Note: Descriptions are shown in the official language in which they were submitted.
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System, Apparatus And Method For Facilitating Retrieval
Of An Item From A Well
This is a divisional application of Canadian Patent
Application Serial No. 2,319,258 filed on January 22, 1999.
This invention relates to a system, an apparatus and a
method for facilitating retrieval of an item from a well
and more particularly, but not exclusively, for retrieving
a well head from a sub-sea well. It should be understood
that the expression ~~the invention" and the like
encompasses the subject matter of both the parent and the
divisional applications.
A well head is used to control the flow of well fluids
in a well bore. The well head is usually located at the top
of the well bore. In marine environments the well head is
usually located on the seabed. The well head is generally
mounted on a base plate and attached to a casing string
which forms part of the well bore.
When the well runs dry, or it becomes uneconomic to
obtain oil or gas therefrom, the well is closed down. Well
heads are expensive, therefore it is desirable to retrieve
well heads. It is also mandatory to remove well heads in
certain areas.
Prior to the present invention, well heads were
retrieved using apparatus similar to that disclosed in GB-
A-2 259 930. GB-A-2 259 930 discloses a tool suspended on a
drill string, which tool comprises a grapple for engaging
the top of a string of casing to which a well head is
attached and which is to be retrieved. The tool further
comprises a mud motor and a rotary cutter depending from a
rotor of the mud motor for cutting the casing at a location
below the grapple. The well head can be cut and lifted to
the surface in one operation.
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There have been problems with prior art apparatus for
facilitating retrieval of a well head from a subsea well.
In particular, during retrieval of the well head, the arms
of the grapple underlie a flange on the casing. The
apparatus relies on the weight of the wellhead acting on
the arms of the grapple preventing inadvertent release of
the wellhead. After the casing is cut the wellhead is
lifted through the sea to the surface. In certain sea
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states, particularly sea states with large swells, an
upward force can be applied to the well head which is ,
sufficient to disengage the well head from the grapple.
This unfortunate event has occurred at least once. .
The first aspect of the present invention attempts
to reduce this problem.
According to a first aspect of the invention there
is provided an apparatus for facilitating retrieval of an
item from a well, said apparatus comprising means for
10 engaging an item, for example a grapple characterised in
that said apparatus further comprises locking means for
inhibiting said means from inadvertently releasing said
item.
Preferably, said apparatus further comprises a
mandrel, said means for engaging an item, for example a
well head, mounted thereon.
Preferably, said locking means is actuable by
movement of said mandrel.
Advantageously, one of said mandrel and said means
20 comprises at least one lug moveably arranged in a channel
in the other of said mandrel and .said means; such that,
in use, one of said lug and said channel can move from a
first position in which said means: is able to release
said item to a second position in which said means is
25 inhibited from releasing said item. Preferably, one of
lug and said channel, in use, moves from said first
position to said second position on rotation of said
mandrel with respect to said means. Alternatively, one of
said lug and said channel, in use, moves from said first
30 position to said second position by longitudinal movement
of said mandrel with respect to said means. Preferably,
one of said lug and said channel, in use, moves from said
first position to said second position by a combination
of rotating said mandrel and longitudinal movement of
35 said mandrel with respect to said means.
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Preferably, said means comprises a housing and at
least one arm moveable- thereon.
Advantageously, said at least one arm is moveable
about a pivot on said housing.
~ Preferably, said mandrel comprises a shoulder, which
in use, moves said arm into engagement with said item to
be retrieved upon movement of said mandrel.
There is also provided a system incorporating a
cutting tool, for example a casing cutter and an
apparatus in accordance with the first aspect of the
invention.
Preferably, said system further comprises a mud
motor.
Another problem with prior art apparatus for
facilitating retrieval of a well head from a submerged
well is that swarf generated by the cutting tool can
Impede the operation of the grapple.
A second aspect of the present invention attempts to
reduce this problem.
According to a second aspect of the invention there
is provided a system for facilitating retrieval of a item
from a well, the system comprising a grapple, and a
cutting tool arranged therebelow, characterised in that
said system further comprises means for expelling fluid
under pressure, disposed above said cutting tool.
In use, the fluid tends to inhibit the swarf
travelling upwardly and interrupting with the operation
of the grapple. -
Advantageously, said means is located above said
cutting tool and below said grapple.
Preferably, said system comprises a downhole motor
driven by a fluid, wherein at least part of the exhausted
fluid is expelled through said means.
Advantageously, said means comprises at least one
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hole. Preferably, said at least one hole is located in a
rotating part of said mud motor. Alternatively, said hole ,
may be located in the housing of the grapple.
Advantageously, said means is located in a sub.
~ There is also provided a method for facilitating
retrieval of an item from a subsea well using the
apparatus of the invention, the method comprising the
steps of inserting at least part of said apparatus into a
tubular, rotating said cutting tool, at least part of
said cutting tool engaging said tubular to cut said
tubular, which cutting action generates swarf
characterised in that said method comprises the step of
expelling fluid above said cutting tool for inhibiting
said swarf reaching said grapple.
An apparatus for facilitating retrieval of an item
from a well bore, said apparatus comprising at least one
arm, characterised in that said at least one arm
comprises at least one groove for receiving debris that
might otherwise inhibit the operation of said apparatus.
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For a better understanding of the present invention,
reference will now be made, by way of example, to the
accompanying drawings, in which.
Figure I is a side view of one embodiment of a
system for retrieving a well head, the system
incorporating an apparatus in accordance with a first
aspect of the invention;
Figure 2 is a side view of a modified system for
retrieving well head;
Figure 3A is a side cross-sectional view of part of
the apparatus of Figures 1 and 2;
Figure 3B is a cross-sectional view taken along line
3B-3B of Figure 3A at a first stage of operation;
Figure 3C is a cross-sectional view taken along line
3C-3C of Figure 3A at a first stage of operation;
Figure 3D is a cross-sectional view taken along line
3B-3B of Figure 3A at a second stage of operation;
Figure 3E is a cross-sectional view taken along line
3C-3C of Figure 3A at a second stage of operation;
Figure 3F is an end view of a first embodiment of an
arm of the apparatus of Figure 3A;
Figure 3G is an end view of a second embodiment of
an arm of the apparatus of Figure 3A;
Figure 4A is a bottom view of part of the apparatus
of Figure 3A;
Figures 4B - 4C are cross-sectional views of the
parts of the apparatus shown in Figure 4A;
Figure 4D is a top view of part of the apparatus of
Figure 3A;
Figures 4E - 4G are cross-sectional views of parts
of the apparatus of Figure 3A;
Figure 5A is a top view, partly in cross-section, of
a part of the apparatus of Figure 3A;
Figure 5B is a cross-sectional view taken along line
5B-5B of Figure SA; ,
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Figure 6 is a side cross-sectional view of a part of
the apparatus of Figure 2; ,
Figure 7A is a side cross-sectional view of a part
of the apparatus of Figure 3A;
Figure 7B is a cross-sectional view taken along line
7B-7B of Figure 7A;
Figure 7C is a cross-sectional view taken along line
7C-7C of Figure 7A;
Figure 8A is a top view of a part of the apparatus
of Figure 3A;
Figure 8B is a cross-sectional view taken along line
8B-8B of Figure 8A; and
Figure 8C is a side cross-sectional view of the part
of the apparatus of Figure 8A.
Figure 1 shows a system for retrieving a well head.
The system is generally identified by reference numeral
10.
The system 10 comprises an apparatus 20 and a casing
cutter 30 arranged therebelow. An upper part 40' of a
mud motor 12 is positioned in a drill string 14. Two
safety clamps 16 are secured around the upper part of the
mud motor 12. A lower part 22 of a central mandrel 21 of
the apparatus 20 is threadedly connected to a stabilizer
18_ A lower part 40 of mud motor 12 (e. g. as is typical
with a bearing assembly and into which the power shaft
extends) is connected in the string 14 below the
stabilizer 18 and a lower stabilizer 18' is connected
below the lower part 40 of the mud motor 12. The casing
cutter 30 is threadedly connected below the lower
stabilizer 18'. A bull sub 42, made of rubber-coated
steel is connected below the casing cutter 30 and
inhibits damage to the wellhead as the apparatus is moved
through it prior to cutting of the casing.
The safety clamps 16 are used on the upper part 40'
of the mud motor 12 above the gripping apparatus to limit
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the downward movement of the upper part 40' of the mud
motor 12 thereby limiting the length of casing that is
cut (and to be retrieved) and to ensure that cutting
ceases at a desired point. In another aspect in which a
drill string is used that is rotatable (e. g. in a common
rotary rig) without a mud motor, no safety clamps are
used; and, in one aspect of such a system, a marine
swivel is used on top of the system 10 to facilitate
rotation.
Figure 2 shows a system generally identified by
reference numeral 50.
The system 50 is similar to the system 10 shown in
Figure 1, with the addition of a drain sub 94 located
between the lower stabilizer 18' and the casing cutter
30. The drain sub 49 exhausts into a wellbore annulus
outside the drain sub 44 above the cutting blades 31.
This reduces the pressure drop across the casing cutter
30 or increases the pressure above the casing cutter 30
to that below the cutting blades 31. The reduction in
fluid pressure across the cutting tool 30 results in a
reduced tendency for swarf including cuttings and debris
to be pumped up the wellbore annulus. A portion of the
fluid under pressure flowing from the lower part 40 of
the mud motor flows through the cutting tool 30 and is
applied thereto in order to maintain activation of the
cutting blades 31.
Figure 6 shows the drain sub 44 which has a flow
bore 121 therethrough from top to bottom and an exhaust
port 122 in the wall 44 thereof. There may be several
exhaust ports arranged about the drain sub 44. The system
50 may include any known drain sub or dump sub or a sub
with orifices or ports originally blocked by ruptureable
discs or shear members. An orifice 123 is held in place
in the exhaust port 122 by a snap ring 129. Use of such
an orifice 123, or one of a series of orifices with
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different inner diameters, permits precise control of the
fluid flowing from the drain sub 44. The exhaust port 122 ,
is angled downwards towards the blades of the casing
cutter 30, when the cutting blades 31 are in an extended
position.
In one particular embodiment the total flow to the
mud motor 12 is about 3300 litres per minute (875 gallons
per minute) , the flow out the exhaust port 122 is about
1800 litres per minute (475 gallons per minute), and the
flow to the cutting tool 30 is about 1500 litres per
minute (400 gallons per minute). In this aspect the
orifice 123 has a diameter of about 1.75cm (0.689
inches) and the exhaust port 122 has a diameter of about
l.9cm (0.75 inches). The drain sub 44 can be positioned
anywhere below the lower part 40 of the mud motor 12 and
above the casing cutter 30.
Figure 3A shows a part of the apparatus 20. The
central mandrel 21 has a flow bore 67 therethrough and-
extends movably longitudinally and rotatably through a .
bonnet 23 and through a housing 24. The housing 24 has a
three arm supports 25, each provided with a pin 26 about
which each arm 28 is moveable. Each pin 26 is made from
hardened steel or a similar material, and secured in a
slot 27 in each arm support 25. Each pin 26 may be
circular or, in one aspect they may be elongated (as
viewed from above) and shaped to correspond to the shape
of each slot 27. Each arm 28 is pivotably and latchably
mounted on each pin 26 so that upon upward movement of
the central mandrel 21 an upper shoulder 29 thereof
contacts a lower surface 61 of the arms 28 causing them
to pivot downwardly in arm slots 161 of the housing to a
position as shown in Figure 3A with a lip latch portion
62 engaging an item to be held, for example, a wellhead
(not shown).
A spline spacer 46 (Figure 58) is secured on the
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central mandrel 21, by bolts and/or welding. The top 48
of the spline spacer 46 serves to assure correct
positioning of the central mandrel 21 with respect to the
housing 24 both for correct activation of each azm 28 and
to correctly position co-operative locking apparatus to
be described below. A spring (not shown) may be disposed
between each arm 28 and the bonnet 23 to urge each axm 28
to an unlatched position.
The bonnet 23 is secured to the housing 24 with a
series of bolts 52 extending through a series of support
pillars 54 placed between the bonnet 23 and the housing
24. The bonnet 23 also sits on pillars 152 extending
upwardly from the housing 24. Holes 154 permit fluid
under pressure to flow to a top surface 56 of the arms 28
to flush debris and cuttings away so that proper movement
of the arms 28 is not impeded when the central mandrel 21
moves up to activate the arms.
Figures 3F and 3G show an end view of an end 58 of
one of the arms 28, illustrating a series of notches or
valleys 59 (Figure 3F) or one notch 59a (Figure 3G) made
or formed integrally in the arm. These notches or
valleys may collect debris in such a way that it does not
impede proper arm movement. They also facilitate
flushing of debris from the top of the arm by providing a
channel for movement therefrom_
The system and apparatus according to the present
invention can be used, among other things, to retrieve a
wellhead and the parts that engage and/or accommodate the
wellhead can be customized, configured, and positioned
for any particular wellhead. This includes a space 64
between the arms 28 and the central mandrel 21_
Referring to Figures 3B to 3E there is shown the
central mandrel 21 with a plurality of projecting lugs 66
which are positioned for movement into and out of a
,groove 68 which extends around an interior of the housing
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24 and into which, through slots 72 in the housing 24,
the lugs 66 are movable to achieve co-operative
releasable locking of the mandrel 21 in place. The slots
72 permit the lugs 66 to move into alignment with the
5 groove 68 as the central mandrel 21 is raised (and the
latching arms 28 grip a wellhead) so the lugs 66 can then
be rotated into the groove 68.
Initially as the central mandrel 21 is moved
upwardly, the lugs 66 move up within the housing 24 in
10 slots 72 until they are at the level of the groove 68.
Then the central mandrel 21 is rotated (to the lef t about
60 degrees - counter-clockwise viewed from above) to move
the lugs 66 into the groove 68, thus releasably locking
the central mandrel 21 in place so that the arms 28, now
15 engaging an item, such as a wellhead, and inhibiting
inadvertent release. Upon further subsequent right-hand
rotation of the central mandrel 21, the lugs 66 again
align with the slots 72 at which point the lugs 66 can.
move out of the grooves 68 , downwardly in the slots 72 , ,
20 and away from the housing 24, permitting release of the
arms 28 and disengagement of the arms 28 from the item
being held. In Figure 4H, a lug 66 is locked in place in
the groove 68 if it is in the area 75_
Lugs 77 projecting downwardly from the housing 24
25 are movable in the areas 171 of the spline spacer 46_
When the lugs 66 enter the groove 68 , it is the lugs 77
abutting the raised areas 78 of the spline spacer 46 that
stop movement of the lugs 66 in the groove 68 and prevent
the lugs 66 from entering the next slot 72 in the housing
30 24, i_e_, it is the stopping of the lugs 77 that prevents
the central mandrel 21 from unlocking from the housing
24, that is until the central mandrel's rotation is
reversed (right-hand rotation) to again align the lugs 66
with a slot 72 and thereby free the lugs 66 from the
35 groove 68. ,
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Figure 7A shows a central mandrel 100 like the
central mandrel 21 which is particularly suited for an
embodiment of the present invention in which a marine
swivel is used as described herein. In such an
application a system according to the present invention
may be like the systems of Figs_ 1 and 2, but without any
mud motor or safety clamps. With such an apparatus, a
marine swivel is disposed on top of the bonnet 23 and the
marine swivel preferably has a lower beveled edge that
corresponds to a top beveled edge of the bonnet 2,3. The
system 10, 50 is interconnected with a drill string that
passes through the marine swivel and the drill string
rotates the system 10, 50 from above.
Figure 8A shows a central mandrel 150 for use in a
system (as shown a.n Figures 1 and 2 with a mud motor 12.
Appropriate subs (not shown) are connected above and
below the central mandrel 150 so the resulting
combination looks like the mandrel of Figure 7A, but the
inner diameter of the mandrel 150 is sized to accommodate
the power shaft of the mud motor 12. The lugs 166
correspond to the lugs 66 of the mandrel of Figure 3A. A
grove 181 in the housing 24 accommodates a seal (not
shown) and/or one or more removable shims of different
dimensions so that the housing 24 can fit over a variety
of wellheads and can accommodate each of them.
