The present invention relates to a platform arrangement for offshore energy exploitation, in particular for oil and gas exploitation. The platform arrangement may also be used for other offshore energy exploitation, such as wind energy, solar energy, etcetera. The arrangement comprises an elongated structure comprising a base portion and a top portion. The base portion is adapted to be anchored in the seabed of the sea so that the elongated structure extends away from the seabed towards the surface of the sea. The top portion is adapted to hold process equipment for said exploitation. The arrangement comprises further a plurality of pipes for the operation of said exploitation extending from the base portion to the top portion of the structure.

Prior art

Prior art marine oil platforms generally comprises a structure of minimum three legs solidly anchored in the seabed. These platforms provide a stable structure for withstanding harsh marine conditions of wind, currents, waves, etcetera, such as the conditions in the North Sea. While providing a rigid structure, the prior art platforms are costly to produce. In regards to energy exploitation, such as oil and gas exploitation, the platforms are generally maintained at the locations of energy exploitation, such at the locations of the oil and gas fields, both during establishing and exploitation. Accordingly, exploitation using prior art platforms can only be economical motivated for sufficiently large fields of stored energy, such as sufficiently large oil and gas fields.

A further problem with prior art platforms is that a large number of pipes for various functions in the establishment and exploitation are extending from the platform down to the seabed to the respective well opening or well opening to be established. These pipes are, likewise to the structure of the platform, subjected to interaction from the environment, such as from wind, currents, waves, etcetera, and must therefore be dimensioned to withstand such interaction with appropriate safety margin. Furthermore, as the pipes may be of significant length , the interaction may set the pipes in oscillation, which can result in fatigue of the pipes. Under unfavourable conditions, the oscillations may be at a resonance frequency of the pipes, which can result in a catastrophic rupture of one or more of the pipes. Accordingly, the pipes must be dimensioned to withstand such conditions and in regards to fatigue alternatively be exchanged at predetermined time interval during the exploitation. US4704051 discloses an offshore platform structure comprising a plurality of vertical columns accommodating well conductors.

Summary of the invention

The invention has for its object to remedy or to reduce at least one of the drawbacks of the prior art, or at least provide a useful alternative to prior art. In particular, a first object of the invention is to provide a simplified and cost effective platform arrangement for energy exploitation, such as oil and gas exploitation. A second object of the invention is to reduce the dimensioning of the plurality of pipes for the operation of the exploitation.

These objects are achieved by means of a platform arrangement according to claim 1 . The platform arrangement comprises an elongated structure comprising a base portion and a top portion, wherein the base portion is adapted to be anchored in the seabed of the sea so that the elongated structure extends away from the seabed towards the surface of the sea, wherein the top portion is adapted to hold process equipment for said exploitation, and a plurality of pipes for the operation of said exploitation extending from the base portion to the top portion of the structure. The platform arrangement is characterized in that the structure comprises an outer casing and an inner casing arranged so that an outer space is formed between the outer casing and the inner casing, wherein the plurality of pipes are arranged so that they extend in said outer space from the base portion to the top portion of the structure.

By means of the outer space formed by the outer and the inner casing, the plurality of pipes are guided protected in the outer space between the base portion and the top portion of the structure. Thereby, the interaction with from wind, currents, waves, etcetera, on the pipes is reduced. Accordingly, the dimensioning of the pipes in view of interaction, fatigue and resonance oscillation can be reduced compared with prior art platform arrangements. Accordingly, the cost of the platform arrangement can be reduced.

According to an embodiment of the invention, the inner casing is forming an inner space that at least partly is adapted to be controllable be filled with air and water. The inner space is used for controlling the stability of the structure. By means of the inner space, the centre of mass can be displaced towards the base portion. Thereby, the stability of the structure is improved and the dimensioning of anchoring arrangement of the structure can be reduced. In order to accommodate the plurality of pipes in the outer space, the structure needs to be of considerable size and the structure may be subjected to significant interaction from the environment, such as from wind, currents, waves, etcetera. Accordingly, the structure may be set in oscillations that under unfavourable condition may correspond to a resonance frequency of the structure. By means of controllable regulating the water in the inner space, the resonance frequency of the structure can be adjusted so that the amplitude of the oscillations does not exceed certain level. According to an embodiment of the invention, the platform arrangement comprises means for controllable introducing and removing water to/from the inner space. The means are for example pumps, valves, etcetera. Preferably, the means comprises a control system for regulating the amount of water contained with the inner space. By means of controllable introducing and removing water to the inner space, the process of installing and de-installing of the structure is facilitated.

According to an embodiment of the invention, the inner space comprises a lower chamber adapted to be filled with water for stability of the structure.

According to an embodiment of the invention, the inner space comprises a lower chamber adapted to be controllable filled with air and water, and an upper chamber adapted to be mainly be free from water and adapted to hold the process equipment for said exploitation, wherein the lower chamber is arranged closer the base portion than the upper chamber. By means of arranging the lower chamber to be controllable filled and removed from water, the process of installing the structure is facilitated in that the lower chamber will be forced towards the seabed. According the lower part of the structure will natural be directed towards the seabed.

According to an embodiment of the invention, the upper chamber comprises a sealing arrangement for preventing water to be introduced into the upper chamber.

According to an embodiment of the invention, the upper chamber is arranged above the surface of the sea.

According to an embodiment of the invention, the outer casing is arranged so that the plurality of pipes are fully protected along the length of the structure from interaction with the surrounding outside the structure.

According to an embodiment of the invention, the outer casing and the inner casing form a closed space for the plurality of pipes excluding possible openings in the base portion and the top portion of the structure.

According to an embodiment of the invention, the outer space is extending towards a well opening or a well opening to be formed by a drilling operation, and wherein at least one pipe of said plurality of pipes is a guide pipe extending towards the well opening or well opening to be formed and is adapted to guide a drilling operation and/or a well intervention.

According to an embodiment of the invention, the platform arrangement is configured for exploitation at at least a first well opening and a second well opening located spaced apart from each other in the seabed, wherein the platform arrangement comprises a first bundle of pipes for exploitation at the first well opening and a second bundle of pipes for exploitation at the second well opening, and wherein the structure is dimensioned so that the outer space reaches the first well opening and the second well opening, and at least a first guide pipe of said first bundle of pipes is extending towards the first well opening and at least a second guide pipe of said second bundle of pipes is extending towards the second well opening.

According to an embodiment of the invention, the outer space is arranged to accommodate pipes for up to 12 separate well openings. Accordingly, the outer casing and inner casing are dimensioned so the outer space extends between the well openings.

According to an embodiment of the invention, the outer casing comprises a first tubing and the inner casing comprises a second tubing.

According to an embodiment of the invention, the first tubing and second tubing are circular tubes comprising circular cross sections.

According to an embodiment of the invention, the first tubing and second tubing are concentric arranged.

According to an embodiment of the invention, the platform arrangement is configured for exploitation at a plurality of wells openings located spaced apart from each other in the seabed, and the platform arrangement comprises a respective bundle of pipes for each well opening, wherein the bundles of pipes are equidistance spaced apart in the outer space.

According to an embodiment of the invention, the base portion of the structure comprises one or more openings for one or more of said plurality of pipes.

According to an embodiment of the invention, the structure comprises a single unit or a single interconnection of units that extends from the base portion in the seabed towards the surface of the sea.

According to an embodiment of the invention, the structure extends from the from the base portion in the seabed towards and above the surface of the sea.

According to an embodiment of the invention, the platform arrangement comprises a platform for holding the process equipment for said exploitation, which platform is arranged above the surface of the sea.

According to an embodiment of the invention, the structure is adapted to be anchored at a well opening or a well opening to be formed by a drilling operation in the seabed, wherein the platform arrangement comprises a primary anchoring arrangement connected to the structure. Preferably, the anchors are suction anchors and the structure is anchored by means of a suction anchor at the base portion.

According to an embodiment of the invention, the primary anchoring arrangement comprises a first set of three or more guy-wire arrangements comprising a respective first anchor and a respective first guy-wire connected between the first anchors and the structure. Preferably, the primary anchoring arrangement comprises four guy-wire arrangements.

According to an embodiment of the invention, the platform arrangement comprises a first damper arrangement at connections between the first guy-wires of the primary anchoring arrangement and the structure, wherein the first damper arrangement comprising one or more remotely controllable first damper devices.

According to an embodiment of the invention, the first anchors are suction anchors and the structure is anchored by means of a suction anchor at the base portion.

According to an embodiment of the invention, the platform arrangement comprises a secondary anchoring arrangement connected to the structure.

According to an embodiment of the invention, the secondary anchoring arrangement comprises a second set of three or more guy-wire arrangements comprising a respective second anchor and a respective second guy-wire connected between the anchors and the structure. Preferably, the secondary anchoring arrangement comprises four guy-wire arrangements.

According to an embodiment of the invention, the platform arrangement comprises a second damper arrangement at connections between the respective second guy-wires of the secondary anchoring arrangement and the structure, wherein the second damper arrangement comprising one or more remotely controllable second damper devices.

According to an embodiment of the invention, the primary anchoring arrangement is arranged so that a connection between the first guy-wires of the primary anchoring arrangement and the structure are arranged at a respective first angle, and a connection between the second guy-wires of the secondary anchoring arrangement and the structure are arranged at a respective second angle, wherein said second angle is larger than the first angle. Accordingly, the primary anchoring arrangement outside the secondary anchoring arrangement.

According to an embodiment of the invention, the second anchors are suction anchors.

According to an embodiment of the invention, the platform arrangement comprises a fixture comprising a plurality of support beams arranged between the anchors and the base portion of the structure.

According to an embodiment of the invention, the fixture comprises a third damper arrangement comprising one or more remotely controllable third damper devices provided in connection between at least one of the beams and the structure.

According to an embodiment of the invention, the platform arrangement comprises a control unit adapted to receive information on the position of the structure and control at least one the one or more of the first damper devices, second damper devices and third damper devices in dependency of said information.

The present invention also relates to an offshore platform arrangement in general other than for the purpose of energy exploitation, such as for use in regards to surveillance, and etcetera. The general platform arrangement comprises above mentioned features excluding the process equipment and the plurality of pipes for the operation of oil and gas exploitation. It shall also be understood that this offshore platform arrangement for general use may comprises the structure in different configuration, such as without the outer spacing comprising only the inner spacing, as a solid structure comprising no outer or inner spacing, and etcetera.

Brief description of drawings

In the following is described examples of preferred embodiments illustrated in the accompanying drawings, wherein :

Fig. 1 discloses an overview of a platform arrangement with an elongated structure according to an embodiment of the invention ;

Fig. 2 discloses the platform arrangement in fig. 1 with cutaway view of the elongated structure;

Fig. 3 discloses an overview of a platform arrangement with an elongated structure according to a further embodiment of the invention ;

Fig. 4 discloses the platform arrangement in fig. 3 with cutaway view of the elongated structure;

Fig. 5 discloses a cross section of the elongated structure according to an embodiment of the invention;

Fig. 6 discloses a side view of a base portion of the elongated structure in fig. 5.

Detail description of the invention

With reference to fig 1 and 2, an overview of a platform arrangement 1 for offshore oil and gas exploitation according to an embodiment of the invention is disclosed. The platform arrangement 1 is in particular suitable for water depth from 40-120 m. The platform arrangement 1 comprises an elongated structure 3 and an anchoring arrangement 4.

The elongated structure 3 comprises a base portion 5 and a top portion 7. The base portion 5 is anchored in the seabed of the sea so that a part of the base portion 5 is embedded in the seabed and another part of base portion 5 is above the seabed in the sea. The structure 3 is anchored in the seabed so that the structure 3 extends from the seabed towards and above the surface of the sea. The structure 3 is adapted to be anchored at a well opening 9 or a well opening 9 to be formed by a drilling operation in the seabed.

The platform arrangement 1 further comprises a platform 10 and a plurality of pipes 12. The platform 10 is adapted to hold process equipment 1 1 for said exploitation. The plurality of pipes 12 extend from the base portion 5 to the top portion 7 of the structure 3. The plurality of pipes 12 is adapted to conduct various flowable material, such as liquids or gases for the exploitation. The flowable material may also be a mixture of different phases, such as a slurry of liquid and solids, a mixture of liquid and gas, and etcetera.

At least one of the pipes 12 is adapted to be directly connected to the well opening 9 to enable a drilling operation or a well intervention. For reason of simplicity, a single well opening 9 is indicated in fig. 1 and 2. However, as will be explain in the following, preferably, the platform arrangement 1 is configured for oil and gas exploitation from a plurality of well openings 9, 9a, 9b.

The structure 3 is maintained at the desired position and extension from the seabed by means of the anchoring arrangement 4 that is connected to the structure 3. The anchoring arrangement 4 comprises three or more guy-wire arrangements 22 each comprising an anchor 24 and a guy-wire 26 connected between the anchor 24 and the structure 3. In the disclosed embodiment, the anchoring arrangement 4 comprises four guy-wire arrangements 22 arranged around the structure 3. Furthermore, the structure 3 is anchored in the seabed by means of an anchor 24 at the base portion 5 of the structure 3. The anchors 24 of guy-wire arrangements 22 and the structure 3 are preferably suction anchors.

The anchoring arrangement 4 further comprises a fixture 30 comprising a plurality of support beams 32 arranged between the anchors 24 and the base portion 5 of the structure 3. The fixture 30 further comprises a damper arrangement 40 comprising one or more remotely controllable damper devices 42 provided in connection between at least one of the beams 32 and the structure 3, and a control unit 44 adapted to receive information on the position of the structure 3 and control the one or more damper devices 42 in dependency of said information. In the disclosed embodiment, each of the beams 32 of the fixture 30 is provided with the damper device 42.

The platform arrangement 1 further comprises a shock absorber device 45 on an outer surface of the top portion 7 of the structure 3 for preventing damage to the structure 3 in the event of collision with a vessel or similar. The shock absorber device 45 comprises an elastic element, such as a composite of a polymeric material.

Fig. 5 discloses a cross section perpendicular to a longitudinal axis L of the elongated structure 3 in fig. 1 or fig. 3. The structure 3 comprises an outer casing 50 and an inner casing 52 arranged so that an outer space 54 is formed between the outer casing 50 and the inner casing 52, and the inner casing 52 forms an inner space 56.

The plurality of pipes 12 are arranged so that they extend in said outer space 54 from the base portion 5 to the top portion 7 of the structure 3. Thereby, the plurality of pipes 12 are protected from interaction from wind, currents, waves, etcetera. Accordingly, the dimensioning of the plurality of pipes 12 can be reduced compared with prior art platform arrangements and accordingly the cost of the platform arrangement 1 can be reduced.

In the disclosed embodiment, at least one damper cable 55 is connected between the control unit 44 and the damper devices 42. The damper cable 55 is adapted to transfer control signals to the damper devices 42. The damper cable 55 may also be used for powering the damper devices 42. In the disclosed embodiment, the damper cable 55 is extending in the outer space 54 along the structure 3.

The platform arrangement 1 further comprises means for controllable filling the inner space 56 with water. The means comprise for examples, valves, pumps, and etcetera. In the discloses embodiment, the structure 3 is arranged so that the inner space 56 comprises a lower chamber 60 and an upper chamber 62, see fig. 1 and 2.

The lower chamber 60 is connected to the means for controllable filling the inner space 56 with water. Thereby, the resonance frequency of the structure 3 can be adjusted so that the amplitude of oscillations of the structure 3 does not exceed certain level.

The upper camber 62 adapted to be free from water or essentially free from water, and may be used for holding the process equipment 1 1 or part of the processing equipment 1 1 for said exploitation. In the disclosed embodiment, the upper chamber 62 is located above the surface of the sea. However, it shall be understood that the upper chamber 62 at least partly may be located below the surface of the sea.

With reference to fig 3 and 4, an overview of a platform arrangement 1 for offshore oil and gas exploitation according to a further embodiment of the invention is disclosed.

The further embodiment differs from the embodiment in fig. 1 and 2 in that the platform arrangement 1 comprises a primary anchoring arrangement 4 and a secondary anchoring arrangement 4a.

The structure 3 is maintained at the desired position and extension from the seabed by means of the primary anchoring arrangement 4 and the secondary anchoring arrangement 4a that are connected to the structure 3. The primary anchoring arrangement 4 and the secondary anchoring arrangement 4a each comprises three or more guy-wire arrangements 22, 22a each comprising an anchor 24, 24a and a guy-wire 26. 26a connected between the anchor 24, 24a and the structure 3. In the disclosed embodiment, the anchoring arrangements 4, 4a each comprises four guy-wire arrangements 22, 22a arranged around the structure 3. Furthermore, the structure 3 is anchored in the seabed by means of an anchor at the base portion 5 of the structure 3. The anchors 24, 24a of guy-wire arrangements 22, 22a and the structure 3 are preferably suction anchors.

The primary anchoring arrangement 4 and the secondary anchoring arrangement 4a are configured so that connections between the first guy-wires 26 of the primary anchoring arrangement 4 and the structure 3 are arranged at a respective first angle α1 , and connections between the second guy-wires 26a of the secondary anchoring arrangement 4a and the structure 3 are arranged at a respective second angle a2, and wherein the second angle a2 is larger than the first angle a1 . Accordingly, the primary anchoring arrangement 4 is extending and connected to the structure 3 so that the second anchoring arrangement 4a is between the primary anchoring arrangement 4 and the structure 3.

The platform arrangement 1 further comprises a first damper arrangement 40 at connections between the first guy-wires 26 of the primary anchoring arrangement 4 and the structure 3. The first damper arrangement 40 comprising one or more remotely controllable first damper devices 42. By means of the first damper devices 42, the stability of the structure 3 when subjected to streams, waves and wind is improved. This is particular of importance in when the structure 3 is of considerable length, such as 80-120 m or longer.

Correspondingly, the platform arrangement 1 further comprises a second damper arrangement 40a at connections between the second guy-wires 26a of the secondary anchoring arrangement 4a and the structure 3. The second damper arrangement 40a comprising one or more remotely controllable second damper devices 42a. By means of the second damper devices 42a, the stability of the structure 3 when subjected to streams, waves and wind is further improved.

It shall be understood that the platform arrangement 1 may comprise only one of the first damper devices 42 and second damper devices 42a. For example, platform arrangement 1 may be configured only with second damper devices 42a at the secondary anchoring arrangement 4a. The platform arrangement 1 further comprises a fixture 30 comprising a plurality of support beams 32 arranged between the anchors 24 and the base portion 5 of the structure 3. The fixture 30 further comprises a third damper arrangement 40b comprising one or more remotely controllable third damper devices 42b provided in connection between at least one of the beams 32 and the structure 3, and a control unit 44 adapted to receive information on the position of the structure 3 and control the one or more damper devices 42 in dependency of said information. In the disclosed embodiment, each of the beams 32 of the fixture 30 is provided with the damper device 42.

With reference to fig. 5 and 6, the platform arrangement 1 may be configured for exploitation of oil or gas from one or more well openings 9, 9a, 9b. In the disclosed embodiment in fig. 3, the platform arrangement 1 is arranged for exploitation from a first well opening 9a and a second well opening 9b located spaced apart from each other in the seabed. The platform arrangement 1 comprises a first bundle 70a of pipes 12 for exploitation at the first well opening 9a and a second bundle 70b of pipes 12 for exploitation at the second well opening 9b. In the disclosed embodiment, the bundles 70a, 70b of pipes 12 are equidistance spaced apart in the outer space 54. The structure 3 is dimensioned so that the outer space 54 reaches both the first well opening 9a and the second well opening 9b.

In the disclosed embodiment, the outer space 54 accommodates the pipes 12 to the first well opening 9a and the second well opening 9b. Preferably, the structure 3 is arranged so that the outer space 54 extends over up to twelve separate well openings 9.

The first bundle 70a of pipes 12 and second bundle 70b of pipes 12 comprises a respective first guide pipe 72a and second guide pipe 72b that are extending directly towards the respective first well opening 9a and second well opening 9b. The first guide pipe 72a and second guide pipe 72b are adapted to guide a drilling operation and/or a well intervention. The bundles 70a, 70b of pipes 12 further comprises processing tubes 74 for various flowable material as previously mentioned. In fig. 5, four processing tubes 74 are arranged around the respective first guide pipe 72a and second guide pipe 72b. However, it shall be understood that the bundles 70a, 70b are not restricted to any specific number of pipes 12 or constellation of different types of pipes 12.

The base portion 5 of the structure 3 comprises one or more openings 76 for one or more of said plurality of pipes 12. In particular, the opening 76 is adapted to allow one or more of the processing tubes 74 to be guided away from the structure 3 along the seabed. In the disclosed embodiment, the base portion 5 comprises separate openings 76 for the first bundle 70a of pipes 12 and second bundle 70a of pipes 12. However, it shall be understood that a single opening 76 may be used.

The outer casing 50 and inner casing 52 are preferably arranged so that the outer space 54 and the inner space 56 are closed spaces with the exceptions to the opening 76 for the production pipes 74 and at the ends of the structure 3. However, for reason of stability, the outer casing 50 and inner casing 52 may comprises one or more further openings for reducing the subjected force on the structure 3 due to interaction with from wind, currents, waves, etcetera.

In the disclosed embodiment, the outer casing 50 comprises a first circular tubing and the inner casing 52 comprises a second circular tubing. The first tubing and second tubing are concentric arranged. However, it shall be understood that the outer casing 50 and inner casing 52 may be arranged of different shape and form, such as square and rectangular cross section, etcetera.

It should be noted that the above-mentioned embodiments illustrate rather than limit the invention, and that those skilled in the art will be able to design many alternative embodiments without departing from the scope of the appended claims. In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. Use of the verb "comprise" and its conjugations does not exclude the presence of elements or steps other than those stated in a claim. The article "a" or "an" preceding an element does not exclude the presence of a plurality of such ele- merits.

The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.