Method For Recovering Tubular Structures From A Well And A Downhole Tool String

Abstract

This invention relates to a method for recovering a tubular structure (3) from a well (1), wherein a so-called free point is defined as the location where the tubular structure is stuck in the well. The method comprising providing a downhole tool string comprising a pipe-severing tool and an upper part of the downhole tool string; lowering the downhole tool string into the tubular structure to release the free pipe. Before the step of triggering the pipe-severing tool to sever the tubular structure, the method includes releasing the pipe-severing tool and subsequent withdrawing the upper part, of the downhole tool string away from the free point towards the surface over at least a predefined distance. The invention relates to a downhole tool string for use in such method.

Claims

1. Method for recovering a tubular structure (3) from a well (1), wherein a free point (4) is defined as a location (2) where the tubular structure (3) got stuck in the well (1), wherein a free pipe is defined as a part (3u) of the tubular structure (3) which is downstream of the free point (4), and wherein a stuck pipe is defined as another part (3d) of the tubular structure (3) which is upstream of the free point (4), the method comprising steps of: providing a downhole tool string (100) comprising a pipe-severing tool (5) and an upper part (7) of the downhole tool string (100); lowering the downhole tool string (100) into the tubular structure (3) to a depth that the pipe-severing tool (5) is at the free point (4) of the tubular structure (3), and triggering the pipe-severing tool (5) to severe said tubular structure (3) to release the free pipe (3u), before the step of triggering the pipe-severing tool (5) to severe said tubular structure (3), releasing the pipe-severing tool (5) and subsequently withdrawing the upper part (7) of the downhole tool string (100) away from the free point (4) towards a surface over at least a predefined distance (d).

2. The method according to claim 1, further comprising, before releasing the pipe-severing tool (5), anchoring said pipe-severing tool (5) in the tubular structure (3).

3. The method according to claim 1, further comprising, after triggering the pipe-severing tool (5) to severe said tubular structure (3), steps of: lowering the upper part (7) of the downhole tool string (100) to the pipe severing tool; coupling the upper part (7) of the downhole tool string (100) to the pipe severing tool, and lifting the downhole tool string (100) to a surface.

4. The method according to claim 1, further comprising removing the free pipe (3u) from the well (1).

5. The method according to claim 1, wherein, in the step of providing the downhole tool string (100), the pipe-severing tool (5) comprises a pipe-severing unit (10) selected from a group consisting of: a chemical cutter tool, a jet cutter tool, a radial cutting torch, a drill collar-severing tool, and a string-shot back-off tool.

6. The method according to claim 1, wherein, in the step of providing the downhole tool string (100), the downhole tool string (100) further provides a wireline tractor (60) in the upper part (7) for conveying the downhole tool string (100) to a depth in the well (1).

7. The method according to claim 1, wherein the tubular structure (3) comprises a drill pipe string.

8. The method according to claim 1, wherein the well (1) comprises a highly deviated or horizontal well bore.

9. A downhole tool string (100), said tool string comprising: a pipe-severing tool (5); and an upper part (7) of the downhole string (100).

10. The downhole tool string (100) according to claim 9, wherein the upper part (7) of the downhole tool string (100) comprises a release tool (40) for releasably coupling with the pipe-severing tool (5).

11. The downhole tool string (100) according to claim 9, wherein the pipe-severing tool (5) comprises an anchor tool (20) connected in series with a pipe-severing unit (10).

12. The downhole tool string (100) according to claim 11, wherein the pipe-severing unit (10) is selected from a group consisting of: a chemical cutter tool, a jet cutter tool, a radial cutting torch, a drill collar-severing tool, and a string-shot back-off tool.

13. The downhole tool string (100) according to claim 9, wherein the upper part (7) of the downhole tool string (100) further provides a wireline tractor (60) for conveying the downhole tool string (100) to a depth in a well (1).

Description

[0040] In the following is described an example of a preferred embodiment illustrated in the accompanying drawings, wherein:

[0041] FIG. 1 shows an embodiment of the downhole tool string in accordance with the invention, and

[0042] FIGS. 2 to 7 show different stages of an embodiment of the method in accordance with the invention.

[0043] It should be noted that the above-mentioned and below-discussed embodiments illustrate rather than limit the invention, and that those skilled in the art will be able to design many alternative embodiments without departing from the scope of the appended claims. In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. Use of the verb “comprise” and its conjugations does not exclude the presence of elements or steps other than those stated in a claim. The article “a” or “an” preceding an element does not exclude the presence of a plurality of such elements. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

[0044] FIG. 1 shows an embodiment of the downhole tool string 100 in accordance with the invention. This embodiment uses a drill collar-severing tool, but the invention is not limited to such severing tool. The invention is applicable to any kind of cutter or severing tool, which is harmful towards downhole equipment. The downhole tool string 100 comprises a pipe-severing tool 5 (or tool string) connected to an upper part 7 of the downhole tool string 100. The pipe-severing tool 5 comprises a pipe-severing unit 10 and an anchor tool 20 connected to it. The anchor tool 20 is further connected on its on end to a firing head tool 30. The upper part 7 of the downhole tool string 100 comprises a string comprising a release tool 40, a depth correlation tool 50 (or position tool), a wireline tractor 60, a swivel 70, and a cable head 80 as illustrated in FIG. 1. The release tool 40 is coupled to the firing head tool 30 of the pipe severing tool string 5. The cable head 80 is coupled to a wireline cable (not shown) that runs to the surface.

[0045] The release tool 40 is a tool, which facilitates releasing of a part of a tool string that is connected to it. In an embodiment it is the release tool 40, which separates in two parts, one part remaining in connection with the wireline and one part staying behind. In an alternative embodiment the release tool 40 is designed for holding and releasing another tool. In yet another embodiment the release tool 40 maintains a wired connection between the separated parts (electrical or optical) for communication and/or power transport. All such variants may be advantageously used in the invention.

[0046] It must be further noted that the embodiment of FIG. 1 is just an example. The tool string 100 may comprises fewer or more components. What is important in the invention is that there is a pipe-severing tool (string) 5 and that there is the feature of releasing said severing tool (string) 5 from the remainder (or upper part) of the tool string 7, while the remainder of the tool string 7 is lifted up away from the cutting area. The recovery of the pipe-severing tool (string) 5 may be done right after the cutting operation or at a (much) later stage.

[0047] FIGS. 2 to 7 show different stages of an embodiment of the method in accordance with the invention. It must be noted that the ratio between the horizontal and vertical scaling in FIGS. 2 to 7 deviates a bit from that of FIG. 1, which has been done for illustration purposes only. Moreover, neither one of the figures has been drawn to scale. FIG. 2 shows a first stage of the method. In this stage a downhole tool string 100 as illustrated in FIG. 1 is provided and lowered into a well bore 1 via a cable 90.

[0048] FIG. 2 further shows a tubular structure 3 (here a drill pipe string) which is stuck at a well bore obstacle or deviation 2 as shown. The problem is particularly present in highly deviated or horizontal wells, where typically a tractor is needed to bring the equipment down. This deviation 2 defines the so-called free point 4 as discussed earlier in this description. The main goal of the drill pipe string recovery operation is to cut or split the tubular structure 3 as close as possible to the free point 4. Therefore, the downhole tool string 100 is lowered in the well bore 1 to such a depth that the pipe-severing unit 10 is very close to the free point 4.

[0049] FIG. 3 shows a further stage of the method, wherein the anchor tool 20 has been triggered to lock the position of the pipe-severing unit 10.

[0050] FIG. 4 shows a further stage of the method, wherein the release tool 40 has been triggered to release the lower part (pipe-severing tool) 5 of the tool string connected to it and subsequently the upper part 7 of the tool string has been withdrawn over a predefined distance d.

[0051] FIG. 5 shows a further stage of the method, wherein the pipe-severing unit 10 has been triggered to severe the tubular structure 3 by means of an explosion 11 (but other ways exists also, such as chemicals, jet or torch). The explosion 11 will consequently severe the tubular structure 3 and create a lower part 3d (referred to as stuck pipe) and an upper part 3u (referred to as free pipe).

[0052] FIG. 6 shows a further stage of the method, wherein the upper part or remainder 7 of the downhole tool string 100 has been lowered again, and the release tool 40 has reengaged with the lower part of the tool. The anchor tool 20 has released its anchor.

[0053] FIG. 7 shows a further stage of the method, wherein the downhole tool string 100 is pulled up to the surface via the cable 90. The free pipe 3u may be retrieved in the same run (for instance by retriggering the anchor tool 20) or in a separate run using conventional techniques.

[0054] The invention provides for a method of recovering a tubular structure from a well bore, wherein the downhole equipment is protected from harm by the pipe severing operation through at least partial withdrawal of the equipment before triggering the severing operation. In order to make such method possible the downhole equipment must be adapted so that it can release the severing unit and reconnect to it at a later stage. The invention is particularly useful in a method of recovering a stuck drill pipe from a well bore in highly deviated or horizontal wells, where typically conveyor tools like wireline tractors are used to bring the equipment at the desired location.