Disconnectable production dock (DPD) for turret free disconnectable weather vaning FPSO

Abstract

System for mooring a large vessel for production of hydrocarbons, such vessel for example being a FPSO vessel, the mooring system comprising at least two floating bodies of the hang-off type, moored by means of differentiated compliance spread anchoring system to the sea bed, allowing partly weathervaning of the large vessel; a riser system extending from the sea bed to each the floating bodies, and means for transfer of fluids from the two floating bodies to the large vessel, the floating bodies and the large vessel being provided with locking means, locking floating bodies to the large vessel at the bow and the stern of the vessel in a mechanically rigid manner, thus providing a integrated, rigidly fixed unit comprising the large vessel and the floating bodies.

Claims

1. A system for mooring a vessel for production of hydrocarbons, the system comprising: at least two floating bodies, moored by means of a differentiated compliance spread anchoring system to a sea bed, allowing partial weathervaning of the vessel; at least two riser systems; and a fluid transfer system configured to transfer fluids from the at least two floating bodies to the vessel, wherein a first one of said riser systems extends from the sea bed to a first one of said floating bodies, wherein a second one of said riser systems extends from the sea bed to a second one of said floating bodies, wherein the at least two floating bodies and the vessel are provided with a locking device configured to lock the at least two floating bodies to the vessel at a bow and a stern of the vessel in a mechanically rigid manner, thus providing an integrated, rigidly fixed unit comprising the vessel and the at least two floating bodies, wherein the locking device comprises a releasable groove and tongue connection, forming a rigid interconnection preventing relative motion of the vessel and the at least two floating bodies, and wherein the at least two floating bodies comprise four floating bodies, said four floating bodies being rigidly interconnected by longitudinal, transverse bracings together with a truss work interconnecting pairs of diametrically positioned floating bodies.

2. The system according to claim 1, wherein the groove is arranged on the vessel and the corresponding tongue is arranged on the at least two floating bodies, the groove being open downwards and the tongue being in the form of an upwards extending fin or flange.

3. The system according to claim 1, wherein the fluid transfer system is configured to communicate with a corresponding fluid transfer system on the vessel, the fluid transfer system being a quick release hard pipe system provided with flanges/hinges.

4. The system according to claim 1, wherein the vessel is an FPSO vessel.

5. A method for mooring a floating vessel to at least two floating bodies, the method comprising: providing at least two floating bodies; mooring each of the at least two floating bodies to a sea bed by means of a plurality of mooring lines; providing at least two riser systems, wherein a first one of said riser systems extends from the sea bed to a first one of said floating bodies and a second one of said riser systems extends from the sea bed to a second one of said floating bodies; positioning the floating vessel adjacent to or over and between the at least two floating bodies, whereupon the at least two floating bodies are pulled in towards the vessel, establishing a spread mooring for the vessel; providing the at least two floating bodies and the vessel with a locking device; and the at least two floating bodies to the vessel at a bow and a stern of the vessel in a mechanically rigid manner, thus providing an integrated, rigidly fixed unit comprising the vessel and the at least two floating bodies, wherein the locking device comprises a releasable groove and tongue connection, forming a rigid interconnection preventing relative motion of the vessel and the at least two floating bodies, and wherein the at least two floating bodies comprise four floating bodies, the method further comprising rigidly interconnecting said four floating bodies using longitudinal, transverse bracings together with a truss work interconnecting pairs of diametrically positioned floating bodies.

6. The method according to claim 5, wherein the locking step further comprises deballasting the at least two floating bodies when the at least two floating bodies are in position adjacent the vessel, thereby moving the at least two floating bodies upwards to engage the groove and tongue connection thereby establishing the rigid, mechanical connection with the vessel.

7. The method according to claim 5, wherein the groove is arranged on the vessel and the corresponding tongue is arranged on the at least two floating bodies, the groove being open downwards and the tongue being in the form of an upwards extending fin or flange.

8. The method according to claim 5, the method further comprising providing each of the at least two floating bodies with a fluid transfer system communicating with a corresponding fluid transfer system on the vessel, the fluid transfer system being a quick release hard pipe system provided with flanges/hinges.

9. The method according to claim 5, wherein the floating vessel is an FPSO vessel to the at least two floating bodies.

Description

SHORT DESCRIPTION OF THE DRAWINGS

(1) In the following an embodiment of the invention will be described in further details, referring to the drawings, wherein:

(2) FIG. 1 shows a top view of a vessel for production of hydrocarbons such as oil and gas through a riser system, the vessel being moored to the sea bed by means of a mooring system;

(3) FIG. 2 shows a view in perspective of the vessel shown in FIG. 1, showing both types of riser systems 13,14;

(4) FIG. 3 shows a view in perspective of a vessel provided with a floating dock riser and mooring system according to the present invention;

(5) FIG. 4 shows schematically a top view of the floating dock according to the present invention; and

(6) FIG. 5 shows a side view of the floating dock shown in FIG. 4.

DESCRIPTION OF THE INVENTION

(7) FIG. 1 shows schematically a top view of a vessel 10 for production of hydrocarbons, such as oil and/or gas. The vessel 10 is moored to a sea bed 11 by means of a spread mooring comprising two front set of mooring lines 12 extending downwards and outwards from the bow of the vessel 10, and two corresponding aft set of mooring hawsers extending downwards and outwards from the rear of the vessel 10.

(8) Further, as shown both in FIGS. 1 and 2, the vessel 10 is provided with four sets of risers 13,14, extending between the sea bed 11 and the vessel 10. Two of the sets of risers 13 are provided with a submerged buoy 15 to compensate for possible vertical and/or horizontal motion of the vessel 10. The risers 13,14 are attached to the vessel 10 by means of a riser attachment arrangement 17.

(9) FIG. 3 shows schematically in perspective a hull 10 provided with a hull/dock connection 16 and a floating dock 17, such floating dock 17 being moored to the sea bed by means of several dock moorings 12. The floating dock 17 is in the form of a buoyant body. Further, several risers 13, 14 are terminated at the deck of the floating dock 17. Further, the system comprises a fluid transfer system 19 for transfer of the hydrocarbons from the riser termination on the deck of the floating dock to the vessel 10. The fluid transfer system 19 is in communication with a corresponding fluid transfer system 18 on the vessel 10. the fluid transfer system 19 being a quick release hard pipe system provided with flanges/hinges.

(10) The vessel 10 is provided with attachment means 16, rigidly fixed to the hull side of the vessel 10. Such attachment means 16 may for example be in the form of a groove type connection, while the floating dock is provided with a corresponding tongue means rigidly fixed to the floating dock 17, the two connecting means thereby providing a groove and tongue connection of a rigid type, providing a rigid structure comprising the vessel 10 and the floating bodies 17 when the floating dock 17 is in locking engagement with the vessel 10. It should be appreciated that during the positioning of the floating bodies 17 with respect to the vessel 10, temporary hawsers may be used on order to pull the floating bodies 17 sideways into position with respect to the vessel 10. Once a floating body 17 is in proper position along the hull side of the vessel 10, the floating body 17 may be de-ballasted and/or the vessel 10 ballasted, so that the tongue engages the groove, establishing a rigid connection.

(11) The hull/floating dock connection 16 is configured in such way that the floating dock 17 may be quickly disconnected from the vessel 10. The connection 16 may for this purpose be of a groove and tongue type. It should be appreciated however, that the connection between the vessel and the floating dock may be of any other suitable mechanical type.

(12) Preferably, the connection may be of a type based on thrust upwards, provided by means of buoyancy from the floating dock 17, the only thrust producing point on the vessel 10 being through the contact 16 above sea level between the vessel 10 and the floating dock 17.

(13) FIGS. 4 and 5 show schematically one embodiment of a floating dock 17, in accordance with the present invention. The floating dock 17 comprises four buoyant bodies 20, the four bodies 20 being interconnected by means of transverse and longitudinal stiffeners or braces 21 and also of diagonally arranged trusses 19. As shown in FIG. 5, the trusses and/or braces are arranged at the lower end of the buoyant bodies 20.

(14) According to the present invention, the idea is to use a standard FPSO hull, with local adoptions around the connection areas to handle the mooring forces. The mooring will be a compliant system allowing for partly weathervaning. The offloading system will allow for an even larger offloading sector with its turn-table. The hang-off/mooring unit may be based on the principle of the Seadock system, in that case it is recommend having two units (i.e. one in bow and one in stem). Alternatively, there may be four smaller units (i.e. 2 at the bow and 2 at the stern). In both cases, the units need to be connected to form a rigid body motion.

(15) The new elements is the combination of various systems to build a new floating production unit that allows for quick disconnection in case of extreme weather (e.g. hurricanes in Gulf of Mexico). While the various elements forming the assembled unit according to the present invention may be known per se, the combined integration and system adoption of hull design, operation, and riser/mooring hang-off unit, and offloading system are unique.

(16) The floating body/bodies may be provided with a fendering system of any suitable type. Since such fendering systems are well known by the person skilled in the art, thus the fendering system will not disclosed or described in further details.

(17) As shown in the Figures, the floating bodies are preferably of a type which is intended to extend under the hull and not intended to be in supporting contact with the hull bottom of the vessel.