Assembly of a vessel and a turret

Abstract

An assembly of vessel and turret is provided. The vessel comprises a moonpool and the turret is mounted in said moonpool for a rotation around a turret axis relative to the vessel. The turret comprises a chain table to which mooring lines are connected and through which risers are conveyed, and a turret table vertically spaced above the chain table and connected therewith by a connecting structure. The connecting structure comprises at least three vertically extending columns positioned such at angular intervals that radially outer sides of the columns are located in the vicinity of an outer circumference of the turret. The risers are conveyed through the chain table in such a way that riser sections above the chain table extend towards the turret table within an internal space of the columns.

Claims

1. An assembly of a vessel and a turret, wherein the vessel comprises a moonpool and wherein the turret is mounted in said moonpool for a rotation around a turret axis relative to the vessel, which turret comprises a chain table to which mooring lines are connected and through which risers are conveyed, and a turret table vertically spaced above the chain table and connected therewith by a connecting structure, wherein the connecting structure comprises at least three vertically extending columns positioned such at angular intervals that radially outer sides of the columns are located in a vicinity of an outer circumference of the turret and wherein the risers are conveyed through the chain table in such a way that riser sections above the chain table extend towards the turret table within an internal space of the columns, and wherein lateral sides of the columns, as viewed in a horizontal cross section, are defined by two straight lines extending radially outwards from the turret axis and enclosing an angle, an inner circle segment extending between said two straight lines concentrically around and at a distance from the turret axis, and an outer circle segment extending between said two straight lines concentrically around the turret axis and in a region of the outer circumference of the turret.

2. The assembly according to claim 1, wherein the columns at least in their lower parts connecting to the chain table define an internal space sealed against the surroundings.

3. The assembly according to claim 2, wherein the columns over their entire vertical extension between the chain table and turret table define an internal space sealed against the surroundings.

4. The assembly according to claim 3, and further comprising atmosphere control means provided for controlling the atmosphere within the internal space.

5. The assembly according to claim 3, and further comprising ventilation equipment coupled to the internal space.

6. The assembly according to claim 1, wherein each column comprises an access device configured to allow a person to pass through and into the internal space of the column.

7. The assembly according to claim 1, wherein the columns at a vertical spacing above the chain table are provided with support members configured to support the risers.

8. The assembly according to claim 7, wherein the support members are at least part of a horizontally extending bulk head.

9. The assembly according to claim 1, wherein emergency shut down valves for the risers or other equipment are located in a vicinity of the chain table or turret table.

10. The assembly according to claim 1, wherein the columns, at least in their lower parts connecting to the chain table, have a tapering shape with a wider part near to the chain table and a narrower part at a higher level.

11. The assembly according to claim 10, wherein the tapering shape at least is defined at the radially outer sides of the columns.

12. The assembly according to claim 11, wherein the risers enter the turret from below the chain table under at most a maximum angle which substantially corresponds with the tapering shape.

13. The assembly according to claim 1, wherein the mooring lines, as viewed in a vertical direction, are connected to the chain table at locations between the columns.

14. The assembly according to claim claim 1, and further comprising at least three columns.

15. The assembly according to claim 1, wherein the turret has a diameter between 15 and 20 meters and wherein a length of the straight lines between the inner and outer circle segments is between 4 and 6 meters.

16. The assembly according to claim 1, wherein the chain table comprises vertically extending bulk heads and wherein the lateral sides of the columns defined by the straight lines are prolongations of said bulk heads.

17. The assembly according to claim 16, wherein turret table comprises vertically extending bulk heads and wherein the lateral sides of the columns defined by the straight lines are prolongations of said bulk heads.

18. The assembly according to claim 14, wherein the turret has a diameter of about 17 meters and a length of the straight lines between the inner and outer circle segments is about 5 meters.

19. The assembly according to claim 1, wherein in the moonpool, substantially at a level of the turret table, a main bearing is provided between the turret and the vessel and wherein there is not provided an additional bearing at a lower level, or there is provided a fail-safe bearing, preferably a sliding bearing, at a lower level having cooperating bearing parts at the turret and at the vessel which under design operational conditions do not engage each other.

20. The assembly according to claim 1, wherein the risers comprise any type of riser configurations including steel, plastic or composite lazy wave risers.

21. The assembly according to claim 1 wherein the at least three vertically extending columns are positioned at regular angular intervals.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) Hereinafter aspects of the invention will be elucidated while referring to the drawings, in which:

(2) FIG. 1 illustrates a schematic vertical cross section of an assembly;

(3) FIG. 2 illustrates a schematic view according II-II in FIG. 1; and

(4) FIG. 3 illustrates the lazy wave riser concept.

DETAILED DESCRIPTION OF THE ILLUSTRATIVE EMBODIMENT

(5) In FIG. 1 a schematic cross-sectional representation is illustrated of an embodiment of an assembly in accordance with an aspect of the present invention. In a vessel 1 a moonpool 2 is provided in which a turret 3 by means of a main (upper) bearing 20 (which may have a twin design) is mounted for a rotation relative to the vessel around a central turret axis 4. The turret 3 in its lower part comprises a chain table 5. Mooring lines (such as mooring chains or wires or a combination thereof) 6 are connected to the chain table 5 (directly or indirectly in a manner known per se and not further discussed here) and thus keep the turret 3 moored in a specific rotational position with respect to a fixed point, such as the sea bed (although generally slight horizontal movements of the turret 3 will be allowed).

(6) Such a design generally will be used to moor the vessel 1 while allowing it to weathervane around the turret 3, as is well-known in the field of oil and gas production.

(7) The chain table 5 further defines an access for risers 7 which are conveyed through dedicated passages in the chain table and upward to a turret table 8 which is located in the turret at a higher level, vertically spaced from the chain table 5. The turret table 8 may support equipment, such as manifolds and swivels, needed for the operation of the turret 3, for example a lift 29 for pulling in a riser 7 and mooring lines 6.

(8) The risers 7 (which may comprise a combination of lead-in and flex-joint members 26 near to the chain table 5 for leading in a riser 7 and for preventing an excessive degree of bending of the riser 7) generally convey oil or gas (or even water) from (or towards) an underwater source (for example a well) to an upper part of the turret 3, for example swivels not represented for establishing a rotatable connection with vessel-mounted equipment or piping.

(9) The turret 3 also may support umbilicals 36 which extend downwardly through and beyond the chain table 5. The chain table 5 and turret table 8 are interconnected by a connecting structure comprises at least three columns 9 which extend vertically between the chain table 5 and the turret table 8. In FIG. 1 only one of these columns 9 has been shown.

(10) These columns 9 are positioned at (for example regular) angular intervals (as will appear below while referring to FIG. 2) in such a manner that radially outer sides 10 of the columns 9 are located in the vicinity (or even define part) of an outer circumference of the turret 3. The risers 7 are conveyed through the chain table 5 in such a manner that sections 7′ thereof above the chain table 5 extend upwards towards the turret table 8 within an internal space 11 of the columns 9.

(11) It is noted that in FIG. 1 a riser ending 12 of the riser 7 is shown. During operation a piping (not illustrated) will be connected to said riser ending 12 for establishing a fluid path towards the turret table 8 (and other equipment, such as a swivel). Within the context of the present invention the indication ‘riser’ or ‘riser section’ also indicates such piping.

(12) In the illustrated embodiment the columns 9 over their entire vertical extension between the chain table 5 and turret table 8 define the internal space 11 sealed (shielded) against the surroundings. In other embodiments not illustrated the columns 9 only in their lower parts (for example extending from the chain table 5 upwards to a level somewhat above sea level) define such a sealed internal space 11.

(13) Ventilation equipment 22, e.g. ventilation openings with or without door(s) or the like to open and close the opening(s), fan(s), blower(s), air handler(s), etc., and combinations thereof, may be provided for controlling the atmosphere within the internal space (for example for discharging hazardous or dangerous gases or mixtures of gas/oil with air).

(14) As illustrated schematically by a person 13, the dimensions of the internal space 11 (specifically its diameter) are sufficient to allow access of a person into said internal space. An access door 14 to the internal space 11 may be provided, as well as stairways 35 or ladders (here partly illustrated outside of the column 9, but possibly also inside the column).

(15) At a vertical spacing above the chain table 5 a horizontally extending bulk head 15 is provided in the column 9 which is provided with a support member (such as a well-known hang-off support) 16 for the riser 7 (or riser section 7′). The bulk head 15 also may support an emergency shut down valve (indicated schematically at 17) or other equipment located in the vicinity of the support member 16 or riser ending 12.

(16) As illustrated clearly in FIG. 1, the column 9 in its lower part has a tapering shape 18 with a wider lower part and a narrower upper part. The taper may substantially correspond with an angle α under which the riser 7 enters the chain table 5. In the illustrated embodiment the column 9 tapers only at its radially outer side 10, but in other embodiments not illustrated it (also) may taper at other sides.

(17) Next reference is made to FIG. 2 which basically is a schematic representation of a view downwards according to II-II in FIG. 1. It shows three columns 9 of which lateral sides 19 are defined by two straight lines 19′ extending radially outwards from the turret axis 4 and enclosing an angle β (illustrated for the left column 9 in FIG. 2) which in this embodiment is taken as 60 degrees for illustration. The columns 9 further are defined by an inner circle segment 21 extending between said two straight lines 19′ concentrically around and at a distance from the turret axis 4, and an outer circle segment 23 extending between said two straight lines 19′ concentrically around the turret axis 4 and in the region of the outer circumference of the turret 3 (this outer circle segment 23 corresponds with the radially outer side 10 of a column 9). Thus, a cross section of each column 9 corresponds with a (pie-shaped) sector delimited by the sides 19 and the inner and outer circle segments 21 and 23.

(18) In the illustrated embodiment with three columns 9 there thus are three sectors in which the angle β is about 60 degrees. Between these sectors three additional sectors 24 are located (in this embodiment each equally spanning an angle of 60 degrees) and the mooring lines 6 (of which the number may vary) are connected to the chain table 5 at these sectors 24, thus between the columns 9 as viewed in a vertical direction.

(19) The angles mentioned may vary, and the angles spanned by the columns (sectors) 9 may differ from the angle spanned by the additional sectors 24. In yet another embodiment the angles spanned between successive columns 9 may vary (but preferably in accordance with a regular pattern, for example a first angle between a first and second column, a different second angle between the second and a third column, again the first angle between the third and a fourth column and so forth).

(20) The chain table 5 may comprises vertically extending bulk heads which are located such that the sides 19 of the columns 9 are defined by upper prolongations of said bulk heads (which as a result in FIG. 2 also are indicated by reference 19). Said prolongations also may coincide or correspond with vertically extending bulk heads of the turret table 8 (which then likewise would be indicated by the reference 19).

(21) In the illustrated embodiment of the assembly in which in the moonpool 2, substantially at the level of the turret table 8, a main (upper) bearing 20 is provided between the turret 3 and the vessel 1, there is no additional bearing provided at a lower level. However, in an alternative embodiment a lower bearing or a fail-safe bearing 25, preferably a sliding bearing, may be provided at a lower level, preferably substantially at the level of the chain table 5, having cooperating bearing parts 26,27 (for example a slide ring and slide pads) at the turret 3 and at the vessel 1 which under design operational conditions do not (or may not) engage each other.

(22) Finally referring to FIG. 3, it is noted that the risers 7 may comprise any type of riser configurations and in particular steel, plastic or composite lazy wave risers. The assembly allows the use of such a riser configuration in a very effective manner without introducing detrimental loads in the turret. Further it avoids the risk of congestion, or even clashes between these lazy wave risers when hung-off above the turret table, as is typically done in turrets with flexible risers. It also allows (deliberately) angled entry of risers without the need to be pulled above water level up to or above the turret table.

(23) The invention is not limited to the embodiments described before, which may be varied widely within the scope of the invention as defined by the appending claims.