Tapered Blade Profile on an Outer Bit
In one aspect of the present invention, a drill bit assembly is configured for downhole drilling. The drill bit assembly comprises an outer bit with a plurality of outer blades and a bore disposed within an outer cutting face. In addition, the outer bit comprises a rotational axis. The drill bit assembly comprises an inner cutting face that is configured to cut a hole with an inner gauge diameter in front of the outer bit. At least one outer blade on the outer bit comprises a central most cutter configured to degrade the inner gauge diameter. The central most cutter is axially and laterally displaced from the second most central cutter on the at least blade such that less than fifty percent of the central most cutter axially and laterally overlaps the second most central cutter.
1 . A drill bit assembly for downhole drilling, comprising:
an outer bit with a plurality of outer blades and a bore disposed within an outer cutting face;
the outer bit comprises a rotational axis;
an inner bit that is rotationally isolated from the outer bit is disposed within the bore and comprises an inner cutting face;
the inner bit is configured to cut a hole with an inner gauge diameter in front of the outer bit;
at least one outer blade comprises a central most cutter configured to degrade the inner gauge diameter; and
the central most cutter is axially and laterally displaced from the second most central cutter on the at least blade such that less than 50% of the central most cutter axially and laterally overlaps the second most central cutter.
2 . The drill bit assembly of claim 1 , wherein the central most cutter and the second most central cutter are aligned on a linear segment of the at least outer blade.
3 . The drill bit assembly of claim 1 , wherein the central most cutter and the second most central cutter are aligned on a convex segment of the at least one outer blade.
4 . The drill bit assembly of claim 1 , wherein the central most cutter and the second most central cutter are aligned on a concave segment of the at least one outer blade.
5 . The drill bit assembly of claim 1 , wherein the inner bit is configured to rotate faster than the outer bit.
6 . The drill bit assembly of claim 1 , wherein the inner bit comprises a center indenter.
7 . The drill bit assembly of claim 1 , wherein the inner bit protrudes from the outer bit.
8 . The drill bit assembly of claim 1 , wherein the outer bit is rigidly connected to a drill string and the inner bit is rigidly connected to a torque transmitting device disposed within the drill string.
9 . The drill bit assembly of claim 8 , wherein the torque transmitting device is configured to provide the inner bit with power such that the work done per unit area of the inner bit is greater than work done per unit area of the outer bit.
10 . The drill bit assembly of claim 1 , further comprising at least one fluid nozzle disposed on both the inner bit and the outer bit.
11 . The drill bit assembly of claim 1 , wherein at least one fluid nozzle is incorporated in a gauge of the inner bit, wherein the nozzle is configured to convey fluid across a working face of the outer bit.
12 . The drill bit assembly of claim 1 , wherein the inner bit is configured to steer the drill bit assembly by pushing off the outer bit.
13 . The drill bit assembly of claim 1 , wherein the outer bit is configured to rotate in a first direction and the inner bit is configured to rotate in a second direction.
14 . The drill bit assembly of claim 1 , wherein the inner bit is disposed eccentric with respect to the outer bit.
15 . The drill bit assembly of claim 1 , wherein the shape of the outer blade is configured to apply force to the inner gauge diameter, degrading it beginning at the center and progressing outwards.
16 . The drill bit assembly of claim 1 , wherein the protruding inner bit is configured to weaken a formation, prior to the outer bit degrading the formation.
17 . The drill bit assembly of claim 16 , wherein the outer bit is configured to degrade the weakened formation at a higher rate than a formation that has not been weakened.
18 . The drill bit assembly of claim 1 , wherein the central most cutter is axially displaced from the second most central cutter such that there is no axial overlap.
19 . The drill bit assembly of claim 1 , wherein the central most cutter is laterally displaced from the second most central cutter such that there is no lateral overlap.
20 . The drill bit assembly of claim 1 , wherein the inner and outer bit are rotationally fixed to each other.