The spring 56 operates to bias the
collar 44 to move in a direction toward the pivot pin 42.
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Each link 34 comprises two link elements 58 and 60. The link elements 58 and
60 are pivotally coupled together via a pivot pin 62. The link element 58
incorporates the end 36 of the link 34 while the link element 60 incorporates
the
end 38 of the link 34. The link element 60 is bifurcated at an end coupled
with
the element 58, and accommodates a roller 64 which is rotatably mounted on a
pin 66 connected at opposite ends to the bifurcation.
The end 38 of each link element 60 is formed with a notch 68. Together, the
notches 68 form a seat 70 having a mouth 72. When the expandable structure
28 is in the collapsed position the mouth 72 has a maximum diameter M1 (see
Figure 6), whereas when the expandable structure moves toward the expanded
state, the mouth 72 has a reduced diameter M2, shown in Figure 5.
The locking system 30 is located at an end of the expandable structure 28 near
the ends 38 of the links 34. The locking system 30 comprises four main
components namely a stop mechanism in the form of a piston 74, a locking
body 76, a number of elements in the form of balls 78, and a spring 80. The
piston 74 has an engaged position shown in Figure 6 where it engages the links
34 and more particularly passes through the mouth 72 into the seat 70. The
piston also has a disengaged position shown in Figure 5 where it is disengaged
from the links 34 allowing the links 34 to move relative to the piston 74.
When
the piston 74 is in the engaged position shown in Figure 6, the link elements
60
are prevented from rotating about their respective pivot pins 62 and thus
locking
the expandable structure 28 in the collapsed state. However when the piston
74 is in the disengaged position, the link elements 60 are unlocked and able
to
rotate about the pins 42 thereby switching the expandable structure 28 to the
expanded state.
The piston 74 is formed with a constant diameter cylindrical portion 82, and
at
an end distant the links 34, a bearing surface 84 which has an increased outer
diameter in the up hole direction U. Moreover, the bearing surface 84 is
concavely curved with a radius substantially the same as or greater than a
radius of the balls 78. The cylindrical portion 82 is able to slide within an
axial
passage 86 formed at an up hole end of the body 46.
The body 76 is provided with a plurality of radially extending holes 88 each
of
which retains a respective ball 78. The radius of the holes 88 where they open
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onto an outer circumferential surface 90 of the body 76 is smaller than the
radius of the balls 78.
This prevents the balls 88 from being ejected in the radial outward direction
from the holes 88.
A down hole end of the locking body 76 is screwed onto the up hole end of the
body 46. The up
hole end of the locking body 76 is screwed onto an adapter 92. The adapter 92
is in turn
coupled to the orientation bull plug 24 (see Figure 1). The spring 80 is
retained between the
piston 74 and the adapter 92 and biases the piston 74 toward the engaged
position.
The operation of the central locking tool 14ad is described in relation to
figure 7a and 7b. The
tool 14ad has its corresponding expandable structure 28 in the collapsed state
and is travelling
in the down direction D through the drill string 18. The drill string 18 is
located in the bore hole
16 but lifted a predetermined distance above the toe of the hole which
constitutes the core face
of the next core 22 to be drilled. The expandable structure 28 is in the
collapsed position by
virtue of the piston 74 residing in the seat 70 thereby engaging the
respective notches 68 of the
15 links 34. In this condition, the spring 56 is in a relatively compressed
state and the spring 80 is
in a relatively expanded state pushing and holding the pistons 74 in the seat
70. In addition, the
spring 80 also in effect biases the balls 78 in the radial outward direction
through their
respective holes 88 by action of the contact between an upper portion of the
bearing surface 84
with the balls 78.
As the apparatus 10 travels in a down hole direction D through the drill
string 18, eventually the
locking system 30 of tool 14a will encounter the inner surface of the drill
bit 32. The locking
body 76 is dimensioned to pass through the drill bit 72 however the balls 78
are configured to
engage the inner surface by virtue of a portion of each ball 78 extending
radially from their
respective hole 88.
As a result of the contact between the balls 78 and the drill bit 32, the
balls are forced to move
radially inward toward each other. Space is provided for this to occur by
virtue of the shape of
the bearing surface 84. As the balls 78 move inwardly, they bear against the
bearing surface 84
and in effect force the piston 74 to move in the up hole direction U against
the bias of the spring
80. This movement retracts the piston 74 and in particular the cylindrical
portion 82 from the
seat 70 so that the piston 74 no longer engages the links 34. This
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configuration is shown in Figures 5 and 7b. With the piston 74 retracted from
the seat 70, the bias of the spring 56 acts to push the collar 44 to slide
axially in
the up hole direction U along the portion 48 of the body 46. This moves or
expands the links 34 in a radial outward direction by action of the link
elements
58 and 56 rotating about their respective pins 40 and 42, which is accompanied
by a reduction in the distance between the respective ends 36, 38 of the links
34. As the links 34 move in a radial outward direction their respective
rollers 64
contact the inner surface of the bore hole 16. In this instance as the tool
14a is
provided with four evenly spaced links 34 the tool will contact the inner
surface
of the bore hole 16 at points which are circumferentially spaced by 900, i.e.
there are two sets of diametrically spaced contact points.
The remainder of the apparatus 10 continues to travel in a down hole direction
D out of the core bit 32 until eventually the up hole centralising tool 14au
engages the core bit 32 and switches from the collapsed state to the expanded
state in the same manner as described above for the down hole centralising
tool 14ad. With both of the tools 14a now in the expanded state, the core
orientation system 12 is centrally located within the bore hole 16.
When it is required to retrieve the apparatus 10 from the bore hole 16, a head
assembly (not shown) attached to an uphole end of the apparatus 10 is
engaged by a conventional overshot and wire line and the wire line reeled in.
As this occurs, each of the expandable structures 28 is automatically switched
to the collapsed state by action of engagement with the core bit 32 as shown
sequentially in Figures 8a, 8b and 8c, and locked in the collapsed state by
the
locking system 30.
Figure 8a shows one of the tools 14a commencing to pass through the core bit
32 in the up hole direction U. The locking body 30 is able to pass through the
core bit 32 as the balls 78 are able to freely move in the radial inward
direction
toward each other. However eventually, the link elements 60 engage the inner
surface of the core bit 32. As the apparatus 10 is continually pulled in the
up
hole direction U, the link elements 60 commence to rotate inwardly toward each
other and toward the body 46 about their respective pivot pins 42. As this
occurs, the diameter of the mouth 72 continually increases as shown in Figure
8b. Eventually, approximately at the time that the rollers 64 contact the
inner
surface of the drill bit 32, the link elements 60 and are positioned in the
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collapsed state and the diameter of the mouth 72 is now at the maximum
diameter Ml.
Accordingly the spring 80, which is continually biasing the piston 74 in the
down hole direction
toward the engaged position, pushes the piston 74 through the mouth 72 to sit
in the seat 70.
The expandable system 28 of the centralising tool 14 is now locked in the
collapsed state. The
balls 78 are also returned to a position where they extend radially outward
from their respective
holes 88 to a maximum extent. Thus the locking system 30 and indeed the entire
tool 14 is self
primed ready for the next appointment of the apparatus 10.
The core face position matching the apparatus 12a may take many different
forms such as a
Van Ruth System, a simple pencil marker or a pad of mouldable materials such
as plasticine.
By way of brief explanation and with reference to Figures 2, 3 and 9, the core
face position
matching apparatus 12a comprises a cylindrical body 94 formed with a plurality
of axially
extending holes 96 which open onto a lower face 98 of the body 94. Respective
pins 100 are
seated in each of the holes 96. The holes 96 and pins 100 are relatively
configured so that an
interference fit is created. This interference fit allows the pins 100 to be
retracted into the holes
96 when the core face position matching apparatus 12a contacts the core face
20, and is
sufficient to maintain the pins in a fixed position in their respective holes
in the absence of a
force applied in the axially direction to the pins 100. Thus, when the core
face position matching
apparatus 12a contacts the core face 20, the pins 100 are able to retract into
their respective
holes 96 to provide a plurality of profile points matched to the profile of
the core face 20. The
body 94 also includes a further axial hole 102 for seating a marker such as a
pencil 103 (see
Figure 2) which extends from the face 98. The pencil 103 initially extends
from the face to the
same distance as the pins 100. When the core face position matching apparatus
12a first
contacts the core face 20, the pencil 103 provides a point mark on the core
face 20. Thus, the
core face position matching apparatus 12a in this embodiment enables matching
of the profile of
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the core face 20 by two independent means: firstly by matching the profile
points created by the pins 100; and, secondly by alignment of the mark on the
core face 20 with the pencil 103.
A bearing scale 104 is also marked on the outer circumferential surface of the
body 94. This bearing scale is marked in five degree increments from 0 to
360 . The 0 mark is in alignment with a key (not shown) formed inside of the
body 94 that engages a slot formed in a spigot (not shown) coupled with the
adapter 50.
With reference to Figures 2 and 3, the electronic bearing recording system 12b
is coupled to the core face position matching apparatus 12a via the
orientation
bull plug 24. The bull plug 24 is a standard piece of down hole equipment
which enables the coupling of two components together in a manner where the
rotational orientation of the components to be adjusted and locked. This
enables the rotational orientation of the core face position matching
apparatus
12a to be fixed in a known manner relative to the rotational orientation of
the
system 12b. For ease of description, the system 12b in this embodiment is
assumed to be a down hole camera. The down hole camera 12b includes a
compass and a reference mark represented by phantom line 110 in Figures 2
and 3. This reference is aligned with the zero marking on the core face
position
matching apparatus 12a, the alignment being achieved by use of the orientation
bull plug 24. The camera 12b operates to take a photo of the compass and the
reference mark 110 at the time that the core face position matching core face
position matching apparatus 12a contacts the core face 20. At this time the
apparatus 10 is deployed outside of or extends from the drill string 18 with
the
centralising system 14 in the expanded condition, centralising the camera 12b
and the core face position matching apparatus 12a in the bore hole 16.
Assume that the camera utilises the North bearing on the compass as a
reference bearing for the reference mark 110. Lets say for example that at the
time that the core face position matching apparatus 12a contacts the core face
20, the camera 12b takes a photograph which indicates that the reference mark
110 is at a bearing 6 of 85 from the north reference end, shown in Figure 10.
The apparatus 10 is withdrawn from the drill string 18, the drill string 18
then
lowered to the toe of the hole and operated to cut the core sample 22. The
core sample 22 is retrieved and placed on a core tray. Since the reference
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mark 110 is in a known rotational relationship to the zero mark on the bearing
scale 104 then the bearing of the zero mark on the scale 104 is the same as
the
bearing angle e of 85 .
The core face position matching apparatus 12a can be decoupled from the
apparatus 10 and located on the core tray adjacent the core face 20 of the
extracted core sample 22. The core face position matching apparatus 12a can
then be rotated to a position where the orientation of the pins matches the
profile of the core face 20. When the pencil 103 is used, this should also
result
in the mark made by the pencil on the core face 20 aligning with the position
of
the pencil 103.
As the bearing of the zero mark on the scale 104 is known to be 85 a
geologist
can make one of two markings on the outer circumferential surface of the core
sample. Firstly, a geologist may simply align a ruler or template with a zero
degree bearing on the scale 104 and rule a line axially along the outer
circumferential surface of the core sample 22 in alignment with the zero mark.
It is known that this marking is at a bearing of 85 . The bearing of 85 may
also
be written on the core sample. Thus as when the sample 22 is later analysed,
its actual in situ rotational position can be replicated by simply rotating
the core
sample so that the marking is at a bearing of 85 . In an alternate method, the
geologist knowing the recorded bearing of 85 can use the bearing scale 104 to
locate the 85 and align a ruler or template with that mark and the outer
surface
of the core sample 22 and then rule a line at that location along the core
sample
22. This line now coincides with a zero bearing (i.e. aligned with the north
reference). Thus again the rotational position of the core sample 22 has been
determined.
Now that this embodiment of the present invention has been described in detail
it will be apparent to those skilled in the relevant art that numerous
modifications and variations may be made without departing from the basic
inventive concepts. For example, the electronic bearing recording system 12b
is described as a down hole camera. However the electronic bearing recording
system 12b may comprise any one of: (a) a down hole survey tool which
digitally records the bearing of the reference mark such as a magnetic
electronic single or multi shot survey tool; or, (b) a non magnetic gyro type
system to record rotational deviation of the reference mark to a known
bearing.
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In the later case, the gyro need not extend from the core bit 22 and may
indeed
be retained within the drill string 18 so that only the core face position
matching
apparatus 12a initially extends from the core bit 22. In this case, alternate
restrictions for example rings may be placed inside the drill string 18 to
operate
the centralising system 14 and in particular the locking systems 30. Also in
this
event, the centralising system 12 operates to centralise the core orientation
system 12 within the drill string 18 rather than the bore hole 16.
In a further variation, in addition to the electronic bearing recording system
12b,
a gravitational bottom of hole indicator system may also be incorporated in
the
apparatus 10. Such a system may comprise for example one or more balls
disposed in corresponding annular races which will rotate to the lowest point
within the race when the ball hole deviates away from the vertical. Also while
the present embodiment describes the each link 34 as comprising two pivotally
coupled link elements 58 and 60; each link 34 may comprise a single strip of
resilient material such as fibreglass, or spring steel.
All such modifications and variations together with others that would be
obvious
to persons skilled in the art are deemed to be within the scope of the present
invention the nature of which is to be determined from the above description
and the appended claims.
