Backup cutting elements on non-concentric reaming tools

Abstract

An apparatus for reaming or enlarging a borehole comprising a bi-center drill bit having backup cutters thereon.

1 . A bi-center drill bit for drilling subterranean formations, comprising:
 a pilot bit section having a longitudinal axis, defining a first gage diameter and carrying a a first cutting structure for rotationally engaging a subterranean formation; and   a reamer bit section adjacent the pilot bit section, a portion of the reamer bit section extending radially beyond the first gage diameter along a minor portion of a side periphery of the bi-center drill bit and carrying a second cutting structure on the reamer bit section for rotationally engaging the subterranean formations; and   a third cutting structure disposed on at least one of the pilot bit section and the reamer bit section, the third cutting structure being positioned rotationally aft of at least one of the first cutting structure and the second cutting structure.   
     
     
         2 . The bi-center drill bit of  claim 1 , wherein the pilot bit section comprises a fixed-cutter bit and the first cutting structure comprises at least one superabrasive cutter. 
     
     
         3 . The bi-center drill bit of  claim 1 , wherein the second cutting structure and the third cutting structure each comprises at least one superabrasive cutter. 
     
     
         4 . The bi-center drill bit of  claim 1 , wherein the reamer bit section comprises a plurality of substantially radially-extending, circumferentially spaced blades, at least one blade of the plurality of substantially radially extending, circumferentially spaced blades extending radially beyond the first gage diameter. 
     
     
         5 . The bi-center drill bit of  claim 1 , wherein the pilot bit section includes a face carrying the first cutting structure. 
     
     
         6 . The bi-center drill bit of  claim 1 , wherein the third cutting structure is disposed on the reamer bit section and positioned rotationally aft of the second cutting structure, wherein the pilot bit section further comprises a fourth backup cutting structure rotationally aft of the first cutting structure for rotationally engaging a subterranean formation and, wherein the reamer bit section further comprises a fifth backup cutting structure rotationally aft of the third cutting structure for rotationally engaging a subterranean formation. 
     
     
         7 . A bi-center drill bit for drilling subterranean formations, comprising:
 a pilot bit section having a longitudinal axis, defining a first gage diameter and carrying a first cutting structure and a second cutting structure rotationally aft of the first cutting structure thereon for engaging a subterranean formation; and   a reamer bit section adjacent the pilot bit section, a portion of the reamer bit section extending radially beyond the first gage diameter along a minor portion of a side periphery of the bi-center drill bit and carrying a third cutting structure and a fourth cutting structure rotationally aft of the third cutting structure on the reamer bit section for engaging the subterranean formations.   
     
     
         8 . The bi-center drill bit of  claim 7 , wherein the pilot bit section comprises a fixed-cutter. 
     
     
         9 . The bi-center drill bit of  claim 7 , wherein the first cutting structure and the second cutting structure each comprise a plurality of superabrasive cutters. 
     
     
         10 . The bi-center drill bit of  claim 7 , wherein the reamer bit section comprises a plurality of substantially radially-extending, circumferentially spaced blades, at least one blade of the plurality of substantially radially extending, circumferentially spaced blades extending radially beyond the first gage diameter. 
     
     
         11 . The bi-center drill bit of  claim 7 , wherein the pilot bit section includes a face carrying the first cutting structure. 
     
     
         12 . The bi-center drill bit of  claim 7 , wherein the pilot bit section further comprises a fifth backup cutting structure rotationally aft of the first cutting structure for engaging a subterranean formation and wherein the reamer bit section comprises a sixth backup cutting structure rotationally aft of the third cutting structure for engaging a subterranean formation. 
     
     
         13 . The bi-center drill bit of  claim 7 , wherein the second cutting structure includes at least one of a back rake angle and a side rake angle. 
     
     
         14 . The bi-center drill bit of  claim 7 , wherein the fourth cutting structure includes at least one of a back rake angle and a side rake angle. 
     
     
         15 . The bi-center drill bit of  claim 7 , wherein the second cutting structure and the fourth cutting structure each includes at least one of a back rake angle and a side rake angle. 
     
     
         16 . A bi-center drill bit for drilling subterranean formations, comprising:
 a pilot drag bit section having a longitudinal axis, defining a first gage diameter and including a body with a face having a first plurality of superabrasive cutters secured thereto and a second plurality of backup superabrasive cutters located rotationally aft of the first plurality of superabrasive cutters and a gage section extending longitudinally from a periphery of the face; and   a reamer bit section adjacent the pilot drag bit section including at least one blade extending radially beyond the first gage diameter on one peripheral side portion of the bi-centered drill bit and carrying a third plurality of superabrasive cutters thereon and a fourth plurality of superabrasive cutters thereon located rotationally aft of the third plurality of superabrasive cutters.   
     
     
         17 . The bi-center drill bit of  claim 16 , wherein the at least one blade comprises a plurality of circumferentially spaced blades. 
     
     
         18 . The bi-center drill bit of  claim 16 , wherein the gage section includes gage pads. 
     
     
         19 . The bi-center drill bit of  claim 18 , wherein the gage pads provide a bearing surface area on a portion of the gage section. 
     
     
         20 . The bi-center drill bit of  claim 19 , wherein the gage pads comprise a plurality of circumferentially spaced, longitudinally elongated gage pads separated by longitudinally extending junk slots.