Fixed Cutter Drill Bits and Cutter Element with Secondary Cutting Edges for Same

Abstract

A cutter element for a fixed cutter drill bit configured to drill a borehole in a subterranean formation includes a base having a central axis, a first end, a second end, and a radially outer cylindrical surface extending axially from the first end to the second end. In addition, the cutter element includes a cutting layer fixably mounted to the first end of the base. The cutting layer includes a stepped cutting face distal the base and a radially outer cylindrical surface extending axially from the cutting face to the radially outer cylindrical surface of the base. The radially outer cylindrical surface of the cutting layer is contiguous with the radially outer cylindrical surface of the base. The stepped cutting face includes a first step, a second step axially spaced from the first step, and a riser axially positioned between the first step and the second step. The first step is axially positioned between the riser and the base.

What is claimed is: 
     
         1 . A cutter element for a fixed cutter drill bit configured to drill a borehole in a subterranean formation, the cutter element comprising:
 a base having a central axis, a first end, a second end, and a radially outer cylindrical surface extending axially from the first end to the second end;   a cutting layer fixably mounted to the first end of the base, wherein the cutting layer includes a stepped cutting face distal the base and a radially outer cylindrical surface extending axially from the cutting face to the radially outer cylindrical surface of the base, wherein the radially outer cylindrical surface of the cutting layer is contiguous with the radially outer cylindrical surface of the base;   wherein the stepped cutting face comprises:
 a first step; 
 a second step axially spaced from the first step; 
 a riser axially positioned between the first step and the second step; 
 wherein the first step is axially positioned between the riser and the base; 
 wherein the step has a W-shaped geometry in a top view of the cutter element. 
   
     
     
         2 . The cutter element of  claim 1 , wherein the cutting layer has a thickness T cl  measured axially from the base to the second step;
 wherein the first step is axially spaced from the second step by a distance D s  measured axially from the first step to the second step, wherein the ratio of the distance D s  to the thickness T cl  is greater than or equal to 0.25.   
     
     
         3 . The cutter element of  claim 1 , wherein the first step comprises a planar surface disposed in a plane oriented perpendicular to the central axis. 
     
     
         4 . The cutter element of  claim 3 , wherein the riser comprises a plurality of circumferentially adjacent planar surfaces. 
     
     
         5 . The cutter element of  claim 4 , wherein the first step, the second step, and the riser are symmetric about a reference plane that contains the central axis of the base and bisects the cutter element. 
     
     
         6 . The cutter element of  claim 4 , wherein the riser comprises:
 a pair of central planar surfaces;   a first lateral planar surface extending from one of the pair of central planar surfaces to the radially outer cylindrical surface of the cutting layer; and   a second lateral planar surface extending from the other of the pair of central planar surfaces to the radially outer cylindrical surface of the cutting layer, wherein the first lateral planar surface and the second lateral planar surfaces are disposed on opposite sides of the reference plane and the pair of central planar surfaces.   
     
     
         7 . The cutter element of  claim 6 , wherein the first lateral planar surface and the second lateral planar surface are angularly spaced apart by an angle θ in the top view of the cutter element, wherein the angle θ ranges from 70° to 140°. 
     
     
         8 . The cutter element of  claim 6 , wherein the pair of central planar surfaces are oriented at an angle λ relative to each other in the top view of the cutter element, wherein the angle λ ranges from 70° to 140°. 
     
     
         9 . The cutter element of  claim 1 , wherein the second step is convex in front view of the cutter element and side view of the cutter element. 
     
     
         10 . The cutter element of  claim 9 , wherein the second step comprises a cutting region extending from the riser and a relief region extending from the riser and the cutting region, wherein the relief region extends about the cutting region. 
     
     
         11 . The cutter element of  claim 10 , wherein the cutting region of the second step is disposed in a plane oriented perpendicular to the central axis of the base; and
 wherein the relief region is oriented at an acute angle η relative to a plane oriented perpendicular to the central axis of the base in a side view of the cutter element, wherein the angle η ranges from 1° to 20°.   
     
     
         12 . The cutter element of  claim 1 , wherein the first step defines a primary cutting surface comprising a surface finish including a plurality of elongate raised ridges and a plurality of recesses positioned between the raised ridges, wherein the plurality of raised ridges are arranged in a plurality of parallel rows. 
     
     
         13 . The cutter element of  claim 12 , wherein each of the plurality of raised ridges has a linear central axis, a first end, a second end opposite the first end, a length measured axially from the first end to the second end, and a width measured perpendicular to the central axis;
 wherein the plurality of raised ridges are oriented parallel to each other;   wherein the width of each raised ridge ranges from 2.0 micron to 250.0 micron; and   wherein the length of each raised ridge ranges from 25.0 micron to 750.0 micron.   
     
     
         14 . The cutter element of  claim 1 , further comprising a pair of circumferentially-spaced planar flats, wherein each planar flat extends axially from the first step surface across the radially outer cylindrical surface of the cutting layer and the radially outer cylindrical surface of the substrate. 
     
     
         15 . A cutter element for a fixed cutter drill bit configured to drill a borehole in a subterranean formation, the cutter element comprising:
 a substrate having a central axis, a first end, a second end, and a radially outer cylindrical surface extending axially from the first end to the second end;   a cutting layer having a first end distal the substrate, a second end fixably attached to the first end of the substrate, and a radially outer cylindrical surface extending from the first end of the cutting layer to the second end of the cutting layer, wherein the first end of the cutting layer includes a stepped cutting face, wherein the radially outer cylindrical surface of the cutting layer is contiguous with the radially outer cylindrical surface of the base;   wherein the stepped cutting face comprises:
 a primary cutting surface extending from a first cutting tip of the cutter element, wherein the first cutting tip is configured to engage and shear the subterranean formation; 
 a secondary cutting surface axially spaced from the primary cutting surface, wherein the secondary cutting surface extends from a second cutting tip of the cutter element, wherein the second cutting tip is configured to engage and shear the subterranean formation; 
 a riser axially positioned between the primary cutting surface and the secondary cutting surface; 
 wherein the primary cutting surface is axially positioned between the secondary cutting surface and the substrate; 
 wherein the riser comprises:
 a plurality of circumferentially adjacent planar surfaces including:
 a pair of central planar surfaces extending axially from the primary cutting surface to the second bevel, wherein the pair of central planar surfaces are oriented at an angle λ relative to each other in a top view of the cutter element, wherein the angle λ ranges from 70° to 140°; 
 a first lateral planar surface extending from one of the pair of central planar surfaces to the radially outer cylindrical surface of the cutting layer; and 
 a second lateral planar surface extending from the other of the pair of central planar surfaces to the radially outer cylindrical surface of the cutting layer, wherein the first lateral planar surface and the second lateral planar surfaces are disposed on opposite sides of the reference plane and the pair of central planar surfaces; 
 wherein the first lateral planar surface and the second lateral planar surface are angularly spaced apart by an angle θ in the top view of the cutter element, wherein the angle θ ranges from 70° to 140°; 
 
 
   wherein the primary cutting surface is configured to engage and shear the subterranean formation before the secondary cutting surface.   
     
     
         16 . The cutter element of  claim 15 , wherein the riser has a W-shaped geometry in the top view of the cutter element. 
     
     
         17 . The cutter element of  claim 15 , further comprising a pair of circumferentially-spaced planar flats, wherein each planar flat extends axially from the primary cutting surface across the radially outer cylindrical surface of the cutting layer and the radially outer cylindrical surface of the substrate. 
     
     
         18 . The cutter element of  claim 15 , wherein the cutting layer has a thickness T cl  measured axially from the substrate to the secondary cutting surface;
 wherein the primary cutting surface is axially spaced from the secondary cutting surface by a distance D s  measured axially from the primary cutting surface to the secondary cutting surface, wherein the ratio of the distance D s  to the thickness T cl  is greater than or equal to 0.25.   
     
     
         19 . The cutter element of  claim 15 , wherein the first cutting tip is radially aligned with the second cutting tip, and wherein the first cutting tip and the second cutting tip are radially spaced apart a radial offset distance R measured radially from the first cutting tip to the second cutting tip in top view, wherein the radial offset distance R ranges from 0.45 mm to 2.0 mm. 
     
     
         20 . The cutter element of  claim 15 , wherein first cutting tip, the second cutting tip, and the riser are symmetric about a reference plane that contains the central axis of the base and bisects the cutter element. 
     
     
         21 . The cutter element of  claim 15 , wherein the primary cutting surface comprises a planar surface disposed in a plane oriented perpendicular to the central axis; and
 wherein the secondary cutting surface comprises:
 a planar cutting region disposed in a plane oriented perpendicular to the central axis; and 
 a relief region disposed about the cutting region and extending from the cutting region to the a radially outer cylindrical surface of the cutting layer. 
   
     
     
         22 . The cutter element of  claim 15 , wherein the secondary cutting surface is convex in front view of the cutter element and side view of the cutter element. 
     
     
         23 . The cutter element of  claim 15 , wherein the primary cutting surface comprises a surface finish including a plurality of elongate raised ridges and a plurality of recesses positioned between the raised ridges, wherein the plurality of raised ridges are arranged in a plurality of parallel rows. 
     
     
         24 . The cutter element of  claim 23 , wherein each of the plurality of raised ridges has a linear central axis, a first end, a second end opposite the first end, a length measured axially from the first end to the second end, and a width measured perpendicular to the central axis;
 wherein the plurality of raised ridges are oriented parallel to each other;   wherein the width of each raised ridge ranges from 2.0 micron to 250.0 micron; and   wherein the length of each raised ridge ranges from 25.0 micron to 750.0 micron.