WO2009017419A1

WO2009017419A1 - Method and device for removing elements which are stuck in pipe lines

Info

Publication number: WO2009017419A1
Application number: PCT/NO2008/000277
Authority: WO
Inventors: Viggo Brandsdal
Original assignee: Tco As
Priority date: 2007-07-27
Filing date: 2008-07-25
Publication date: 2009-02-05
Also published as: NO328978B1; NO20073934L

Abstract

A method is described for handling of a first pig (20) that has become trapped inside a pipeline (10), in that inserted into the pipeline is a second pig (30) which is led up to and adjoining the pig and blocks flow of fluid through the pipeline, as pressuring upstream of the second pig (30) can loosen the first pig so that it can be collected, while when the pig is still trapped, the position of the first pig in the pipeline is determined so that it can be brought up. The method is characterised in that a pig in the form of a channel-forming (50) casing body that incorporates a removable blocking element (32) which blocks the flow of fluid through the channel (50) is inserted into the pipeline, and if the pig does not become loose, said pig position is determined by an itself known way, and the blocking element is removed to open for flow of fluid through the channel of the pig. An especially preferred pig construction is also described.

Description

Method and device for removing elements which are stuck in nin* im∞

The present invention relates to a method for handling of a first pig which has become trapped inside a pipeline, in that inserted into the pipeline is a second pig which is led up to and is adjacent to the first pig and blocks the flow of fluid through the pipe, as pressurising upstream of the second pig can loosen the first pig for retrieval, whilst when the pig remains trapped, the position in the pipeline of the first pig is determined such that it can be collected.

The invention also relates to a pig construction comprising an extended casing body set up to be led through a pipeline, and which defines a channel for through flow of fluid which is transported in a pipeline, as it appears in the preamble of claim 8.

Thus, the invention relates to removing elements from pipelines. With the invention one aims to provide solutions concerning operation of pipelines that can run between one or more of, for example, different rigs, production vessels, installations ashore, oil terminals, loading buoys, etc., and where hydrocarbons, oil, gas possibly with water are carried.

The term "pig" is used on apparatus that are sent into hydrocarbon-carrying pipelines to carry out various maintenance and inspections inside the pipeline. They can, for example, have as a task the removal of deposits, provide for ultrasound images or X-rays images of the pipe wall to consider the status of the wall, such as for example, wear and tear. A pig can also be used to measure flow velocities, temperature and other essential parameters.

Such pigs that are sent into pipelines that lie on the ocean bottom have always had a through-going axial channel which enables fluid of oil/water/gases to pass through the pig even if the pig should become trapped in the pipeline. Therefore, one chooses to let the pipeline remain where it is and produce and carry hydrocarbons through the available through-flow area in the pig if it becomes trapped.

As the trapped pig does not close completely for the through-flow, the fluid can not be pressurised up to such a level that the pig will hopefully come loose and can be led out of the pipeline either. This will only increase the through-flow correspondingly.

Then it is necessary to use an extra solid pig which is sent down to the trapped pig until it abuts the trapped pig. The solid pig can block the through-flow in that it forms a seal against the inner wall of the pipeline. At pressurisation of fluid in the pipeline, the trapped pig will, as a rule, come loose and can be pumped further forward and be collected out of the pipeline at the surface or other suitable locations.

Another situation arises when the trapped pig will not come unstuck. Then the whole pipeline must be opened to take out the two pigs. This can be carried out either by performing a costly underwater operation on the lying pipeline, or by bringing the pipeline up to the deck of a pipe handling vessel where the two pigs are removed, the pipeline is joined together again and is placed back on the sea bed.

To carry out this operation, one must localise the exact position of the pigs in the pipeline, and for this one uses the aforementioned pig which completely seals off the passage through the pipe.

The position is estimated by increasing the fluid pressure by pumping in liquid up toward the sealing pig and from the amount of liquid in m³ pumped in and in relation to the internal cross section of the pipeline before the pressure builds up, one can very accurately calculate the position of the pig in the pipe.

By sending down the sealing pig, one runs the risk that this pig will also become trapped as one did not succeed in making the originally inserted pig become loose. The pipeline is thereby completely blocked, and it must be brought up and be opened to remove the plug. The risk with this is therefore that the whole production stops, something which is very costly. Furthermore, it is a very complex operation to bring out a pig that seals the pipeline and the operation itself normally requires large resources both to plan and to carry out.

It is an object of the present invention to provide a new method and an apparatus which will eliminate the above mentioned problems.

It is an object of the invention to provide a new method and a new pig apparatus that can be used in the pressurising to loosen a trapped pig.

Furthermore, it is an object that a new pig instrument which initially blocks through-flow of fluid in the pipeline, can be opened such that through-flow of fluid can be set up again.

It is a further object of the invention to provide a solution where one can continue production in the pipeline even if the rescue action fails.

Furthermore, it is a specified object of the invention to be able to delay an eventual action in the pipeline for bringing up the pigs, if the attempt to loosen the pig fails. One wishes for solutions where one can plan a stop in production a long time ahead, as one can then carry out other revisions of the platform at the same time in addition to removing the pigs. All platforms go through such revision stops at regular intervals.

It is a further object to provide a pig which does not so easily become trapped in a pipeline.

The method according to the invention is characterised in that a pig in the form of a channel-forming casing element which incorporates a removable blocking body that blocks the flow of fluid through the channel is inserted in the pipeline, and if the pig can not be made loose, said pig position is determined in a method known per se, and the blocking body is removed to open for flow of fluid through the channel of the pig.

The preferred embodiments of the method appear in claims 2-7. The new pig instrument according to the invention is characterised in that the inner channel of the casing body comprises a blocking element which blocks for flow of fluid through the casing, and the blocking element can be removed to open for flow of fluid through the channel.

According to a preferred embodiment the blocking element is a disc of a crushable material, such as a ceramic material or glass, and it is preferably set up for crushing at an elevated fluid pressure or upstream of the pig and/or by remote detonation of an explosive charge fitted on the pig in connection with the disc. The blocking element in the form of a disc is arranged to stand internally across the casing part and perpendicularly to an intended direction of flow.

According to a preferred embodiment, the sealing means on the outer side of the pig is set up to radially expand out toward the inner wall of the pipeline, such as when the pressure in the fluid in the pipeline increases. According to a preferred embodiment, the pig is composed of a number of sections which are mutually connected and mutually movable with the help of ball joints.

From the above, it can be seen that the flow through the rescue pig is initially blocked with the help of a plug made from a crushable material. Glass is preferably used, but other materials that can be crushed by pressure effects from a fluid can also be used, such as ceramic materials.

According to a preferred embodiment the plug body of the pig is fitted with a small explosive charge which can be used to blow away the glass plug. This can take place by remote control by the operator from the surface.

The invention shall be explained in more detail with reference to the subsequent figures, in which:

Figure 1 shows schematically a pipeline that lies on the ocean bottom and runs from a wellhead up to a production vessel for hydrocarbons. The figure shows in more detail a pig which is trapped in the pipeline and a rescue pig according to the invention which is transported with the flow of fluid in through the pipeline so to abut the rear side of the pig. Figure 2 shows an enlarged perspective of the rescue pig according to the invention.

Figure 3 shows a longitudinal section of the rescue pig according to the invention.

Figure 4 shows an enlarged, longitudinal section of the rescue pig.

Figure 5 shows how the rescue pig according to the invention can be articulated so that it can bend to ease the passages inside the pipeline.

Shown in figure 1 as an introduction, is a pipeline 10 that lies on the ocean bottom 12, and which, for example, runs from a wellhead 14 up to a production vessel 16 for hydrocarbons, and which can comprise a processing installation 18 that can process and separate the stream of hydrocarbons.

As an example, an inspection and sensor pig 20 that has become trapped in the pipeline is shown. This pig 20 has a longitudinal channel 50 enabling through flow of fluid even when it has become trapped.

A rescue pig 30 is transported inwardly upstream of the sensor pig 20 which according to prior art shall completely block the flow of fluid to be able to pressurise the fluid and hopefully get the pig 20 to come loose so that both pigs 20 and 30 can be pumped back to the production ship 16.

The rescue pig is shown in a principle diagram in figure 2. It comprises a pipe- formed housing part 30 across which is fitted a disc that can disintegrate, perpendicular to the direction of flow inside the housing part. The disc is preferably a glass disc 32, and which is also called a "burst disc". The disc 32 is set up to completely block flow of fluid through the pig 30.

The glass plug 32 is constructed so that it can withstand a given high pressure as an upper limit before it is crushed by the pressure. In relation to the actual pipeline 10, the so-called burst pressure must be a pressure which is somewhat lower than the maximum pressure the pipeline can withstand. Furthermore, the burst pressure which the glass disc 32 shall withstand is set at a level which a customer wants. The pig according to the invention is shown in a longitudinal section in figure 2 and an enlarged longitudinal section in figure 3.

The pig 30 is shown located in the pipeline 10, and comprises a number of pig sections 34 which are mutually coupled together into a longer unit. The figure shows that it is put together by five such sections 34A-34E to form the pig 23. The glass disc 32 is fitted inside the one section 34D of these sections.

Two adjoining sections 34A-E are coupled together with the help of a short connecting coupling 36 which has a special form so that its inside surrounds the outer side of the outer periphery of a section at the ends. The actual section is movable in relation to the short casing 36 so that the rescue pig can partially meander forward during the travel through the pipeline when this has a winding path forward.

For example, this mobility can be performed in that the two ends of the section each comprises a ball form 38 around the outer periphery of the section 34E and with an axially directed through bore for free flow of fluid, see also figure 3.

Correspondingly, the connecting element has a hollow dome shape 40 with a correspondingly axially directed through bore for free flow of fluid and which can surround perfectly, and ride on, the ball form.

Thus the two parts cannot be pulled apart but, at the same time, retain full mobility in relation to each other as is normal for ball and socket joints, and the pig can easily be moved through any curves and swings and also easily pass through branching points that may be found in the pipeline.

This construction reduces the risk of the rescue pig becoming trapped in a winding pipeline.

According to another essential aspect of the present invention, the pig comprises, according to the invention, a combined centralising and sealing construction that can be reset from a passive, non-sealing position to a sealing position, and which can hold the pig centred in the pipe 10. The seals are activated to said readjusted position by increasing the fluid pressure at the upstream side of the pig. The sealing according to the invention is shaped as an elastic, ring-formed, pressure-influenced, adjustable gasket body 49 which is arranged around each outer side periphery of each joining section 34. The gasket body 40 is formed with an open, bellow-formed/lip-form 42 that faces upward to the upstream side. When the fluid pressure increases, the pressure will influence the lip of the gasket 42 so that this is pressed radially outwards so that it finally pushes against the inner wall 43 of the pipeline. When the first contact with the inner wall 43 of the pipe is made, the fluid pressure increases rapidly and the gasket will provide an even greater sealing force against the inner wall 43 of the pipe.

From this pig position, the pressure can be increased further until the glass disc 32 bursts and once again gets a full through flow of fluid. This gasket system is set up to be activated against the pipe wall at a pressure which is lower than the bursting pressure of the glass disc.

Application of the construction

As mentioned previously, the aim of this is that when the rescue pig hits the sensor pig 20, one can work out where this pig 20 is situated in the pipeline, to prepare for a future collecting, as explained previously.

If the sensor pig 20 does not move and become loose so that it can be brought to the surface, the fluid pressure is increased instead, after one has performed said localisation, so that the glass disc 32 breaks and the production is restarted by opening for a new flow of fluid through the hollow sensor pig 20 and the rescue pig 30.

This construction with a glass disc that can be crushed can, of course, be used in a pig, something that will give it the same advantages. That means that it is sent down in the pipeline with a glass disc that blocks the through flow.

An advantage with this is that one can reduce the time it takes to drive the pig through the pipeline, as the plug at the same time does not have any channel for through-flow, it is driven forward with greater speed. The present plug with glass disc can reach the same speeds as the ordinary flow of fluid in the pipeline and it is therefore much less likely that it will get stuck.

Claims

P A T E N T C L A I M S

1. Method for handling of a first pig (20) that has become trapped inside a pipeline (10), in that inserted into the pipeline is a second pig (30) that is led up to and is adjacent to the first pig (20) and blocks the flow of fluid through the pipe, as pressurising upstream of the second pig (30) can loosen the first pig so that it can be collected, while when the pig is still trapped, the position of the first pig in the pipeline is determined for collection of the pig, characterised in that a pig (30) is inserted into the pipeline (10) in the form of a channel-forming (50) casing element which incorporates a removable blocking body (32) that blocks the flow of fluid through the channel, and if the pig does not become loose, said pig position is determined in a manner known per se, and the blocking body (32) is removed to open for flow of fluid through the channel (50) of the pig.

2. Method according to claim 1, characterised in that a blocking element in the form of a disc is used, and which is removed in that it is crushed in that the fluid pressure upstream of the rescue pig is increased.

3. Method according to claim 1, characterised in that the blocking element is removed in that it is crushed by remote controlled detonation of an explosive charge fitted onto the pig in connection to the disc.

4. Method according to one of the preceding claims, characterised in that a blocking body is used in the form of a disc of a ceramic material which can disintegrate, preferably from glass.

5. Method according to one of the preceding claims, characterised in that when the pig remains trapped, the position is determined by the in itself known features by increasing the fluid pressure to pump in fluid up to the second pig so that sealing means in connection with the second pig is activated for sealing against the inner wall of the pipe, whereupon the fluid pressure is increased further, and, before the pressure builds up even more, the exact position in the pipeline of the first pig is determined based on the amount of pumped-in fluid in m³ and in relation to the inner cross section of the pipeline, followed by the new feature where the fluid pressure is increased further until the pig eventually becomes loose from its trapped position or the disc of glass is crushed and thus opens for free flow through the pipeline again.

6. Method according to one of the preceding claims, characterised in that sealing means is arranged to the outer side of the second pig and which expands radially in that the pressure of the fluid increases.

7. Method according to one of the preceding claims, characterised in that a pig composed of a number of sections that are mutually connected and mutually movable with the help of ball joints is used.

8. Construction of a pig comprising an extended casing body set up to be led through a pipeline and which defines a channel for through flow of fluid which is brought forward in the pipeline, characterised in that the inner channel of the casing body comprises a blocking element that blocks for fluid flow through the casing and the blocking element can be removed to open for flow of fluid through the channel (50).

9. Construction according to claim 8, characterised in that the blocking element is a disc made from a material that can be crushed, such as a ceramic material or glass.

10. Construction according to claims 8-9, characterised in that it is set up for crushing at an elevated fluid pressure upstream of the rescue pig and/or at remote control detonation of an explosive charge fitted in the pig in connection with the disc.

11. Construction according to claims 8-10, characterised in that the blocking element in the form of a disc is arranged across inside the casing part and stands perpendicular to an intended direction of flow.

12. Construction according to claims 8-11 , characterised in that the outer side of the pig comprises sealing means set up to be expanded radially outwards towards the inner wall of a pipeline such as by the pressure of the fluid in the pipeline being increased.

13. Construction according to claims 8-11, characterised in that the pig is composed of a number of sections which are mutually connected and mutually movable with the help of ball and socket joints.