Note: Descriptions are shown in the official language in which they were submitted.
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1 APPARATUS AND METHOD FOR FORMING STANDS
2
3 FIELD OF THE INVENTION
4 [0001] The present invention relates to pipe handling apparatuses and, more
specifically, to
apparatuses and methods for drilling operations wherein stands are formed from
tubulars.
6 DESCRIPTION OF THE PRIOR ART
7 100021 Various ground drilling operations are known such as exploring and/or
extracting oil
8 from subterranean deposits. The drilling operation is conducted on a drill
rig comprising a raised
9 drilling platform located above the drilling location. A derrick is provided
on the platform to
raise, support and rotate a drill string. A drill string includes a drill bit
for boring into the
11 ground. As the drilling operation continues, tubular members, commonly
referred to as
12 "tubulars" are connected in an end to end manner to form a drill string.
Tubulars are commonly
13 about 30 feet in length and have opposing female and male ends. The ends
are threaded in a
14 complementary manner so that opposing male and female ends can be joined
together.
[0003] The addition of a tubular to an existing drill string is a relatively
time consuming and
16 dangerous procedure. Tubulars are provided on a rack from which they are
individually rolled
17 onto a horizontal support, such as a catwalk. Both the rack and catwalk are
generally located
18 adjacent to the drilling platform with the catwalk being generally
positioned perpendicular to the
19 platform. Once on the catwalk, one end of the tubular is attached to a
hoist connected either
directly of indirectly to the derrick and raised to a vertical position on the
drilling platform. The
21 lower end of the tubular is then oriented over the existing drill string
and connected to the
22 terminal, surface end of thereof. Following connection of the tubular to
the drill string and
23 "torquing" to establish a tight connection, the drilling operation is
continued. As indicated
24 above, tubulars are generally about 30 feet (lOm) in length. As such, the
frequency of adding
tubulars to the drill string is high and, therefore, the efficiency of the
drilling operation is
26 hampered. In addition, the above described manipulation of the tubulars
often requires manual
27 handling and, therefore, increases the risks to the drill rig personnel.
28 [0004] Various apparatuses and methods have been proposed for handling
tubulars such as
29 those provided in the following US patents: 4,547,110; 4,486,137;
6,220,807; 6,705,414;
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1 6,854,520; 6,969,223; 6,976,540; and 6,997,265. The entire disclosures of
which are
2 incorporated herein by reference.
3 [0005] In order to increase the efficiency of the drilling operation,
various methods have
4 been proposed to pre-connect at least two tubulars, to form a "stand", prior
to connection to the
drill string. Such a process is often referred to as "standbuilding". As will
be appreciated, such
6 pre-connection step involving two tubulars will reduce by half the number of
connections
7 required to be made to the drill string and, therefore, allows the drilling
process to continue with
8 fewer interruptions. An example of such a standbuilding procedure is
provided in related US
9 patents 6,976,540 and 6,997,265. In these references, a tubular is rolled
from a rack onto a ramp
positioned adjacent the drilling platform. One end of the tubular is raised by
a hoist to a vertical
11 orientation above the drilling platform. The tubular is then inserted into
an opening in the
12 drilling platform adjacent to the existing drill string. A further tubular
is then vertically hoisted
13 and aligned above the first tubular. The opposing ends are of the two
tubulars are then connected
14 together to form a vertical, dual tubular stand. The stand is then raised
and secured to the drill
string. During formation of the stand, the drilling operation is continued
without interruption.
16 [0006] Another example of a standbuilding operation is provided in US
patent 6,705,414. In
17 this reference, a stand is formed on a horizontal catwalk associated with a
drilling platform.
18 According to the disclosed method, two pairs of tubulars are positioned end
to end on the
19 catwalk. A "bucking machine" is then used to join the two tubulars. The
bucking machine
includes jaws that grasp and axially rotate the tubulars in opposite
directions so as to engage the
21 threads on the respective ends and to torque the connection to the desired
value. Two stands are
22 formed in this manner, which are then loaded onto a"trolley". The trolley,
carrying the two
23 stands, is hoisted onto the drill rig platform and oriented vertically. The
stands are then removed
24 from the trolley and either connected to the drill string or stored in the
vertical position for later
connection to the drill string.
26 [0007] Thus, there exists a need for a simple and efficient means for
forming stands.
27 SUMMARY OF THE INVENTION
28 [0008] In one aspect, the present invention provides a method of forming a
stand from
29 tubulars comprising:
- providing a supply of tubulars;
2
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1 - providing an elongate stand forming apparatus comprising a front end, rear
end
2 and mid section;
3 - loading a first tubular on the stand forming apparatus, wherein the first
tubular is
4 positioned generally parallel therewith;
- pulling the first tubular towards the rear end of the apparatus;
6 - loading a second tubular on the stand forming apparatus, wherein the
second
7 tubular is positioned generally parallel therewith and wherein the second
tubular is
8 positioned in general coaxial alignment with the first tubular;
9 - rotating the first and second tubulars about their longitudinal axes and
in
opposite directions; and,
I 1 - advancing the first tubular against the second tubular during the
rotation
12 whereby cooperating threads on each opposing end of the first and second
tubulars are
13 engaged to form a stand.
14 [0009] In another aspect, the present invention provides an apparatus for
forming a stand
from tubulars comprising:
16 - a generally horizontal, elongate catwalk having a frame with a top
surface
17 adapted to receive at least two of the tubulars aligned in a coaxial
manner, the frame
18 having a front end, a rear end, and a mid section;
19 - a pulling means adapted to grip and pull a first of the tubulars towards
the rear
end of the catwalk;
21 - a pushing means adapted to advance the first tubular to the front end of
the
22 frame; and,
23 - a rotating means for rotating the tubulars about their longitudinal axes.
24 BRIEF DESCRIPTION OF THE DRAWINGS
100101 These and other features of the invention will become more apparent in
the following
26 detailed description in which reference is made to the appended drawings
wherein:
27 [0011] Figure 1 is a side elevation of a stand forming apparatus according
to an aspect of the
28 invention with a first tubular loaded thereon.
29 [0012] Figure 1 a is a front elevation along the line A-A of Figure 1.
[0013] Figure 2 is a plan view of the apparatus of Figure 1.
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1 [0014] Figure 3 is a side elevation of the apparatus of Figure 1 with a
second tubular loaded
2 thereon.
3 [0015] Figure 3a is a front elevation along the line B-B of Figure 3.
4 [0016] Figure 4 is a side elevation of the apparatus of Figure 1 wherein the
formed stand is
elevated towards a drilling rig.
6 [0017] Figure 4a is a front elevation along the line C-C of Figure 4.
7 [0018] Figure 5 is a side elevation of the apparatus of Figure 1 shown in a
folded state
8 without tubulars.
9 DETAILED DESCRIPTION OF THE INVENTION
[0019] As described further below in more detail, the present invention
provides an
11 improved apparatus for forming stands from individual tubulars. In general,
the invention
12 comprises a catwalk onto which are loaded two tubulars. The tubulars are
positioned generally
13 coaxially on the catwalk in an end-abutting arrangement. The catwalk is
provided with lifting
14 devices comprising, in one aspect, actuating arms having rollers that
contact and raise the
tubulars above the level of the catwalk. The rollers are driven by one or more
motors and are
16 arranged so that the tubulars are axially spun in opposite directions with
respect to each other.
17 During the spinning operation, the tubulars are advanced against each other
whereby the
18 complementary threads on each end engage to form a connection, thereby
forming a dual tubular
19 stand. As will be understood, the tubulars are arranged so that the male
and female ends are in
abutting arrangement so as to permit engagement. The arms are then lowered
whereby the now
21 formed stand is allowed to rest on the catwalk, preferably in a trough or
groove provided thereon.
22 The stand is then pushed towards the drilling rig. A ramp provided either
on the catwalk or on
23 the rig causes one end of the stand to be raised during the pushing process
up to a point where a
24 hoist on the drill rig can engage and pull the stand to the desired
vertical position over the
drilling platform. The stand can then be stored or immediately connected to an
existing drill
26 string. The apparatus of the invention is transportable and certain
sections can be folded to
27 facilitate such transport.
28 [0020] Thus, the invention provides a simple and efficient means of forming
a stand. The
29 invention can also be operated to load individual tubulars as well directly
onto a rig in situations
where a stand is not needed. In another aspect, the apparatus of the invention
can operate in the
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1 opposite manner wherein stands are received from the rig and then separated
or dismantled into
2 individual tubulars.
3 [0021] Figure 1 illustrates an embodiment of the apparatus of the invention.
The catwalk
4 apparatus 10 comprises a frame having a front end section 12, a rear end
section 16 and a mid
section 14. The structure of the frame is commonly known and may comprise
struts and support
6 members and the like. As will be understood by persons skilled in the art,
various structures for
7 the frame are possible. In one embodiment, the apparatus 10 is adapted to
rest on the ground;
8 however, in other embodiments, the apparatus may include tracks, wheels or
other such devices
9 upon which the frame rests. The front end 12 of the apparatus 10 is inclined
upwards and is
preferably adjustable so as to reach to the level of the drilling platform. In
general, the front end
11 12 can be inclined to a point where a tubular or stand resting thereon can
be grasped by a hoist or
12 similar device provided on the drill rig. In another embodiment, the
catwalk apparatus 10 does
13 not include a front end portion 12 as shown in the accompanying drawings.
Such a situation may
14 occur where the drilling rig itself includes a suitable ramp that functions
in the same manner as
the front end 12.
16 100221 The catwalk 10 includes a top surface 17 which receives and
manipulates tubulars as
17 will be described further below. In a preferred embodiment, the top surface
17 includes a groove
18 or "V" or "U" shaped surface for locating the tubular in a desired location
thereon. An example
19 of such a groove is illustrated as element 19 in Figure 4a. Various other
means for retaining
tubulars on the top surface 17 will be known to persons skilled in the art. It
will be understood
21 that such retaining means serve to prevent tubulars from rolling or other
such unwanted
22 movements.
23 [0023] In operation, the catwalk apparatus 10 is first positioned adjacent
a drilling rig (not
24 shown) such that the catwalk extends generally perpendicularly from the rig
and such that the
front end section 12 is adjacent the rig. As indicated above, the front end
section 12 is inclined
26 upwards so as to be roughly at the level of drilling platform (not shown)
of the rig. As
27 mentioned above, in another aspect, the catwalk apparatus 10 does not
include a front end
28 section 12 and such functionality is instead provided by a ramp provided on
the drill rig.
29 [0024] Figure 2 illustrates a plan view of the catwalk apparatus wherein
the front end section
12 is not shown for convenience. Moreover, various other elements of the
catwalk 10 such as
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1 decking etc. are not illustrated but will be apparent to persons skilled in
the art. As shown in
2 Figure 2, a supply rack 18 containing a supply of tubulars 20 is positioned
adjacent to the
3 catwalk apparatus 10. The tubulars 20 are preferably provided in a generally
parallel
4 arrangement on the rack 18. As discussed above, the tubulars, as commonly
known in the art,
have male and female ends each provided with complementary threads. Thus, in a
preferred
6 embodiment, the tubulars 20 on the rack 18 are arranged so that all of the
respective male and
7 female ends are positioned in the same orientation. More preferably, in
order to facilitate the
8 present method, the tubulars are oriented such that all female ends are
pointed towards the
9 catwalk front end 12 (i.e. pointed towards the drilling rig). The purpose of
such preferred
arrangement will be apparent from the following description.
11 [0025] As shown in Figure 2, the supply rack 18 is positioned close to the
catwalk 10 so as to
12 facilitate transfer of tubulars 20 from the rack 18 to the catwalk 10. In
one embodiment, the
13 catwalk 10 and rack 18 are arranged so as to allow a tubular to roll from
the rack onto the top
14 surface 17 of the catwalk 10. As will be understood, in such arrangement,
the catwalk top
surface 17 would be slightly lower than the rack 18 so as to allow such
rolling. In one
16 embodiment, the catwalk apparatus 10 would be vertically adjustable whereby
the catwalk could
17 be lowered to allow a tubular to roll thereon from the rack. The catwalk
can then be raised to a
18 height above the rack so that, during a stand dismantling operation
(discussed further below), the
19 tubulars can roll from the catwalk onto the rack. It will be understood
that in other
embodiments, any difference in height may also be overcome by using a forcing
means to urge
21 tubulars between the catwalk and the rack. In such case, a difference in
height would not pose a
22 problem for the tubular transfer step. In yet another embodiment, tubulars
can be transferred
23 between the rack 18 and the catwalk apparatus 10 by means of a crane or any
other similar
24 device. Various other tubular transfer mechanisms will be known to persons
skilled in the art.
[0026] The catwalk apparatus 10 of the invention also preferably includes a
skate 22 that is
26 arranged to generally traverse the length of the catwalk from the rear end
section 16 to the front
27 end section 12. The skate 22 includes a clamp to grasp one end, preferably
the male end, of a
28 tubular after being loaded on the catwalk top surface 17 and to pull same
towards the rear end
29 section 16 of the catwalk apparatus. The skate 22 also includes a bearing
surface for pushing the
tubular along the length of the catwalk towards the front end section 12. The
skate 22 can be
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1 provided on a track or groove on the catwalk. One example of an arrangement
for the skate is
2 taught in US patent 6,969,223 wherein a "pusher" member is described for
advancing tubulars
3 longitudinally along a catwalk. As will be apparent to persons skilled in
the art, the skate 22 can
4 be advanced in either direction by a mechanical means (such as using a cable
attached to a
motor), a hydraulic means (such as by using a cylinder and piston combination)
or any other
6 means. Further, as described above, the skate is provided with a clamp for
attaching to an end of
7 one tubular. Such clamps are commonly known in the art and any suitable
clamp mechanism
8 can be used for the skate. For example, one such clamp is shown in US patent
6,976,540, which
9 teaches a "gripping device" for grasping an end of a tubular. It will be
understood that the skate
22 may, in one embodiment, include a threaded portion (not shown) with threads
that are
11 complementary to those provided on the end of the tubular. In this way,
instead of clamping or
12 grasping a tubular, the threaded portion of the skate 22 may be rotated to
engage the end of the
13 tubular. Rotation in an opposite direction would then disengage the skate.
Various other
14 gripping means for the skate will be apparent to those skilled in the art.
100271 In operation, as shown in Figures 1 and 2, a first tubular 20a is
rolled or otherwise
16 placed onto the top surface 17 of the catwalk apparatus 10. As shown, in
the preferred
17 arrangement, the female end 24 of the tubular 20a is directed towards the
front end of the
18 catwalk apparatus 10. The skate 22 is then advanced towards the tubular and
grips the male end
19 26 thereof. The skate 22, in a "pull" mode, is then retracted to the rear
end portion 16 of the
catwalk apparatus 10. In this way, the first tubular 20a is pulled towards the
rear end portion 16.
21 This position is illustrated in Figure 1 which also shows the skate 22
gripping the tubular 20a.
22 Once the skate 22 has reached its terminal point on the catwalk apparatus
10, the gripping
23 mechanism is released. This position is shown in Figure 3. As will be
understood by the
24 discussion herein, the terminal position of the skate 22 on the rear end 16
of the apparatus 10 is
the position that pulls the first tubular 20a a sufficient distance so as to
allow another tubular 20
26 to be loaded onto the top surface 17.
27 [0028] Figure 3 illustrates the next step in the process wherein a second
tubular 20b is
28 provided on the top surface 17 of the catwalk apparatus 10. As with the
first tubular 20a, the
29 second tubular 20b is oriented with its female end 28 directed towards the
front end section 12 of
the catwalk apparatus 10. The male end 30 of the second tubular 20b is
positioned adjacent and
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1 in opposition to the female end 24 of the first tubular 20a. Further, as can
be seen in Figure 3,
2 both tubulars 20a and 20b are positioned on the top surface 17 of the
catwalk 10 and aligned so
3 as to be coaxial with each other. As will be understood, the groove 19 (as
shown in Figure 4a)
4 serves to maintain the desired alignment of the tubulars 20a and 20b. Once
the two tubulars 20a
and 20b are provided on the top surface 17, a plurality of lifting devices 32
(a - d), provided on
6 the catwalk apparatus 10, are actuated. The lifting devices 32 preferably,
and in one aspect,
7 comprise actuating arms 33 at the ends of which are provided driven rollers
34. Such lifting
8 devices are illustrated in Figures la, and 3a. As can be seen, according to
one embodiment, each
9 arm is provided with a pair of opposed rollers. As shown in Figure 1a, the
rollers are arranged so
as to form a pinch point 31 there-between, which is adapted to receive a
portion of a tubular as
11 explained further below.
12 100291 In the embodiment shown in Figures 1 and 3, the catwalk apparatus 10
is provided
13 with four lifting devices, 32a to 32d, such that each of the first and
second tubulars, 20a and 20b,
14 are engaged by two lifting devices. Thus, as shown, lifting devices 32a and
32b engage the
second tubular 20b while lifting devices 32c and 32d engage the first tubular
20a. In operation,
16 the roller-bearing ends of actuating arms 33 are raised by any known means,
such as
17 hydraulically, mechanically etc. In such manner, the rollers 34 are raised
up to receive the
18 tubular within the pinch 31 there-between. The arms 33 are raised further
so that the tubular is
19 raised above the top surface 17 of the catwalk apparatus 10. For example,
Figure 3a illustrates
the second tubular 20b contained between two rollers 34 and raised above the
top surface 17.
21 [0030] It will be understood that the top surface 17 of the catwalk is
provided with openings
22 through which the rollers 34 and/or arms 33 may be extended. The rollers 34
are driven either
23 directly or indirectly by motors and the like so as to rotate the tubular
engaged therein about its
24 longitudinal axis. In one embodiment, the rollers 34 are reversibly driven
as will be further
explained below. It will be understood that the arms 33 and rollers 34 are
designed with
26 sufficient strength to support the tubular. It will also be understood from
the present description
27 that the rollers 34 are made of a material that includes a sufficient
coefficient of friction to cause
28 rotation of the tubular. Such materials and other specifications will be
apparent to persons
29 skilled in the art. In addition, although two pairs of lifting devices are
described for the purpose
of lifting the entire lengths of each of the tubulars, it will be appreciated
that any number of
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1 devices may also be provided for achieving the same purpose. For example, it
would also be
2 possible to include only one lifting device per tubular in which case, the
rollers may be elongated
3 to support the length of the tubulars.
4 [0031] Once the two tubulars 20a and 20b are raised above the top surface
17, the rollers are
activated as mentioned above. However, it should be noted that the rollers
engaging the first
6 tubular 20a (i.e. the rollers provided on lifting devices 32c and 32d) are
rotated in a direction
7 opposite to the rollers engaging tubular 20b (i.e. the rollers provided on
lifting devices 32a and
8 32b). In this way, the two tubulars are rotated in opposite directions. Once
axial rotation of the
9 tubulars 20a and 20b is begun, the skate 22, now in "push" mode (as shown in
Figure 3) is used
to advance the first tubular 20a towards the front end 12 of the apparatus 10.
Thus, the female
1 I end 24 of the first tubular 20a is advanced towards the male end 30 of the
second tubular 20b.
12 Due to the opposite rotation of each tubular, and the complementary
threading between the male
13 and female ends (as discussed above), the first and second tubulars are
allowed to engage one
14 another thereby forming a stand. In this process, it will be understood
that the rotation directions
of each of the rollers associated with the two tubulars are selected so as to
allow the respective
16 male end to be threaded onto the respective female end and vice versa.
17 [0032] Once the stand, comprising the joined tubulars 20a and 20b, is
formed, the lifting
18 devices 32 are lowered so as to allow the stand to rest on the top surface
17 of the catwalk
19 apparatus 10. The skate 22 continues in the "push" mode and is advanced
towards the front end
section 12 of the apparatus 10. In this way, the skate 22 bears against the
male end 26 of the first
21 tubular 20a and, therefore, urges the stand in a direction towards the
front end section 12 and
22 towards the drilling rig (not shown).
23 [0033] As illustrated in Figure 4, due to the inclination of the front end
section 12, the
24 section of the stand proximal to the front end section is gradually
elevated as the skate 22 is
advanced. Such elevation continues until the female end 28 of the second
tubular 20b reaches a
26 height wherein a hoist mechanism (not shown) provided on the drilling rig
is able to reach and
27 grip the end of the stand. The hoist mechanism then raises the stand to its
vertical orientation on
28 the drilling platform and the stand is then either connected to the
existing drill string or is stored
29 in the vertical position for future connection. It will be understood that
the stand may require
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1 torquing on the drilling rig to provide a sufficiently tight connection
between the tubulars 20a
2 and 20b. Such torquing can be effected by known devices commonly provided on
the rig.
3 [0034] As will be known to persons skilled in the art, the terminal, surface
exposed end of a
4 drill string is normally the female end. As such, the lower end of the now
vertical stand should
comprise the male end in order to mate with the existing drill string. As will
be understood from
6 the above description, by positioning the tubulars on the rack with the
female ends directed
7 towards the front end section 12 of the catwalk apparatus 10, the formation
of the stand takes
8 place in such a manner that the formed stand, when oriented vertically, is
in the desired position
9 with the male end pointed downwards. It will also be understood that the
opposite orientation of
the tubulars and stands will be required should the exposed drill string end
be male.
11 [0035] As will be understood by persons skilled in the art, the above
described process can
12 also be operated in reverse order to dismantle stands. That is, the hoist
on the drilling rig can
13 first extract a stand from a drill string and lower it on to the front end
section 12 of the catwalk
14 apparatus. The skate 22 is then advanced and activated to grip the free end
(usually the male
end) of the stand. The skate is then retracted towards the rear end section 16
of the catwalk
16 apparatus 10 until the stand is rests on top surface 17 in a generally
horizontal orientation and
17 wherein each tubular segment of the stand is positioned above the
respective pairs of lifting
18 devices 32. The lifting devices 32 are then activated as above to raise the
stand above the top
19 surface 17. The rollers are then actuated to rotate in opposite directions
as before, but in this
case, such rolling is used to disconnect (i.e. unscrew) the tubulars. Once
separated, one of the
21 tubulars is then loaded onto the rack 18 by either rolling or by means of a
device such as a crane
22 etc. The remaining tubular is then pushed by the skate 22 to a position on
the top surface 17 that
23 enables the tubular to be moved to the rack as well.
24 [0036] Another feature of the present invention is the capability to
automate the
standbuilding operation. That is, as described above, very little manual
manipulation of the
26 tubulars or stands is needed. Thus, the entire process can be coordinated
by an operator
27 positioned away from the catwalk. In this way, the present invention
provides a stand make-up
28 and break-up system which comprises a safer alternative than processes
known in the art. It will
29 be understood that the apparatus discussed above will include suitable and
commonly known
electrical connections and/or processors etc. to enable such automation. For
example, the system
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1 of the invention would include a control system to enable one or more
operators to control
2 various mechanisms on the catwalk 10, the rack 18 and/or the drill rig (i.e.
the hoist). In such
3 case, the rack may be provided with an automated feeder to feed single
tubulars to the catwalk
4 top surface 17. The skate 22 and lifting devices 32 may in turn be
controlled remotely by means
of commonly known control circuitry. Similarly, the hoist described above may
also be
6 controlled remotely by the same operator so as to cause vertical lifting of
the stand onto the rig.
7 In one embodiment, the system may be controlled by a computer based control
system, which
8 can coordinate all of the above functions.
9 [0037] Figure 5 illustrates a further feature of the invention. As shown,
the front end 12 and
rear end 16 sections of the catwalk apparatus 10 can be folded over the mid
section 14. In this
11 way, the apparatus 10 can be reduced in size to facilitate transportation
between sites.
12 [0038] The above description has focussed on "making up" a dual tubular
stand. However, it
13 will be appreciated that the present apparatus also provides a safe and
efficient means of loading
14 even single tubulars onto a drilling platform. In such a process, a tubular
is loaded onto the top
surface 17 of the catwalk apparatus 10 as described above and the skate 22 is
used to push the
16 tubular towards the rig. As described above, the combination of the pushing
action by the skate
17 22 and the inclination of the front end section 12, causes the front end of
the tubular to be raised
18 towards the drilling platform. A hoist mechanism (as described above) on
the drill rig can then
19 be used to raise the tubular to a vertical orientation and positioned on
the drilling platform. As
discussed above, the automation of the process enables an operator or a
control system to
21 remotely control this operation.
22 [0039] It will be understood that the above description has focussed on the
formation of
23 stands including two tubulars (i.e. a dual make-up stand). However, the
apparatus described
24 above may also be adapted to form stands with any number of tubulars.
Persons skilled in the art
will recognize that a functional limit in the length of stands lies in the
height of the derrick
26 provided on the drill rig.
27 [0040] In the above description, the skate 22 has been described as
performing two
28 functions, namely the "pulling" and "pushing" of tubulars. However, it will
be understood that
29 such dual role of the skate is a preferred embodiment. In other embodiments
of the invention,
each of these functions can be performed with two separate skate-like devices.
Thus, one device
1
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1 may comprise a gripping mechanism to pull tubulars while a second device may
comprise a
2 bearing surface for pushing tubulars.
3
4 [0041] Although the invention has been described with reference to certain
specific
embodiments, various modifications thereof will be apparent to those skilled
in the art without
6 departing from the spirit and scope of the invention as outlined herein. The
disclosures of all
7 prior art recited herein are incorporated herein by reference in their
entirety.
8
9
12
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