Roller cone drill bit having designed walk characteristics

Abstract

A roller cone drill bit having selected left hand walk is disclosed. The bit includes a bit body adapted to couple to a drill string, and a plurality of legs depending from the bit body. Each leg has a roller cone rotatably mounted thereon. Each cone includes a plurality of cutting elements thereon. At least one cone has a nose point of its profile displaced radially inward with respect to a nose point of the profile of the other cones. A roller cone drill bit having selected right hand walk is also disclosed. The bit include a bit body adapted to couple to a drill string, and a plurality of legs depending from the bit body. Each leg has a roller cone rotatably mounted thereon, each cone including a plurality of cutting elements thereon defining a profile. At least one cone has a nose point of the profile displaced radially outward with respect to a nose point of the profile of the other cones.

What is claimed is:  
     
         1 . A roller cone drill bit having selected left hand walk, comprising: 
 a bit body adapted to couple to a drill string;    a plurality of legs depending from the bit body, each leg having a roller cone rotatably mounted thereon, each cone including thereon a plurality of cutting elements defining a profile, at least one cone having a nose point of the profile displaced radially inward with respect to a nose point of the profile of the other cones.    
     
     
         2 . The bit of  claim 1  wherein the leg on which the at least one cone is mounted is arranged so that a cone axis offset is greater than a cone axis offset of the other cones.  
     
     
         3 . The bit of  claim 1  wherein the leg on which the at least one cone is mounted is arranged so that it has a smaller journal angle than a journal angle of the other legs.  
     
     
         4 . The bit of  claim 1  wherein the at least one cone has at least one larger cutting elements than the other cutting elements.  
     
     
         5 . The bit of  claim 1  wherein the at least one cone has more aggressive cutting elements than on the other cones.  
     
     
         6 . The bit of  claim 1  wherein the at least one cone comprises a spear point cutting element.  
     
     
         7 . A roller cone drill bit having selected right hand walk, comprising: 
 a bit body adapted to couple to a drill string;    a plurality of legs depending from the bit body, each leg having a roller cone rotatably mounted thereon, each cone including a plurality of cutting elements thereon defining a profile, and wherein at least one cone has a nose point of the profile displaced radially outward with respect to a nose point of the profile of the other cones.    
     
     
         8 . The bit of  claim 7  wherein the leg on which the at least one cone is mounted is arranged so that a cone axis offset is greater than a cone axis offset of the other cones.  
     
     
         9 . The bit of  claim 7  wherein the leg on which the at least one cone is mounted is arranged so that it has a greater journal angle than a journal angle of the other legs.  
     
     
         10 . The bit of  claim 7  wherein the at least one cone has larger cutting elements than on the other cones.  
     
     
         11 . The bit of  claim 7  wherein the at least one cone has more aggressive cutting elements than on the other cones.  
     
     
         12 . A roller cone bit having a selected walk tendency, comprising: 
 a bit body adapted to couple to a drill string; and    a plurality of legs depending from the bit body, each leg having a roller cone rotatably mounted thereon, each cone including a plurality of cutting elements thereon, at least one cone having a different journal angle than the other cones.    
     
     
         13 . The bit of  claim 12  wherein the at least one cone has a different cone axis offset than the other cones.  
     
     
         14 . The bit of  claim 12  wherein the cutting elements on the at least one cone define a profile having a different nose point than the other cones.  
     
     
         15 . The bit of  claim 12  wherein the cutting elements are arranged on the roller cones to provide a net lateral force in an azimuthal direction of the at least one cone when the bit is drilling.  
     
     
         16 . The bit of  claim 12  wherein the at least one cone has a different axial profile position than the other cones.  
     
     
         17 . The bit of  claim 12  wherein the at least one cone comprises at least one larger cutting element than the cutting elements on the other cones.  
     
     
         18 . The bit of  claim 12  wherein the at least one cone comprises at least one more aggressive cutting element than the cutting elements on the other cones.  
     
     
         19 . A roller cone bit having a selected walk tendency, comprising: a bit body adapted to couple to a drill string; and 
 a plurality of legs depending from the bit body, each leg having a roller cone rotatably mounted thereon, each cone including a plurality of cutting elements thereon, at least one cone having a different cone axis offset than the other cones.    
     
     
         20 . The bit of  claim 19  wherein the cutting elements on the at least one cone define a profile having a different nose point than the other cones.  
     
     
         21 . The bit of  claim 19  wherein the cutting elements are arranged on the roller cones to provide a net lateral force in an azimuthal direction of the at least one cone when the bit is drilling.  
     
     
         22 . The bit of  claim 19  wherein the at least one cone has a different axial profile position than the other cones.  
     
     
         23 . The bit of  claim 19  wherein the at least one cone comprises at least one larger cutting element than the cutting elements on the other cones.  
     
     
         24 . The bit of  claim 19  wherein the at least one cone comprises at least one more aggressive cutting element than the cutting elements on the other cones.  
     
     
         25 . A roller cone bit having a selected walk tendency, comprising: 
 a bit body adapted to couple to a drill string; and    a plurality of legs depending from the bit body, each leg having a roller cone rotatably mounted thereon, each cone including thereon a plurality of cutting elements, at least one cone having a different axial profile position than the other cones.    
     
     
         26 . The bit of  claim 25  wherein the cutting elements on the at least one cone define a profile having a different nose point than the other cones.  
     
     
         27 . The bit of  claim 25  wherein the cutting elements are arranged on the roller cones to provide a net lateral force in an azimuthal direction of the at least one cone when the bit is drilling.  
     
     
         28 . The bit of  claim 25  wherein the at least one cone comprises at least one larger cutting element than the cutting elements on the other cones.  
     
     
         29 . The bit of  claim 25  wherein the at least one cone comprises at least one more aggressive cutting element than the other cones.  
     
     
         30 . The bit of  claim 25  wherein the at least one cone has a different cone axis offset than the other cones.  
     
     
         31 . The bit of  claim 25  wherein the at least one cone has a different journal angle than the other cones.  
     
     
         32 . A roller cone bit having a selected walk tendency, comprising: 
 a bit body adapted to couple to a drill string; and    a plurality of legs depending from the bit body, each leg having a roller cone rotatably mounted thereon, each cone including thereon a plurality of cutting elements thereon, the cutting elements arranged so that at least one cone exerts a different axial force during drilling than the other cones.    
     
     
         33 . The bit of  claim 32  wherein the at least one cone has a different axial profile position than the other cones.  
     
     
         34 . The bit of  claim 32  wherein the at least one cone comprises at least one larger cutting element than the cutting elements on the other cones.  
     
     
         35 . The bit of  claim 32  wherein the at least one cone comprises at least one more aggressive cutting element than the other cones.  
     
     
         36 . The bit of  claim 32  wherein the cutting elements on the at least one cone define a profile having a different nose point than the other cones.  
     
     
         37 . The bit of  claim 32  wherein the cutting elements are arranged on the roller cones to provide a net lateral force in an azimuthal direction of the at least one cone.  
     
     
         38 . The bit of  claim 32  wherein the at least one cone has a different cone axis offset than the other cones.  
     
     
         39 . The bit of  claim 32  wherein the at least one cone has a different journal angle than the other cones.  
     
     
         40 . A method for designing a roller cone drill bit having selected walk tendency, comprising: 
 selecting initial bit design parameters;    simulating response of the bit during drilling;    adjusting at least one of the initial bit design parameters on at least one of a plurality of roller cones on the drill bit; and    repeating the simulating and adjusting until the selected walk tendency is determined.    
     
     
         41 . The method of  claim 40  wherein the at least one initial bit design parameter comprises a lateral position of a nose point of a profile defined by cutting elements on the at least one roller cone.  
     
     
         42 . The method of  claim 40  wherein the at least one initial bit design parameter comprises a cone axis offset.  
     
     
         43 . The method of  claim 40  wherein the at least one initial bit design parameter comprises a journal angle.  
     
     
         44 . The method of  claim 40  wherein the at least one initial bit design parameter comprises a cutting element size.  
     
     
         45 . The method of  claim 40  wherein the at least one initial bit design parameter comprises a cutting element aggressiveness.  
     
     
         46 . The method of  claim 40  wherein the at least one initial bit design parameter comprises arrangement of cutting elements on the roller cones to provide a net lateral force in an azimuthal direction of the at least one roller cone during drilling.