Abstract:
A diversion assembly to protect a leg of an maritime structure from floating debris includes at least one upper inclined surface and at least one flotation element to buoy the diversion assembly around the leg of the maritime structure, wherein the at least one inclined surface is configured to divert floating debris away from the leg of the maritime structure. A method to protect an offshore platform from damage due to floating debris includes attaching a diversion assembly about the periphery of at least one leg of the offshore platform and diverting the floating debris away from the at least one leg of the offshore platform with at least one inclined surface.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority from Application 61/177,190, filed on May 11, 2009, in the United States. 
    
    
     BACKGROUND OF THE DISCLOSURE 
     1. Field of the Disclosure 
     Embodiments of the present disclosure relate to protection devices and methods to shield maritime structures from damage that may result from impact with floating debris. 
     2. Description of the Related Art 
     Major operating oil and gas companies are now developing exploratory programs to tap into such natural resources in Arctic (and other extreme low-temperature) regions such as the Chukchi and Beaufort Seas. The success and sustainability of such projects may depend on the successful management of risks to personnel and the environment and the deployment of proven and cost effective alternatives to minimize financial risk and maximize the financial return to investment. 
     Drilling operations are at the forefront of such effort and jack-up drilling rigs represent one flexible and attractive mobile drilling unit (“MODU”) solution that may be adaptable to the extreme cold offshore environment. In contrast to a year-round, dedicated (new-build or converted) rig, an existing MODU may offer a proven and cost effective solution as it may be deployed in the summer to take advantage of the warmer Arctic climate and then transferred to other areas of the world during the winter months. 
     Recent studies indicate that while some current jack-up leg chord designs are strong enough to withstand an impact of several inches of ice, the bracing members of the jack-up platforms are generally not. While the risk of such damage may be reduced with an effective ice management plan, it is desirable to have system in place that may protect the legs against ice exposure as an added risk mitigation measure. 
     SUMMARY OF THE CLAIMED SUBJECT MATTER 
     In one aspect, embodiments disclosed herein relate to a diversion assembly to protect a leg of an maritime structure from floating debris, including at least one upper inclined surface, and at least one flotation element to buoy the diversion assembly around the leg of the maritime structure, wherein the at least one inclined surface is configured to divert floating debris away from the leg of the maritime structure. 
     In another aspect, embodiments disclosed herein relate to an offshore platform, including a plurality of legs extending from a working deck of the platform toward a sea floor and a diversion assembly coupled to at least one of the plurality of legs, wherein the diversion assembly includes at least one upper inclined surface, and at least one flotation element to buoy the diversion assembly around the leg of the offshore platform, wherein the at least one inclined surface is configured to divert floating debris away from the leg of the offshore platform. 
     In another aspect, embodiments disclosed herein relate to a method to protect an offshore platform from damage due to floating debris, including attaching a diversion assembly about the periphery of at least one leg of the offshore platform and diverting the floating debris away from the at least one leg of the offshore platform with at least one inclined surface. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       Features of the present disclosure will become more apparent from the following description in conjunction with the accompanying drawings. 
         FIGS. 1A and 1B  are schematics of a diversion assembly in accordance with one or more embodiments of the present disclosure. 
         FIG. 2  is a schematic of a diversion assembly in accordance with one or more embodiments of the present disclosure as installed on a leg of a jack-up rig. 
         FIG. 3  is a close-up view of the installation of  FIG. 2  in accordance with one or more embodiments of the present disclosure. 
         FIGS. 4A and 4B  are schematic view drawings of a ratchet chock system in accordance with embodiments disclosed herein shown in a disengaged ( 4 A) position and an engaged ( 4 B) position. 
         FIG. 5  is a close-up detailed rendering of a roller and chock system in accordance with embodiments disclosed herein. 
         FIG. 6  is a schematic view drawing of a diversion assembly in accordance with embodiments disclosed herein prior to installation. 
         FIGS. 7 ,  8 A,  8 B,  9 , and  10  depict a procedure to install the diversion assembly of  FIG. 6  to a leg of a jack-up rig in accordance with embodiments disclosed herein. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments disclosed herein relate to a diversion assembly configured to protect the legs (or other structures) of offshore drilling rigs in the event of an impact with sheets of water-borne ice. Although embodiments disclosed herein are described in reference to jack-up rigs, those having ordinary skill in the art will appreciate that the embodiments disclosed herein may be applicable to any maritime structure including, but not limited to, various offshore moorings, piers, pilings, permanent platforms, semisubmersible platforms, drillships, tension-leg platforms, spar platforms, and the like. As such, the embodiments disclosed herein may also be applicable to sea-going vessels configured for purposes other than oilfield exploration and production without departing from the subject matter as claimed. Additionally, it is contemplated by the applicants that embodiments disclosed herein may also be useful and applicable in circumstances where various types of floating debris (including, but not limited to, ice flows) are to be diverted away from maritime structures. For example, embodiments disclosed herein may be useful in protecting maritime structures from trash flows, hydrilla, and/or seaweed flows in addition to ice flows. 
     A diversion assembly is proposed to protect maritime structures, including but not limited to jack-up leg members, with minimal impact on the operations of the maritime structure (e.g., rig deployment) and on the structural integrity of the maritime structure (e.g., the legs of the rig). A diversion assembly may comprise a ring having three or four identical modular segments (depending on the vessel class in question) which may form a protective ring around each jack-up leg. Alternatively, any number of modular segments may be provided without deviating from the scope of the present disclosure. Additionally, while a diversion assembly is depicted in the Figures and described below as a generally circular-shaped ring, it should be understood to those having ordinary skill that additional geometric configurations may be constructed without departing from the scope of the attached claims. The various components that make up an exemplary embodiment of one type of diversion assembly are illustrated in  FIGS. 1-5  and keyed to the descriptions below. 
     Referring to  FIG. 1A , a semi-circular diversion assembly  100  may include a number of segments, for example, segments  131 ,  132 ,  133 , and  134 . The structure of each segment  131 ,  132 ,  133 , and  134  may include a central wedge-shaped section having an integral inner buoyant box  101 . The outer wedge may be free-flooding, with an upper inclined surface  102  that may break up encountered ice and a lower inclined surface  103  that may reduce towing resistance and forces due to tidal currents. A vertical ice defector plate  104  may be located atop the upper inclined surface  102 . The buoyant inner box  101  may provide buoyancy to keep the segments  131 ,  132 ,  133 , and  134  afloat. 
     Strong boxes  105  may be provided at ends of the segments  131 ,  132 ,  133 , and  134  to provide additional stiffness to connection points between segments  131 ,  132 ,  133 , and  134 . In certain embodiments, the connection points may be large hinged joints  106  that may have hinge rings attached in a staggered fashion to permit interleaving connection with an adjoining segment. In selected embodiments, the segments  131 ,  132 ,  133 , and  134  may be fastened together by large removable steel hinge pins  107 . 
     Additionally, a roller system may be located adjacent to the hinged points at each end of a segment. Each roller system may comprise two or more split horizontal rubber-coated rollers  108  and supports. An independently-rotating ratchet gear  109  may be attached to the rollers  108  at the center of each roller by a torsion spring (not shown). 
     A movable ratchet chock bar  111  may be located behind the rollers  108  at the ends of each segment. In certain embodiments, chock bar  111  may comprise a slender movable vertical member with a plurality of chock pins  110  attached corresponding to the ratchet gears  109  in each of the split roller assemblies  108 . The chock bar  111  may be free to move in the vertical direction, but may be restrained horizontally by steel guides (not shown). 
     Adjacent to the rollers  108  at each end of the segments  131 ,  132 ,  133 , and  134  may be a buoyant flotation box  112 . Flotation box  112  may be free to move in the vertical direction, but may be restrained horizontally by steel guides and/or tracks  113 . The lowest position to which flotation box  112  may slide may be limited by a stop plate or chock (not shown) fixed to the inner buoyant box  101  and located at the lower end of the track  113 . 
     An actuating lever arm  114  comprised of a steel bar may be connected to both the flotation box  112  on one end, and the ratchet chock bar  111  on the other, by sliding pins  115 . At a point between these two ends the lever arm  114  may be attached to fixed shell-mounted pivot pin  116  such that the lever arm  114  may be free to rotate about the pivot pin  116 , and thus may act as a lever between the flotation box  112  and the ratchet chock bar  111 . Pivot pin  116  may be rigidly attached to the inner buoyant box  101 . 
     Lifting pad eyes  117  may be attached to and/or an integral part of each segment of the diversion assembly  100  that may enable an installed diversion assembly to be lifted clear of the water by cables and/or other mechanisms. 
       FIG. 2  is a schematic of a diversion assembly  200  in accordance with one or more embodiments of the present disclosure as installed on a leg  250  of a maritime structure, such as a jack-up rig.  FIG. 3  is a close-up view of the installation of  FIG. 2 . Diversion assembly  300  is shown as attached to leg  350 . A hinge pin  307  may join two segments of diversion assembly  300 . A chock pin  310  may engage with a ratchet gear  309  thereby holding rollers  308  in place while in contact with leg  350 . 
       FIGS. 4A and 4B  are schematic view drawings of a ratchet chock system in accordance with embodiments disclosed herein shown in a disengaged position ( 4 A) and an engaged position ( 4 B). Chock bar  411  may have chock pins  410  located at distal ends, and may be configured to engage with ratchet gears  409 . Ratchet gears  409  may be configured to lock and/or hold rollers  408  in place, such that rollers  408  may engage with a leg of a maritime structure (see  FIGS. 2 and 3 ). Further, chock bar  411  may be movably connected to a lever arm  414  by a sliding pin  415 . The lever arm  414  and the sliding pin  415  may be rotatable about a pivot pin  416 . 
     Referring to  FIG. 5 , a schematic of the roller assembly is shown. Diversion assembly  500  may have strong boxes  505  adjacent to connecting points between two segments, which may be connected by hinged joints  506  and a hinge pin  507 . Further, each segment may have flotation boxes  512 . The flotation boxes  512  may be engaged with the roller assembly by sliding pins  515  and lever arms  514 . Accordingly, a sliding pin  515  may engage with the flotation box  512  on one end of the lever arm  514 , and another sliding pin  515  may engage with a chock bar  511 . Chock bar  511  may have chock pins  510  that may engage with ratchet gears  509  and rollers  508 . 
     Additionally, while various components described above are indicated as constructed from a particular kind or type of material (e.g., steel, rubber, etc.), it should be understood that the disclosed embodiments shall not be so limited. In particular, as marine environments are notoriously corrosive, various materials disclosed herein may be constructed to minimize galvanic cell and other types of corrosion. Furthermore, as various components are likely to be moveably connected to other components, certain wear-resistant materials may be employed. Finally, as buoyancy is used to “float” components of embodiments disclosed herein, certain light weight (e.g., aluminum, magnesium, titanium, etc) and/or buoyant (e.g., polymers, elastomers, etc) materials may also be used without departing from the scope of the claims listed below. 
     Based upon the embodiments described above, an exemplary procedure to install a diversion assembly as described above will be described with reference to  FIGS. 6 and 7 . Free-floating diversion assemblies  600  and  700  may be transported to installation locations of a drilling vessel (one for each leg) and may be installed around each leg once the drilling vessel has completed normal preload and is jacked up to its intended height above the water surface, or otherwise secured to the ocean floor. 
     For installation, one (or more) of the hinge pins  621  may be removed from each diversion assembly  600  to allow tugs ( 761  and  762  of  FIG. 7 ) to “unfold” the diversion assembly about one or more of the remaining hinge points. Once the diversion assembly is open (see  FIGS. 8-10 ), the tugs  761  and  762  may then maneuver the rollers on the still connected segments into contact with the leg (as shown in  FIG. 3 ). Because the segments of the diversion assembly are buoyant, they may be tugged to an installation location in their partially or completely open state. The open ends of the ring may then be pulled closed and fastened together around the leg (or any other type of structure) by replacing the hinge pin(s)  621 . This is then repeated for each of the remaining legs. 
     Once installed, each diversion assembly may remain free-floating in a vertical direction, but with motion in the horizontal plane restrained by rubber-coated rollers in contact with the outside profile of each leg, such as jack-up leg chords (as shown in  FIG. 3 ). The rollers may allow the diversion assembly to move vertically in either direction in response to wave action and/or changes in water depth due to tidal changes. This arrangement provides a non-permanent attachment to the jack-up legs that may avoid the need for welded connections or straps that might otherwise damage the jack-up leg chords and braces. 
     Additionally, the vertical freedom of motion means that when a diversion assembly encounters an ice sheet, other debris flows, and/or other floating debris, the weight of the ice and/or other debris may tend to push the diversion assembly further into the water as the ice and/or other debris rides up on the upper inclined surface of the diversion assembly (see  FIG. 1A ). To counter this, the roller system may include a chocking mechanism (as described above) to prevent the diversion assembly from becoming too deeply immersed. 
     Behind the rollers at the ends of each diversion assembly segment module may be a vertically mounted ratchet chock bar which may be free to slide in the vertical direction. Integral to this bar may be a number of ratchet pins corresponding to a ratchet gear in each of the roller assemblies. Adjacent to the rollers, a buoyant flotation box may be attached which may be free to move vertically within a shell-mounted track in response to changes in the draft of the diversion assembly. The flotation box may be connected to the ratchet chock bar by a rotating lever arm (see  FIGS. 4A ,  4 B, and  5 ). 
     Whenever the diversion assembly may be submerged beyond an arbitrary limit draft, the flotation box may be pushed up along its track (see  FIG. 1B ). The flotation box may then pull up on the attached lever arm and force the lever bar to rotate about the pivot pin, which in turn may push the connected ratchet chock bar down. This may force the ratchet gears on the chock bar into the corresponding ratchet gear at the center of each roller. Once engaged by the ratchet gears, the chock bar may prevent the diversion assembly from becoming any further immersed and allow the diversion assembly to resist the force of the ice and/or other debris load. 
     After the ice and/or other debris pressure may be released, the process may work in reverse. The inherent buoyancy of the diversion assembly may apply an upward force on the diversion assembly, which may reduce the draft and lower the flotation box. This may in turn raise the chock bars clear of the ratchet gears and rollers. The ratchet gears may allow the rollers to easily disengage and begin rolling back up the leg. 
     Because the diversion assembly may normally be restrained only in the horizontal direction, the diversion assembly may be free to move up and down the outside edge of the leg chord as the diversion assembly responds to wave action. To prevent or reduce sudden impact loads on the rollers in the event the diversion assembly is temporarily immersed far enough to engage the chocks, each ratchet gear may be attached to its roller by means of a torsion spring. This may dampen the initial impact on the rollers (and by extension the rest of the diversion assembly) due to the chock being engaged suddenly while the diversion assembly is heaving up and down. 
     The diversion assembly may remain deployed in most conditions, even if ice is not an immediate possibility, and may be deployed and/or maintained in use to prevent impacts and/or interactions with other debris. However, in order to allow for the possibility of severe weather, it may be possible to lift each diversion assembly clear of the water. Two or more portable winches may be mounted at the edge of each leg well. Cables from these winches may be attached to opposing pad-eyes  117  at the top of the segments, as shown in  FIG. 1A . In the event that the wave height exceeds safe operating limits for the diversion assembly in afloat mode, the winches may lift the diversion assemblies out of the water and retract them to a point just below the hull of the maritime structure. 
     In one exemplary embodiment, steel weight was estimated based on the arbitrary assumption of using 12.7 mm (½″) plate for the ice contact surfaces, and 6.5 mm (¼″) plate elsewhere, along with a very conservative margin. The buoyant volume used to maintain draft may be adjusted as necessary by increasing or decreasing the depth of the lower “current” slope area Additionally, the flotation boxes for the chock system may be tuned based on the final weight and motion characteristics of the diversion assembly. 
     Further, an alternative to using inclined contact surfaces may be to adopt a wall-sided approach and rely on merely deflecting the ice and/or other debris around the leg rather than breaking it up. While this may result in higher total horizontal loads on the leg, it may also eliminate the need for the roller chock system. 
     In the exemplary embodiments disclosed above, the diversion assembly is shown configured for a Letourneau 240C class vessel, but it should be understood that the design may be easily adapted to other rig and/or other maritime designs, including, for example, triangular three-chord legs like those of the KFELS Mod VIb. 
     Referring now to  FIGS. 6-10 , an exemplary procedure for installing a diversion assembly in accordance with one or more of the embodiments described above will be described. Although an exemplary procedure is disclosed, it should be understood that numerous variations may be performed, depending on a variety of factors including rig design, local regulations, and the location of installation. 
     Transport 
     The diversion assemblies may be transported on the same Heavy Lift Vessel (HLV) used to convey the rig or other maritime structure to a desired location, such as to the area of a drilling site. A number of diversion assemblies may be carried to the site corresponding to the number of legs employed by the structure to be protected, with each occupying a space on deck of approximately 20 m×20 m. The diversion assemblies may normally be transported with all three (triangular configuration) or four (square configuration) hinge pins fixed in place. However, it should be understood that when in transport (or when put in storage) the diversion assembly may be transported (or stored) with all hinge pins removed so that each segment of the diversion assembly may be completely disconnected form the remaining segments. Thus, the diversion assembly may be transported (or stored) in less space than in the assembled state. 
     Launch 
     Once the HLV is on location with a diversion assembly  600 , hinge pins  621  may be installed on the outside edge of the segments  631 ,  632 ,  633 , and  634  at hinge points (joints A, B, C, and D of  FIG. 6 ). The hinge pins  621  may serve to keep joints A, B, C, and D closed in a fixed position during towage and/or installation, such as shown in  FIGS. 6 and 7 . The hinge pin at joint B may be removed  620  so that the segments  632  and  633  of the diversion assembly  600  may be “opened” for installation (as shown in  FIG. 6 ). Further, a closing line  640  may be attached to segment  632  to enable control over the segment during installation. 
     Quick release pins (not shown) may be provided to attach temporarily to the outside of the segments. The quick release pins may be used to rigidly attach the hinges between segments such that the hinge may be prevented from swinging open or closed. Accordingly, the diversion assembly may be easier to install and/or handle. Quick release pins may be used between the segments of the diversion assembly that may not open during transportation, installation, and/or removal. The quick release pins may then be removed after installation. 
     Now, referring to  FIG. 7 , a transport and pre-installation of a diversion assembly  700  is shown. Prior to the launch, a 40 m length of 40 mm wire, closing line  740 , may be flaked and attached to segment  732  by a pad eye and shackle at one end and held by quick release dips to the top deck of segment  732 . The closing line  740  may have a hard eye at the bitter end for the purposes of safety compliance. Primary towing vessel  761  may be connected via a bridle  770  secured to segment  732  of diversion assembly  700  on a shortened tow line  771  (e.g., less than 600 m in length). The HLV may then be ballasted down into the water so that the diversion assembly  700  may float free. 
     Towage 
     As the diversion assembly  700  may come off the HLV&#39;s deck, the primary towing vessel  761  may ease forward until it is approximately one-half nautical mile from the HLV. This may allow a secondary towing vessel  762  to take segment  733  on its hip and secure its tow line to segment  734 , as shown in  FIG. 7 . The group may then proceed, slowly, towards the drilling rig. 
     Installation 
     Referring to  FIGS. 8-10 , an installation process in accordance with one or more embodiments of the present disclosure will now be described. Upon arrival in the vicinity of the drilling rig  890  the primary towing vessel  861  may stop the tow, check with the rig to ensure that it may proceed further, and then confirm the actual height of the rig&#39;s air gap (i.e., the height of the rig&#39;s deck above the sea level). Primary towing vessel  861  may then recover its tow line and disconnect the bridle, moving to take segment  831  on its hip. Although not shown, primary towing vessel  861  would flank diversion assembly  800  at segment  831 , similar to how secondary towing vessel  862  has segment  833  on its hip. 
     Referring to  FIG. 8A , both primary and secondary towing vessels  861  and  862 , respectively, may turn the diversion assembly  800  and approach the bow leg  880  of rig  890  from the starboard side of rig  890  with segment  832  facing the leg  880 . At a distance of approximately 30 to 40 m off, the maneuver may stop and secondary towing vessel  862  may stay attached to diversion assembly  800  while primary towing vessel  861  may disconnect and pass around rig  890  such that it may be positioned stern to the leg  880  on the port side of rig  890 . Primary towing vessel  861  may then put its work boat  865  into the water. The work boat  865  may attach a messenger line  866  to the hard eye of the closing line  840  flaked along segment  832 , as shown in  FIG. 8B . The work boat  865  may then pull the messenger line  866 , with closing line  840  attached, under rig  890  abaft the leg  880 . The work boat  865  may return to primary towing vessel  861  which may then heave in the messenger line  866 . 
     Now, referring to  FIG. 9 , once the messenger line  966  and attached closing line  940  have been recovered to a winch drum of primary towing vessel  961 , the work boat  965  may return to the diversion assembly  900  and remove the quick release pin at point B (as shown in  FIGS. 6 and 7 ). This may allow the diversion assembly  900  to swing open slightly, as shown. Primary towing vessel  961  may then pull in closing line  940  so that segment  932  may be opened far enough such that diversion assembly  900  may fit around the forward jack-up leg  980  of rig  990 . 
     Now, referring to  FIG. 10 , diversion assembly  1000  is shown in an open position such that a gap between segments  1032  and  1033  may be wide enough to wrap around jack-up leg  1080  of rig  1090 . Both primary and secondary towing vessels  1061  and  1062 , respectively, may then proceed to position the diversion assembly  1000  so that segments  1032  and  1033  may be secure alongside the facing sides of the leg  1080  and the rollers (as discussed above) about joint C are held against the intended leg chord. Secondary towing vessel  1062  may remain in position holding the diversion assembly  1000  in place while primary towing vessel  1061  may bring segment  1032  of diversion assembly  1000  across to engage with segment  1033  at joint B, thus closing diversion assembly  1000  and holding diversion assembly  1000  in place. The hinge pin at joint B may then be replaced to securely connect diversion assembly  1000  about jack-up leg  1080 . 
     Secondary towing vessel  1062  may then disengage from segment  1033  and primary towing vessel  1061  may recover its tow line and secondary wire after the work boat  965  has disconnected the tow line from segment  1031 . The above procedures may then be repeated on the remaining legs of the jack-up rig. 
     For jack-up rigs or other maritime structures having triangular legs, the legs may be approached in a similar manner but will have only three sections and require only one quick release pin. Preferably, this operation shall take place only in minimum sea/swell and light winds. 
     To remove a diversion assembly from a jack-up rig or other maritime structure, the above steps may be performed in reverse of the above description and should take place in similar sea/swell and wind conditions. 
     While the disclosure has been presented with respect to a limited number of embodiments, those skilled in the art, having benefit of this disclosure, will appreciate that other embodiments may be devised which do not depart from the scope of the present disclosure. Accordingly, the scope of the invention should be limited only by the attached claims.