Fixed cutter drill bits including cutter elements with variable exposures

Abstract

A fixed cutter drill bit for drilling an earthen formation includes a bit body having a central axis and a bit face. The bit body is configured to rotate about the central axis in a cutting direction of rotation. The bit face includes a concave cone region extending radially from the central axis, a convex shoulder region extending radially from the cone region, a nose at the intersection of the cone region and the shoulder region, and a gage region extending radially from the shoulder region to a full gage diameter of the drill bit. The drill bit also includes a cutting structure disposed on the bit face. The cutting structure includes a primary blade extending radially from proximal the bit axis through the cone region and the shoulder region to the gage region. The blade has a leading side relative to the cutting direction of rotation, a trailing side relative to the cutting direction of rotation, and a cutter-supporting surface extending from the leading side to the trailing side. In addition, the drill bit includes a plurality of high-aspect ratio cutter element assemblies mounted to the cutter-supporting surface of the primary blade in the cone region. The cutter element assemblies are arranged in a radially extending row proximal the leading side of the primary blade, wherein each cutter element assembly includes a cutter element carrier and a first cutter element fixably attached to the cutter element carrier. Still further, the drill bit includes a plurality of low-aspect ratio second cutter elements directly mounted to the cutter-supporting surface of the primary blade in the shoulder region or the gage region. The second cutter elements are arranged in a radially extending row proximal the leading side of the primary blade. Each high-aspect ratio cutter element assembly has an exposure H1 measured perpendicularly from the cutter-supporting surface of the primary blade to a cutting tip of the first cutter element of the cutter element assembly distal the primary blade. Each low-aspect ratio second cutter element has an exposure H2 measured perpendicularly from the cutter-supporting surface of the primary blade to a cutting tip of the second cutter element distal the primary blade. The exposure H1 of one or more high-aspect ratio cutter element assemblies in the cone region is greater than the exposure H2 of one or more low-aspect ratio second cutter elements in the shoulder region or the gage region.

What is claimed is: 
     
         1 . A fixed cutter drill bit for drilling an earthen formation, the drill bit comprising:
 a bit body having a central axis and a bit face, wherein the bit body is configured to rotate about the central axis in a cutting direction of rotation, wherein the bit face includes a concave cone region extending radially from the central axis, a convex shoulder region extending radially from the cone region, a nose at the intersection of the cone region and the shoulder region, and a gage region extending radially from the shoulder region to a full gage diameter of the drill bit;   a cutting structure disposed on the bit face, wherein the cutting structure includes a primary blade extending radially from proximal the bit axis through the cone region and the shoulder region to the gage region, wherein the blade has a leading side relative to the cutting direction of rotation, a trailing side relative to the cutting direction of rotation, and a cutter-supporting surface extending from the leading side to the trailing side; and   a plurality of high-aspect ratio cutter element assemblies mounted to the cutter-supporting surface of the primary blade in the cone region, wherein the cutter element assemblies are arranged in a radially extending row proximal the leading side of the primary blade, wherein each cutter element assembly includes a cutter element carrier and a first cutter element fixably attached to the cutter element carrier;   a plurality of low-aspect ratio second cutter elements directly mounted to the cutter-supporting surface of the primary blade in the shoulder region or the gage region, wherein the second cutter elements are arranged in a radially extending row proximal the leading side of the primary blade;   wherein each high-aspect ratio cutter element assembly has an exposure H 1  measured perpendicularly from the cutter-supporting surface of the primary blade to a cutting tip of the first cutter element of the cutter element assembly distal the primary blade;   wherein each low-aspect ratio second cutter element has an exposure H 2  measured perpendicularly from the cutter-supporting surface of the primary blade to a cutting tip of the second cutter element distal the primary blade;   wherein the exposure H 1  of one or more high-aspect ratio cutter element assemblies in the cone region is greater than the exposure H 2  of one or more low-aspect ratio second cutter elements in the shoulder region or the gage region.   
     
     
         2 . The fixed cutter drill bit of  claim 1 , wherein each high-aspect ratio cutter element assembly has a longitudinal axis oriented perpendicular to the central axis, a maximum length measured parallel to the longitudinal axis in front view, and a maximum width measured perpendicular to the longitudinal axis in front view;
 wherein each high-aspect ratio cutter element assembly has an aspect ratio equal to the ratio of the maximum length of the high-aspect ratio cutter element assembly to the maximum width of the high-aspect ratio cutter element assembly, wherein the aspect ratio of each high-aspect ratio cutter element assembly is greater than 1.0 and less than or equal to 2.0.   
     
     
         3 . The fixed cutter drill bit of  claim 1 , wherein the exposure H 1  of one or more high-aspect ratio cutter element assemblies in the cone region is at least 1.5 times greater than the exposure H 2  of each second cutter element in the shoulder region and the gage region. 
     
     
         4 . The fixed cutter drill bit of  claim 3 , wherein the exposure H 1  of each high-aspect ratio cutter element assembly in the cone region ranges from 6.0 mm to 15.0 mm and the exposure H 2  of each low-aspect ratio second cutter element in the shoulder region and the gage region ranges from 5.0 mm to 20.0 mm 
     
     
         5 . The drill bit of  claim 1 , wherein each pair of radially adjacent high-aspect ratio cutter element assemblies are spaced apart a minimum distance D 1  measured parallel to the cutter-supporting surface of the primary blade between the pair of radially adjacent high-aspect ratio cutter element assemblies;
 wherein each pair of radially adjacent low-aspect ratio second cutter elements are spaced apart a minimum distance D 2  measured parallel to the cutter-supporting surface of the primary blade between the pair of radially adjacent low-aspect ratio second cutter elements;   wherein the spacing D 1  of each pair of radially adjacent high-aspect ratio cutter element assemblies in the cone region is greater than the spacing D 2  of each pair of radially adjacent low-aspect ratio second cutter elements in the shoulder region and the gage region.   
     
     
         6 . The fixed cutter drill bit of  claim 5 , wherein the minimum distance D 1  between each pair of radially adjacent high-aspect ratio cutter element assemblies in the cone region ranges from 4.0 mm to 20.0 mm and the minimum distance D 2  between each pair of radially adjacent low-aspect ratio second cutter elements in the shoulder region and the gage region ranges from 1.0 mm to 3.0 mm. 
     
     
         7 . The fixed cutter drill bit of  claim 6 , wherein the minimum distance D 1  between each pair of radially adjacent high-aspect ratio cutter element assemblies in the cone region ranges from 10.0 mm to 12.0 mm. 
     
     
         8 . The fixed cutter drill bit of  claim 5 , wherein the minimum distance D 1  between each pair of radially adjacent high-aspect ratio cutter element assemblies in the cone region is at least 1.5 times the minimum distance D 2  between each pair of radially adjacent low-aspect second cutter elements in the shoulder region and the gage region. 
     
     
         9 . The fixed cutter drill bit of  claim 8 , wherein the minimum distance D 1  between each pair of radially adjacent high-aspect ratio cutter element assemblies in the cone region is at least 2.0 times the minimum distance D 2  between each pair of radially adjacent low-aspect ratio second cutter elements in the shoulder region and the gage region. 
     
     
         10 . The fixed cutter drill bit of  claim 1 , wherein each low-aspect ratio second cutter element is cylindrical. 
     
     
         11 . The fixed cutter drill bit of  claim 1 , wherein each cutter element carrier has a leading end relative to the cutting direction of rotation and a trailing end relative to the cutting direction of rotation;
 wherein each cutter element carrier includes a base extending axially from the leading end to the trailing end, wherein the base has an outer surface including a semi-cylindrical cutter element facing surface extending from the leading end, wherein the corresponding first cutter element is seated against the semi-cylindrical cutter element facing surface and fixably attached to the cutter element carrier.   
     
     
         12 . The fixed cutter drill bit of  claim 11 , wherein each cutter element carrier further comprises a support block extending axially relative to the longitudinal axis of the high-aspect ratio cutter element assembly from the base;
 wherein the semi-cylindrical cutter element facing surface extends from the leading end to the support block;   wherein the support block includes a leading face fixably attached to the corresponding first cutter element.   
     
     
         13 . The fixed cutter drill bit of  claim 1 , wherein one or more high-aspect ratio cutter element assemblies is oriented at a non-zero tilt angle α measured in a front view of the primary blade from the longitudinal axis of the high-aspect ratio cutter element assembly to a reference axis A passing through a cutting tip of the corresponding first cutter element and oriented perpendicular to a cutting profile of the plurality of high-aspect ratio cutter element assemblies and the plurality of low-aspect ratio second cutter elements mounted to the primary blade. 
     
     
         14 . A fixed cutter drill bit for drilling an earthen formation, the drill bit comprising:
 a bit body having a central axis and a bit face, wherein the bit body is configured to rotate about the central axis in a cutting direction of rotation, wherein the bit face includes a concave cone region extending radially from the central axis, a convex shoulder region extending radially from the cone region, a nose at the intersection of the cone region and the shoulder region, and a gage region extending radially from the shoulder region to a full gage diameter of the drill bit;   a cutting structure disposed on the bit face, wherein the cutting structure includes a plurality of circumferentially-spaced primary blades, wherein each primary blade extends radially from proximal the bit axis through the cone region and the shoulder region to the gage region, wherein each primary blade has a leading side relative to the cutting direction of rotation, a trailing side relative to the cutting direction of rotation, and a cutter-supporting surface extending from the leading side to the trailing side;   a plurality of gage pads, wherein each gage pad extends from an end of each primary blade distal the bit axis in the gage region;   a plurality of high-aspect ratio cutter element assemblies mounted to the cutter-supporting surface of each primary blade and arranged in a row proximal the leading side of the primary blade that extends radially from proximal the bit axis through the cone region to the shoulder region, wherein each high-aspect ratio cutter element assembly includes a cutter element carrier and a first cutter element mounted to the cutter element carrier; and   a plurality of low-aspect ratio second cutter elements directly mounted to the cutter-supporting surface of each primary blade and arranged in a row proximal the leading side of the primary blade that extends from the row of high-aspect ratio cutter element assemblies through the shoulder region or the gage region to the gage pad.   
     
     
         15 . The fixed cutter drill bit of  claim 14 , wherein each first cutter element has a central axis, a leading end relative to the cutting direction of rotation, a trailing end relative to the cutting direction of rotation and opposite the leading end, and a cutting face at the leading end;
 wherein each high-aspect ratio cutter element assembly has a longitudinal axis oriented perpendicular to the central axis of the corresponding first cutter element, a maximum length measured parallel to the longitudinal axis and a maximum width measured perpendicular to the longitudinal axis;   wherein each high-aspect ratio cutter element assembly has an aspect ratio equal to the ratio of the maximum length of the high-aspect ratio cutter element assembly to the maximum width of the high-aspect ratio cutter element assembly, wherein the aspect ratio of each high-aspect ratio cutter element assembly is greater than 1.0 and less than or equal to 2.0.   
     
     
         16 . The fixed cutter drill bit of  claim 14 , wherein each pair of radially adjacent high-aspect cutter element assemblies on each primary blade are spaced apart a minimum distance D 1  measured parallel to the cutter-supporting surface of the primary blade between the pair of radially adjacent high-aspect ratio cutter element assemblies;
 wherein each pair of radially adjacent low-aspect second cutter elements on each primary blade are spaced apart a minimum distance D 2  measured parallel to the cutter-supporting surface of the primary blade between the pair of radially adjacent low-aspect ratio second cutter elements;   wherein the minimum distance D 1  between each pair of radially adjacent high-aspect ratio cutter element assemblies is greater than the minimum distance D 2  between each pair of radially adjacent low-aspect ratio second cutter elements.   
     
     
         17 . The fixed cutter drill bit of  claim 16 , wherein the minimum distance D 1  between each pair of radially adjacent high-aspect ratio cutter element assemblies ranges from 4 mm to 20 mm and the minimum distance D 2  between each pair of radially adjacent low-aspect ratio second cutter elements ranges from 1.0 mm to 3.0 mm. 
     
     
         18 . The fixed cutter drill bit of  claim 16 , wherein the minimum distance D 1  between each pair of radially adjacent high-aspect ratio cutter element assemblies is at least 1.5 times the minimum distance D 2  between each pair of radially adjacent low-aspect ratio second cutter elements. 
     
     
         19 . The fixed cutter drill bit of  claim 14 , wherein each high-aspect ratio cutter element assembly has an exposure H 1  measured perpendicularly from the cutter-supporting surface of the corresponding primary blade to a cutting tip of the first cutter element of the high-aspect ratio cutter element assembly distal the corresponding primary blade;
 wherein each low-aspect ratio second cutter element has an exposure H 2  measured perpendicularly from the cutter-supporting surface of the corresponding primary blade to a cutting tip of the low-aspect ratio second cutter element distal the corresponding primary blade; 
 wherein the exposure H 1  of one or more high-aspect ratio cutter element assemblies is greater than the exposure H 2  of each low-aspect ratio second cutter element. 
 
     
     
         20 . The fixed cutter drill bit of  claim 19 , wherein the exposure H 2  of each of the low aspect-ratio second cutter element is the same;
 wherein the exposure H 1  of the radially outermost high-aspect cutter element assembly positioned radially adjacent the row of the low-aspect ratio second cutter elements is the same as the exposure H 2  of each of the low aspect-ratio second cutter elements; 
 wherein the exposure H 1  of each high-aspect ratio cutter element assembly radially positioned between the central axis of the drill bit and the radially outermost high-aspect ratio cutter element assembly is greater than the exposure H 2  of each low-aspect ratio second cutter element. 
 
     
     
         21 . The fixed cutter drill bit of  claim 20 , wherein the exposure H 1  of each high-aspect ratio cutter element assembly is at least 1.25 times greater than the exposure H 2  of each low-aspect ratio second cutter element. 
     
     
         22 . The fixed cutter drill bit of  claim 15 , wherein one or more high-aspect ratio cutter element assembly is oriented at a non-zero tilt angle α measured in a front view of the corresponding primary blade from the longitudinal axis of the high-aspect cutter element assembly to a reference axis A passing through a cutting tip of the high-aspect ratio cutter element assembly and oriented perpendicular to a cutting profile of the plurality of high-aspect ratio cutter element assemblies and the low aspect-ratio second cutter elements mounted to the primary blade.