GB2419627A

GB2419627A - Variable volume sub-sea storage facility

Info

Publication number: GB2419627A
Application number: GB0423943A
Authority: GB
Inventors: David Bone
Original assignee: Tamacrest Ltd
Current assignee: Tamacrest Ltd
Priority date: 2004-10-28
Filing date: 2004-10-28
Publication date: 2006-05-03
Anticipated expiration: 2024-10-28
Also published as: GB2419627B; GB0423943D0

Abstract

A sub-sea storage facility has a foundation structure 1, a cover support device 2, and a cover 3. A fluid pipeline 4 is routed through holes in the foundation structure 1 and the cover support device 2, into the cover 3, such that the cover 3 can be raised by fluid pressure from the fluid pipeline 4. The cover 3 is fitted with watertight seals 6. Vertical motion of the cover 3 can be limited by metal stops 7. The storage facility may also be used in conjunction with a wind or current turbine to store LNG, hydrogen, or fresh water. The sliding cover allows the volume of the storage facility to be varied to eliminate the need for voids in the storage space.

Description

SUB-SEA STORAGE FACILITY

This invention relates to sub-sea storage structures for the offshore oil and gas industry.

Currently the sub-sea storage of hydrocarbon fluids is achieved by using containment structures wherein the space not occupied by the hydrocarbon fluid is occupied either by water or by air. The consequence of these storage methods is that in the former case either a mobile (or flexible) physical barrier is required to separate the hydrocarbon fluid from the water, or alternatively that a certain amount of mixing of the fluids is allowed to occur and that the contaminated fluid is subsequently cleaned resulting in a requirement for complex and expensive fluid separation and processing equipment. In the latter case where air is present, a much greater mass is required to counteract the buoyant upthrust of the air resulting in more expensive storage facilities.

We have now devised a sub-sea storage facility, which alleviates the above problems.

According to the present invention there is provided a sub-sea storage facility comprising a support structure, and a slidably mounted or expandable or inflatable cover, the support structure consisting of a foundation structure or a cover support device mounted on and connected to or moulded to a foundation structure, the cover having integrated seals attached thereto so as to form a watertight connection between the support structure and said cover, said support structure also providing access holes for fluid pipes into the side of and out of the top of said support structure, said cover being arranged so as to fit closely to the outside of the cover support device or to the foundation structure, and said cover being capable of vertical sliding motion, said vertical sliding motion being limited by stop mechanisms located on the outside of the cover support device or by restrictors attached to the cover.

The cover can be constructed in steel, glass fibre, concrete or any combination of these or other suitable materials, and can be insulated to restrict heat loss.

The vertical sliding motion of the cover can be facilitated by the upward force of fluid pressure caused by the ingress of fluid into the cover through said fluid pipes located in the support structure, and can be aided by hydraulic mechanisms or by buoyancy devices or both.

In an alternative embodiment the cover consists of bellows that are attached below and support a cover lid. The bellows are mounted on and connected to the foundation structure and are designed to expand as fluid is pumped into the cover thereby raising the cover lid. In this case the bellows also act as integrated watertight seals, and can assist to restrict the limit of upward motion of the cover.

The cover support device is preferably in the form of a circular hollow steel or concrete shell closed at the top with bottom end open, but can be shaped in a square, rectangular or polygonal bisected open ended hollow shell form.

Preferably the foundation structure forms a continuous layer of support material underneath the cover support device, and can extend beyond the perimeter of the cover support device in order to provide additional stability. The foundation structure can have steel or concrete flanges protruding around the outside bottom perimeter of the cover support device.

Alternatively, the foundation structure may take the form of an annulus upon which the cover support device is mounted and connected or moulded.

Preferably the support structure maintains its position on the seabed due to the large mass of concrete and or steel from which it is fabricated, being well in excess of the buoyancy and environmental forces acting on it.

Alternatively the support structure can be held in position by piles or anchors driven through holes in the steel or concrete flanges, thus securing the structure to the seabed.

Preferably the stop mechanism is one or more metal bars attached to the outside of the structure near the top, in order to engage the cover near its bottom and stop its upward motion.

Alternatively, restrictors can be used to limit the upward motion of the cover and can be in the form of chains, rods, or wires attached to the cover.

In another embodiment the storage facility can be very large, typically 30,000m"3, and can be used to store LNG far offshore in water depths of typically lOOm. This is convenient for large LNG carrier ships to load up from or to if necessary. Transfer of the LNG can be achieved using a large flexible pipe suitably equipped with valves, insulation, etc connected between the storage facility and the ship. In this embodiment a special coimector is built into the side of the cover for attachment of the LNG pipe.

In the embodiment related to the storage of LNG the ambient water pressure outside the storage facility is transferred directly to the stored fluid thus assisting in keeping the fluid, which would otherwise boil off, in its liquid phase. Any remaining boil-off gaseous fluid can be re-liquefied and returned to storage or used to power associated facilities. In this case the cover is extensively insulated in order to reduce the costs of maintaining the fluid in liquid phase. Furthermore, the energy available in the surrounding seawater can be utilised to assist in the regassification of the LNG for subsequent export from the storage facility to consumers. Alternatively, export can be achieved in the liquid phase by the use of an insulated fluid loading system to export LNG tankers. In addition to the cost benefits from using hydrostatic head to help maintain the fluid in a liquid state, the storage of a volatile liquid under water and remote from the land has considerable safety benefits.

A further use of the storage facility can be to provide buffer storage for gas in a gaseous phase. In this case the increased pressure applied by the cover increases the stored mass.

The storage facility with stored LNG can be used in conjunction with a wind or current turbine attached to a floating or fixed support structure. This allows the wind or current turbine to provide electrical output for operation of pumps and associated equipment necessary to maintain the LNG in its liquid state at approximately minus 163 degrees centigrade. The water depth will further aid the process of maintaining the temperature of the LNG due to the hydrostatic pressure encountered at this depth.

Excess electrical power generated by the wind or current turbine can be transferred to a grid system.

When used in association with a wind or current turbine the system as a whole can be used to create and store hydrogen. In this embodiment hydrogen is created by electrolysis or other suitable means using electricity produced by the turbine. The electrolysis equipment can he housed within the hull of the floating or fixed unit and the produced gas can be stored in either a liquid or gaseous phase inside the storage facility.

An alternative use of the storage facility when used in conjunction with an offshore wind or current turbine is the storage of fresh water, generated either by distillation or reverse osmosis or any other suitable means using electricity generated by the turbine, with the necessary equipment being located in the support structure hull.

A specific embodiment of the invention will now be described by way of example only and with reference to the accompanying drawings in which: Figure 1 shows a sub-sea storage facility with the cover raised during storage of oil or gas.

Figure 2 shows a sub-sea storage facility used in conjunction with a wind turbine to store LNG.

Referring to Figure 1, there is shown a sub-sea storage facility consisting of a foundation structure 1, a cover support device 2, and a cover 3, with fluid stored inside the cover 3. A fluid pipeline 4 is routed through holes in the foundation structure I and the cover support device 2, into the cover 3. The cover 3 is raised by fluid pressure from the fluid pipeline 4.

A valve 5 is provided on the pipeline 4 to control the fluid flow into the cover 3. A watertight seal 6 is provided between the cover 3 and the cover support device 2. The vertical motion of the cover 3 is limited by metal stops 7.

Figure 2 shows a sub-sea storage facility used with a floating wind tower 8 and a wind turbine 9. The cover 3 is filled with LNG that can be piped to a ship via a connecting pipe (not shown). The LNG is maintained in liquid state using electrical output supplied by the wind turbine 9 to operate cooling process equipment (not shown).

Claims

I. A sub-sea storage facility comprising a support structure, and a slidably mounted or expandable or inflatable cover, the support structure consisting of a foundation structure or a cover support device mounted on and connected to or moulded to a foundation structure, the cover having integrated seals attached thereto so as to form a watertight connection between the support structure and said cover, said support structure also providing access holes for fluid pipes into the side of and out of the top of said support structure, said cover being arranged so as to fit closely to the outside of the cover support device or to the foundation structure, and said cover being capable of vertical sliding motion, said vertical sliding motion being limited by stop mechanisms located on the outside of the cover support device or by restrictors attached to the cover.
2. A sub-sea storage facility as claimed in Claim 1, wherein the cover can be constructed in steel, glass fibre, concrete or any combination of these, and can be insulated to restrict heat loss.
3. A sub-sea storage facility as claimed in any preceding claim, wherein the vertical sliding motion of the cover can be facilitated by the upward force of fluid pressure caused by the ingress of fluid into the cover through said fluid pipes located in the support structure, and can be aided by hydraulic mechanisms or by buoyancy devices or both.
4. A sub-sea storage facility as claimed in any preceding claim, wherein the cover consists of bellows that are attached below and support a cover lid, the bellows being mounted on : ** and connected to the foundation structure and designed to expand as fluid is pumped into the cover thereby raising the cover lid, said bellows also act as integrated watertight seals, * SS*** and can assist to restrict the limit of upward motion of the cover. **..
5. A sub-sea storage facility as claimed in any of claims I to 3, wherein the cover support device is preferably in the form of a circular hollow steel or concrete shell closed at the top with bottom end open, but can be shaped in a square, rectangular or polygonal bisected open ended hollow shell form.
6. A sub-sea storage facility as claimed in any preceding claim, wherein the foundation . .: structure forms a continuous layer of support material underneath the cover support device, and can extend beyond the perimeter of the cover support device in order to provide additional stability.
7. A sub-sea storage facility as claimed in any preceding claim, wherein the foundation structure can have steel or concrete flanges protruding around the outside bottom perimeter of the cover support device.
8. A sub-sea storage facility as claimed in any preceding claim, wherein the foundation structure can take the form of an annulus upon which the cover support device is mounted and connected or moulded.
9. A sub-sea storage facility as claimed in any preceding claim, wherein the support structure maintains its position on the seabed due to the large mass of concrete and or steel from which it is fabricated, being well in excess of the buoyancy and environmental forces acting on it.
10. A sub-sea storage facility as claimed in any of claims I to 8, wherein the support structure can he held in position by piles or anchors driven through holes in the steel or concrete flanges, thus securing the structure to the seabed.
11. A sub-sea storage facility as claimed in any preceding claim excluding Claim 4, wherein the stop mechanism is one or more metal bars attached to the outside of the structure near the top, in order to engage the cover near its bottom and stop its upward motion.
12. A sub-sea storage facility as claimed in any preceding claim, wherein restrictors can be used to limit the upward motion of the cover and can be in the form of chains, rods, or wires attached to the cover.
13. A sub-sea storage facility as claimed in any preceding claim, wherein the storage facility can be very large, typically 30,000mA3, and can be used to store LNG far offshore in water depths convenient for large LNG carrier ships to load up from or to if necessary.
14. A sub-sea storage facility as claimed in Claim 13, wherein transfer of the LNG can be achieved using a large flexible pipe suitably equipped with valves, insulation, etc connected between the storage facility and the ship, a special connector being built into the side of the cover for attachment of the LNG pipe.
15. A sub-sea storage facility as claimed in Claim 13 or 14, wherein the ambient water pressure outside the storage facility is transferred directly to the stored fluid thus assisting in keeping the fluid, which would otherwise boil off, in its liquid phase. * * S *

*
16. A sub-sea storage facility as claimed in any of claims 13 to 15, wherein any boil-off *::* gaseous fluid can be re-liquefied and returned to storage or used to power associated facilities. S...

S
17. A sub-sea storage facility as claimed in any of claims 13 to 16, wherein the cover is * * * extensively insulated.

*....:
18. A sub-sea storage facility as claimed in any of claims 13 to 17, wherein the energy available in the surrounding seawater can be utilised to assist in the regassification of the LNG for subsequent export from the storage facility to consumers.
19. A sub-sea storage facility as claimed in any of claims 13 to 16, wherein export can be achieved in the liquid phase by the use of an insulated fluid loading system to export LNG tankers.
20. A sub-sea storage facility as claimed in any of claims 13 to 19, wherein the storage facility with stored LNG can be used in conjunction with a wind or current turbine attached to a floating or fixed support structure.
21. A sub-sea storage facility as claimed in Claim 20, wherein the wind or current turbine provides electrical output for operation of pumps and associated equipment necessary to maintain the LNG in its liquid state at approximately minus 163 degrees centigrade.
22. A sub-sea storage facility as claimed in Claim 20 or 21, wherein excess electrical power generated by the wind or current turbine can be transferred to a grid system.
23. A sub-sea storage facility as claimed in any of claims 1 to 12, wherein the storage facility is used in conjunction with a wind or current turbine attached to a floating or fixed support structure, and can be used to create and store hydrogen.
24. A sub-sea storage facility as claimed in Claim 23, wherein hydrogen is created by electrolysis or other suitable means using electricity produced by the turbine.
25. A sub-sea storage facility as claimed in Claim 22 or 23, wherein electrolysis equipment can be housed within the hull of the floating or fixed support structure, and the produced gas can be stored in either a liquid or gaseous phase inside the storage facility.
26. A sub-sea storage facility as claimed in any of claims I to 12, wherein the storage facility is used in conjunction with a wind or current turbine attached to a floating or fixed support structure, and can be used for the storage of fresh water.
27. A sub-sea storage facility as claimed in Claim 26, wherein fresh water is generated either by distillation or reverse osmosis or any other suitable means using electricity generated by the turbine, with the necessary equipment being located in the support structure hull.
28. A sub-sea storage facility as claimed in any of claims ito 12, wherein the storage facility can be used to provide buffer storage for gas in a gaseous phase, and the increased pressure applied by the cover increases the stored mass.
29. A reusable offshore multifunctional monitoring system substantially as herein described : ** and illustrated in the accompanying drawings. S.. * S.

S IS.. I...

S S...

*SSI.. * I

S

S..... * S

S 0 * * S 55