Hybrid drill bit

Abstract

A drill bit includes a bit body having a longitudinal bit axis extending there through, a plurality of journals extending from the bit body, each journal having a journal axis extending from a base of the journal through the length of the journal, a roller cone rotatably mounted to each of the journals, and at least one blade protruding from the bit body center and extending radially outward to less than an outer diameter of the drill bit.

What is claimed is: 
     
         1 . A drill bit, comprising:
 a bit body having a longitudinal bit axis extending there through;   a plurality of journals extending from the bit body, each journal having a journal axis extending from a base of the journal through the length of the journal;   a roller cone rotatably mounted to each of the journals; and   at least one blade protruding from the bit body center and extending radially outward to less than an outer diameter of the drill bit.   
     
     
         2 . The drill bit of  claim 1 , wherein the at least one blade comprises a plurality of cutting elements having planar cutting faces. 
     
     
         3 . The drill bit of  claim 2 , wherein the blades extend to a nose region of the drill bit. 
     
     
         4 . The drill bit of  claim 2 , wherein the blades extend to a shoulder region of the drill bit. 
     
     
         5 . The drill bit of  claim 1 , wherein the plurality of journals extend downward and radially outward such that an acute angle ranging from about 15 degrees to about 25 degrees is formed between the journal axis and the longitudinal bit axis. 
     
     
         6 . The drill bit of  claim 5 , wherein the plurality of roller cone cutting elements having an installation back rake angle ranging from about 10 degrees to about 90 degrees. 
     
     
         7 . The drill bit of  claim 5 , wherein the plurality of roller cone cutting elements having an installation side rake angle ranging from about 0 degrees to about 60 degrees. 
     
     
         8 . The drill bit of  claims 6  and  7 , wherein the plurality of roller cone cutting elements having an equivalent back rake ranging from about 10 degrees to about 30 degrees. 
     
     
         9 . The drill bit of  claims 6  and  7 , wherein the plurality of roller cone cutting elements having an equivalent side rake ranging from about 0 degrees to about 30 degrees. 
     
     
         10 . A drill bit, comprising:
 a bit body having a longitudinal bit axis extending there through;   a plurality of journals, extending from the bit body; and   a roller cone having an outer diameter rotatably mounted to each of the journals, wherein at least two of the outer diameters are different, and   wherein an offset angle ranging from about 0 degrees to about 90 degrees is formed between a line perpendicular to the bit axis and extending through the bit axis and a center of a backface of the roller cone.   
     
     
         11 . The drill bit of  claim 10 , wherein the roller cone comprises a plurality of roller cone cutting elements having planar cutting faces, wherein the roller cone cutting elements comprise a roller cone cutting profile. 
     
     
         12 . The drill bit of  claim 11 , wherein the smallest roller cone cutting profile extends an axial height greater than the largest roller cone cutting profile. 
     
     
         13 . The drill bit of  claim 12 , wherein the smallest roller cone cutting profile radially overlaps with the largest roller cone cutting profile. 
     
     
         14 . A drill bit, comprising:
 a bit body having a longitudinal bit axis extending there through;   a plurality of journals, extending 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 plurality of journals extend from the bit body such that an acute angle ranging from about 15 degrees to about 25 degrees is formed between the journal axis and the bit axis; and   a roller cone rotatably mounted to each of the journals,
 wherein at least one roller cone comprises a plurality of roller cone cutting elements having planar cutting faces and at least one roller cone comprises a plurality of roller cone cutting elements having non-planar cutting faces, 
   wherein the roller cone cutting elements comprise a roller cone cutting profile.   
     
     
         15 . The drill bit of  claim 14 , wherein the roller cones each have an outer diameter, and wherein at least two of the outer diameters are different. 
     
     
         16 . The drill bit of  claim 15 , wherein each of the roller cone cutting profiles radially overlaps with one another. 
     
     
         17 . The drill bit of  claim 16 , wherein the plurality of roller cone cutting elements having an installation back rake angle ranging from about 10 degrees to about 90 degrees. 
     
     
         18 . The drill bit of  claim 16 , wherein the plurality of roller cone cutting elements having an installation side rake angle ranging from about 0 degrees to about 60 degrees. 
     
     
         19 . The drill bit of  claims 17 , wherein the plurality of roller cone cutting elements having an equivalent back rake ranging from about 10 degrees to about 30 degrees. 
     
     
         20 . The drill bit of  claims 17 , wherein the plurality of roller cone cutting elements having an equivalent side rake ranging from about 0 degrees to about 30 degrees.