DRILL BIT WITH STAGED DURABILITY, STABILITY AND ROP CHARACTERISTICS
Drill bit with multiple stages of durability and ROP characteristics is disclosed. The drill bit has multiple layers of cutters established by deploying the cutters on blades of different heights or maintaining the blades at the same height and deploying the cutters to have different heights on one or more blades. Each layer provides independent bottom hole coverage and has independent stabilization, ROP, and durability characteristics so as to effectively drill through different subsurface formations. Cutters deployed on the different layers have their respective centers at substantially different radial positions. Due to the different radial positions, cutters in different layers cut different swaths in the subsurface formation. Cutters in different layers may also have different initial peripheral portions or shear lengths, resulting in different impact resistance characteristics for the different layers. This changes the wear and/or cutter deterioration processes for the different layers, resulting in different and/or improved toughness characteristics.
1 . A drill bit, comprising:
a drill bit body;
blades formed on said drill bit body, said blades having a plurality of cutting element positions radially located thereon; and
cutting elements deployed on said blades, said cutting elements forming a primary layer of cutting elements and a secondary layer of cutting elements, said primary layer of cutting elements having a different height relative to said drill bit body from said secondary layer of cutting elements;
wherein at least one primary layer cutting element and a corresponding secondary layer cutting element occupy substantially different cutting element positions on said blades such that their cutting element profiles overlap, said at least one primary layer cutting element and said corresponding secondary layer cutting element together defining a cutting zone equal to a diameter of one of said at least one primary layer cutting element and said corresponding secondary layer cutting element plus a predetermined fraction of said diameter.
2 . The drill bit according to claim 1 , wherein said predetermined fraction is from approximately 1/10 to approximately ⅓.
3 . The drill bit according to claim 1 , wherein said predetermined fraction is approximately ⅕.
4 . The drill bit according to claim 1 , wherein said diameter is a diameter of said at least one primary layer cutting element.
5 . The drill bit according to claim 1 , wherein said diameter is a diameter of said corresponding secondary layer cutting element.
6 . The drill bit according to claim 1 , wherein said cutting elements in said primary layer and said cutting elements in said secondary layer have substantially different shear lengths.
7 . The drill bit according to claim 6 , wherein said shear lengths are average shear lengths derived from multiple shear lengths for said cutting elements in said primary layer and said cutting elements in said secondary layer.
8 . The drill bit according to claim 1 , wherein said cutting elements in said primary layer and said cutting elements in said secondary layer have substantially different sizes.
9 . The drill bit according to claim 1 , wherein said cutting elements in said primary layer and said cutting elements in said secondary layer have substantially different shape.
10 . The drill bit according to claim 9 , wherein said substantially different shapes result in said cutting elements in said primary layer and said cutting elements in said secondary layer having substantially different axial volumes.
11 . The drill bit according to claim 1 , wherein said cutting elements in said primary layer and said cutting elements in said secondary layer have substantially different abrasion resistances.
12 . The drill bit according to claim 1 , wherein said cutting elements in said primary layer and said cutting elements in said secondary layer have substantially different impact resistances.
13 . The drill bit according to claim 1 , wherein said cutting elements in said primary layer and said cutting elements in said secondary layer have substantially different thermal stabilities.
14 . The drill bit according to claim 1 , wherein said cutting elements in said primary layer and said cutting elements in said secondary layer have substantially different back rake angles.
15 . The drill bit according to claim 14 , wherein one or more cutting elements in said primary layer have a larger back rake angle than one or more cutting elements in said secondary layer.
16 . The drill bit according to claim 14 , wherein one or more cutting elements in said primary layer have a smaller back rake angle than one or more cutting elements in said secondary layer.
17 . The drill bit according to claim 1 , wherein said cutting elements form a tertiary layer of cutting elements and said primary layer of cutting elements have a different height relative to said drill bit body from said tertiary layer of cutting elements, and wherein at least one primary layer cutting element and a corresponding tertiary layer cutting element occupy substantially different cutting element positions on said blades such that their cutting element profiles overlap, said at least one primary layer cutting element and said corresponding tertiary layer cutting element together defining a cutting zone equal to a diameter of one of said at least one primary layer cutting element and said corresponding tertiary layer cutting element plus a predetermined fraction of said diameter.
18 . A method of assembling a drill bit, comprising:
providing a drill bit body having blades formed thereon said blades having a plurality of cutting element positions radially located thereon; and
deploying cutting elements on said blades, said cutting elements forming a primary layer of cutting elements and a secondary layer of cutting elements, said primary layer of cutting elements having a different height relative to said drill bit body from said secondary layer of cutting elements;
wherein at least one primary layer cutting element and a corresponding secondary layer cutting element occupy substantially different cutting element positions on said blades such that their cutting element profiles overlap, said at least one primary layer cutting element and said corresponding secondary layer cutting element together defining a cutting zone equal to a diameter of one of said at least one primary layer cutting element and said corresponding secondary layer cutting element plus a predetermined fraction of said diameter.
19 . The method according to claim 18 , wherein said cutting elements of said primary layer and said cutting elements of said secondary layer are mounted on blades having substantially different heights relative to said drill bit body.
20 . The method according to claim 18 , wherein said cutting elements of said primary layer and said cutting elements of said secondary layer are mounted on blades having substantially identical heights relative to said drill bit body.
21 . The method according to claim 20 , wherein said cutting elements of said primary layer and said cutting elements of said secondary layer are mounted on separate blades.
22 . The method according to claim 20 , wherein one or more cutting elements of said primary layer and one or more cutting elements of said secondary layer are mounted on a single blade.
23 . The method according to claim 20 , wherein said one or more cutting elements of said primary layer and said one or more cutting elements of said secondary layer are mounted on said single blade in multiple rows.
24 . The method according to claim 23 , wherein at least one of said rows contains a combination of cutting elements from said primary layer and cutting elements from said secondary layer.
25 . The method according to claim 23 , wherein at least one of said rows contains only cutting elements from said primary layer or only cutting elements from said secondary layer.
26 . The method according to claim 18 , wherein said primary layer of cutting elements establishes approximately 100% bottom hole coverage.
27 . A drill bit body, comprising:
blades formed on said drill bit body, and
cutting element positions formed on said blades, said cutting element positions radially located thereon such that when cutting elements are deployed on said blades, said cutting elements form a primary layer of cutting elements and a secondary layer of cutting elements, said primary layer of cutting elements having a different height relative to said drill bit body from said secondary layer of cutting elements;
wherein at least one primary layer cutting element and a corresponding secondary layer cutting element occupy substantially different cutting element positions on said blades such that their cutting element profiles overlap when said cutting elements are deployed on said blades, said at least one primary layer cutting element and said corresponding secondary layer cutting element together defining a cutting zone equal to a diameter of one of said at least one primary layer cutting element and said corresponding secondary layer cutting element plus a predetermined fraction of said diameter.