Disconnectable bow turret

Abstract

The invention concerns a vessel (1) for storing and/or producing hydrocarbons and a buoyant turret buoy (6) to be connected to the vessel (1). The outer surface of the bow (2) of the vessel (1) comprises a receiving structure (5) for connecting a buoyant turret buoy (6) to the bow (2). The main part of the receiving structure (5) protrudes from the lower part (4) of the bow (2) in the vessel's (1) direction of travel and an interface of the receiving structure (5) is complementary to an interface of a connecting section (17) of the buoyant turret buoy (6). Further the lower part (4) of the bow (2) is below the water line (w) during connection of the buoyant turret buoy (6) at sea. The invention also concerns a method for connecting the buoyant turret buoy (6) to receiving structure (5) of the vessel (1).

Claims

1. A method for connecting a buoyant turret buoy located at sea to a receiving structure of a bow of a vessel for storing and/or producing hydrocarbons, wherein the vessel comprises a deck and a hull, wherein the hull further comprises a bow having an upper part and a lower part, wherein the bow further comprises a receiving structure fixed to the bow by welding for connecting a buoyant turret buoy to the bow, such that the receiving structure protrudes from an outer surface of the bow in the vessel's direction of travel, and wherein a minor part of the receiving structure protrudes from the upper part of the outer surface of the bow, while a main part of the receiving structure protrudes from the lower part of the outer surface of the bow, wherein an interface of the receiving structure is complementary to an interface of a connecting section of the buoyant turret buoy, and wherein the upper part of the bow is arranged above a water line and the lower part of the bow is arranged below the water line during connection and/or disconnection of the buoyant turret buoy at sea, and wherein the turret buoy comprises a buoyancy section for making the buoyant turret buoy neutrally or positively buoyant when submerged in a body of water and a turret shaft section for guiding one or more risers therein, a connecting section for connecting the buoyant turret buoy to the receiving structure of the bow of the vessel, wherein an interface of the connecting section is complementary to an interface of the receiving structure, and wherein the method comprises the steps of: a) connecting a winch wire hanging from a winch fixed to the vessel to a pick-up assembly connected to the buoyant turret buoy floating at or below the water line of a body of water, b) lifting the buoyant turret buoy by the winch until the connecting section of the buoyant turret buoy is in a position where an upper end of the connecting section is in line with, or near in line with, an upper end of the receiving structure, and c) locking the buoyant turret buoy to the receiving structure by utilizing at least one locking arrangement fixed to the upper end of the receiving structure and at least one attaching arrangement fixed to the upper end of the connection section of the buoyant turret buoy, d) connecting the winch wire to a mooring line, e) pulling the mooring line through a mooring line connection and a mooring line stopper, until the mooring line is tightened, f) removing the part of the mooring line which has passed through the mooring line stopper and the mooring line connection, g) repeating steps d) to f) for all the mooring lines, h) connecting the winch wire to a lifting and torque section attached to a vertically extending channel within or above an upper end of the turret shaft section of the buoyant turret buoy, wherein the buoyant turret buoy comprises at least one riser attached to the lifting and torque section, i) lifting the vertically extending channel comprising the lifting and torque section and the at least one riser through a rotary table protruding from the upper part of the bow using the winch, j) attaching the lifting and torque section to a hang off structure on or above a rotary table, and k) connecting a swivel arrangement to the at least one riser.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a perspective side view of a buoyant turret buoy connected to a receiving structure on a vessel according to the invention.

(2) FIG. 2 is a perspective top view of a buoyant turret buoy to be connected to a receiving structure on a vessel according to the invention.

(3) FIGS. 3 a), b), c) and d) show a perspective side view of the process of connecting a buoyant turret buoy to a receiving structure on a vessel according to the invention.

(4) FIGS. 4 a), b), c, and d) show a perspective side view of a buoyant turret buoy connected to a receiving structure of the vessel and the process of connecting risers to a swivel arrangement according to the invention.

(5) FIGS. 5 a), b) and c) show a perspective side view of disconnecting a buoyant turret buoy from a receiving structure of a vessel according to the invention.

(6) FIGS. 6 a), b), c) and d) show a perspective side view of connecting mooring lines to a buoyant turret buoy situated on the receiving structure of the vessel according to the invention.

(7) FIGS. 7 a), b), c) and d) show a perspective side view of connecting risers to a buoyant turret buoy connected to the receiving structure of a vessel according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

(8) FIG. 1 shows an embodiment of the mooring arrangement for inter alia mooring a vessel 1 connected to a buoyant turret buoy 6. The buoyant turret buoy 6 is connected to a protruding receiving structure 5 fixed to the outer surface of the bow 2 of the vessel 1. The vessel 1 comprises a deck (D) having a protruding deck structure 11, and a hull comprising a bow 2 having an upper part 3 and a lower part 4, where the lower part is defined as the part of the hull situated below the water line (w) during connection of the buoyant turret buoy 6 to the receiving structure 5. As seen in FIG. 1, almost the entire bulk, for example between 70% to 99.5% of the bulk of the receiving structure 5, protrudes from the lower part 4 of the bow 2, i.e. below water level (w) during connection and/or disconnection of the buoyant turret buoy 6. The receiving structure 5 comprises a recess 7 serving as an opening for receiving the turret buoy 6. The recess 7 is illustrated in FIG. 2.

(9) The interface of the receiving structure 5 is complementary to the interface of the buoyant turret buoy 6. In the embodiment shown in FIG. 1 the receiving structure 5 displays a cavity 8 at the structure's lower end 5b. The buoyant turret buoy 6 comprises a connecting section 17 which in FIG. 1 includes a hook 17a situated at the buoy's lower end 6b. The hook 17a has a complementary shape to the cavity 8. Further, the upper part of the buoyant turret buoy 6 comprises an incision 17b having a complementary shape as the protrusion at the structure's upper end 5a, thus achieving a stable and tight fit therebetween.

(10) It can further be seen from FIG. 1 that the buoyant turret buoy 6 is locked to the receiving structure 5 through a locking jack 9. The locking jack 9 is situated at the structure's upper end 5a and locks to a vertically protruding hank 23 or similar situated at the buoy's upper end 6a. The resulting lock 9,23, combined with the structure of the interfaces of both the receiving structure 5 and the buoyant turret buoy 6, provides a reliable and stable connection of the buoyant turret buoy 6 to the receiving structure 5 of the vessel 1 during tough weather conditions like storms. Further, the locking jack 9 provides an easy disconnection of the buoyant turret buoy 6 in that the locking jack 9 is simple to open.

(11) The buoyant turret buoy 6 has a buoyancy section 24 enabling the turret buoy 6 to float at a designated submerged water depth or to float on the water surface when the turret buoy 6 is not attached to the vessel 1.

(12) Since the buoyant turret buoy 6 has risers 14 and mooring lines 13 attached thereto, the buoyancy of the turret buoy 6 matches the total weight of the turret buoy 6, including the risers 14 and mooring lines 13, to ensure equilibrium at the required submerged depth.

(13) Further, the buoyant turret buoy 6 has a turret shaft section 15 comprising mooring lines 13 attached at its lower section 16. When the turret buoy 6 is connected to the vessel 1, the mooring lines 13 moors the vessel, 1 wherein the turret shaft section 15 allows the vessel 1 to weathervane during storage and production of hydrocarbons. The turret shaft section 15 has an integrated lower section 16 onto which the mooring lines 13 are connected via a mooring line connection 13a. A mooring line stopper 13b allows the mooring lines 13 to be tightened (see also FIG. 6).

(14) The turret shaft section 15 further comprises an extendable rotatable channel 15a having a lifting and torque section 20. The lifting and torque section 20 has risers 14 connected thereto. The channel 15a can slide inside the turret shaft section 15 along guides which can lock the rotation of the channel 15a to the turret shaft section 15. The risers 14 attached to the channel 15a are thus kept geostationary and are transferring the torsion movement to the inner part of the risers 14 when the vessel 1 weathervanes.

(15) FIG. 1 illustrates the risers 14 connected to a swivel arrangement 21 attached to the protruding deck structure 11 on the vessel 1, well above the loaded draft of the vessel 1. As can be seen from the figure, the lifting and torque section 20 is attached to a hang-off structure 22 on or above the rotary table 10. Thus, the risers 14 are kept geostationary in this position while the vessel 1 weathervanes. Further, a winch 12 is situated on the deck (D) with a winch wire 18 connected thereto. The wire 18 is configured to inter alia move the swivel arrangement 21 above the risers 14 to connect them together for production of hydrocarbons.

(16) The winch 12 comprising the wire 18 is further configured to move and lift the buoyant turret buoy 6 from a submerged position at sea to the receiving structure 5 of the vessel 1 where the buoyant turret buoy 6 is connected to the receiving structure 5, which is illustrated in more detail in FIG. 3.

(17) A top view of the buoyant turret buoy 6 including mooring lines 13 and risers 14 to be connected to the receiving structure 5 can be seen in FIG. 2. The figure shows the bow 2 of the vessel 1 comprising the protruding receiving structure 5. The receiving structure 5 displays a recess 7 for receiving the connecting section 17 of the buoyant turret buoy 6. Further the receiving structure 5 displays a cavity 8 compatible with the hook 17a of the turret buoy 6. As shown, the turret shaft section 15 with risers 14 is positioned substantially central inside the turret buoy 6.

(18) As can be seen from the figure, only the interface at one side of the turret buoy 6 matches the interface of the receiving structure 5 of the vessel 1.

(19) FIG. 3 (a) to (d) illustrates the method for connecting a buoyant turret buoy 6 in its idle position, e.g. at 30 meters' depth, to a receiving structure 5 on a vessel 1. As can be seen, the main part, for example between 70% and 99.5% of the receiving structure 5, is below the water level (w) during connection. The turret buoy 6 is submerged, having a pick-up assembly 19 connected to the turret buoy 6. A part of the pick-up assembly 19 is floating on top of the water level (w) and is picked up from the winch wire 18 hanging from the vessel's 1 winch 12. The winch 12 pulls the turret buoy 6 towards the receiving structure 5. The vessel's 1 heading should be controlled to match with the heading of the turret buoy 6. Finally, the turret buoy 6 is pulled-in and locked to the receiving structure 5 by the locking jack 9 on the receiving structure 5 and the protruding hank 23 on the turret buoy 6 as shown in FIG. 3 (d). During the connection of the buoyant turret buoy 6 to the vessel 1, a minor part of the buoyant turret buoy 6 is raised above the water level (w), for example between 0.5% and 30%.

(20) After the turret buoy 6 is locked to the vessel 1, the mooring lines 13 extending to the seabed are tightened if needed, and the connection of the risers 14 to the swivel arrangement 21 can follow as seen in FIG. 4.

(21) FIG. 4 (a) to (d) illustrates how the risers 14 are connected to the swivel arrangement 21.

(22) Step (a): The turret buoy 6 is connected to the receiving structure 5 of the vessel 1. The turret shaft section 15 (shown in FIG. 1) on the turret buoy 6 comprises risers 14 connected to the lifting and torque section 20.

(23) Step (b): The winch wire 18 is connected to the lifting and torque section 20 situated on the extending channel 15a.

(24) Step (c): The lifting and torque section 20 is lifted from a resting position 25 up to a rotary table 10 (shown in FIG. 1). The lifting and toque section 20 comprising the risers 14 is attached to a hang-off structure 22 (shown in FIG. 1) on or above the rotary table 10. The rotary table 10 allows the vessel 1 to weathervane while the risers 14 are kept geostationary.

(25) Step (d): The winch wire 18 moves the swivel arrangement 21 into position above the risers 14 to connect the swivel arrangement 21 to the valve arrangement on the risers 14. The risers 14 may be locked to the swivel arrangement 21 by using bolts.

(26) After flow lines/risers 14 are connected to the swivel arrangement 21, the FPSO/FSO can start operating.

(27) FIG. 5 (a) to (c) illustrates the disconnection of the turret buoy 6 from the receiving structure 5 of the vessel 1.

(28) Step (a): The flow lines/risers 14 bolted to the swivel arrangement 21 are disconnected and the swivel arrangement 21 is moved to its stored position on deck (D).

(29) Step (b): The risers 14 are removed from the hang-off structure 22 and lowered by the extending channel 15a to its resting position 25 at the upper end 6a of the turret buoy 6. A pick-up assembly 19 is connected to the turret buoy 6 and the turret buoy 6 is now prepared for disconnection.

(30) Step (c): The turret buoy 6 is disconnected by opening the locking jack 9. The disconnection may occur within a few seconds.

(31) After disconnection, the buoyant turret buoy 6 is in an idle position and may float submerged at e.g. 30 meters' depth, but can also be left floating on the water surface. When the turret buoy 6 is left in its idle position floating on the water surface it will simplify the pick up and buoy connection to the receiving structure 5 compared to when the turret buoy 6 is submerged. This idle position may be adopted for operations where the disconnect is related to various stages of operations, while the submerged idle position may be adopted for operations where the disconnect is related to avoid severe weather conditions.

(32) The risers 14 comprise a valve arrangement which is connected to the swivel arrangement 21 during operation. This valve arrangement is closed by e.g. closing valves and/or Emergency Shut Down (ESD) valves 26. These valves may be protected by a protective cover when the risers 14 are not operative, including the time when turret buoy 6 is submerged. When the risers 14 are to be connected to the swivel arrangement 21, the protective cover, closing valves and ESD valves 26 are removed by the winch wire 18 and stored on deck (D) during operation of the risers 14. Before the turret buoy 6 is to be removed from the vessel 1, the closing valves and ESD valves 26, and optionally the protective cover, are reconnected on to the risers 14 before lowering the risers 14 and the channel 15a to the resting position 25.

(33) FIG. 6 illustrates the connection of mooring lines/mooring chains 13 to a turret buoy 6 the first time the turret buoy 6 arrives at the production area where the production of hydrocarbons will occur.

(34) Step (a): The vessel 1 has the turret buoy 6 locked thereto.

(35) Step (b): The winch 12 utilized the winch wire 18 to pull in the mooring lines 13 one by one through the mooring line stopper 13b and the mooring line connection 13a.

(36) Step (c): The mooring lines 13 are pretensioned.

(37) Step (d): The extra length after the mooring line stopper 13b is cut off and removed. The mooring lines 13 may later be retensioned by using the same winch 12 if needed.

(38) FIG. 7 (a) to (d) illustrates the connection of risers 14 to the turret buoy 6 when locked to the vessel 1. The connection of the risers 14 occurs after the mooring lines 13 have been connected to the turret buoy 6 as shown in FIG. 6.

(39) Step (a): The winch wire 18 is lead through the turret shaft section 15 (shown in FIG. 1) and connected to a riser 14 situated below the turret buoy 6.

(40) Step (b): The winch 12 pulls in the riser 14 and connects the riser 14 to the lifting and torque section 20 of the turret shaft section 15.

(41) Step (c): Steps (a) to (b) are repeated until all the risers 14 are connected to the lifting and torque section 20.

(42) Step (d): Closing valves and ESD valves 26 are connected to the valve arrangement on top of the risers 14. A protective structure can be placed on top thereof covering the valves.

(43) After the process described in FIG. 7, the risers 14 are ready to be connected to the swivel arrangement as illustrated in FIG. 4.

(44) It should be understood that the processes described in FIG. 3-7 are operations that can be automated by the use of sensors, receivers, distance meters, angle meters and the like.

(45) In the preceding description, various objects, features, aspects and advantages according to the invention have been described with references to the illustrative embodiments. For purposes of explanation, specific numbers, systems and configurations were set forth in order to provide a thorough understanding of the system and its workings. However, this description is not intended to be construed in a limiting sense. Various modifications and variations of the illustrative embodiment, as well as other embodiments of the system, which are apparent to persons skilled in the art to which the disclosed subject matter pertains, are deemed to lie within the scope of the present invention.

LIST OF REFERENCE NUMERALS/LETTERS

(46) 1 vessel 2 bow 3 upper part of the bow/upper bow 4 lower part of the bow/lower bow 5 protruding receiving structure/buoy support 5a upper end of the receiving structure 5b lower end of the receiving structure 6 buoyant turret buoy 6a upper end of the buoyant turret buoy 6b lower end of the buoyant turret buoy 7 recess/buoy opening 8 cavity 9 locking arrangement/buoy lock/clamp 10 rotary table 11 protruding deck structure 12 winch 13 mooring line (of the buoyant turret buoy) 13a mooring line connection 13b mooring line stopper 14 riser 15 turret shaft section (of the turret buoyant buoy)/turret shaft 15a extending channel of the turret shaft section 16 lower section of the turret shaft 17 connecting section/connecting face (of the buoyant turret buoy)/radial extension 17a hook of the connecting section 17b incision of the connecting section 18 winch wire 19 pick-up assembly/pick up cable 20 lifting and toque section 21 swivel arrangement 22 hang-off structure 23 attaching arrangement/hank 24 buoyancy section of the buoyant turret buoy 25 resting position 26 closing valves/ESD valves D deck w water line/water level