Claims
- 1. A side track cutting apparatus for cutting a secondary borehole through the wall in an existing borehole, comprising:
- a cutting tool affixed to the end of a shaft, the cutting tool having a full diameter cutting surface and a reduced diameter cutting surface; and
- a whipstock having a ramp;
- said reduced diameter cutting surface contacting said ramp at a first contact area and said full diameter cutting surface contacting the interior of the wall of the borehole at a second contact area; and
- said first contact area being greater than said second contact area.
- 2. The apparatus of claim 1 wherein a weight is applied to said cutting tool creating a first contact stress between said reduced diameter surface and said ramp at said first contact area and a second contact stress between said full diameter cutting surface and the interior of the wall of the borehole, the ratio of said first contact stress divided by said second contact stress being less than one.
- 3. The apparatus of claim 1 wherein said whipstock has a first cutability and the wall of the borehole has a second cutability and wherein a weight is applied to said cutting tool creating a first contact stress between said tapered cutting surface and said ramp at said first contact area and a second contact stress between said full diameter cutting surface and the interior of the wall of the borehole, a first ratio of said first cutability divided by said second cutability and a second ratio of said first contact stress divided by said second contact stress, said first ratio times said second ratio being less than one.
- 4. The apparatus of claim 1 wherein said reduced diameter surface has a first height and said full cutting surface has a second height, said first height being greater than said second height.
- 5. The apparatus of claim 1 wherein said reduced diameter surface has a first height and said full cutting surface has a second height, said first height being at least 30% of said first and second heights.
- 6. The apparatus as set forth in claim 1 further comprising a second mill, said window mill and said second mill being affixed to a shaft, the second mill being spaced upstream of the window mill, the second mill substantially simultaneously cutting into the casing when the window mill is laterally directed into the casing.
- 7. The invention as set forth in claim 6 wherein the diameter of the second mill is about the same as the diameter of the window mill.
- 8. The invention as set forth in claim 7 further comprising a third mill affixed to a shaft, the third mill being spaced from the second mill and serving to elongate the window cut by the window mill and the second mill, the third mill also serving to dress the window formed in the casing.
- 9. The apparatus as set forth in claim 8 wherein the third mill is a watermelon shaped mill with about the same diameter as the window mill and the second mill.
- 10. The invention as set forth in claim 7 wherein the whipstock forms a ramp surface below said end of the whipstock that is substantially parallel to the axis of the whipstock, the non-angled whipstock ramp surface allowing the window mill and the second upstream mill to simultaneously cut a window, when the second mill window cut merges with the window cut formed by the window mill, the parallel ramp surface transitions into a slightly angled ramp to direct the window mill and the second upstream mill further out through the casing.
- 11. A one trip side track window cutting apparatus for cutting sidetracking windows in a casing having an inside and outside diameter and a second cutability, the casing being positioned in previously drilled boreholes comprising;
- a window cutting mill having a full diameter cutting surface and a reduced diameter tapered cutting surface; and
- a whipstock having a ramp with a taper adjacent to an end and a first cutability, said ramp having a reduced thickness adjacent said end and increasing to an enlarged thickness;
- said reduced diameter cutting surface contacting said ramp at a first contact area and said full diameter cutting surface contacting the inside diameter of the casing at a second contact area; and
- said cutting tool creating a first contact stress between said reduced diameter cutting surface and said ramp and a second contact stress between said full diameter cutting surface and the inside diameter of the casing, a first ratio of said first cutability divided by said second cutability and a second ratio of said first contact stress divided by said second contact stress, said first ratio times said second ratio being less than one.
- 12. The apparatus of claim 11 wherein said ramp has an angle in the range of 1 to 45.degree. with respect to the axis of the whipstock.
- 13. The apparatus of claim 11 wherein said ramp has an angle in the range of 2 to 30.degree. with respect to the axis of the whipstock.
- 14. The apparatus of claim 11 wherein said ramp has an angle in the range of 3 to 15.degree. with respect to the axis of the whipstock.
- 15. The apparatus of claim 11 wherein said reduced diameter cutting surface has a first height and said full diameter cutting surface has a second height, said first height being greater than said second height.
- 16. The apparatus of claim 4 wherein said reduced diameter cutting surface has a first height and said full diameter cutting surface has a second height, said first height being at least 30% of said first and second heights.
- 17. The apparatus of claim 11 wherein the tapers of said ramp at said end and said reduced diameter cutting surface are substantially the same.
- 18. The apparatus of claim 11 wherein said mill has a radius and said enlarged thickness of said ramp plus said mill radius are larger than the outside diameter of the casing causing said mill to move laterally through the wall of the casing.
- 19. The apparatus of claim 11 wherein said full diameter cutting surface has a diameter over 75% of the inside diameter of the casing.
- 20. A method of drilling a window in a casing having an inside and outside diameter and disposed in a well comprising:
- disposing a first cutting member and a whipstock within the casing;
- engaging a first contact surface on the first cutting member with a first ramp surface on the whipstock;
- engaging a second contact surface on the first cutting member with the interior of the casing;
- applying a force to the first cutting member creating a first contact stress at said first contact area and a second contact stress at said second contact area;
- providing a first ratio of the cutability of the whipstock to the cutability of the casing and a second ratio of the first contact stress to the second contact stress with the first ratio times the second ratio being less than one; and
- passing the centerline of the first cutting member from the inside diameter to the outside diameter of the casing.
- 21. A cutter apparatus for cutting a window through the wall in an existing borehole, comprising:
- a body having a generally flat bottom cutting surface, a full diameter cutting surface, and a reduced diameter cutting surface disposed between said bottom cutting surface and said full diameter cutting surface;
- said full diameter cutting surface having a first axial height and being substantially full gauge;
- said reduced diameter cutting surface having a second axial height;
- said second axial height being at least 30% of said first plus said second axial heights; and
- said bottom cutting surface having a diameter which is at least 30% of the diameter of said full diameter cutting surface.
- 22. A method of drilling a window in a casing comprising:
- engaging a tapered cutting surface on a mill with a whipstock in the cased borehole;
- increasing the contact area between the mill and whipstock until the contact stress between the mill and whipstock is less than the contact stress between the mill and casing; and
- cutting a window in the casing.
- 23. The method of claim 22 further comprising deflecting the center of a bottom cutting surface of the mill from the interior to the exterior of the casing.
- 24. The method of claim 22 wherein the cutability of the whipstock is less than the cutability of the casing.
- 25. A side track cutting apparatus for cutting a secondary borehole through the wall of an existing borehole and into the formation, comprising:
- a cutting tool affixed to the end of a shaft, the cutting tool having a tapered cutting surface forming a cutting angle;
- said cutting tool having a plurality of cutting elements including carbide cutters and polycrystalline diamond cutters; and
- a whipstock having a ramp with a ramp angle substantially the same as the cutting angle of the tapered cutting surface, said ramp having a range of thickness deflecting the center of the cutting tool into the wall of the existing borehole to drill the secondary borehole through the wall of the existing borehole and into the formation.
- 26. A one trip side track window cutting apparatus for cutting sidetracking windows in a pipe casing positioned in previously drilled boreholes comprising;
- a window cutting mill affixed to an end of a shaft, a body of the mill with a tapered cutting end forming a cutting angle;
- said cutting mill having a plurality of cutting elements including carbide cutters and polycrystalline diamond cutters; and
- a whipstock having an axis and a ramp forming a ramp angle, the ramp angle substantially parallels the cutting angle of the tapered cutting end of the window mill, said ramp acting as a bearing surface for laterally forcing the center of the window mill from the interior to the exterior of the pipe casing to drill through the wall of the pipe casing and into the formation.
- 27. A mill for engaging an angled bearing surface on a whipstock to cut a secondary borehole through an existing steel casing of an existing borehole and into the earth formation comprising:
- a body having a longitudinal axis;
- a plurality of cutting blades arrayed around the body, at least a portion of the cutting blades comprising:
- a lower end cutting portion transverse to the axis of the body and extending to approximately the axis of the body;
- a first elongated milling portion extending along a principal portion of the body and having an angle which substantially parallels the angled bearing surface of the whipstock;
- a second milling portion near the upper end of the body and being substantially parallel to the axis of the body; and
- a plurality of carbon cutters and polycrystalline diamond cutters on said cutting blades milling the steel casing and drilling into the earth formation.
- 28. A mill according to claim 27 wherein each blade also comprises a third milling portion extending along the body and having a relatively smaller angle to the axis of the body cutting the secondary borehole.
- 29. A mill according to claim 27 wherein the maximum diameter of the body corresponds to the desired diameter of the secondary borehole.
- 30. A mill for engaging a whipstock to cut a secondary borehole through a steel casing in an existing borehole and into the earth formation comprising:
- a generally round body having a longitudinal axis;
- a plurality of cutting blades arrayed around the body, at least a portion of the cutting blades comprising:
- a lower end cutting portion transverse to the axis of the body and extending to approximately the axis of the body;
- a first elongated milling portion extending along a principal portion of the body and having a relatively larger angle relative to the axis of the body engaging the whipstock;
- a second milling portion extending along the body and having a relatively smaller angle to the axis of the body;
- a third milling portion near the upper end of the body and being substantially parallel to the axis of the body; and
- a plurality of carbon cutters and polycrystalline diamond cutters on said cutting blades milling a window through steel casing and drilling a secondary borehole in the earth formation.
CROSS REFERENCE TO RELATED APPLICATIONS
This application is a continuation-in-part of U.S. patent application Ser. No. 08/642,829 filed May 3, 1996, now U.S. Pat. No. 5,771,972, and is related to a patent application entitled Two Trip Window Cutting System, Ser. No. 572,592, filed Dec. 14, 1995, both incorporated herein by reference.
US Referenced Citations (26)
Foreign Referenced Citations (2)
Number |
Date |
Country |
2299105 |
Sep 1996 |
GBX |
2303158 |
Feb 1997 |
GBX |
Non-Patent Literature Citations (3)
Entry |
Track Master Sidetracking System; Feb. 24, 1995; (1 sheet). |
A-Z Grant International; Casing Sidetrack Systems; undated; (7 pgs.). |
A-Z SERVCO Performance Bulletin; Smith International, Inc.; 1995 (1 pg.). |
Continuation in Parts (1)
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Number |
Date |
Country |
Parent |
642829 |
May 1996 |
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