Backup cutting elements on non-concentric earth-boring tools and related methods

Abstract

An apparatus for engaging a subterranean borehole includes a bi-center bit having backup cutting elements thereon. The bi-center bit includes a pilot bit section and a reamer bit section adjacent to the pilot bit section. The pilot bit section includes at least one primary cutting element and at least one backup cutting element rotationally trailing and laterally offset from the at least one primary cutting element. Methods of drilling a subterranean borehole include engaging a first portion of a borehole with a reamer bit section of a drill bit and simultaneously engaging a second, opposing portion of the borehole with a pilot bit section adjacent to the reamer bit section.

1 . A bi-center bit for drilling subterranean formations, comprising:
 a pilot bit section having a first gage diameter and including at least one primary cutting element and at least one backup cutting element rotationally trailing the at least one primary cutting element disposed thereon for engaging a subterranean formation, wherein the at least one backup cutting element is offset from the at least one primary cutting element in a direction substantially transverse to an intended rotational path of the at least one primary cutting element during rotational operation of the bi-center bit; and   a reamer bit section adjacent to the pilot bit section, the reamer bit section comprising at least one blade extending radially beyond the first gage diameter for rotationally engaging a subterranean formation.   
     
     
         2 . The bi-center bit of  claim 1 , wherein the pilot bit section comprises a plurality of blades, each blade of the plurality of blades having a plurality of primary cutting elements and a plurality of backup cutting elements rotationally trailing at least one primary cutting element of the plurality of primary cutting elements. 
     
     
         3 . The bi-center bit of  claim 2 , wherein at least one backup cutting element of the plurality of backup cutting elements on at least one blade of the plurality of blades is offset from at least one primary cutting element of the plurality of primary cutting elements on at least another blade of the plurality of blades. 
     
     
         4 . The bi-center bit of  claim 1 , wherein the reamer bit section comprises a reamer wing and wherein the pilot bit section comprises a fixed-cutting element drill bit, the reamer wing and the fixed-cutting element drill bit being coupled to form the bi-center bit. 
     
     
         5 . The bi-center bit of  claim 1 , wherein the at least one blade of the reamer bit section comprises two blades extending radially beyond the first gage diameter. 
     
     
         6 . The bi-center bit of  claim 5 , wherein the at least one backup cutting element comprises a plurality of backup cutting elements and wherein at least one backup cutting element of the plurality of backup cutting elements is positioned to substantially laterally oppose at least one blade of the two blades of the reamer bit section. 
     
     
         7 . The bi-center bit of  claim 6 , wherein at least one backup cutting element of the plurality of backup cutting elements is positioned on a shoulder region of the pilot bit section, wherein at least another backup cutting element of the plurality of backup cutting elements is positioned on a cone region of the pilot bit section, and wherein the at least one backup cutting element of the plurality of backup cutting elements has an exposure greater than the exposure of the at least another backup cutting element of the plurality of backup cutting elements. 
     
     
         8 . The bi-center bit of  claim 1 , further comprising at least one additional backup cutting element rotationally trailing the at least one backup cutting element. 
     
     
         9 . The bi-center bit of  claim 1 , wherein the at least one backup cutting element is oriented at a back rake angle of about ninety (90) degrees. 
     
     
         10 . The bi-center bit of  claim 9 , wherein the at least one backup cutting element comprises an ovoid shape. 
     
     
         11 . A bi-center bit for drilling subterranean formations, comprising:
 an eccentric reamer comprising at least one radially extending blade, the at least one radially extending blade including at least one reamer cutting element disposed thereon for rotationally engaging a first portion of a subterranean borehole; and   a pilot bit coupled to the eccentric reamer comprising:
 at least two primary cutting elements disposed on the pilot bit for engaging a subterranean borehole; and 
 at least one backup cutting element rotationally trailing the at least two primary cutting elements and disposed at least partially laterally intermediate the at least two primary cutting elements. 
   
     
     
         12 . The bi-center bit of  claim 11 , wherein the at least one reamer cutting element of the eccentric reamer is configured to rotationally engage a first portion of a subterranean borehole while the at least one backup cutting element of the pilot bit is configured to rotationally engage a second, opposing portion of a subterranean borehole. 
     
     
         13 . The bi-center bit of  claim 11 , wherein the at least one backup cutting element is disposed laterally intermediate the at least two primary cutting elements at an equal lateral distance from each of the at least two primary cutting elements. 
     
     
         14 . The bi-center bit of  claim 11 , wherein at least one radially extending blade of the eccentric reamer comprises two radially extending, circumferentially spaced blades. 
     
     
         15 . The bi-center bit of  claim 14 , wherein the at least one backup cutting element comprises a plurality of backup cutting elements and wherein at least one backup cutting element of the plurality of backup cutting elements is positioned to substantially laterally oppose at least one radially extending blade of the two radially extending, circumferentially spaced blades. 
     
     
         16 . A method of drilling a subterranean borehole, the method comprising:
 engaging a first portion of a borehole with a portion of a reamer bit section of a drill bit; and   simultaneously engaging a second, opposing portion of the borehole with a portion of a pilot bit section adjacent to the reamer bit section, comprising:
 engaging the second, opposing portion of the borehole with at least two primary cutting elements; and 
 engaging the second, opposing portion of the borehole with at least one backup cutting element rotationally trailing and disposed laterally intermediate the at least two primary cutting elements. 
   
     
     
         17 . The method of  claim 16 , further comprising positioning at least two backup cutting elements on a shoulder region of the pilot bit section. 
     
     
         18 . The method of  claim 17 , wherein positioning at least two backup cutting elements on a shoulder region of the drill bit comprises at least partially preventing wear of a matrix portion of the pilot bit by locating the at least two backup cutting elements on a shoulder region of the pilot bit section. 
     
     
         19 . The method of  claim 16 , further comprising positioning a plurality of backup cutting elements on a portion of the pilot bit section. 
     
     
         20 . The method of  claim 19 , wherein positioning a plurality of backup cutting elements on a portion of the pilot bit section comprises positioning at least one backup cutting elements of the plurality of backup cutting elements on a shoulder region of the pilot bit section to exhibit an exposure greater than an exposure of at least one backup cutting elements of the plurality of backup cutting elements on a cone region of the pilot bit section.