Drill Bits With Rolling Cone Reamer Sections

Abstract

A drill bit for drilling a borehole in earthen formations comprises a bit body having a central bit axis, a first end adapted to be connected to a drillstring, and a second end opposite the first end. In addition, the bit comprises a pilot bit extending from the second end of the bit body. Further, the bit comprises a reamer section extending radially from the bit body and axially positioned between the first end of the bit body and the pilot bit. The reamer section comprises a rolling cone cutter rotatably mounted to a journal shaft extending from the bit body. Moreover, the rolling cone cutter has a cone axis of rotation, a backface proximal the bit body, and a nose opposite the backface and distal the bit body.

1 . A drill bit for drilling a borehole in earthen formations, the bit comprising:
 a bit body having a central bit axis, a first end adapted to be connected to a drillstring, and a second end opposite the first end;   a pilot bit extending from the second end of the bit body;   a reamer section extending radially from the bit body and axially positioned between the first end of the bit body and the pilot bit;   wherein the reamer section comprises a rolling cone cutter rotatably mounted to a journal shaft extending from the bit body;   wherein the rolling cone cutter has a cone axis of rotation, a backface proximal the bit body, and a nose opposite the backface and distal the bit body.   
     
     
         2 . The drill bit of  claim 1 , wherein the cone axis is oriented at a cone axis angle relative to the bit axis as viewed in a plane that contains the cone axis and is parallel to the bit axis, wherein the cone axis angle is between 45° and 90°. 
     
     
         3 . The drill bit of  claim 2 , wherein the cone axis angle is between 60° and 90°. 
     
     
         4 . The drill bit of  claim 2 , wherein the rolling cone cutter has a maximum outer diameter and a length measured axially between the backface and the nose, wherein the ratio of the maximum outer diameter to the axial length is between 2.0 and 4.0. 
     
     
         5 . The drill bit of  claim 4 , wherein the ratio of the maximum outer diameter to the length is between 2.0 and 3.0. 
     
     
         6 . The drill bit of  claim 4 , wherein the rolling cone cutter has a cone offset between 0.5 in. and 3.00 in. 
     
     
         7 . The drill bit of  claim 2 , the rolling cone cutter includes a frustoconical heel surface adjacent the backface and a cone surface extending between the heel surface and the nose;
 wherein a plurality of cutting elements extend from the cone surface; and   wherein the heel surface is substantially free of cutting elements.   
     
     
         8 . The drill bit of  claim 4 , wherein the pilot bit is a fixed cutter bit or a rolling cone bit. 
     
     
         9 . The drill bit of  claim 8 , wherein the pilot bit is a rolling cone bit including a plurality of outwardly facing pilot cone cutters, wherein each pilot cone cutter is rotatably mounted to a journal extending from the second end of the bit body. 
     
     
         10 . The drill bit of  claim 9 , wherein each pilot cone cutter has a cone axis of rotation, a backface proximal the bit body, and a nose opposite the backface and distal the bit body; and
 wherein the cone axis of each pilot cone cutter is oriented at a cone axis angle relative to the bit axis as viewed in a plane that contains the cone axis and is parallel to the bit axis, wherein the cone axis angle of the cone axis of each pilot cone cutter is between 60° and 90°.   
     
     
         11 . The drill bit of  claim 10 , wherein each pilot cone cutter has a maximum outer diameter and a length measured axially between the backface and the nose of the pilot cone cutter, wherein the ratio of the maximum outer diameter of each pilot cone cutter to the axial length of each pilot cone cutter is between 2.0 and 4.0. 
     
     
         12 . The drill bit of  claim 1 , wherein the reamer section includes a plurality of rolling cone cutters, each rolling cone cutter being rotatably mounted to a journal shaft extending from the bit body; and
 wherein each rolling cone cutter has a cone axis of rotation, a backface proximal the bit body, and a nose opposite the backface and distal the bit body.   
     
     
         13 . The drill bit of  claim 12 , wherein each cone axis is oriented at a cone axis angle relative to the bit axis as viewed in a plane that contains the cone axis and is parallel to the bit axis, wherein the cone axis angle of each cone axis is between 45° and 90°;
 wherein each rolling cone cutter has a maximum outer diameter and a length measured axially between the backface and the nose, wherein the ratio of the maximum outer diameter to the axial length of each rolling cone cutter is between 2.0 and 4.0. 
 
     
     
         14 . A drill bit for drilling a borehole in earthen formations, the bit comprising:
 a bit body having a central bit axis, a first end adapted to be connected to a drillstring, and a second end opposite the first end;   a pilot bit extending from the second end of the bit body;   a reamer section extending radially from the bit body and axially positioned between the first end of the bit body and the pilot bit;   wherein the reamer section comprises a plurality of outwardly facing rolling cone cutters, each rolling cone cutter rotatably mounted to a journal shaft extending from the bit body.   
     
     
         15 . The drill bit of  claim 14 , wherein each rolling cone cutter has a cone axis of rotation, a backface proximal the bit body, and a nose opposite the backface and distal the bit body; and
 wherein the cone axis of each rolling cone is oriented at a cone axis angle relative to the bit axis as viewed in a plane that contains the cone axis and is parallel to the bit axis, wherein the cone axis angle of each rolling cone cutter is between 60° and 90°.   
     
     
         16 . The drill bit of  claim 15 , wherein each rolling cone cutter has a maximum outer diameter and a length measured axially between the backface and the nose, wherein the ratio of the maximum outer diameter to the axial length of each rolling cone cutter is between 2.0 and 3.0. 
     
     
         17 . The drill bit of  claim 15 , wherein each rolling cone cutter has a cone offset between 0.5 in. and 3.00 in. 
     
     
         18 . The drill bit of  claim 17 , wherein a first of the rolling cone cutters has a positive cone offset and a second of the rolling cone cutters has a negative cone offset. 
     
     
         19 . The drill bit of  claim 15 , wherein the plurality of rolling cone cutters are uniformly circumferentially spaced about the bit body. 
     
     
         20 . The drill bit of  claim 15 , wherein the pilot bit comprises a fixed cutter bit or a rolling cone bit. 
     
     
         21 . A method for drilling a wellbore in an earthen formation, comprising:
 (a) rotating a drill bit coupled to a lower end of a drillstring, wherein the drill bit comprises a bit body having a bit axis;   (b) forming a pilot borehole having a diameter D 1  with a pilot bit disposed at a lower end of the bit body;   (c) forming an enlarged borehole having a diameter D 2  with a reamer section extending from radially the bit body, wherein the reamer section is positioned axially above the pilot bit;   wherein (c) comprises rotating a plurality of reamer rolling cone cutters, each reamer cone cutter depending from a journal extending from the bit body;   wherein each reamer rolling cone cutter comprises a central axis, a backface, and a nose positioned proximal the diameter D 2 .   
     
     
         22 . The method of  claim 21 , further comprising passing the drill bit through a bore having a diameter less than diameter D 2 . 
     
     
         23 . The method of  claim 21 , wherein each reamer cone cutter has a positive or negative cone offset. 
     
     
         24 . The method of  claim 23 , wherein the cone offset of each reamer cone cutter is between 0.5 in. and 3.00 in. 
     
     
         25 . The method of  claim 21 , wherein (b) comprises rotating a plurality of pilot rolling cone cutters, each pilot cone cutter depending from a journal extending from the lower end of the bit body;
 wherein each pilot rolling cone cutter comprises a central axis, a backface, and a nose positioned proximal the diameter D 1 .