BACKUP CUTTING ELEMENTS ON NON-CONCENTRIC REAMING TOOLS
An apparatus for reaming or enlarging a borehole comprising a bi-center drill bit having backup cutters thereon.
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The present invention relates generally to enlarging the diameter of a subterranean borehole, and more specifically to enlarging the borehole below a portion thereof which remains at a lesser diameter. The method and apparatus of the present invention effects such enlargement using a bi-center bit.
BACKGROUNDIt is known to employ both eccentric and bi-center bits to enlarge a borehole below a “tight,” or undersized. portion thereof.
An eccentric bit includes a pilot section, above which (as the bit is oriented in the borehole) lies an eccentrically laterally extended or enlarged cutting portion which, when the bit is rotated about its axis, produces an enlarged borehole. An example of an eccentric bit is disclosed in U.S. Pat. Nos. 4,635,738 and 5,957,223.
A bi-center bit assembly employs two longitudinally superimposed bit sections with laterally offset axes. The first axis is the center of the pass-through diameter, that is, the diameter of the smallest borehole the bit will pass through. This axis may be referred to as the pass-through axis. The second axis is the axis of the hole cut as the bit is rotated. This axis may be referred to as the drilling axis. There is usually a first, lower and smaller diameter pilot section employed to commence the drilling and establish the drilling axis. Rotation of the bit remains centered about the drilling axis as the second, upper and larger radius, main, or reamer, bit section extending beyond the pilot bit section diameter to one side of the bit engages the formation to enlarge the borehole. The rotational axis of the bit assembly then rapidly transitions from the pass-through axis to the drilling axis when the full diameter or “gage” borehole is drilled.
Rather than employing a one-piece drilling structure, such as an eccentric bit or a bi-center bit, to enlarge a borehole below a constricted or reduced-diameter segment, it is known to employ an extended bottomhole assembly (extended bi-center assembly) with a pilot bit at the distal end thereof and a reamer assembly some distance above. This arrangement permits the use of any standard bit type, be it a rock bit or a drag bit, as the pilot bit, and the extended nature of the assembly permits greater drillstring flexibility when passing through tight spots in the borehole as well as the opportunity to effectively stabilize the pilot bit so that the pilot hole and the following reamer will take the path intended for the borehole. The assignee of the present invention has designed as reaming structures so-called “reamer wings” which generally comprise a tubular body having a fishing neck with a threaded connection at the top thereof, and a tong die surface at the bottom thereof, also with a threaded connection. The upper mid-portion of the reamer wing includes one or more longitudinally extending blades projecting generally radially outwardly from the tubular body, the outer edges of the blades carrying superabrasive (also termed superhard) cutting elements, commonly termed PDCs (for Polycrystalline Diamond Compacts). The lower mid-portion of the reamer wing may include a stabilizing pad having an arcuate exterior surface the same or slightly smaller than the radius of the pilot hole on the exterior of the tubular body and longitudinally below the blades. The stabilizer pad is characteristically placed on the opposite side of the tubular body with respect to the reamer wing blades so that the reamer wing will ride on the pad due to the resultant force vector generated by the cutting of the blade or blades as the enlarged borehole is cut. U.S. Pat. No. 5,497,842, assigned to the assignee of the present invention and the disclosure of which is incorporated herein for all purposes by this reference, is exemplary of such reamer wing designs. U.S. Pat. No. 5,765,653, also assigned to the assignee of the present invention and the disclosure of which is incorporated in its entirety herein, discloses and claims more recent improvements in reamer wings and bottomhole assemblies for use therewith, particularly as regards stabilizing reamer wings and bottomhole assemblies.
One-piece bi-center bits are more compact, easier to handle for a given hole size, more suitable for directional drilling bottom-hole assemblies (particularly those drilling so-called “short” and “medium” radius non-linear borehole sections), and also less expensive to fabricate than reamer wing assemblies.
Thus, there remains a need for an improved one piece bi-center bit for use in short and medium radius wells.
BRIEF SUMMARY OF THE INVENTIONEmbodiments of the present invention are directed to a bi-center bit having backup cutters on the blades thereof.
Referring to
Bi-center bit 100 also includes reamer bit section 114 comprising a plurality of blades 140 preferably having PDC cutters 120 and backup PDC cutters 120′ mounted thereto. As can be seen in
Bit shank 150, having a threaded pin connection 152, is used to connect bi-center bit 100 to a drill collar or to an output shaft of a downhole motor, as known in the art.
Referring now to
The pockets for the backup cutters 120′ are located aft of the cutter pocket for the cutters 120 so that the backup cutters 120′ do not interfere with the cutters 120. The backup cutters 120′ are underexposed by approximately 0.025 inch in diameter from the cutters 120 along the cutter profile for a blade 118. Additional backup cutters (not shown) may be located behind the backup cutters 120′ having any desired back rake angle therefor, to provide an indication when the bi-center bit 100 becomes under-gage by a desired amount, such as under-gage by 0.200 inch in diameter. If the backup cutters 120′ are positioned to have a 90° back rake angle, a backup cutter such as described in U.S. Pat. No. 6,408,958 may be used by being so oriented and located on a blade 118/140 approximately underexposed by 0.100 inch to provide a decrease in the rate of penetration of the bi-center bit 100 when contacting the formation being drilled. Such a reduction in the rate of penetration of the formation being drilled is an indicator that the bi-center bit 100 is under-gage with respect to the desired diameter of a borehole being formed.
An arrangement of the above-described 90° backrake orientation of backup cutters 120′ on a blade 118/140 is illustrated in
If the blades 118/140 have multiple rows of PDC backup cutters 120′/120″ thereon (See
To form the backup cutter pockets in the primary portion of the bi-center bit 100 a flat bottom milling tool cuts the drill bit body by plunging directly into the blade 118/140 and travels along the center line of the cutter 120 located in front thereof. If the bit 100 is a particle matrix type bit formed of sintered tungsten carbide particles in a suitable matrix, the backup cutter pockets in the primary portion of the bit 100 are formed by casing the backup cutter pockets in the bit 100 as well as the pockets for other cutters for the bit 100. Methods of manufacturing the bit 100 as a particle matrix composite bit are set forth in U.S. application Ser. No. 11/272,439, filed Nov. 10, 2005, entitled “Earth-Boring Rotary Drill Bits and Methods of Manufacturing Earth-Boring Bits Having Particle Matrix Composite Bit Bodies, the disclosure of which is incorporated herein in its entirety by reference.
Ports 132, which preferably contain nozzles therein as known in the art, direct drilling fluid as shown by the arrows associated therewith, into fluid courses 122 of bit face 130. Likewise, passages within the bit body feed drilling fluid to ports 142 from a central passage or plenum, which also feeds ports 132.
Pilot bit gage diameter is defined by the gage cutters 120′/120″ at the periphery of bit face 130, and thus corresponds generally to (but is nominally larger than) a circle defined by connecting the radially outer pad surface of gage pads 128 (See
The backup cutters 120′/120″ in the bit reamer section 114 are located in a manner similar to those of the bit face 130 on blades 118 and have the same or similar respective back rake angles.
The addition of backup cutters 120′, 120″ on the bi-center bit 100 provides an extended reamer blade profile and increased shoulder radius allowing the placement of additional cutters on a blade of the bi-center bit 100, increasing the wear resistance of the bi-center bit 100 in the formation being drilled. Additionally, while the backup cutters 120′/120″ have been located directly behind a cutter 120, if desired, backup cutters 120′ may be somewhat laterally (with respect to the cutter path) offset therefrom while still following in the same kerf of the cutter 120.
Illustrated in
The cutter/backup cutter 120/120′/120″ is shown in
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While the bi-center bit according to the present invention has been disclosed herein with reference to an illustrated embodiment, those of ordinary skill in the art will understand and appreciate that the invention is not so limited, and that additions, deletions and modifications to the disclosed embodiment may be made without departing from the scope of the invention as hereinafter claimed, and legal equivalents.
Claims
1. A bi-center drill bit for drilling subterranean formations, comprising:
- a pilot bit section having a longitudinal axis, defining a first gage diameter and carrying a a first cutting structure for rotationally engaging a subterranean formation; and
- a reamer bit section adjacent the pilot bit section, a portion of the reamer bit section extending radially beyond the first gage diameter along a minor portion of a side periphery of the bi-center drill bit and carrying a second cutting structure on the reamer bit section for rotationally engaging the subterranean formations; and
- a third cutting structure disposed on at least one of the pilot bit section and the reamer bit section, the third cutting structure being positioned rotationally aft of at least one of the first cutting structure and the second cutting structure.
2. The bi-center drill bit of claim 1, wherein the pilot bit section comprises a fixed-cutter bit and the first cutting structure comprises at least one superabrasive cutter.
3. The bi-center drill bit of claim 1, wherein the second cutting structure and the third cutting structure each comprises at least one superabrasive cutter.
4. The bi-center drill bit of claim 1, wherein the reamer bit section comprises a plurality of substantially radially-extending, circumferentially spaced blades, at least one blade of the plurality of substantially radially extending, circumferentially spaced blades extending radially beyond the first gage diameter.
5. The bi-center drill bit of claim 1, wherein the pilot bit section includes a face carrying the first cutting structure.
6. The bi-center drill bit of claim 1, wherein the third cutting structure is disposed on the reamer bit section and positioned rotationally aft of the second cutting structure, wherein the pilot bit section further comprises a fourth backup cutting structure rotationally aft of the first cutting structure for rotationally engaging a subterranean formation and, wherein the reamer bit section further comprises a fifth backup cutting structure rotationally aft of the third cutting structure for rotationally engaging a subterranean formation.
7. A bi-center drill bit for drilling subterranean formations, comprising:
- a pilot bit section having a longitudinal axis, defining a first gage diameter and carrying a first cutting structure and a second cutting structure rotationally aft of the first cutting structure thereon for engaging a subterranean formation; and
- a reamer bit section adjacent the pilot bit section, a portion of the reamer bit section extending radially beyond the first gage diameter along a minor portion of a side periphery of the bi-center drill bit and carrying a third cutting structure and a fourth cutting structure rotationally aft of the third cutting structure on the reamer bit section for engaging the subterranean formations.
8. The bi-center drill bit of claim 7, wherein the pilot bit section comprises a fixed-cutter.
9. The bi-center drill bit of claim 7, wherein the first cutting structure and the second cutting structure each comprise a plurality of superabrasive cutters.
10. The bi-center drill bit of claim 7, wherein the reamer bit section comprises a plurality of substantially radially-extending, circumferentially spaced blades, at least one blade of the plurality of substantially radially extending, circumferentially spaced blades extending radially beyond the first gage diameter.
11. The bi-center drill bit of claim 7, wherein the pilot bit section includes a face carrying the first cutting structure.
12. The bi-center drill bit of claim 7, wherein the pilot bit section further comprises a fifth backup cutting structure rotationally aft of the first cutting structure for engaging a subterranean formation and wherein the reamer bit section comprises a sixth backup cutting structure rotationally aft of the third cutting structure for engaging a subterranean formation.
13. The bi-center drill bit of claim 7, wherein the second cutting structure includes at least one of a back rake angle and a side rake angle.
14. The bi-center drill bit of claim 7, wherein the fourth cutting structure includes at least one of a back rake angle and a side rake angle.
15. The bi-center drill bit of claim 7, wherein the second cutting structure and the fourth cutting structure each includes at least one of a back rake angle and a side rake angle.
16. A bi-center drill bit for drilling subterranean formations, comprising:
- a pilot drag bit section having a longitudinal axis, defining a first gage diameter and including a body with a face having a first plurality of superabrasive cutters secured thereto and a second plurality of backup superabrasive cutters located rotationally aft of the first plurality of superabrasive cutters and a gage section extending longitudinally from a periphery of the face; and
- a reamer bit section adjacent the pilot drag bit section including at least one blade extending radially beyond the first gage diameter on one peripheral side portion of the bi-centered drill bit and carrying a third plurality of superabrasive cutters thereon and a fourth plurality of superabrasive cutters thereon located rotationally aft of the third plurality of superabrasive cutters.
17. The bi-center drill bit of claim 16, wherein the at least one blade comprises a plurality of circumferentially spaced blades.
18. The bi-center drill bit of claim 16, wherein the gage section includes gage pads.
19. The bi-center drill bit of claim 18, wherein the gage pads provide a bearing surface area on a portion of the gage section.
20. The bi-center drill bit of claim 19, wherein the gage pads comprise a plurality of circumferentially spaced, longitudinally elongated gage pads separated by longitudinally extending junk slots.
Type: Application
Filed: Jul 7, 2009
Publication Date: Jan 13, 2011
Applicant: BAKER HUGHES INCORPORATED (Houston, TX)
Inventors: Matthew S. Wood (Spring, TX), James O. Sinkinson (The Woodlands, TX)
Application Number: 12/498,516
International Classification: E21B 10/26 (20060101); E21B 10/42 (20060101); E21B 10/56 (20060101);