Rotary drill bits exhibiting cutting element placement for optimizing bit torque and cutter life

A rotary drag bit for drilling a subterranean formation, comprising:

• a bit body having a longitudinal axis and extending radially outward therefrom to a gage, the bit body further comprising a first region radially proximate the longitudinal axis, a second region radially proximate the gage, and a third region radially intermediate the first and second regions, and a plurality of circumferentially spaced blade structures wherein at least some of the plurality of circumferentially spaced blade structures extend longitudinally along a face of the bit body from generally the first region through the third region to generally the second region;
• and
• a plurality of cutters having preselected cutter backrake angles carried by at least some of the plurality of circumferentially spaced blade structures and being positioned within each of the three regions of the bit body, the plurality of cutters each comprising a longitudinal axis and at least one primary superabrasive cutting face having a preselected size and geometry and being positioned substantially transverse to a direction of cutter movement during drilling;
• wherein a majority of the cutters located in the first region are oriented within a first range of relatively more aggressive cutter backrake angles, a majority of the cutters located in the second region are oriented within a second range of relatively less aggressive cutter backrake angles, and a majority of the cutters located in the third region are oriented within a third range of relatively intermediately aggressive cutter backrake angles;
• and
• wherein the first region comprises a plurality of cutters having chamfers, the second region comprises a plurality of cutters having chamfers, and the third region comprises a plurality of cutters having chamfers.

A method of drilling a subterranean formation comprising:

• providing a rotary drag bit comprising:
• a bit body having a longitudinal axis and extending radially outwardly therefrom to a gage, the bit body configured to comprise at least a first region radially proximate the longitudinal axis, a second region radially proximate the gage, and a third region radially intermediate the first and second regions;
• a plurality of cutters located on the bit body in the first, second, and third regions, the plurality of cutters each comprising a superabrasive cutting face having preselected geometry and exhibiting a preselected effective cutting face backrake angle with respect to a line generally perpendicular to the formation, as taken in a direction of intended bit rotation, wherein the respective cutting faces of a majority of the cutters located in the first region exhibit effective cutting face backrake angles which are substantially less aggressive than the effective cutting face backrake angles of the respective cutting faces of a majority of cutters located in the second and third regions;
• orienting a face of the bit body toward a subterranean formation;
• rotating the bit body at a selected rotational speed while applying a weight upon the rotary drag bit;
• and
• engaging the subterranean formation with cutters located on at least one of the first, second, and third regions of the bit body so as to penetrate the subterranean formation at a greater rate of penetration and at a lower torque-on-bit as compared to a rate-of-penetration and a torque-on-bit generated by a conventional rotary drag bit drilling the same subterranean formation at approximately the same rotational speed.

A method of drilling a subterranean formation comprising:

• providing a rotary drag bit comprising:
• a bit body having a longitudinal axis and extending radially outwardly therefrom to a gage, the bit body configured to comprise at least a first region radially proximate the longitudinal axis, a second region radially proximate the gage, and a third region radially intermediate the first and second regions;
• a plurality of cutters located on the bit body in the first, second, and third regions, the cutters each comprising a superabrasive cutting face having preselected geometry and exhibiting a preselected effective cutting face backrake angle with respect to a line generally perpendicular to the formation, as taken in a direction of intended bit rotation, wherein the respective cutting faces of a majority of the cutters located in the first region are on cutters oriented within a first range of relatively more aggressive cutter backrake angles, a majority of the cutting faces located in the second region are on cutters oriented within a second range of relatively less aggressive cutter backrake angles, and a majority of the cutting faces located in the third region are on cutters oriented within a third range of relatively intermediately aggressive cutter backrake angles;
• configuring the respective superabrasive cutting faces of at least some of the plurality of cutters to include a chamfer of a preselected width and to exhibit a chamfer angle with respect to a longitudinal axis of each of the plurality of cutters;
• orienting a face of the bit body toward a subterranean formation;
• rotating the bit body at a selected rotational speed while applying a weight upon the rotary drag bit;
• and
• engaging the subterranean formation with at least one of the first, second, and third regions of the bit body so as to penetrate the subterranean formation at a greater rate of penetration and at a lower torque-on-bit as compared to a rate-of-penetration and a torque-on-bit generated by a conventional rotary drag bit drilling the same subterranean formation at approximately the same rotational speed.

A rotary drag bit for drilling a subterranean formation, comprising:

• a bit body having a longitudinal axis and extending radially outward therefrom to a gage, the bit body further comprising at least a first region, a second region, and a third region, radially intermediate the first and second regions, extending over a face of the bit body to be oriented toward the subterranean formation during drilling;
• and
• a plurality of cutters located on the bit body in the first, second, and third regions, the cutters each comprising a superabrasive cutting face of a preselected geometry and including a preselected effective cutting face backrake angle with respect to a line generally perpendicular to the formation, as taken in the direction of intended bit rotation, wherein at least one cutting geometry characteristic selected from the group consisting of cutter backrake angle, effective cutting face backrake angle, chamfer angle, chamfer width, and chamfer backrake angle of at least one first region cutter, at least one second region cutter, and at least one third region cutter are mutually different;
• wherein the respective superabrasive cutting face of at least some of the plurality of cutters includes a chamfer of a preselected width and a chamfer angle with respect to a longitudinal axis of each of the plurality of cutters;
• wherein the bit exhibits a lower torque-on-bit for a given rate-of-penetration as compared to a torque-on-bit generated by a conventional rotary drag bit drilling the same subterranean formation at approximately the same rotational speed.

A rotary drag bit for drilling a subterranean formation, comprising:

• a bit body having a longitudinal axis and extending radially outward therefrom to a gage, the bit body further comprising a face to be oriented toward the subterranean formation during drilling;
• and
• a plurality of cutters located on the bit body over the face, the cutters each comprising a superabrasive cutting face of a preselected geometry and including a preselected effective cutting face backrake angle with respect to a line generally perpendicular to the subterranean formation, as taken in the direction of intended bit rotation;
• wherein the respective superabrasive cutting face of at least some of the plurality of cutters includes a chamfer of a preselected width and a chamfer angle with respect to a longitudinal axis of each of the plurality of cutters;
• and
• wherein at least one cutting geometry characteristic selected from the group consisting of cutter backrake angle, effective cutting face backrake angle, chamfer angle, chamfer width and chamfer backrake angle of at least some of the plurality of cutters are selected to enable the bit to exhibit a lower torque-on-bit for a given rate-of-penetration as compared to a torque-on-bit generated by a conventional rotary drag bit drilling the same subterranean formation at approximately the same rotational speed.

A method of altering a torque response of a rotary drag bit for drilling a subterranean formation, comprising:

• selecting a configuration for a bit body having a longitudinal axis and extending radially outward therefrom to a gage, the bit body further comprising a face of the bit body to be oriented toward the subterranean formation during drilling and exhibiting a profile along which a plurality of cutters are to be placed;
• selecting a plurality of cutters to be located on the bit body over the face and along the profile, the cutters of the plurality each comprising a superabrasive cutting face, wherein each cutter of the plurality exhibits at least one cutting geometry characteristic selected from the group consisting of cutter backrake angle, effective cutting face backrake angle, chamfer angle, chamfer width and chamfer backrake angle;
• and
• modifying at least one cutting geometry characteristic of at least one cutter of the plurality in relation to a torque response associated therewith.

A method of altering a torque response of an existing rotary drag bit for drilling a subterranean formation, comprising:

• providing an existing rotary drag bit including:
• a bit body having a longitudinal axis and extending radially outward therefrom to a gage, the bit body further comprising a face of the bit body to be oriented toward the subterranean formation during drilling and exhibiting a profile along which a plurality of cutters are placed;
• and
• a plurality of cutters located on the bit body over the face and along the profile, the cutters of the plurality each comprising a superabrasive cutting face, wherein each cutter of the plurality exhibits at least one cutting geometry characteristic selected from the group consisting of cutter backrake angle, effective cutting face backrake angle, chamfer angle, chamfer width and chamfer backrake angle;
• and
• replacing at least one cutter of the plurality with another cutter exhibiting at least one different cutting geometry characteristic to alter a torque response of the replaced at least one cutter.