Multi-directional cutters for drillout bi-center drill bits

Abstract

A drillout bi-center bit includes first and second axes of rotation separated by a distance D, a first region of radius D centered on one of the axes of rotation, a second region of radius D centered on the other of the axes of rotation, and a third region defined by the overlap between the first and second regions, wherein the cutters provided within the third region are designed to withstand cutting in opposing cutting directions. This may be achieved by providing each cutter with two cutting faces, or by providing two groups of cutters, one group arranged to cut in one direction, the other group being designed to cut upon rotation in the other direction, one of the groups protruding from the bit body of the bit to a greater depth than the other group.

We claim:  
     
         1 . A drillout bi-center drill bit comprising a bit body with a first end adapted to be detachably secured to a drill string, a pilot section on a second, opposite end of the bit body, a reamer section intermediate the first and second ends, and a drilling face on the pilot section; 
 a first drilling center of rotation of the pilot section;    a second, passthrough center of rotation of the pilot section spaced apart from the first center of rotation by a non-zero distance D;    a first region of the drilling face centered about the first center of rotation having a radius D, a second region of the drilling face centered about the second center of rotation having a radius D, and a third region of the drilling face formed by the intersection of the first region and the second region;    a cutting element being fixed on the bit body within the third region, the cutting element having a first cutting face generally oriented perpendicular to the direction of travel of the cutting element about the first center of rotation of the pilot section and a second cutting face generally oriented perpendicular to the direction of travel of the cutting element about the second center of rotation.    
     
     
         2 . The drillout bi-center drill bit of  claim 1 , wherein the cutting element is formed of cemented tungsten carbide.  
     
     
         3 . The drillout bi-center drill bit of  claim 1 , wherein the cutting element is formed of an infiltrated material comprising metallic powders mixed with diamond particles and a binder.  
     
     
         4 . The drillout bi-center drill bit of  claim 1 , wherein a polycrystalline diamond compact cutter is mounted on one of the cutting faces of the cutting element.  
     
     
         5 . The drillout bi-center drill bit of  claim 1 , wherein the cutting element is of generally conical form, the first and second cutting faces being defined by different parts of a generally conical surface of the cutting element.  
     
     
         6 . A drillout bi-center drill bit comprising a bit body with a first end adapted to be detachably secured to a drill string, a pilot section on a second, opposite end of the bit body, a reamer section intermediate the first and second ends, and a drilling face on the pilot section; 
 a first drilling center of rotation of the pilot section;    a second, passthrough center of rotation of the pilot section spaced apart from the first center of rotation by a non-zero distance D;    a first region of the drilling face centered about the first center of rotation having a radius D, a second region of the drilling face centered about the second center of rotation having a radius D, and a third region of the drilling face formed by the intersection of the first region and the second region;    a plurality of first cutters being positioned in the third region, each with superhard cutting faces generally oriented perpendicular to the direction of travel of their respective first cutters about the first center of rotation, said first cutters projecting a distance from the bit body;    at least one second cutter on the bit body within the third region and projecting a distance from the bit body greater than the projection of the first cutters, with a cutting face orientated generally perpendicular to the direction of travel of the second cutter about the second center of rotation.    
     
     
         7 . The drillout bi-center drill bit of  claim 6 , wherein the at least one of second cutters is formed of cemented tungsten carbide.  
     
     
         8 . The drillout bi-center drill bit of  claim 6 , wherein a polycrystalline diamond compact cutter is mounted on one of the cutting faces the at least one of the second cutters is of an infiltrated material comprising a mixture of metallic powders, diamond particles and a binder.  
     
     
         9 . The drillout bi-center drill bit of  claim 6 , wherein the bit body is of infiltrated powdered metal matrix form and is shaped to define the or each second cutter.  
     
     
         10 . The drillout bi-center drill bit of  claim 6 , wherein a polycrystalline diamond compact cutter is mounted on the cutting face of the at least one of said second cutters.