Offshore top site system

Abstract

The invention relates to an offshore top site system comprising a subsea facility, a floating unit arranged above the subsea facility and at least one transportation line extending between the subsea facility and the floating unit. The transportation line comprises a catenary riser section and comprises an uppermost end and a top site section with a lowermost end. The catenary riser section and the top site section are in flow connection with each other. The transportation line further comprises a connecting portion preferably arranged within a vertical floating unit zone and between the top site section and the uppermost end of the riser section. The connection portion is pivotally connected to the floating unit. The connection portion is preferably pivotally connected to the floating unit such that at least a major part of pulling force from the riser section is alleviated by the connection to the floating unit.

Claims

1. An offshore top site system comprising a floating unit configured to float at a water line and at least one transportation line extending from the floating unit, the floating unit has a bottom facing downwards and an outer periphery of the bottom defining a horizontal periphery of a vertical floating unit zone, the transportation line comprises a catenary riser section with an uppermost end and a top site section with a lowermost end, the catenary riser section and the top site section being in flow connection with each other, the catenary riser section has a length of at least about 1500 m, the transportation line further comprises a connection portion arranged between the top site section and the uppermost end of the riser section, the connection portion being pivotally connected to the floating unit, such that at least a major part of pulling force from the riser section is borne by the connection portion, wherein the connection portion between the uppermost end of the catenary riser section and the lowermost end of the top site section comprises a rigid section that is substantially nonlinear with respect to longitudinal axes of the catenary riser section and the top site section.

2. The offshore top site system as claimed in claim 1, wherein at least about 75% of a weight of the catenary riser section determined in water is transferred to the floating unit via the connection portion.

3. The offshore top site system as claimed in claim 1, wherein essentially all of a weight of the catenary riser section determined in water is transferred to the floating unit via the connection portion.

4. The offshore top site system as claimed in claim 1, wherein the catenary riser section has a length of at least about 2000 m.

5. The offshore top site system as claimed in claim 1, wherein at most about 25% of a weight of the catenary riser section is borne by buoyancy module(s).

6. The offshore top site system as claimed in claim 1, wherein the catenary riser section is free of any buoyancy module.

7. The offshore top site system as claimed in claim 1, wherein the connection portion is arranged outside the vertical floating unit zone.

8. The offshore top site system as claimed in claim 1, wherein the floating unit has an outer frame defining the outer periphery of the bottom, wherein the connection portion is pivotally connected to the floating unit at its outer frame.

9. The offshore top site system as claimed in claim 1, wherein the connection portion is arranged within the vertical floating unit zone.

10. The offshore top site system as claimed in claim 1, wherein the connection portion is arranged below the bottom of the floating unit.

11. The offshore top site system as claimed in claim 1, wherein the connection portion is arranged above the bottom of the floating unit.

12. The offshore top site system as claimed in claim 1, wherein the catenary riser section comprises two or more sub sections which sub-sections are different from each other.

13. The offshore top site system as claimed in claim 1, wherein the catenary riser section and the top site section of the transportation line are connected to each other via respective end-fittings, wherein at least one of the respective end-fittings provides the connection portion pivotally connected to the floating unit.

14. The offshore top site system as claimed in claim 1, wherein the catenary riser section and the top site section of the transportation line are connected to each other via respective end-fittings and with one or more intermediate transition pieces, wherein at least one of the transition pieces provides the connection portion pivotally connected to the floating unit.

15. The offshore top site system as claimed in claim 14, wherein the at least one of the transition pieces is shaped as a pull-head.

16. The offshore top site system as claimed in claim 1, wherein the floating unit is a vessel having a hull with a bow and a stern.

17. The offshore top site system as claimed in claim 16, wherein the connection portion is pivotally connected to the vessel.

18. The offshore top site system as claimed in claim 16, wherein the connection portion is pivotally connected to the vessel by being directly and pivotally connected to the bow.

19. The offshore top site system as claimed in claim 16, wherein the vessel comprises a load support shelf connected to and protruding from the hull, wherein the connection portion is pivotally connected to the vessel by being pivotally connected to the load support shelf.

20. The offshore top site system as claimed in claim 16, wherein the vessel comprises an opening through the hull, the catenary riser section extends through the opening in the hull and the connection portion is pivotally connected to the floating unit by being connected to an internal bearing structure of the vessel.

21. The offshore top site system as claimed in claim 1, wherein the connection portion is pivotally connected to the floating unit using one or more tether lines.

22. The offshore top site system as claimed in claim 1, wherein the connection portion is pivotally connected to the floating unit via at least one non-elongating connection.

23. The offshore top site system as claimed in claim 1, wherein the connection portion is pivotally connected to the floating unit using at least one tether line, the tether line is connected to the floating unit in a connection point, the system further comprises a bell mouth mounted to adjust a pivotal movement of the tether line.

24. The offshore top site system as claimed in claim 1, wherein the system further comprises a hanging support structure arranged below the bottom of the floating unit, wherein the connection portion is pivotally connected to the floating unit via the hanging support structure.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) The invention will be explained more fully below in connection with a preferred embodiment and with reference to the drawings in which:

(2) FIG. 1 is a schematic side view of an offshore top site system of the invention comprising a not shown subsea facility, a floating unit arranged above the subsea facility and a transportation line with a top site section, a catenary riser section and a connection portion pivotally connected to the floating unit.

(3) FIG. 2 is a schematic side view of another offshore top site system of the invention comprising two or more transportation lines and where the floating unit is a vessel.

(4) FIG. 3 is a schematic side view of a further offshore top site system of the invention where the floating unit is a vessel and the connection portion is pivotally connected to a bottom side of the bow.

(5) FIG. 4a is a schematic side view of a further offshore top site system of the invention where the floating unit is a vessel and the connection portion is pivotally connected via an opening in the bottom of the floating unit.

(6) FIG. 4b is a cross-sectional view of the offshore top site system of FIG. 4a seen in the line A-A, where the floating unit is a vessel and the connection portion is pivotally connected via an opening in the bottom of the floating unit.

(7) FIG. 5 is a cross-sectional view of another offshore top site system of the invention where the floating unit is a vessel and the connection portions of two or more transportation lines are pivotally connected via respective openings in the bottom of the floating unit.

(8) FIG. 6 is a schematic side view of a further offshore top site system of the invention where the floating unit is a vessel and connection portions of a plurality of transportation lines are pivotally connected via respective openings in the bottom of the floating unit.

(9) FIG. 7a is a schematic side view of a further offshore top site system of the invention where the floating unit is a vessel and the connection portions of transportation lines are pivotally connected to a hanging support structure which is pivotally connected to the vessel.

(10) FIG. 7b is a cross-sectional view of the offshore top site system of FIG. 7a seen in the line B-B.

(11) FIG. 8 is a schematic side view of a part of a transportation line comprising the connection portion as well as a part of the top site section and the catenary riser section.

(12) FIG. 9 is a schematic side view of a transportation line comprising the connection portion and where the top site section and the catenary riser section are integrated parts.

(13) FIG. 10 is a schematic side view of a further offshore top site system of the invention where the floating unit is a vessel and comprising a transporting line where the catenary riser section is supported by a plurality of buoyancy modules.

(14) FIG. 11a is a schematic side view of an offshore top site system of the invention comprising of transportation lines outside the VF zone.

(15) FIG. 11b is a cross-sectional view of the offshore top site system of FIG. 7a seen in the line A-A.

(16) The offshore top site system shown in FIG. 1 comprises a not shown subsea facility, a floating unit 1 arranged above the subsea facility and at least one transportation line 2 extending between the not shown subsea facility and the floating unit 1.

(17) The transportation line 2 comprises a catenary riser section 3 with an uppermost end 3a and a top site section 4 with a lowermost end 4a and the catenary riser section 3 and the top site section 4 are in flow connection with each other.

(18) The floating unit 1 is floating at the water line WL.

(19) As it can be seen the catenary riser section 3 extends downwards towards the seabed SB with a catenary curve C and touches the seabed SB in a touch down point P. The catenary riser section 3 leads to the not shown subsea facility which as mentioned above can be e.g. a well or a connection to another pipeline.

(20) The top site section 4 extends upwards e.g. towards a not shown tank or similar onboard the floating unit.

(21) The transportation line 2 further comprises a connecting portion 5 connecting the uppermost end 3a of the catenary riser section 3 with the lowermost end 4a of the top site section 4.

(22) The floating unit 1 has a bottom B facing downwards and an outer periphery of the bottom defining a horizontal peripherymarked with dotted linesof a vertical floating unit zone VF Zone. The connecting portion 5 is arranged within the vertical floating unit zone VF Zone.

(23) The connection portion 5 is pivotally connected directly to the floating unit via a tether line 6, such that at least a major part of pulling force from the riser section is alleviated by the connection to the floating unit. The pivotally connection implies that both the connection between the tether line 6 and the floating unit 1 as well as the connection between the tether line 6 and the connection portion 5 are pivotal.

(24) The offshore top site system shown in FIG. 2 comprises a floating unit in the form of a vessel 11 floating at the water line WL and a plurality of transportation lines extending between a not shown subsea facility at the seabed SB and the vessel 11.

(25) Each transportation line comprises a catenary riser section 13 and a top site section 14 in flow connection with each other.

(26) As it can be seen the catenary riser sections 13 extend downwards towards the seabed SB and touch the seabed SB in respective touch down points P.

(27) The top site sections 14 extend upwards e.g. towards a not shown tank or similar onboard the floating unit. Due to the construction the top site sections 14 are not subjected to any load from the weight of the connected catenary riser sections 13.

(28) Each transportation line further comprises a connecting portion 15 connecting the catenary riser section 13 with the top site section 14.

(29) The vessel 11 has a bottom B facing downwards and an outer periphery of the bottom defining a horizontal peripherymarked with dotted linesof a vertical floating unit zone VF Zone. The connecting portions 15 are arranged within the vertical floating unit zone VF Zone.

(30) The connection portion 15 is pivotally connected directly to the vessel 11 via a tether line 16, such that any pulling force from the riser section is alleviated by the connection to the vessel 11. The pivotally connection implies that the respective connections 16a between the tether line 16 and the vessel 11 as well as the respective connections 16b between the tether line 16 and the connection portion 15 are pivotal.

(31) The offshore top site system shown in FIG. 3 comprises a floating unit in the form of a vessel 21 floating at the water line WL and a transportation line extending between a not shown subsea facility at the seabed SB and the vessel 21.

(32) The transportation line comprises a catenary riser section 23 and a top site section 24 in flow connection with each other.

(33) As it can be seen the catenary riser section 23 extends downwards towards the seabed SB and touches the seabed SB in a touch down point P.

(34) The top site section 24 extends upwards where it is guided by a bellmouth 27 and further e.g. towards a not shown tank or similar onboard the floating unit.

(35) Such bellmouth is well known in the art and is generally applied to protect against undesired bends and movements of a flexible pipeline. Such bellmouths are generally relatively simple to install and apply and are relative low-cost equipment.

(36) The transportation line further comprises a connecting portion 25 connecting the catenary riser section 23 with the top site section 24.

(37) The vessel 21 comprises a forward protruding bow 21a and has a bottom B also including the bottom of the bow 21a. The bottom is facing downwards and an outer periphery of the bottom defines a horizontal peripherymarked with dotted linesof a vertical floating unit zone VF Zone. The connecting portion 25 is arranged within the vertical floating unit zone VF Zone.

(38) The connection portion 25 is pivotally connected directly to the bottom B of the bow 21a via a tether line 26, such that at least a major part of pulling force from the riser section 24 is alleviated by the connection to the vessel 21.

(39) The offshore top site system shown in FIG. 4a comprises a floating unit in the form of a vessel 31 floating at the water line WL and a transportation line extending between a not shown subsea facility at the seabed SB and the vessel 31.

(40) The transportation line comprises a catenary riser section 33 and a top site section 34 in flow connection with each other.

(41) As it can be seen the catenary riser section 33 extends downwards towards the seabed SB to touch the seabed SB.

(42) The top site section 34 extends upwards to a not shown position.

(43) The transportation line further comprises a connecting portion 35 connecting the catenary riser section 33 with the top site section 34.

(44) The vessel 31 comprises a bottom B facing downwards and an outer periphery of the bottom defines a horizontal peripherymarked with dotted linesof a vertical floating unit zone VF Zone. The connecting portion 35 is arranged within the vertical floating unit zone VF Zone.

(45) The connection portion 35 is pivotally connected to the vessel by being directly and pivotally connected to a not shown internal bearing structure of the vessel 31.

(46) FIG. 4b is a cross-sectional view of the offshore top site system shown in FIG. 4a seen in the line A-A. As it can be seen the connection portion 35 is pivotally connected via a tether line 36 directly to a not shown internal bearing structure of the vessel 31. The tether linewhich here is in form of a chain structurepasses through the bottom B of the hull of the vessel 31 and into a passage 37, where at an appropriate position it is pivotally connected to the bearing structure of the vessel 31.

(47) In an alternative not shown modified version the connection portion also passes through the bottom B of the hull of the vessel 31 and into the passage 37 of the vessel 31, such that the connecting portion 35 is arranged above the bottom of the floating unit and the catenary riser section 33 extends through the bottom B of the hull of the vessel 31.

(48) FIG. 5 is a cross-sectional view of a vessel 41 of another offshore top site system of the invention where connection portions 45 of two or more transportation lines are pivotally connected via respective openings 47 in the bottom B of the vessel 41.

(49) Each transportation line comprises a catenary riser section 43 and a top site section 44 in flow connection with each other and with the connection portion 45 arranged to connect the catenary riser section 43 with the top site section 34.

(50) The vessel 41 has a midpoint M (midships) and the connection portions 45 are pivotally connected via tether lines 46 passing through the bottom B of the hull of the vessel 41 and into a passage 47, where the tether lines 46 at appropriate positions are pivotally connected to the bearing structure of the vessel 41. Preferably the tether lines 46 are pivotally connected to the bearing structure of the vessel 45 as close as possible to the midpoint M, because this will result in that the lowest possible amount of stress is transferred to the connection points and thereby to the transporting lines.

(51) FIG. 6 shows an offshore top site system of the invention comprising a floating vessel 51 floating at the water line WL and a plurality of transportation lines extending between a not shown subsea facility at the seabed SB and the vessel 51.

(52) Each transportation line comprises a catenary riser section 53 and a top site section 54 (jumper) in flow connection with each other.

(53) The vessel 51 comprises a jumper shelve structure 59 arranged to support and guide the top site sections 54 e.g. towards a not shown tank or similar onboard the vessel 51.

(54) Each transportation line further comprises a connecting portion 55 connecting the catenary riser section 53 with the top site section 54.

(55) The vessel 51 has a bottom B facing downwards and the connecting portions 55 are arranged below the bottom B of the vessel 51.

(56) The connection portion 55 is pivotally connected via tether lines 56 which pass through the bottom B of the hull of the vessel 51 and into passages 57, where they are connected to a beam structure 58 near the midpoint M of the vessel 51. The beam structure 58 is arranged along the midline of the hull from the bow to the stern and forms part of the bearing structure of the vessel 51.

(57) FIG. 7a and FIG. 7b show an offshore top site system of the invention comprising a floating vessel 61 floating at the water line WL and a plurality of transportation lines extending between a not shown subsea facility at the seabed SB and the vessel 61.

(58) Each transportation line comprises a catenary riser section 63 and a top site section 64 (jumper) in flow connection with each other.

(59) Each transportation line further comprises a not shown connecting portion 65 connecting the catenary riser section 63 with the top site section 64.

(60) The offshore top site system of further comprises a hanging support structure 69 which is pivotally connected to the vessel 61 via tether lines 66. The hanging support structure 69 has a beam like structure and is arranged along the midline of the hull from the bow to the stern of the vessel 61

(61) The connection portions connecting the respective catenary riser sections 63 and top site sections 64 are pivotally connected to the hanging support structure 69.

(62) FIG. 8 shows a connection portion in the form of an intermediate transition piece 75 connecting a top site section 74 and a catenary riser section 73 of a transportation line. The top site section 74 comprises a lowermost end 74a in the form of an end fitting and the catenary riser section 73 comprises an uppermost end 73a also in the form of an end fitting.

(63) The intermediate transition piece 75 comprises a first end 75a fluidically connected to the uppermost end 73a of the catenary riser section 73 and a second end 75b fluidically connected to the lowermost end 74a of the top site section 74. The intermediate transition piece 75 further comprises a rigid mid section 75c and a pull-head 75d. A tether line is pivotally connecting the pull-heal 75d to a not shown floating unit. The tether line is guided to the floating unit via a bellmouth 77. The top site section 74 extends upward to a not shown position also guided by a bellmouth 79.

(64) FIG. 9 shows a connection portion 85 of an embodiment where the catenary riser section 83 and the top site section 84 are integrated parts.

(65) The catenary riser section 83 and the top site section 84 each comprise a plurality of layers 83a, 84a e.g. such as the unbonded flexible pipes described in Recommended Practice for Flexible Pipe, ANSI/API 17 B, fourth Edition, July 2008, and the standard Specification for Unbonded Flexible Pipe, ANSI/API 17J, Third edition, July 2008.

(66) The connection portion 85 is composed of metal elements 85a and one or more of the layers 83a, 84a of each of the catenary riser section 83 and the top site section 84. One or more of the outermost layers, such as an outer sheath 83c, 84c and a tensile armor layer 83b, 84b are terminated in the connection portion 85. As seen the respective tensile armor layers 83b, 84b are terminated by being fixed using a fixing cement 80 such as epoxy.

(67) The remaining layers 89 of the catenary riser section 83 and the top site section 84 pass through the connection portion 85.

(68) The connection portion 85 further comprises a flange 85d pivotally connected to a tether line 86 which again is pivotally connected to a not shown floating unit.

(69) The offshore top site system shown in FIG. 10 comprises at least one not shown subsea facility, a floating unit 91 floating at the water line WL above the subsea facility and two transporting lines comprising catenary riser sections 93a, 93b and with not shown top site sections.

(70) The catenary riser sections 93a, 93b are pivotally connected to the floating unit 91 via their connection portions and tether lines 96.

(71) The catenary riser section 93a extends downwards towards the seabed SB with a catenary curve and touches a subsea structure 92 in a touch down point P from where the transportation line leads further to a subsea facility.

(72) The catenary riser section 93b extends downwards towards the seabed SB with a catenary curve and touches the seabed SB in a touch down point P from where the transportation line leads further to a subsea facility. The catenary riser section 93b comprises a plurality of buoyancy modules 94, which bears up to about 25% of the weight of the catenary riser section 93b.

(73) The catenary riser section 93b is anchored to the seabed via an anchor 95 e.g. comprising a dead-man tethered to a clamp fixed to the catenary riser section 93b.

(74) The offshore top site system shown in FIGS. 11a and 11b comprises a floating unit 101 floating at the water line WL a number of transporting lines comprising catenary riser sections 103a, 103b, 103c and with top site sections 104a, 104b, 104c.

(75) The catenary riser sections 103a, 103b, 103c are pivotally connected to the floating unit 101 via their connection portions and tether lines 106.

(76) The catenary riser section 103a is pivotally connected to the floating unit 101 with in the vertical floating unit zone VF Zone.

(77) The catenary riser section 103b is pivotally connected to the floating unit 101 outside the vertical floating unit zone VF Zone in that it is connected at a periphery of the floating unit 101.

(78) The catenary riser section 103c is pivotally connected to the floating unit 101 outside the vertical floating unit zone VF Zone in that it is connected at a hang-off structure 107 connected to the floating unit 101.

(79) Some preferred embodiments have been shown in the foregoing, but it should be stressed that the invention is not limited to these, but may be embodied in other ways within the subject-matter defined in the following claims.