METHOD FOR RETRIEVING A PIPELINE

Abstract

A method for retrieving a pipeline from a seabed in the body of water to a vessel includes the steps of suspending at least a portion of the pipeline in the body of water between the seabed and the vessel, plastically deforming the portion of the pipeline to form a plastically deformed portion, and retrieving the plastically deformed portion to the vessel.

Claims

1. A method for retrieving a pipeline from a seabed in a body of water to a vessel, the method comprising: (a) suspending at least a portion of the pipeline in the body of water between the seabed and the vessel; (b) plastically deforming the portion of the pipeline to form a plastically deformed portion; and (c) retrieving the plastically deformed portion onto the vessel.

2-4. (canceled)

5. The method according to claim 1, wherein the pipeline includes a fluid, and wherein the pipeline is sealed at one or both ends.

6-12. (canceled)

13. The method according to claim 1, wherein the step of suspending at least a portion of the pipeline includes applying a first longitudinal tension to the pipeline.

14. The method according to claim 13, wherein the first longitudinal tension is up to 150 Te, and wherein the first longitudinal tension is provided by the vessel connected to the pipeline.

15. (canceled)

16. The method according to claim 14, wherein the vessel provides the first longitudinal tension by applying a first thrust, and wherein the first longitudinal tension is provided at least partially by a tensioner or a combination of a brake, a clamp and a winch.

17. (canceled)

18. The method according to claim 1, wherein the step of suspending at least a portion of the pipeline includes forming of an overbend and a sag bend.

19-22. (canceled)

23. The method according to claim 13, wherein the step of plastically deforming the portion of the pipeline includes applying a second longitudinal tension to the pipeline.

24. The method according to claim 23, wherein the second longitudinal tension is sufficient to allow plastic deformation of the pipeline that results in no more than 7.5% ovality and no more than 1% axial strain, and wherein the second longitudinal tension is up to 150 Te.

25. (canceled)

26. (canceled)

27. The method according to claim 23, wherein the second longitudinal tension is provided by the vessel connected to one end of the pipeline, wherein the vessel provides the second longitudinal tension by applying a second thrust, and wherein the second longitudinal tension is provided at least partially by a tensioner or a combination of a brake, a clamp and a winch.

28. (canceled)

29. (canceled)

30. The method according to claim 1, wherein the plastically deformed portion has a radius of curvature of about 30 m, 50 m, 70 m, 90 m or 110 m, and wherein the plastically deformed portion is formed at or near an overbend in the pipeline.

31. (canceled)

32. The method according to claim 1, wherein the plastically deformed portion is formed at or near an extension that projects from the vessel, wherein the plastically deformed portion has a length of up to 250 m, and wherein the plastically deformed portion is retrieved via one or more tensioners or a combination of a brake, a clamp and a winch.

33-35. (canceled)

36. The method according to claim 1, the method further comprising: straightening the plastically deformed portion after retrieving the plastically deformed portion to the vessel; wherein the step of straightening includes passing the plastically deformed portion through a straightening mechanism to effectuate the straightening.

37. (canceled)

38. The method according to claim 36, the method further comprising: cutting the pipeline into one or more sections after the pipeline was retrieved to the vessel.

39-42. (canceled)

43. The method according to 27, the method further comprising: in response to an insufficient friction at the seabed to control the plastic deformation of the pipeline applying a third longitudinal tension to a distal end of the pipeline; wherein the distal end is an opposite end of the one end of the pipeline connected to the vessel; and wherein the third longitudinal tension is applied by a second vessel connected to the distal end of the pipeline.

44. (canceled)

45. A system for managing a plastically deformed pipeline that has been retrieved from a body of water, the system comprising a means for straightening the plastically deformed pipeline to form a straightened pipeline, and a means for applying a longitudinal tension to the straightened pipeline; wherein the means for straightening is arranged in-line with and before the means for applying.

46. The system according to claim 45, wherein the means for straightening is selected from the group comprising of: a) one or more pairs of rollers that are adjusted so that a gap between the one or more rollers is smaller than an outside diameter of the pipeline passing through the one or more rollers, b) one or more heating members, and c) one or more pressing members.

47. The system according to claim 45, wherein the means for applying the longitudinal tension is selected from the group consisting of a tensioner that clamps or secures the pipeline or a brake or clamping device that is capable of releasably holding the pipeline.

48-50. (canceled)

51. The system according to claim 45 further comprising a support member for controlling a deformation of the pipeline, wherein the support member is a stinger, boom, frame or some other similar device.

52. The system according to claim 51, wherein the support member is arranged in-line with the means for straightening and the means for applying and before the means for straightening.

53. (canceled)

54-58. (canceled)

Description

BRIEF DESCRIPTION OF THE DRAWING

[0103] FIGS. 1A-1C are a schematic series of images to illustrate one embodiment of the method of the first aspect of the invention; and

[0104] FIG. 2 is a side view of a vessel including one embodiment of the system of the second aspect of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0105] One embodiment of a first aspect of the present invention is depicted in FIG. 1A-1C, and comprises a method for retrieving a pipeline in the form of a subsea pipeline generally indicated by the numeral 10, from a seabed 12 in a body of water 14 to a topside location in the form of a dynamically positioned vessel 16.

[0106] FIG. 1A shows the method at a point where pre-operation site survey and preparation works have been completed at both ends of the pipeline 10. Both free ends of the pipeline 10 have been sealed with water tight closures, plugs or caps (not shown) to retain any fluid therein such as contaminated water. This sealing of the pipeline can be effected by ROV or some other suitable means. A topside location in the form of a vessel 16 is in position above the pipeline 10.

[0107] In FIG. 1B, the vessel 16 is shown still positioned at one end of the pipeline 10 and is set to hold a predetermined location via Dynamic Positioning (DP) Another vessel such as an Anchor Handling Tug (17), is positioned above the other end of the pipeline 10.

[0108] A first winch line IS extends from a winch 19 on the vessel 16 and is attached to the cap at one end of the pipeline 10.

[0109] Step (a) of the first aspect of the present invention is exemplified in FIG. 10 where, the winch 19 is actuated and winch line 18 retrieves the free end of the pipeline 10 to the vessel 16. As more of the pipeline 10 is suspended during the winching process (see FIG. 1B), the vessel 16 “takes up” the tension from the weight of the suspended pipeline 10. This is largely addressed by the vessel applying thrust to move astern via its DP, which ensures the vessel 16 applies a first longitudinal tension in the form of a predetermined longitudinal tension.

[0110] With respect to exemplifying step (b) of the first aspect of the present invention, in FIG. 10 the second longitudinal tension in the form of a predetermined longitudinal tension applied results in a suspended portion 22 of the subsea pipeline 10, that is unsupported and spans between a contact point 22 on the seabed 12 and the vessel 16, in this case, the distal end of a support member in the form of a stinger or chute 20. As a result, the pipeline 10 plastically deforms at or near and preferably over the entire overbend section 24 in the pipeline 10. It will be understood that this plastic deformation is a result of the relatively low tension applied to the pipeline 10 resulting in a tight radius of curvature of the pipeline 10, when compared to prior art retrieval methods based on the reverse of installation methods. A sagbend 26 in the pipeline 10 is also shown in FIG. 1C.

[0111] With respect to an example of step (c) of the method of the present invention, FIG. 10 also shows the pipeline 10, having been plastically deformed, being retrieved over the stinger 20 mounted on the vessel 16. While running over the stinger 20 the outside of the pipeline 10 is cleaned using a high-pressure water jet system or some other cleaning apparatus.

[0112] After leaving the stinger 20, the pipeline 10 is straightened, such as through the use of a straightener 28, which can be hydraulically actuated. The straightening process re-bends the plastically deformed pipeline 10 so that it is straight before contacting the tensioning means in the form of a series of two tensioners 30A, 30B that can retrieve the pipeline 10 along the full length of the deck of the vessel 16.

[0113] In an alternate embodiment of the invention, at least one of the two tensioners 30A. 30B could be replaced with a brake or clamping device that is capable of releasably holding the pipeline 10 on the deck of the vessel 16. When a brake or clamping device is included, a winch on the deck of the vessel 16 can be used to retrieve the pipeline 10 and the brake or clamping device can be used to hold the pipeline in position as required.

[0114] After being straightened, the retrieved pipeline may be further handled by any one or more of the following steps that seek to deal with any fluid contained within the pipeline: [0115] (i) the pipeline may be cut, such as with shears, that may be supported from a crane on board vessel 16; [0116] (ii) any caps on the ends of the pipeline may be removed; and [0117] (iii) fluid from the pipeline can be drained to a reservoir and then pumped to other locations on the vessel 16 as required.

[0118] After being straightened and having any fluid therein removed, the pipeline cut into sections to ease further handling and storage aboard vessel 16.

[0119] When the amount of pipeline retrieved reaches the point where the amount of unretrieved pipeline is insufficient to provide the requisite amount of the third longitudinal tension, due essentially to insufficient friction between the unretrieved pipeline and the seabed 10, a line (not shown) from the tug 17 is attached to the distal end of the pipeline and thrust from tug 17 applies the requisite third longitudinal tension to allow the first and/or second longitudinal tension to be effectively applied and the pipeline 10 to be retrieved.

[0120] FIG. 2 depicts a system according to one embodiment of the second aspect of the present invention. The system for managing a plastically deformed pipeline is shown fitted to a vessel 116 with following general specifications DP Construction Support Vessel, with long deck of at least 50-100 m or 150 m. The system comprises a means for straightening the plastically deformed pipeline in the form of a hydraulic straightener 128 that is able to straighten pipe up to 36″ diameter that has had <0.4% strain and a means for applying longitudinal tension to the straightened pipeline in the form of first tensioner 130A with four tracks and capacity of 50 Te and second tensioner 130B with four tracks and capacity of 50 Te. The system allows for the pipeline to be straightened before engaging the tensioners 130A_130B.

[0121] The system also includes a support member for controlling the deformation of the pipeline in the form of stinger 120 which extends rearward and is supported from the stem of the vessel 116 by frame 150. The stinger 120 has a departure angle of about 30° to the horizontal, and allows for plastic deformation of the pipeline 110 and supports the plastically deformed pipeline 110 before it contacts the straightener 128 and tensioners 130A, 130B.

[0122] The system depicted in FIG. 2 includes additional components including, but not limited to: [0123] (i) cable hoist 152A including cutting means in the form of a shear assembly 154 for cutting pipeline 110 into sections 110A after it has been straightened and passed tensioners 130A, 130B; [0124] (ii) cable hoist 152B for lifting and moving the pipeline sections; and (iii) a work platform 156 for pipeline sections that may include rollers and other components to ease movement of the sections.

[0125] Below is an exemplary set of parameters that may be employed alone or in combination in the method or the system of the present invention: [0126] (i) the mass of the portion of the pipeline suspended according to step (a) is 20 kg/m to 900 kg/m; [0127] (ii) the length of the pipeline suspended according to step (a) is 20 m to 300 m; (iii) the plastically deformed portion has a an ovality of <3%; [0128] (iv) the plastically deformed portion has an axial strain<0.4%; [0129] (v) the support member has a length of 25-70 m; [0130] (vi) the support member will have a radius of curvature of 30 m to 100 m. [0131] (vii) the step of plastically deforming the pipeline will comprise the application of a first or second longitudinal tension of 20 Te-80 Te.

[0132] Changes and modifications in the specifically-described embodiments may be carried out without departing from the principles of the present invention, which is intended to be limited only by the scope of the appended claims as interpreted according to the principles of patent law including the doctrine of equivalents.