U.S. patent application number 11/555713 was filed with the patent office on 2008-05-08 for cutter assembly.
This patent application is currently assigned to SCHLUMBERGER TECHNOLOGY CORPORATION. Invention is credited to Paul Molina, Allyn Pratt, John Yarnold.
Application Number | 20080105436 11/555713 |
Document ID | / |
Family ID | 39226921 |
Filed Date | 2008-05-08 |
United States Patent
Application |
20080105436 |
Kind Code |
A1 |
Molina; Paul ; et
al. |
May 8, 2008 |
Cutter Assembly
Abstract
A cutter module includes a piston and a shear blade. The piston
includes at least two movable telescoping elements that are adapted
to expand from a first retracted length to a second expanded
length. The shear blade is connected to the first piston to sever a
tubing in response to the piston expanding from the retracted
length to the second expanded length. The shear blade has a cutting
edge that has a radius greater than 0.01 inches.
Inventors: |
Molina; Paul; (Pearland,
TX) ; Pratt; Allyn; (Stafford, TX) ; Yarnold;
John; (Webster, TX) |
Correspondence
Address: |
SCHLUMBERGER RESERVOIR COMPLETIONS
14910 AIRLINE ROAD
ROSHARON
TX
77583
US
|
Assignee: |
SCHLUMBERGER TECHNOLOGY
CORPORATION
Sugar Land
TX
|
Family ID: |
39226921 |
Appl. No.: |
11/555713 |
Filed: |
November 2, 2006 |
Current U.S.
Class: |
166/365 ;
166/297; 166/55.6 |
Current CPC
Class: |
E21B 33/063
20130101 |
Class at
Publication: |
166/365 ;
166/55.6; 166/297 |
International
Class: |
E21B 29/08 20060101
E21B029/08 |
Claims
1. A cutter module to sever a tubing in a well, comprising: a
piston comprising at least two moveable telescoping elements
adapted to expand the piston from a retracted length to an expanded
length; and a shear blade connected to the first piston to sever
the tubing in response to the piston expanding from the retracted
length to the expanded length, wherein the shear blade has a
cutting edge having a radius greater than 0.01 inches.
2. The cutter module of claim 1, wherein the radius of the cutting
edge is approximately 0.06 inches.
3. The cutter module of claim 1, wherein the shear blade comprises
S53 stainless steel.
4. The cutter module of claim 1, wherein said at least two moveable
telescoping elements comprises a first telescoping element and
disposed in a second telescoping element, the cutter module further
comprises: a retainer to protect the shear blade and retraction of
the cutter pistons and disassembly of the cutter module.
5. The cutter module of claim 4, wherein the retainer comprises a
backup mechanism to prevent the first telescoping element from
coming out of the second telescoping element if the shear blade
breaks.
6. The cutter module of claim 4, wherein the retainer is adapted to
prevent the shear blade from contacting the second telescoping
element.
7. The cutter module of claim 4, wherein the retainer comprises a
ring.
8. The cutter module of claim 1, wherein one of said at least two
moveable telescoping elements comprises a first telescoping element
that telescopes inside a stationary tubular body and a second
telescoping element that telescopes inside the first telescoping
element.
9. The cutter module of claim 1, further comprising: another piston
opposable to the first piston; a second shear blade connected to
said another piston, wherein said another piston is adapted to move
in concert with the first piston to cause the first and second
shear blades to sever the tubing.
10. The cutter module of claim 1, further comprising: a housing to
contain the shear blade, the housing comprising a slot to guide the
shear blade as the blade extends and retracts.
11. A method to sever a tubing in a well, the method comprising:
moving at least two moveable telescoping elements of a first piston
to cause the first piston to expand from a first retracted length
to a second expanded length; and driving a first shear blade with
the piston to sever the tubing, comprising contacting the tubing
with a cutting edge that has a radius greater than 0.01 inches.
12. The method of claim 11, wherein the contacting comprise
contacting the tubing with a cutting edge that has a radius of
approximately 0.06 inches.
13. The method of claim 11, wherein said at least two movable
telescoping elements comprises a first telescoping element disposed
to move in a cylinder of a second telescoping element, further
comprising: providing a retainer inside the cylinder to limit
motion of the first telescoping element.
14. The method of claim 11, wherein the act of moving comprises:
moving one of said at least two moveable telescoping elements
inside a stationary tubular body and moving another of said at
least two moveable telescoping elements inside said one of said at
least two moveable telescoping elements.
15. The method of claim 11, further comprising: guiding the shear
blade along a slot form in a housing that contains the first shear
blade.
16. A system comprising: a blowout preventer stack adapted to seal
and contain pressure in a well, the blowout preventer having a
passageway through which a tubular string may extend into the well;
a subsea wellhead; a safety shut-in system having a valve assembly
adapted to control flow and adapted to allow tools to be lowered
therethrough on tubing; and a cutter module adapted to be run into
the passageway and adapted to allow tools to be lowered into the
passageway on tubing, the cutter module comprising: a piston
comprising at least two moveable telescoping elements adapted to
expand the piston from a retracted length to an expanded length;
and a shear blade connected to the piston to sever the tubing in
response to the piston expanding from the retracted length to the
expanded length, wherein the shear blade has a cutting edge having
a radius greater than 0.01 inches.
17. A method comprising: providing a kit that includes a set of
differently-sized spacers and a cutter module assembly having
opposable shear blades; and configuring the spacers to establish
different offsets between the shear blades when installed in the
cutter module to accommodate different characteristics of tubing to
be severed by the cutter module.
18. The method of claim 17, wherein the cutter module assembly
comprises at least two movable telescoping elements that comprises
a first telescoping element that telescopes inside a stationary
tubular body and a second telescoping element that telescopes
inside the first telescoping element, the method further
comprising: configuring the spacers to establish different
distances that the first telescoping element travels with respect
to the second telescoping element.
19. The method of claim 17, wherein the first telescoping element
comprises a shaft that extends to one of the shear blades, the
method further comprising: configuring each of the spacers to be
fitted around the shaft.
20. An apparatus comprising: a cutter module comprising opposable
shear blades to sever a tubing in a well; and differently-sized
spacers adapted to be selectively installed in the cutter module to
establish different offsets between the shear blades to accommodate
different characteristics of the tubing.
21. The apparatus of claim 20, wherein the cutter module comprises
at least two movable telescoping elements that comprises a first
telescoping element that telescopes inside a stationary tubular
body and a second telescoping element that telescopes inside the
first telescoping element, and spacers are adapted to establish
different distances that the first telescoping element travels with
respect to the second telescoping element.
22. The apparatus of claim 20, wherein the first telescoping
element comprises a shaft that extends to one of the shear blades,
and each of the spacers is adapted to be fitted around the shaft.
Description
BACKGROUND
[0001] The invention relates generally to a cutter assembly.
[0002] Offshore systems which are employed in relatively deep water
for well operations generally include a riser which connects a
surface vessel's equipment to a blowout preventer stack on a subsea
wellhead. The marine riser provides a conduit through which tools
and fluid can be communicated between the surface vessel and the
subsea well.
[0003] Offshore systems which are employed for well testing
operations also typically include a safety shut-in system which
automatically prevents fluid communication between the well and the
surface vessel in the event of an emergency, such as loss of vessel
positioning capability. Typically, the safety shut-in system
includes a subsea test tree which is landed inside the blowout
preventer stack on a pipe string.
[0004] The subsea test tree generally includes a valve portion
which has one or more normally closed valves that can automatically
shut-in the well. The subsea test tree also includes a latch
portion which enables the portion of the pipe string above the
subsea test tree to be disconnected from the subsea test tree.
[0005] If an emergency condition arises during the deployment of
tools on coiled tubing, for example, the safety shut-in system is
first used to sever the coiled tubing. In a typical safety shut-in
system, a ball valve performs both the function of severing the
coiled tubing and the function of shutting off flow.
[0006] Although somewhat effective, the use of ball valves to sever
the coiled tubing has proven difficult with larger sizes of coiled
tubing. Additionally, use of the ball valves to perform cutting
operations can have detrimental sealing effects on the sealing
surfaces of the valve. Specifically, the sealing surfaces can
become scarred, reducing the sealing efficiency.
[0007] There exists, therefore, a need for an efficient tubing
cutter.
SUMMARY
[0008] In an embodiment of the invention, a cutter module includes
a piston and a shear blade. The piston includes at least two
movable telescoping elements that are adapted to expand the piston
from a retracted length to an expanded length. The shear blade is
connected to the piston to sever a tubing in response to the piston
expanding from the retracted length to the expanded length. The
shear blade has a cutting edge that has a radius greater than 0.01
inches.
[0009] In another embodiment of the invention, an apparatus
includes differently-sized spacers and a cutter module assembly
that includes opposable shear blades that are adapted to sever a
tubing. The spacers are adapted to establish different cutting
offsets between the shear blades.
[0010] Advantages and other features of the invention will become
apparent from the following description, drawing and claims.
BRIEF DESCRIPTION OF THE DRAWING
[0011] FIG. 1 illustrates an offshore system with a subsea tree
having an embodiment of the cutter module of the present
invention.
[0012] FIG. 2 illustrates a subsea system with a subsea tree having
an embodiment of the cutter module of the present invention.
[0013] FIG. 3 shows an embodiment of the cutter module of the
present invention with its blades in their open position.
[0014] FIG. 4 illustrates an embodiment of the cutter module housed
within a subsea tree and with its cutting blades retracted.
[0015] FIG. 5 provides a top view of the V-shaped geometry of one
embodiment of the cutting blades.
[0016] FIG. 6 provides a top view of the curved radii geometry of
one embodiment of the cutting blades.
[0017] FIG. 7 provides a top view of an embodiment of the cutter
module having telescoping pistons.
[0018] FIG. 8 provides a side view of an embodiment of the cutter
module having telescoping pistons.
[0019] FIG. 9 illustrates an embodiment of the cutter module
wherein the cutter module is located below the ball valve.
[0020] FIG. 10 is a schematic diagram of a cutter module assembly
with its blades retracted according to an embodiment of the
invention.
[0021] FIG. 11 is a more detailed view of a shear blade of a cutter
module of FIG. 10 according to an embodiment of the invention.
[0022] FIG. 12 is a more detailed view of a small piston element
and associated components of the cutter module of FIG. 10 according
to an embodiment of the invention.
[0023] FIG. 13 is a perspective view of the shear blade according
an embodiment of the invention.
[0024] FIG. 14 is a cross-sectional view taken along line 14-14 of
FIG. 13 according to an embodiment of the invention.
DETAILED DESCRIPTION
[0025] It should be clear that the present invention is not limited
to use with the particular embodiments of the subsea systems shown,
but is equally used to advantage on any other well system in which
severing of coiled tubing, wireline, slickline, or other production
or communication lines may become necessary.
[0026] Furthermore, although the invention is primarily described
with reference to intervention tools deployed on coiled tubing, it
should be understood that the present invention can be used to
advantage to sever wireline, slickline, or other production or
communication line as necessary.
[0027] Referring to the drawings wherein like characters are used
for like parts throughout the several views, FIG. 1 depicts a well
10 which traverses a fluid reservoir 12 and an offshore system 14
suitable for testing productivity of the well 10. The offshore
system 14 comprises a surface system 16, which includes a
production vessel 18, and a subsea system 20, which includes a
blowout preventer stack 22 and a subsea wellhead 24.
[0028] The subsea wellhead 24 is fixed to the seafloor 26, and the
blowout preventer stack 22 is mounted on the subsea wellhead 24.
The blowout preventer stack 22 includes ram preventers 28 and
annular preventers 30 which may be operated to seal and contain
pressure in the well 10. A marine riser 32 connects the blowout
preventer stack 22 to the vessel 18 and provides a passage 34
through which tools and fluid can be communicated between the
vessel 18 and the well 10. In the embodiment shown, the tubing
string 36 is located within the marine riser 32 to facilitate the
flow of formation fluids from the fluid reservoir 12 to the vessel
18.
[0029] The subsea system 20 includes a safety shut-in system 38
which provides automatic shut-in of the well 10 when conditions on
the vessel 18 or in the well 10 deviate from preset limits. The
safety shut-in system 38 includes a subsea tree 40 that is landed
in the blowout preventer stack 22 on the tubing string 36. A lower
portion 42 of the tubing string 36 may be supported by a fluted
hanger 44 or may alternatively be secured to the wellhead 24 with a
tubing hanger running tool.
[0030] The subsea tree 40 has a valve assembly 46 and a latch 48.
The valve assembly 46 acts as a master control valve during testing
of the well 10. The valve assembly 46 includes a normally-closed
flapper valve 50 and a normally-closed ball valve 52. The flapper
valve 50 and the ball valve 52 may be operated in series. The latch
48 allows an upper portion 54 of the tubing string 36 to be
disconnected from the subsea tree 40 if desired.
[0031] In an embodiment of the present invention, the subsea tree
40 further comprises a cutter module 56 having opposing shear
blades 58. The cutter module 56 is located below the valve assembly
46. If an emergency condition arises during deployment of
intervention tools lowered through the tubing string 36 on coiled
tubing, the blades 58 of the cutter module 56 are activated to
sever the coiled tubing prior to the well being shut-in.
[0032] FIG. 2 illustrates a subsea system 20 having an embodiment
of the cutter module 56 of the present invention. The subsea system
20 is adapted to facilitate production from a well 10 to an
offshore vessel (not shown). The subsea system includes a blowout
preventer stack 22, a subsea wellhead 24, and a safety shut-in
system 38. The subsea wellhead 24 is fixed to the seafloor 26, and
the blowout preventer stack 22 is mounted on the subsea wellhead
24. The blowout preventer stack 22 includes ram preventers 28 and
annular preventers 30 which may be operated to seal and contain
pressure in the well 10. A marine riser 32 connects the blowout
preventer stack 22 to an offshore vessel and provides a passage
through which tools and fluid can be communicated between the
vessel and the well 10. In the embodiment shown, the tubing string
36 is located within the marine riser 32 to facilitate the flow of
formation fluids from the fluid reservoir to the vessel.
[0033] The safety shut-in system 38 of the subsea system 20
provides automatic shut-in of the well 10 when conditions on the
vessel deviate from preset limits. The safety shut-in system 38
includes a subsea tree 40 that is landed in the blowout preventer
stack 22 on the tubing string 36. A lower portion 42 of the tubing
string 36 may be supported by a fluted hanger 44 or may be secured
to the wellhead 24 with a tubing hanger running tool. The subsea
tree 40 has a valve assembly 46 and a latch 48. The valve assembly
46 acts as a master control valve during testing of the well 10.
The valve assembly 46 includes a normally-closed flapper valve 50
and a normally-closed ball valve 52. The flapper valve 50 and the
ball valve 52 may be operated in series. The latch 48 allows an
upper portion 54 of the tubing string 36 to be disconnected from
the subsea tree 40 if desired.
[0034] Housed within the subsea tree 40 is an embodiment of the
cutter module 56 of the present invention. The cutter module 56 is
located below the valve assembly 46 and is shown in FIG. 2 with its
blades 58 in their open position. If an emergency condition arises
during deployment of intervention tools lowered through the tubing
string 36 on coiled tubing, the blades 58 of the cutter module 56
are activated to sever the coiled tubing prior to the well being
shut-in.
[0035] FIG. 3 shows an embodiment of the cutter module 56 of the
present invention with its blades 58 in their open position. An
intervention tool 60 is lowered through the cutter module 56 on
coiled tubing 62.
[0036] The blades 58 are shown in their open position and are
affixed to a piston 64 located within a piston housing 66. A
pressure chamber 68 is defined by the piston housing 66 and the
outer wall 70 of the cutter module 56. One or more pressure ports
72 are located in the outer wall 70 of the cutter module 56 and
enable communication of fluid (e.g., gas, hydraulic, etc.) pressure
via control lines (not shown) into the pressure chamber 68.
[0037] The pressure port(s) 72 are depicted in FIG. 3 as being
located on the side of the cutter module 56. However, in other
embodiments of the invention, the pressure port(s) 72 may be
located on the top surface of the cutter module 56, as little or no
space may be available on the side of the cutter module 56 for the
pressure port(s) 72. More specifically, in these embodiments of the
invention in which the pressure port(s) 72 are located at the top
surface of the cutter module 56, the pressure port(s) 72 are in
communication with the pressure chamber 62 via passageways that are
formed in the outer wall 70.
[0038] To activate, or extend, the blades 58, fluid pressure is
supplied by the control lines to the one or more pressure ports 72.
The fluid pressure acts to push the pistons 64 toward the coiled
tubing 62 until the blades 58 shear the coiled tubing 62 running
within. After the coiled tubing 62 has been cut by the blades 58,
the fluid pressure supplied by the control lines is discontinued
and the pressurized pistons 64 and blades 58 return to their open
state as a result of the much higher bore pressure existing within
the tubing string 36. When testing at surface with no bore
pressure, the pistons 64 and blades 58 can be returned to their
open state by pressurizing alternate control lines.
[0039] In some embodiments, to accommodate the retraction of the
blades 58, material was removed from the supporting side large
piston or piston housing 66. This material was removed from the
complete diameter such that rotation of the large piston or piston
housing 66 does not affect the cutter blade.
[0040] FIG. 4 illustrates an embodiment of the cutter module 56
with the cutting blades 58 retracted. The cutter module 56 is
housed within a subsea tree 40 that includes a valve assembly 46
having a ball valve 52. The cutter module 56 is located below the
ball valve 52.
[0041] Upon activation by applying pressure to the piston 64, the
cutting blades 58 act to sever any coiled tubing located within the
cutter module 56. After the coiled tubing has been severed and
removed from the subsea tree 40, the ball valve 52 is closed to
shut-in the well.
[0042] The blades 58 utilized by the cutter module 56 are designed
specifically for cutting and thus provide a more efficient cut than
traditional equipment such as ball valves used to cut coiled
tubing. In tests conducted within Schlumberger's labs, the
efficiency of a ball valve in cutting is approximately 20% versus a
basic shear approximation. By contrast, the cutting blades 58 of
the cutter module 56 have shown an efficiency of over 100%.
[0043] Additionally, cutting large diameter coiled tubing with ball
valves can require the coiled tubing to be subjected to a large
amount of tension. By contrast, the cutter module 56 of the present
invention can cut larger diameter coiled tubing in the absence of
tension.
[0044] The blades 58 of the cutter module 56 are designed to
prevent the collapse of the coiled tubing being cut. As a result,
the cut coiled tubing is much easier to fish following the severing
process. While any number of blade geometries can be used to
advantage by the present invention, for purpose of illustration,
two example geometries are shown in FIGS. 5 and 6.
[0045] In the top view illustration of FIG. 5, the cutting surface
74 has a V-shaped geometry that acts to prevent the collapse of the
coiled tubing being cut. Similarly, in the top view illustration of
FIG. 6, the cutting surface 74 of the cutting blade 58 has a curved
radii that closely matches the diameter of the coiled tubing
deployed therebetween. Both geometries act to prevent the collapse
of the coiled tubing to enable easier fishing operations.
[0046] As stated above, any number of blade geometries can be used
to advantage to sever without collapsing the coiled tubing. In
fact, most shapes, other than flat blade ends, will accomplish the
same.
[0047] In other embodiments the cutter module 56 utilizes
telescoping pistons. Due to the limited size in the tubing string
36 within which to hold cutting equipment, the use of telescoping
pistons enables greater travel of the pistons, and thus attached
blades, than that achievable with traditional pistons.
[0048] An embodiment of the telescoping pistons 76 is illustrated
in FIGS. 7 and 8. FIG. 7 provides a top view of the telescoping
piston 76 and FIG. 8 provides a side view.
[0049] The telescoping pistons 76 utilize multiple piston layers
and a cutting blade 58. In the embodiment shown, the cutting
surface 74 of the cutting blade 58 is a V-shaped geometry. However,
it should be understood that a curved radii or other applicable
geometry can be used to advantage.
[0050] The cutter module 56 utilizes two telescoping pistons 76
that lie opposite of each other. Upon pressurization, the piston
layers begin their stroke and expand to a length greater than that
achievable with a traditional piston. The telescoping pistons 76
expand until they overlap and the blades 58 shear any material
running between them. To allow for the overlap, the blades 58 have
material removed from specific areas to accommodate the opposite
blade geometry. For example, in some embodiments of the invention,
hollow slots 78 are provided on the face of the pistons 76 above
one of the blades 58 and below the mating blade 58.
[0051] Following the cutting procedure, the supplied pressure is
discontinued and the non-pressurized piston layers of the
telescoping pistons 76 return to their non-extended positions as a
result of the much higher bore pressure within the tubing string.
When testing at surface with no bore pressure, the pistons 76 and
blades 58 may be retracted to their open states by pressuring
alternate control lines.
[0052] In operation, and with reference to FIG. 1, the subsea tree
40 is landed in the blowout preventer stack 22, comprising ram
preventers 28 and annular preventers 30, on the tubing string 36.
The flapper valve 50 and the ball valve 52 in the subsea tree 40
are open to allow fluid flow from the lower portion 42 of the
tubing string 36 to the upper portion 54 of the tubing string 36.
Additionally, the open valves 50, 52 allow for tools to be lowered
via coiled tubing (or wireline, slickline, communication lines,
etc.) through the tubing string 36 to perform intervention
operations.
[0053] In the event of an emergency during an intervention
operation, the cutter module 56 is activated to sever the coiled
tubing. Once severed, coiled tubing remaining in the upper portion
54 of the tubing string 36 is raised until its severed end clears
both the ball valve 52 and the flapper valve 50 of the valve
assembly 46. At this point, the valves 50, 52 can be automatically
closed to prevent fluid from flowing from the lower portion 42 of
the tubing string 36 to the upper portion 54 of the tubing string
36. Once the valves 50, 52 are closed, the latch 48 is released
enabling the upper portion 54 of the tubing string 36 to be
disconnected from the subsea tree 40 and retrieved to the vessel 18
or raised to a level which will permit the vessel 18 to drive off
if necessary.
[0054] After the emergency situation, the vessel 18 can return to
the well site and the marine riser 32 can be re-connected to the
blowout preventer stack 22. The safety shut-in system 38 can be
deployed again and the coiled tubing that remains in the lower
portion 42 of the tubing string 36 can be retrieved through various
fishing operations.
[0055] It is important to note that the above embodiment is useful
in both vertical and horizontal wells. Because the cutter module 56
severs the coiled tubing below the valves 50, 52, the severed
portion of the coiled tubing will not interfere with the closing of
the valves 50, 52.
[0056] Another embodiment of the present invention is shown in FIG.
9. In this embodiment, the cutter module 56 is located above the
flapper valve 50 and the ball valve 52. As such, this embodiment is
useful in vertical wells.
[0057] In operation, the subsea tree 40 is landed in the blowout
preventer stack 22, comprising ram preventers 28 and annular
preventers 30, on the tubing string 36. The flapper valve 50 and
the ball valve 52 in the subsea tree 40 are open to allow fluid
flow from the lower portion 42 of the tubing string 36 to the upper
portion 54 of the tubing string 36. Additionally, the open valves
50, 52 allow for tools to be lowered via coiled tubing (or
wireline, slickline, communication lines, etc.) through the tubing
string 36 to perform intervention operations.
[0058] In the event of an emergency during an intervention
operation, the cutter module 56 is activated to sever the coiled
tubing. Once severed, coiled tubing remaining in the lower portion
42 of the tubing string 36 falls within the vertical well until it
has cleared both the ball valve 52 and the flapper valve 50 of the
valve assembly 46. At this point, the valves 50, 52 can be
automatically closed to prevent fluid from flowing from the lower
portion 42 of the tubing string 36 to the upper portion 54 of the
tubing string 36. Once the valves 50, 52 are closed, the latch 48
is released to enable the upper portion 54 of the tubing string 36
to be disconnected from the subsea tree 40 and retrieved to the
vessel (not shown) or raised to a level which will permit the
vessel to drive off if necessary.
[0059] After the emergency situation, the vessel can return to the
well site and the marine riser 32 can be re-connected to the
blowout preventer stack 22. The safety shut-in system 38 can be
deployed again and the coiled tubing that remains in the lower
portion 42 of the tubing string 36 can be retrieved through various
fishing operations.
[0060] Referring to FIG. 10, in accordance with some embodiments of
the invention, a cutter module assembly 100 may be installed in
place of the above-described cutter modules 56 or 76 in a subsea
string or tree, such as the subsea tree 40. In other embodiments of
the invention, the cutter module assembly 100 may be used in a
subterranean well. A longitudinal axis 110 of the cutter module 100
is generally aligned with the longitudinal axis of the subsea tree
40 where the cutter module assembly 100 is installed. The cutter
module assembly 100 includes two opposing cutter modules 115A and
115B, each of which has a similar design and includes a telescoping
piston. When an activation pressure is concurrently applied to both
cutter modules 115A and 115B, each of the telescoping pistons
extend (each from a length of approximately five inches to a length
of approximately nine inches, for example) to correspondingly
extend two opposing cutter blades, or shear blades 160, for
purposes of shearing a tubing that extends through a central
passageway 102 of the cutter module assembly 100. The shear blades
160, may be curved about the longitudinal axis 110 for purposes of
guiding the tubing to be cut into the shear blades 160.
[0061] As described below, the cutter module assembly 100 has
certain features to prevent breakage and/or damage that may
otherwise occur to cutter blades in connection with cutting a
tubing.
[0062] More specifically, in accordance with some embodiments of
the invention, each shear blade 160 is made of S53 stainless steel,
which is a high strength, high hardness stainless steel that is
significantly ductile. The use of the S53 stainless steel allows
the shear blade 160 to perform multiple cuts with significantly
little wear or deformation.
[0063] Referring to FIG. 11 in conjunction with FIG. 10, in
accordance with some embodiments of the invention, the shear blade
160 may have a general V-shaped cross-sectional profile, which
forces cut tubing pieces apart. The shear blade 160 may also have a
cutting edge 210, which is purposefully rounded. In particular, in
accordance with some embodiments of the invention, a radius R of
the cutting edge 210 may be at least 0.01 inches and may be 0.06
inches (as a more specific example). Other radii are possible and
are within the scope of the appended claims.
[0064] The radius R is small enough so that the tubing is cut,
instead of being collapsed. The radius R is kept sufficiently
large, however, to prevent chips of the shear blade 160 from
breaking off during a cut, which may otherwise occur for a sharper
cutting edge. Additionally, the rounded shape of the cutting edge
210 improves the distribution of stresses within the shear blade
160. More specifically, the rounded profile of the cutting edge 210
prevents high stress along the cutting edge 210, which may occur in
connection with a sharper cutting profile.
[0065] Referring back to FIG. 10, the cutter module assembly 100
has additional features directed to preventing breakage of the
shear blades 160. Turning to the more specific details, the cutter
modules 115A and 115B are disposed in a pressure housing 120 of the
cutter module assembly 100. The central passageway 102 extends
through the housing 120 to form a segment of the overall central
passageway of the subsea tree 40. The housing 120 includes
radially-disposed openings, or pockets 122, which receive the
cutter modules 115A and 115B. In accordance with some embodiments
of the invention, the housing 120 may be made of alloy 718
material.
[0066] The cutter module 115A is described below, with it being
understood that the cutter module 115B has a similar design, in
accordance with some embodiments of the invention. The telescoping
piston of the cutter module 115A is formed from two piston layers
in accordance with some embodiments of the invention, although the
telescoping piston may be formed from more than two piston layers
in accordance with other embodiments of the invention. In the
specific example that is depicted in FIG. 10, the piston layers
include a small piston element 140 (forming one piston layer),
which is disposed inside an inner cylinder 132 of a large piston
element 130 (forming another piston layer). O-rings may be used to
form a seal between the small 140 and large 130 piston
elements.
[0067] Referring to FIG. 12 in conjunction with FIG. 10, the small
piston element 140 includes a piston head 230 which has an upper
surface 231 that develops a force for driving the element 140 when
fluid pressure is applied to activate the cutter module 115A. The
piston head 230 is concentric with the inner cylinder 132 of the
large piston element 130, is closely sized with the diameter of the
inner cylinder 132 and is generally configured to operate within
the inner cylinder 132. The small piston element 140 also includes
a stem 236 that radially extends from the piston head 230 through
an opening 131 (see FIG. 10) of the larger piston element 130. As
depicted in FIG. 10, o-rings may form seals between the outer
surface of piston stem 236 and the opening 131.
[0068] The end of the stem 236 farthest away from the piston head
230 includes an opening 238 that is concentric with the stem 236
for purposes of connecting the small piston element 140 to the
shear blade 160. More specifically, in accordance with some
embodiments of the invention, the shear blade 160 may have a shaft
142 (see FIG. 11), and the shaft 142 may contain outer threads
which engage corresponding threads that line the opening 238.
[0069] Among the other features of the small piston element 140,
the small piston element 140 may be made of alloy 718 material, in
accordance with some embodiments of the invention, and its piston
head 230 may include a profile 232 (see FIG. 12) that facilitates
removal of the small piston element 140 (and attached to shear
blade 160) during disassembly of the cutter module 115A, as further
discussed below.
[0070] As can be seen from the preceding description, the small
piston element 140 translates and transfers hydraulic force into
the shear blade 160 during a cutting operation.
[0071] Referring to FIG. 10, the large piston element 130, in
accordance with some embodiments of the invention, is also
configured to move in response to pressure that is applied to
activate the cutting module 115A. As shown in FIG. 10, the large
piston element 130 is generally disposed in the pocket 122 of the
housing 120 and in general, circumscribes the small piston element
140. A piston cap 124 closes off the otherwise exposed opening of
the pocket 122. Thus, the pocket 122 and cap 124 form a piston
chamber in which the large 130 and small 140 piston elements
operate.
[0072] In accordance with some embodiments of the invention, the
piston cap 124 radially extends into the pocket 122 such that a
cylindrical wall 125 of the piston cap 124 extends between a piston
head 131 of the large piston element 130 and the inner wall (of the
housing 120) that defines the pocket 122. One or more o-rings may
form seals between the piston head 131 and the wall 125 of the
piston cap 124. Additionally, o-rings may form seals between the
piston cap 124 and the inner wall of the pocket 122. The piston cap
124 may be formed from alloy 718 material, in accordance with some
embodiments of the invention.
[0073] As depicted in FIG. 10, the cutter housing 120 includes an
opening 123 between the pocket 122 and central passageway 120
through which the large piston element 130 extends when the cutter
module 115A is activated. O-rings may form a seal between the
housing 122 and the outer surface of the large piston element 130
at the opening 123. Thus, the large piston element 130 may move
radially inwardly in response to pressure; and the movement of the
large piston element 130 also carries the small piston element 140,
which further extends (due to the telescoping arrangement) with the
attached shear blade 160. The large piston element 130 may be
formed of alloy 718 material, in accordance with some embodiments
of the invention.
[0074] For purposes of actuating the telescoping piston, the cutter
module 115A, in accordance with some embodiments of the invention,
includes at least one passageway 126 for purposes of communicating
fluid pressure to the large 130 and small 140 piston elements. More
specifically, in accordance with some embodiments of the invention,
the passageway(s) 126 are routed through the piston cap 124, and
o-rings may straddle the passageway(s) 126 for purposes of sealing
off the passageway(s). The passageway(s) 126 deliver pressure to
the outer surface of the piston heads of the large piston elements
130.
[0075] Among its other features, the large piston element 130 may
also include one or more passageways 133 for purposes of resetting
the position of the telescoping piston when the driving pressure is
released. More specifically, in accordance with some embodiments of
the invention, the passageway (s) 133 extend from a region below
the piston head of the large piston element 130 to a region 132 (in
the inner cylinder) below the piston head of the small piston
element 140. Therefore, after the driving pressure on the
telescoping piston is released, the passageway(s) 133 communicate
pressure to restore the small piston element 140 back to its
recessed position.
[0076] The cutter module assembly 100 may have one or more
additional features to limit or prevent breakage of the shear
blades 160, in accordance with embodiments of the invention. For
example, as depicted in FIG. 10, in accordance with some
embodiments of the invention, the cutter module 115A includes a
piston spacer 150, which may generally be, for example, a ring,
which circumscribes the stem 236 (see also FIG. 12) of the small
piston element 140.
[0077] The piston spacer 150, in general, limits the extension of
the shear blade 160 during operation of the cutter module 115A.
More specifically, the spacer 150 limits the travel of the small
piston element 140 with respect to the large piston element 130
during a cutting operation, as the spacer 150 establishes a fixed
offset between the bottom 233 (see FIG. 12) of the piston head 230
of the small piston element 140 and the otherwise contacting
surface 161 (see FIG. 10) of the large piston element 130. Due to
this travel limitation, a minimum offset, or gap, between the
opposing shear blades 160 may be controlled based on the size of
the tubing to be cut.
[0078] More specifically, it has been discovered that as the shear
blades 160 travel past the point at which the tubing is cut, the
blades and tubing may impact into each other, which causes
excessive transverse stresses (not present during the actual
cutting operation) in the blades 160. These transverse stresses, in
turn, may cause the blades 160 to break. Thus, by limiting the
travel of the shear blades 160, a successful tubing cut may be
achieved, while preventing breakage of the shear blades 160.
[0079] Therefore, in accordance with some embodiments of the
invention, a set, or kit, of differently-sized (i.e., different
thicknesses) piston spacers 150 may be provided with the cutter
module assembly 100 so that the appropriate spacer 150 (i.e., the
piston spacer 150 having the appropriate thickness) may be selected
and installed in the cutter modules 115A and 115B based on one or
more characteristic(s) (size and/or ductility of the tubing, as
examples) of the tubing to be cut. In accordance with some
embodiments of the invention, the same thickness spacer 150 may be
installed in each cutter module 115A and 115B for a particular
cutting application.
[0080] The appropriate thicknesses for the piston spacers 150 may
be determined by test cuts using job-specific tubing samples, for
example. In this regard, by taking measurements off of a
successfully cut tubing, the measurements may be used to select the
correct spacer thickness, so that the appropriately sized set of
spacers 150 (i.e., one for each cutter module 115A, 115B) may be
selected for the tubing that may need to be cut downhole. The
piston spacers 150 may be formed from 316 stainless steel, in
accordance with some embodiments of the invention.
[0081] Referring to FIG. 12 in conjunction with FIG. 10, among the
other features of the cutter module 115A, in accordance with some
embodiments of the invention, the cutter module 115A may include a
retainer ring 138 (see FIG. 12) for purposes of limiting the
movement of the small piston element 140 (and its attached shear
blade 160) during the disassembly of the cutter module 115A. In
this regard, when the cutter module 115A is disassembled and the
piston cap 124 is removed, the small piston element 140 must be
pulled with significant force to remove the entire small piston
element 140, large piston element 130, and shear blade subassembly
(the shear blade 160, shaft 140). The retainer ring 138 prevents
the shear blade 160 from making contact with the large piston
element 130 during this operation thus protecting the shear blade
160 from being damaged or broken.
[0082] To prevent premature disengagement of the small piston
element 140 from the cutter module 115A, the retainer ring 138
forms a stop to hold the small piston element 140 within the large
piston element 130. More specifically, in accordance with some
embodiments of the invention, the small piston element 140 includes
an annular shoulder 250 (see FIG. 12) that is configured to contact
an inner annular portion of the retainer ring 138. An outer annular
portion 260 of the retainer ring 138 extends into a corresponding
annular groove, which is formed in the inner wall of the large
piston element's inner cylinder 132.
[0083] Thus, when the cutter module 115A is completely assembled,
the retainer ring 138 is attached to the large piston element 130
to establish farthest point of retraction for the small piston
element 140. When the cutter module 115A is disassembled, a tool
may be used to engage the profile 232 of the small piston assembly
140 before the retainer ring 138 is removed to allow extraction of
the small piston element 140 and attached shear blade 160. The
retainer ring 138 may be formed from 300 series stainless steel, in
accordance with some embodiments of the invention.
[0084] Referring back to FIG. 10, among the other features of the
cutter module assembly 100, in accordance with some embodiments of
the invention, guide slots 171 (one guide slot 171 being depicted
in FIG. 10) may be machined into the cutter housing 122 for
purposes of guiding and supporting the shear blades 160 as the
shear blades 160 extend and retract. The guide slots 171 keep the
shear blades 160 properly aligned for cutting, normal to the bore.
In some embodiments of the invention, a blade key 170 (formed from
alloy 718 material, for example) may be assembled inside each guide
slot 171 for purposes of providing additional support for the shear
blades 160 during their entire open/close cycle.
[0085] In accordance with some embodiments of the invention, the
cutter module assembly 100 may also include a bore seal sub 190
that forms a scaled connection (via o-rings, for example) with one
end of the cutter assembly housing 122. Additionally, the cutter
module assembly 100 may include a turnbuckle coupling 180 (formed
from high strength steel, for example) that is used for purposes of
connecting the cutter module assembly 100 to the subsea string. The
turnbuckle coupling 180 provides structural support for the cutter
module assembly 100, carries any load that hangs below the cutter
module assembly 100 and may serve as a centralizer when the
assembly 100 is run in and out of hole. The assembly of the cutter
module assembly 100 may further be aided by one or more alignment
pins 181, which guide the assembly 100 into alignment with the rest
of the string or tree.
[0086] FIG. 13 depicts a perspective view of a shear blade 400 in
accordance with some embodiments of the invention. FIG. 14 depicts
a corresponding cross-sectional view taken along line 14-14 of FIG.
13. As can be seen, the shear blade 400 has a cutting surface 414
that has a general curved profile 410, which extends partially
around the longitudinal axis of the cutter module assembly.
Referring to FIG. 14, the cutting surface 414 is also sloped with
respect to the cutter module assembly's longitudinal axis to form a
corresponding V-shaped cross section. Although not depicted in
FIGS. 13 and 14, a cutting edge 418 of the shear blade 400 has a
rounded radius, such as a radius of at least 0.01 inches (0.06
inches, for example), as depicted in FIG. 11. Among its other
features, the shear blade 400 may include a shaft 402, which
includes a threaded receptacle 420 for purposes of attaching the
shear blade 400 to the small piston element 40. It is noted that
the shear blade 400 is one out of many possible embodiments, which
may fall under the scope of the appended claims.
[0087] Other embodiments are within the scope of the appended
claims. For example, in accordance with some embodiments of the
invention, the cutter housing 120 (see FIG. 10, for example) may
include an annular groove on its outer surface for purposes of
lifting and handling the cutter module assembly 100 to assemble the
assembly 100 in a tree. The annular groove permits clamps, which
have corresponding shoulders, to latch on to the cutter module
assembly 100 so that the assembly 100 does not slip during
operation. Thus, the cutter module assembly 100 may be shipped
horizontally and used vertically. The handling gear rotates the
test tree from horizontal to vertical, which may be a significant
operation because of the size and weight of the test tree (a size
of approximately 20,000 pounds and 20+ feet as an example).
[0088] While the invention has been disclosed with respect to a
limited number of embodiments, those skilled in the art, having the
benefit of this disclosure, will appreciate numerous modifications
and variations therefrom. It is intended that the appended claims
cover all such modifications and variations as fall within the true
spirit and scope of the invention.
* * * * *