NO20151447A1 - A modular subsea load transfarring system and a subsea system comprising a subsea load transferring system - Google Patents

Abstract

It is disclosed a modular subsea load transfer system (11) for a subsea system (10) for transfer and distribution of external loads acting on the subsea system to a plurality of subsea support elements (95), as well as casings, arranged in respective subsea wells. The subsea load transfer system (11) comprises a plurality of modular frames (12) where each modular frame (12) is adapted for connection to at least one support element (95) for transfer of external loads to the at least one support element. The subsea load transfer system (11) further comprises a frame structure (14) formed by either a load distributing frame (98) which is connectable to the plurality of support elements (95) such that the load distributing frame (98) can distribute loads between the support elements (95), or by the modular frames (12) being interconnected to form a modular frame structure such that the modular frame structure can distribute loads between the support elements (95).

Description

The present invention is related to a modular subsea load transfer system for transfer and distribution of external loads on a subsea system to a plurality of support elements, and a subsea system comprising such a modular subsea load transfer system.

Development of subsea oil and gas fields is very expensive, and various methods have been sought to reduce the cost of such development.

Subsea equipment installed on the seabed can be large and heavy and large vessels are required to transport and install subsea equipment. Such large installation vessels are expensive to hire, and significant savings can be achieved if equipment can be installed with a smaller vessel.

Another factor that increases the cost of development of oil and gas fields is that as all fields are different, and requirements are different, the equipment installed at each field is designed for each new field development.

Advanced drilling methods have made it possible to develop subsea oil fields with wellheads installed on templates which have multiple well slots in the same frame. With several wells placed on the same template, well fluid transportation, well control and communication, well intervention etc. are simplified and drilling of several wells can be done at the same location. However, a great disadvantage with well templates is that the structure usually becomes large and heavy, reducing flexibility in manufacturing, handling, transportation and installation. Furthermore, well templates are usually anchored to the seabed with suction anchors which significantly contribute to increased weight.

The subsea equipment arranged on the well templates usually requires protection against dropped objects. Furthermore, at areas where fishing can take place, the wells are normally required to deflect fishing gear and/or to be overtrawlable without snagging of the fishing gear on subsea installed equipment. Additional structures may therefore be added to the well template increasing the size and weight even more. In any case, the subsea equipment installed on the seabed must be capable of transferring loads that may be caused by external sources such as trawls that can cause substantial horizontal loads on the subsea structures installed on the seabed.

The objective of the present invention is therefore to provide a subsea system for hydrocarbon wells which is flexible and readily adaptable for use in various well configurations.

It is further an objective of the present invention to provide a subsea system which can be deployed with a drilling rig or vessel and without the need for large installation vessels.

It is further an objective to provide a subsea system which can transfer external loads, especially horizontal loads, on the subsea system to the seabed without the use of suction anchors or piles.

These objectives are solved by a modular subsea load transfer system as defined in claim 1 and a subsea system as defined in claim 16. Additional features of the modular subsea load transfer system are defined in the dependent claims 2-15 and additional features of the subsea system are defined in the dependent claims 16-21.

The idea behind the present invention is to provide a subsea system that can replace the known well templates. By modularizing the subsea system, it is possible to develop separate modules such that some modules are common for different fields and such that modules can be assembled differently for each field to be fit for purpose. By standardization, the amount of engineering hours required can be reduced considerably. It is also probable that if a number of the same components are made, the manufacturing cost for each component can be reduced.

The present invention further solves the problem of size reduction, particularly of large frames like template structures, by employing modularization. The present invention makes use of modular structural frame elements that can be assembled and interconnected to a larger structure like a multi-well template. The structural frame elements can be connected to each other or a separate load distributing frame may be connected to support elements, such as well casings, to provide load transfer between frame elements to the extent necessary to transfer external loads and loads from i.e. a manifold to foundations, typically well casings, and to distribute the loads between several support elements, such as well casings, rather than only one as for satellites. Other elements can be connected to the modular frame elements to provide additional functions, such as trawl deflectors and protection covers, connection elements, manifold frame etc. The structural elements may be connected though standardized joints or interfaces. Each modular element can be installed separately with a small vessel or, if desired, through a moon pool such that an option would be to do the installation during well drilling and completion.

The modular frame elements can be made so that they are connectable to a support element on the sea floor such as a subsea well casing, i.e. the conductor casing, the surface casing or another casing element, or the well head or any other existing frame element for foundation.

The frame elements can also be connected before installation, at sea or on land if that is found to be more convenient. This will be decided by optimal utilization of available facilities for handling, storage, transportation and installation in each project.

The purpose of the system is to provide maximum flexibility and minimum total cost for different installations. Possible logistic arrangements may for instance be: 1. Manufacturing of elements at distributed suppliers, transportation by truck to on shore base, assembly of elements at base, offshore transportation and installation of the assembly by large vessel. 2. Manufacturing of elements at distributed suppliers, transportation of some elements to drilling operations base for installation during drilling. Other elements can be installed as separate elements and installed with a small vessel. These elements can be installed independently or connected to previously installed elements subsea to form a larger structure. 3. Manufacturing of elements at distributed suppliers, transportation by truck to installation vessel, installation and connection of elements at seabed by small vessel.

The elements in questions are typically guide base structures, which is basically a modular frame interconnectable with other modular frames, trawl deflector systems, connection elements and foundation elements.

One possible design of the invention is to connect a number of specially designed permanent guide base (PGS), i.e. modular frames, to each other such that it is possible to obtain several of the well template design benefits combined with the benefits of single well solutions. It is possible to connect any number of wells to each other in one or possibly two rows or more rows. By connecting PGB's, low foundation costs are achieved, but at the same time the load transfer capacity is increased for each well that is connected. Accurate positioning of wells are preferable to obtain the easiest connection between PGB elements. This can be achieved by drilling with a drilling guide base template which is configured such that the distance between wells are as required for the configuration of PGB connections. By configuring wells to allow space for a manifold between, full production template functionality can be achieved built with modules that can be standardized.

Typically, elements have connection interfaces that can be used to connect to other elements, to guiding or other functions. Elements may be equipped with means to fit and or lock to the connection interfaces. Guiding for connection between elements can be by guide wire, or guidewireless. It can also be connection without guiding, or by use of tools, including hydraulic tools or other special tools. Elements can be mounted together in another configuration than the final installed configuration, for instance to minimize space for transportation and installation.

Elements may include secondary elements like lifting pads, hinges, strapping points for BOP etc. A PGB-element may include piping, valves or connectors as a flowbase. The present invention can also be configured such that each PGB element is for example a two well slot template, but such that each of these can be connected. This can be beneficial in some instances.

There is provided a modular subsea load transfer system for a subsea system for transfer and distribution of external loads acting on the subsea system to a plurality of support elements which are securely arranged in or on respective subsea wells, wherein the subsea load transfer system comprises a plurality of modular frames where each modular frame is adapted for connection to at least one support element for transfer of external loads to the at least one support element. The subsea load transfer system further comprises a frame structure which is formed by either a load distributing frame which is connectable to the plurality of support elements such that the load distributing frame can distribute loads between the support elements, or by the modular frames being interconnected to form a modular frame structure such that the modular frame structure can distribute loads between the support elements.

The support element is preferably the well casing of the well, i.e. the conductor casing or the surface casing or another casing element, but may also be the well head or any other existing foundation element of the well which is capable of taking up loads and transferring the loads to the sea bed.

With this modular subsea load transfer system, which is securely connected to several support elements, typically a conductor casing, the external loads, especially horizontal loads or loads with a substantial horizontal component, can be transferred and distributed between the support elements which means that there is less chance that damage to the support elements will occur. Furthermore, since external loads can be transferred and distributed to a plurality of support elements with the present invention, there is no need for the conventional suction anchors or piles that are usually employed today.

In an embodiment of the present invention, the modular frames may comprise at least one support element connecting element for connecting the modular frames to respective support elements.

The modular frames preferably comprise at least one first joint element for interconnection of the modular frames and/or for connection of equipment to the subsea load transfer system. Such equipment may for example be load deflecting elements which are designed to deflect trawls.

Preferably two or more adjacent modular frames are interconnected with at least one connecting member to form a load transferring and load distributing frame structure. These connecting members may have different shapes. In an embodiment, two or more adjacent modular frames are interconnected with a centre frame to form a load transferring and load distributing frame structure.

Alternatively, two or more adjacent modular frames may be interconnected with at least one connecting member and a centre frame to form a load transferring and load distributing frame structure. The centre frame may be adapted for support of a subsea manifold and/or other types of subsea equipment, or the load distributing frame may be an integrated part of the manifold.

The load distributing frame preferably comprises a plurality of support element connecting elements for connecting the load distributing frame to the plurality of support elements.

In addition, the load distributing frame may be adapted for support of a subsea manifold and/or other types of subsea equipment, or the load distributing frame may be an integrated part of the manifold.

The load distributing frame may comprise a first frame member and a second frame member and/or a third frame member which is/are rotatably connected to the first frame member. The second frame member and/or the third frame member may further comprise the support element connecting elements. The first frame member may also be adapted for support of a subsea manifold and/or other types of subsea equipment. It should be noted that the load distributing frame can be designed in a number of different variants.

It should be noted that the load distributing frame may be designed such that a

various number of frame members may be connected to the first frame member. For example, the load distributing frame comprises the first frame member to which one further frame member, i.e. the second frame member, can be rotatably connected, or two further frame members, i.e. the second frame member and the third frame member, can be rotatably connected, or three or more frame members, i.e. the second and third frame members and one or more further frame members, can be rotatably connected. If the first frame member is given for example a hexagonal

shape then six frame members can be rotatably connected to the first frame member.

The load transfer system preferably comprises at least one housing support element for a protective housing structure. The at least one housing support element may be rotatably mounted to a modular frame.

The subsea load transfer system is particularly adapted to transfer and distribute horizontal or substantially horizontal external loads.

There is also provided a subsea system for hydrocarbon wells where the subsea system is deployed on the seabed and comprises a plurality of support elements which are securely arranged in or on respective hydrocarbon wells. The subsea system further comprises a subsea load transfer system as described herein for transfer and distribution of external loads acting on the subsea system to the plurality of subsea support elements.

Again, the support element is preferably the well casing of the well, i.e. the conductor casing or the surface casing or another casing element, but may also be the well head or any other existing foundation element of the well which is capable of taking up loads and transferring the loads to the sea bed.

Preferably, the subsea system further comprises a protective housing structure for protection of well heads and other equipment comprised in the subsea system from external loads. Preferably, the housing structure is connected to the at least one housing support element of the modular frames.

The subsea system may further comprise a plurality of load deflecting elements for at least partial deflection of external loads such as loads from a trawl gear, dragged anchor chains etc. that passes over the subsea system. The load deflecting elements may be adapted for connection to the first joint element of the modular frames of the subsea load transfer system.

The subsea load transfer system according to the present invention will now be explained in detail with reference to the figures, where

Figures 1-2 show a modular frame according to the present invention.

Figures 3-4 show various joint elements for connecting modular frames together and external equipment to the modular frames. Figures 5-6 show a variant of the modular frame according to the present invention.

Figure 7 shows a dual modular frame according to the present invention.

Figure 8 shows a subsea load transfer system where two modular frames are interconnected so that they form a modular frame structure. Figure 9 shows a subsea load transfer system where four modular frames are interconnected so that they form a modular frame structure. Figure 10 shows two modular frames being interconnected with dual joint elements. Figure 11 shows a subsea load transfer system where three modular frames are interconnected so that they form a modular frame structure. Figure 12 shows a subsea load transfer system where four modular frames are interconnected so that they form a modular frame structure. Figure 13 shows a subsea load transfer system where five modular frames are interconnected so that they form a modular frame structure. Figure 14 shows a subsea load transfer system where four modular frames are interconnected with a centre frame so that a modular frame structure is formed. Figure 15 shows a subsea system including the subsea load transfer system shown in figure 14 covered by a housing structure. Figure 16 shows a load distributing frame according to the present invention. Figure 17 shows a frame structure including which includes the frame shown in figure 16 connected to a support element, typically a conductor casing, and a modular frame as shown in figures 1-2 being connected to the same well casing. Figure 18 shows a subsea load transfer system with four modular frames connected to respective four support elements, typically conductor casings, and a load distributing frame as shown in figure 16 connected to all four support elements. Figure 19 shows a subsea system including the subsea load transfer system shown in figure 18 covered by a housing structure. Figure 20 shows a subsea system including the subsea load transfer system shown in figure 11 covered by a housing structure. Figure 21 shows a subsea system including the subsea load transfer system shown in figure 12 covered by a housing structure. Figure 22 shows a subsea system including the subsea load transfer system shown in figure 13 covered by a housing structure.

Firstly, it should be noted that the same reference numbers have been used for the same features in the figures.

Figure 1 and 2 shows a first embodiment of a modular frame 12 according to the present invention. The modular frame 12 comprises a first frame element 17, a second frame element 18, a third frame element 19 and a fourth frame element 20 which are connected, for example by welding, to form a substantially rectangular frame. The modular frame 12 preferably has a rectangular or a square shape, but may obviously be given a different shape if that is desired.

The modular frame 12 comprises a support element connecting element 23 which is connected to the frame elements 17, 18, 19, 20 by inner frame elements 21. The inner frame elements 21 may be connected to the frame elements 17, 18, 19, 20 and the support element connecting element 23 by welding or any other suitable connection, such as bolting, which provides the modular frame 12 with the required strength. The support element connecting element 23 comprises a through-going opening 24 through which a support element 95 of a hydrocarbon well can pass. When the modular frame 12 is arranged in place on a support element, it can be securely fastened to the support element by a clamp connected to the modular frame, with bolts, by welding or with any other suitable fastening method.

It should be noted that the support element is preferably the well casing of the well, i.e. the conductor casing or the surface casing or another casing element, but may also be the well head or any other existing foundation element of the well which is capable of taking up loads and transferring the loads to the sea bed.

The modular frame 12 further comprises at least one, but preferably two housing support elements 42 as indicated on the figures. The housing support elements 42 are shown rotatably or hingedly connected to the first frame element 17 and second frame element 18 in a first connection 45 and a second connection 46 respectively, but the housing support elements 42 may also be fixedly connected to the modular frame 12. The housing support elements 42 shown in figures 1-2 are rotatable between a transport position, as shown in figure 2, and an operational position, as shown in figure 1, in which a housing structure 92 can be mounted to the housing support elements 42. For that purpose, the housing support elements 42 are provided with housing connecting elements 47 as indicated in the figures. The housing connecting elements can be made in any well known manner and will not be described in further detail. The housing support elements 42 may obviously be designed in many different ways. In the figures there is shown one option comprising two sidebars 43 which are connected with a crossbar 44. The sidebars 43 are rotatably connected to the first frame element 17 and the second frame element 18 respectively.

The modular frame 12 is further provided with at least one, but preferably a plurality of a first frame joint element 27. In the figures, the modular frame 12 is shown with four such first frame joint elements 27, one in each corner of the substantially rectangular frame. The first frame elements 27 is used for interconnection of two or more adjacent modular frames 12 or for connecting external equipment, such as a load deflecting element 90, to the modular frame 12.

The first frame joint element 27 can obviously be given different designs. The first frame joint element 27 shown in the figures has cylindrical shape with an upper opening 28 and a lower opening 30 for insertion of various types of joint elements or external equipment. On top of the cylindrically shaped first joint element 27 there is provided a plurality of first aligning elements 29 which will prevent elements which are inserted into the opening 28 from rotating. The first joint elements 27 may also be provided with guiding elements as indicated in the figures to ensure that elements and equipment inserted into the opening 28 are inserted in the correct position.

In figures 5 and 6 there is shown a slightly different design of the modular frame 12. The modular frame 12 comprises a first modular frame element 50 comprising a first frame element 51, a second frame element 52, a third frame element 53 and a fourth frame element 54 which are connected, preferably by welding, to form a frame. The first modular frame element 50 further comprises a support element connecting element 23 which is connected to the frame elements 51, 52, 53, 54 with a number of inner frame elements 55 in the same way as described above. The support element connecting element 23 can be securely connected to a support element such as a well casing element, for example by using a bolted connection or by welding as described above. The first frame element 51 and the second frame element 52 are provided with first connecting means 56, for example in the form of flange elements as indicated in the figures.

The modular frame 12 shown in figures 5 and 6, further comprises a second modular frame element 58 comprising a first frame element 59 and a second frame element 60 and a third frame element 61 which are securely attached to the first frame element 59, for example by welding or a bolt connection. The second frame element 60 and the third frame element 61 are provided with second connecting means 62, for example in the form of flange elements as indicated in the figures, which have a complementary design to the first connecting means 56 such that the second modular frame elements 58 can be securely attached to the first modular frame element 50.

To the second modular frame elements 58 there are secured at least one, but

preferably two or more housing support elements 64. The housing support elements 64 are provided with housing connecting elements 65 such that a protective housing structure 92 can be attached to the housing support elements 64 in the same way as explained in connection with the housing support elements 42 of the embodiment shown in figures 1 and 2.

The second modular frame elements 58 are further provided with two first joint

elements 27 which may be securely attached to the first frame element 59 as shown in figures 5 and 6. The first joint elements 27 have the same design and function as the first joint elements 27 of the embodiment shown in figures 1 and 2 and will not be explained in detail again.

When the second modular frame elements 58 are securely attached to the first modular frame element 50, a modular frame 12 is obtained that are substantially equal to the embodiment of the modular frame 12 shown in figures 1 and 2. The difference is that the embodiment shown in figures 5 and 6 can be made, stored and transported in separate parts and assembled into the complete modular frame 12 when desired. This can be a desirable solution when it is important to keep the weight and size of the modular frames during transport and/or deployment of the modular frames as small as possible or to enable the use of the first modular frame element 50, i.e. a standard guide base (PGB) without first joint elements 27, in situations where addition of load deflecting elements 90 or other types of auxiliary equipment is not required.

In figure 7 there is shown a further embodiment of the modular frame which is formed as a dual modular frame 86. This embodiment basically comprises two modular frames 12 as shown in figures 1 and 2 which are securely fixed to each other with connecting bars 87. Each end of the connecting bars 87 are preferably welded to each of the two modular frames 12 as shown in figure 7 such that the dual modular frame 86 is formed. The dual modular frame 86 therefore comprises two support element connecting elements 23 and four first joint elements 27 arranged in each corner of the substantially rectangularly shaped dual modular frame 86 such that two or more dual modular frames 86 may connected to each other or external equipment, such as load deflecting elements 90, may be connected to the dual modular frame 86.

In figures 3, 3a-c and 4, 4a-i there are shown a few elements which can be used to interconnect two adjacent modular frames 12 or dual modular frames 86, or to connect external, auxiliary equipment, such as load deflecting elements 90 or support elements, to the modular frames 12 or dual modular frames 86.

In figure 3 there is shown a modular frame 12 comprising four first joint elements 27 as explained above. In figures 3a-3c there are shown second joint elements 31 which are designed to be inserted into the lower opening 30 of the first joint elements 27. These elements are typically used for supporting a modular frame 12 and comprise a conical section 33 that enters the lower opening 30 and a stop element 32 on which the first joint element 27 will rest. In figure 3c there is also shown a dual joint element 35 which can be used to interconnect two adjacent modular frames 12 or dual modular frames 86. The dual joint element 35 comprises a second connecting member 49 which can be entered into the lower opening 30 of a modular frame 12 or a dual modular frame 86, and a first connecting member 48 which can be entered into the lower opening 30 of an adjacent modular frame 12 or dual modular frame 86. The two adjacent modular frames 12 or dual modular frames 86 will thereby be interconnected and form a frame structure 14 that is capable of transferring and distributing external loads to the support elements to which the modular frames 12 or dual modular frames 86 are connected.

In figure 4 there is again shown a modular frame 12 comprising four first joint elements 27 as explained above. In figures 4a-4i there are shown various elements which are adapted for entering the upper opening 27 of the first joint element 27. All of these elements comprises a the third joint element 36 which is adapted to be entered into upper opening 28 of the first joint element 27 to form a frame joint 26. The third joint element 36 preferably comprises a conical section 38 and a guide pin 34 to facilitate the entering of the third joint element 36 into the upper opening 28 of the first joint element 27. The third joint element 36 preferably comprises second aligning elements 37. The second aligning elements 37 and the first aligning elements 29 of the first joint elements 27 are complementary designed such that rotation of the third joint element is prevented when the third joint element 36 is positioned in the first joint element 27.

In figure 4a there is shown a second connecting member 74 which can be used to connect two adjacent modular frames 12. The second connecting member 74 comprises a straight element 75 to which there is connected a third joint element 36 at each end of the straight element 75. The two third joint elements 36 of the second connecting member 74 are entered into respective first joint element 27 of the two adjacent modular frames 12 and the second connecting members 74 thereby connects the two modular frames 12 such that external loads can be transferred between the two modular frames. Examples of the use of second connecting members 74 are shown in figures 9 and 11-14 which are further described below.

In figures 4b and 4c there are shown two alternative designs of the straight element 75 of the second connecting member 74. In figure 4b the straight element 75 comprises a first element 75a and a second element 75b where the first element 75a and the second element 75b are rotatably connected to each other in a rotational joint 136. The rotational joint may comprise a bolt that the first element 75a and/or the second element 75b can rotate about as indicated in figure 4b. With such a design of the second connecting member 74 the two third joint elements 36 may be arranged in a position where their longitudinal axes are not parallel. The rotational joint preferably includes a locking device that can lock the first element 75a and the second element 75b at a desired angle. In figure 4c there is shown a second connecting member 74 where one of two third joint elements 36 are securely fastened to the straight element 75, while the other third joint element 36 is mounted on a sliding element 137 that is adapted for movement along the straight element 75 to a desired position and then fastened to the straight element with a locking device like a clamping device or similar.

With a second connecting member 74 including a rotational joint 136 and/or a sliding element 137, it will be possible to join two adjacent modular frames 12 which are mounted on support elements which are not parallel or where the distance between the support elements are slightly off the planned distance. Such irregularities of a hydrocarbon well, and the support element mounted in the well, may arise and the adjustable second connecting members 74 shown in figures 4b and 4c may then be used to interconnect two adjacent modular frames 12. These two third joint elements 36 show that the frame joints 26 can be made to lock only some and not all degrees of freedom. The third joint element 36 in figure 4b show an example where a free rotation about an axis, i.e. a bolt or similar, is possible, while the third joint element 36 in figure 4c show an example where a free translational movement along an axis, i.e. along the straight element 75, is possible.

In figures 4d there is shown a third joint element 36 which is provided with a telescopic element 129. The length of the third joint element 36 is therefore adjustable which can be useful in situations, for example when load deflecting elements 90 are mounted to the four corners of the modular frame 12 and the distance to the seabed varies from one side to the opposite side of the modular frame 12 or because different types of auxiliary equipment requires different heights of the third joint elements 36. In figure 4e there is shown a third joint element 36 which is provided with a through-going opening for a bolt such that the third joint element 36 can be rotatably mounted on the auxiliary equipment.

Figure 4g and 4h shows two examples where an extension element has been mounted on the third joint element 36. In figure 4g a third joint element 36 is shown with a straight connector element 39 mounted on top of the third joint element 36 whereby the length of the third joint element 36 is extended with a fixed amount. In figure 4g a third joint element 36 is shown with an angular connector element 40 mounted on top of the third joint element 36. The auxiliary equipment is mounted to the straight connector element 39 or the angular connector element of third joint element 36 with a suitable coupling device such as the flange elements 138 and bolts as shown in the figures.

In figure 4f a third joint element 36 is shown mounted to a piece of auxiliary equipment which in this case is a load deflecting element 90. The third joint element 36 can be mounted to the auxiliary equipment with bolts, welding or any other suitable connecting means.

In figures 4i there are shown dual joint element 41 which is adapted for the upper opening 28 of the first joint elements 27. The dual joint element 41 comprises a first connecting member 48 and a second connecting member 49 which can be inserted into the upper openings of two adjacent modular frames 12 or dual modular frames 86 respectively, whereby two adjacent modular frames 12 or dual modular frames 86 are interconnected and capable of transferring and distributing external loads to the support elements that the modular frames 12 or dual modular frames 86 are connected.

The dual joint element 41 is preferably also provided with second aligning elements 37 which are complementary to the first aligning elements 29 of the first joint elements 27. When the dual joint element 41 is entered into the upper opening of a first joint element 27, the complementary shaped first aligning elements 29 and second aligning elements 37 will prevent the dual joint element 41 from rotating in the first joint element 27.

All the second, third and dual joint elements 31, 35, 36 shown in figures 3a-3c and 4a-4i and/or the corresponding first joint elements 27, are preferably provided with locking means that lock the second, third or dual joint elements 31, 35, 36 in their positions in the first joint elements 27. Such locking means are preferably chosen to be standard locking means which are well known in the art and readily available and will not be further described here.

Figures 8-14 show various ways of interconnecting two or more modular frames 12 so that a frame structure 14 is obtained and a subsea load transfer system 11 is formed which is capable of transferring external loads and distributing the external loads to the support elements 95.

In figure 8 there is shown two modular frames 12 which are interconnected using a first connecting member 68 which is a frame structure comprising a first frame element 69, a second frame element 70, a third frame element 71 and a fourth frame element 72 which are connected to each other, preferably by welding or a bolted connection, such that a substantially rectangular frame is obtained. An inner frame element 73 may also be provided as shown in figure 8 to strengthen the first connecting member 68. In each corner of the first connecting member 68 there is further provided an L-shaped connecting element 93 to which a third joint element 36 is mounted. When the third joint elements 36 are inserted into their respective first joint elements 27 on the two modular frames 12 as indicated in figure 8, a subsea load transfer system 11 according to the present invention is formed. As indicated in figure 8, load deflecting elements 90 are mounted in the first joint elements 27.

In figure 9 there is shown a load transfer system comprising two load transfer systems as shown in figure 8. Two assemblies each comprising two modular frames 12 interconnected with a first connecting member 68 as described above in frame joints 26. Two such assemblies are interconnected with two second connecting members 74 as shown in figure 9. The second connecting members 74 comprise a straight element 75. At each end of the first frame element there is mounted a third joint element 36 which are entered into respective first joint elements 27 of two adjacent modular frames 12. Together, the four modular frames 12 which are interconnected with two first connecting members 68 and two second connecting members 74, forms a frame structure 14 which, when the support element connecting elements 23 of the four modular frames 12 are mounted on respective support elements, the frame structure 14 is capable of transferring and distributing external loads acting on the frame structure to the support elements. In each corner of the frame structure 14 there is mounted a load deflecting element 90 as explained above.

In all embodiments of the present invention, the frame joints 26 comprises a first frame joint 27 and at least one second joint element 31 or a dual joint element 35 or a third joint element 36 which has been connected to the first joint element 27, i.e. entered into and locked in either the lower opening 30 or the upper opening 28 of the first joint element 27.

In figures 11-13 further alternatives of the frame structure 14 of the load transfer system 11 are shown. In figure 11 there is shown three modular frames 12 which are arranged in a row and where two adjacent modular frames are interconnected with two second connecting members 74 as explained above. The resulting frame structure 14 is rectangularly shaped and in each corner of the frame structure 14 there may be mounted a load deflecting element 90 as described above and shown in the figure.

In figure 12 there is shown a frame structure 14 of the load transfer system 11 comprising four modular frames 12 arranged in a rectangular, nearly square shape. The four modular frames 12 are interconnected at the centre with a substantially square shaped fourth connecting member 80. The fourth connecting member 80 comprises first frame element 81, a second frame element 82, a third frame element 83 and a fourth frame element 84 which are securely attached to each other, preferably by welding or bolted connections, to form a rectangular or square shaped fourth connecting member 80. In each corner of the fourth connecting member 80 there is mounted a third joint element 36 which are entered into respective first joint elements 27 of the four modular frames 12. In addition, the adjacent modular frames 12 are, at the periphery of the frame structure 14, connected with respective second connecting elements 74 as described above. Again, in the four corners of the frame structure 14 there may be mounted load deflecting elements 90.

The frame structure 14 of the subsea load transfer system 11 shown in figure 13 is similar to the frame structure shown in figure 12 except that a fifth modular frame 12 has been added to one side of the frame structure 14. The fifth modular frame 12 is connected to the adjacent two modular frames 12 with a straight second connecting member 74 in the same way as described above, and a triangularly shaped third connecting member 76. The third connecting member 76 comprises a first frame element 77, a second frame element 78 and a third frame element 79 which are securely attached to each other, preferably by welding or bolted connections, to form a triangular shaped third connecting member 76. In each corner of the third connecting member 76 there is mounted a third joint element 36 which are entered into respective first joint elements 27 of the three adjacent modular frames 12 as shown in the figure. In the corners of the resulting frame structure 14 there may be mounted load deflecting elements 90 as shown.

In figures 10 and 14 there is shown yet another alternative for forming the frame structure 14 of the subsea load transfer system 11. In this alternative, four modular frames 12 are interconnected at the centre with a centre frame 130. The centre frame 130 comprises four first joint elements 27 with respective lower openings 30 and upper openings 29. In the lower openings 30 of the first joint elements 27 a dual joint element 35 is arranged as shown in figure 10. Similarly, a dual joint element 41 is arranged in the upper opening 29 of the first joint element 27 of the corner of each of the four modular frames 12 which are to be connected to the centre frame 130. This is indicated for one of the modular frames 12 in figure 10. When the modular frames 12 are connected to the centre frame 130, the first connecting member 48 of the dual joint element 35 will enter into the lower openings 30 of the first joint elements 27 of the modular frames 12, and first connecting member 48 of the dual joint element 41 enters the upper opening 29 of the first joint elements 27 of the centre frame 130. In addition, the adjacent modular frames 12 are interconnected with second connecting members 74 as shown in the figure and described in detail above. The resulting frame structure 14 of the subsea load transfer system 11 is capable of transferring and distributing external loads to the support elements to which the modular frames 12 are connected. As for all the other alternative frame structures 14, in each corner of the frame structure 14 there may be mounted a load deflecting element 90.

The centre frame 130 may comprise a first frame element 131, a second frame element 132, a third frame element 133 and fourth frame element which are securely attached to each other, preferably by welding or bolted connections, to form a substantially rectangularly shaped centre frame. Any number of inner frame elements 135 may be included in the centre frame as shown in figure 14 in order to obtain the required strength. In addition to interconnecting the four modular frames 12 and thereby creating a frame structure 14 which is capable of transferring and distributing external loads to the support elements, the centre frame may also serve as a support for a manifold and other types of equipment which may desirable or required to be installed on the seabed in connection with the wells.

As should be clear from the examples above, a large number of variants of the frame structure 14 may be formed by interconnecting different numbers of modular frames 12. However, only a small number of standard elements are needed to form the different frame structures 14 which, when the modular frames 12 are connected to respective support elements, are capable of transferring external loads to the support elements and distributing external loads between the different support elements.

Above, various forms of the subsea load transfer system 11 has been described wherein a plurality of modular frames 12 are connected to respective support elements and interconnected so that a frame structure 14 is formed which is capable of transferring and distributing external loads on the subsea load transfer system 11 to the support elements 95. These subsea load transfer systems 11 are preferably included in a subsea system 10 where well heads and X-mas trees are mounted on well casings and further subsea equipment, such as piping, connectors, valves, manifolds, and so on can be included in the subsea system 10. In order to protect the subsea equipment the subsea system are preferably provided with a housing structure 92 which is mounted to the housing support elements 42 on the modular frames 12 as explained above. The housing structure 92 comprises housing elements 91 and preferably covers the frame structure 14 and any equipment which are arranged on the frame structure 14. In addition, the load deflecting elements 90 as described above are preferably included in the subsea systems 10.

In figures 15 and 20-22 examples of such subsea systems are shown. In figure 15, the subsea system 10 comprises the subsea load transfer system 11 shown in figure 14, a housing structure 92 which is mounted to the housing support elements 42 of the modular frames 12 and load deflecting elements 90. When external loads, for example from trawling, is exerted on the subsea system 10, the external loads are tåken up by the subsea load transfer system 11 and transferred and distributed through the interconnected modular frames 12 to the support elements, typically well casings, to which the modular frames 12 are connected.

In figure 20 there is shown a subsea system 10 comprising the subsea load transfer system 11 shown in figure 11 and described above and a housing structure 92 which covers the subsea load transfer system 11 and the equipment installed on the frame structure 14.

In figure 21 there is shown a subsea system 10 comprising the subsea load transfer system 11 shown in figure 12 and described above and a housing structure 92 which substantially covers the subsea load transfer system 11 and the equipment installed on the frame structure 14.

In figure 22 there is shown a subsea system 10 comprising the subsea load transfer system 11 shown in figure 13 and described above and a housing structure 92 which substantially covers the subsea load transfer system 11 and the equipment installed on the frame structure 14.

In figure 16-19 there is disclosed a further embodiment of the present invention where the modular frames 12 are not interconnected in the same way as described above. In this embodiment, a plurality of modular frames 12, or dual modular frames 86, comprising respective support element connecting elements 23, are connected to respective support elements. To distribute external loads between the plurality of support elements, the subsea load transfer system is provided with a load distributing frame 98. The load distributing frame 98 comprises a plurality of support element connecting elements 128 as shown in figures 16-17 for connection to the same support elements as the modular frames 12 or dual modular frames 86 are connected to. The load distributing frame 98 may be formed by a single frame or, as shown in the figures, by a first frame member 100 to which at least a second frame member 113 is rotatably connected with frame joints 107, for example a bolt that the second frame member 113 is capable of rotating about. As shown in the figures, a third frame member 120 may also be rotatably connected to the first frame member 100 with frame joints 107, for example a bolt that the second frame member 113 is capable of rotating about. Since the second frame member 113 and the third frame member 120 are rotatably connected to the first frame member 100, the load distributing frame 98 may be collapsed during transport and installation, reducing the size of the load distributing frame 98 considerably. As mentioned above, it would also be possible to provide the load distributing frame 98 with one, two, three, four or more rotatable frames mounted to the central, first frame member 100 by choosing the shape of the first frame member 100 accordingly.

The first frame member 100 may comprise a first frame member 101, a second frame member 102, a third frame member 103 and a fourth frame member 104 which are securely attached to each other, preferably by welding or bolted connections, to form a substantially rectangularly shaped first frame member 100. Any number of inner frame elements 105 may be included in the first frame as shown in the figures 16-18 in order to obtain the required strength and stiffness.

The second frame member 113 may comprise a first frame member 114, a second frame member 115, a third frame member 116 and a fourth frame member 117 which are securely attached to each other, preferably by welding or bolted connections, to form a substantially rectangularly shaped second frame member 113. Any number of inner frame elements 118 may be included in the second frame as shown in the figures 16-18 in order to obtain the required strength and stiffness.

The third frame member 120 may comprise a first frame member 121, a second frame member 122, a third frame member 123 and a fourth frame member 124 which are securely attached to each other, preferably by welding or bolted connections, to form a substantially rectangularly shaped third frame member 120. Any number of inner frame elements 125 may be included in the second frame as shown in the figures 16-18 in order to obtain the required strength.

In addition to interconnecting the support elements and thereby creating a load distributing frame structure which is capable of transferring and distributing external loads between the support elements, the load distributing frame 130 may also serve as a support for a manifold and other types of equipment which may desirable or required to be installed on the seabed in connection with the wells.

As shown in figure 18, the subsea load transfer system 11 may comprise four modular frames 12 which are mounted on four support elements and a load distributing frame 98 which is connected to all four support elements. The modular frames 12 comprise housing support elements 42 as described in further detail above, to which a housing structure 92 can be mounted. Although figure 18 shows a load distributing frame which is connectable to four different support elements, the load distributing frame 98 may obviously be designed to be connected to more than or less than four support elements.

A complete subsea system 10 is shown in figure 19 which comprises the subsea load transfer system 11 shown in figure 18 and a housing structure 92 which is mounted on the subsea load transfer system 11. In addition there is provided a load deflecting element 90 in each corner of the subsea system 10 which are mounted to first joint elements 27 of respective modular frames 12 as explained above.

External loads, and particularly horizontal loads, for example from a trawl gear

passing over the subsea system 10, will mostly be exerted on the modular frames 12 and often one of the modular frames 12 receives a large portion of the external load. The external loads are thereafter transferred through the support element or support elements 95 of the modular frame or frames that receive the external load to the load distributing frame 98 which transfers and distributes the external load between the support elements 95 to which the load distributing frame 98 is connected.

With the present invention, whether a plurality of interconnected modular frames 12 or a load distributing frame 98 is used, large external loads, especially substantially horizontal loads, will be transferred and distributed to several support elements which considerably reduces the chance of any damages to a support element occurring, which is advantageous, especially if the support elements form a structural part of the well, such as if the support elements are respective casing elements. Furthermore, since the external loads are transferred to the support elements, there is no need for the suction anchors which are used with well templates today. Finally, because of the modular design of the subsea load transfer system and the subsea system disclosed herein, the weight and the size of the individual elements can be kept small which enables the use of drilling rig/vessel for deployment or small vessels for transport and deployment of the subsea system. The modular design also makes it possible to put together a large number of various designs for the subsea load transfer system 11.

The invention has now been explained with reference to a number of non-limiting examples. A person skilled in the art will appreciate that modifications and changes may be made to these embodiments which will be within the scope of the invention as defined in the following claims.

Claims (21)

1. A modular subsea load transfer system (11) for a subsea system (10) for transfer and distribution of external loads acting on the subsea system to a plurality of support elements (95) which are securely arranged in or on respective subsea wells, wherein the subsea load transfer system (11) comprises a plurality of modular frames (12) where each modular frame (12) is adapted for connection to at least one support element (95) for transfer of external loads to the at least one support element, and wherein the subsea load transfer system (11) further comprises a frame structure (14) which is formed by either a load distributing frame (98) which is connectable to the plurality of support elements (95) such that the load distributing frame (98) can distribute loads between the support elements (95), or by the modular frames (12) being interconnected to form a modular frame structure such that the modular frame structure can distribute loads between the support elements (95).

2. The subsea load transfer system according to claim 1, wherein the modular frames (12) comprise at least one support element connecting element (23) for connecting the modular frames to respective support elements (95).

3. The subsea load transfer system according to claim 1 or 2, wherein the modular frames (12) comprises at least one first joint element (27) for interconnection of the modular frames (12) and/or for connection of equipment to the subsea load transfer system (11).

4. The subsea load transfer system according to one of the claims 1-3, wherein two or more adjacent modular frames (12) are interconnected with at least one connecting member (68, 74, 76, 80) to form a load transferring and load distributing frame structure (14).

5. The subsea load transfer system according to one of the claims 1-3, wherein two or more adjacent modular frames (12) are interconnected with a centre frame (130) to form a load transferring and load distributing frame structure (14).

6. The subsea load transfer system according to one of the claims 1-3, wherein two or more adjacent modular frames (12) are interconnected with at least one connecting member (68, 74, 76, 80) and a centre frame (130) to form a load transferring and load distributing frame structure (14).

7. The subsea load transfer system according to claim 5 or 6, wherein the centre frame (130) is adapted for support of a subsea manifold or the centre frame (130) is an integrated part of the manifold.

8. The subsea load transfer system according to one of the claims 1-3, wherein the load distributing frame (98) comprises a plurality of support element connecting elements (128) for connecting the load distributing frame (98) to the plurality of support elements (95).

9. The subsea load transfer system according to claim 8, wherein the load distributing frame (98) is adapted for support of a subsea manifold or the load distributing frame (98) is an integrated part of the manifold.

10. The subsea load transfer system according to claim 8, wherein the load distributing frame (98) comprises a first frame member (100) and a second frame member (113) and/or a third frame member (120) which is/are rotatably connected to the first frame member (100), and wherein the second frame member (113) and/or the third frame member (120) comprise/comprises the support element connecting elements (128).

11. The subsea load transfer system according to claim 10, wherein the first frame member (100) is adapted for support of a subsea manifold.

12. The subsea load transfer system according to one of the claims 1-11, wherein the load transfer system (11) comprises at least one housing support element (42, 64) for a protective housing structure (92).

13. The subsea load transfer system according to claim 12, wherein the at least one housing support element (42, 64) is rotatably mounted to a modular frame (12).

14. The subsea load transfer system according to one of the claims 1-13, wherein the subsea load transfer system (11) transfers and distributes horizontal or substantially horizontal external loads.

15. The subsea system according to one of the claims 1-14, wherein each of the plurality of the support elements (95) is a conductor casing or a surface casing or another casing element.

16. A subsea system (10) for hydrocarbon wells, the subsea system being deployed on the seabed and comprising a plurality of support elements (95) which are securely arranged in or on respective hydrocarbon wells, wherein the subsea system (10) further comprises a subsea load transfer system (11) according to any one of claims 1-14 for transfer and distribution of external loads acting on the subsea system (10) to the plurality of subsea support elements (95).

17. The subsea system according to 16, wherein the subsea system further comprises a protective housing structure (92) for protection of well heads and other equipment comprised in the subsea system (10) from external loads.

18. The subsea system according to claim 16, wherein the housing structure (92) is connected to the at least one housing support element (42, 64) of the modular frames (12).

19. The subsea system according to one of the claims 16-18, wherein subsea system (10) further comprises a plurality of load deflecting elements (90) for at least partial deflection of external loads.

20. The subsea system according to claim 19, wherein the load deflecting elements (90) are adapted for connection to the first joint element (27) of the modular frames (12) of the subsea load transfer system (11) .

21. The subsea system according to one of the claims 16-20, wherein each of the plurality of the support elements (95) is a conductor casing or a surface casing or another casing element.