Section mill and method for abandoning a wellbore

1. A method for milling a tubular cemented in a wellbore, comprising:

deploying a bottomhole assembly (BHA) into the wellbore through the tubular, the BHA comprising a window mill and a section mill; and

rotating the BHA and extending arms of the window mill, thereby forming a window by radially cutting through the tubular,

wherein a body portion of each window mill arm engages an inner surface of the tubular after a blade portion of each window mill arm cuts through the tubular;

rotating and longitudinally advancing the BHA with the extended window mill while the engaged body portions stabilize the window mill, thereby opening the window,

wherein:

each mill comprises a tubular housing and a piston for extending the arms, and

the section mill piston is initially fastened to the section mill housing, thereby restraining arms of the section mill in a retracted position while the window is formed and opened; and

extending the arms of the section mill through the open window and longitudinally milling a section of the tubular while maintaining the window mill in the extended position for stabilization.

2. The method of claim 1 , wherein the window is opened to a length less than a length of a joint of the tubular.

3. The method of claim 2 , wherein the window is formed at a location between couplings of the tubular.

4. The method of claim 2 , wherein the window is opened until the window mill is exhausted.

5. The method of claim 2 , wherein the tubular is an inner casing disposed within an outer casing.

6. The method of claim 5 , wherein a blade portion of each section mill arm extends to a drift diameter of the outer casing.

7. The method of claim 5 , wherein:

the BHA further comprises an outer window mill,

the method further comprises extending arms of the outer window mill through the milled window or section of the inner casing and radially cutting through the outer casing, thereby forming an outer window through the outer casing, and

a body portion of each outer window mill arm engages and stabilizes from an inner surface of the outer casing after a blade portion of each outer window mill arm cuts through the outer casing.

8. The method of claim 7 , further comprising longitudinally advancing the BHA while longitudinally milling the outer casing using the extended outer window mill, thereby opening the outer window to a length less than a length of a joint of the outer casing.

9. The method of claim 8 , wherein:

the BHA further comprises an outer section mill,

arms of the outer section mill are locked in a retracted position while the outer window is formed and opened, and

the method further comprises extending arms of the outer section mill through the outer window and longitudinally milling a section of the outer casing while maintaining the outer window mill in the extended position for stabilization.

10. The method of claim 8 , wherein the outer window is formed at a location between couplings of the outer casing.

11. The method of claim 8 , wherein the outer window is opened until the outer window mill is exhausted.

12. The method of claim 2 , further comprising:

forming and opening a second window using the window mill;

retracting the window mill; and

extending the section mill arms through the second window and milling a second section of the tubular.

13. The method of claim 2 , further comprising releasing the arms of the section mill.

14. The method of claim 13 , wherein the arms are released by dropping or pumping a closure member to the BHA.

15. The method of claim 13 , wherein the arms are released by sending an instruction signal to the BHA via telemetry.

16. The method of claim 15 , wherein the telemetry is an RFID tag.

17. The method of claim 2 , wherein:

the section mill is a first section mill,

the BHA further comprises a second section mill,

the method further comprises extending arms of the second section mill through the milled section of the tubular and longitudinally milling the section of the tubular while maintaining the first section mill in the extended position for stabilization.

18. The method of claim 1 , wherein:

the window mill arms each extend from a pocket formed in the housing of the window mill,

the housing has a rib formed in an outer surface thereof at each side of each pocket, and

a ribbed diameter of the housing is essentially equal to a drift diameter of the tubular.

19. The method of claim 1 , wherein the tubular is an inner casing disposed within an outer casing.

20. The method of claim 19 , further comprising

deploying a second BHA into the wellbore through the inner casing, the second BHA comprising an outer window mill and an outer section mill; and

extending arms of the outer window mill through the milled window or section of the inner casing and radially cutting through the outer casing, thereby forming an outer window through the outer casing,

wherein a body portion of each outer window mill arm engages and stabilizes from an inner surface of the outer casing after a blade portion of each outer window mill arm cuts through the outer casing.

21. The method of claim 20 , further comprising longitudinally advancing the second BHA while longitudinally milling the outer casing using the extended outer window mill, thereby opening the outer window.

22. The method of claim 21 , wherein:

arms of the outer section mill are locked in a retracted position while the outer window is formed and opened, and

the method further comprises extending arms of the outer section mill through the outer window and longitudinally milling a section of the outer casing while maintaining the outer window mill in the extended position for stabilization.

23. The method of claim 1 , wherein:

the window mill blade portions are short and tapered, and

blade portions of the section mill arms are long and straight.

24. The method of claim 1 , wherein:

each housing has eccentrically arranged pockets formed in a wall thereof and an inclined guide formed in each pocket for extending the respective arm, and

each piston extends the respective arms by pushing the respective arms along the respective inclined guides.

25. The method of claim 1 , wherein each body portion carries a pad and the pads engage the inner surface of the tubular and stabilize the window mill.

26. The method of claim 1 , wherein the piston is initially fastened by one or more frangible fasteners.

27. A method for milling an inner casing disposed within an outer casing cemented in a wellbore, comprising:

deploying a bottomhole assembly (BHA) into the wellbore through the inner casing, the BHA comprising inner and outer window mills and a section mill; and

extending arms of the inner window mill and radially cutting through the inner casing, thereby forming an inner window through the inner casing,

longitudinally advancing the BHA while longitudinally milling the inner casing using the extended inner window mill, thereby opening the inner window to a length less than a length of a joint of the inner casing;

extending arms of the section mill through the inner window and longitudinally milling a section of the inner casing while maintaining the inner window mill in the extended position for stabilization;

extending arms of the outer window mill through the milled window or section of the inner casing and radially cutting through the outer casing, thereby forming an outer window through the outer casing; and

longitudinally advancing the BHA while longitudinally milling the outer casing using the extended outer window mill, thereby opening the outer window to a length less than a length of a joint of the outer casing,

wherein:

a body portion of each inner window mill arm engages and stabilizes from an inner surface of the inner casing after a blade portion of each inner window mill arm cuts through the inner casing,

the arms of the section mill are locked in a retracted position while the inner window is formed and opened, and

a body portion of each outer window mill arm engages and stabilizes from an inner surface of the outer casing after a blade portion of each outer window mill arm cuts through the outer casing.

28. The method of claim 27 , wherein:

the BHA further comprises an outer section mill,

arms of the outer section mill are locked in a retracted position while the outer window is formed and opened, and

the method further comprises extending arms of the outer section mill through the outer window and longitudinally milling a section of the outer casing while maintaining the outer window mill in the extended position for stabilization.

29. The method of claim 27 , wherein the outer window is formed at a location between couplings of the outer casing.

30. The method of claim 27 , wherein the outer window is opened until the outer window mill is exhausted.

31. The method of claim 27 , wherein:

the BHA is rotated while each window is formed and opened and while the section is milled,

the body portion of each window mill arm engages and stabilizes from the respective casing by carrying a pad.

32. A method for milling a tubular cemented in a wellbore, comprising:

deploying a bottomhole assembly (BHA) into the wellbore through the tubular, the BHA comprising a window mill and a section mill;

extending arms of the window mill and radially cutting through the tubular, thereby forming a window through the tubular;

longitudinally advancing the BHA while longitudinally milling the tubular using the extended window mill, thereby opening the window to a length less than a length of a joint of the tubular;

extending arms of the section mill through the window and longitudinally milling a section of the tubular while maintaining the window mill in the extended position for stabilization;

forming and opening a second window using the window mill;

retracting the window mill; and

extending the section mill arms through the second window and milling a second section of the tubular,

wherein:

a body portion of each window mill arm engages and stabilizes from an inner surface of the tubular after a blade portion of each window mill arm cuts through the tubular, and

the arms of the section mill are locked in a retracted position while the window is formed and opened.

33. The method of claim 32 , wherein:

the BHA is rotated while each window is formed and opened and while each section is milled, and

the body portion of each window mill arm engages and stabilizes from the inner surface of the tubular by carrying a pad.

34. A method for milling a tubular cemented in a wellbore, comprising:

deploying a bottomhole assembly (BHA) into the wellbore through the tubular, the BHA comprising a window mill; and

extending arms of the window mill and radially cutting through the tubular, thereby forming a window through the tubular,

wherein:

a body portion of each window mill arm engages and stabilizes from an inner surface of the tubular after a blade portion of each window mill arm cuts through the tubular,

the window mill arms each extend from a pocket formed in a housing of the window mill,

the housing has a rib formed in an outer surface thereof at each side of each pocket, and

a ribbed diameter of the housing is essentially equal to a drift diameter of the tubular.

35. The method of claim 34 , wherein:

the BHA further comprises a section mill,

the BHA is rotated while the window is formed,

the body portion of each window mill arm engages and stabilizes from the inner surface of the tubular by carrying a pad,

the method further comprises rotating and longitudinally advancing the BHA with the extended window mill while the engaged pads stabilize the window mill, thereby opening the window,

arms of the section mill are locked in a retracted position while the window is formed and opened, and

the method further comprises extending the arms of the section mill through the open window and longitudinally milling a section of the tubular while maintaining the window mill in the extended position for stabilization.

36. A method for milling an inner casing disposed within an outer casing cemented in a wellbore, comprising:

deploying a bottomhole assembly (BHA) into the wellbore through the inner casing, the BHA comprising an inner window mill and an inner section mill;

extending arms of the inner window mill and radially cutting through the inner casing, thereby forming an inner window through the inner casing;

longitudinally advancing the BHA while longitudinally milling the inner casing using the extended inner window mill, thereby opening the inner window;

extending arms of the inner section mill through the inner window and longitudinally milling a section of the inner casing while maintaining the inner window mill in the extended position for stabilization;

deploying a second BHA into the wellbore through the inner casing, the second BHA comprising an outer window mill and an outer section mill; and

extending arms of the outer window mill through the milled window or section of the inner casing and radially cutting through the outer casing, thereby forming an outer window through the outer casing,

wherein:

a body portion of each inner window mill arm engages and stabilizes from an inner surface of the inner casing after a blade portion of each inner window mill arm cuts through the inner casing,

the arms of the inner section mill are locked in a retracted position while the inner window is formed and opened, and

a body portion of each outer window mill arm engages and stabilizes from an inner surface of the outer casing after a blade portion of each outer window mill arm cuts through the outer casing.

37. The method of claim 36 , further comprising longitudinally advancing the second BHA while longitudinally milling the outer casing using the extended outer window mill, thereby opening the outer window.

38. The method of claim 37 , wherein:

arms of the outer section mill are locked in a retracted position while the outer window is formed and opened, and

the method further comprises extending arms of the outer section mill through the outer window and longitudinally milling a section of the outer casing while maintaining the outer window mill in the extended position for stabilization.

39. The method of claim 36 , wherein:

the BHA is rotated while the window is formed and opened and while the section is milled, and

the body portion of each inner window mill arm engages and stabilizes from the inner surface of the inner casing by carrying a pad.