Milling Tool

Abstract

A milling tool for enlarging portions of a wellbore. The milling tool includes a housing that defines a central bore along its length. A piston is moveably disposed within the central bore, and axial movement of the piston moves support arms radially outwardly from the housing. The support arms carry milling blades for enlarging portions of a wellbore.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates generally to the design of milling tools used for enlarging subterranean wellbores.

2. Description of the Related Art

Milling tools are used to enlarge or reopen sections of subterranean wellbores. In some instances, milling tools are used to remove casing from sections of wellbores.

SUMMARY OF THE INVENTION

The invention provides improved milling tools and methods for operation of these tools. An exemplary milling tool is described which has support arms that are moveable radially outwardly from a housing. The support arms have milling blades that carry milling cutters that can cut away the surrounding wellbore. In a described embodiment, there are three milling blades mounted on each of the support arms. Also in a described embodiment, each of the milling blades has a length that is at least one-fifth of the length of the housing. In a particular embodiment, the milling blades are at least a foot in length. Additionally, the milling blades are preferably affixed to the support arms using a dovetail connection.

The milling arms are moved radially outwardly by a translation mechanism that uses fluid pressure to mechanically urge the milling arms radially outwardly from the housing. In a described embodiment, the translation mechanism includes a piston that is axially moveable with respect to the housing. A piston chamber is defined within the housing of the milling tool, and an enlarged diameter piston portion is located within the piston chamber. In a described embodiment, the piston is shifted with respect to the housing by injection of pressurized fluid through the piston and into the piston chamber. Fluid pressure is applied to the enlarged diameter piston portion and shifts the piston axially downwardly with respect to the housing. Downward movement of the piston causes the support arms to be urged radially outwardly. Rotation of the milling tool with the support arms radially extended will enlarge the surrounding borehole.

BRIEF DESCRIPTION OF THE DRAWINGS

The advantages and further aspects of the invention will be readily appreciated by those of ordinary skill in the art as the same becomes better understood by reference to the following detailed description when considered in conjunction with the accompanying drawings in which like reference characters designate like or similar elements throughout the several figures of the drawing and wherein:

FIG. 1 is a side, cross-sectional view of a subterranean wellbore containing a running string with an exemplary milling tool constructed in accordance with the present invention.

FIG. 2 is a side, cross-sectional view of an exemplary mill constructed in accordance with the present invention with the mill being in an undeployed condition.

FIG. 3 is a side, cross-sectional view of the mill shown in FIG. 2, now in a deployed condition.

FIG. 4 is an axial cross-section taken along lines 4-4 in FIG. 2.

FIG. 5 is an axial cross-section taken along lines 5-5 in FIG. 3.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 illustrates an exemplary wellbore 10 that has been drilled through the earth 12. A running string 14 is shown disposed within the wellbore 10. The running string 14 in FIG. 1 is constructed of coiled tubing. However, it will be understood by those of skill in the art that the running string 14 might also be constructed of standard production tubing string sections. A fluid flowbore 16 is defined along the length of the running string 14. The running string 14 includes a milling tool 18 that is constructed in accordance with the present invention. The milling tool 18 is used to enlarge sections of the wellbore 10.

An exemplary milling tool 18, constructed in accordance with the present invention is shown in greater detail in FIGS. 2-5. The milling tool 18 includes a tubular housing 20 that defines an axial central bore 22 along its length. In the depicted embodiment, the housing 20 is includes an upper end cap 24 that is threadedly secured to a blade housing 26. The lower end of the blade housing 26 is threadedly affixed to a lower piston housing 28.

A piston 30 is disposed within the central bore 22 and is axially moveable between an upper position shown in FIG. 2, and a lower position shown in FIG. 3. The piston 30 includes an upper flow tube portion 32, an enlarged diameter piston portion 34 and a lower flow tube portion 36. An axial flow passage 38 is defined along the length of the piston 30. Lateral flow openings 40, 42 are formed in the upper flow tube portion 32 and permit fluid communication between the flow passage 38 and the radial exterior of the piston 30. The upper flow tube portion 32 presents an outwardly projecting flange 44. A fluid flow restriction 45 is provided within the flow passage 38.

An enlarged diameter piston chamber 46 is formed within the lower piston housing 28, and the piston portion 34 is disposed within the piston chamber 46. The piston portion 34 seals against the sidewall of the piston chamber 46. A compressible spring 48 also resides within the piston chamber 46 and biases the piston portion 34 of the piston 30 axially upwardly within the piston chamber 46 so that the piston 30 is biased toward the upper position shown in FIG. 2.

A plurality of windows 50 are formed in the blade housing 26. In the depicted embodiment, there are three windows 50. However, those of skill in the art will understand that there may be more or fewer than three. A support arm 52 is located within each of the windows 50. Each support arm 52 is radially moveable within its window 50 between a radially retracted position (FIG. 2) and a radially extended position (FIG. 3).

Milling blades 54 extend radially outwardly from each of the support arms 52. In the depicted embodiment, there are three milling blades 54 that are secured to each support arm 52, resulting in nine total milling blades 54. In a current embodiment, a dovetail attachment is used to secure the milling blades 54 to their support arms 52. Hardened milling cutters 56, of a type known in the art, are secured to each of the milling blades 54. In a particular embodiment, the milling blades 54 have a length that is approximately one-fifth of the total length of the housing 20 or greater. Also in a particular embodiment, the milling blades 54 are at least one foot in length.

A wedge member 58 is located axially adjacent each of the cutting arms 52. The wedge member 58 presents an angled, downwardly-facing slot surface 60 into which the cutting arm 52 is disposed. The upper end of the wedge members 58 are in contact with the flange 44 of the piston 30. The lower end of each blade window 50 presents an angled upwardly-facing surface 62. When the piston 30 is moved axially downwardly within the housing 20, the flange 44 urges the wedge members 58 axially downwardly as well, and the support arms 52 are urged radially outwardly in each blade window 50 due to sliding action along each of the angled surfaces 60, 62.

In operation, the running string 14 and attached milling tool 18 are lowered into the wellbore 10 until the milling tool 18 is located adjacent a portion of the wellbore 10 which it is desired to enlarge. Pressurized fluid is flowed into the flowbore 16 of the running string 14. Fluid passes downwardly through the axial flow passage 38 of the piston 30 and outwardly through lower lateral flow opening 42 into the piston chamber 46. Fluid pressure will build up above the flow restriction 45. In addition, fluid pressure will be exerted upon the enlarged diameter piston portion 34 to also urge the piston 30 axially downwardly to compress the spring 48 (see FIG. 3). Applying pressure to the enlarged piston portion 34 to activate the milling tool 10 permits significant force to be generated to move the support arms outwardly. Downward movement of the piston 30 with respect to the housing 20 will move the support arms 52 radially outwardly so that the cutters 56 of milling blades 54 are placed into cutting engagement with the wellbore 10. Rotation of the running string 14 will cause the cutters 56 to cut away and enlarge portions of the wellbore 10.

When milling is complete, the support arms 52 can be retracted by reducing fluid pressure within the flowbore 16 of the running string 14. The spring 48 will urge the piston 30 axially upwardly and back to the initial position shown in FIG. 2, thereby permitting the support arms 52 to move radially inwardly.

In addition to the milling tool 18, the invention provides a milling assembly that is useful for enlarging sections of a wellbore 10. In a described embodiment, a milling assembly is made up of a running string 14 and a milling tool 18 that is affixed to the running string 14.

The foregoing description is directed to particular embodiments of the present invention for the purpose of illustration and explanation. It will be apparent, however, to those skilled in the art that many modifications and changes to the embodiment set forth above are possible without departing from the scope and the spirit of the invention.

Claims

1. A milling tool comprising:

a housing defining a central bore along its length;

a piston moveably disposed within the bore between a first position and a second position;

a support arm that is moveable radially outwardly from the housing when the piston is moved to the second position; and

a milling blade affixed to the support arm and having at least one milling cutter for milling a surrounding portion of wellbore.

2. The milling tool of claim 1 wherein there are three milling blades affixed to the support arm.

3. The milling tool of claim 1 further comprising:

a piston chamber formed within the bore; and

the piston having an enlarged diameter piston portion that resides within the piston chamber.

4. The milling tool of claim 3 wherein the piston is moved from the first position to the second position by fluid pressure upon the enlarged diameter piston portion.

5. The milling tool of claim 4 wherein fluid is flowed through an axial flow passage formed within the piston to enter the piston chamber.

6. The milling tool of claim 1 wherein the milling blade has a length that is at least one-fifth of the length of the housing.

7. The milling tool of claim 1 wherein there are three support arms.

8. The milling tool of claim 3 further comprising a compressible spring that biases the enlarged diameter piston portion axially such that the piston is biased toward the first position.

9. A milling assembly for enlarging a portion of a wellbore, the milling assembly comprising:

a running string having a central flowbore defined along its length;

a milling tool affixed to the running string, the milling tool comprising: a housing defining a central bore along its length; a piston moveably disposed within the bore between a first position and a second position; a support arm that is moveable radially outwardly from the housing when the piston is moved to the second position; and a milling blade affixed to the support arm and having at least one milling cutter for milling a surrounding portion of wellbore.

10. The milling assembly of claim 9 wherein there are three milling blades affixed to the support arm.

11. The milling assembly of claim 9 further comprising:

a piston chamber formed within the bore; and

the piston having an enlarged diameter piston portion that resides within the piston chamber.

12. The milling assembly of claim 11 wherein the piston is moved from the first position to the second position by fluid pressure upon the enlarged diameter piston portion.

13. The milling assembly of claim 12 wherein fluid is flowed through an axial flow passage formed within the piston to enter the piston chamber.

14. The milling assembly of claim 9 wherein the milling blade has a length that is at least one-fifth of the length of the housing.

15. The milling assembly of claim 9 wherein there are three support arms.

16. The milling assembly of claim 11 further comprising a compressible spring that biases the enlarged diameter piston portion axially such that the piston is biased toward the first position.