Coiled tubing cutter

[0001] This application claims the benefit of U.S. Provisional Application No. 60/341,449 filed Dec. 17, 2001.

[0002] The present invention relates generally to safety shut-in systems employed during testing or other operations in subsea wells. More specifically, the invention relates to a coiled tubing cutter for use with a safety shut-in system in a subsea well.

[0003] 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.

[0004] 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.

[0005] 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.

[0006] 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.

[0007] 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.

[0008] There exists, therefore, a need for an efficient coiled tubing cutter.

[0018] 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.

[0019] 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.

[0020] 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.

[0021] 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.

[0022] 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 is supported by a fluted hanger 44.

[0023] 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.

[0024] In an embodiment of the present invention, the subsea tree 40 further comprises a cutting module 56 having opposing shear blades 58. The cutting 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 cutting module 56 are activated to sever the coiled tubing prior to the well being shut-in.

[0025] FIG. 2 illustrates a subsea system 20 having an embodiment of the cutting 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.

[0026] 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 is supported by a fluted hanger 44. 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.

[0027] Housed within the subsea tree 40 is an embodiment of the cutting module 56 of the present invention. The cutting 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 cutting module 56 are activated to sever the coiled tubing prior to the well being shut-in.

[0028] FIG. 3 shows an embodiment of the cutting module 56 of the present invention with its blades 58 in their open position. An intervention tool 60 is lowered through the cutting module 56 on coiled tubing 62.

[0029] 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 cutting module 56. One or more pressure ports 72 are located in the outer wall 70 of the cutting module 56 and enable communication of fluid (e.g., gas, hydraulic, etc.) pressure via control lines (not shown) into the pressure chamber 68.

[0030] To activate 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 overlap and 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.

[0031] In some embodiments, to accommodate the overlap of the blades 58, hollow slots 78 (shown in hidden lines) are provided in the face of the opposing blades 58.

[0032] FIG. 4 illustrates an embodiment of the cutting module 56 with the cutting blades 58 activated. The cutting module 56 is housed within a subsea tree 40 that includes a valve assembly 46 having a ball valve 52. The cutting module 56 is located below the ball valve 52.

[0033] Upon activation by applying pressure to the piston 64, the cutting blades 58 act to sever any coiled tubing located within the cutting 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.

[0034] The blades 58 utilized by the cutting 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 cutting module 56 have shown an efficiency of over 100%.

[0035] 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 cutting module 56 of the present invention can cut larger diameter coiled tubing in the absence of tension.

[0036] The blades 58 of the cutting 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.

[0037] 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.

[0038] 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.

[0039] In other embodiments the cutting 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.

[0040] 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.

[0041] 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.

[0042] The cutting 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, hollow slots 78 are provided on the face of the pistons 76 above one of the blades 58 and below the mating blade 58.

[0043] 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.

[0044] 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.

[0045] In the event of an emergency during an intervention operation, the cutting 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.

[0046] 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.

[0047] It is important to note that the above embodiment is useful in both vertical and horizontal wells. Because the cutting 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.

[0048] Another embodiment of the present invention is shown in FIG. 9. In this embodiment, the cutting module 56 is located above the flapper valve 50 and the ball valve 52. As such, this embodiment is useful in vertical wells.

[0049] 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.

[0050] In the event of an emergency during an intervention operation, the cutting 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.

[0051] 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.

[0052] While the invention has been described with respect to a limited number of embodiments, those skilled in the art will appreciate numerous variations therefrom without departing from the spirit and scope of the invention.