WO2017171646A1

WO2017171646A1 - Offshore storage facility

Info

Publication number: WO2017171646A1
Application number: PCT/SG2017/050169
Authority: WO
Inventors: Brian Chang
Original assignee: Blue Capital Pte. Ltd.
Priority date: 2016-03-30
Filing date: 2017-03-29
Publication date: 2017-10-05

Abstract

The present invention relates to an offshore storage facility comprising a structure having a chamber operable to store two or more fluids immiscible with one another; and a cover adapted to float on a topmost fluid when in use, wherein the cover is shaped and operable to funnel the topmost fluid out from the chamber.

Description

OFFSHORE STORAGE FACILITY

FIELD OF THE INVENTION

The present invention relates to a storage facility for storing matter (e.g. solids, liquids and gases). In particular, the present invention relates to an offshore storage facility for storing hydrocarbons.

BACKGROUND TO THE INVENTION

Storing crude oil after production in an offshore environment is typically a time- consuming, risky, complex and costly affair. The difficulties in the storage process and/or operation is further exacerbated by the unpredictable environmental conditions, giving rise to additional operational and safety concerns. Floating facilities such as Floating Storage and Offloading vessels (FSOs) are prominently used worldwide for oil storage during production. While FSOs are widely used as a reliable solution for storing crude oil in offshore fields, they are associated with several issues which include but are not limited to:

• The design and construction of an FSO is complex, costly and a time- consuming affair.

• FSOs use expensive and complex mooring system to maintain its position under varying environmental conditions.

• The tanks of FSOs to store oil are complex.

• FSOs being a manned facilities, involve heavy maintenance costs and high operating expenses.

• FSOs are exposed to high fatigue rates because they are not specifically built for frequent loading and unloading of oil which results in frequently changing bending moments and shear force.

• Unequal loading of the tanks in FSOs exposes the structures of FSOs to unequal hydraulic pressure, thereby exacerbating the fatigue experienced by FSOs. • Unpredictable environmental loads further aggravate the problem and increases the likelihood of high fatigue and associated failure.

Other than FSOs, subsea storage facilities are also used to store crude oil in offshore fields. Examples of such facilities include the MOPUstor tank and the Subsea Storage Tank of Atkins Engineering. Generally, they are installable on the sea-bed and due to developments in the design of such facilities, they can be built, installed and operated successfully. In the installed condition, they are completely submerged in the water. However, such subsea storage facilities also have some significant limitations which include but are not limited to:

• They have a very complex design, especially due to the high pressure differential acting on the structure near the sea-bed.

• Such complexities lead to a time-consuming construction process and high cost.

• Installation of such facilities requires construction vessels and involves huge cost.

• Such facilities have not only high design and construction cost but also high maintenance cost.

• Usually such facilities require piling to provide the additional grounding support to the facility, where such piling can create fatigue problems.

• The decommissioning process of such facilities is complex and expensive.

• Such facilities are difficult to inspect and repair because of the subsea environment.

US Patent No. 3791 152 discloses an offshore storage tank adapted to be ballasted to rest on the sea floor and to hold a liquid which aids the ballasting of the tank and prevents the collapse of the tank during storm conditions of crude oil. The tank includes a floating roof which is displaceable vertically to a limited extent with the rise and fall of liquid in the tank. However, the water and oil in the tank are mixed at their interface such that there is a risk that the oil-water mixture may leak out to sea during the operation of the tank. Moreover, the construction of the tank is complicated and time-consuming due to the use of horizontal rings to form the tank walls. There is a risk of oil leakage if the interface between adjacent horizontal rings becomes damaged. It would be appreciated that any oil leakage will have catastrophic effect on the environment and marine life.

US Patent No. 3,869,388 and WO 02/42182 A1 disclose storage tanks that utilize a liquid layer with a specific chemical composition that can separate oil and water, where said liquid layer is not miscible in oil and water. The use of a liquid layer however is disadvantageous because agitation of the components of such storage tanks may disrupt the liquid layer and cause it to break apart, for example during the loading of oil into the tanks. Disruption of the liquid layer can reduce its effectiveness as a separator of the oil and water and such disruption may ultimately cause the loss of the entire liquid layer. Therefore, the liquid layer may need constant maintenance such as topping up of liquid into the liquid layer. In addition, there is a risk that such liquid layer may leak out into the surrounding sea water and affect the environment and marine life.

Therefore, there exists a need for a better solution to ameliorate the aforementioned problems.

SUMMARY OF THE INVENTION

The present invention seeks to address and/or ameliorate the problems in the prior art by providing a solution for storing matter in an offshore facility, which may be adapted for use with gas, liquid or solid. In particular, the offshore facility is suitable for storage of hydrocarbons such as crude oil.

The offshore facility of the present invention is robust, easy to fabricate and install, safe and economical to build and operate. It is also easy to relocate and has a longer operational life with less maintenance because the structure of the offshore storage facility of the present invention experiences minimal fatigue rates. Further, the offshore facility is easier to mobilize and operate as compared to other existing offshore storage facilities. It can be operated unmanned. Hence, its affordability and safety are drastically improved. This offshore storage and offloading facility can be a good alternative to Floating Storage Systems such as FSO, particularly in shallow water depth in the range of 10 m to 70 m since it has a self-installing mechanism without the requirement of heavy construction vessel.

In accordance with a first aspect of the present invention, there is an offshore storage facility comprising a structure having a chamber operable to store two or more fluids immiscible with one another; and a cover adapted to float on a topmost fluid when in use, wherein the cover is shaped and operable to funnel the topmost fluid out from the chamber.

Preferably, the cover is movable along an internal surface of the structure. Preferably, the cover is convex with an apex extending away from a base of the structure.

Preferably, the cover comprises a first outlet arranged substantially at the apex for channelling the topmost fluid out from the chamber. More preferably, the first outlet is operable to connect to a conduit movable with the cover.

Preferably, the cover comprises a first inlet for channelling the topmost fluid into the chamber.

Preferably, the cover comprises a specific gravity of less than about 0.85. More preferably, the cover is rigid.

Preferably, the facility further comprises a venting system operable to vent vapours out and away from the chamber.

Preferably, the facility further comprising a solid separator operable to separate the two or more fluids, wherein the separator is movable along the internal surface of the structure.

Preferably, the separator comprises a specific gravity in between that of the two or more fluids. More preferably, the separator comprises a specific gravity of about 0.90 to about 0.99.

Preferably, the separator is arranged at an interface of the two or more fluids in the chamber.

Preferably, the separator is impermeable to the two or more fluids.

Preferably, the structure comprises an inner wall and an outer wall, the inner and outer walls configured to define at least one compartment therebetween, wherein the compartment is adapted to receive at least one ballast. Preferably, the structure comprises a second inlet for channelling a bottommost fluid into the chamber and a second outlet for channelling the bottommost fluid away from the chamber.

Preferably, the two or more fluids comprise water and a hydrocarbon, wherein the hydrocarbon is the topmost fluid.

Preferably, the facility further comprises at least one berthing stanchion arranged on an outer surface of the structure. More preferably, the facility comprises two sets of at least one berthing stanchion, wherein the two sets are arranged opposite one other on the outer surface of the structure. Even more preferably, the berthing stanchion comprises one or more access points for personnel to access the offshore storage facility.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

Figure 1 provides a perspective view of an embodiment of an offshore storage facility of the present invention.

Figure 2 provides a cross-sectional side view of an embodiment of an offshore storage facility of the present invention.

Figure 3 provides a top down view of an embodiment of an offshore storage facility of the present invention.

Figure 4 provides a perspective view of another embodiment of an offshore storage facility of the present invention.

Figure 5 provides a cross-sectional side view of another embodiment of an offshore storage facility of the present invention.

Figure 6 provides a top down view of another embodiment of an offshore storage facility of the present invention.

Figure 7 provides a close up cross-sectional view of a portion of the separator of an embodiment of an offshore storage facility of the present invention. Figure 8 provides a close up cross-sectional of a portion of a cover of an embodiment of an offshore storage facility of the present invention.

Figures 9a to 9e provide the stages of installing an offshore storage facility of the present invention.

DEFINITIONS

Throughout the specification, unless the context requires otherwise, the word "comprise" or variations such as "comprises" or "comprising, will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers.

Furthermore, throughout the specification, unless the context requires otherwise, the word "include" or variations such as "includes" or "including" will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers.

The terms "vertical" and "horizontal" used throughout the specification will have ordinary meaning in the art and will be understood by a skilled person to refer to the orientation of an object or structure with respect to the vector direction of gravity. For example, Figure 2 shows that the offshore storage facility is substantially vertical.

The terms "top" and "bottom" used throughout the specification will have ordinary meaning in the art and will be understood by a skilled person to refer to how far an article is placed with respect to a ground level, for example, an article is located at the bottom if it is closer to a ground level compared to an article located at the top. For the avoidance of doubt, Figure 2 shows the crude oil being located on top of the sea water.

The term "fluid" used throughout the specification will be understood to include liquids and gases. Further, the term "water" used throughout the specification includes but is not limited to lake water and sea water.

The term "hydrocarbon" refers to processed or unprocessed organic compounds which include but are not limited to petroleum, crude oil, natural gases and bitumen.

The term "specific gravity" used throughout the specification will have ordinary meaning in the art and will be understood by a skilled person to refer to the ratio of the density of a substance to the density of water at 4°C. "Specific gravity" is also known as and can be used synonymously with the terms "relative density" and "relevant density".

DESCRIPTION OF EMBODIMENTS OF THE INVENTION

Particular embodiments of the present invention will now be described with reference to the accompanying drawings. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of the present invention. Other definitions for selected terms used herein may be found within the detailed description of the invention and apply throughout the description. Additionally, unless defined otherwise, all technical and scientific terms used herein have the same meanings as commonly understood by one or ordinary skill in the art to which this invention belongs. Where possible, the same reference numerals are used throughout the figures for clarity and consistency.

Offshore Storage Facility

The present invention is an offshore storage facility designed with specific dimensions and structural configuration such that the facility can bear all the environmental loads safely and stay stationed at the same location even under the extreme weather conditions. The offshore storage facility is suitable for shallow water offshore sites with a water depth in the range of 10 m to 70 m.

In accordance with an embodiment of the invention as shown in Figures 1 to 3, there is an offshore storage facility 100 comprising a cylindrical structure 1 10 that can be installed on a lake-bed or sea-bed 180 and can be partially submerged in water 190 when in operation. The sea bed 180 may be a natural or man-made surface depending on application. The cylindrical structure 1 10 has a height that extends above a water level 191 at a site where the structure 1 10 is to be submerged. The cylindrical structure 1 10 comprises an inner wall (hull) 1 1 and an outer wall (hull) 1 12, and a base 1 13. The inner wall 1 1 1 defines a chamber 1 14 for storing at least two fluids immiscible in one another, for example water 160 and hydrocarbon 150. As the specific gravity of the hydrocarbon 150 is lower than the specific gravity of water 160, the hydrocarbon 150 floats on top of the water 160. The hydrocarbon 150 is preferably the topmost fluid while the water 160 is preferably the bottommost fluid in the chamber 1 14. The shape of the structure 1 10 is defined by the outer wall 12. Depending on the application, the structure 110 may have different shapes, for example the structure 110 may be a cuboidal structure. The shape of the inner wall 1 11 may be different from the shape of the outer wall 1 12. The inner wall 1 1 1 and outer wall 112 define at least one compartment 1 15 therebetween for receiving a ballast, for example water or concrete. The compartment 1 15 may be single continuous compartment that extends around the circumference of the structure 10. The compartment 115 is used to store ballast needed during installation of the structure 1 10 and to provide additional downward weight to the facility 100 towards the seabed 180. The double hull structure also provides double protection to the environment such that hydrocarbon will not be spilt out to water 190 in the case of a breach of the outer hull 1 12. The structure 1 10 comprises water inlet 1 16 (second inlet) and water outlet 1 17 (second outlet) arranged substantially at a base portion of the structure 110, near the base 1 13. The water 160 in the chamber 1 14 is in fluid communication with the surrounding sea water 190 via inlet 116 and outlet 1 17. Water can enter into the chamber 1 14 via inlet 116 and exit the chamber 114 via outlet 117. It is also possible for water to enter the chamber 1 14 via the outlet 1 17 and exit the chamber 1 14 via the inlet 116. The structure 1 10 may comprise more than one inlet 116 and outlet 117. In various embodiments, the structure 1 10 comprises a combined inlet and outlet, where water from the chamber 1 14 enters and exits the chamber 1 4 from the same inlet/outlet.

The structure 1 10 comprises mechanisms to supply and remove the ballast to and from the compartment 1 16. The walls 11 1 , 112 may be stiffened to increase the rigidity of the structure 1 10. Depending on the application, the structure 1 10 may comprise only one hull (wall), for example in shallow waters where the hydrostatic pressure of the surrounding water 190 may not be as great as that of open seas.

The base 1 13 is a solid ballast (e.g. metal, concrete or compositions thereof) that anchors or aids in the anchorage of the facility 100 on sea bed 180. The base 1 13 can comprise a hollow core adapted to be filled with ballast during the installation of the facility 100 at a desired location. The walls 111 , 1 12 and the base 1 13 may form a unitary structure 1 10, or may be attached to one another via suitable attachments known in the art, for example via welding and rivets. The base 1 13 can comprise a skirt that extends downwards and penetrates into the seabed 180 as the structure 1 10 is submerged to rest thereon. The skirt holds the structure 1 10 firmly in position and prevents/reduces movement of the structure 1 10 along the surface of seabed 180.

The structure 1 10 comprises a deck 140 at a top portion above the water surface 191 . The deck 140 is arranged about the periphery of the structure 110. The deck 140 can be a continuous deck, or a discontinuous deck as shown in the figures. The deck 140 may be integral with the structure 1 10 or may be removable from the structure 1 10 for ease of installation of the facility 100. The deck 140 is installed with offloading equipment/mechanisms such as pumps 142 for the pumping of the hydrocarbon 150 to and from the chamber 1 14. These systems can be remotely operated and/or monitored, and hence the storage facility 100 may be unmanned.

The structure 1 10 comprises a separator 120 (diaphragm) is designed to be partially immersed in the water 160 and partially in the hydrocarbon 150, and to stay afloat at or near the interface between hydrocarbon 150 and water 160. The separator 120 is movable relative to the interface of the water 160 and the hydrocarbon 150 in the chamber 1 14 and to the walls 11 1 , 1 12 of the storage facility 100. Preferably, the separator 120 is arranged to maintain a consistent position at the interface of the water and the oil in the chamber. More preferably, the separator 120 is displaceable and moves together with an interface of the water 160 and the hydrocarbon 50, i.e. the separator 120 will rise and fall with the rise and fall of said interface (e.g. through the loading and/or offloading of the hydrocarbon 150). The separator 120 moves along vertical guides/tracks on the internal surface of the inner wall 11 1 , via roller or skidding systems. Figure 7 shows another embodiment of the present invention where the separator 220 moves along one or more vertical guides 236b on the internal surface of the structure 210. The separator 220 is attachable to the guides 236b via rollers 237b. The separator 120 preferably comprises a specific gravity in between that of the water 160 and the hydrocarbon 150. More preferably, the separator 120 comprises a specific gravity of about 0.90 to about 0.99. With a specific gravity between that of the water 160 and the hydrocarbon 150, the net downward weight (i.e. towards the lake- bed or sea-bed 180) of the separator 120 is more than the buoyancy force exerted by the hydrocarbon 150 but less than the buoyancy force exerted by the water 160. In other words, as a lower portion of separator 120 is immersed in water 160, this lower portion of the separator 120 will experience a buoyancy force (B1 ) since it displaces a specific volume of water 160. Similarly, an upper portion of separator 120 immersed in the hydrocarbon 150 will also experience a buoyancy force (B2) since the upper portion displaces a specific volume of hydrocarbon 150. Therefore the total weight (W) of the separator 120 would be equal or substantially equal to the combination of the two buoyancy forces i.e. B1 + B2. This allows the separator 120 to maintain its equilibrium position at the interface of the hydrocarbon 150 and the water 160. Therefore when the amount/volume of the hydrocarbon 150 and/or water 160 changes due to for example, the loading/unloading of the hydrocarbon 150, the buoyancy forces acting on the separator 120 changes. The separator 120 accordingly moves along with the interface of the hydrocarbon 150 and the water 160, in response to the changes in the buoyancy forces acting on it. The separator 120 is preferably a physical and solid separator, which is advantageous because the separator 120 would not contaminate the hydrocarbon 150 or water 160 when the facility 100 is in use. The separator 120 may be rigid or flexible depending on the application. Preferably, the separator 120 is planar, and impermeable to the water 160 and hydrocarbon 150. The thickness of the separator 120, i.e. the distance from the surface of the separator 120 in contact with the water 160 to the surface of the separator 120 in contact with the hydrocarbon 150, will depend on the application. The separator 120 may be formed from metals (e.g. aluminium, steel, etc.), metallic alloys, polymers and compositions thereof. The separator separates, preferably completely separates, the hydrocarbon 150 and water 160, and hence maintains the purity of the hydrocarbon 150, which can be directly used as a fuel without any further processing. The separator 120 preferably ensures that the hydrocarbon 150 remains completely separated from water 160. Further, the hydrocarbon-water separation through the separator 120 ensures environmental safety by preventing leakage of the hydrocarbon 150 to the surrounding water 190 when the facility 100 is in use. As the hydrocarbon 150 is pumped (i.e. loaded) into the chamber 1 14, the separator 120 moves down towards the base 1 13 to a limiting point, which prevents the hydrocarbon 150 from leaking out to the surrounding water 190 via outlet 117. When the hydrocarbon 150 is offloaded from the chamber 114, the separator 120 moves up to a particular vertical location near the top portion of the structure 1 10.

The structure 110 comprises a cover 130 (diaphragm) arranged to float on a top surface of the hydrocarbon 150 when the facility 100 is in use. The cover 130 is displaceable/movable relative to a level of the hydrocarbon 150 in the chamber 1 14 and to the walls 1 11 , 1 12 of the storage facility 100. Preferably, the cover 130 is adapted to maintain a consistent position relative to the level of the hydrocarbon 150 in the chamber 1 14. More preferably, the cover 130 moves together with a top surface level of the hydrocarbon 150, i.e. the cover 130 will rise and fall with the rise and fall of said top surface level of the hydrocarbon 150 (e.g. through the loading and/or offloading of the hydrocarbon 150). The cover 130 moves along vertical guides/tracks on the internal surface of the inner wall 1 11 , via roller or skidding systems. Figure 8 shows another embodiment of the present invention where the cover 230 moves along one or more vertical guides 236a on the internal surface of the structure 210. The cover 230 is attachable to the guides 236a via rollers 237a. The cover guides 236a may be the same and/or integral with the separator guides 236b. In other embodiments, the cover guides 236b are different from the separator guides 236b, particularly if there is a lower vertical limit to which the cover 230 can descend within the structure 210. Depending on the application, the vertical movement of the cover 130 may be restricted to a particular specific portion in the structure 110, i.e. the cover 130 may not move along the entire vertical distance (i.e. height) of the structure. The cover 130 preferably comprises a specific gravity less than the hydrocarbon 150. More preferably, the cover 130 comprises a specific gravity of less than about 0.85. With a specific gravity less than that of the hydrocarbon 150, the net downward weight (i.e. towards the lake-bed or sea-bed 180) of the cover 130 is less than the buoyancy force exerted by the hydrocarbon 150. The hydrocarbon 150 accordingly exerts a buoyancy force on a bottom surface of the cover 130 that keeps the cover 130 afloat. In various embodiments where the specific gravity of the cover 130 may be more than that of the hydrocarbon 150, the cover 130 displaces a sufficient amount/volume of the hydrocarbon 150, which creates a buoyancy force more than the downward weight of the cover 130. The structure 1 10 comprises cross-beams 118 that restrict the cover

130 from moving beyond a topmost vertical position in the structure 1 10. The crossbeams 1 18 can also be used for access to various portions of the cover 130 for the purposes of for example maintenance. Depending on the application and requirements, the offshore storage facility 100 may not include a separator 120, and only includes the cover 130 which is movable relative to the walls 1 1 1 , 1 12 of the offshore storage facility 100 and the level of the hydrocarbon 50 in the chamber 1 14.

The cover 130 comprises a hydrocarbon inlet 131 (first inlet) and a hydrocarbon outlet 132 (first outlet). The inlet 131 and outlet 132 are arranged on a surface of the cover 130. The cover 130 is connected to an inlet hydrocarbon conduit 135a via inlet

131 and an outlet hydrocarbon conduit 135b via outlet 132. The loading (filling up) of the chamber 1 14 with the hydrocarbon 150 occurs via inlet 131 and inlet hydrocarbon conduit 135a, and the offloading (removal) of the hydrocarbon 150 into from the chamber 114 occurs via the outlet 132 and outlet hydrocarbon conduit 135b. The hydrocarbon conduits 135a, 135b are preferably flexible and capable of moving together with the movement of the cover 130 according to the top surface level of the hydrocarbon 150 in the chamber 114. The hydrocarbon conduit 135a is connected to pumps (not shown) and metering system 141 and the hydrocarbon conduit 135b is connected to pumps 142 via conduit outlet 134. The cover 130 may comprise more than one inlet 135a and outlet 135b.

The cover 130 has a convex shape with an apex portion (topmost portion) that extends away from the base 1 13 of the structure 110. Preferably, the top surface of the hydrocarbon 150 conforms to the convex shape of the cover 130 when the cover 130 floats on the hydrocarbon 30. Depending on the application, the convex cover 30 may comprise more than one apex and/or have different geometrical shapes (e.g. polygons) provided the cover 130 comprises at least one sloping surface. The surfaces of the convex cover 130 are preferably curved. The outlet 132 is arranged substantially at the apex portion of the convex cover 130. Where the cover 130 has a different geometrical shape, the outlet(s) 132 is preferably arranged at a topmost portion of the cover 130. The cover 130 has several advantages. The convex shape of the cover 130 ensures that there is no accumulation of water on the top of the structure 1 10 due to wave action or rain. Further, the convex cover 130 facilitates the accumulation of vapour and gases released/emitted from the hydrocarbon 150 at the top portion of the structure 110, which can be subsequently released and vented out through a venting system (not shown) from the chamber 1 14. The cover 130 furthermore prevents the hydrocarbon vapours and gases from mixing with air, which can be a combustion hazard. In particular, there is minimal space between the cover 130 and the top surface of the hydrocarbon 150 which prevents hydrocarbon vapours from mixing with air to build up a combustible mixture. Additionally, since the outlet 132 is preferably located substantially at the apex portion of the convex cover 130, an "oil coning effect" is minimized/avoided. An "oil coning effect" is a common phenomenon in oil production where the water is drawn into an offloading pipe (for example at high speeds) if the offloading point in oil is too close to the water layer beneath the oil. The location of outlet 132 at the apex of convex cover 130 preferably ensures a safe minimum distance from a top surface of the water 160 when the facility 100 is in operation. In particular, the convex cover 130 creates a reverse funnel that allows the hydrocarbon 150 to be funnelled and channelled out, preferably at high speeds from the chamber 114 through outlet 132 and hydrocarbon conduit 135b, without creating an "oil coning effect". The convex shape of the cover 130 also adds more strength to the structure of the cover 130 as compared to a flat planar shape. Preferably, the cover 130 is a physical and solid barrier, which is advantageous because the cover 130 would not contaminate the hydrocarbon 150 when the facility 100 is in use. The cover 130 may be rigid or flexible depending on the application. Preferably, the cover 130 is impermeable to the hydrocarbon 150. The thickness of the cover 130, i.e. the distance from the surface of the cover 130 in contact with the hydrocarbon 150 to the surface of the cover 130 in contact with air surrounding the structure 110, will depend on the application. The cover 130 may be formed from metals (e.g. aluminium, steel, etc.), metallic alloys, polymers and compositions thereof.

In accordance with another aspect of the present invention as shown in Figures 4 to 6, the offshore storage facility 200 comprises a structure 210 having one or more berths, such as berthing stanchions 219 arranged on an outer surface of an outer wall 212. The stanchions 219 are rigid structures used to support the berthing of vessels that come alongside for loading/offloading of hydrocarbons. The stanchions 219 may be appropriately stiffened to withstand impact resulting from severe motion of berthed vessels moving against the structure 210 in severe weather conditions, e.g. a storm. The stanchions 219 are vertically attached to the outer surface of the structure 210 as shown in Figure 4 and 5, one point of attachment is arranged above the water line 291 and the other point of attachment is arranged below the water line 291. Each stanchion 219 comprises one or more access points along its length. The design of the stanchion 219 is advantageous because due to the variation of tide at the site, berthed vessels may be located at different vertical positions with respect to the structure 2 0, therefore the arrangement of the access points along the length of the stanchion allows personnel to easily board the storage facility 200 from the berthed vessel. This also provides improved accessibility to the facility 200 by personnel of berthed vessels which experience variations in draft. The stanchions 219 can comprise suitable attachments for securing berthing vessels to the structure 210. Where there are more than one stanchion 219, the stanchions 219 may be arranged in sets 219a, 219b, where each set is arranged opposite one another on the outer surface of the structure 210, for example in Figure 6, where the stanchions 219 are arranged on diametrically opposite sides of the structure 210 for ease of berthing operations. In various embodiments, the structure 210 comprises suitable attachments arranged on the peripheral circumferential surface of the structure 210 above the water 290, for example on deck 240, instead of berthing stanchions. Such attachments may be arranged to rotate around the structure 210 so that any vessel moored to the storage facility 200 can weathervane easily.

Method of Installing the Offshore Storage Facility

The offshore storage facility 00, 200 is self-installing and can be easily installed at a desired location. With reference to Figures 9a to 9e, the offshore storage facility 100 is dry-towed to an offshore site by a barge 170 (Figure 9a). The offshore storage facility 100 can be wet-towed by suitable vessels known in the art. At the offshore site, the barge 170 is submerged to allow the offshore storage facility 100 to float on water 190 (Figure 9b). Once the offshore storage facility 100 is floated off the barge 170, the barge 170 moves away from the offshore site (Figure 9c). The offshore storage facility 100 is lowered and submerged down into water 190 through controlled flooding of the compartment 1 15, the core of the base 113 and/or chamber 1 14 such that the base 1 13 of the structure 1 10 rests on the lake-bed or sea-bed 180 (Figures 9d and 9e). The skirt of the base 1 13 can penetrate into the sea-bed 180 as the structure 1 10 is lowered into the water 190. The structure 110 remains substantially stable at all the stages of settling down of its base 113 onto the lake-bed or sea-bed 180. Once installed on the sea-bed 180 with a portion of the structure 110 being located above the water 190, i.e. above the mean water level 191 , the facility 100 can be operated for storage and loading/offloading use. The self-installing mechanism avoids the need of heavy construction vessels and heavily cuts down installation costs. The facility 100 also does not require expensive mooring systems to maintain its position since it completely rests on the sea-bed 180 and is stable even in extreme weather conditions owing to its design and dimensions.

The stages of uninstalling the offshore storage facility 100 is the reverse of the installation stages, in that to commence uninstallation, the offshore storage facility is de-ballasted where the ballast in the compartment 115, the core of the base 1 13 and/or chamber 1 14 are removed in a controlled manner to cause the structure 1 10 to float in water 190. The base 113 (and skirt) detaches from sea-bed 180 as the base 1 13 floats closer to the mean water level 191 . Once the facility 100 is sufficiently de-ballasted, the facility may be dry- or wet-towed by vessels to another location.

Method of Operating the Offshore Storage Facility

With reference to Figures 1 to 3, during operation of the facility 100 where the hydrocarbon 150 is loaded into the facility 100, the hydrocarbon 150 is supplied to the chamber 1 14 via hydrocarbon inlet 131 , hydrocarbon conduit 135a and pumps. Any water 160 in the chamber 114 is displaced out of the chamber through the outlet 117 by continuous supply of the hydrocarbon 150 into the chamber 114, whereby a substantial volume of the chamber 1 14 becomes occupied by the hydrocarbon 150. During offloading, as the hydrocarbon 150 is offloaded (e.g. pumped out) to a vessel via hydrocarbon outlet 132, hydrocarbon conduit 135b and pumps 142, the volume of the hydrocarbon 150 decreases and volume of water 160 increases as water 190 surrounding the structure 1 10 enters the chamber 14 via inlet 116. During the loading and offloading of hydrocarbon 150, the volume and ratio of hydrocarbon 150 to water 160 in the chamber 114 changes, thereby causing the interface between the hydrocarbon 150 and water 160 to move vertically in the chamber 1 14. The separator 120 positioned at the interface will accordingly be displaced and will move together with the interface. The movement of the separator 120 and the interface can be affected by the rate of flow of the hydrocarbon 150 into and out of the chamber 1 14. Further, the amount and rate of flow of the hydrocarbon 150 into and out of the chamber 1 14 can cause displacement and vertical movement of the cover 130. The rate of flow of the hydrocarbon 150 into and out of the chamber 1 14 can be monitored and/or controlled by metering system 141 .

It will be further appreciated by the person skilled in the art that variations and combinations of features described above, not being alternatives or substitutes, may be combined to form yet further embodiments falling within the intended scope of the invention.

Claims

An offshore storage facility comprising a structure having a chamber operable to store two or more fluids immiscible with one another; and a cover adapted to float on a topmost fluid when in use, wherein the cover is shaped and operable to funnel the topmost fluid out from the chamber.

The offshore storage facility of claim 1 , wherein the cover is movable along an internal surface of the structure.

The offshore storage facility according to claim 1 or 2, wherein the cover is convex with an apex extending away from a base of the structure.

The offshore storage facility according to claim 3, wherein the cover comprises a first outlet arranged substantially at the apex for channelling the topmost fluid out from the chamber.

The offshore storage facility according to claim 4, wherein the first outlet is operable to connect to a conduit movable with the cover.

The offshore storage facility according to any one of the preceding claims, wherein the cover comprises a first inlet for channelling the topmost fluid into the chamber.

The offshore storage facility according to any one of the preceding claims, wherein the cover comprises a specific gravity of less than about 0.85.

The offshore storage facility according to any one of the preceding claims, wherein the cover is rigid.

9. The offshore storage facility according to any one of the preceding claims, the facility further comprising a venting system operable to vent vapours out and away from the chamber.

10. The offshore storage facility according to any one of the preceding claims, the facility further comprising a solid separator operable to separate the two or more fluids, wherein the separator is movable along the internal surface of the structure.

1 1. The offshore storage facility according to claim 10, wherein the separator comprises a specific gravity in between that of the two or more fluids.

12. The offshore storage facility according to claim 11 , wherein the separator comprises a specific gravity of about 0.90 to about 0.99.

13. The offshore storage facility according to any one of claims 10 to 12, wherein the separator is arranged at an interface of the two or more fluids in the chamber.

14. The offshore storage facility according to any one of claims 10 to 13, wherein the separator is impermeable to the two or more fluids.

15. The offshore storage facility according to any one of the preceding claims, wherein the structure comprises an inner wall and an outer wall, the inner and outer walls configured to define at least one compartment therebetween, wherein the compartment is adapted to receive at least one ballast.

16. The offshore storage facility according to any one of the preceding claims, wherein the structure comprises a second inlet for channelling a bottommost fluid into the chamber and a second outlet for channelling the bottommost fluid away from the chamber.

17. The offshore storage facility according to any one of the preceding claims, wherein the two or more fluids comprise water and a hydrocarbon, wherein the hydrocarbon is the topmost fluid.

18. The offshore storage facility according to any one of the preceding claims, the facility further comprising at least one berthing stanchion arranged on an outer surface of the structure.

19. The offshore storage facility according to claim 18, the facility comprising two sets of at least one berthing stanchion, wherein the two sets are arranged opposite one other on the outer surface of the structure.

20. The offshore storage facility according to claim 18 or 19, wherein the berthing stanchion comprises one or more access points for personnel to access the offshore storage facility.