GB1581325A - Single point mooring and fluid handling system - Google Patents

Description

(54) SINGLE POINT MOORING AND FLUID HANDLING SYSTEM (71) We, SEA TERMINALS LI MITED, a Company organised under the laws of the Cayman Islands, of 4th Floor, West Wind Building, P.O. Box 156, Grand Caymon, Caymon Islands, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to a mooring device and to a single point mooring and fluid handling system.

There is currently considerable development taking place in off-shore waters where drilling for, and recovery of, oil is taking place. At present. off-shore oil wells generally feed their output into a crude oil pipeline which stretches along the seabed to a suitable point on the shore. Oil from the pipeline is then generally stored in large capacity storage facilities at or near the coast. The construction of land-based oil storage facilities and, more particular, the construction of submerged crude oil pipelines involves very large capital expenditure.

An aim of the present invention is to provide a mooring device and single point mooring and fluid handling system which may be used to convey oil from a submarine pipeline to a conduit through which it passes into a marine vessel. The mooring device and system can advantageously be used in conjunction with an oil storage vessel as described and claimed in our co-pending patent application No. 42251/79 - Specification No. 1581326 - (divided out of the present application) and with the method of delivering oil which is also described and claimed in that application.

According to the present invention, there is provided a single point mooring and fluid handling system for the transfer of a fluid from a submarine pipeline to a conduit connectable to a marine vessel moored at the system, which system comprises (a) a base which in use is located on the seabed; (b) a riser connected to the base by a universal joint, the riser being totally submerged in use; (c) a fluid swivel located at the top of the riser; and (d) a buoyancy chamber mounted on top of the fluid swivel via a universal joint, the arrangement being such that, in use, a hose connected to said fluid swivel can rotate independently of both the riser and the buoyancy chamber.

Preferably, a hose guide tray is attached to the fluid swivel so as to act as a lever to facilitate rotation of the fluid swivel in response to movement of a hose passing over the hose guide tray and extending to the marine vessel which is to receive the fluid (e.g. oil) from the fluid swivel.

Advantageously, the fluid swivel is located at air-dive depth. A platform is preferably provided in the vicinity of the fluid swivel so as to facilitate any maintenance work which may be required.

The buoyancy chamber (which may also be termed a spacer buoy) is preferably totally submerged in the system of this invention. The spacer buoy may be generally cylindrical in shape, although other shapes may be employed instead. A mooring chain or hawser is preferably attached to the top of the buoyancy chamber, advantageously via a rigid extension projecting sidewardly from the top of the buoyancy chamber.

The base for location on the seabed is advantageously a weighted (e.g. gravity) base. The hose guide tray is preferably balanced to facilitate rotation about the axis of the riser. An oil line is preferably provided aside the riser itself.

Where the mooring system includes a mooring chain attached to the buoyancy chamber, this chain may hang vertically from the buoyancy chamber when it is not in use; the free end of the chain may be attached to a pendant line and a surface marker buoy. One or more submarine hoses may be attached to the fluid swivel even when there is no marine vessel moored at the mooring; the hose(s) can hang in a catenary with its or their free end(s) held at a depth of 70 feet by a pendant line and a marker buoy.

The buoyancy chamber or spacer buoy is preferably constructed for maximum drag and speedy righting ability; it will usually be fully submerged. A section may be added to it so that the combined structure will penetrate the surface; in this case, the added section can be flanged to the spacer buoy and a mooring shackle can be attached to the top of the added section. A floating mooring rope rather than chain is preferably used with this arrangement.

For a better understanding of the invention, and to show how the same may be carried into effect, reference will now be made, by way of example, to the accompanying drawings, in which: Figure 1 shows an oil storage vessel connected to a single point mooring and fluid handling system of this invention; and Figure 2 shows a modification to part of the mooring of Figure 1.

In Figure 1 of the drawings, an oil storage vessel of the type described and claimed in our copending patent application No.

7942251 (Specification No. 1581326) is connected via a conduit 44 to the single point mooring and fluid handling system of this invention. A ferry tanker is located a stern of the oil storage vessel and is connected thereto via a catenary hose system as illustrated. The oil storage tanker and the ferry tanker may be used in the method of transferring oil which is described and claimed in our co-pending patent application No. 7942251 (Specification No.

1581326).

The mooring comprises a weighted (i.e.

gravity) base 30 located on the seabed, to which a riser tube 32 is attached by means of a universal joint 31. An oil pipeline 33 located on the seabed is connected, via manifold 34 and flexible bottom hose 35, to oil line 36 which is located aside the riser 32.

At the top of the riser (which is totally submerged) there is a platform 37 located about a coupling 38 (which may be of the Graylock type) on top of which is a fluid swivel 39 which is coupled to a universal joint 40. A submerged buoyancy chamber or spacer buoy 41 is attached to the universal joint 40, and a mooring chain or hawser 42 extends from a generally horizontal projection called a chain beam attached to the top of spacer buoy 41 to the oil storage vessel. The spacer buoy illustrated in the drawing is generally cylindrical in structure; other designs may be used, the general aim being to employ a shape which has maximum drag combined with speedy righting properties. One alternative design employs a generally flat surface portion extending downwardly from the point at which mooring chain 42 is connected thereto.

A hose guide tray 43 is attached to the fluid swivel 39 and provides a channel through which oil hose or conduit 44 is conveyed. This hose serves to supply oil from oil line 36 to storage capacity in the oil storage vessel. The spacer buoy 41 is located sufficiently deep to be free from severe wave action. The hose guide tray 43 is balanced, and functions as a lever to facilitate rotation of the fluid swivel 39 in response to movement of the hose 44. The universal joint 40 and the coupling 38 are such that, in use, a hose connected to the fluid swivel 39 can rotate independently of both the riser 32 and the spacer buoy 41.

In the embodiment shown in Figure 2, the spacer is modified and extended up to the surface of the sea by means of a cylindrical element 45. This is connected above the water line by a rope mooring 46 to the bows of the oil storage vessel or to a ferry service tanker.

The oil hose 44 may advantageously be 20 or 24 inches in diameter, which allows a high rate of oil transfer.

Delivery of oil from line 33 on the sea bed into the oil storage vessel takes place continuously; thus, problems associated with sudden changes of pressure in the oil lines are eliminated.

One method of installing the mooring arrangement shown in Figure 3 will now be described by way of example.

After the base and riser are in place, the "assembly" which may consist of a Graylock-Type coupling fluid swivel, hose guide tray universal joint and spacer buoy will be connected to the riser in the following manner utilising either an anchored barge, a dynamically-positionable service vessel or a dynamically-assisted storage tanker which eventually will he moored to the mooring.

An extendable gantry with an outreach from the vessel of 25 feet and large enough to lift and move the assembly is employed.

This gantry will swing the assembly into a vertical attitude in a controlled fashion utilizing winches and a sled which is mounted on guide rails and the position of which is controlled by a winch. (This sled can be the sled 7 shown in Figures 1 and 2 of our copending patent application No. 42251/ 72 - Specification No. 1581326. In the vertical position, the top of the spacer buoy is captured in a frame to avoid oscillations.

Guide wires from 2 self-tensioning winches or other heave compensating devices are passed from their respective sheave posi tions on the gantry frame through carbinertype fixtures which are fixed to the spacer buoy. Two divers take these wires down to the diving platform on top of the riser and fix them in pre-determined positions opposite each other. The wires are tensioned by self-tensioning winches oi other tensioned devices.

Two openable ports with adjacent valves (not shown) on the spacer buoy have by this stage been opened, one at the bottom of the buoy and the other at or near the top. In the buoy construction itself there is a specially constructed buoyant section not affected by the internal buoy space open to the two ports. The special buoyant section serves the purpose of keeping the assembly vertical when in the water and submerged in the water but does not keep the assembly buoyant i.e. it provides no positive buoyancy for the complete assembly.

As the assembly is lowered in the water, slowly to allow the ingress of water and to expel air from the buoy main body, it is guided by the two taut wires attached to the diver's platform 37 at the top of the riser.

With communication to the surface, the divers control the final descent and connection of the assembly to the riser. The Graylock type coupling is made fast. The line used to lower the assembly is made slack. The top port on the spacer buoy is closed and a pre-determined quantity of water is expelled through the bottom port by pumping air into the spacer buoy utilizing an airline from the surface. The lifting/ lowering wire is separated from the buoy, and the two guide wires are detached from the carabiner type guide on the buoy. The chain is lowered and attached to the chain seam of the spacer buoy. The oil hose is lowered and attached to the swivel. The guide wires are utilized to lower both the chain and the hose. The guide wires are dis-connected from the diver's platform.

The type of vessel on the surface which assists in the attachment of the assembly dictates the final procedure of attachment of pendant lines and marker buoys or attachment to the mooring and hose positions on the storage tanker.

The assembly once in position, will be ordinarily maintained by an air diving team from the floating storage tanker which is moored to the submerged single anchor leg mooring (SSALM). When major overhaul or replacement of parts are required that cannot be accomplished underwater or the mooring is being dis-assembled the assembly can be lifted to the surface and put aboard ship either by an anchored barge, a dynamically-positionable service vessel or the dynamically-assisted storage tanker which has been moored to the SSALM. In the case of the anchored barge or the dynamically-positionable service vessel, the mooring chain and oil hose are disconnected from the storage tanker and attached to pendant wires having marker buoys; the mooring chain hangs straight down along the whole buoy and the oil hose hangs in a catenary.In the case where the dynamicallyassisted storage tanker is going to lift the assembly, the mooring chain and oil hose do not have to be disconnected from the ship.

Two divers take down the guidewires which are attached to the diver's platform.

The pass the wires through the carabinertype fixtures which are part of the spacer buoy. The oil hose and chain are disconnected at this time and lifted to the surface.

The lifting line is attached to the top of the buoy and hung loosely. The main body of the spacer buoy is flooded using a water ingress valve and an air valve at the bottom and top, or near top, respectively of the buoy. There is enough buoyancy in the specially constructed buoyant section at the top of the buoy to keep it upright. When the main body is filled with water, the two large ports, one at the top and one at the bottom, are opened. The coupling under the fluid swivel is loosened and the slack in the lifting line is made taut. The assembly is lifted to the surface whereupon water will automatically drain from the spacer buoy as the assembly is lifted clear of the water. At the top of the lift the buoy fits into a capture frame to avoid oscillations.The guidewires are disconnected from the carabiner type fixtures on the buoy and they are also disconnected from the diver's platform on top of the riser. A marker buoy is floated to mark the riser position. The gantry holding the assembly is retracted inboard until the assembly is in a position to be secured to the sled, which is in an oblique position. When secured, the sled is lowered to the horizontal position. The lifting line is detached from the assembly. The sled is guided inboard on its rails to where maintenance on the assembly can be carried out or parts replaced.

Lifting tackle on the gantry is available to move the large pieces of the assembly about.

When required, e.g. in an emergency, the submarine hose will automatically disconnect and pass through the bottom of the ship, hang in a catenary, and be identified by a surface buoy released over the side of the ship. The mooring line secured at the ship's windlass will be released and pass through the hawser pipe and be marked by the surface buoy attached to the chain by a pendant line. The chain hangs in a vertical attitude.

In one embodiment of the invention, the spacer buoy is constructed so that it can be modified to give the structure as shown in Figure 2. This involves a two-part construc tion the upper part of which can be changed to provide the extension to the surface 45 as shown in Figure 2. This extension can be used as follows. The service tanker will approach the surface extension of the SSALM which has a floating hawser and strayline (messenger line). The submarine hose which is hung in a catenary with the probe end at the 70 foot water depth is buoyed and its stray line is attached to the strayline of the floating hawser line. From the ship's bows the strayline will be grappled for and brought onboard, hauled in and the hawser will follow it and be secured through the use of a tugger winch.The strayline for the oil hose will have been brought on deck and the oil hose will follow it and its probe end will be attached to the quick release coupling. After the loading of the tanker is completed, the procedure is reversed and the lines dropped in the water.

A floating storage vessel can get onto the submerged mooring as shown in Figure 1 of the drawings unaided once it is ascertained that the submarine hose 44 has not, through water current action, wrapped itself around the mooring chain 42. Prior to the vessel being moored, both the submarine hose 44 and the mooring chain 42 will occupy positions different from those illustrated in Figure 1; the mooring chain will hang vertically, with its free end attached to a pendant line and marker buoy, while the submarine hose 44 will hang in a loop, with its free end likewise attached to a pendant line and marker buoy. In one system, the storage vessel will approach the mooring between the marker buoy for the hose and the marker buoy for the mooring chain. The mooring chain buoy and pendant line will then be hauled aboard the vessel, e.g. on the starboard side. and stowed.The mooring chain will be attached to a continuous wire line which passes around the hull of the vessel on fairleads and into and through a mooring pipe. When the chain reaches the top of the mooring pipe it will be passed over a windlass and the excess chain stored in a chain locker. The buoy and pendant line marker the submarine hose will then be hauled aboard the vessel, e.g. on the port side. Likewise. the hose or hose bundle will be attached to a continuous wireline which passes around the hull on fairleads and into and through a hose pipe. When the free end of the hose 44 reaches its receptacle, the connection will be secured. If a hose bundle is employed, each of the hoses in the bundle will then be connected to their respective receptacles.

WHAT WE CLAIM IS: 1. A single point mooring and fluid handling system, for the transfer of a fluid from a submarine pipeline to a conduit connectable to a marine vessel moored at the system, which system comprises (a) a base which in use is located on the seabed; (b) a riser connected to the hose by a universal joint, the riser being totally submerged in use; (c) a fluid swivel located at the top of the riser; and (b) a buoyancy chamber mounted on top of the fluid swivel via a universal joint. The arrangement being such that, in use, a hose connected to said fluid swivel can rotate independently of both the riser and the buoyancy chamber.

2. A system as claimed in claim 1, which includes a hose guide tray attached to the fluid swivel such that it acts as a lever to facilitate rotation of the fluid swivel.

3. A system as claimed in claim 1 or 2, wherein the said buoyancy chamber is generally cylindrical in shape.

4. A system as claimed in any preceding claim, wherein a pipeline is located aside the riser.

5. A system as claimed in any preceding claim, wherein a mooring chain or hawser is connected to the top of said buoyancy chamber.

6. A system as claimed in any preceding claim, which further comprises an oil hose attached to said fluid swivel.

7. A system as claimed in any preceding claim, wherein the base is a gravity base.

8. A system as claimed in any preceding claim. which is positioned so that the fluid swivel is at air-dive depth.

9. A single point mooring and fluid handling system substantially as hereinbefore described with reference to, and illustrated in, Figure 1 of the accompanying drawings.

10. A single point mooring and fluid handling system substantially as hereinbefore described with reference to, and as illustrated in, Figure 1 when modified in accordance with Figure 2 of the accompanying drawings.

11. A method of mooring a vessel to the sea bed using mooring apparatus in accordance with claim 1, substantially as hereinbefore described with reference to, and as illustrated in, the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (12)

**WARNING** start of CLMS field may overlap end of DESC **. tion the upper part of which can be changed to provide the extension to the surface 45 as shown in Figure 2. This extension can be used as follows. The service tanker will approach the surface extension of the SSALM which has a floating hawser and strayline (messenger line). The submarine hose which is hung in a catenary with the probe end at the 70 foot water depth is buoyed and its stray line is attached to the strayline of the floating hawser line. From the ship's bows the strayline will be grappled for and brought onboard, hauled in and the hawser will follow it and be secured through the use of a tugger winch. The strayline for the oil hose will have been brought on deck and the oil hose will follow it and its probe end will be attached to the quick release coupling.After the loading of the tanker is completed, the procedure is reversed and the lines dropped in the water. A floating storage vessel can get onto the submerged mooring as shown in Figure 1 of the drawings unaided once it is ascertained that the submarine hose 44 has not, through water current action, wrapped itself around the mooring chain 42. Prior to the vessel being moored, both the submarine hose 44 and the mooring chain 42 will occupy positions different from those illustrated in Figure 1; the mooring chain will hang vertically, with its free end attached to a pendant line and marker buoy, while the submarine hose 44 will hang in a loop, with its free end likewise attached to a pendant line and marker buoy. In one system, the storage vessel will approach the mooring between the marker buoy for the hose and the marker buoy for the mooring chain. The mooring chain buoy and pendant line will then be hauled aboard the vessel, e.g. on the starboard side. and stowed.The mooring chain will be attached to a continuous wire line which passes around the hull of the vessel on fairleads and into and through a mooring pipe. When the chain reaches the top of the mooring pipe it will be passed over a windlass and the excess chain stored in a chain locker. The buoy and pendant line marker the submarine hose will then be hauled aboard the vessel, e.g. on the port side. Likewise. the hose or hose bundle will be attached to a continuous wireline which passes around the hull on fairleads and into and through a hose pipe. When the free end of the hose 44 reaches its receptacle, the connection will be secured. If a hose bundle is employed, each of the hoses in the bundle will then be connected to their respective receptacles. WHAT WE CLAIM IS:

1. A single point mooring and fluid handling system, for the transfer of a fluid from a submarine pipeline to a conduit connectable to a marine vessel moored at the system, which system comprises (a) a base which in use is located on the seabed; (b) a riser connected to the hose by a universal joint, the riser being totally submerged in use; (c) a fluid swivel located at the top of the riser; and (b) a buoyancy chamber mounted on top of the fluid swivel via a universal joint. The arrangement being such that, in use, a hose connected to said fluid swivel can rotate independently of both the riser and the buoyancy chamber.

2. A system as claimed in claim 1, which includes a hose guide tray attached to the fluid swivel such that it acts as a lever to facilitate rotation of the fluid swivel.

3. A system as claimed in claim 1 or 2, wherein the said buoyancy chamber is generally cylindrical in shape.

4. A system as claimed in any preceding claim, wherein a pipeline is located aside the riser.

5. A system as claimed in any preceding claim, wherein a mooring chain or hawser is connected to the top of said buoyancy chamber.

6. A system as claimed in any preceding claim, which further comprises an oil hose attached to said fluid swivel.

7. A system as claimed in any preceding claim, wherein the base is a gravity base.

8. A system as claimed in any preceding claim. which is positioned so that the fluid swivel is at air-dive depth.

9. A single point mooring and fluid handling system substantially as hereinbefore described with reference to, and illustrated in, Figure 1 of the accompanying drawings.

10. A single point mooring and fluid handling system substantially as hereinbefore described with reference to, and as illustrated in, Figure 1 when modified in accordance with Figure 2 of the accompanying drawings.

11. A method of mooring a vessel to the sea bed using mooring apparatus in accordance with claim 1, substantially as hereinbefore described with reference to, and as illustrated in, the accompanying drawings.

12. A method of emplacing a single point mooring and fluid handling system, as claimed in any one of claims 1 to 10, substantially as hereinbefore described.