WO2008054224A1

WO2008054224A1 - A method and a device for closing an underground conduit to throughput of particulate material

Info

Publication number: WO2008054224A1
Application number: PCT/NO2007/000380
Authority: WO
Inventors: Rune Freyer
Original assignee: Rune Freyer
Priority date: 2006-11-03
Filing date: 2007-10-26
Publication date: 2008-05-08
Also published as: NO20065023L; NO325584B1

Abstract

A method and a device for closing an underground conduit (8) to throughput of particulate or settable material, comprising to place a plug (1) in the conduit (8), the plug (1) being formed from an elastic material (2) with open pores (4) as well as openings (4) of a dimension conducive to fluid, but retentive to the particulate or settable material.

Description

A METHOD AND A DEVICE FOR CLOSING AN UNDERGROUND CONDUIT TO THROUGHPUT OF PARTICULATE MATERIAL

This invention concerns a method for closing an underground conduit to throughput of particulate material . More particularly, it concerns a method for closing an underground conduit to throughput of particulate or settable material, comprising placing a plug in the conduit, the plug being formed from an elastic material with open pores as well as openings of a shape conducive to fluid, but retentive to the particulate or settable material . The invention also concerns a device for practising the method.

In this context, the term conduit implies lengthy openings, e.g. a borehole, a pipe bore or an annulus .

During some subsurface work operations, typically operations known from petroleum production, it is desirable or required to be able to close a conduit permanently or temporarily.

Cementing a portion of a conduit is a typical example of such a work operation. Due to dissimilar density as compared to the fluid located at the cementing location, the cement may sink downwards within the conduit and also mix with said fluid if the conduit is not closed. Uncertainty as to the success of the cementing operation thereby results .

Thus, it is common to place a plug in the conduit at the cementing location in order to ensure that the cement remains in the intended portion of the conduit.

Normally, prior art plugs are comprised of relatively complicated mechanical devices formed so as to be able to provide a relatively large degree of expansion. Plugs of this type are typically made from metal or rubber. Most commonly such prior art plugs are set by means of a setting tool in a separate setting operation.

Use of prior art plugs are thus relatively time-consuming and, as such, costly. Due to the plug construction, in which metals form a substantial part, it may prove complicated to remove the plug upon completion of the cementing operation.

A novel plug construction is described in document

WO 2005/116394. The document relates to a plug which, when in a compressed state, is arranged in a manner allowing it to be set in a region exposed to overpressure, and in which the plug expands by virtue of cavities in the plug material being filled with fluid. The plug according to WO 2005/116394, however, is not formed so as to be conducive to fluid.

The object of the invention is to remedy or reduce at least one of the disadvantages of the prior art .

The object is achieved according to the invention by means of the features disclosed in the following description and in the subsequent claims .

In accordance with the invention, a method for closing an underground conduit to throughput of particulate or settable material is characterized in placing a plug in the conduit, the plug being formed from an elastic material with open pores as well as openings of a shape conducive to fluid, but retentive to the particulate or settable material .

Pressure differences across the plug are balanced by allowing fluid to flow through the plug material .

The plug may be compressed before placing it in the conduit, and then, upon placing it in the conduit, releasing the plug for expansion whilst filling the open pores with fluid. For transportation down into the conduit, the plug may for example be pumped down via a pipe. At that point in time, the plug may have been compressed, or it may bear against the pipe wall during the pumping operation down from e.g. the surface. The plug may also be located in a receptacle from which it is displaced at the user location; or it may be kept in the compressed state by means of an enclosure that is breakable at the installation location. The enclosure may be broken mechanically, electrically or chemically.

Advantageously, the plug may be placed in a so-called cement dump bailer where it forms a sealing plug that keeps the cement in the bailer until the bailer is positioned at the cementing location. Then, the plug is displaced from the bailer so as to seal the conduit by means of expansion.

Normally, the pores in the elastic material form both cavities being filled with fluid when the plug expands, and openings through which fluid flows in order to achieve pressure balancing. Advantageously, the elastic material may be comprised of foam rubber or compressible composite material with open pores .

The pores are formed by virtue of e.g. suitable dimensioning, whereby particulate material above a certain predetermined size cannot pass into or through the pores.

The pores may be formed so as to allow one fluid to pass, but to retain another fluid, for example due to capillary forces or the viscosity of the fluid. This solution may be suitable to facilitate the setting of e.g. polymer materials capable of gelling, epoxies or other liquid-based, settable materials .

The plug is particularly suitable for use during casting operations in which cement is filled above the plug, whereby the plug prevents the cement from flowing downwards within the conduit. The plug is also suitable for keeping gravel separated from another material, for example during fracturing operations .

Typically, the cross-sectional dimension of the plug before being compressed is somewhat larger than the cross-section of the conduit. When expanding, the plug will thus exert a certain bias against the conduit wall.

In one embodiment, one portion of the plug may be assigned a cross-section that fills the conduit, whereas another portion thereof is assigned a dimension that does not fill the conduit. In the event of filling cement in the annulus around the plug, a ring-shaped cement plug will form when the cement is cured.

It may also prove advantageous to filter e.g. a part of the fluid away from the casting mass, and trough the plug, in order to achieve a faster curing of the casting mass.

As compared to the use of prior art plugs, the present invention provides a significant simplification of e.g. setting of a plug during casting operations. The plug according to the invention may be removed easily, either mechanically or by means of chemical agents.

An example of a preferred method and embodiment is described in the following and is depicted in the accompanying drawings, in which:

Fig. 1 schematically shows a borehole, in which a plug according to the invention is being displaced from a pipe;

Fig. 2 schematically shows, in substantially larger scale, a section through the elastic material of fig. 1;

Fig. 3 schematically shows a plug being displaced from a receptacle and into an annulus; and

Fig. 4 schematically shows a borehole, in which an alternative embodiment of a plug is set in the borehole, and in which cement is placed so as to surround an upper portion of the plug.

In the drawings, reference numeral 1 denotes a plug formed from an elastic material 2 , the material 2 being provided with open pores 4, see fig. 2. In this preferred example of an embodiment, the elastic material 2 is comprised of foam rubber.

As mentioned in the general part of the description, the pores 4 in the elastic material 2 normally comprise both cavities being filled with fluid when the plug 1 expands, and openings 4 through which fluid flows in order to achieve pressure balancing.

Conditions permitting, the functions may be maintained by dissimilarly shaped pores 4 and openings 4. It is noted that the same reference numeral 4 is used both for pores and openings given that they normally are comprised of the same pores .

In fig. 1, the plug 1 is shown during its displacement from a pipe 6 and into an underground borehole 8. The borehole 8 5 forms a typical conduit. The plug 1 was compressed before it was placed in the pipe 6, or whilst being placed in the pipe 6, and it expands gradually as it leaves the pipe 6, the plug 1 seeking to assume its original shape. Thereby, the plug 1 expands against the borehole 8. During the expansion, theo pores 4 are filled with fluid from the surroundings.

The plug 1 may have been placed in an end portion of the pipe 6 before the pipe 6 was run into the borehole 8. Alternatively, the plug 1 may have been pumped down through the pipe 6, for example by means of a cementing mass 10. s During and after the expansion event, a potential pressure difference across the plug 1 will be balanced by virtue of fluid flowing through the pores 4 of the plug 1.

Subsequent to expansion of the plug 1, casting mass is placed in the region above the plug 1, keeping in mind that only ano insignificant amount of casting mass may flow into the plug 1.

Fig. 3 shows a plug 1 whilst being displaced from a receptacle 12 and into an annulus 14 by means of an actuator 16, which displaces a ring-shaped piston 18. The plug 1 may5 thus seal an annulus between the borehole 8, or a casing (not shown), and the pipe 6.

In an alternative embodiment, see fig. 4, a lower first portion 20 of the plug 1 is formed with a cross-section that fills the borehole 8, whereas an upper second portion 220 thereof is assigned a cross-section that does not fill the borehole 8 .

An annulus 24 between the plug 1 and the borehole 8 is filled with cementing mass 10. Upon curing, the cementing mass 10 forms a ring-shaped plug.

Claims

C l a i m s

1. A method for closing an underground conduit (8) to throughput of particulate or settable material, c ha r a c t e r i z e d i n placing a plug (1) in the conduit (8) , the plug (1) being formed from an elastic material (2) with open pores (4) as well as openings (4) of a shape conducive to fluid, but retentive to the particulate or settable material .

2. The method according to claim 1, c har a c t e r i z e d i n compressing the plug (1) before placing it in the conduit (8) ; and

- after being placed in the conduit (8) , releasing the plug (1) for expansion whilst filling the open pores (4) with fluid.

3. The method according to claim 1, ch ar ac t e r i z ed i n placing particulate material above the plug (1) .

4. The method according to claim 1, c h a r a c t e r i z e d i n placing curable particulate material above the plug (1) .

5. A device for a plug (1) for closing an underground conduit (8) to throughput of particulate or settable material, c h a r a c t e r i z e d i n that the plug

(1) is formed from an elastic material (2) with open pores (4) ; and

- wherein the plug (1) also comprises openings (4) of a shape conducive to fluid, but retentive to the particulate or settable material .

6. The device according to claim 5 , c h a r a c t e r i z e d i n that the openings (4) of the plug (1) are formed in a manner conducive to one fluid, but retentive to another fluid.

7. The device according to claim 5, char act eri z ed i n that the plug (1) , in a first portion (20) thereof, is assigned a dimension that fills the conduit (8) , whereas a second portion (22) thereof is assigned a dimension that does not fill the conduit (8) .