WO2014053655A1

WO2014053655A1 - Protective structure for an off-shore platform

Info

Publication number: WO2014053655A1
Application number: PCT/EP2013/070750
Authority: WO
Inventors: Gregers Kudsk
Original assignee: A.P. Møller - Mærsk A/S
Priority date: 2012-10-04
Filing date: 2013-10-04
Publication date: 2014-04-10
Also published as: DK201470323A

Abstract

A structure for protecting an off-shore platform against ice and/or other sea forces. The structure is configured to be lowered onto the sea floor and includes a base portion and one or more protective columns. Each protective column defines a channel upwardly extending from the base portion when the structure is installed on the sea floor. The structure further includes one or more receptors each for receiving at least one foot of at least one leg of the off-shore platform. The protective column(s) are configured to laterally surround at least one leg of the offshore platform when the leg is received by one of the at least one receptors.

Description

PROTECTIVE STRUCTURE FOR AN OFF-SHORE PLATFORM

FIELD OF THE PRESENT DISCLOSURE

[0001 ] The invention generally relates to off-shore platforms, often also referred to as off-shore rigs. More particularly, the invention relates to such drilling units that are suitable for use in artic or sub-arctic environments.

BACKGROUND

[0002 ] Off-shore drilling units are widely used in the exploration and exploitation of hydrocarbon reservoirs under the sea floor. In particular, the exploration and exploitation of reservoirs in arctic and sub-arctic regions involves challenges as regards to low temperatures and seasonal incursion of ice which may threaten the off-shore drilling structures.

[0003] One type of drilling structure are the so-called jack-up rigs that typically comprise a hull and a number of legs adapted to be lowered towards the sea floor. Such rigs may thus be towed towards their desired off-shore location with the legs in a raised position. Once the rig is at its intended position the legs are lowered and brought into contact with the sea floor. Further lowering of the legs relative to the hull causes the hul l to be elevated out of the water.

[0004 ] US 2012/0128435 discloses an ice worthy jack-up rig where the hul l has a special ice-deflecting shape, and the legs are held in place by cans embedded in the sea floor. In the event of ice conditions, the hul l is lowered into the water in an ice defensive configuration where the ice-bending shape of the hull bends and breaks up ice that comes in contact with the hul l . This prior art rig further comprises a conical piled monopod. Dril l ing operations are performed through the conical piled monopod. To this end, the rig is arranged to extend over the conical piled monopod. One leg of the rig is secured in a socket of the conical piled monopod. Even though this prior art system provides some protection against ice, it is a disadvantage of this prior art system that it requires operation of the jack-up rig to be moved between the ice defensiv e position and the operational position abov e the monopod. [0005] It would thus be desirable to provide protection of an off-shore drilling structure that allows efficient installation and operation of the drill ing structure while providing efficient protection against ice.

SUMMARY

[0006] Disclosed herein are embodiments of a protective structure for protecting an off-shore platform against ice and/or other sea forces. The platform is a jack-up platform (also referred to as a jack-up rig) with extendable legs as explained above. Embodiments of the structure are configured to be lowered onto the sea floor and comprise a base portion and one or more protective columns each defining a channel that extends from the base portion upward when the structure is installed on the sea floor. Embodiments of the structure comprise one or more receptors each for receiving at least one foot (i.e. the lower end) of at least one leg of the off-shore platform; and the one or more protective columns are configured to laterally surround at least one leg of the offshore platform when the leg is received by one of the at least one receptors.

[0007] Embodiments of the structure disclosed herein thus provide an efficient protection against ice or similar transverse forces while al lowing for a convenient installation and only minimally affecting, if at al l, the operational efficiency of the platform. Furthermore, the structure may be used with conv entional off-shore platforms without requiring major modifications, if any. to the platform. Hence, a conventional jack-up rig without the need for major modifications to the jack-up rig, if any, may be used in cooperation w ith an embodiment of the structure disclosed herein in arctic or sub-arctic environments. The same jack-up rig may subsequently be moved to areas not requiring additional protection against ice or similar challenges and used without a protective structure as described herein. Consequently, embodiments of the structure disclosed herein facil itate a high degree of flexibil ity of use of standard off-shore jack-up platforms.

[0008] It will further be appreciated that the structure disclosed herein allows for an efficient operation of an off-shore platform where the downtime due to ice is reduced.

[0009] It will further be appreciated that the weight of the off-shore platform may be increased without changing the structure of the legs, as the transverse forces to which the legs are exposed are reduced by the protective structure. Such weight increase may for instance be in an increased loading capacity of the rig. This may be important as prov iding suppl ies in ice filled and/or remote waters may be costly so allowing the jack-up rig to carry more load may expand its operational window before supplies are necessary e.g. during the winter season where access to the rig may be particularly difficult .

[0010] It will further be appreciated that the operational depth of the platform may be expanded with the height of the base and/or the legs may be shortened which in turn reduces forces imposed on the rig due to the extensive length of the legs.

[0011] The term structure for protecting an off-shore platform is intended to comprise any structure configured to at least reduce the impact of transverse forces from e.g. sea movements, ice, etc. on the off-shore platform. Embodiments of the structure disclosed herein reduce the risk of an off-shore platform being damaged by ice and/or other forces, in particular transverse forces, e.g. from wav es, sea currents, collision w ith other structures or vessels, etc. Here and in the following the terms transverse and lateral refer to a direction transverse relative to the longitudinal extent of the legs of the platform.

[0012] The off-shore platform may be a drilling platform or an off-shore platform for other types of operations which may or may not include drilling operations. Examples of such platforms include exploration platforms, production platforms, drilling platforms, and/or the l ike.

[0013] A receptor may be a recess such as a blind hole or a through hole for receiving a foot of a leg. The recess may be partially or completely filled by gravel or another suitable stabilising medium. This will typical ly be useful when legs of the jack-up are mounted with spud-cans. For the purpose of the present description, such a recess will also be referred to as gravel box. It is to be understood that in general a receptor is defined as locations on base of the structure suitable for receiving legs of a jack-up platform. In some embodiments the structure may be suitable for receiving a jack-up without spud-cans mounted on the bottom end of the leg thus forming the foot of the leg. Spud-cans are well-known in the art and are typical ly mounted on the end of jack-up legs to provide an enlarged bearing area in order to distribute the load of the rig evenly over a larger area and reduce the pressure exerted on the soil of the seabed. The goal of this is to reduce the penetration depth of the legs required by the support structure to support the jack-up rig. However, in some embodiments this function is achieved by the protective structure and hence the spud cans may be omitted. Spud cans are costly and can introduce drag during rig moves so avoiding the use of spud cans may be beneficial. In the event that the jack-up rig is later to be used without the protective structure spud cans may be mounted e.g. by lowering them onto the seabed in a shallow area extending the legs to obtain contact and latching or welding on the spud-cans. This method may also be extended to a jack-up rig with spud cans where the spud cans are removed prior to being mounting the jack-up onto the structure e.g. by reversing the procedure just described for mounting spud cans. Examples of receptors include a socket with which a foot of a leg can enter a mating engagement, a flat surface suitable for receiv ing the load from the leg and platform and a single gravel pit for receiving all legs of the platform. The receptor may comprise clamps or other mounting members for securing the leg to the structure. With the platform resting on the structure the weight of the combined structure, i.e. the off-shore platform including the protective structure, is increased, thus causing an increased stability against sideways pushes. General ly, the depth of the channel defined by the protectiv e columns and the receptors may be selected such that a major portion, e.g. at least 70% such as at least 80% of the legs under platform protrude into the channel .

[0014] Depending on the structure of the sea floor it may be adv antageous that the weight of the combined structure is distributed across the relatively large bottom surface of the base portion. In some embodiments, ballast compartments of the off-shore platform may f urther be used to control the weight of the combined structure.

[0015] The columns surround the legs lateral ly relative to the longitudinal direction defined by the legs when the legs extend into the channel defined by at least one of the columns. In some embodiments the columns may completel y surround the legs. i.e. the columns may circumferentially extend around the entire leg so as to protect the leg against impact from al l directions. In some embodiments, a column may only partial ly surround the leg. e.g. in a situation where there is a risk of impact from certain directions only, or at least predominantly. It will be appreciated that the columns may have various different shapes. For example, they may be formed as elongated, tubular, conical or similar structures extending upwards from a base portion. Alternatively, they may be formed as tubular conduits inside a plate- or box-shaped structure. The channel may hav e a tubular shape, shaped and sized so as to allow the legs of the platform to extend through the channels. The channels may have a circular cross-section or another suitable cross-sectional shape, e.g. a polygonal cross-section.

[0016] In some embodiments, the platform comprises a plurality of protectiv e columns, each surrounding one of the legs, thus providing a relativ ely sl im structure that allows easy access to the hul l of the platform. [0017] In some embodiments, the structure comprises a bottom base section and an upper section, separate from the bottom base section, wherein the bottom base section comprises the receptors. From a strength perspective it may be advantageous to design the columns to fit closely around each leg. In some embodiments the upper section is therefore designed specifically for the leg spacing of a specific platform whereas the base section is more generically applicable so that the receptor(s) are arranged and sized to accept a variety of leg arrangements. This may be accompl ished by increasing the area of each receptor or having a single large receptor.

[0018] The upper section comprises the one or more protective columns and defines one or more channels that extend upwardly through the entire upper section so as to allow each leg of the platform to extend through one of the channels when the leg is secured to the bottom base section also referred to as simply the base or the base structure.

[0019] Embodiments of the structure disclosed herein allow for an efficient movement of the off-shore platform to a new position. For example, an additional base section may be installed at a new location while the off-shore platform is still operating at an old location. Once the base section is installed, the off-shore platform and, optional ly, the upper section may be moved to the new location without unnecessary delay. The base section at the old location may then be recovered, if desired. Alternatively, a movement may be accomplished by controlling the buoyancy of the entire structure so as to cause the structure to be lifted above the sea floor, towing the structure to a new position and lowering the structure at the new position. During this operation, the legs may be lifted, so as to lower the hull until it rests on top of the protective columns.

[0020] In some embodiments, the bottom base section comprises a recess for receiving the upper section and for securing the upper section against transverse shifting relative to the base portion.

[0021] The upper section may thus have a periphery mating the recess of the bottom base section, e.g. in the form of a suitably shaped and sized edge. The recess may thus function as a load transfer recess for transferring transverse loads between the upper and bottom base sections.

[0022] In some embodiments, the upper section is made up from at least a first and a second subsection wherein the first and second subsections each form respective segments of one or more of the protective columns, such as of each of the protective columns. [0023] In particular, each of the subsections may comprise an upwardly extending, laterally open, e.g. U-shaped, channel or groove having a rim. When the subsections are brought in contact with each other, their respective laterally open channels together form the protective columns. To this end the rims of the respective laterally open channels may be brought in contact with each other or ev en in a mating engagement with each other, e.g. so as to prevent transverse displacement or tilt ing of the subsections relativ ely to each other.

[0024] In some embodiments, each of the first and second subsections is configured to be transversely moved inwards from respective sides towards the legs so as to jointly form the protective columns surrounding the one or more legs of the offshore platform when the first and second subsections are positioned on top of the bottom base section. The transverse inward mov ement may be accompanied or fol lowed by a low ering of the subsections onto the base section.

[0025] Hence, embodiments of the structure may easily be completed once the platform is secured in its operational position. The subsections of the upper section form respective parts of split columns, i.e. each subsection forms a part of the circumferential periphery of at least one protective column. Each protective column for protecting one or more legs is thus jointly formed by two or more subsections that are transversely mov ed in place once the platform is secured at its desired position.

[0026] In some embodiments, the structure comprises a respective column for each leg of the platform, and wherein each subsection comprises a part of each of the columns.

[0027] In some embodiments, each of the first and second subsections comprises a base portion from which one or more column segments extend upw ardly, each column segment defining a part of a periphery of a protective column.

[0028] In some embodiments, the structure further comprises a well-protection column defining a conduit channel extending from a top to a bottom of the structure al lowing a drill or pipe to be advanced from the off-shore platform to the sea floor. On some embodiments the wel l-protection column is arranged to perform the function of a drill ing jacket template platform or a drilling template well known in the art. In such and other embodiments the base or well protection column may further be arranged to receiv e and/or be fitted with a dril ling template. In this way drilling, such as dev elopment drilling, may be performed from the combined structure in a similar manner to a regular jack-up platform arranged in relation to a dril ling jacket platform and/or template. [0029] In some embodiments where the protective columns are formed by two or more subsections, one of the subsections may comprise the well protection column. As the subsections of the upper section may be put in place before the dril ling or other wel l operation is initiated, the well protection column may be formed as a single generally tubular structure. It will be appreciated, however, that the well protecting column may also be formed joint ly by two or more subsect ions of the upper sect ion as described herein. The subsect ions may have corresponding mating shapes including guiding elements that facilitate bringing the subsections into a desired relative position with each other. For example, the first subsection may have a lateral ly protruding element having en end portion forming a segment of a protective column. The second subsection may have a slit into which the lateral ly protruding element of the first subsection may be slidingly inserted.

[0030] In some embodiments, the structure comprises a bottom surface of the structure for engaging the sea floor, and one or more members protruding downwardly from the bottom surface. Hence, when the structure is lowered to the sea floor, the protrusions may be driven into the sea floor and reduce the risk for the structure being horizontal ly displaced across the sea floor. For example the protrusions may include a skirt along a periphery of the bottom surface. Alternatively or additionally, the protrusions may include spikes or other suitable anchoring structures.

[0031] In some embodiments, at least one of the base portion and the protective columns has an ice deflecting periphery. For example, the base portion and/or the protective coiumn(s) may have a sloped periphery, so that transverse and lateral forces from ice impact are reduced by directing the ice upwards (or downwards).

[0032] In some embodiments, one or more sections of the structure disclosed herein arc embodied as so-cal led gravity-based structures arranged to at least partly be held in place by gravity. The sections of the structure may be formed by reinforced concrete. Howev er, alternative materials such as steel arc also possible as w el l. The structure may comprise a system of buoyancy compartments, such as tanks or cells, which can be used to control the buoyancy of the structure. To sink the structure, bal lasting may be applied w hich is a well- known technique within offshore instal lations. Hence, in some embodiments, the structure comprises one or more enc I osu res/ co m pa rt men t s configured to be filled w ith fluid, such as water, so as to change the buoyancy of the structure and al low ing a control led lowering of the structure. In embodiments where the structure comprises multiple, separate sections, e.g. a bottom base section and an upper section formed by multiple subsections, each of the separate sections may comprise one or more of such buoyancy compartments. The weight of the combined structure on the seafloor and thereby its resistance to transverse and lateral forces may be increased by fil l ing the ballasting tanks with a substance that is heav ier than water, such as brine.

[0033] In some embodiments, the stracture has a height defined between its bottom surface and a top end of a highest one of the protective column large enough for the structure to extend out of the water when the structure is positioned on the sea floor. It will be appreciated that the protective columns may all have the same height, in which case each of them may be regarded as a highest one. The height by which the columns extend above the water may be chosen according to the expected sea conditions, such as expected height of waves, the expected thickness of ice, etc. In some embodiments the structure may be between 30m and 120m high, e.g. between 40m and 100m high, such as between 50m and 1 00m high. In some embodiments, the protectiv e columns may protrude between 5m and 1 5m abov e the water. The base section may have a height smaller than the water depth, and leaving sufficient room between its upper surface and the water level so as to allow the platform to be towed into a position above the base section. In some embodiments the base section has a height leaving at least 5m between its upper surface and the water level, when the base section is submerged onto the sea floor. For example, the base section may hav e a height betw een 1 5 and 55m, such as betw een 20m and 55m, such as between 35m and 55m. The columns may in general be arranged so that the channel defined by them extends 5 meters abov e sea level or more, such as 10 meters above sea level or more, such as 15 meters above sea lev el or more, such as 20 meters above sea level or more, such as 25 meters above sea level or more. In some embodiments the height of the structure is 50 meters or more, such as 60 meters or more, such as 70 meters or more, such as 80 meters or more, such as 90 meters or more, such as 100 meters or more, such as 1 10 meters or more, such as 120 meters or more, such as 130 meters or more, such as 140 meters or more, such as 150 meters or more, such as 1 75 meters or more, such as 200 meters or more.

[0034] In some embodiments, the transverse extent of the upper portion may decrease w ith increasing height abov e the base portion. For example, the outer periphery of the upper portion may be inw ardly and upwardly sloped. Alternatively, or additional ly, the protective columns may comprise tubular or conical structures upwardly extending from a base portion. Such a shape may facilitate convenient manoeuvring of vessels in the v icinity of the platform and convenient access to the hull and upper portion of the legs. Moreover, transverse forces imparted on the structure by ice or water may at least partly be redirected to have a downward component by a downward and outward slope so as to increase the load that secures the structure to the sea floor.

[0035] One challenge of operating in arctic and subarctic regions is the influence of low temperatures on material properties, such as the load capacity of steel. For this and other reasons it is in some embodiments beneficial to take measurements to reduce this impact particularly on the leg structures of the jack-up. The legs are typically designed for a certain load capacity at e.g. - 1 5 degrees Celsius. In some embodiments the one or more of the protective columns (such as all) arc arranged to carry at least part of the weight of the jack-up plat form, such as al l of the weight of the jack-up platform. Accordingly, after instal lation of the upper section of the protective structure the jack-up may be jacked down (i.e. raising the legs) so as to bring the hull into contact with the upper end of the columns. The columns may be arranged to carry al l or just a part of the weight. In this way the requirements on load capacity of the legs during colder weather is reduced or removed. Typically a jack-up hull has a significant load bearing capabil ity surrounding the leg-wells (typical ly via bulkheads arranged around the leg-wel ls) and the columns are therefore preferably adapted to match this. Relying on the columns for carrying weight further has the advantage of increasing the combined weight of the upper section and the rig which will improve resistance to transverse and lateral forces impacting on the upper section by increasing the friction/force between the base section and the upper section. The upper part of the columns and/or the underside of the rig is preferably fitted with grippings to prevent the rig from moving horizontally relative to the columns.

[0036] in combination or as an alternative the space and/or water inside the protective columns are in some embodiments arranged to be heated for instance to ensure that ice formation inside the columns is prevented or reduced. The heating means could be any suitable means and preferably utilizes excess heating from the rig. This may in some embodiments be performed by injecting cooling water from the rig e.g. via the legs. The w armer cooling w ater from the rig is preferable injected in or near the top layers of the water column where ice is most likely to form. In the alternative or in combination insulating materials, such as insulating material such as Styrofoam, may be placed in the surface of the water in the columns to prevent or reduce ice formation and/or packing which may otherwise create forces against the leg and/or columns. The material preferably has a density lower than salt water so that it floats while at the same time hav ing an K-value of less than 50, such as less than 1 0, such as less than 5, such as less than 1 , such as less than 0.5, such as less than 0.05, such as less than 0.005. To avoid influx of cold sea water the protective columns are in one embodiment water tight. In some of such embodiments the weight of the protective structure may be further improved by filling the columns e.g. with water.

[0037] In embodiments where the legs of the jack-up rig are arranged to carry the whole weight of the platform a spacing may be present between the upper end of the protective columns and the underside of the platform. In some embodiments this is preferably minimized to minimize the influence from the environment on the legs and/or drill string. In one embodiment the gap is enclosed e.g. by a curtain of isolating material to reduce the impact of weather and preferably combined with heating of the inside of the columns (as discussed above).

[0038] In embodiments with a gap as well as for the embodiment where the columns carry at least some of the weight it may be preferable that the legs are available to lift the rig higher in case of impending high waves. This will allow the protective columns to be shorter. Extreme wave heights are at least in some locations only relevant when there is little or no ice so that the temperature may be higher with a higher load capacity of the legs as well as l ittle risk of ice impact above the columns.

[0039] The present disclosure relates to different aspects including the protective structure described above and in the following, corresponding methods, dev ices, and/or product means, each yielding one or more of the benefits and advantages described in connection with the first mentioned aspect, and each having one or more embodiments corresponding to the embodiments described in connection with the first mentioned aspect and/or disclosed in the appended claims.

[0040] In particular, according to one aspect, disclosed herein are embodiments of a base section for supporting an off-shore platform, the base section being configured to be lowered onto the sea floor; wherein the ba.se comprises one or more receptors each for receiving at least one foot of at least one leg of the off-shore platform. In some embodiments the base comprises at least one through hole arranged in relation to the receptors to allow drilling to be conducted from the jack-up platform through the through hole. In some embodiments, the base comprises receptors for receiving every leg of the platform, thus allowing the entire platform to be securely mounted on top of the base section. In some embodiments, the base section comprises an upwardly open recess for receiving one or more upwardly extending protective sections for protecting the legs of the platform against ice and/or other sea forces. In some embodiments, the receptor comprises a bl ind hole or a through hole at least partially filled by a stabilising medium. Furthermore, this base may comprise one or more of the features discussed in relation to the base of the structure elsewhere in this document such as the form of the receptors discussed above.

[0041] According to yet another aspect, disclosed herein are embodiments of a system for protecting an off-shore platform, against ice and/or other sea forces, the system comprising two or more protective column sections configured to be lowered towards the sea floor, wherein the first and second column sections each form respective segments of one or more protective column, wherein each of the one or more protective columns laterally surrounds at least one leg of the offshore platform, and wherein each of the first and second protective column sections is configured to be transversal ly moved inwards from respective sides and towards the legs so as to jointly form the protective columns. The protective column sections may be lowered directly onto the sea floor or on top of a bottom base section as described herein. In the latter case, the protective column sections are thus subsections that jointly form an upper section of a protective structure.

[0042] According to yet another aspect, disclosed herein are embodiments of a method of securing an off-shore platform to the sea floor, the method comprising

- lowering a base section as disclosed above and in the following onto the sea floor;

- moving the off-shore platform to a position above the base section;

- lowering one or more legs of the off-shore platform so as to bring respective feet of the legs into contact with the base section;

- moving two or more protective column sections of a system as disclosed above and in the following transversely inwards to a position above the base section and below a hul l of the platform so as to cause the protective column sections to jointly form one or more protective columns laterally surrounding the one or more legs; and

- positioning the protective column sections on top of the base section.

[0043] In some embodiments, lowering the base section comprises:

- positioning the protective column sections on top of the base section. - lowering the base section with the protective column sections positioned on top of the base section onto the sea floor;

- moving the protective column sections transversely outwards so as to allow movement of the offshore platform to a position above the base section.

[0044] Accordingly, the base section is stabilised during the lowering operation, as a portion of the combined structured extends out of the water during the entire operation. Moreover, the mass of the column sections facilitates a secure positioning of the base section on the sea floor. As both the base section and the protective column sections may have buoyancy compartments, the buoyancy of the base section and of the protective column sections may be controlled separately. In some embodiments, the method comprises controlling the buoyancy of the base section such that the base section does not sink on its own, or would even float on the surface; and controlling the buoyancy of the protective column sections such that their apparent weight pushes the base section to the sea floor, thus allowing for a controlled and stable lowering of the base section.

[0045] Alternatively, the platform and the protective structure may be assembled in sufficiently deep water, where the protective structure may be submerged, brought into a position below the platform, and elevated. The thus assembled structure may subsequently be towed to its desired position.

[0046] According to yet another aspect, disclosed herein is an off-shore platform comprising

- a hull and one or more legs extending from the hull downward towards the sea floor; and

- a protective structure as disclosed abov e and in the following.

BRIEF DESCRIPTION OF TH E DRAWINGS

[0047] The above and/or additional objects, features and advantages of embodiments and aspects of the present invention, will be further elucidated by the follow ing il lustrative and non-limiting detailed description with reference to the appended draw ings, wherein:

[0048] Fig. 1 a schematically il lustrates a jack up protection structure (jack-up protection structure) according to some embodiments of the inv ention,

[0049] Fig. lb schematically illustrates compartments in the jack-up protection structure of Fig. 1 a. [0050] Fig. 2 schematically illustrates the base of the jack-up protection structure of

Fig. 1 ,

[0051] Fig. 3 schematically illustrates a subsection of the upper section of the jack-up protection structure of Fig. 1 ,

[0052] Fig. 4 schematically illustrates another subsection of the upper section of the jack-up protection structure of Fig. 1

[0053] Fig. 5 schematically illustrates a Jack-up seen from above,

[0054] Fig. 6-9 schematically illustrates an installation procedure installing the jack- up of Fig. 5 into the jack-up protection structure of Fig. 1 , so that

[0055] Fig. 6a schematically illustrates the jack up placed over the base of Fig. 2 in a top view and Fig. 6b show s the corresponding side view,

[0056] Fig. 7a further schematically il lustrates the subsection of Fig. 3 placed on the base and Fig. 7b shows the corresponding side v iew,

[0057] Fig. 8a further schematically illustrates the subsection of Fig. 4 in process of being skidded into place base, and

[0058] Fig. 9a schematically illustrates the complete jack-up protection structure installed in a top view and Fig. 9b shows the corresponding side view.

[0059] Fig. 10 schematically illustrates another embodiment of a jack-up protection structure.

[0060] Fig. 1 1 schematical ly prov ides a perspective view of an embodiment of an offshore platform of the invention comprising the jack-up protection structure with a jack-up rig installed.

[0061 ] Fig. 1 2 schematical ly illustrates another embodiment of a jack-up protection structure.

DETAILED DESCRIPTION

[0062] In the follow ing description, reference is made to the accompanying figures, which show by way of illustration how the invention may be practiced. Several features of the presented embodiments are discussed; how ever, as will be clear to the skil led person features that arc not mutually exclusive may be combined in other embodiments even if not show n as combined in the fol lowing. [0063] Fig. la schematically illustrates a cross section along the line 201 (see Fig. 2) of some embodiments of a protection structure 100 according to the invention particularly suitable for receiving a jack up. This embodiment is divided into two lateral sections with a bottom base section 101 (also referred to as simply bottom base) and an upper section formed by two subsections 108, 109. In general the structure may be subdivided into a variety of sections which may be lateral sections as in the case of Fig. 1 a such as a single piece, two lateral sections, three lateral sections or more. In the present case, the bottom base (which in general may be further sub divided or in one piece) is arranged to receive the legs of a jack up platform, in this example in gravel boxes 1 05 with gravel 106. Gravel boxes with gravel are often preferable as they allow the feet of the legs of the jack up platform to settle in a similar manner as when the feet are placed on the seafloor which is a normal mode of operat ion for many jack up platforms; however, any suitable receptors such as specialised sockets are feasible e.g. shaped to fit spud-cans mounted in the legs or the legs themselves if no spud-cans are mounted. At the same time the bottom base is arranged so that, when resting on the seafloor, the platform can sail over the base and jack up on top of the base (see e.g. the below discussion of an example of an installation process in relation to figures 6-9).

[0064] Fig. l b shows a more detailed view of the cross section if fig. 1 a. In particular, fig. l b further shows exemplary compartments 1 1 6.1 1 7 in the bottom base 1 01 and the subsections 108, 1 09. Fig. 2 shows a top v iew of the bottom base where the line 201 of the cross sections of Fig. 1 is shown.

[0065] The structure 100 has a bottom surface 115 for engaging the sea floor and may further comprise a skirt 102 which is arranged to penetrate the seabed and increase resistance against transverse motion of the structure. The skirt 102 may have any suitable shape along the bottom surface but is here shown to extend along the edge of the bottom surface. Multiple skirts may be provided and the bottom surface may further comprise one or more spikes which may be arranged in any suitable pattern. In some embodiments the structure comprises a deflecting slope 103, 1 13 such as for deflecting the force of transversal I y impacting ice. The slope may also deflect other transverse forces such as from waves, but ice impact is used as an example throughout this text. The slope 1 03, 1 13 may hav e the effect of directing the ice upwards while transferring at least part of the force of the impact into a downward force which further increases transverse resistance ( i.e. the resistance against transverse movement of the structure). The deflecting slope 103, 1 13 preferably extends around the structure 101 to deflect the force of impacting ice and thus forms an ice deflecting periphery. The slope may have an angle between 10° and 80°, e.g. between 30° and 60°, such as between 40° and 50° relative to the bottom surface 1 1 5. The deflecting slopes may extend to or even above the water level. The base section 101 may further have a load transfer recess (also referred to as load recess) or edge such that transverse forces, such as impacting ice, are prevented from sliding upper section 108,109 relative to the base section 101 , as the load edge 1 12 of the upper section engages with the edge 104 and stops the upper section by transferring the force acting on the upper section to the bottom section. The recess 104 preferably extends around the periphery so that transverse motion may be stopped regardless of its direction of attack. In some embodiments the recess 1 04 has an increased height along 1 , 2 or 3 sides so that the edge can also act as a guide when skidding the upper portion 108,109 into place. When the upper section 108, 109 is in place it may be ballasted to sit on the base section inside the recess regardless of the height of the recess.

[0066] In the general the base section 101 may further comprise guide posts 1 14 arranged along a part of the periphery. The guide posts may be formed along one side, two sides or three sides. The guide posts may provide guiding and/or act as a stop as the upper section 108,109 is floated into position over the bottom base section. In some embodiments the length of one or more of the guide posts 1 14 is arranged so that a top part of the posts are above sea level when the bottom section rests on the sea floor. Accordingly, in some embodiments one or more of the guidepost (such as ail) is 5 meters or longer, such as 7 meters or longer, such as 10 meters or longer, such as 12 meters or longer, such as 1 5 meters or longer, such as 20 meters or longer.

[0067] The structure comprises leg protective columns 1 10 and a well protection column 1 1 1 , each defining a downward channel for receiv ing a leg of the platform or a drill, respectively. In some embodiments the well protection is instead arranged as a separate protective structure e.g. by enforcing a jacket platform, some embodiments

[0068] As noted above, Fig. 2 illustrates the bottom base of the jack-up protection structure of Fig. 1 . The gravel boxes are positioned and shaped and sized so as to each receive a respective one of the legs of the jack up rig. The legs are typically between 30m and 150m spaced apart, such as between 30 and 100m spaced apart, such as between 30 and 75m spaced apart, such as between 40 and 75 m spaced apart. The ice deflecting periphery 103 is identified along with the load transfer recess 104 prov iding a recess for the upper section to sit in. In general it may be preferable that the angles formed by corners of 202 the load recess are minimised to avoid the risk of high point loads arising e.g. from ice impacting in the direction of the corner. In the present embodiment this has been achieved by increased the number of sides in the polygenic shape of the outer periphery. Accordingly, in some embodiments the top view of the load recess has a polygonal shape with 3 sides or more, such as 4 sides or more, such as 5 sides or more, such as 6 sides or more, such as 7 sides or more, such as 8 sides or more, such as 10 sides or more. However, in order to facilitate the alignment to form the channels defined by the protective columns, it may be preferable to have one or more substantially straight edges in the top view of the load recess.

[0069] Fig. 3 schematically illustrates a top view of a subsection 109 of the upper section of the jack-up protection structure of Fig. 1. The subsection comprises segments 303 of the leg protective columns 1 10. When this subsection is combined with the other subsection (e.g. the subsection shown in fig. 4 ) the combined segments will form the protective columns. Note that in general the upper section may be div ided into more than two subsections. Also, in some embodiments the protective columns only partly surround the legs, such as more than 30% or more of the circumference of the legs is shielded by the protective column, such as 40% or more, such as 50% or more, such as 60% or more, such as 70% or more, such as 80%) or more, such as 90%> or more, such as 95 %> or more, such as 98%> or more, such as 99% or more, such as 100% is shielded. In general it is often preferable that the upper section is div ided into subsections in a manner so that a guiding effect is obtained when mating the subsections. The subsection may, as an example, form a plug and socket pair so that one subsection may guide the other when the subsections are moved relative to each other and brought into a mating position. This is exempli fied by the subsections 108, 109 where the subsection 109 comprises a socket- like channel 302 where the edges 301 of the channel is provides to guide the other subsection.

[0070] Fig. 4 schematically illustrates another subsection 108 of the upper section of the jack-up protection structure of Fig. 1. The subsection includes a protrusion 401 which is arranged to be mated with the channel 302 acting as socket so that the subsection may mutually guides each other v ia the interface between the edges 301 , 401 . The top part of the wel l protecting column 1 1 1 is in this embodiment completely comprised on the subsection 108.

[0071 ] Fig. 5 schematical ly illustrates a Jack-up drill rig 505 seen from above. The jack up includes a cantilever 502 which al lows the dril ling equipment to be skidded so that the position of the wel l center can be moved. The legs 501 are in this embodiment placed substantially in each corner of the rig and extend through the hul l via the pathways 505.

j 0072 j Fig. 6-9 schematically illustrates an instal lation procedure installing the jack- up of 500 into the jack-up protection structure 100. After the bottom base section has been installed e.g. as previously discussed, the platform 500 is floated over the base section 101 as shown in Fig. 6. Fig. 6a is a top view after the platform 500 is in place over the base section 101 and Fig. 6b and 6c shows a side view before and after the platform 500 has been jacked up on the base 101 with the legs in the gravel boxes 1 05. Depending on the gravel and the weight of the rig the feet of the legs will sink more or less into the gravel .

[0073] Subsequently the subsection 109 is floated into place and brought to rest on the base section 101. As discussed above part of the edge provided by the load recess 104 and/or guide post may be arranged to guide the subsection 109 into place thus reducing the risk of an impact between the subsection 109 and the rig 500 during instal lation. Fig. 7a is a top view after the subsection has been floated into place and Fig. 7b is a side view showing the subsection 109 resting on the base section 101 (the spacing between sections 101 , 109 is only illustrative to illustrate that the structure is sectioned).

[0074] Next the other subsection 108 is floated into place and guided by the subsection 1 09 as shown in Fig. 8. Final ly Fig. 9a shows a top view of the complete assembly of rig 500 and protective structure 100 whereas the corresponding side view is provided in Fig. 9b.

[0075] In some embodiments the gravel boxes are arranged so that the base section can receive rigs with more than one spacing between the legs, such as between 35m and 90m, such as between 35 m and 75m, such as between 35m and 50 m.

[0076] In some embodiments a jack up may be is operating on a protective structure as described herein at one site, while a second jack-up protection structure is being prepared at a secondary site. In some embodiments only a bottom base section is installed at the secondary site and the jack up rig and upper section are floated to the secondary site for installation of the jack-up rig.

[0077] In some embodiments a protective structure as described herein, or a part thereof (such as the bottom base), may be reused for a second platform to be installed on the site after the jack-up rig has been removed. The second platform may e.g. be a production platform. The production platform is in some embodiments a gravity based structure which can be floated over the bottom base and ballasted down on the bottom base. In some embod- iments the ice deflecting surface of the bottom base is and the rest of the base is arranged so that the bottom base can withstand the impact from the bottom of an iceberg trailing while keeping any subsea equipment production equipment intact. Installing such subsea production equipment may in one embodiment entail incorporating/pre -installing piping in the base to allow production line to run protected by the base to either side of the base and optionally arranged for allowing such lines to continue below the seabed. In some embodiments the upper section or part thereof is reused as support structure for the topside of a production platform.

[0078] As an alternative use of the invention the bottom base may in some embodiments be applied alone as a means of increasing the operational depth of a jack up and/or to provide a more secure foundation where direct installation of the legs of a jack up on the sea floor is undesirable.

[0079] Fig. 10 shows a cross sectional view of an embodiment of a protective structure similar to the embodiment shown in fig. l b. However, fig. 10 illustrates that the columns may be shaped in different ways. In particular illustrates that the side wails of the columns may be shaped in different ways. For example side wall I 19 of one of the columns of the embodiment of tig. 1 0 has a conical shape where the sloped periphery extends all the way to the top end of the column. Moreover, the central space between the columns is covered by a lid 1 18. It will be appreciated, that many further modifications of the shape of the upper section are possible.

[0080] Fig. 1 1 shows an overview of a jack-up drill rig 500 placed on the protective structure 100. The legs of the jack-up drill rig 501 are protected by the leg protective columns 1 1 0 protruding from the protective structure. Dril l ing operations may be performed through the well protection column 1 1 1 by skidding the cantilever 502 into place such that the wel l centre is aligned with the desired well location within and underneath the w ell protection column. In general, the w ell-protection column is preferably large enough (in the lateral and transverse direction) to accommodate the necessary number of wells to be drilled. In some embodiments this means that the wel l protection column allows drilling from substantially all positions of a cantilever drill floor on the jack-up platform, such as more than 10% of the positions, such as more than 25% of the positions, such as more than 50% of the positions, such as more than 75% of the positions, such as 90% of the positions, such as al l of the posi- tionsThe protective structure of this embodiment is shown to include a base section 101 and two upper sub sections 108 and 1 09 from which the well and leg protective columns are extending upwards above the sea surface.

[0081] Fig. 12 shows an embodiment of the protective structure 100 similar to that of

Fig. 9b. However in this case the protective columns 1 10 have been arranged to support at least part of the weight of the jack-up. In this embodiment the upper end has been revised to provide a large upper surface by adding a flared portion 1 201 . Furthermore a gripping layer 1202 has been added to ensure that the rig does not move laterally or transversely relative to the protective structure. Installation of the rig 500 may be performed similar to that of figures 6-9 follow by lowering the rig onto the protective structure to let the columns take some or al l of the weight of the platform.

[0082] Although some embodiments have been described and shown in detail, the invention is not restricted to them, but may also be embodied in other ways within the scope of the subject matter defined in the following claims. In particular, it is to be understood that other embodiments may be utilised and structural and functional modifications may be made without departing from the scope of the present invention.

[0083] In device claims enumerating several features, several of these features can be embodied by one and the same item of hardware. The mere fact that certain measures are recited in mutually different dependent claims or described in different embodiments does not indicate that a combination of these measures cannot be used to advantage.

[0084] It should be emphasized that the term "comprises comprising" when used in this specification is taken to specify the presence of stated features, integers, steps or components but does not preclude the presence or addition of one or more other features, integers, steps, components or groups thereof.

Claims

1 . A structure for protecting an off-shore jack-up platform, such as a dril ling jack-up platform, against ice and/or other sea forces, the structure being configured to be lowered onto the sea floor and comprising a base portion and one or more protective columns, each protective column defining a channel upwardly extending from the base portion when the structure is installed on the sea floor; wherein the structure comprises one or more receptors each for receiving at least one foot of at least one leg of the off-shore platform; and wherein the one or more protective columns arc configured to laterally surround at least one leg of the offshore platform when the leg is received by one of the at least one receptors.

2. The structure according to claim 1 , wherein the platform comprises a plurality of protectiv e columns, each surrounding one of the legs.

3. The structure according to any one of the preceding claims, comprising a bottom base section and an upper section, separate from the bottom base section, wherein the bottom base section comprises the receptors.

4. The structure according to any one of the preceding claims wherein said receptors are selected from the group of a blind hole, a through hole, a grav el box, a socket with which a foot of a leg can enter a mating engagement, a flat surface suitable for receiv ing the load from the leg and platform and a single grav el pit for receiv ing all legs of the platform.

5. The structure according to any one of the preceding claims wherein said receptors are each arranged to receive the foot of single leg.

6. The structure according to one or more of claims 3 to 5, wherein the bottom base section comprises a recess for receiving the upper section and for securing the upper section against transverse shifting relative to the base portion.

7. The structure according to one or more of claim 3 to 6, wherein the upper section is made up from at least a first and a second subsection wherein the first and second subsections each form respective segments of one or more of the protective columns, such as of each of the protective columns.

8. The structure according to any one of the preceding claims wherein said protective columns are arranged to be substantially water tight when installed, such as water tight.

9. The structure according to any one of the preceding claims wherein said structure further comprises a well protection column.

1 0. The structure according to claim 9 further wherein said well protection column is arranged to function as a template platform.

1 1. The structure according to claim 9 or 10 further wherein said well protection column is arranged to allow dril ling from substantial ly al l positions of a cantilever drill floor on the platform, such as more than 50% of the positions, such as more than 75% of the positions, such as 90% of the positions, such as all of the positions.

12. The structure according to any one of the preceding claims wherein the protective columns are arranged to carry at least part of the weight of the jack-up platform, such as all of the weight of the jack-up platform.

13. The structure according to any one of claims 7 to 12, wherein each of the first and second subsections is configured to be transversely moved inwards from respective sides towards the legs so as to jointly form the protective col umns surrounding the one or more legs of the offshore platform when the first and second subsections are positioned on top of the bottom base section.

14. The structure according to claim 13, wherein the structure comprises a respective column for each leg of the platform, and wherein each subsection comprises a part of each of the columns.

1 5. The structure according to any one of claims 7 through 14, wherein one of the subsections comprises a well protection column.

16. The structure according to any one of claims 7 through 15, wherein each of the first and second subsections comprises a base portion from which one or more column segments extend upwardly, each col umn segment defining a part of a periphery of a protective column.

1 7. The structure according to any one of the preceding claims, further comprising a well protection column defining a conduit extending from a top to a bottom of the structure allowing a drill or pipe to be advanced from the off-shore platform to the sea floor.

18. The structure according to any one of the preceding claims comprising a bottom surface of the structure for engaging the sea floor, and one or more members protruding downwardly from the bottom surface.

19. The structure according to any one of the preceding claims, wherein at least one of the base portion and the protective column have an ice deflecting periphery.

20. The structure according to any one of the preceding claims, comprising one or more enclosures/compartments configured to be fil led with fluid, such as water, so as to change the buoyancy of the structure and allowing a controlled lowering of the structure.

21. The structure according to any one of the preceding claims wherein the structure has a height defined between its bottom surface and a top end of a highest one of the protective column large enough for the structure to extend out of the water when the structure is positioned on the sea floor.

22. A base section for supporting an off-shore jack-up platform, the base section being configured to be lowered onto the sea floor; wherein the base comprises one or more receptors each for receiv ing at least one foot of at least one leg of the off-shore platform and at least one through hole arranged in relation to the receptors to allow drill ing to be conducted from the jack-up platform through the through hole.

23. The base section according to claim 22 comprising a recess for , such as a load transfer recess, receiving one or more upwardly extending protective sections for protecting the legs of the platform against ice and/or other sea forces.

24. The base section according to claim 22 or 23, wherein the receptor comprises a blind hole or a through hole at least partially filled by a stabilizing medium.

25. The base section according to any of claims 22 to 24 wherein the ba.se has a height between 15 and 55m, such as between 20m and 55m, such as between 35m and 55m

26. The base section according to any of claims 22 to 25 further comprising one or more features of the base sections of claims 1 to 21.

27. A system for protecting an off-shore jack-up platform against ice and/or other sea forces, the system comprising two or more protective column sections configured to be lowered towards the sea floor, wherein the first and second column sections each form respective segments of one or more protective column, wherein each of the one or more protective columns laterally surrounds at least one leg of the offshore platform, and wherein each of the first and second protective column sections is configured to be transversal I y moved inwards from respective sides and towards the legs so as to jointly form the protective columns.

28. A system of claim 27 further comprising one or more of the features of claims 7 to 25.

29. A method of securing an off-shore jack-up platform to the sea floor, the method comprising

- lowering a base section as defined in any one of claims 15-17 onto the sea floor;

- moving the off-shore platform to a position above the base section;

- mov ing two or more protective column sections of a system as defined in claim 18 transversely inwards to a position above the base section and below a hull of the platform so as to cause the protective column sections to jointly form one or more protective columns laterally surrounding the one or more legs; and

- positioning the protective column sections on top of the base section.

30. The method according to claim 29, wherein lowering the base section comprises:

- positioning the protective column sections on top of the base section.

- lowering the base section with the protective column sections positioned on top of the base section onto the sea floor;

- mov ing the protective column sections transversely outw ards so as to al low movement of the offshore platform to a position above the base section.

31. The method according to claim 29 or 30 further comprising raising the legs so as to al low the columns to carry at least part of the weight of the platform, such as al l of the w eight.

32. An off-shore platform comprising

- a hul l and one or more legs extending from the hull downward towards the sea floor; and

- a structure as defined in any one of claims 1 through 14.

33. The off-shore platform of claim 32 comprising an insulation of a gap between the top of protective columns and the hul l of the platform.

34. The off-shore platform of claim 33 or 34 further arranged to heat the inside of the protective columns and/or a well protecting column, such as by injecting cool ing water from the platform or other excess heat.

35. A base section for supporting an off-shore jack-up platform, the base section being configured to be lowered onto the sea floor; wherein the base comprises one or more receptors each for receiv ing at least one foot of at least one leg of the off-shore platform.

36. A base section according to claim 35 further comprising one or more of the features of the base of claims 22 to 28.