Drill bit
A rotating bit with cutters used in drilling operations to advance a borehole in the earth. The bit includes column cutters in the bit body in a recessed central area. The column cutters contact a column of borehole material that is formed during operation. The column cutters are oriented to fracture the column, producing larger cuttings or chips, and to exert a force on the column to limit lateral movement of the bit during operation.
1. A drill bit that rotates about a bit longitudinal axis to advance a borehole comprising:
a bit body with a mounting fixture at a mounting end, a recess at a leading end of the bit, a face within the recess, and blades that partially define the recess;
one or more column cutters, each including a base end mounted in the face within the recess, and a contact end, and each having a cutter longitudinal axis generally parallel to the bit longitudinal axis to fracture by crushing force a column of rock extending toward the face in the recess that is formed as the borehole is advanced;
shoulder cutters mounted on the blades to fracture rock by shearing force and to form the column of rock; and
wherein each column cutter faces generally forward and inward with a positive back rake in an inclusive range of 30 to 70 degrees and a negative side rake in an inclusive range of 45 and 135 degrees.
2. The drill bit of claim 1 where at least a portion of each of the column cutters is within the recess.
3. The drill bit of claim 1 where the shoulder cutters face in the direction of rotation of the bit about the longitudinal axis.
4. The drill bit of claim 1 where the drill bit is a roller cone drill bit.
5. The drill bit of claim 1 , wherein the recess defines an area subject to reverse rotation and a downward and inward orientation of the column cutter limits damage to the column cutter by reverse rotation.
6. A drill bit with a threaded pin at a mounting end for connecting to a drill string, a leading end spaced from the mounting end and a bit longitudinal axis comprising:
a bit body with blades extending from the body and generally converging close to a central cone region, the blades having ends that define at least in part a recess in the bit body, the recess defining a recess face and recess walls;
at least three column cutters mounted in the recess face at least partially within the recess, each of the column cutters with a cutter longitudinal axis and a contact face extending from the bit face to fracture by crushing force a column of rock extending toward the recess face as the borehole is advanced, the cutter longitudinal axis generally parallel to the bit longitudinal axis;
wherein the column cutters are configured to eject fractured portions in a direction from the front of the bit; and
wherein each column cutter faces generally downhole with a positive back rake angle in an inclusive range of 30 and 70 degrees and a side rake angle in an inclusive range of 45 and 135 degrees in a negative direction in relation to a reference surface forward of the recess face and perpendicular to the longitudinal axis.
7. The drill bit of claim 6 where the recess defines an area subject to reverse rotation and a downward and inward orientation of the column cutter limits damage to the column cutter by reverse rotation.
8. The drill bit of claim 6 where shoulder cutters are mounted on the blades facing generally in the direction of bit rotation about the longitudinal axis.
9. The drill bit of claim 8 where the shoulder cutters advance a borehole by shearing rock along a circular path as the bit rotates and forming the column that extends into the recess as the borehole advances.
10. The drill bit of claim 9 where the column cutters contact the column of rock formed as the bit advances to fail the rock of the column.
11. The drill bit of claim 10 where the column cutters contacting the column oppose lateral movement of the bit during operation.
12. A drill bit comprising
three column cutters mounted within a recess about a longitudinal axis of a drill bit for advancing a borehole where each said column cutter has a cutter longitudinal axis generally parallel to the longitudinal axis of the drill bit with a positive back rake in an inclusive range of 35 and 55 degrees and a side rake angle in an inclusive range of 70 and 90 degrees in a negative direction in relation to a reference surface perpendicular to the longitudinal axis; and
shoulder cutters that advance the borehole with shearing force and create a column that extends into a recess at the advancing end of the bit where the column cutters fail the rock of the column by crushing force.
13. The drill bit of claim 12 where the shoulder cutters are outside the recess.
14. The drill bit of claim 13 where the column cutters contacting the column oppose lateral movement of the bit during operation.
15. The drill bit of claim 12 where only three of said column cutters are at least partially within a recess at the front of the drill bit.
16. The drill bit of claim 12 where the drill bit is a drag bit.
17. The drill bit of claim 12 where the drill bit is a roller cone drill bit.
18. The drill bit of claim 12 , wherein the recess defines an area subject to reverse rotation and a downward and inward orientation of the column cutter limits damage to the column cutter by reverse rotation.
19. A drill bit that rotates about a longitudinal axis to advance a borehole comprising:
a bit body with blades, a recess at a leading end in a central cone area of the bit for forming a column of rock as the drill bit is rotated to advance a borehole, and including a longitudinal bit axis;
first cutters mounted in the recess having a cutter longitudinal axis generally parallel to the longitudinal bit axis so as to fail rock by crushing force;
second cutters mounted on the blades facing generally in the direction of bit rotation about the longitudinal axis so as to fail rock by shearing force;
wherein the recess is generally in the shape of a cylinder, dome, cone, or pyramid;
wherein the column cutters are configured to eject fractured portions in a direction from the front of the bit; and
wherein each first cutter faces in the direction of advancement and inward with a positive back rake in an inclusive range of 35 and 55 degrees and a negative side rake in an inclusive range of 70 and 90 degrees in relation to a surface forward of the recess face and perpendicular to the longitudinal axis.
20. The drill bit of claim 19 where the second cutters advance the borehole and create a column of rock that extends into the recess at the leading, cone region of the bit which then contacts the first cutters which fail the rock of the column.
21. The drill bit of claim 19 where each first cutter faces in the direction of advancement and inward with a positive back rake in an inclusive range of 40 and 50 degrees and a side rake in an inclusive range of 75 and 85 degrees in a negative direction in relation to a surface forward of the recess face and perpendicular to the longitudinal axis.
22. The drill bit of claim 21 , wherein the recess defines an area subject to reverse rotation and a downward and inward orientation of the column cutter limits damage to the column cutter by reverse rotation.
23. The drill bit of claim 19 where the first cutters contacting the column oppose lateral movement of the bit during operation.
24. A drill bit attached to a drill string that rotates about a bit longitudinal axis to advance a borehole comprising:
a bit body with a drill string mounting fixture at a upper, mounting end, a recess in the bit body having a recessed face, a fluid channel for injecting drilling fluid and a conduit from the recessed face to a side of the bit body, wherein the fluid channel and the conduit intersect;
column cutters with a base end mounted in the recessed face, a contact end of each column cutter extending from the recessed face and having a cutter longitudinal axis generally parallel to the bit longitudinal axis to fracture a column of the borehole extending into the recessed surface as the borehole is advanced,
wherein the injection of drilling fluid flushes the fractured portions of the column through the conduit and up the borehole; and
wherein each column cutter faces downward and inward with a positive back rake in an inclusive range of 35 and 55 degrees and a negative side rake in an inclusive range of 70 and 90 degrees in a negative direction in relation to a reference surface perpendicular to the longitudinal axis forward of the recess face.
25. The drill bit of claim 24 where the recess is defined at least in part by the inner ends of blades that extend from the bit body and which support shoulder cutters that fail rock to advance the borehole.
26. The drill bit of claim 25 where at least three column cutters are mounted at least in part within the recess.
27. The drill bit of claim 24 where the conduit increases in cross sectional area, or diameter, extending from the recessed face to the junk slot or annulus of the bit to limit binding the fractured column cuttings in the conduit.
28. The drill bit of claim 24 , wherein the recess defines an area subject to reverse rotation and a downward and inward orientation of the column cutter limits damage to the column cutter by reverse rotation.