Systems and Methods for Tethering Subsea Blow-Out-Preventers

Abstract

A tensioning system includes a combined rope gripper and tension cylinder. A rope passes through the combined rope gripper and tension cylinder. Once the length and/or tension of the rope has been adjusted, a reel lock handle can be actuated to prevent further rotation of the reel. The combined rope gripper and tension cylinder can be actuated to hold the rope. The combined rope gripper and tension cylinder can also be actuated to reduce or prevent the release of tension in the rope.

Claims

1. A tethering system for tethering a subsea BOP, comprising: an anchor; and a tensioning system, the tensioning system including: a frame; a tensioning cylinder attached to the frame; a tensioning piston reciprocally disposed in the tensioning cylinder; a mechanical lock releasably attached to the frame, wherein the tensioning cylinder is held by the mechanical lock; a mechanical lock handle configured to release the mechanical lock from the frame; a gripper assembly movable together with the tensioning piston, the gripper assembly being hollow; and a rope, a first end of the rope being attached to the tensioning system; wherein the gripper sleeve has an expanded position that allows the rope to pass through the gripper assembly without excessive resistance and a collapsed position that holds the rope; wherein a second end of the rope is attached to one of the subsea BOP and the anchor; wherein the tensioning system is mounted on the other of the subsea BOP and the anchor.

2. The tethering system of claim 1, wherein the gripper assembly includes a gripper sleeve, and wherein the tensioning piston is hollow.

3. The tethering system of claim 1, wherein further comprising: a capstan rotatably coupled to the frame, the capstan having a locked position wherein rotation of the capstan is prevented, and an unlocked position wherein the capstan is capable of rotating freely; wherein the rope is wrapped around the capstan.

4. A method of tethering a subsea BOP, comprising: providing a tensioning system, the tensioning system including: a frame; a tensioning cylinder attached to the frame; a tensioning piston reciprocally disposed in the tensioning cylinder; a gripper assembly movable together with the tensioning piston, the gripper assembly being hollow; and a mechanical lock attached to the frame, wherein the tensioning cylinder is held by the mechanical lock; and attaching a first end of a rope to tensioning system; attaching a second end of the rope to one of the subsea BOP and the anchor; mounting the tensioning system on the other of the subsea BOP and the anchor; and releasing the mechanical lock using a mechanical lock handle;

5. The method of claim 3, wherein the gripper assembly includes a gripper sleeve, wherein the tensioning piston is hollow, and wherein the method further comprises moving the gripper sleeve from an expanded position that allows the rope to pass through the gripper assembly without excessive resistance and to a collapsed position that holds the rope.

6. The method of claim 3, comprising: wrapping the rope around a capstan coupled to the frame; unlocking the capstan rotatably whereby the capstan is capable of rotating freely relative to the frame; and locking the capstan whereby rotation of the capstan is prevented.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0022] For a more detailed description of the embodiments of the disclosure, reference will now be made to the accompanying drawings, wherein:

[0023] FIG. 1 is an elevation view of a tensioning system in accordance with a first embodiment;

[0024] FIG. 2 is a top view of the tensioning system shown in FIG. 1;

[0025] FIG. 3 is a sectional view of a gripper of the tensioning system shown in FIG. 1;

[0026] FIG. 4 is an elevation view of a tensioning system in accordance with a second embodiment;

[0027] FIG. 5 is a top view of the tensioning system shown in FIG. 4;

[0028] FIG. 6 is a sectional view of the capstan shown in FIG. 5 and illustrated in an unlocked position;

[0029] FIG. 7 is the second sectional view of the capstan shown in FIG. 5 and illustrated in a locked position;

[0030] FIG. 8 is a perspective view of a tethering system in accordance with a first embodiment; and

[0031] FIG. 9 is a perspective view of a tethering system in accordance with a second embodiment.

DETAILED DESCRIPTION

[0032] FIGS. 1 and 2 show a tensioning system 10, which may be used to tether a subsea BOP to anchors—for example, a suction pile, a Gravity Based Anchor (“GBA”), or a driven pile, secured to the seafloor. The tensioning system 10 includes a frame 12. A pin 14 is secured to the frame 12. In use, the pin 14 may be coupled on either an anchor secured to the seafloor or on the frame of the subsea BOP.

[0033] The tensioning system 10 includes a reel 16 rotatably mounted on the frame 12 on which the first end of a rope (not shown) may be attached. The rope may be wound on and/or unwound from the reel 16 by an ROV engaging interface 18 to accommodate for variable distances between the subsea BOP and one of the anchors. As best seen in FIG. 2, the tensioning system 10 includes a combined rope gripper and tension cylinder 20, which is optionally held by a mechanical lock 22 releasably attached to frame 12. The rope passes through the combined rope gripper and tension cylinder 20. Once the length and/or tension of the rope has been adjusted by the ROV, the ROV may actuate a reel lock handle 24 to prevent further rotation of the reel 16. Also, the combined rope gripper and tension cylinder 20 may be actuated to hold the rope and reduce or prevent the release of tension in the rope. The combined rope gripper and tension cylinder 20 is actuated hydraulically by the ROV, preferably via one or more stabbed connections such as stabbed connection 26 provided in the ROV panel 28. The rope gripper engages hydraulically, and the tension cylinder then provides tension/pays in by application of hydraulic pressure.

[0034] The combined rope gripper and tension cylinder 20, including the rope held therein, can rapidly be released from the frame 12 by the ROV by actuating the mechanical lock handle 30. Actuating the mechanical lock handle 30 releases the mechanical lock 22 from the frame 12, thereby freeing the combined rope gripper and tension cylinder 20 and the rope held therein.

[0035] The frame 12 includes a rope deflector 32 with may be used to ensure that the rope is aligned with the combined rope gripper and tension cylinder 20 when it is in tension.

[0036] The ROV panel 28 may include a gauge 34 that indicates the tension in the rope.

[0037] FIG. 3 shows the combined rope gripper and tension cylinder 20. The combined rope gripper and tension cylinder 20 includes a tensioning cylinder 36, which is held by the mechanical lock 22 (shown in FIGS. 1 and 2). A tensioning piston 38 is reciprocally disposed in the tensioning cylinder 36. Hydraulic fluid pumped in chambers 40 and 40′ displace the tensioning piston 38 relative to the tensioning cylinder 36 and the frame 12. Thus, when the rope is held in the combined rope gripper and tension cylinder 20, the tension in the rope may be varied. The tensioning piston 38 is hollow. An insert 42 is provided inside the tensioning piston 38 and rests on a shoulder 44 of the tensioning piston. The insert 42 has two tapered inner surfaces 46 and 48. Tapered inner surface 48 is preferably curved and is used to guide the rope. Tapered inner surface 46 may be conical, and is used to receive and retain a gripper assembly 50.

[0038] The gripper assembly 50 includes a nose 52 that is sized to engage the tapered inner surface 46. The nose 52 is hollow. A gripper sleeve 60 is provided inside the nose 52. The gripper sleeve 60 has a rough inner surface (e.g., having a plurality of wedges) to grip on the rope. The gripper sleeve 60 is secured inside the nose 52. The gripper sleeve 60 is elastically deformable. For example, the gripper sleeve may have a longitudinal cut providing a C-shaped cross-section. As such, the gripper sleeve 60 has an expanded position that allows the rope to pass through the gripper assembly 50 without excessive resistance and a collapsed position that holds the rope. To function properly, rope properties may be important: high internal friction between the fibers of the rope and a high strength jacketing are preferred. The gripper assembly 50 includes a gripper cylinder 54 that is attached to a base of the nose 52. A gripper piston 56 is reciprocally disposed in the gripper cylinder 54. A lock sleeve 64 is attached to the gripper cylinder 54. The lock sleeve 64 is configured to selectively engage the outer diameter of an end of the gripper sleeve 60 and elastically deform the gripper sleeve 60. Hydraulic fluid pumped in chambers 58 and 58′ displace the gripper piston 56 relative to the gripper cylinder 54, the nose 52, and the gripper sleeve 60. Thus, the gripper sleeve 60 may be selectively collapsed, and when the rope passes through the gripper sleeve, the rope may selectively be held.

[0039] In use, when rope loops wound on the reel drum move relative to one another, hydraulic fluid may enter in chamber 40 from a pressure source, such as an accumulator or a pump. Hydraulic fluid may also leave chamber 40′. This displacement of the hydraulic fluids can allow the movement of the tensioning piston 38 relative to the tensioning cylinder 36 and the frame 12 in a direction toward the reel 16 (shown in FIG. 1 or 2). Since the gripper assembly 50 is movable together with the tensioning piston 38, the gripper assembly 50 may pull on the rope held in the gripper sleeve 60. Accordingly, the tension in the rope may be controlled by the fluid pressure in the chambers 40 and 40′.

[0040] The tensioning system 10 shown in FIGS. 1 and 2 may be suitable for low tension capacity—approximately forty to seventy MTs. The tensioning system 10 may be sufficient to address concerns of BOP fatigue, where the rope stiffness may be more important than tension capacity. Other uses, such as to drive-off BOPs, can require substantially more tension capacity (e.g., in the order of hundreds of MTs).

[0041] The tensioning system 10′ illustrated in FIGS. 4 and 5 shares several elements with tensioning system 10 shown in FIGS. 1 and 2, although some elements of the tensioning system 10′ may be designed for a tension capacity of four hundred MTs.

[0042] One of the differences between the tensioning system 10′ illustrated in FIGS. 4 and 5 and the tensioning system 10 shown in FIGS. 1 and 2 is that the rope deflector 32 of the tensioning system 10 is replaced with a capstan 62 in the tensioning system 10′. Compared to the tension capacity of tensioning system 10 shown in FIGS. 1 and 2, the tension capacity of tensioning system 10′ can be greatly enhanced by the use of the capstan 62, even if the tension capacity of the combined rope gripper and tension cylinder 20 remains essentially the same. Indeed, when the rotation of the capstan 62 is prevented, a large portion of the tension in the rope can be resisted by the friction between the wraps of the rope and the capstan 62. Only a small portion of the tension in the rope may need to be resisted by the combined rope gripper and tension cylinder 20. For example, the hold tension on the back side of the capstan 62 may be reduced by a factor close to ten compared to the load tension on the front side of the capstan 62 for three to four wraps of wire.

[0043] The capstan 62 has the capability to free-wheel during the tensioning operations and then hold its orientation once the rope has been properly adjusted for both length and tension. Accordingly, the capstan 62 has a locked position illustrated in FIG. 6 and an unlocked position illustrated in FIG. 7. For example, the locking mechanism of the capstan 62 may be similar to the locking mechanism shown in FIGS. 10-13 of U.S. Pat. No. 9,359,852, which is included herein by reference. The locking mechanism may be selectively actuated via hydraulic pressure provided by the ROV via stabbed connections provided in the ROV panel 28. Thus, another of the differences between the tensioning system 10′ illustrated in FIGS. 4 and 5 and the tensioning system 10 shown in FIGS. 1 and 2 is that the ROV panel 28 provides additional ROV control for locking and unlocking of the capstan 62 in the tensioning system 10′.

[0044] Turning to FIG. 8, a tethering system 200 includes a plurality of anchors 220, a plurality of tensioning systems 240, and a plurality of ropes 260. Each of the plurality of ropes 260 is connected to the top of each of the plurality of anchors 220 and extends from each anchor 220 to a tensioning system 240 mounted on frame 47 of BOP 41. In this embodiment, each of the plurality of tensioning systems 240 may be similar to the tensioning system 10 shown in FIGS. 1 and 2, or similar to the tensioning system 10′ shown in FIGS. 4 and 5. Tethering system 200 reinforces BOP 41, by resisting lateral loads and bending moments applied thereto. As a result, the tethering system 200 offers the potential to enhance the strength and fatigue resistance of BOP 41. Alternatively, the tethering system 200 may be used to drive-off the BOP 41.

[0045] Turning to FIG. 9, another embodiment of a tethering system 200 for reinforcing BOP 41, wellhead 53, and primary conductor 51. Tethering system 200 includes a plurality of anchors 220, a plurality of pile top assemblies 212 mounted to anchors 220, a plurality of tensioning systems 240 releasably coupled to pile top assemblies 212, and a plurality of ropes 260. In this embodiment, each of the plurality of tensioning systems 240 may be similar to the tensioning system 10 shown in FIGS. 1 and 2, or similar to the tensioning system 10′ shown in FIGS. 4 and 5. Tethering system 200 reinforces BOP 41, wellhead 53, and primary conductor 51 by resisting lateral loads and bending moments applied thereto. As a result, tethering system 200 offers the potential to enhance the strength and fatigue resistance of BOP 41, wellhead 53, and primary conductor 51. Alternatively, the tethering system 200 may be used to drive-off the BOP 41, wellhead 53, or primary conductor 51.

[0046] Preferably, as the BOP 41 shown in FIG. 8 or 9 oscillates, the tensioning cylinder 38 does not cyclically retract and extend together with the rope 260, and the rope 260 may remain held in the short term. For example, a locking mechanism, such as a valve or another restriction, that relies on hydraulic pressure by limiting or preventing fluid from entering in and/or leaving chambers 40 and 40′, may be provided. Furthermore, the rope 260 preferably remains held in the long term. For example, another locking mechanism, such as the reel lock handle 24, the mechanical lock 22, and/or another mechanical lock, that relies on the mechanical fastening of the rope 260, may be provided. In various embodiments, only one or both of the two locking mechanisms may be provided.

[0047] It is to be understood that the disclosure describes several exemplary embodiments for implementing different features, structures, or functions of the invention. Exemplary embodiments of components, arrangements, and configurations are described below to simplify the disclosure; however, these exemplary embodiments are provided merely as examples and are not intended to limit the scope of the invention.