Well abandonment and slot recovery

Abstract

A method and apparatus for single-trip casing cutting and pulling for well abandonment and slot recovery. Perforations (28) are made in the casing (12) at a maximum depth using a punch tool (18) and fluid circulated through the perforations to determine a return at surface. In the event of a return at surface being detected, the casing (12) is cut and pulled. When no return is detected, perforations are made at increasingly shallower depths until a return is detected and the casing (12) is then cut and pulled. This ensures the maximum length of casing (12) is cut and pulled on a single trip in the well bore (10).

Claims

1. A method of removing casing from a well, in which an annulus between the outside of the casing and the inside of a surrounding downhole body is at least partially filled by a viscous and/or solid mass, the method comprising: (a) lowering a string into the well, a packer, a punch tool, and a cutting tool being connected to the string, and the string being arranged to carry a fluid; (b) locating an end of the string in relation to a plug in the casing, the plug providing a seal across the bore of the casing at a first depth; (c) forming one or more perforations through the casing with said punch tool at a second depth in the well, the second depth being shallower than the first depth; (d) setting the packer at a third depth, the third depth being shallower than the second depth; (e) pumping fluid through the string and through the one or more perforations; (f) a circulation test is performed by looking for a return at surface which determines if fluid has managed to pass through material in the annulus between the outside of the casing and the surrounding downhole body; (g) in the event that a return is detected at surface, cutting the casing using the cutting tool to separate a length of cut casing from plugged casing; and (h) pulling the length of cut casing from the well.

2. The method according to claim 1 wherein in the event that a return is not detected, the punch tool is moved to a fourth depth, shallower than the second depth and steps (c) to (f) are repeated.

3. The method according to claim 2 wherein steps (c) to (f) are repeated at increasingly shallower depths until a return is detected at surface and steps (g) and (h) are then completed.

4. The method according to claim 1 wherein all the steps are performed on a single trip in the well.

5. The method according to claim 1 wherein the method includes the step of circulating fluid through the cutting tool, the casing at the cut and up the annulus between the outside of the casing and the inside of the surrounding downhole body.

6. The method according to claim 1 wherein tension is applied to the string to expand the packer.

7. The method according to claim 1 wherein tension is applied to the string to operate the punch tool.

8. The method according to claim 1 wherein the packer is set and the punch tool is activated simultaneously.

9. The method according to claim 1 wherein the method includes the step of anchoring the string to the casing.

10. The method according to claim 1 wherein the method includes an initial step of creating one or more upper perforations using the punch tool towards an upper end of the casing to be cut.

11. The method according to claim 1 wherein the method includes the step of creating one or more test perforations using the punch tool, such test perforations being at a depth shallower than the third depth, and performing a circulation test by circulating fluid between the perforations and the test perforations to detect circulation at surface.

12. The method according to claim 1 wherein in step (g) the casing is cut by making a circumferential cut through the casing.

13. The method according to claim 1 wherein the string is a coiled tubing string.

14. The method according to claim 1 wherein the string is a drill string.

15. The method according to claim 1 wherein the method includes the step of setting the plug at the first depth to provide the seal across the bore of the casing.

16. A method of removing casing from a well, in which an annulus between the outside of the casing and the inside of a surrounding downhole body is at least partially filled by a viscous and/or solid mass, the method comprising: (a) lowering a string into the well, a packer, a punch tool, and a cutting tool being connected to the string, and the string being arranged to carry a fluid; (b) locating an end of the string in relation to a plug in the casing, the plug providing a seal across the bore of the casing at a first depth; (c) forming one or more perforations through the casing with said punch tool at a second depth in the well, the second depth being shallower than the first depth; (d) setting the packer at a third depth, the third depth being shallower than the second depth; (e) pumping fluid through the string and through the one or more perforations; (f) looking for a return at surface; (g) in the event that a return is detected at surface, cutting the casing using the cutting tool to separate a length of cut casing from plugged casing, including circulating fluid through the cutting tool, the casing at the cut and up the annulus between the outside of the casing and the inside of the surrounding downhole body; and (h) pulling the length of cut casing from the well.

Description

(1) Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings of which:

(2) FIGS. 1(a) to 1(f) illustrate a method, carried out on a single trip in a well bore, according to an embodiment of the present invention;

(3) FIGS. 2(a) to 2(f) illustrate a method, carried out on a single trip in a well bore, according to a further embodiment of the present invention; and

(4) FIG. 3 is an illustration of a well in which punch hole positions in casing have been indicated.

(5) Reference is initially made to FIG. 1 of the drawings which illustrates a method of removing casing from a well, carried out on a single trip, according to an embodiment of the present invention. In FIG. 1(a) there is shown a cased well bore, generally indicated by reference numeral 10, in which casing 12 lines the bore 14. A tool string 16 is run in the casing 12. Tool string 16 includes a punch tool 18, a cutting tool 20, a packer 26 and a casing spear 22.

(6) The punch tool 18, cutting tool 20, packer 26 and casing spear 22 may be formed integrally on a single tool body or may be constructed separately and joined together by box and pin sections as is known in the art. Two or more parts may also be integrally formed and joined to any other part.

(7) Tool string 16 may be a drill string or coiled tubing having a central bore for the passage of fluid pumped from surface, as is known in the art.

(8) The punch tool 18 may be any tool which can create individual holes in casing. Preferably this is achieved without explosives and may be achieved by applying tension to the tool 18. The punch tool 18 may create a single hole. Alternatively the punch tool creates a plurality of holes spaced around a circumference of the inner wall 34 of the casing 12. The cutting tool 20 may be any tool which is capable of cutting casing downhole in a well bore. A pipe cutter, section mill, jet cutter, laser cutter and chemical cutter are a non-exhaustive list of possible cutting tools. The packer 26 is preferably a tension set packer wherein an elastomeric band is compressed to expand radially outwards and seal across the annulus 32 between the string 16 and the inner wall 34 of the casing 12. The casing spear 22 is an anchor 40 arranged as a slip designed to ride up a wedge and by virtue of wickers or teeth on its outer surface grip and anchor to the inner wall 34 of the casing 12. In a preferred embodiment the cutting tool 20, packer 26 and casing spear 22 are the TRIDENT system as provided by the present Applicants.

(9) In FIG. 1 ports 30 are shown on the cutting tool 20. The ports 30 are arranged adjacent to the punch tool 18 so that fluid pumped down the string and ejected at high pressure from the ports has only a short distance to travel to exit the punched holes forming the perforations 28. Alternatively ports 30 can be arranged on a separate sub or may be combined with another tool. Where no ports are present, there will be a flow path through the string to the end thereof.

(10) It will be recognised that other tools such as a bumper sub, logging tools, mills or drill bits may be incorporated on the tool string 16. Such tools are not illustrated on the figure merely to aid clarity.

(11) In FIG. 1 there is shown a plug 36 located in the casing 12. Plug 16 creates a seal across the casing 12 and provides a sealed section to the casing 12 preventing the passage of fluids across the plug 16 in either direction. Plug 36 may be a cement plug present in the casing. The tool string 16 may include a drill bit (not shown) at a lower end 38 to dress the cement plug 36 when the string 16 is run into the casing 12. Alternatively, a bridge plug 36 may be provided at the lower end 38 of the string 16 and run-in on the string 16. The bridge plug 36 is then set as a first step in the method. If desired, cement can be pumped through the string 16 to land on the bridge plug 36 to create an additional cement plug. This can be done when a longer seal is required in the well bore 10. The plug 36 is set at a maximum depth in the cased well bore 10.

(12) In the embodiment shown in FIG. 1, an anchor 40 is set on the casing spear 22. The anchor fixes the string 16 to the inner wall 34 of the casing 12. If desired, the string 16 can then be pulled to create sufficient tension to set the packer 26 located above the anchor 40. Preferably, the punch tool 18 is operated to punch one or more holes or perforations 28 around a circumference of and through the wall 34 of the casing 12. A single perforation 28 may be punched if desired.

(13) Packer 26 is then expanded into sealing engagement with the inner wall 26 of the casing 12 at a location above the perforations 28, if this was not done before the punch tool 18 was operated. In a preferred embodiment the punch tool 18 and packer 26 are operated in a simultaneous action by applying tension to the string 16. Where the packer 26 is set before the punch tool 18, the packer 26 can be used to stabilize the punch tool 18 during the punching operation. With the packer 26 now set, a sealed section of the annulus 32 between the plug 36 and packer 26 is provided. This is illustrated in FIG. 1B.

(14) Ports 30 are now opened to provide a circulation path for fluid from the throughbore 42 of the string 16, into the sealed section of annulus 32. Fluid pumped from surface at high pressure, will exit the string 16, enter the perforations 28 and try to find a path through the material 44 in the annulus 46 between the outer wall of the casing 12 and the inner wall of the bore 14. In FIG. 1C, a potential flow path is shown with the fluid returning up the annulus 46 to surface. This may be considered as a circulation test and the detection of a return at surface means that the test is positive.

(15) On a positive circulation test, the cutting tool 20 is activated and the casing 12 is cut. The cut can be made in any way, for example by slicing, milling, grinding, melting, dissolving or ablation as long as it achieves independent upper 48 and lower 50 lengths of casing 12. This is illustrated in FIG. 1D. In the preferred embodiment cutting is achieved using blades and fluid is circulated out of the string 16 at the position of the blades to lubricate and cool the blades while providing further circulation up both annuli 32,46. In this way, cuttings can be returned to surface via the inner annulus 32 while material 44 can be encouraged to circulate to surface through the annulus 46. It will be noted that the packer 26 has been unset during cutting. This is done to provide the inner circulation path up annulus 32 and also to allow rotation of the string 16, if required, to operate the cutting tool 20. Cutting tool 20 could also be operated via a downhole motor.

(16) With the casing cut, FIG. 1E, the anchor 40 is released and the tool string 16 is raised to a position for the casing spear 22 to grip the upper 48 length of casing 12. This is best achieved by setting the anchor 40 on the length 48 towards its upper end. Pulling the tool string 16 out of the well bore 10 recovers the upper 46 length of casing 12. The wellbore 10 is now left with a permanent barrier, in the form of the plug 36, in the lower length 50 of casing 12. This is illustrated in FIG. 1F. The upper 48 length of casing 12 has been recovered from the well bore 10.

(17) All the steps shown in FIGS. 1A to 1E have been achieved on a single trip into the well bore 10 and a maximum length of casing 12 has been recovered.

(18) Referring now to FIGS. 2A to 2F, there is illustrated further steps in the method which occur when the circulation test performed in FIG. 1C is negative. Like parts to those of FIGS. 1A to 1F, have been given the same reference numeral to aid clarity. FIG. 2A shows the step of circulating fluid through the ports 30 and into the perforations 28. However, there is no flow path available for the fluids to return to surface as the material 44 in the annulus 46 is solid or of a sufficient density to block fluid flow. In these circumstances it can be assumed that the casing 12 will be stuck in the bore 14 by the action of the material 44 therebetween. As the perforations are near the maximum depth, it is also unlikely that washing through the perforations 28 can create sufficient pressure to lift the material 44 and circulate it up the annulus 46 to surface. Thus on noting that a return is not recorded at surface and the circulation test is negative, the anchor 40 and/or packer 26 are released and the tool string 16 is pulled a distance out of the bore 14 to position the punch tool 18 at a shallower depth. This is as illustrated in FIG. 2B. The punch tool 18 is operated to provide a second set of perforations 128. Fluid is pumped through the throughbore 42, out of the ports 30 and allowed to enter the perforations 128. A return at surface is looked for. If this is obtained, as illustrated by the arrows in FIG. 2C, the cutting tool 20 is operated and a shorter upper length 48 of casing 12 is cut from a longer length of lower 50 casing 12 and pulled from the well bore 10. This is shown in FIGS. 2D to 2F and is achieved in an identical manner to that shown and described with reference to FIGS. 1D to 1F.

(19) If the circulation test at FIG. 2A was also negative then the steps of perforating at a shallower depth and performing a circulation test would be repeated until a positive circulation test result is achieved. Only on noting a positive circulation test would the casing be cut and an attempt to pull would be made. This saves valuable time in cutting and pulling when the casing is likely to be stuck.

(20) In the unlikely event of a positive circulation test, a cut being made and then the casing cannot be pulled, which may be due to uneven cement distribution in the annulus 46, the spear 22 can be released and the method steps repeated with perforations at a shallower depth which will hopefully be above the stuck point. This will still be achieved on a single trip in the well bore 10.

(21) Thus the method of the present invention provides for a single trip casing cutting and pulling system in which the tool string is run to a maximum depth, testing is performed via perforations to see if a circulation path to surface exits which is used to indicate the likelihood of being able to pull the casing at the perforated depth. If circulation is not achieved, further perforations and testing are performed at progressively shallower depths until a positive circulation test is achieved and the casing is pulled. This is in direct contrast to the prior art systems which begin at a shallower depth and move to greater depths, washing, cutting and pulling casing sections at each step which means multiple steps into the well bore are required.

(22) In the present invention once the casing section has been recovered, one could re-enter the lower length of casing and see if a circulation path to the cut can be found, now that a weight of material has been removed.

(23) Further, as illustrated in FIG. 3 the method can include the step(s) of providing perforations at shallower depths in the well bore 10. In FIG. 3, like parts to those of FIGS. 1 and 2 have been given the same reference numeral to aid clarity. In FIG. 3 a wellhead seal assembly 54 is in place at surface 56. The assembly 54 blocks the annulus 46 and thus perforations 58 are provided near surface 56 to provide a path for returned fluids to test for circulation. By creating such perforations, the assembly 54 can remain in place until pulling of the cut length of casing 12 is required. For prior art systems the assembly 54 would need to be removed in order to perform the washing step. By keeping the assembly 54 in place, well control is maintained and less damage occurs at the wellhead. In the present invention, the wellhead seal assembly 54 can be removed on the same single trip as the casing recovery.

(24) Perforations 58 advantageously allow the migration of gas from the annulus 46 between the casing 12 and the bore 14.

(25) Further test perforations 60 can be made at different depths in the casing 12. The test perforations 60 are arranged to lie between the packer 26 and the perforations 28. In this way, a circulation test can be performed over a shorter length of casing between the two sets of perforations 28,60. This technique can be used to locate a fill level 62 of material 44 in the annulus 46.

(26) The principle advantage of the present invention is that it provides a method of cutting and pulling the maximum possible length of casing in a single trip into a well bore.

(27) A further advantage of the present invention is that it provides a method of cutting and pulling casing wherein the casing is cut and pulled only when an indication of the likelihood of being able to pull the casing is given.

(28) It will be apparent to those skilled in the art that modifications may be made to the invention herein described without departing from the scope thereof. For example, the tool string may include a downhole pulling tool, such as the DHPT available from the present Applicants, or a jar to assist in pulling the cut casing from the well bore. Additionally, reference has been made to shallower and deeper, together with upper and lower positions in the well bore. It will be recognised that these are relative terms though a vertical well bore is illustrated the method and apparatus apply equally to deviated and horizontal well bores.