WO2015082543A1 - Subsea storage system with multiple flexible storage bags and method for filling and εμρτυινg such subsea storage system - Google Patents

Subsea storage system with multiple flexible storage bags and method for filling and εμρτυινg such subsea storage system Download PDF

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Publication number
WO2015082543A1
WO2015082543A1 PCT/EP2014/076411 EP2014076411W WO2015082543A1 WO 2015082543 A1 WO2015082543 A1 WO 2015082543A1 EP 2014076411 W EP2014076411 W EP 2014076411W WO 2015082543 A1 WO2015082543 A1 WO 2015082543A1
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WIPO (PCT)
Prior art keywords
fluid
storage system
storage
subsea
bags
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Application number
PCT/EP2014/076411
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French (fr)
Inventor
Astrid Rusås KRISTOFFERSEN
Freddy PAULSEN
Gudmund Roger TOTLAND
Arild K. Samuelsen
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Kongsberg Oil & Gas Technologies As
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Publication of WO2015082543A1 publication Critical patent/WO2015082543A1/en

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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B65—CONVEYING; PACKING; STORING; HANDLING THIN OR FILAMENTARY MATERIAL
    • B65D—CONTAINERS FOR STORAGE OR TRANSPORT OF ARTICLES OR MATERIALS, e.g. BAGS, BARRELS, BOTTLES, BOXES, CANS, CARTONS, CRATES, DRUMS, JARS, TANKS, HOPPERS, FORWARDING CONTAINERS; ACCESSORIES, CLOSURES, OR FITTINGS THEREFOR; PACKAGING ELEMENTS; PACKAGES
    • B65D88/00—Large containers
    • B65D88/78—Large containers for use in or under water

Definitions

  • the present invention relates to a subsea storage system comprising a closed protection structure with one or more storage units. Especially the present invention relates to a protection structure configured to hold a first fluid wherein the protection structure comprises one or more flexible storage units adapted to store one or more second fluids, wherein the first and second fluids can be different or similar fluids.
  • FPSO Floating Production Storage and Offloading
  • FSU Floating Storage Units
  • FPSO' s and FSU are today often based on rebuild older ships or new customized ships.
  • FSUs are used together with floating platforms or SPAR solutions without oil storage. The oil is then separated at the floating platforms or SPAR, and transferred to the FSU using buoyant pipes to an anchored FSU.
  • FSUs arc generally used where pipeline to shore or platform-located storage is deemed un-economically or too spacious or/and too heavy. From the FSU. the oil will be transported to a shuttle tanker using a load transferring system. The shuttle tanker transports the oil to shore.
  • Such chemicals include corrosion inhibitors, hydrate inhibitors. pH adjusting chemicals, lubricants, stabi l isers, wax inhibitors etc. Some of these chemicals may not be used continuously but are injected prior to or after special occasions such as temporari ly shutdowns. At geographic cites where the weather conditions may interrupt the delivery of supplies of such chemicals the storage capacity must be increased to secure safe operation also during periods of bad weather.
  • EP 1554197B 1 describes a subsea storage unit for storage of oil at the scafloor without introducing the risk of creating an emulsion layer.
  • the protection structure is designed such that the need to design against scafloor pressure is eliminated. This design includes the need for a subsca oil pump for emptying of the oil at shallow water depths.
  • the goal of the present invention is to provide a subsea storage system for storage of oil or chemicals or other fluids normally stored topside, thereby replacing FPSOs/FSU's and release expensive platform deck-space with a cost effective and more environmental friendly solution.
  • the present invention aims at providing a storage system enabling arctic and subsea factory solutions.
  • a further aim is to provide a solution which makes marginal fields and smaller field developments cost effective without adding the risk contaminating the stored fluid by mixing it with another fl uid in the subsea storage unit.
  • a further aim is to provide a storage system which enables a totally unmanned production system.
  • Another aim is to provide a system applicable for securely storing more than one fluid in the same tank without mixing the fluids.
  • the present invention aims at reducing the risk of leakage of contaminants to the environment.
  • the present invention also aims at providing a storage system with reduced risk of explosion and thereby increased safety.
  • a further aim is to provide a storage system applicable as an alternative solution for todays "burn-off strategy for oil produced during extended well testing (EWT).
  • EWT extended well testing
  • the present invention aims at providing a low cost solution of storing fresh water, water injection fluids or other fluids usually stored topside.
  • One or more of these goals are obtained by the storage system according to the present invention.
  • the present invention provides a subsea storage system, wherein said system comprises
  • protection structure providing a first closed volume with at least one first fluid opening connectablc to a first fluid pipeline for fluid communication between the first closed volume and the first fluid pipeline
  • a first fluid pressure management system for managing a first fluid pressure within the protection structure.
  • the two or more of the flexible storage bags are in fluid communication with the same second fluid conduit, thereby the storage system can store the same type of second fl uid in two or more bags and supplying and emptying the second fluid trough the same second fluid conduit.
  • This may be advantages when for instance storing chemicals which may degenerate over time.
  • it is advantages to selectively empty the storage bag with the longest storage time first but there is no need for more than one second fluid conduit and one supply pipeline and one discharge pipeline.
  • the second fluid conduit may comprise valves for selectively controlling the inlet and outlet to and from the flexible storage bags.
  • the two or more of the flexible storage bags are in fluid communication with different second fluid conduits such that the storage system is adapted to store two or more different second fluids.
  • the first fluid pressure management system provides the pressure to empty two or more di fferent second fluids from the flexible storage bags and to their intended place of use.
  • valves installed on the second fluid conduit the flexible storage bags can be fi led and emptied selectively.
  • the first fluid pipeline can be any conduit of any length applicable for supplying and/or removing said first fluid to/from the first closed volume.
  • the storage system comprises two or more flexible storage bags.
  • the two and more bags are in one aspect of the invention separated by partition elements comprising openings for the first fluid.
  • the second fluid conduit is connectable to a second fluid supply pipeline and a second fluid discharge pipeline and the second fluid conduit comprises one or more valves controlling the supply and discharge of the second fluid.
  • the first fluid pressure management system comprises a first fluid pressure means connected to the first fluid pipeline.
  • the first fluid pressure means may comprise a pump and the first fluid management system may further comprise at least one first fl uid control valve arranged on the first fluid pipeline.
  • the first fluid pressure means is an open container arranged such that the first fluid can be supplied to the protection structure by gravity force. In this aspect the open container is open to the top side atmospheric environment and arranged above the seabed to provide gravity force.
  • Subsea storage system may comprise a control system controlling the first fluid pressure means, the one or more valves controlling the supply and discharge of the second fluid, and optionally the at least one first fluid control valve.
  • Subsea storage system comprises in one aspect thereof a leak detection system comprising one or more leak detectors arranged within the closed volume and adapted to detect leakage of the second fluid into the first fluid.
  • the density of the second fluid is less than the density of the first fluid.
  • the density of the second fluid i s similar to the density of the first fluid.
  • the density of the second fluid is above the density of the first fluid. The density referred to here is the density of the fluids within the subsea storage system.
  • the first fluid comprises water and is selected from produced water, scawater or fresh water.
  • the present invention further provides a method for filling and emptying a subsea storage system comprising
  • protection structure providing a first closed volume with at least one first fluid opening connectable to a first fluid pipeline for fluid communication between the first closed volume and the first fluid pipeline.
  • the method comprises filling at least one second fluid into at least one of the flexible storage bags thereby emptying at least part of the first fluid from the closed volume and at least partly emptying at least one of the flexible storage bags of the at least one second fluid by supplying pressurized first fluid to the closed volume.
  • all of the two or more flexible storage bags are fil led and emptied according to the method according to the present invention.
  • one or more valves are arranged on the second fluid conduit and the method comprises controlling the one or more valves such that when supplying pressurized first fluid the emptying of the two or more storage bags is controlled by controlling the one or more valves.
  • the two or more storage bags are filled and emptied selectively.
  • the present invention will be applicable for any type of first fluid, as there are no limitations to the density thereof.
  • the first fluid is protected by one barrier, the protection structure, only, and environmental regulations may require that the first fluid is relatively environmental friendly.
  • the first fluid may be limited to water, such as produced water, fresh water etc.
  • Second fluids include crude oil, stabilized oi l. produced water, oil-water emulsions, fresh water, and chemicals such as hydrate inhibitors corrosion inhibitors, pH adj usting chemicals, l ubricants, stabilisers, wax inhibitors, sand or mud etc.
  • protection structure refers to a closed structure defining an inner storage volume for the first fluid, the bag(s) and second fluid.
  • the protection structure protects the flexible bag( s) arranged therein.
  • the protection structure can be pressurised thereby allowing for the pressure within the protection structure to be above or below the pressure outside the protection structure.
  • the internal pressure may increase with maximum 2 bar preferably maximum 1 bar.
  • the pressure increase may be from 10 to 30 bar.
  • Figure 1 illustrates schematically a storage system according to the present invention connected to a platform and a tanker.
  • Figure 2 illustrates a cross sectional side view- of a third embodiment of the storage system.
  • Figure 3 shows a cross sectional top view of a first embodiment of the storage system.
  • Figure 4 shows a cross sectional top view of a second embodiment of the storage system.
  • Figure 5 il lustrates a cross sectional side view of a fourth embodiment of the storage system.
  • the present invention compared to the prior art disclosed in EP1554197B 1 eliminates the need for a subsea oil pump without adding emulsion layer challenges.
  • the second fluid within the flexible bag is crude oil, such as stabilized crude oi l then this oil can in the present invention be transferred from the bag and to a shuttle tanker or another facility by pumping the first fluid such as water into the closed volume of the storage system . Accordingly the crude oil is not connected to any subsea pump and the pump for increasing the pressure of the first fluid may be arranged topside with easier access for maintenance.
  • a storage system according to the present invention may be applicable for use in connection with marginal fields and smaller field thereby making the developments cost effective without adding the risk contaminating the stored fluid by mixing it with another fluid in the subsea storage unit. This is possible as the stored fluid is separated from the seawater /produced water by the flexible bags. If scawater is used as the first fluid it may in one embodiment of the present invention be possible to allow the first fluid to flow freely into the environment when filling the bag(s) of the storage unit with produced oil.
  • the vessel/tanker employed for emptying the bag( s) may be equipped with a seawater pump and connection means for pumping seawater into the protection structure to empty the flexible bag(s). Limited equipment wi l l in this embodiment be installed in connection with subsea storage.
  • the present subsea storage system will increase the profitability of marginal fields compared to a FSU sol ution.
  • Stabilized oil can be stored subsea and facilitates a leaner system with the possibility to use smal l shuttle tankers for more frequent off- loading.
  • the control of the storing in a storing system according to the present invention can be fully automated and combined with automated well systems.
  • the present invention enables a totally unmanned production system as the FSU can be eliminated, hence reducing CAPEX costs.
  • Remotely controlled well system have previously been described and if such a well system is combined with a storing system according to the present invention equipped with sensor systems for monitoring the storage system then the whole system can be remotely controlled with no personal present subsea nor top side at the location. Risk of explosion is also reduced, hence health and safety is increased.
  • the present invention provides a solution for storing several types of fluids at the scafloor inside the same protection structure without mixing the fluids. It provides a low cost solution by eliminating costly subsea equipment by allowing the control system to be mainly operated by topside equipment ( i.e. pumps, valves).
  • the present invention provides a storage solution subsea at site.
  • the solution can be employed independently of any pipelines from shore and pipeline terminals.
  • Pipelines from shore and pipeline terminals require large investment cost and long term commitments. Thereby the present system allows for independent selection and exchange of supplier of oil product transport services.
  • a subsea storage unit solution can provide a mobile unit for storage of produced oil for extended well testing (EWT), which represents a far more environmental friendly solution than todays "burn-off strategy.
  • EWT extended well testing
  • This invention provides a low cost solution of storing fresh water, water injection fluids or other fluids usually stored topside.
  • the present solution it is possible to store mixable first and second fluids without risking forming mixtures under normal operations.
  • the flexible bags can be used for storing produced water and the closed volume for fresh water.
  • chemicals that would normally react with each other in separate bags or in the closed volume can be adopted to handle any density situation.
  • valves controlling the fluid streams in and out thereof may be arranged within the protection structure for reduced risk of pollution of the environment. A valve at the opening for the first fluid will then only be exposed to the first fluid on the inside as well as the outside.
  • the same first fluid is pressurised to empty di fferent bags with different fluid content.
  • the common system today requires an equal number of pressurisers such as pumps as the number of fluids.
  • pressurisers such as pumps
  • an emulsion layer is formed at the phase transition.
  • changes in pressure may in fiuence the separation of the phases as the phase transition is pressure sensitive.
  • the present invention is a more flexible and robust system than the traditional .
  • the storage system comprises a leak detection system.
  • the sensitivity of the leak detection system can be specifical ly adapted to the fluids stored within the system. Accordingly if crude oil or chemicals are stored in the flexible bags leak detectors that can detect any increased amounts of these substances are arranged within the protection structure.
  • the arrangement of the detectors is similarly adapted to the density of the possible leak compared to the first fluid.
  • Leak detectors may also be arranged at the inlet and outlet of the first fluid respectively and the detection results can be compared to identi fy any increase in any substance stored within the flexible bag(s). This solution is especially applicable where the first fluid is produced water which may comprises fluctuating amounts of chemicals inj ected into the wel l and where these chemicals are stored as the second fluid.
  • each surface wil l normally only be in contact with one of the fluids and the surface material can be selected to handle the specific fluid and need not be compatible w ith both (all) fluids as well as mixtures thereof. This generally allows for use of less expensive materials which could not be used if a mixture of the fluids would be expected to be in contact with the surface. For instance steel in contact with a mixture of oil and water will result in pitting MIC (Microbiological Induced Corrosion).
  • a first fluid is stored in the internal volume of the protection structure.
  • a second fluid is stored in a flexible bag arranged within the protection structure.
  • the subsea storage system may comprise additional flexible bags within the protection structure to store additional fluids.
  • FIG. 1 On the enclosed figure 1 a schematic illustration of the subsea storage system 10 connected via a second fluid pipeline 14 to a vessel 30.
  • the vessel 30 can be a transport vessel or a FSU connectable to a transport vessel .
  • the subsea storage system 1 0 is further connected to a platform 20, which can be any type of platform, floating or placed on the seabed.
  • the platform 20 can also be a FPSO.
  • the platform 20 is connected to the storage unit by first fluid pipelines 22, 24, 26 and by second fluid conduit 1 2. Also visible in this illustration are a first fluid opening 1 9 and a hatch structure 16 on top of the storage unit I f).
  • the details of the interior o f the storage system 1 0 will initial be described with reference to figure 2 illustrating a cross sectional side view of a first embodiment thereof.
  • the storage system comprises a ridged protection structure 2 forming an inner closed volume 7 with an opening 19 connected to a first fluid pipeline comprising a valve 23.
  • Within the protection structure two flexible bags 18, 18 ' are arranged. Each bag is illustrated comprising one inlcl/outlct opening 1 7, 17' respectively.
  • the openings are arranged on a common hatch 16 removable connected to the protective structure 2.
  • the closed volume 7 is partly partitioned by partitioning element 4 with opening 5 for free fluid flow between the sections of the volume 7.
  • the purpose of the partition elements is to control the position of the flexible bags 1 8, 18 ' when they are filled or emptied.
  • the bottom section 6 of the storage system is configured for placement on the seabed and may include anchoring means or caisson means (not shown) for placement on and securing to the sea bed.
  • the stored second fluid is stored in one or more flexible bags 18. 1 8 * . Visible on figure 2 are two flexible bags, but any number of bags may be arranged within the protection structure in this and in any one of the disclosed embodiments of the present invention.
  • the bag is made of a flexible material that is resistant to the first fluid and the stored second fluid. Different second fluids can be stored in different bags. Second fluids include crude oil, stabilized oil.
  • the bag( s) 1 8, 18 ' are located inside a closed protection structure 2.
  • a normally more environmentally friendly first fl uid (ex. fresh/sea water or produced water) is fil led within the protection structure, but outside the bags 18, 18 " .
  • Several units can be placed in connection with each other to bui ld a flexible structure of subsea storage units - not shown here.
  • a hatch 1 6 is attaching the bag(s) to the protection structure 2 at the top of the dome.
  • the hatch is attached to the pipeline used for filling of the second fluid.
  • First fluid such as water
  • First fluid is filled in the volume 7 outside the bag through a riser system 22. 26.
  • a di fferent (or same) riser system 26. 24 the water can be emptied.
  • the water pressure in the storage unit is controlled using level tanks 28 located on the platform and associated with the fill/empty water risers. Utilizing level tanks 28. a control system for the fill/empty of fluids can be established without adding complex subsea products.
  • a control unit 40 is arranged on the platform.
  • the control unit is controlling the opening and closing of the valves 41 , 42, 45 and 46, thereby controll i ng the inlet and outlet of the first and second fluid of the storage system and also controlling a first fluid pressure means such as level tanks 28 or first fluid pumps.
  • a first fluid pressure means such as level tanks 28 or first fluid pumps.
  • valve 23 it is possible to control the first fluid pressure and flow in and out of the volume 7 by the valve 23 combined with a pressure supplying system such as a subsca pump.
  • a pressure supplying system such as a subsca pump.
  • all the equipment can be placed on the sea bed eliminating the need of a connection to a platform or floating production unit.
  • Emptying of the bags is performed through a riser system 14 to a vessel 30 or through the pipeline system 12 back to the topside facility 20.
  • first fluid flows into the protection structure.
  • a pump located on the first fluid side 28 may be applied to increase the flow rate of the first fluid and thereby the flow rate of the second fluid out of the bag.
  • the pump may also be used to provide appropriate pressure increase inside the storage unit to lift the stored fluid to the vessel 30 or alternatively inject the second fluid in a well stream (not shown).
  • the pump can be located topside or subsca, shown topside here.
  • the increase in pressure is designed such that the stored fluid can be elevated to the topside facility, vessel or injected into a higher pressure volume. Pumping of first fluid into the protection structure will continue until the bag(s) is/are emptied as intended or the intended amount of chemical has been supplied.
  • a control system comprising flow metering, pressure sensors and level metering may be included to manage the filling and empty process (not shown here).
  • the supply of first fluid from 28 is solely based on gravity.
  • the first fluid is supplied to the first fluid pipeline 22 or 24 at or above the level of the outlet of the second fluid.
  • the outlet of the line 14 supplying the second fluid to the tanker 30 is at a level below inlet to the 22 and 24 below unit 28. If the second fluid is injected to a stream on the sea floor the opening of the first fluid pipeline should be arranged at a level high enough to provide needed pressure at the seatloor solely by gravity. In one aspect of such a system the valves 41 and 42 may be obsolete. If the first fluid is
  • first fluid When second fluid is supplied to the system the first fluid is pushed up the first fluid line 22 or 24 into the open container and any excess fluid is release to the sea via the overflow.
  • second fluid When the second fluid is emptied from the bag the valve 46 is opened and gravity force supplies the first fluid into the storage. For this operation sufficient first fluid must be supplied to the open container.
  • One protection structure 2 can include several bags.
  • the different bags 18, 18' are connected to the protection structure through a hatch and piping assembly 17, 17 " .
  • Each pipe is attached to each bag.
  • a valve (not shown) is associated with each bag, so that the emptying and filling of the bags can be easily controlled. In case of the need for a subsea valve, this can be located inside the protection structure 2 to ensure that any leakage will be captured, detected and emptied through a leak detection system arranged within the protection structure.
  • a leak recovery system is located inside the protection structure.
  • Leak detection sensors 15 are located on the top of the structure to detect fluid leakage of low density fluid; the density of the second fluid is lower than the density of the first fluid.
  • additional conduits and valves may be included near the top of the protection structure to transfer any leaked fluid out of the protection structure.
  • the tank In case of a leakage, the tank will be emptied through a nozzle 13 located at the upper hatch. The location is outside the bags, but inside the protection structure. The leaked fluid is lead to an appropriate storage tank on a vessel, platform or on shore for further treatment. In case of storing heavy fluids in the bag(s) ( heavier than the first fluid), an appropriate leak sensor will need to be located at the bottom of the protection structure 2 (not shown here). The leaked fluid will need to be emptied through the opening 19 and transported to a vessel, platform or shore for further treatment.
  • Figure 3 illustrates a cross sectional top view of a second embodiment of the storage system 10 according to the present invention.
  • four flexible bags are arranged within a protection structure 2.
  • a first fluid is stored in the closed volume 107 and the four bags 1 8 may contain the same or different fluids.
  • separate inlets and outlets 1 1 7, 1 1 7 " are provided for each bag.
  • FIG 4 illustrates a cross sectional top view of a third embodiment of the storage system 10 according to the present invention.
  • three flexible bags are arranged within a protection structure 2.
  • the bags 21 8. 21 8 * 218" are connected to the protection structure via a hatch 21 6 arranged on the side of the protection structure.
  • Partition elements 204 with openings 205 limit the movement of the bags.
  • a first fluid is stored in the closed volume 207 and one or more second fluids are stored in the bags.
  • the hatch 216 comprises fluid connection means 217, 217' 217 " to each of the respective bags 21 8, 218', 21 8 " .
  • a fourth embodiment of the storage system 10 is disclosed.
  • One flexible bag 3 1 8 is arranged within the protection structure 2.
  • the conduit 3 17 provides fluid communication in and out of the bag.
  • a first fluid is stored in the closed volume 307. Filling and emptying of the first fluid takes place through the opening (inlet/outlet) 3 1 9 arranged on top of the dome.
  • This embodiment of the storage system is particularly applicable for storing heavy second fluids, where the density of the second fluid is larger than the density of the first fluid.

Abstract

Subsea storage system, wherein said system comprises a protection structure (2) providing a first closed volume (7) with at least one first fluid opening (19) connectable to a first fluid pipeline for fluid communication between the first closed volume and the first fluid pipeline, two or more flexible storage bags (18, 18') arranged within the first closed volume and each comprising at least one opening connected to a second fluid conduit (17, 17") for fluid communication between the flexible storage bag and the second fluid conduit wherein the second fluid conduit passes through the protection structure and a first fluid pressure management system for managing a first fluid pressure within the protection structure and a method for filling and emptying thereof.

Description

SUBSEA STORAGE SYSTEM WITH MULTIPLE FLEXIBLE STORAGE BAGS AND METHOD FOR FILLING AND EMPTYING SUCH SUBSEA STORAGE SYSTEM
The present invention relates to a subsea storage system comprising a closed protection structure with one or more storage units. Especially the present invention relates to a protection structure configured to hold a first fluid wherein the protection structure comprises one or more flexible storage units adapted to store one or more second fluids, wherein the first and second fluids can be different or similar fluids.
Background
Storage of oil and chemicals in connection with subsea oil and/or gas wells are today mostly provided on ships. Floating Production Storage and Offloading (FPSO) or Floating Storage Units (FSU). FPSO' s and FSU are today often based on rebuild older ships or new customized ships. FSUs are used together with floating platforms or SPAR solutions without oil storage. The oil is then separated at the floating platforms or SPAR, and transferred to the FSU using buoyant pipes to an anchored FSU. FSUs arc generally used where pipeline to shore or platform-located storage is deemed un-economically or too spacious or/and too heavy. From the FSU. the oil will be transported to a shuttle tanker using a load transferring system. The shuttle tanker transports the oil to shore.
The production related to FSU solutions are restricted by weather-related
shutdowns, especially in regions with rough weather such as the Norwegian sector. The weather related difficulties affects the offshore loadings. By introducing subsea storage of oil injection chemicals, there will be less weather- related shutdowns as the storage unit is not affected by bad weather.
Other concerns are related to guerril la attacks. These attacks will also be less likely, as the storage is outside reach by sea or air born vehicles.
Different chemicals for injection into a well stream or a well arc presently being stored on the platforms or FPSO' s. A number of such chemicals may be present, and all though the amount/volume required of each chemical may not require huge tanks for storage, the total storage volume when considering all the different chemicals may add up to a significant volume.
Examples of such chemicals include corrosion inhibitors, hydrate inhibitors. pH adjusting chemicals, lubricants, stabi l isers, wax inhibitors etc. Some of these chemicals may not be used continuously but are injected prior to or after special occasions such as temporari ly shutdowns. At geographic cites where the weather conditions may interrupt the delivery of supplies of such chemicals the storage capacity must be increased to secure safe operation also during periods of bad weather.
Prior art
Other subsca oil storage tanks have previously been suggested, examples thereof are disclosed in US5.899.637 and US4.662,386. 1 lowever, the existing technology allows for an oil/water interface with the risk of building an emulsion layer.
comprising a mix of chemicals, oily water and wax. Another threat in these existing solutions is bacteria growth (SRB - Sulphur Reducing Bacteria). These bacteria form colonies that sticks to steel -surfaces/hulls and as part of their metabolic process they liberate sulphuric acid that again attacks the surface/hull of the tank. The emulsion layer may increase over time, reducing the oil storage space. To separate the emulsion, the oil/water mixture will need to be pumped to a ship and transported to a process plant. This is a costly process with no added value.
EP 1554197B 1 describes a subsea storage unit for storage of oil at the scafloor without introducing the risk of creating an emulsion layer. The protection structure is designed such that the need to design against scafloor pressure is eliminated. This design includes the need for a subsca oil pump for emptying of the oil at shallow water depths.
Objectives of the inv ention The goal of the present invention is to provide a subsea storage system for storage of oil or chemicals or other fluids normally stored topside, thereby replacing FPSOs/FSU's and release expensive platform deck-space with a cost effective and more environmental friendly solution.
The present invention aims at providing a storage system enabling arctic and subsea factory solutions.
A further aim is to provide a solution which makes marginal fields and smaller field developments cost effective without adding the risk contaminating the stored fluid by mixing it with another fl uid in the subsea storage unit.
It is also a goal to provide a storage system that would increase the profitability of marginal fields compared to a FSU/FPSO solution. A further aim is to provide a storage system which enables a totally unmanned production system.
Another aim is to provide a system applicable for securely storing more than one fluid in the same tank without mixing the fluids. The present invention aims at reducing the risk of leakage of contaminants to the environment.
It is also an objective to provide a solution that is independent of pipelines from shore and pipeline terminals.
The present invention also aims at providing a storage system with reduced risk of explosion and thereby increased safety.
A further aim is to provide a storage system applicable as an alternative solution for todays "burn-off strategy for oil produced during extended well testing (EWT).
Additionally the present invention aims at providing a low cost solution of storing fresh water, water injection fluids or other fluids usually stored topside. One or more of these goals are obtained by the storage system according to the present invention.
The present invention provides a subsea storage system, wherein said system comprises
- a protection structure providing a first closed volume with at least one first fluid opening connectablc to a first fluid pipeline for fluid communication between the first closed volume and the first fluid pipeline,
- two or more flexible storage bags arranged within the first closed volume and each comprising at least one opening connected to a second fluid conduit for fluid communication between the flexible storage bag and the second fluid conduit wherein the second fluid conduit passes through the protection structure, and
- a first fluid pressure management system for managing a first fluid pressure within the protection structure.
In one aspect of the present invention the two or more of the flexible storage bags are in fluid communication with the same second fluid conduit, thereby the storage system can store the same type of second fl uid in two or more bags and supplying and emptying the second fluid trough the same second fluid conduit. This may be advantages when for instance storing chemicals which may degenerate over time. Here it is advantages to selectively empty the storage bag with the longest storage time first but there is no need for more than one second fluid conduit and one supply pipeline and one discharge pipeline. The second fluid conduit may comprise valves for selectively controlling the inlet and outlet to and from the flexible storage bags.
In a further aspect of the present invention the two or more of the flexible storage bags are in fluid communication with different second fluid conduits such that the storage system is adapted to store two or more different second fluids. 1 lcrc the first fluid pressure management system provides the pressure to empty two or more di fferent second fluids from the flexible storage bags and to their intended place of use. By valves installed on the second fluid conduit the flexible storage bags can be fi led and emptied selectively. The first fluid pipeline can be any conduit of any length applicable for supplying and/or removing said first fluid to/from the first closed volume.
In one aspect of the subsea storage system according to the present invention the storage system comprises two or more flexible storage bags. The two and more bags are in one aspect of the invention separated by partition elements comprising openings for the first fluid.
In a further aspect of the subsea storage system, the second fluid conduit is connectable to a second fluid supply pipeline and a second fluid discharge pipeline and the second fluid conduit comprises one or more valves controlling the supply and discharge of the second fluid. In another aspect of the present invention the first fluid pressure management system comprises a first fluid pressure means connected to the first fluid pipeline. The first fluid pressure means may comprise a pump and the first fluid management system may further comprise at least one first fl uid control valve arranged on the first fluid pipeline. In one aspect of the subsea storage system the first fluid pressure means is an open container arranged such that the first fluid can be supplied to the protection structure by gravity force. In this aspect the open container is open to the top side atmospheric environment and arranged above the seabed to provide gravity force.
Subsea storage system according to the present invention may comprise a control system controlling the first fluid pressure means, the one or more valves controlling the supply and discharge of the second fluid, and optionally the at least one first fluid control valve.
Subsea storage system comprises in one aspect thereof a leak detection system comprising one or more leak detectors arranged within the closed volume and adapted to detect leakage of the second fluid into the first fluid. In yet another aspect of the subsca storage system the density of the second fluid is less than the density of the first fluid. In another aspect the density of the second fluid i s similar to the density of the first fluid. In a further aspect the density of the second fluid is above the density of the first fluid. The density referred to here is the density of the fluids within the subsea storage system.
In a further aspect of the subsea storage system the first fluid comprises water and is selected from produced water, scawater or fresh water.
The present invention further provides a method for filling and emptying a subsea storage system comprising
- a protection structure providing a first closed volume with at least one first fluid opening connectable to a first fluid pipeline for fluid communication between the first closed volume and the first fluid pipeline.
- two or more flexible storage bags arranged within the first closed volume and each comprising at least one opening connected to a second fluid conduit for fluid communication between the flexible storage bag and second fluid conduit wherein the second fluid conduit passes through the protection structure,
wherein the method comprises filling at least one second fluid into at least one of the flexible storage bags thereby emptying at least part of the first fluid from the closed volume and at least partly emptying at least one of the flexible storage bags of the at least one second fluid by supplying pressurized first fluid to the closed volume.
In one aspect of the present invention all of the two or more flexible storage bags are fil led and emptied according to the method according to the present invention.
In one aspect of the method one or more valves are arranged on the second fluid conduit and the method comprises controlling the one or more valves such that when supplying pressurized first fluid the emptying of the two or more storage bags is controlled by controlling the one or more valves.
In a further aspect of the method the two or more storage bags are filled and emptied selectively. The present invention will be applicable for any type of first fluid, as there are no limitations to the density thereof. However the first fluid is protected by one barrier, the protection structure, only, and environmental regulations may require that the first fluid is relatively environmental friendly. In this sense the first fluid may be limited to water, such as produced water, fresh water etc. Second fluids include crude oil, stabilized oi l. produced water, oil-water emulsions, fresh water, and chemicals such as hydrate inhibitors corrosion inhibitors, pH adj usting chemicals, l ubricants, stabilisers, wax inhibitors, sand or mud etc. The term "protection structure" as used here in refers to a closed structure defining an inner storage volume for the first fluid, the bag(s) and second fluid. The protection structure protects the flexible bag( s) arranged therein. In a preferred embodiment the protection structure can be pressurised thereby allowing for the pressure within the protection structure to be above or below the pressure outside the protection structure. For large subsea storage systems for storing stabilised oil the internal pressure may increase with maximum 2 bar preferably maximum 1 bar. for smaller subsea storage systems for storing one or more chemicals in separate bag for injection subsea the pressure increase may be from 10 to 30 bar.
Brief description of the drawings
The present invention will be described in further detail with reference to the enclosed figures wherein
Figure 1 illustrates schematically a storage system according to the present invention connected to a platform and a tanker.
Figure 2 illustrates a cross sectional side view- of a third embodiment of the storage system.
Figure 3 shows a cross sectional top view of a first embodiment of the storage system. Figure 4 shows a cross sectional top view of a second embodiment of the storage system.
Figure 5 il lustrates a cross sectional side view of a fourth embodiment of the storage system.
Principal description of the inv ention
The present invention compared to the prior art disclosed in EP1554197B 1 eliminates the need for a subsea oil pump without adding emulsion layer challenges. If the second fluid within the flexible bag is crude oil, such as stabilized crude oi l then this oil can in the present invention be transferred from the bag and to a shuttle tanker or another facility by pumping the first fluid such as water into the closed volume of the storage system . Accordingly the crude oil is not connected to any subsea pump and the pump for increasing the pressure of the first fluid may be arranged topside with easier access for maintenance. A storage system according to the present invention may be applicable for use in connection with marginal fields and smaller field thereby making the developments cost effective without adding the risk contaminating the stored fluid by mixing it with another fluid in the subsea storage unit. This is possible as the stored fluid is separated from the seawater /produced water by the flexible bags. If scawater is used as the first fluid it may in one embodiment of the present invention be possible to allow the first fluid to flow freely into the environment when filling the bag(s) of the storage unit with produced oil. The vessel/tanker employed for emptying the bag( s) may be equipped with a seawater pump and connection means for pumping seawater into the protection structure to empty the flexible bag(s). Limited equipment wi l l in this embodiment be installed in connection with subsea storage.
The present subsea storage system will increase the profitability of marginal fields compared to a FSU sol ution. Stabilized oil can be stored subsea and facilitates a leaner system with the possibility to use smal l shuttle tankers for more frequent off- loading.
The control of the storing in a storing system according to the present invention can be fully automated and combined with automated well systems. The present invention enables a totally unmanned production system as the FSU can be eliminated, hence reducing CAPEX costs. Remotely controlled well system have previously been described and if such a well system is combined with a storing system according to the present invention equipped with sensor systems for monitoring the storage system then the whole system can be remotely controlled with no personal present subsea nor top side at the location. Risk of explosion is also reduced, hence health and safety is increased. The present invention provides a solution for storing several types of fluids at the scafloor inside the same protection structure without mixing the fluids. It provides a low cost solution by eliminating costly subsea equipment by allowing the control system to be mainly operated by topside equipment ( i.e. pumps, valves).
The present invention provides a storage solution subsea at site. The solution can be employed independently of any pipelines from shore and pipeline terminals.
Pipelines from shore and pipeline terminals require large investment cost and long term commitments. Thereby the present system allows for independent selection and exchange of supplier of oil product transport services.
A subsea storage unit solution can provide a mobile unit for storage of produced oil for extended well testing (EWT), which represents a far more environmental friendly solution than todays "burn-off strategy.
This invention provides a low cost solution of storing fresh water, water injection fluids or other fluids usually stored topside. In the present solution it is possible to store mixable first and second fluids without risking forming mixtures under normal operations. For instance the flexible bags can be used for storing produced water and the closed volume for fresh water. It is also possible to store chemicals that would normally react with each other in separate bags or in the closed volume. The solution according to the present invention does not require a signi ficant density difference between the stored fluids but can be adopted to handle any density situation.
In one aspect o f the present invention valves controlling the fluid streams in and out thereof may be arranged within the protection structure for reduced risk of pollution of the environment. A valve at the opening for the first fluid will then only be exposed to the first fluid on the inside as well as the outside.
In a further aspect of the invention the same first fluid is pressurised to empty di fferent bags with different fluid content. The common system today requires an equal number of pressurisers such as pumps as the number of fluids. In a traditional gravity based storage wherein oil is stored on top o f the water and separated by the phase transition between the oil and the water an emulsion layer is formed at the phase transition. In this traditional storage system changes in pressure may in fiuence the separation of the phases as the phase transition is pressure sensitive. This is a further limitation of the traditional system overcome by the present invention where the fluids are separated by the flexible bag also in situations where the pressure in the system would otherwise course increased mixing of the fluids.
Sudden changes in pressure during on- or off-loading of the fluid and current occurring at the same time are in the traditional system likely to result in increased mixing of the phases and thereby increased growth of the emulsion layer, which is undesirable. In the system according to the present invention rapid pressure changes or increased fluid current does not have any negative effect on the stored fluids as the fluids are kept separated by the flexible bag.
Additional ly, in the traditional system, temperature differences between the oil and water phases will result in thermic convection current which again would result in increased mixing and formation of emulsion. Flow patterns introduced in the tank during filling and discharging the tank, may also introduce mixing of the fluids in a traditional system. In the present invention any temperature di fference wil l not result in any mixing due to the separation, and no flow condition will introduce mixing.
Accordingly the present invention is a more flexible and robust system than the traditional . In one embodiment of the present invention the storage system comprises a leak detection system. The sensitivity of the leak detection system can be specifical ly adapted to the fluids stored within the system. Accordingly if crude oil or chemicals are stored in the flexible bags leak detectors that can detect any increased amounts of these substances are arranged within the protection structure. The arrangement of the detectors is similarly adapted to the density of the possible leak compared to the first fluid. Leak detectors may also be arranged at the inlet and outlet of the first fluid respectively and the detection results can be compared to identi fy any increase in any substance stored within the flexible bag(s). This solution is especially applicable where the first fluid is produced water which may comprises fluctuating amounts of chemicals inj ected into the wel l and where these chemicals are stored as the second fluid.
The selection of construction materials for a system according to the present invention is made based on the substances with which the materials will be in contact. Due to the separation of the fluids each surface wil l normally only be in contact with one of the fluids and the surface material can be selected to handle the specific fluid and need not be compatible w ith both (all) fluids as well as mixtures thereof. This generally allows for use of less expensive materials which could not be used if a mixture of the fluids would be expected to be in contact with the surface. For instance steel in contact with a mixture of oil and water will result in pitting MIC (Microbiological Induced Corrosion). Another example is acidic produced water, which could be stored as a second fluid within a flexible bag adapted to tolerate acidic solutions which if stored in a concrete protection structure could result in degeneration of the concrete. The present invention can be used for subsea storage of oil. chemicals, water injection fluid or other fl uids from the production system or fluids needed for the residential areas in addition to storage of sand and mud remaining from a drilling operation. A first fluid is stored in the internal volume of the protection structure. A second fluid is stored in a flexible bag arranged within the protection structure. The subsea storage system may comprise additional flexible bags within the protection structure to store additional fluids.
On the enclosed figure 1 a schematic illustration of the subsea storage system 10 connected via a second fluid pipeline 14 to a vessel 30. The vessel 30 can be a transport vessel or a FSU connectable to a transport vessel . The subsea storage system 1 0 is further connected to a platform 20, which can be any type of platform, floating or placed on the seabed. The platform 20 can also be a FPSO. The platform 20 is connected to the storage unit by first fluid pipelines 22, 24, 26 and by second fluid conduit 1 2. Also visible in this illustration are a first fluid opening 1 9 and a hatch structure 16 on top of the storage unit I f). The details of the interior o f the storage system 1 0 will initial be described with reference to figure 2 illustrating a cross sectional side view of a first embodiment thereof. The storage system comprises a ridged protection structure 2 forming an inner closed volume 7 with an opening 19 connected to a first fluid pipeline comprising a valve 23. Within the protection structure two flexible bags 18, 18 ' are arranged. Each bag is illustrated comprising one inlcl/outlct opening 1 7, 17' respectively. In this embodiment the openings are arranged on a common hatch 16 removable connected to the protective structure 2. In this embodiment the closed volume 7 is partly partitioned by partitioning element 4 with opening 5 for free fluid flow between the sections of the volume 7. The purpose of the partition elements is to control the position of the flexible bags 1 8, 18 ' when they are filled or emptied. The bottom section 6 of the storage system is configured for placement on the seabed and may include anchoring means or caisson means (not shown) for placement on and securing to the sea bed. The stored second fluid is stored in one or more flexible bags 18. 1 8* . Visible on figure 2 are two flexible bags, but any number of bags may be arranged within the protection structure in this and in any one of the disclosed embodiments of the present invention. The bag is made of a flexible material that is resistant to the first fluid and the stored second fluid. Different second fluids can be stored in different bags. Second fluids include crude oil, stabilized oil. produced water, oil -water emulsions, fresh water, and chemicals such as hydrate inhibitors. The bag( s) 1 8, 18 ' are located inside a closed protection structure 2. A normally more environmentally friendly first fl uid (ex. fresh/sea water or produced water) is fil led within the protection structure, but outside the bags 18, 18" . Several units can be placed in connection with each other to bui ld a flexible structure of subsea storage units - not shown here.
Referring to figure 1 and 2 combined, a hatch 1 6 is attaching the bag(s) to the protection structure 2 at the top of the dome. The hatch is attached to the pipeline used for filling of the second fluid. First fluid, such as water, is filled in the volume 7 outside the bag through a riser system 22. 26. Through a di fferent (or same) riser system 26. 24, the water can be emptied. The water pressure in the storage unit is controlled using level tanks 28 located on the platform and associated with the fill/empty water risers. Utilizing level tanks 28. a control system for the fill/empty of fluids can be established without adding complex subsea products. On figure 1 a control unit 40 is arranged on the platform. The control unit is controlling the opening and closing of the valves 41 , 42, 45 and 46, thereby controll i ng the inlet and outlet of the first and second fluid of the storage system and also controlling a first fluid pressure means such as level tanks 28 or first fluid pumps. When filling one or more flexible bags with the second fluid valve 45 is open and valve 46 closed. At least one of the valves 41 and 42 are also open allowing a part of the first fluid to leave the protection structure and enter the level tank 28. The first fluid is pushed up to the level of the plat form by the pressure provided by the flexible bag(s) increasing in size. To empty the second fluid into the vessel 30 valve 45 is closed and valve 46 opened. Pressure is supplied to the first fluid by a first fluid pressure unit in connection with the level tank 28 and the first fluid is forced into the protection structure via open valve 41 and line 22 or valve 42 and line 24.
Alternatively it is possible to control the first fluid pressure and flow in and out of the volume 7 by the valve 23 combined with a pressure supplying system such as a subsca pump. In such an embodiment all the equipment can be placed on the sea bed eliminating the need of a connection to a platform or floating production unit.
Emptying of the bags is performed through a riser system 14 to a vessel 30 or through the pipeline system 12 back to the topside facility 20. During the emptying of a bag, first fluid flows into the protection structure. A pump located on the first fluid side 28 may be applied to increase the flow rate of the first fluid and thereby the flow rate of the second fluid out of the bag. The pump may also be used to provide appropriate pressure increase inside the storage unit to lift the stored fluid to the vessel 30 or alternatively inject the second fluid in a well stream (not shown). The pump can be located topside or subsca, shown topside here. By pumping the first fluid into the structure, pressure increases inside the protection structure 2. The increase in pressure is designed such that the stored fluid can be elevated to the topside facility, vessel or injected into a higher pressure volume. Pumping of first fluid into the protection structure will continue until the bag(s) is/are emptied as intended or the intended amount of chemical has been supplied. A control system comprising flow metering, pressure sensors and level metering may be included to manage the filling and empty process (not shown here).
In an alternative embodiment the supply of first fluid from 28 is solely based on gravity. The first fluid is supplied to the first fluid pipeline 22 or 24 at or above the level of the outlet of the second fluid. In the embodiment illustrated on figure 1 the outlet of the line 14 supplying the second fluid to the tanker 30 is at a level below inlet to the 22 and 24 below unit 28. If the second fluid is injected to a stream on the sea floor the opening of the first fluid pipeline should be arranged at a level high enough to provide needed pressure at the seatloor solely by gravity. In one aspect of such a system the valves 41 and 42 may be obsolete. If the first fluid is
environmental friendly such as seawater than 28 can be an open container with an overflow to sea. When second fluid is supplied to the system the first fluid is pushed up the first fluid line 22 or 24 into the open container and any excess fluid is release to the sea via the overflow. When the second fluid is emptied from the bag the valve 46 is opened and gravity force supplies the first fluid into the storage. For this operation sufficient first fluid must be supplied to the open container.
One protection structure 2 can include several bags. The different bags 18, 18' are connected to the protection structure through a hatch and piping assembly 17, 17" . Each pipe is attached to each bag. A valve (not shown) is associated with each bag, so that the emptying and filling of the bags can be easily controlled. In case of the need for a subsea valve, this can be located inside the protection structure 2 to ensure that any leakage will be captured, detected and emptied through a leak detection system arranged within the protection structure.
A leak recovery system is located inside the protection structure. Leak detection sensors 15 are located on the top of the structure to detect fluid leakage of low density fluid; the density of the second fluid is lower than the density of the first fluid. As disclosed in the prior art, additional conduits and valves may be included near the top of the protection structure to transfer any leaked fluid out of the protection structure.
In case of a leakage, the tank will be emptied through a nozzle 13 located at the upper hatch. The location is outside the bags, but inside the protection structure. The leaked fluid is lead to an appropriate storage tank on a vessel, platform or on shore for further treatment. In case of storing heavy fluids in the bag(s) ( heavier than the first fluid), an appropriate leak sensor will need to be located at the bottom of the protection structure 2 (not shown here). The leaked fluid will need to be emptied through the opening 19 and transported to a vessel, platform or shore for further treatment.
Figure 3 illustrates a cross sectional top view of a second embodiment of the storage system 10 according to the present invention. In this embodiment four flexible bags are arranged within a protection structure 2. A first fluid is stored in the closed volume 107 and the four bags 1 8 may contain the same or different fluids. In this embodiment separate inlets and outlets 1 1 7, 1 1 7" are provided for each bag.
Figure 4 illustrates a cross sectional top view of a third embodiment of the storage system 10 according to the present invention. In this embodiment three flexible bags are arranged within a protection structure 2. In this embodiment the bags 21 8. 21 8* 218" are connected to the protection structure via a hatch 21 6 arranged on the side of the protection structure. Partition elements 204 with openings 205 limit the movement of the bags. A first fluid is stored in the closed volume 207 and one or more second fluids are stored in the bags. The hatch 216 comprises fluid connection means 217, 217' 217" to each of the respective bags 21 8, 218', 21 8". On figure 5 a fourth embodiment of the storage system 10 is disclosed. One flexible bag 3 1 8 is arranged within the protection structure 2. The conduit 3 17 provides fluid communication in and out of the bag. A first fluid is stored in the closed volume 307. Filling and emptying of the first fluid takes place through the opening (inlet/outlet) 3 1 9 arranged on top of the dome. This embodiment of the storage system is particularly applicable for storing heavy second fluids, where the density of the second fluid is larger than the density of the first fluid.

Claims

1 . Subsea storage system, wherein said system comprises
- a protection structure providing a first closed volume with at least one first fluid opening conncctable to a first fluid pipeline for fluid communication between the first closed volume and the first fluid pipeline.
- two or more flexible storage bags arranged within the first closed volume and each comprising at least one opening connected to a second fluid conduit for fluid communication between the flexible storage bag and the second fluid conduit wherein the second fluid conduit passes through the protection structure, and
- a first fluid pressure management system for managing a first fluid pressure within the protection structure.
2. Subsea storage system according to claim 1, wherein two or more of the flexible storage bags are in fluid communication with the same second fluid conduit.
3. Subsea storage system according to claim 1 or 2. wherein two or more of the flexible storage bags are in fluid communication with different second fluid conduits such that the storage system is adapted to store two or more different second fluids.
4. Subsea storage system according to any one of the claims 1 to 3. wherein the two and more bags are separated by partition elements comprising openings for the first fluid.
5. Subsea storage system according to any one of the claims 1 to 4, wherein the one or more second fluid conduits are each connectable to a second fluid supply pipeline and a second fluid discharge pipeline and the one or more second fluid conduits each comprise one or more valves controlling the supply and discharge of the one or more second fluids.
6. Subsea storage system according to any one of the claims 1 -5, wherein the first fluid pressure management system comprises a first fluid pressure means connected to the first fluid pipeline.
7. Subsea storage system according to claim 6, wherein the first fluid pressure means comprises a pump and the first fluid management system further comprises at least one first fluid control valve arranged on the first fluid pipeline.
8. Subsca storage system according to claim 6, wherein the first fluid pressure means is an open container arranged such that the first fluid can be supplied to the protection structure by gravity force.
9. Subsea storage system according to any one of the claims 6, 7 or 8, wherein the system comprises a control system controlling the first fluid pressure means, the one or more valves controlling the supply and discharge of the one or more second fluids, and optionally the at least one first fluid control valve.
10. Subsca storage system according to any one of the previous claims, wherein the system comprises a leak detection system comprising one or more leak detectors arranged within the closed volume and adapted to detect leakage of one or more of the one or more second fluids into the first fluid.
1 1 . Subsca storage system according to any one of the previous claims, wherein the density of the second fluid is less than or similar to or above the density of the first fluid.
12. Subsca storage system according to any one of the previous claims, wherein the first fluid comprises water and is selected from produced water, seawatcr and fresh water.
13. Method for filling and emptying a subsca storage system comprising
- a protection structure providing a first closed volume with at least one first fluid opening connectable to a first fluid pipeline for fluid communication between the first closed volume and the first fluid pipeline,
- two or more flexible storage bags arranged within the first closed volume and each comprising at least one opening connected to a second fluid conduit for fluid communication between the flexible storage bag and second fluid conduit wherein the second fluid conduit passes through the protection structure,
wherein the method comprises fil ling at least one second fluid into at least one of the flexible storage bags thereby emptying at least part of the first fluid from the closed volume and at least partly emptying at least one of the flexible storage bags of the at least one second fluid by supplying
pressurized first fluid to the closed volume.
14. Method according to claim 13. wherein one or more valves are arranged on the second fluid conduit and the method comprises controlling the one or more valves such that the when supplying pressurized first fluid the emptying of the two or more storage bags is control led by controlling the one or more valves.
5. Method according to claim 14, wherein the two or more storage bags are filled and emptied selectively.
PCT/EP2014/076411 2013-12-03 2014-12-03 Subsea storage system with multiple flexible storage bags and method for filling and εμρτυινg such subsea storage system WO2015082543A1 (en)

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