GB2195738A

GB2195738A - Method of isolating a portion of a pipeline

Info

Publication number: GB2195738A
Application number: GB08623947A
Authority: GB
Inventors: Paul Robert Marks
Original assignee: Shell Internationale Research Maatschappij BV
Current assignee: Shell Internationale Research Maatschappij BV
Priority date: 1986-10-06
Filing date: 1986-10-06
Publication date: 1988-04-13
Also published as: GB8623947D0

Abstract

To enable repair of a damaged pipeline a gel plug or pig 3 is injected into the pipeline such that it spans the length of the damaged zone 2 and refrigeration jackets 4, 5 are installed around the pipeline at either side of said zone (2) so as to isolate the zone 2 by creating a frozen gel plug 3 at the locations of the jackets 4, 5. The damaged zone 2 may be replaced by a new section. The gel may be formed from cycohexane, pyrogenic silica, polystyrene and toluene. If the gel is in the form of a pig the latter may be separated from the driving fluid by an electromagnetic or acoustic sensitive piston. <IMAGE>

Description

SPECIFICATION Method of isolating a portion of a pipeline The invention relates to a method of isolating a portion of the interior of a pipeline from other parts of the pipe interior.

If inspection or repair of elongate gas or other fluid-containing pipelines is required it may be undesirable or difficult to flood the whole length of the pipe interior with water in order to remove the gas or other fluid. In particular in subsea pipelines such flooding is a time consuming and expensive operation.

Thus there is a need for a reliable and less time consuming method of isolating a pipe section which requires inspection or repair.

The invention aims to facilitate the isolation of a portion of a gaseous or other fluid containing pipeline to enable inspection or repair operations to be undertaken.

The method according to the invention thereto comprises - installing a refrigeration jacket at the pipeline at either side of said portion, - injecting a gel into the pipeline such that in the pipe interior a gel plug is formed having a length larger than the spacing between the jackets, - manoeuvring the plug through the pipe in terior such that the plug is at both ends thereof surrounded by the jackets, and - actuating the refrigeration jacket to cool the pipeline thereby forming a plug of frozen gel in said interior at least at the location of each of said jackets.

Preferably the gel consists of cyclohexane and a gelling agent. Said gelling agent prefera -bly consists of pyrogenic silica. The pyrogenic silica may be mixed with either polystyrene or toluene.

The invention will now be explained in more detail, by way of example, with reference to the accompanying drawing in which a pipeline for transport of gaseous or other fluids is shown and provided with the reference numeral 1. The pipeline 1 comprises a damaged zone 2 which requires inspection and/or repair.

To facilitate the isolation of the damaged zone 2 from the fluid in the remaining part of the pipe interior a gel has been injected into the pipeline 1 in such a manner that an elongate gel plug 3 is formed in the pipe interior which gel plug 3 straddles the damaged zone 2. A pair of refrigeration jackets 4 have been installed around the pipeline 1 at either side of the damaged zone 2 in such a manner that the jackets 4 surround each a portion of the gel plug 3.

The refrigeration jackets 4 may each consist of a pair of interconnected cylinder-halves to form a collar which surrounds the pipe wall.

The jackets are each provided with a cooling circuit which may operate on the principle of a heat pump or Stirling motor. Alternatively the cooling circuit may consist of a self contained compressor driven refrigeration system.

The cooling capacity of the refrigeration jackets 4 is selected sufficiently large to cool the pipe wall and interior of the pipe in the region of the jackets well below the freezing temperature of the gel plug 3, so that in the region of each jacket 4 a frozen gel plug 5 is formed throughout the pipe interior. The cooling capacity of the jackets 4 is preferably selected such that the pipe wall at the location of the jackets 4 can be cooled to at least -100C.

The length of each cooling jacket is designed in conjunction with the hydrostatic pressure which the frozen gel plug 5 should be able to withstand, the interfacial bond strength of the frozen gel plug 5 on the pipe wall and the interlaminar shear strength of the frozen gel plug 5 itself. The length of the spacing between the cooling jackets 4 will usually be selected between 3 and 30 m.

After having operated the refrigeration jackets 4 over a period of time sufficiently long to allow formation of the frozen gel plugs 5 the damaged zone 2 may be repaired in the usual manner such as by removing the pipe section in the region of the damaged zone 2 and inserting a replacement section in the pipeline 1.

The gel may be injected into the pipe interior through an opening, for example an existing tap point, located close to the damaged zone 2, but if such an opening is not present and canndt be made, the gel may be injected at a located remote from the damaged zone 2 and then pumped towards said zone 2. In particular if the pipe is a subsea oil or gas line the latter procedure is attractive and injection of the gel may take place at an offshore platform or onshore terminal from where the gel is pumped through the pipeline 1 towards the damaged zone 2 which may be located many kilometres away from the point of injection.It is preferred to keep the gel plug isolated from the driving fluid behind it by means of a movable pipeline piston to avoid mixing of the gel with said fluid and to enable accurate detection of the gel plug on the basis of currently available electromagnetic and acoustic techniques for detecting the location of a piston in a pipeline.

The gel forming the gel plug 3 preferably is a hydrocarbon based gel. A particularly suitable hydrocarbon based gel comprises cyclohexane as the major constituent which is mixed with a suitable gelling agent. The gelling agent preferably consists of pyrogenic silica.

The gelling agent may further comprise polystyrene and/or toluene to depress the freezing point and vapor pressure of the gel thus making the gel more stable.

It will be understood that the embodiment of the invention shown is only examplary and that various modifications of the present in vention will become apparent to those skilled in the art from the foregoing- description and accompanying drawing. Such modifications are intended to fall within the scope of the ap

Claims

pended claims. CLAIMS

1. Method of isolating a portion of the interior of a pipeline from other parts of said interior, the method comprising: - installing a refrigeration jacket at the pipeline at either side of said portion, - injecting a gel into the pipeline such that in the pipe interior a gel plug is formed having a length larger than the spacing between the jackets, - manoeuvring the plug through the pipe in terior such that the plug is at both ends thereof surrounded by the jackets, and ~actuating the refrigeration jackets to cool the pipeline thereby forming a plug of fro zen gel in said interior at least at the loca tion of each of said jackets.

2. The method of claim 1, wherein the pipeline is an underwater gas line.

3. The method of claim 1, wherein the gel is injected into the pipeline at a location remote from said portion of the pipe interior and the gel plug is subsequently pumped towards said portion of the pipe interior by means of a driving fluid while the gel plug is isolated from said driving fluid by means of a movable piston.

4. The method of claim 3, further comprising the step of detecting the location of said piston during the pumping process and interrupting the pumping process when the piston has reached a location close to said portion of the pipe interior.

5. The method of claim 1, wherein the gel is injected through an opening in the pipe wall located close to the portion of the pipeline which is to be isolated.

6. The method of claim 1, wherein the gel comprises cyclohexane and a gelling agent.

7. The method of claim 6, wherein said gelling agent comprises pyrogenic silica.

8. The method of claim 7, wherein said gelling agent further comprises polystyrene.

9. The method of claim 7, wherein said gelling agent further comprises toluene.

10. The method of claim 1, wherein said refrigeration jackets are actuated to cool the pipe wall at the location of the jackets to a temperature lower than - 100C.

11. The method of claim 1, wherein the spacing between the jackets is selected between 3 and 30 m.

1#2. The method of claim 1, wherein said jackets operate on the principle of a heat pump.

13. The method as claimed in claim 1, substantially as described with reference to the accompanying drawing.