Patent Publication Number: US-2023144686-A1

Title: Systems and Methods for Tethering Subsea Blow-Out-Preventers

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. application Ser. No. 17/482,184 filed on Sep. 22, 2021, now U.S. Pat. No. 11,549,325, which is a continuation of U.S. application Ser. No. 17/432,828 filed on Aug. 20, 2021, now U.S. Pat. No. 11,473,387, which is a national stage entry of International application serial no. PCT/US2020/018874 filed on Feb. 19, 2020, which claims priority to U.S. provisional application Ser. No. 62/808,486 filed on Feb. 21, 2019. U.S. application Ser. No. 17/432,828, U.S. application Ser. No. 17/482,184, International application serial no. PCT/US2020/018874, and U.S. provisional application Ser. No. 62/808,486 are hereby incorporated by reference for all and any purposes. 
    
    
     BACKGROUND 
     This disclosure relates to systems and methods for tethering subsea Blow-Out-Preventers. 
     Known tensioning systems for tethering subsea Blow-Out-Preventers (“BOPs”) have included high load capacity—on the order of tens of Metric Tons (“MTs”), reels that are used with high stiffness synthetic ropes, or in-line tensioners that are used with pre-cut ropes—either wire ropes or synthetic ropes. Each of these known tensioning systems has strengths and flaws. On the one hand, the reels and locking mechanisms disclosed in U.S. Pat. No. 9,359,852 can allow adjusting the tension in the rope attached between each reel and the subsea BOP with a good resolution. Also, a broad range of rope length can be unwound from each reel, therefore allowing tethering the subsea BOP to anchors located at variable distances from the subsea BOP using a standard set of ropes. However, the tension in the rope tends to relax during use because the rope loops wound on the reel drum can move relative to other rope loops wound on the reel drum. In general, the longer the rope wound on the reel drum is, the easier the tension relaxes. On the other hand, in-line tensioners are structurally simpler than the reels and locking mechanisms disclosed in U.S. Pat. No. 9,359,852. However, in-line tensioners do not usually allow tethering the subsea BOP to anchors located at variable distances from the BOP using a standard set of ropes because the ropes must be pre-cut based on the measured distance between the subsea BOP to the anchors. Also, it is difficult to reuse the ropes so pre-cut on a different subsea BOP. 
     Thus, there is a continuing need in the art for systems and methods for tethering subsea Blow-Out-Preventers. 
     BRIEF SUMMARY OF THE DISCLOSURE 
     The disclosure describes a tensioning system for tethering a subsea BOP. The tensioning system may comprise a frame and a reel rotatably coupled to the frame. 
     The tensioning system may comprise a tensioning cylinder attached to the frame and a tensioning piston reciprocally disposed in the tensioning cylinder. The tensioning piston may be hollow. 
     The tensioning system may comprise a gripper assembly movable together with the tensioning piston. The gripper assembly may be hollow. The gripper assembly may include a gripper sleeve. The gripper sleeve may have an expanded position that allows a rope to pass through the gripper assembly without excessive resistance. The gripper sleeve may have a collapsed position that holds the rope. The gripper assembly may include a gripper cylinder movable together with the tensioning piston. The gripper assembly may include a gripper piston reciprocally disposed in the gripper cylinder. The gripper assembly may include a lock sleeve attached to the gripper cylinder. The lock sleeve may be configured to selectively engage an outer diameter of an end of the gripper sleeve. For example, the gripper sleeve may be elastically deformable. Engagement of the lock sleeve with the outer diameter of the end of the gripper sleeve may cause the gripper sleeve to elastically deform toward the collapsed position. 
     The tensioning system may comprise an insert provided inside the tensioning piston. The insert may include two tapered inner surfaces. The gripper assembly may include a nose that is at least partially contacting one of the two tapered inner surfaces. The other of the two tapered inner surfaces may be curved. 
     The disclosure also describes a tethering system for tethering a subsea BOP. 
     The tethering system may include an anchor, a tensioning system as described herein, and a rope. A first end of the rope may be attached to the reel of the tensioning system. A second end of the rope may be attached to one of the subsea BOP and the anchor. The tensioning system may be mounted on the other of the subsea BOP and the anchor. 
     The tethering system may comprise a capstan rotatably coupled to the frame of the tensioning system. The rope may be wrapped around the capstan. The capstan may have a locked position wherein rotation of the capstan is prevented. The capstan may have an unlocked position wherein the capstan is capable of rotating freely. 
     The tethering system may comprise a rope deflector. The rope deflector may be positioned such the rope is aligned with the gripper assembly of the tensioning system when the rope is in tension. 
     The tethering system may comprise a reel lock handle configured to prevent further rotation of the reel and an interface configured to wind or unwind the rope on the reel. The reel lock handle and the interface may be engaged by a Remotely Operated Vehicle (“ROV”). 
     The tethering system may comprise a mechanical lock releasably attached to the frame of the tensioning system, and a mechanical lock handle configured to release the mechanical lock from the frame. The tensioning cylinder of the tensioning system may be held by the mechanical lock. 
     The disclosure also describes a method of tethering a subsea BOP. 
     The method may comprise the step of providing a tensioning system and/or a tethering system as described herein. The method may comprise the step of providing a rope. The method may comprise the step of attaching a first end of the rope to the reel of the tensioning system. The method may comprise the step of attaching a second end of the rope to one of the subsea BOP and the anchor. The method may comprise the step mounting the tensioning on the other of the subsea BOP and the anchor. 
     The method may comprise the step of moving the gripper sleeve of the tensioning system 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. For example, the method may comprise the step of moving a gripper piston disposed inside a gripper cylinder of the tensioning system may be moved. The method may comprise the step of engaging an outer diameter of an end of the gripper sleeve with a lock sleeve attached to the gripper cylinder for causing the gripper sleeve to move from the expanded position to collapsed position. Accordingly, the gripper sleeve may be elastically deformed by engaging the lock sleeve with the outer diameter of the end of the gripper sleeve. 
     The method may comprise the step of moving a gripper cylinder together with the tensioning piston for adjusting the tension of the rope. 
     The method may comprise the step of wrapping the rope around the capstan. The method may comprise the step of unlocking the capstan rotatably whereby the capstan is capable of rotating freely relative to the frame. The method may comprise the step of locking the capstan whereby rotation of the capstan is prevented. 
     The method may comprise the step of aligning the rope with the gripper assembly using a rope deflector integrated into the frame. 
     The method may comprise the step of releasing a mechanical lock attached to the frame using a mechanical lock handle, wherein the tensioning cylinder is held by the mechanical lock. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a more detailed description of the embodiments of the disclosure, reference will now be made to the accompanying drawings, wherein: 
         FIG.  1    is an elevation view of a tensioning system in accordance with a first embodiment; 
         FIG.  2    is a top view of the tensioning system shown in  FIG.  1   ; 
         FIG.  3    is a sectional view of a gripper of the tensioning system shown in  FIG.  1   ; 
         FIG.  4    is an elevation view of a tensioning system in accordance with a second embodiment; 
         FIG.  5    is a top view of the tensioning system shown in  FIG.  4   ; 
         FIG.  6    is a sectional view of the capstan shown in  FIG.  5    and illustrated in an unlocked position; 
         FIG.  7    is the second sectional view of the capstan shown in  FIG.  5    and illustrated in a locked position; 
         FIG.  8    is a perspective view of a tethering system in accordance with a first embodiment; and 
         FIG.  9    is a perspective view of a tethering system in accordance with a second embodiment. 
     
    
    
     DETAILED DESCRIPTION 
       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. 
     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. 
     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. 
     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. 
     The ROV panel  28  may include a gauge  34  that indicates the tension in the rope. 
       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 . 
     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. 
     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 ′. 
     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). 
     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. 
     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. 
     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 ′. 
     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 . 
     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 . 
     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. 
     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.