Expandable Junk Mill

Abstract

A borehole mill has blades that extend radially while moving along an inclined dovetail as a result of setting down weight on a mandrel. The blades extend axially beyond the end of the mandrel so that setting down weight disables a retainer that has the blades retracted for running in. Axial displacement of the blades along respective dovetails breaks a shear pin on a follower sleeve that is spring biased off a gage ring on the mandrel such that the spring stays compressed as long as set down weight is applied and once the mill is picked up the spring pushes the blades axially along a dovetail to the radially retracted position. The mill resumes its smallest dimension for pulling out of the hole.

Claims

1. A borehole milling tool for milling an object in the borehole, comprising: a mandrel; a plurality of spaced blades supported from said mandrel in a retracted and extended positions; said blades moving from said retracted to said extended position when brought into contact with the object and said mandrel moves relatively to said blades.

2. The tool of claim 1, wherein: said mandrel is moved with set down weight.

3. The tool of claim 1, wherein: said mandrel moves axially relative to said blades between said retracted and extended positons.

4. The tool of claim 1, wherein: said blades are slidably mounted to said mandrel.

5. The tool of claim 1, wherein: said blades are retained to said mandrel with a dovetail.

6. The tool of claim 1, wherein: said blades are biased to said retracted position.

7. The tool of claim 1, wherein: said blades are selectively secured to said mandrel in said retracted position until force is applied to said mandrel.

8. The tool of claim 7, wherein: said selective securing is accomplished with at least one breakable member.

9. The tool of claim 6, wherein: said biasing comprises a spring or compressible fluid.

10. The tool of claim 6, wherein: wherein said bias on said blades increases as said blades move toward said extended position.

11. The tool of claim 1, wherein: said blades comprise cutting structure on at least a lower end thereof.

12. The tool of claim 1, wherein: the outer peripheral dimension of said blades increases at least 3% between said retracted and said extended positions.

13. The tool of claim 1, wherein: said mandrel further comprises a follower ring initially shear pinned to said mandrel, whereupon setting down weight on said mandrel with said blades contacting the object said shear pin shears and compresses a return spring against a gage ring secured to said mandrel.

14. The tool of claim 1, wherein: said blades extend axially beyond an end of said mandrel in said retracted position.

15. A borehole milling method for removal of an object, comprising: running in a mill with a plurality of movable blades in a retracted position; landing said blades on the object; relatively moving a mandrel with respect to said blades when said blades are landed on the object; extending said blades to an extended position due to said relatively moving said mandrel.

16. The method of claim 15, comprising: using set down weight on said mandrel for relatively moving said mandrel.

17. The method of claim 15, comprising: positioning said blades to initially extend axially beyond an end of said mandrel is said retracted position.

18. The method of claim 15, comprising: initially securing said blades to said mandrel with a breakable member.

19. The method of claim 15, comprising: increasing a bias on said blades toward said retracted position as a result of relative movement between said blades and said mandrel.

20. The method of claim 15, comprising: guiding said blades with respective inclined dovetails such that relative movement of said mandrel with respect to said blades in contact with the object moves said blades radially to said extended position.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0007] FIG. 1 is the run in position of the mill with the blades radially retracted; and

[0008] FIG. 2 is the view of FIG. 1 with the blades radially extended due to setting down weight.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0009] Referring to FIG. 1, a mandrel 10 has a connection 12 for support from coiled or rigid tubing that is not shown. Typically with coiled tubing for the support there will also be a downhole motor to rotate the mandrel while a rigid tubing support string allows imparting rotation to mandrel 10 from a surface location. The mandrel 10 has a gage ring 14 that represents the largest dimension when running in. Ring 14 can be secured with thread 16 to the mandrel 10. Ring 16 is also a support for a coiled or other type of spring 18. Alternatively, Belleville washers or a compressed gas in a variable volume chamber can be used as equivalents to create a bias force against follower 20. Follower 20 is initially shear pinned or releasably secured to the mandrel 10 for running in. The shear pin 22 prevents movement of blades 24 along a rail such as a dovetail 26 into the FIG. 2 extended position in the event the lower ends 28 of blades 24 encounter a projection on the way to the object to be milled. A schematically represented travel stop 30 prevents the blades 24 from separating from the mandrel 10. Mandrel 10 has a passage 32 that conducts fluid from above past the blades 24 and up the hole to remove cuttings. Blades 24 have cutting structure such as carbide or hardened inserts along the bottom end 28 and continuing up the to the vertical sides of the blades 24 as shown in FIG. 1.

[0010] In the FIG. 2 position the blades 24 have landed on the object 34 to be milled and the shear pins 22 are broken with spring 18 compressed as the blades 24 displace the follower 20. As a result of the axial relative movement between the blades which are against the object 34 to be milled and the mandrel 10 the blades also extend further radially due to the inclined orientation of the retaining dovetail 26 on which the blades 24 are guided. As an example of the amount of radial extension of the blades 24 the run in dimension for one size can be 4.375 inches and increase to 4.625 inches in the set position. The slope of the dovetail and the amount of the available axial travel determines the dimensional increase for the outer diameter of the blades 24 in the set position.

[0011] The above description is illustrative of the preferred embodiment and many modifications may be made by those skilled in the art without departing from the invention whose scope is to be determined from the literal and equivalent scope of the claims below: