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Patent Searching and Data


Title:
METHOD AND DEVICE FOR LOOSENING A CAST-IN CASING
Document Type and Number:
WIPO Patent Application WO/2011/093720
Kind Code:
A1
Abstract:
A method for loosening a cast-in casing (4) from a borehole (6) in the ground, and wherein the method comprises moving, through the casing (4), a non-circular object (10, 12) having a largest transverse dimension (22, 24) being larger than the internal diameter of the casing (4).

Inventors:
MONGE PER ARNFINN (NO)
Application Number:
NO2011/000032
Publication Date:
August 04, 2011
Filing Date:
January 28, 2011
Export Citation:
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Assignee:
WELLBORE AS (NO)
MONGE PER ARNFINN (NO)
International Classes:
E21B31/00; E21B29/00; E21B43/10
Domestic Patent References:
WO2003093623A22003-11-13
Foreign References:
US2956626A1960-10-18
US20050011650A12005-01-20
Attorney, Agent or Firm:
HÅMSØ PATENTBYRÅ ANS (Sandnes, NO)
Download PDF:
Claims:
C l a i m s

1. A method for loosening a cast-in casing (4) from a borehole (6) in the ground, c h a r a c t e r i z e d i n that the method comprises moving, through the casing (4), a non-circular object (10, 12) having a largest transverse dimension (22, 24) being larger than the internal diameter of the casing (4).

2. The method according to claim 1, c h a r a c t e r i z e d i n that the method comprises moving, through the casing (4), a non-circular object (10, 12) having a largest transverse dimension (22, 24) being larger than the internal diameter of the casing (4) in two directions.

3. A device for a tool (1) for loosening a cast-in casing (4) from a borehole (6) in the ground, wherein the tool (1) comprises a central part (2),

c h a r a c t e r i z e d i n that the tool (1) comprises a non-circular object (10, 12) having at least two diametrically opposite bodies (14) being radially movable between a retracted, passive position and an extended, active position, and wherein the external distance between the bodies (22, 24), when the bodies (14) are in their active positions, is larger than the internal diameter of the casing (4).

4. The device according to claim 3, c h a r a c t e r i z e d i n that at least one body (14) abut against the central part (2) via inclined surfaces (16, 18).

5. The device according to claim 3, c h a r a c t e r i z e d i n that at least one body (14) is connected to an activator (28) structured in a manner allowing it to move the body (14) between the passive and the active position.

6. The device according to claim 5, c h a r a c t e r i z e d i n that the activator (28) is connected to a friction body (36) abutting in a gliding manner against the casing (4).

7. The device according to claim 3, c h a r a c t e r i z e d i n that at least one body (14), when in its active position, abuts against a stopper (32).

Description:
METHOD AND DEVICE FOR LOOSENING A CAST-IN CASING

This invention relates to a method for loosening a cast-in casing. More particularly, it concerns a method for loosening a cast-in casing from a borehole in the ground. The invention also comprises a device for practising the method.

During final plugging of boreholes in the ground, typically of petroleum wells, it is oftentimes necessary to remove a considerable length of casing from the upper portion of the borehole.

Most frequently, casings are cast-in, by means of a casting substance, against an external casing or against the formation wall. Even though such a casting substance oftentimes is of relatively poor quality, it bonds the particular casing to the external casing or to the formation.

It is therefore common, according to prior art, to machine away considerable amounts of material from the casing in order to weaken the casing sufficiently.

Machining operations of this type are most commonly carried out by means of a drilling vessel. It is obvious that operations of this type are both time- and cost consuming.

The object of the invention is to remedy, or to reduce, at least one of the

disadvantages of the prior art, or at least to provide a useful alternative to the prior art.

The object is achieved by virtue of features disclosed in the following description and in the subsequent claims. A method for loosening a cast-in casing from a borehole in the ground is provided, wherein the method is characterised in that it comprises moving, through the casing, a non-circular object having a largest transverse dimension being larger than the internal diameter of the casing.

During the movement of the non-circular object through the casing, the casting substance located outside the wall of the casing at the largest diameter of the non- circular object, will be deformed or crushed by virtue of the pipe wall of the casing being moved temporarily into the casting substance. At the same time, and due to the same deformation, other portions of the pipe wall of the casing will be retracted temporarily inwards from the casting substance.

Preferably, the movement of the wall of the casing is elastic, insofar as a plastic deformation may increase the diameter of the casing and hence complicate the withdrawal of the casing.

The method may comprise moving, through the casing, a non-circular object having a largest transverse dimension being larger than the internal diameter of the casing in two or more directions.

The method may be carried out by means of a tool for loosening a cast-in casing from a borehole in the ground, wherein the tool comprises a central part, and wherein the tool is characterized in that it comprises a non-circular object having at least two diametrically opposite bodies being radially movable between a retracted, passive position and an extended, active position, and wherein the external distance between the radially opposite bodies, when the bodies are in their active positions, is larger than the internal diameter of the casing.

At least one of the bodies may abut against the central part via inclined surfaces. Thereby, the body may be moved radially by being moved axially relative to the central part.

At least one body may be connected to an activator structured in a manner allowing it to move the body between the passive and the active position. The activator may be connected to a friction body abutting in a gliding manner against the casing glidingly.

By virtue of the friction force between the friction body and the casing acting in a first direction relative to the central part during insertion of the tool in the casing, the body may be held in its passive position during the insertion. When the friction force acts in the opposite direction during movement of the tool out of the casing, the body is brought to its active position.

If desirable, a remote-controlled actuator may be used to move the body between its passive and active position. Typically, the bodies are moved in pairs.

At least one body may, when in its active position, abut against a stopper. By so doing, the body is prevented from being able to be moved unintentionally far out in the radial direction.

The inclined surfaces encircling the central part may be split into sectors of the total periphery. By turning the central part relative to the body, the body may disengage from its cooperating inclined surfaces. The tool may thus be withdrawn from the casing with the bodies in their respective passive positions.

The method and the device according to the invention may facilitate the withdrawal of casing portions from a borehole considerably, insofar as the casing may be divided into suitable lengths upon being loosened, and then be lifted out of the borehole.

In the following, an example of a preferred method and embodiment is described and depicted in the accompanying drawings, wherein :

Fig. 1 shows a tool according to the invention when disposed in a casing in the ground ;

Fig. 2 shows an end view of the tool in Fig. 1 ;

Fig. 3 shows a longitudinal section of the tool in Fig . 1;

Fig. 4 shows one section III-III in Fig . 3 :

Fig. 5 shows a longitudinal section of the tool in Fig . 1 when in an activated

Fig. 6 shows a section V-V in Fig. 5;

Fig . 7 shows a longitudinal section of the tool in Fig. 1 when in a released position;

Fig. 8 shows a section VII-VII in Fig. 7;

Fig. 9 shows a view of a tool in an alternative embodiment; Fig. 10 shows an end view of the tool in Fig. 9;

Fig. 11 shows a view of the tool in Fig. 9 when in an activated position, and

Fig. 12 shows an end view of the tool in Fig. 11;

In the drawings, reference numeral 1 indicates a tool comprising a central part 2 in the form of a lower portion of a drill string extending up to surface. The tool 1 is located in a casing 4 cast in a fixed manner into a borehole 6 by means of a casting substance 8.

The tool 1 comprises an upper, non-circular object 10 and a lower, non-circular object 12, wherein the lower, non-circular object 12 is arranged at an axial distance from the upper, non-circular object 10.

Each of the non-circular objects 10, 12 comprises two diametrically opposite bodies 14. At the side facing the central part 2, each body 14 is formed with a number of saw-tooth-shaped, inclined surfaces 16 fitting, in complementary manner, within sawtooth-shaped, inclined surfaces 18 on the central part 2. The inclined surfaces 16, 18 are directed so as to allow the body 14 to be moved from a retracted, passive position, as shown in Fig. 3, to an extended, active position, as shown in Fig. 5, in response to a movement of the body 14 in the direction of the free end portion 20 of the central part 2.

The saw tooth-shaped, inclined surfaces 18 do not encircle the central part 2, but they are discontinued, as shown in Fig. 6. In the drawings, the inclined surfaces 16, 18 are shown in a simplified form and may be comprised of separate components (not shown).

The largest external distance 22 between the bodies 14 of the lower, non-circular object 12 is perpendicular to the largest distance 24 between the bodies 14 of the upper, non-circular object, see Fig. 2.

The bodies 14 are disposed in respective wall openings 26 in an activator 28. The activator 28 is comprised of a tubular sleeve movably encircling the central part 2.

The bodies 14 are formed with a shoulder 30 on the inside of the activator 28. The shoulder 30 is structured in a manner allowing it to prevent the body 14 from falling out of the activator 28. When the body 14 is in its active position, the shoulder 30 abuts against a stopper 32 on the central part 2. The activator 28 is connected to a holder 34 for friction bodies 36. The friction bodies 36 are preloaded against the casing 4 by means of springs 38.

When a casing 4 is to be loosened from the casting substance 8, the tool 1 is moved into the casing 4. The friction bodies 36 abut against the casing 4. The bodies 14 belonging to the upper, non-circular object 10 and the lower, non-circular object 12 are located in their passive positions, see Figs. 1 and 3.

Then, when the tool 1 is pulled upwards in the casing 4, the friction force between the friction bodies 36 and the casing 4 causes the activator 28 and the bodies 14 to be pulled towards the end portion 20, up along the saw-tooth-shaped, inclined surfaces 18, and to their active positions, see Figs. 5 and 6.

When the bodies 14 are located in their active positions, the largest external distance 22, 24 is larger than the internal diameter of the casing 4. Thereby, the casing 4 is moved into the casting substance 8 near the bodies 14, whereby the casting substance 8 is deformed or crushed. Due to this displacement of the casing 4 near the bodies 14, the casing 4 is retracted from the casting substance between the bodies 14 belonging to the same non-circular object 10, 12, see areas marked 40 in Figs. 5 and 6.

By so doing, the casing 4 is loosened from the casting substance 8 along the entire periphery thereof, even by the passing of only one non-circular object 10, 12.

If the tool 1 is to be deactivated, the central part 2 is rotated 90 degrees about the central axis 42 thereof, whereby the inclined surfaces 18 on the central part 2 are disengaged from the inclined surfaces 16 on the bodies 14.

In Figures 9-12, the tool 1 is shown in an alternative embodiment, wherein the bodies 14 are moved inwards along an inclined surface 44 by means of threads 46.

Figs. 9 and 10 show the tool 1 in its passive position, whereas Figs. 11 and 12 show the tool 1 in its active position, wherein the bodies 14 are moved by means of the threads 46 and abut against a stopper 32.

The mode of operation of the bodies 14 against the casing 4 corresponds to that described above.