Hybrid bit with roller cones near the bit axis

Abstract

A drill bit includes a bit body having a longitudinal axis extending there through, a plurality of journals extending downward and radially outward from the bit body, each journal having a journal axis extending from a base of the journal through the length of the journal, wherein the journal axis at the base is at a first radial distance from the longitudinal axis, a roller cone rotatably mounted to each of the journals, and at least one blade protruding from the bit body and extending axially and radially along the bit body from a first end to a second end, wherein the first end is at a second radial distance from the longitudinal axis greater than the first radial distance, and wherein the second end is at a gage region of the drill bit.

What is claimed is: 
     
         1 . A drill bit, comprising:
 a bit body having a longitudinal axis extending there through;   a plurality of journals extending downward and radially outward from the bit body, each journal having a journal axis extending from a base of the journal through the length of the journal, wherein the journal axis at the base is at a first radial distance from the longitudinal axis;   a roller cone rotatably mounted to each of the journals; and   at least one blade protruding from the bit body and extending axially and radially along the bit body from a first end to a second end, wherein the first end is at a second radial distance from the longitudinal axis greater than the first radial distance, and wherein the second end is at a gage region of the drill bit.   
     
     
         2 . The drill bit of  claim 1 , wherein the first radial distance ranges from greater than 0 to ½ of the bit radius. 
     
     
         3 . The drill bit of  claim 1 , further comprising a center cutting element disposed on the bit body substantially at the longitudinal axis. 
     
     
         4 . The drill bit of  claim 1 , wherein a radial distance from the bit longitudinal axis to the radially outermost point of one of the at least one journals extends radially past the first end of the at least one blade. 
     
     
         5 . The drill bit of  claim 1 , wherein the axially lowermost point of the at least one blade extends lower than the axially lowermost point of the roller cone. 
     
     
         6 . A drill bit, comprising:
 a bit body having a longitudinal axis extending there through;   a bit radius measured from a gage of the bit to the longitudinal axis;   at least one blade protruding from the bit body, wherein the at least one blade extends an axial distance along the gage of the bit body and a radial inward distance from the gage towards the longitudinal axis;   a plurality of blade cutting elements disposed on the at least one blade, wherein the blade cutting elements comprise a blade cutting profile;   a plurality of journals extending downwardly from the bit body;   a roller cone rotatably mounted to each of the journals; and   a plurality of roller cone cutting elements disposed on each roller cone, wherein the roller cone cutting elements comprise a roller cone cutting profile, and wherein the roller cone cutting profile radially extends from a first end to a second end located radially inward from the gage.   
     
     
         7 . The drill bit of  claim 6 , wherein the radial inward distance of the at least one blade ranges from ⅓ to ¾ of the bit radius. 
     
     
         8 . The drill bit of  claim 6 , wherein the roller cone cutting profile is radially adjacent to the blade cutting profile. 
     
     
         9 . The drill bit of  claim 6 , wherein the roller cone cutting profile extends an axial height greater than the blade cutting profile. 
     
     
         10 . The drill bit of  claim 6 , wherein the roller cone cutting profile radially overlaps with at least the radius of a first blade cutting element on the blade cutting profile. 
     
     
         11 . The drill bit of  claim 10 , wherein the roller cone cutting profile radially overlaps with the blade cutting profile a distance less than or equal to ½. of the bit radius. 
     
     
         12 . The drill bit of  claim 10 , wherein the blade cutting profile radially overlaps the roller cone cutting profile up to the entire radial length of the roller cone cutting profile. 
     
     
         13 . The drill bit of  claim 6 , wherein the roller cone cutting profile extends an axial height less than the blade cutting profile. 
     
     
         14 . The drill bit of  claim 6 , further comprising a center cutting element disposed substantially at the longitudinal axis. 
     
     
         15 . The drill bit of  claim 6 , wherein the roller cone comprises an extension length to diameter ratio ranging from greater than 0.5. 
     
     
         16 . A drill bit, comprising:
 a bit body having a longitudinal axis extending there through;   at least one blade protruding from the bit body, wherein the at least one blade extends an axial distance along a gage of the bit body and a radial inward distance from the gage towards the longitudinal axis;   at least one journal extending downwardly from the bit body, wherein the at least one journal extends a length from a base of the journal; and   a roller cone rotatably mounted to the at least one journal;   wherein the lowest axial point of the at least one blade is axially lower than the lowest axial point of the base of the journal.   
     
     
         17 . The drill bit of  claim 16 , wherein the drill bit comprises one journal. 
     
     
         18 . The drill bit of  claim 16 , further comprising:
 a plurality of blade cutting elements disposed on the at least one blade, wherein the blade cutting elements comprise a blade cutting profile; and   a plurality of roller cone cutting elements disposed on each roller cone, wherein the roller cone cutting elements comprise a roller cone cutting profile;   wherein the blade cutting profile axially overlaps the roller cone cutting profile by up to 100 percent of the roller cone cutting profile.   
     
     
         19 . The drill bit of  claim 18 , wherein the blade cutting profile extends an axial distance lower the axially lowest point of the roller cone cutting profile. 
     
     
         20 . The drill bit of  claim 18 , wherein the drill bit comprises two or more journals, and wherein the journals face radially outward.