GB2377000A

GB2377000A - A method of removing a blockage in a fluid filled pipeline

Info

Publication number: GB2377000A
Application number: GB0114077A
Authority: GB
Inventors: Eamonn Mcgennis
Original assignee: Coflexip SA; Coflexip Stena Offshore Ltd
Current assignee: Technip Energies France SAS; Technip UK Ltd
Priority date: 2001-06-09
Filing date: 2001-06-09
Publication date: 2002-12-31
Also published as: WO2002100562A1; GB0114077D0

Abstract

The present invention describes a method of removing a blockage in a fluid-filled pipeline comprising connecting a length of tubing to a pipeline blockage removal tool and transporting the tool along the interior of the pipeline from a first end thereof to engage the blockage, such that said tubing extends from said first end of said pipeline to said tool; the method including injecting fluid into the interior of the tubing such that the tubing is substantially neutrally buoyant in the fluid within the interior of the pipeline. A tubing assembly and apparatus for use in removing blockages from pipelines are also described.

Description

1 Pipeline Blockage Removal 2 3 The present invention relates to methods and 4 apparatus for removing blockages from pipelines.

5 The invention is particularly concerned with the 6 removal of blockages in long, relatively large bore 7 pipelines where the blockage is located thousands of 8 metres from an end of the pipeline, and most 9 particularly in the case of subsea pipelines 10 associated with offshore oil installations or the 11 like.

12 13 Blockages in subsea pipelines (typically caused by 14 wax and/or hydrate formation) cause substantial 15 losses in terms of production downtime and are 16 difficult or impossible to remedy by conventional 17 methods, particularly where the blockage is located 18 at a substantial distance from an accessible end of 19 the pipeline. This can result in pipelines having 20 to be abandoned and replaced, incurring further 21 costs.

22 23 The conventional method of clearing a subsea 24 pipeline blockage is to insert a blockage clearing 25 tool into the pipeline, carried by a tractor unit 26 trailing a length of tubing through which chemical 27 agents and/or fluids and electrical power and/or

1 control signals are supplied to the tractor unit and 2 the blockage clearing tool. The tool may be a 3 drilling or reaming tool for mechanically removing 4 the blockage with or without the assistance of 5 chemical agents or a fluid jetting tool or 6 combinations of these. The tubing trailed by the 7 tractor unit extends from the surface end of the 8 pipeline and is pulled through the pipeline by the 9 tractor. The tubing typically comprises"coiled 10 tubing", generally formed from steel, plastic or 11 composite materials, which is fed into the pipeline 12 from a coil wound on a reel at the surface.

13 14 In use of such conventional methods, the maximum 15 distance that the tractor unit can travel along the 16 interior of the pipeline is limited by friction 17 between the outer surface of the tubing and the 18 interior surface of the pipeline. The maximum 19 practical range for conventional systems of this 20 type is of the order of 3 km. In recent years, 21 pipelines interconnecting offshore platforms and 22 seabed installations commonly have lengths as great 23 as 15 km. Accordingly, blockages beyond the range 24 of conventional intervention methods are impossible 25 to remove, necessitating the abandonment and 26 replacement of the pipeline.

27 28 The present invention concerns improved pipeline 29 blockage removal systems and methods whereby 30 blockages can be removed at greater distances from 31 the end of the pipeline than has hitherto been 32 possible.

1 2 In accordance with a first aspect of the invention, 3 there is provided a method of removing a blockage in 4 a fluid-filled pipeline, comprising: 5 connecting a length of tubing to a pipeline 6 blockage removal tool; and 7 transporting the tool along the interior of the 8 pipeline from a first end thereof to engage the 9 blockage, such that said tubing extends from said 10 first end of said pipeline to said tool; the method 11 including: 12 injecting fluid into the interior of the tubing 13 such that the tubing is substantially neutrally 14 buoyant in the fluid within the interior of the 15 pipeline.

16 17 Preferably, the tubing comprises an outer carrier 18 tube and an inner tube extending along the interior 19 of the carrier tube.

20 21 Preferably also, an electrical power and/or signal 22 cable extends along the interior of the tubing.

23 24 Preferably also, one of the outer and inner tubes 25 carries a first fluid to be supplied to the tool 26 connected to a first, downstream end of the tubing 27 from a second, upstream end thereof and the other of 28 the outer and inner tubes contains a second fluid, 29 the combined density of the tubes, fluids and cable 30 (if any) being such that the tubing is substantially 31 neutrally buoyant in the fluid within the pipeline.

32

1 Preferably also, the second fluid comprises 2 pressurised gas.

3 4 Preferably also, the first end of said other of the 5 outer and inner tubes is connected to a tractor unit 6 adapted to engage the interior surface of the 7 pipeline for pulling the tubing through the interior 8 of the pipeline.

9 10 Preferably also, said one of said outer and inner 11 tubes extends through the interior of the tractor 12 unit for connection to the tool.

13 14 Preferably also, the method includes inserting said 15 tool and said tractor unit into the pipeline and 16 operating said tractor unit to pull said tubing 17 through the interior of the pipeline.

18 19 In accordance with a second aspect of the invention 20 there is provided a tubing assembly for use in 21 removing blockages from pipelines comprising: 22 an outer carrier tube and an inner tube 23 extending along the interior of the carrier tube, 24 wherein one of the outer and inner tubes has a 25 first, downstream end adapted to be connected to a 26 pipeline blockage removal tool and is adapted to 27 carry a first fluid to be supplied to said tool from 28 a second, upstream end thereof, and the other of the 29 outer and inner tubes is adapted to contain a second 30 fluid.

31

1 In accordance with a third aspect of the invention, 2 there is provided apparatus for removing a blockage 3 from a pipeline comprising a tubing assembly in 4 accordance with the second aspect having a first end 5 thereof connected to a tractor unit adapted to 6 engage the interior surface of a pipeline and to a 7 pipeline blockage removal tool.

8 9 The invention substantially reduces or eliminates 10 friction between the exterior surface of the tubing 11 and the interior surface of the pipeline, so that 12 the tubing may be inserted into the pipeline to a 13 greater distance than would otherwise be possible.

14 15 Embodiments of the invention will now be described, 16 by way of example only, with reference to the 17 accompanying drawings in which: 18 19 Fig. 1 is a schematic, sectional side view of a 20 tubing assembly, tractor unit and pipeline blockage 21 removal tool within a pipeline, in accordance with 22 one embodiment of the invention; and 23 24 Fig. 2 is a schematic transverse cross section of a 25 tubing assembly in accordance with one embodiment of 26 the invention.

27 28 Referring now to the drawings, there is shown a 29 pipeline 10 within which is located a tractor unit 30 12, a pipeline blockage removal tool 14 connected to 31 a first, downstream end of the tractor unit 12, and 32 a junction unit 16, connected to a second, upstream

1 end of the tractor unit 12. A tubing assembly 2 embodying one aspect of the present invention 3 comprises an outer, carrier tube 18 having a first, 4 downstream end connected to an upstream end of the 5 junction unit 16, an inner tube 20 extending along 6 the interior of the outer tube 18, through the 7 interior of the junction unit 16 and the tractor 8 unit 12 to the blockage removal tool 14, and an 9 electrical power and/or signal cable 22 extending 10 along the interior of the inner tube 20 for 11 connection to power supplies and/or control systems 12 of the tractor unit 12 and tool 14. The pipeline is 13 filled with fluids, typically hydrocarbon products 14 being transported via the pipeline from a subsea 15 installation such as a wellhead, manifold or the 16 like to a surface installation such as an offshore 17 platform.

18 19 The tractor unit 12 and tool 14 may be of any of a 20 variety of known types and will not be described in 21 detail herein. The tractor 12 is typically 22 centralised in the pipeline 10 and driven 23 therethrough by means of wheels 24 or other friction 24 drive elements or the like. The tool 20 has a 25 working end 26, typically comprising a rotating bit, 26 reaming blades, fluid jets or the like, or 27 combinations thereof as appropriate for engaging 28 various types of blockage, and is supplied with 29 fluids and/or chemical agents via the inner tube 20 30 from an upstream end thereof. The junction unit 16 31 is optional and simply serves to provide a

1 mechanical connection between the outer tube 18 and 2 the tractor 12.

3 4 The tractor unit 12 pulls the tubing through the 5 interior of the pipeline until the tool 14 engages a 6 blockage to be removed. Once the blockage has been 7 removed by the action of the tool, the apparatus is 8 withdrawn from the pipeline.

9 10 In accordance with the invention, the inner tube 11 carries fluids to be supplied to the tool 20, and 12 the outer tube is filled with additional fluids, 13 suitably pressurised gas such as nitrogen, such that 14 the combined densities of the tubing components 18, 15 20 and 22 and the fluids contained therein make the 16 tubing substantially neutrally buoyant in the fluid 17 within the pipeline 10. Preferably, the effective 18 density of the tubing assembly in use is in a range 19 equal to the density of the fluid in the pipeline 10 20 plus or minus 10%, most preferably plus or minus 5%.

21 In this way, the tubing is made to float in the 22 middle of the pipeline 10 as it is pulled 23 therethrough by the tractor 12. Accordingly, there 24 will be no or minimal contact between the exterior 25 surface of the outer tube 18 and the inner surface 26 of the pipeline 10, so that friction between the 27 tubing and the pipeline is substantially reduced or 28 eliminated. Accordingly, the tractor may pull the 29 tubing through the pipeline for distances much 30 greater than would otherwise be possible, allowing 31 the removal of blockages which could not otherwise 32 by reached by conventional means.

1 2 The inner and outer tubes may be formed from any 3 suitable materials, typically plastics or composite 4 materials. Where pressurised gas is used in the 5 outer tube 18, the pressure of the gas must be 6 sufficient to prevent collapse of the outer tube 7 under the fluid pressure in the pipeline and the 8 tubing must be sufficiently strong to bear the gas 9 pressure without inflation (plastic deformation).

10 11 The tubes are preferably formed from thermoplastic 12 materials compatible with the fluid (s) contacting 13 the tubes and the temperatures encountered in the 14 operating environment, such as polyethylene, 15 polyamide and other materials commonly used in the 16 oil industry. Where the tubing is required to 17 resist inflation caused by high differential 18 pressures, the thermoplastic material may be 19 reinforced by any suitable means, such as a textile 20 braid formed from aramid fibre or the like.

21 22 The functions of the outer and inner tubes may be 23 reversed. There may be more than one inner tube for 24 carrying different fluids to the tool, arranged 25 concentrically or side by side, and there may be 26 more than one cable. The cable (s) need not be 27 contained within the inner tube (s).

28 29 Improvements and modifications may be incorporated 30 without departing from the scope of the invention.

Claims

1 Claims 2

3 1. A method of removing a blockage in a fluid-

4 filled pipeline, comprising:

5 connecting a length of tubing to a pipeline

6 blockage removal tool; and

7 transporting the tool along the interior of the

8 pipeline from a first end thereof to engage the

9 blockage, such that said tubing extends from said 10 first end of said pipeline to said tool; the method 11 including: 12 injecting fluid into the interior of the tubing 13 such that the tubing is substantially neutrally 14 buoyant in the fluid within the interior of the 15 pipeline.

16 17

2. The method of claim 1, wherein the tubing 18 comprises an outer carrier tube and an inner tube 19 extending along the interior of the carrier tube.

20 21

3. The method of claim 1 or claim 2, wherein an 22 electrical power and/or signal cable extends along 23 the interior of the tubing.

24 25

4. The method of claim 2 or claim 3, wherein one 26 of the outer and inner tubes carries a first fluid 27 to be supplied to the tool connected to a first, 28 downstream end of the tubing from a second, upstream 29 end thereof and the other of the outer and inner 30 tubes contains a second fluid, the combined density 31 of the tubes, fluids and cable (if any) being such

1 that the tubing is substantially neutrally buoyant

2 in the fluid within the pipeline.

3

4

5. The method of claim 4, wherein the second fluid

5 comprises pressurised gas.

6

7

6. The method of claim 4 or claim 5, wherein the

8 first end of said other of the outer and inner tubes

9 is connected to a tractor unit adapted to engage the 10 interior surface of the pipeline for pulling the 11 tubing through the interior of the pipeline.

12 13

7. The method of claim 6, wherein said one of said 14 outer and inner tubes extends through the interior 15 of the tractor unit for connection to the tool.

16 17

8. The method of claim 6 or claim 7, further 18 comprising inserting said tool and said tractor unit 19 into the pipeline and operating said tractor unit to 20 pull said tubing through the interior of the 21 pipeline.

22 23

9. A tubing assembly for use in removing blockages 24 from pipelines comprising: 25 an outer carrier tube and an inner tube 26 extending along the interior of the carrier tube, 27 wherein one of the outer and inner tubes has a 28 first, downstream end adapted to be connected to a 29 pipeline blockage removal tool and is adapted to 30 carry a first fluid to be supplied to said tool from 31 a second, upstream end thereof, and the other of the

1 outer and inner tubes is adapted to contain a second

2 fluid.

3

4

10. The assembly of claim 2, further including an

5 electrical power and/or signal cable extending along

6 the interior of the tubing.

7

8

11. The assembly of claim 9 or claim 10, wherein

9 the other of the outer and inner tubes is adapted to 10 contain a pressurised gas.

11 12

12. The assembly of any of claims 9 to 11 wherein 13 the first end of said other of the outer and inner 14 tubes is adapted to be connected to a tractor unit 15 adapted to engage the interior surface of a pipeline 16 for pulling the tubing through the interior of the 17 pipeline.

18 19

13. The assembly of claim 12, wherein the said one 20 of said outer and inner tubes is adapted to extend 21 through the interior of the tractor unit for 22 connection to said tool.

23 24

14. Apparatus for removing a blockage from a 25 pipeline comprising a tubing assembly as claimed in 26 any of claims 9 to 13 having a first end thereof 27 connected to a tractor unit adapted to engage the 28 interior surface of a pipeline and to a pipeline 29 blockage removal tool.