AU2005203655A1 - System for managing offshore drilled products - Google Patents

Description

P/00/011 Regulation 3.2

AUSTRALIA

Patents Act 1990 COMPLETE SPECIFICATION STANDARD PATENT Invention Title: System for managing offshore drilled products The following statement is a full description of this invention, including the best method of performing it known to us: SYSTEM FOR MANAGING OFFSHORE DRILLED PRODUCTS Field of the invention This invention relates to offshore drilling operations for extracting deposits of products, such as oil and gas, from below the seabed. More specifically, the invention relates to the transfer of drilled products, such as oil and natural gas, from the drilling platform to processing plants which may be located on land or at sea.

Summary of the Invention In accordance with a first aspect of the present invention, there is provided a system for managing one or more natural products obtained from an offshore platform, the system comprising: an offshore floating storage vessel linked to the offshore platform to enable the product(s) to be transferred from the platform and stored in the vessel, the vessel being moored adjacent to the offshore platform, the vessel further including personnel facilities; a personnel transfer bridge extending between the offshore platform and the offshore floating storage vessel to enable personnel to transfer between the two, the bridge being connected to the offshore platform and the offshore floating storage vessel and operable to accommodate variable loading conditions of the offshore floating storage vessel and variable weather conditions; and a shuttle vessel to periodically receive the stored product(s) and transfer it for further processing.

It will be appreciated that the offshore floating storage vessel operates as a temporary storage facility from which the stored product is periodically discharged to a shuttle vessel for transfer to a land or sea based productprocessing plant. The floating vessel may be moored adjacent the offshore platform for the life of the offshore platform.

ID: 004521897 In the preferred embodiment, the offshore platform comprises a production platform which may be in the form of a mobile offshore applications barge. The offshore production platform is suitably anchored to the seabed in fixed disposition and associated with one or more wells. The offshore production platform may be disposed adjacent a drilling rig. In another less preferred embodiment, the offshore platform may incorporate the drilling rig.

The offshore floating storage vessel may take the form of a ship for transporting a product, for example, the ship may be an oil or gas tanker.

Preferably, a plurality of mooring lines, preferably 12 mooring lines, linked to the seabed, moor the floating vessel adjacent to the offshore platform. To withstand rough weather conditions, the ship may have reinforced connections to the mooring lines, including reinforced bulkheads and chain stoppers.

The personnel facilities provided on the offshore floating storage vessel preferably include accommodation for personnel operating the drilling rig.

Other personnel facilities may include recreation and entertainment facilities.

Personnel move between the offshore platform and the offshore floating storage vessel via the bridge that is responsive to movement of the moored floating vessel relative to the drilling platform. The bridge is designed to withstand 100 year storm design criteria and/or maximum tide conditions and/or full loading of the offshore floating storage vessel. As such, the bridge may be permanently connected between the offshore floating storage vessel and the offshore platform.

The bridge may comprise a plurality of telescopic sections linking the offshore platform to the offshore floating storage vessel. The connections linking the bridge to the offshore platform and the offshore floating storage vessel may allow for universal pivoting relative thereto.

Preferably, the sections telescope freely relative to each other and define an enclosed pathway for the movement of personnel.

Preferably, a first connection includes a rubber ring on which one of said telescopic sections sits so that universal pivoting of the section relative to the platform/vessel to which it is connected is permitted. In a second ID:004521897 -4connection, the other of said telescopic sections is coupled to a support means on the platform/vessel to which the section is connected. The support means enables the bridge to be located in and dislocated from communication with the platform/vessel that said one of the telescopic sections connects with.

In the preferred embodiment, the first connection is between a telescopic section and the offshore platform and the second connection is between the other telescopic section and the floating vessel.

A control centre may be further included in the offshore floating storage vessel for remotely monitoring and controlling operation of the offshore platform, for example to cause emergency shut down of the offshore platform.

Additionally, the floating vessel may include means for performing initial conditioning or processing operations on the drilled product preparatory to discharge of the drilled product to the shuttle vessel.

In a second aspect of the invention, there is provided a mooring apparatus including: a seabed anchor; a mooring line extending from the anchor for linking to a floating vessel and thereby limiting movement of the vessel away from the anchor; buoyancy means fixed to said mooring line intermediate its length such that said buoyancy means provides a force operative to reduce the distance between the vessel and the anchor.

The mooring apparatus may be used with any type of floating vessel which requires a temporary mooring. The mooring apparatus is desirably used with the shuttle vessel described above in connection with the first aspect of the invention. However, the second aspect of the invention is not limited to that use. The mooring apparatus is not intended to be used with the offshore floating storage vessel described above.

When the mooring apparatus is installed in situ, the buoyancy means may be submerged below the water level. An additional buoyancy means may be provided on the mooring line remote from the seabed anchor, most preferably at the end of the mooring line remote from the seabed anchor. The ID: 004521897 additional buoyancy means serves as a surface buoy to aid in location of the mooring line. In use, the surface buoy may also be submerged.

At least a portion of the mooring line may be elastically extendable. For example, the portion between the buoyancy means and the additional buoyancy means may be in the form of nylon grommet i.e. braided nylon rope.

The mooring line may not extend all the way to the floating vessel. The floating vessel may provide an additional mooring line to attach to the mooring apparatus. Preferably, the additional mooring line attaches to the surface buoy.

The seabed anchor may comprise a pile.

In a third aspect of the invention, there is provided a mooring apparatus including: a seabed anchor; a mooring line extending from the anchor for linking to a floating vessel and thereby limiting movement of the vessel away from the anchor; buoyancy means fixed to said mooring line wherein, in use, the buoyancy means is submerged such that said buoyancy means provides a force operative to reduce the distance between the vessel and the anchor.

The third aspect of the invention may include any of the features set out in connection with the second aspect above.

This invention may also be said broadly to consist in the parts, elements and features referred to or indicated in the specification of the application, individually or collectively, and any or all combinations of any two or more of said parts, elements or features, and where specific integers are mentioned herein which have known equivalents in the art to which this invention relates, such known equivalents are deemed to be incorporated herein as if individually set forth.

The invention consists in the foregoing and also envisages constructions of which the following gives examples.

Brief description of the Drawinqs ID: 004521897 In order that the invention may be more fully understood, one embodiment will be described by way of example with reference to the drawings in which: Figure 1 is a schematic plan view of the operational configuration of the transfer system in accordance with a preferred embodiment of the present invention, the figure also illustrating an offshore platform; Figure 2 is a plan view of the offshore vessel for use in the system of Figure 1; Figure 3 is an elevation view of the offshore vessel disclosed in Figure 2; Figure 4 is a schematic view of the mooring arrangement for the shuttle vessel of the system disclosed in Figure 1; Figure 5 is a detail of the mooring pile of Figure 4; Figure 6 is a plan view of the mooring pile of Figure Figure 7 is a detail of the mooring pile of Figure Figure 8 is a schematic view showing the mooring line in disconnected configuration; Figure 9 is a detailed view of the surface buoy shown in Figure 8; Figure 10 is a detailed view of the mid depth buoy shown in Figure 8; Figure 11 is a detail of a connection to the buoy of Figure Figure 12 is a detail of another connection to the buoy of Figure Figure 13 is a detailed view of the bridge connection between the offshore vessel and the offshore platform, illustrating the offshore vessel in a loaded condition; Figure 14 illustrates the relative positions of the offshore vessel and the offshore platform with the offshore vessel at the wave crest for maximum tide condition; ID:004521897 Figure 15 illustrates the relative positions of the offshore vessel and the offshore platform with the offshore vessel at the wave trough for minimum tide condition; Figures 16 to Figure 18 illustrate the relative lateral positions of the offshore vessel and the offshore platform for: firstly no vertical or lateral excursions; secondly for longitudinal excursions; and thirdly for the maximum transverse excursion; Figure 19 is a detail of an anchor pile for the offshore platform; Figure 20 is a detailed view of item a of Figure 19; Figure 21 is a section through A A of Figure Figure 22 is a detailed view of item b of Figure 19; Figure 23 is a section through B B of Figure 22; Figure 24 is a sectional view of a weld detail of Figure 23; Figure 25 is a detailed view of item b of Figure 19 illustrating a mooring line attached; Figure 26 is a detailed view of item c of Figure 19; Figure 27 illustrates a typical cylindrical weld detail; Figure 28 is a plan view of the bow of the offshore vessel; Figure 29 is a detailed view of item a of Figure 28; Figure 30 is illustrative of a section through Figure 29; Figure 31 is a plan view of the chain stopper pedestal shown in Figure Figure 32 is a section through D D of Figure 31; Figure 33 is a section through E E of Figure 31; Figures 34 and 35 are illustrative of stiffening details for the bow; Figure 36 is a view of the stern of the offshore vessel; Figure 37 is a detailed view of item a of Figure 36; Figure 38 is illustrative of a section through Figure 37; ID: 004521897 Figure 39 is a sectional view through C C of Figure 38; Figures 40 and 41 are illustrative of stiffening arrangements for the stern; Figure 42 is an elevational view of an access stairway to the bridge illustrated in Figures 13 to 18; Figures 43 to 45 are various sectional views of the access stairway shown in Figure 42; Figure 47 is a plan view of the edge of the offshore platform shown in Figure 1; Figure 48 is a detailed view of item a of Figure 47; Figure 49 is a detailed view of item b of Figure 47; Figure 50 is a section through A A of Figure 49; Figure 51 is a section through B B of Figure 49; Figures 52 to 54 are various sectional views C C, D D and E E respectively through Figure 48; Figure 55 is a sectional view through F F of Figure 47; Figure 56 is a plan view of the bow of the offshore vessel shown in Figure 1; Figure 57 is a detailed view of item a of Figure 56; Figure 58 is a sectional view through A A of Figure 57; Figure 59 is a sectional view through B B of Figure 58; Figure 60 is a sectional view through C C of Figure 57; Figure 61 is a plan view of the transfer bridge shown in Figures 13 to 18; Figure 62 is an elevational view of the transfer bridge shown in Figure 61 shown in a first extended configuration and a second retracted configuration; and Figure 63 is a sectional view through A A of Figure 62.

ID: 004521897 -9- Description of the Preferred Embodiment Figure 1 illustrates the arrangement of the transfer system including the offshore vessel 10 and the shuttle vessel 12. The offshore vessel 10 is linked to an offshore platform which comprises a mobile offshore applications barge 16 provided adjacent a drilling rig 14. The drilling rig 14 and the mobile barge 16 are fixed relative to the seabed as is known in the art. On the other hand, the offshore vessel 10 is a floating vessel which is moored by a spread mooring system whereby the bow and the stern each have six mooring lines spread at various angles. Further details of the moorings are shown in Figures 19 to 27. The offshore vessel is moored in close proximity to the mobile barge 16. As shown in greater detail in Figure 3, the mobile barge 16 and the offshore vessel 10 are interconnected by product loading lines and fuel/bunker lines 18. These product loading lines are used to transfer the crude oil obtained by the drilling rig 14 to the offshore vessel 10. The crude oil is stored temporarily in the offshore vessel 10 which includes a number of cargo tanks and slop tanks (not shown). Further processing may be conducted on board the offshore vessel 10. For example, produced water remaining in the crude oil may be stripped from the bottom of the cargo tanks and transferred to the slop tanks where further settling may take place. The water in the slop tanks may be further treated via a water treatment plant 20 and then discharged overboard.

Further connections between the mobile barge 16 and the offshore vessel 10 comprise umbilical lines 22 for power and communications. Further, a personnel transfer bridge 24 is provided to enable personnel to transfer between the drilling rig 14 and the offshore vessel The crude oil stored in the offshore vessel 10 is periodically transferred to one or more shuttle vessels 12 which transfer the crude oil to an onshore processing plant or to a pipeline to convey the crude oil to a processing plant.

The shuttle tanker 12 is moored to the offshore vessel by a hawser connection 25. As shown in Figure 1, the bow of the shuttle tanker is moored to the stern of the offshore vessel 10. The stern of the shuttle tanker 12 is further secured to maintain its position by mooring lines. The arrangement of the shuttle ID:004521897 tanker mooring lines 39 will be explained further in connection with Figures 4 to 12.

As shown in Figure 1, a tug optionally provides static tow while the shuttle vessel is being moored.

Crude oil is discharged from the offshore vessel 10 to the shuttle vessel 12 by a floating hose string connected to the manifold of the shuttle vessel. To assist in handling, the hose string is fitted with tail hoses. When there is no shuttle vessel 12 moored to the offshore vessel 10, the hawser and the hose are stored on board the offshore vessel using retractable reels. In Figure 2, numeral 30 indicates the hawser retrieval and stowage and numeral 32 indicates the floating hose offloading platform.

Referring to Figure 2, it can be seen that the offshore vessel further includes a helicopter platform 35, an accommodation block 36 for personnel and a deck crane 38. It is intended that primary access for personnel to the offshore vessel will be by helicopter. Personnel may also transfer to the offshore vessel 10 by boats. This transfer may be undertaken by the deck crane 38 which is equipped with personnel transfer capabilities. The deck crane 38 may also be used to load or discharge supplies and gear from/to supply boats. Access from the offshore vessel to the mobile barge 16 is by transfer bridge 34. As will be explained in connection with Figures 13 to 18, the transfer bridge is designed to remain in position and operable throughout the hundred year storm criteria.

Figures 4 to 12 illustrate the temporary mooring lines 39 for the shuttle vessel 12. The mooring lines 39 comprise an upper mooring line 40 and a lower mooring line 41. Each mooring line 39 is connected to the seabed via a mooring pile 42 shown in greatest detail in Figures 5 to 7. The lower mooring lines 41 consists of a length of stud chain 44 connected to a mid-depth buoy 46 which is connected to a length of elastic nylon grommit 48 which is shackled to a surface buoy 50 shown in greatest detail in Figure 9.

When the lower mooring line 41 is unconnected, it adopts the configuration illustrated in Figure 8 whereby the mid-depth buoy 46 conveys the stud chain 44 to a position generally above the mooring pile 42 and the ID: 004521897 -11 surface buoy 50 is present on the surface of the water, generally above the mooring pile 42, depending upon the strength of the current.

The upper mooring line 40 is deployed from the shuttle vessel 12. The remote end of the upper mooring line 40 connects to a shackle 52 provided on the top of the surface buoy 50 as shown in Figure 9. The connection may be made manually whereas disconnection may be effected remotely. This may be achieved with a McDermott hook available from a rigging supplier.

As will be appreciated, when the shuttle vessel 12 is in the moored configuration both buoys 46, 50 will be submerged. The submerged buoys create an upward force vector which tends to pull the shuttle vessel 12 towards the mooring piles 42 and away from the offshore vessel 10. The presence of the submerged buoys result in a mooring line 39 which may not be straight but bent out of alignment between the mooring pile 42 and the shuttle vessel 12. This feature, together with the elasticity provided by the grommet 48 imparts elasticity to the mooring lines.

Figures 13 to 18 illustrate various relative relationships between the floating vessel 10 and the mobile barge 16 which is stationary relative to the drilling rig and the seabed. As discussed above, the floating vessel 10 and the mobile barge are linked by a personnel transfer bridge 24, umbilical lines 22 and product and fuel/bunker lines 18. As can be seen, the product and bunker lines 18 extend in a loop between the offshore vessel 10 and the mobile barge 16 so as to present a large amount of slack allowing for relative movement between the two. Similarly, but to a lesser degree, the umbilical lines 22 extend in a loop beneath the personnel transfer bridge 22.

As can be seen from Figures 13 to 18, the personnel transfer bridge is designed to adopt varying configurations to accommodate a large variety of conditions including relative vertical movement shown in Figures 13 to 15 to account for loading or wave conditions. Additionally, the transfer bridge allows for transverse execution as shown in Figure 18. The form of the transfer bridge will now be described further in connection with Figures 47, 49 and 61 to 63.

ID:004521897 -12- As shown in Figure 61, the personnel transfer bridge 24 is made of two telescoping sections 60, 62. Each section 60, 62 is in the form of a columnar truss structure providing a hollow surround through which personnel may walk or be conveyed. The bottom of the truss structure may be provided with a walkway while the sides and roof of the truss structure may be provided with appropriate safety barriers. A first connecting portion 66 is provided at one end of one of the sections 60. The connector portion 66 is in the form of a receptacle. A corresponding mount 68 is provided on the mobile barge as shown in Figure 49. The mount 68 is in the form of a bearing pad shaped as a rubber ring which is received by the connector portion 66. The receptacle 66 is locked to the bearing pad in a manner which provides a universal joint type coupling between section 60 and the mobile barge 16.

At the other end of the transfer bridge 24, section 62 is mounted atop a pedestal. This raises the height of this end of the transfer bridge 24 such that during normal loading and weather conditions, the transfer bridge 24 will be approximately level. Atop the pedestal 70 is mounted a pedestal adaptor 74.

Atop the pedestal adaptor 74 is secured a cantilevered platform 76. The end of section 62 is provided with a pair of spaced connector portions 78 which mount onto mounting pins or mounting bosses (not shown) on the cantilevered platform 76. This provides for pivotal motion of the transfer bridge 24 about pivotal access 80. Thus, both ends of the personnel transfer bridge 24 permit the bridge to adopt a wide variety of configurations as shown in Figures 13 to 18. As mentioned, sections 60 and 62 are telescopic to provide a variety of overall lengths of the transfer bridge 24. Nylon bogies (not shown) may be provided to facilitate sliding movement between the two sections. In use, the sections of the bridge move freely relative to one another and the connections 66, 68,78 allow the sections to move freely within the permitted range of movements.

For installation of the bridge in the required configuration, a bridge tower 82 is mounted atop the cantilevered platform 76. An extension cable 84 extends from the remote end of section 62 around a pulley on the top of bridge tower 82 and to the luff winch 85. As will be appreciated from a study of Figures 13 to 15, the length of the extension cable 84 is adjustable according ID: 004521897 -13to the required configuration of the transfer bridge 24. A powered drive (not shown) is provided to extend or retract the transfer bridge sections 60, 62, depending upon the required configuration. Following installation, the extension cable 84 and the luff winch 65 may be disconnected and stowed.

As already discussed, the end of the transfer bridge 24 mounted on the offshore vessel 10 is supported on a pedestal 70. As shown in Figure 3, an access stairway 90 is provided to access the transfer bridge 70 from the deck of the offshore vessel 10. Further detail for the access stairway can be found in Figures 42 to 46.

As shown in Figure 2, the offshore vessel 10 is moored by means of 12 mooring lines 80 arranged as shown. Each of the mooring lines comprises a continuous stud chain 82 which is connected to a pile 84 driven into the seabed. Further details of the pile 84 and the connection to the continuous stud chain 82 are provided by Figures 19 to 27. Prior to connection of the offshore vessel 10, the mooring lines 80 and piles 84 are installed and tensioned. The other ends of the mooring lines are pulled onto the offshore vessel 10 by winches (not shown) onboard the offshore vessel 10 and held in position by chain stoppers 86 as shown in Figure 2.

Figures 28 to 33 show the chain stoppers 86 on the bow in greater detail. Additionally, Figure 30 illustrates modification of the existing profile of the vessel to allow for the mooring chain 82 to pass over the edge of the vessel. Figures 34 and 35 illustrate stiffening arrangements for the deck and bulk head.

Figures 36 to 39 illustrate the chain stoppers 86 at the stern of the offshore vessel 10 in greater detail. The chain stoppers and the stiffening arrangements are similar in many respects to the arrangements of the bow of the offshore vessel Figures 56 to 60 illustrate how the various product and bunker lines are mounted at the bow of the offshore vessel 10. As will be appreciated from Figures 13 to 15, the product and fuel/bunker lines 18 approach the offshore vessel at an angle approximately normal to the deck of the offshore vessel. At a level above the lower deck 90 as shown in Figure 58, the product and ID:004521897 -14bunker lines 90 make a 90° turn and then proceed to be routed towards the various cargo tanks.

The foregoing describes only one embodiment of the present invention and modifications may be made thereto without departing from the scope of the present invention.

ID:004521897

Claims (8)

1. A system for managing one or more natural products obtained from an offshore platform, the system comprising: an offshore floating storage vessel linked to the offshore platform to enable the product(s) to be transferred from the platform and stored in the vessel, the vessel being moored adjacent to the offshore platform, the vessel further including personnel facilities; a personnel transfer bridge extending between the offshore platform and the offshore floating storage vessel to enable personnel to transfer between the two, the bridge being connected to the offshore platform and the offshore floating storage vessel and operable to accommodate variable loading conditions of the offshore floating storage vessel and variable weather conditions; and a shuttle vessel to periodically receive the stored product(s) and transfer it for further processing.

2. The system as claimed in claim 1 wherein the offshore floating storage vessel is in the form of a ship.

3. The system as claimed in claim 1 or claim 2 wherein a plurality of mooring lines, linked to the seabed, moor the offshore floating storage vessel adjacent to the offshore platform.

4. The system as claimed in any one of the preceding claims wherein the personnel facilities provided on the offshore floating storage vessel include accommodation for personnel operating the drilling rig. The system as claimed in any one of the preceding claims wherein the bridge comprises a plurality of telescopic sections.

6. The system as claimed in claim 5 wherein a first connection includes a rubber ring on which one of said telescopic sections sits so that universal pivoting of the section relative to the platform/vessel to which it is connected is permitted and in a second connection, the other of said telescopic sections is coupled to a support means on the platform/vessel to which the section is connected and the support means enables the bridge to ID: 004521897

16- be located and dislocated from communication with the platform/vessel that said one of the telescopic sections connects with. 7. The system as claimed in any one of the preceding claims wherein a control centre is further included in the offshore floating storage vessel for remotely monitoring and controlling operation of the offshore platform. 8. The system as claimed in any one of the preceding claims wherein the floating vessel may include means for performing initial conditioning or processing operations on the drilled product preparatory to discharge of the drilled product to the shuttle vessel. 9. A mooring apparatus including: a seabed anchor; a mooring line extending from the anchor for linking to a floating vessel and thereby limiting movement of the vessel away from the anchor; buoyancy means fixed to said mooring line intermediate its length such that said buoyancy means provides a force operative to reduce the distance between the vessel and the anchor. The mooring apparatus of claim 9 wherein, in situ, the buoyancy means is submerged below the water level. 11. The mooring apparatus of claim 9 or 10 wherein an additional buoyancy means is provided at the end of the mooring line remote from the seabed anchor. 12. The mooring apparatus of any one of claims 9 to 11 wherein a portion of the mooring line is elastically extendable. 13. A mooring apparatus including: a seabed anchor; a mooring line extending from the anchor for linking to a floating vessel and thereby limiting movement of the vessel away from the anchor; ID: 004521897 -17- buoyancy means fixed to said mooring line wherein, in use, the buoyancy means is submerged such that said buoyancy means provides a force operative to reduce the distance between the vessel and the anchor. 14. The mooring apparatus of claim 13 wherein, in situ, the buoyancy means is submerged below the water level. The mooring apparatus of claim 9 or 10 wherein an additional buoyancy means is provided at the end of the mooring line remote from the seabed anchor. 16. The mooring apparatus of any one of claims 9 to 11 wherein a portion of the mooring line is elastically extendable.

17. A system for managing one or more natural products obtained from an offshore platform substantially as herein before described with reference to the accompanying figures.

18. A mooring apparatus substantially as herein before described with reference to the accompanying figures. Aquila Management Services Pty Ltd By Freehills Carter Smith Beadle Registered Patent Attorneys for the Applicant 18 August 2004 ID: 004521897