AU697153B2 - Improvements in or relating to marine pipelaying - Google Patents

Description

i ILY-L- I 4\ WO 96/35902 PCT/GB95/01066 1 1 Improvements in or Relating to Marine Pipelaying 2 3 This invention relates to methods and apparatus for use 4 in marine pipelaying. More specifically, but not exclusively, the invention relates to methods and 6 apparatus whereby a conventional marine drilling vessel 7 may be adapted to perform pipelaying operations.

8 9 In prior-art marine pipelaying systems as employed in laying offshore subsea pipelines (for such uses as the 11 gathering of oil and/or gas from offshore subsea wells, 12 as, for example, in the Gulf of Mexico or the North 13 Sea), it has been conventional to use one of two main 14 methods to lay the pipe. In the first, or "stovepiping" method, a pipeline is fabricated on the 16 deck of a lay barge by welding together individual 17 lengths of pipe as the pipe is paid out from the barge.

18 Each length of pipe is about 40 feet or 80 feet long.

19 Thus, the pay-out operation must be interrupted periodically to permit new lengths of pipe to be welded 21 to the string.

22 23 The stovepiping method requires that skilled welders 24 and their relatively bulky equipment accompany the 23 The stovepip-Ig method requires ta sille welders-' WO 96/35902 PCTGB95/01066 2 1 pipelaying barge crew during the entire laying 2 operation; all welding must be carried out on site and 3 often under adverse weather conditions. Further, the 4 stovepiping method is relatively slow, with experienced crews being able to lay only one or two miles of pipe a 6 day. This makes the entire operation subject to 7 weather conditions which can cause substantial delays 8 and make working conditions quite harsh.

9 The other principal conventional method is the reel 11 pipelaying technique. In this method, a pipeline is 12 wound on the hub of a reel mounted on the deck of a lay 13 barge. Pipe is generally spooled onto the reel at a 14 shore base. There, short lengths of pipe can be welded under protected and controlled conditions to form a 16 continuous pipeline which is spooled onto the reel.

17 The lay barge is then towed to an offshore pipelaying 18 location and the pipeline spooled off the reel between 19 completion points. The pipe, which normally is plastically deformed during spooling onto the reel, has 21 to be straightened as it is unspooled.

22 23 This method has a number of advantages over the 24 stovepiping method, among them: speed (one to two miles per hour); lower operating costs (eg smaller welding 26 crews and less welding equipment must be carried on the 27 lay barge); and less weather dependency.

28 29 Commercial reel pipelaying techniques require the use of certain pipe handling equipment in addition to the 31 reel, including a straightener mechanism. This may 32 take the form of a series of rollers or tracks, or any 33 other arrangement which imparts sufficient reverse 34 bending force to the pipe to remove residual curvature such that after unspooling, the pipe will lay ~ii ii i r;l WO 96/35902 PCT/GB95/01066 3 1 substantially straight on the sea bottom.

2 3 Early reel pipelaying systems employed barges carrying 4 reels mounted for rotation about a vertical axis (referred to herein as "horizontal reels"), the pipe 6 being unspooled and launched from the stern of the 7 barge at relatively shallow angle. Subsequently, a 8 purpose built, dynamically positioned reel pipelay 9 vessel was constructed, known as the "Stena Apache", in I 10 which a horizontal-axis reel (a "vertical reel") was i 11 incorporated into the hull of the vessel. The Stena S12 Apache was also equipped with variable-angle pipe S13 straightening and launching equipment, allowing a wide I 14 variety of pipelaying operations to be undertaken i 15 without significant re-fitting of the vessel. Various I 16 aspects of the "Stena Apache" are described in the 17 following US Patents, to which reference is also made 18 for a fuller discussion of pipelaying techniques in 19 general, and reel pipelaying in particular:- Springett, et al US Patent No. 4,230,421 21 Uyeda, et al US Patent No. 4,269,540 22 Yenzer, et al US Patent No. 4,297,054 23 Springett, et al US Patent No. 4,340,322 24 Uyeda, et al US Patent No. 4,345,855 i 26 All existing pipelaying systems require high capital 27 investment, whether for purpose built vessels or for 28 the extensive re-fitting of existing general purpose 29 vessels. This increases the costs of pipelaying operations, often to the extent of making exploitation 31 of marginal hydrocarbon deposits uneconomical.

32 33 It is an object of the present invention to provide 34 methods and apparatus for marine pipelaying which entail lower capital costs than prior pipelaying I WO 96/35902 PCT/GB95/01066 1 systems. It is a particular object of the invention to 2 provide methods and apparatus allowing an existing 3 drilling vessel to be adapted for pipelaying operations 4 with minimal additional equipment. This provides the possibility of marginal deposits being exploited using 6 the same vessel to perform both drilling and pipelaying 7 operations.

8 9 In accordance with a first aspect of the present invention there is provided a method of marine 11 pipelaying, of the type in which the pipeline to be 12 laid is wound upon a reel carried by a vessel and is 13 unspooled from said reel as the pipeline is laid from 14 said vessel, comprising the steps of: feeding said pipeline from said reel over a 16 bending shoe vertically spaced above the deck of 17 said vessel and downwardly therefrom into a 18 straightening and clamping assembly disposed below 19 said bending shoe; said straightening and clamping assembly 21 being adapted for vertical movement along said 22 pipeline between an uppermost position adjacent 23 said bending shoe and a lowermost position 24 adjacent said deck, being further adapted to straighten said pipe by movement of the assembly 26 along the length of the pipeline, and being 27 further adapted to releasably clamp said pipeline; 28 clamping said straightening assembly to the 29 leading end of said pipeline, whilst said straightening assembly is in its uppermost 31 position; 32 33 lowering said straightening assembly together 34 with the leading end of said pipeline to its lowermost position; 4' WO 96/35902 PCT/GB95/01066 1 clamping said pipeline by means of second 2 clamp means disposed below the lowermost position 3 of said straightening assembly and unclamping said 4 straightening assembly from said pipeline; returning said straightening assembly to its 6 uppermost position along said pipeline, thereby 7 straightening that length of pipeline extending 8 between said uppermost and lowermost positions of 9 said straightening assembly; and repeating the foregoing steps until the 11 required length of pipeline has been laid.

12 13 Preferably, said bending shoe is mounted on a derrick 14 structure extending above said deck.

16 Preferably also, said straightening assembly is 17 suspended from said derrick structure.

18 19 Preferably also, said derrick structure is disposed above a moonpool formed in said vessel and said 21 pipeline enters the water via said moonpool.

22 23 Preferably, said reel is a vertical reel, mounted for 24 rotation about a horizontal axis, and said pipeline is unspooled from the bottom of said spool such that the 26 feeding of said pipeline about said bending shoe causes 27 reverse bending of said pipeline.

28 29 Most preferably, said vessel is a drilling vessel, and said derrick assembly is the existing derrick of the 31 drilling vessel. Preferably also, said reel, said 31 bending shoe and said straightening assembly are 33 removably mounted on the vessel. Preferably also, said 34 straightening assembly is suspended from an existing crane hook of said derrick and is moved between said r i Si WO 96/35902 PCT/GB95/01066 6 1 upper and lower positions by operation of said crane 2 hook.

3 4 In accordance with a second aspect of the invention, there is provided pipelaying apparatus for use in 6 pipelaying operations of the type in which the pipeline 7 to be laid is wound upon a reel carried by a vessel and 8 is unspooled from said reel as the pipeline is laid 9 from said vessel, comprising: a reel adapted for mounting on said vessel for storing the pipeline to be 11 laid; a pipeline bending shoe adapted to be mounted at 12 a vertical distance above the deck of said vessel; and 13 pipeline straightening means adapted to be mounted 14 below said bending shoe for vertical movement between an uppermost position adjacent said bending shoe and a 16 lowermost position adjacent said deck, being further 17 adapted to straighten said pipe by movement of the 18 assembly along the length of the pipeline, and being 19 further adapted to releasably clamp said pipeline.

21 Preferably, said vessel is a drilling vessel including 22 a derrick structure located above a moonpool, said 23 bending shoe being adapted to be mounted on said 24 derrick structure.

26 Preferably also, said derrick structure includes 27 vertically travelling crane means, and said 28 straightening means is adapted to be suspended from 29 said crane means for vertical movement with said crane means.

31 32 Preferably also, the apparatus further includes a 33 pipeline clamp adapted to be located below the 34 lowermoE, position of said straightening means, a pipeline abandonment and recovery winch, and a tugger Sj WO 96/35902 PCT/GB95/01066 7 1 winch for use in initially feeding the end of the 2 pipeline from the reel, over the bending shoe and 3 through the straightening means.

4 Preferably also, said reel is adapted for rotation 6 about a horizontal axis.

7 S8 In accordance with a third aspect of the invention, 9 there is provided a marine pipelaying vessel comprising a vessel having a derrick structure located above a 11 moonpool, said vessel being adapted for pipelaying 12 operations by the provision thereon of a pipeline 13 storage reel and of pipe diverting and straightening 14 means mounted on said derrick structure, whereby pipe from said reel may be laid via said moonpool.

16 17 In accordance with a fourth aspect of the invention, S18 there is provided a method of marine pipelaying 19 comprising adapting a vessel having a derrick structure I 20 located above a moonpool for pipelaying operations by 21 the provision thereon of a pipeline storage reel and of 22 pipe diverting and straightening means mounted on said 23 derrick structure, and feeding the pipeline from said j 24 storage reel via said diverting means through said straightening means, said pipeline exiting said vessel 26 via said moonpool.

j! j27 28 An embodiment of the invention will now be described 29 with reference to the accompanying drawings, in which: 31 Fig.l is a partial side view of a drilling vessel 32 equipped with pipelaying apparatus in accordance 33 with the present invention; 34 Fig.2 is a partial plan view of the vessel of Fig.l; LII~LIIIIIOII~C- -J I I L WO 96/35902 PCT/GB95/01066 8 1 Figs.3(a) to 3(f) are a sequence of side views of 2 the vessel of Fig.l illustrating the method of use 3 of the pipelaying apparatus in accordance with the 4 invention; Fig.4 is a further partial side view of the vessel 6 of Fig.l indicating different pipeline departure 7 angles for a given bend radius; 8 Fig.5 is a plan view showing the base and crown of 9 a derrick structure forming part of the vessel of Figs.l to 4; and 11 Figs.6(a) to are side views of the derrick 12 structure of Fig.5 in the directions A-A, B-B and 13 C-C thereof respectively.

14 Referring firstly to Figs. 1 and 2, there is shown a 16 conventional drilling vessel 10 equipped with a derrick 17 structure 12 located above a moonpool 14. The derrick 18 12 is itself equipped with a vertically travelling 19 crane hook assembly 16. The derrick 12, moonpool 14 and crane 16 would normally be used in conventional 21 drilling operations undertakeh by the vessel 22 23 In accordance with the invention, the vessel 10 is 24 adapted to perform pipelaying operations by the addition of a pipe storage reel 18, upon which a 26 pipeline to be laid is spooled, mounted on the deck of 27 the vessel astern of the derrick 14; a bending shoe 28 assembly 20 mounted on the derrick 12 at a distance 29 above the deck of the vessel; and a pipeline straightening assembly 22 suspended from the crane hook 31 16 beneath the bending shoe 20. Operation of the crane 32 allows the straightening assembly to travel vertically 33 between an uppermost position adjacent the bending shoe 34 20 and a lowermost position adjacent the deck of the vessel.

-I~hl; WO 96/35902 PCT/GB95/01066 9 1 The reel 18 is preferably of the "portable" type, which 2 can be loaded with pipe onshore before being lifted 3 onto the vessel. Various portable reels of this type 4 are known for use in other pipelaying systems, for example from US Patents Nos. 3,855,835, 4,157,023, 6 4,243,345 and 4,260,287. As illustrated the vessel may 7 carry one or more additional reels 18A, according to the available deck space and load capacity, allowing a 9 greater length of pipeline to be carried and laid.

11 The bending shoe 20 performs a substantially similar ,12 function to the "radius controller" of the above 13 referenced US Patents Nos. 4,230,421, 4,269,540, 14 4,297,054, 4,340,322 and 4,345,855; i.e. diverting the pipe as it is unspooled from the reel 18 for 16 presentation to the straightening assembly 22, and at 17 the same time reverse bending the pipeline to a 18 relativeiy uniform radius of curvature so as to 19 facilitate subsequent straightening. The bending shoe provides an arcuate path about which the pipe is bent 21 in being fed to the straightening assembly. The pipe 22 bearing surface of the shoe is normally provided with 23 rollers or a conveyor-belt type track arrangement, 24 which may be formned with a transverse sectional profile for centring the pipeline thereon as is well known in 26 the art.

27 28 The pipeline is preferably fed from the bottom of the 29 reel as shown, such that it is bent in the reverse direction to the curvature imparted to it by being 31 spooled on the reel 18.

32 33 In the present embodiment the bending shoe 22 34 preferably provides an arcuate surface of approximately 240 degrees. For ease of handling and installation, the SI i I L4 SWO 96/35902 PCT/GB95/01066 1 shoe preferably comprises a plurality of arcuate 2 segments which together make up the required arc 3 length, each segment being fitted with its own pipe 4 transporting conveyor or rollers (not shown). The radius of the arc of the shoe will depend upon the 6 characteristics of the maximum size of pipe which is to 7 be laid. For 6 inch diameter pipe, a radius of about 8 3.5 metres will be required.

9 The straightening assembly 22 comprises a three-point 11 straightener, preferably a roller assembly of a type 12 which is known in the art. Three-point straightening of 13 pipelines is discussed in US Patents Nos.3,237,438 and 14 3,372,461. Examples of roller-type straighteners of the generally preferred type, and their operation, are 16 described in the above referenced US Patents Nos.

17 3,855,835, 4,157,023, 4,243,345 and 4,260,287.

18 Alternative "roller-track" type assemblies are 'iso 19 described in above referenced US Patents Nos.

4,230,421, 4,269,540, 4,297,054, 4,340,322 and 21 4,345,855, and further in US Patents Nos. 3,641,778, 22 3,680,342, Re 30,846 and 4,723,874.

23 24 The rollers of the assembly 22 are movable between an open position in which they are disengaged from the 26 pipe and a closed position in which they are in contact 27 with the pipe, and are disposed relative to one another 28 and to the pipe so as to straighten the pipe by reverse 29 bending through movement of the straightener along the length of the pipe, in accordance with principles which 31 are well known in the art.

32 33 In conventional reel pipelay systems straightening 34 takes place by holding the straightener stationary while the pipe is pulled therethrough. In the present -ii~ I I I i WO96135902 PCT/GB95/01066 11 1 case the straightener is moved vertically along a 2 length of pipeline whilst the pipeline is held 3 stationary. The straightening assembly 22 is also 4 adapted to be clamped to the pipeline either by engagement of the rollers thereof or by means of a 6 separate clamp incorporated in the assembly. Clamping 7 arrangements of this type are known in the art and will 8 not be described in further detail herein.

9 A work platform 23 may also be provided on the derrick 11 12, affording access to the straightening assembly 22.

12 The platform may be enclosed if required.

13 14 The pipelaying equipment fitted to the vessel also includes a pipeline clamp 24, an abandonment and 16 recovery winch 26, and a tugger winch 28.

17 18 Referring now to Figs. 3(a) to of the drawings, the 19 operation of the pipelaying apparatus is as follows.

21 Firstly, with the straightening assembly 22 open and at 22 its uppermost position, a tugger cable 30 is fed from 23 the tugger winch 28, through the clamp 24 and 24 straightening assembly 22, and around the bending shoe 20 for attachment to the free end of the pipeline 32 26 emerging from the reel 18 (Fig. The tugger winch 27 28 is then operated to pull the cable 30 and pipeline 28 over the bending shoe 20, and through the straightener 29 22 until the pipeline 32 protrudes approximately metres below the straightener 22, at which point the 31 tugger cable 30 is disconnected (Fig. 32 33 The straightener 22 is clamped to the pipeline 32 and 34 is lowered to its lowermost position, where it is clamped by the pipeline clamp 24, and an initiation leading end of said pipeline, whilst said straightening assembly is in its uppermost position; ./2 WO 96/35902 PCT/GB95/01066 12 1 cable 34 is attached (Fig. The straightener 22 2 is then unclamped from the pipeline 32, is closed and 3 is returned to its uppermost position, thereby 4 straightening the length of pipe extending between the uppermost and lowermost positions (typically a length 6 of about 24 metres)(Fig. 7 8 The clamp 24 is released, the straightener 22 is again 9 clamped to the pipeline 32 and lowered therewith to its lowermost position, the clamp 24 re-engages the 11 pipeline 32, the straightener 22 is unclamped, closed 12 and returned to its uppermost position to straighten 13 the next length of pipe.

14 This cycle of operations is repeated until the free end 16 of the pipe achieves vertical stab-in of the initiation 17 head at a stab-in assembly 36 located on the sea bed 18 (Fig. guided by the initiation cable 34 which 19 extends from the end of the pipe 32, through the stabin assembly 36 and back to the A&R winch 26. Once stab- 21 in is achieved the initiation cable 26 is detached and 22 the vessel proceeds with the pipelay, straightening the 23 pipeline 32 as it is unspooled from the reel 18 in the 24 same manner as described above.

26 As seen in Fig. 1, the pipeline 32 exits the 27 straightening assembly 22 substantially vertically.

28 Operational considerations, including the water depth, 29 may require a pipe launch angle of less than degrees. In this case a stinger assembly 40 may be 31 fitted to the bottom of the vessel so as to divert the 32 pipeline to the required angle as it exits the bottom 33 of the moonpool 14. The use of stingers in controlling 34 the launch angle in pipelaying operations is well known in the art and will not be discussed further herein.

I WO 96/35902 PCT/GB95/01066 13 1 Fig. 4 illustrates a range of departure angles for a 2 given bending radius, showing how the length of the 3 required stinger 40 would increase as the launch angle 4 becomes smaller. An angle of 70 degrees is likely to be suitable for a typical range of operations, requiring a 6 stinger approximately 20 metres in length, extending 7 downwards from the interior of the moonpool 14 8 immediately below the pipeline clamp 24.

9 The method of pipeline straightening described herein 11 straightens the pipe in a piecewise manner, a given 12 length of pipe being straightened in each cycle, rather 13 than in a continuous manner as in systems where the 14 straightener remains stationary and the pipeline is fed continuously therethrough. In shallow water depths, 16 this piecewise mode of straightening may require the 17 forward speed of the vessel to be varied in synchronism 18 with the cycling of the straightener. However, where 19 the water depth is greater, the length of pipe between the vessel and the sea bed will sufficient to 21 accommodate the slack produced by the piecewise 22 unspooling of the pipe from the reel, so that the 23 vessel may proceed along the pipelay path at 24 substantially constant speed.

26 The invention thus provides methods and apparatus 27 allowing pipelaying operations to be conducted at S28 relatively low cost, particularly where a drilling 29 vessel is employed and the existing derrick, crane etc.

of the vessel are exploited.

31 32 Modifications and improvements may be incorporated 33 without departing from the scope of the invention.

34 L, 1

Claims (4)

1. 2. A method as claimed in Claim i, wherein said 6 bending shoe is mounted on a derrick structure 7 extending above said deck. 8 9 3. A method as claimed in Claim 2, wherein said straightening assembly is suspended from said derrick 11 structure. 12 13 4. A method as claimed in Claim 2 or Claim 3, wherein 14 said derrick structure is disposed above a moonpool formed in said vessel and said pipeline enters the 16 water via said moonpool. 17 18 5. A method as claimed in any preceding Claim, 19 wherein said reel is a vertical reel, mounted for rotation about a horizontal axis, and said pipeline is 21 unspooled from the bottom of said spool such that the 22 feeding of said pipeline about said bending shoe causes V 23 reverse bending of said pipeline. 24
2. 6. A method as claimed in any preceding Claim, 26 wherein said vessel is a drilling vessel, and said 27 derrick assembly is the existing derrick of the 28 drilling vessel. 29
3. 7. A method as claimed in Claim 6, wherein said reel, 31 said bending shoe and said straightening assembly are 32 removably mounted on the vessel. 33 34 8. A method as claimed in Claim 6 or Claim 7, wherein said straightening assembly is suspended from an ~c ~r WO 96/35902 PCT/GB95/01066 16 1 existing crane hook of said derrick and is moved 2 between said upper and lower positions by operation of 3 said crane hook. 4
4. 9. Marine pipelaying apparatus for use in pipelaying 6 operations of the type in which the pipeline to be laid 7 is wound upon a reel carried by a vessel and is 8 unspooled from said reel as the pipeline is laid from 9 said vessel, comprising: a reel adapted for mounting on said vessel for 11 storing the pipeline to be laid; 12 a pipeline bending shoe adapted to be mounted at a 13 vertical distance above the deck of said vessel; and 14 pipeline straightening means adapted to be mounted below said bending shoe for vertical movement between 16 an uppermost position adjacent said bending shoe and a 17 lowermost position adjacent said deck, being further 18 adapted to straighten said pipe by movement of the 19 assembly along the length of the pipeline, and being further adapted to releasably clamp said pipeline. 21 22 10. Apparatus as claimed in Claim 9, wherein said 23 vessel is a drilling vessel including a derrick 24 structure located above a moonpool, said bending shoe being adapted to be mounted on said derrick structure. 26 27 11. Apparatus as claimed in Claim 10, wherein said 28 derrick structure includes vertically travelling crane 29 means, and said straightening means is adapted to be suspended from said crane means for vertical movement 31 with said crane means. 32 33 12. Apparatus as claimed in any one of Claims 9 to 11, 34 wherein the apparatus further includes a pipeline clamp adapted to be located below the lowermost position of i 1~~I ii 3 VO 96/35902 PCT/GB95/01066 1 said straightening means, a pipeline abandonment and 2 recovery winch, and a tugger winch for use in initially 3 feeding the end of the pipeline from the reel, over the 4 bending shoe and through the straightening means. 6 13. Apparatus as claimed in any one of Claims 9 to 12, 7 wherein said reel is adapted for rotation about a 8 'horizontal axis. 9 H i 4 4 O 44 *It 4. .4.4 DATED this 18th day of August, 1998 COFLEXIP STENA OFFSHORE LIMITED By its Patent Attorneys Davies Collison Cave