Non-uniform roller cone

1 . A drill bit comprising:

a bit body having a rotational axis;

a first fixed blade fixed relative to the bit body with a first plurality of fixed blade cutting elements affixed to the first fixed blade;

a second fixed blade fixed relative to the bit body with a second plurality of fixed blade cutting elements affixed to the second fixed blade; and

a roller cone supported by the bit body, the roller cone including:

an innermost region having roller cone cutting elements arranged thereon, wherein the roller cone cutting elements of the innermost region are closest to the rotational axis,

an inner first central region having roller cone cutting elements arranged thereon, wherein a first transition from the innermost region to the inner first central region corresponds to a radially innermost fixed cutting element of the first plurality of fixed blade cutting elements, and

an outer first central region having roller cone cutting elements arranged thereon with a cutting element density no less than 75% greater than a cutting element density of the inner first central region, wherein a second transition from the inner first central region to the outer first central region corresponds to a radially innermost fixed cutting element of the second plurality of fixed blade cutting elements.

2 . The drill bit of claim 1 , wherein the roller cone cutting elements in the inner first central region are different from the roller cone cutting elements in the outer first central region.

3 . The drill bit of claim 2 , wherein the roller cone cutting elements in the inner first central region are a different composition from the roller cone cutting elements in the outer first central region.

4 . The drill bit of claim 3 , wherein the roller cone cutting elements in the inner first central region have a greater toughness than the roller cone cutting elements in the outer first central region.

5 . The drill bit of claim 2 , wherein the roller cone cutting elements in the inner first central region are a different geometry from the roller cone cutting elements in the outer first central region.

6 . The drill bit of claim 1 , wherein the inner first central region and the outer first central region comprise 20% to 80% of a cutting profile of the roller cone.

7 . The drill bit of claim 1 , wherein the inner first central region is larger than the outer first central region.

8 . The drill bit of claim 1 , wherein the outer first central region is larger than the inner first central region.

9 . The drill bit of claim 1 , wherein the inner first central region and the outer first central region are separated by a first zone, wherein the first zone has no cutting elements disposed therein.

10 . The drill bit of claim 1 , wherein the inner first central region is adjacent to the outer first central region.

11 . The drill bit of claim 1 , wherein the inner first central region comprises 20% to 50% of a cutting profile in a radial direction and wherein the outer first central region comprises 50% to 80% of the cutting profile in a radial direction.

12 . The drill bit of claim 1 , wherein the roller cone cutting elements are apexed cutting elements.

13 . The drill bit of claim 1 , wherein the fixed blade cutting elements are shear cutting elements.

14 . The drill bit of claim 1 , further comprising a third fixed blade with a third plurality of fixed blade cutting elements affixed thereto radially overlapping the outer first central region and the third fixed blade includes no cutting elements radially overlapping the inner first central region and the innermost region.

15 . The drill bit of claim 14 , wherein a third transition from the outer first central region to a second central region corresponds to a radially innermost fixed cutting element of the third plurality of fixed blade cutting elements.

16 . A drill bit comprising:

a bit body having a rotational axis;

a first fixed blade fixed relative to the bit body with a first plurality of fixed blade cutting elements affixed to the first fixed blade;

a second fixed blade fixed relative to the bit body with a second plurality of fixed blade cutting elements affixed to the second fixed blade;

a third fixed blade fixed relative to the bit body with a third plurality of fixed blade cutting elements affixed to the third fixed blade; and

a roller cone supported by the bit body, the roller cone including:

an innermost region having roller cone cutting elements arranged thereon, wherein the roller cone cutting elements of the innermost region are closest to the rotational axis,

an inner first central region having roller cone cutting elements arranged thereon, wherein a first transition from the innermost region to the inner first central region corresponds to a radially innermost fixed cutting element of the first plurality of fixed blade cutting elements,

an outer first central region having roller cone cutting elements arranged thereon, wherein a second transition from the inner first central region to the outer first central region corresponds to a radially innermost fixed cutting element of the second plurality of fixed blade cutting elements, and

a second central region having roller cone cutting elements arranged thereon, wherein a third transition from the outer first central region to the second central region corresponds to a radially innermost fixed cutting element of the third plurality of fixed blade cutting elements,

wherein a cutting element density of at least one of the inner first central region, the outer first central region, and the second central region is no less than 75% greater than the cutting element density of another of the inner first central region, the outer first central region, and the second central region.

17 . The drill bit of claim 16 , wherein the cutting element density of the outer first central region is no less than 75% greater than the cutting element density of the inner first central region.

18 . The drill bit of claim 16 , wherein the cutting element density of the second central region is no less than 75% greater than the cutting element density of the outer first central region.

19 . The drill bit of claim 16 , further comprising an outermost region of the roller cone, wherein the outermost region has a radial length no less than 10% of a radius of the drill bit relative to the rotational axis.

20 . A drill bit comprising:

a bit body having a rotational axis;

a first fixed blade fixed relative to the bit body with a first plurality of fixed blade cutting elements affixed to the first fixed blade;

a second fixed blade fixed relative to the bit body with a second plurality of fixed blade cutting elements affixed to the second fixed blade; and

a roller cone supported by the bit body, the roller cone including:

an innermost region having roller cone cutting elements arranged thereon, wherein the roller cone cutting elements of the innermost region are closest to the rotational axis,

a first central region having roller cone cutting elements arranged thereon, wherein a first transition from the innermost region to the first central region corresponds to a radially innermost fixed cutting element of the first plurality of fixed blade cutting elements,

a second central region having roller cone cutting elements arranged thereon, wherein a second transition from the first central region to the second central region corresponds to a radially innermost fixed cutting element of the second plurality of fixed blade cutting elements, and

an outermost region having roller cone cutting elements arranged thereon, wherein the outermost region has a radial length no less than 10% of a radius of the drill bit relative to the rotational axis,

wherein a cutting element density of the second central region is no less than 75% greater than the cutting element density of the first central region.