Percussion drill bit with conical cutting elements

Abstract

A percussion drill bit for drilling a borehole. The drill bit includes a bit body having a bit face disposed on an axial end portion thereof. First and second cutting elements are disposed on the bit face. A cutting plane is defined in tangential contact with crest portion of the first and second cutting elements. A third cutting element on the bit face is at least partially positioned between the first and second cutting elements. The third cutting element is at least partially conical, and a crest portion of the third cutting element is offset from the cutting plane.

What is claimed is: 
     
         1 . A percussion drill bit for drilling a borehole, comprising:
 a bit body having a bit face;   first and second cutting elements on the bit face, the first and second cutting elements defining a cutting plane in tangential contact with a crest portion of each of the first and second cutting elements; and   a conical cutting element on the bit face and positioned at least partially between the first and second cutting elements, the conical cutting element having a crest portion offset from the cutting plane.   
     
     
         2 . The percussion drill bit of  claim 1 , the crest portion of the conical cutting element extending beyond the cutting plane by a distance up to about 70% of a total height of the conical cutting element as measured from the bit face. 
     
     
         3 . The percussion drill bit of  claim 1 , the crest portion of the conical cutting element being below the cutting plane by a distance up to about 25% of a total height of the conical cutting element as measured from the bit face. 
     
     
         4 . The percussion drill bit of  claim 1 , the first and second cutting elements being semi-round top cutting elements. 
     
     
         5 . The percussion drill bit of  claim 1 , the first and second cutting elements being at least partially conical. 
     
     
         6 . The percussion drill bit of  claim 1 , a radius of curvature of the crest portion of the conical cutting element being less than a radius of curvature of the crest portions of the first and second cutting elements. 
     
     
         7 . The percussion drill bit of  claim 1 , the first and second cutting elements being circumferentially offset from one another. 
     
     
         8 . The percussion drill bit of  claim 7 , the first and second cutting elements being positioned in a circumferential gage row on the bit face. 
     
     
         9 . The percussion drill bit of  claim 1 , the first and second cutting elements being in first and second circumferential rows of cutting elements, respectively, the first circumferential row of cutting elements being radially outward relative to the second circumferential row of cutting elements. 
     
     
         10 . The percussion drill bit of  claim 1 , at least one of the first, second, or conical cutting elements comprising diamond. 
     
     
         11 . A percussion drill bit for drilling a borehole, comprising:
 a bit body having a bit face;   first and second semi-round top cutting elements in an outer circumferential row on the bit face, the first and second semi-round top cutting elements defining a cutting plane in tangential contact with a crest portion of the first cutting element and a crest portion of the second cutting element; and   a third cutting element on the bit face at least partially overlapping the outer circumferential row, the third cutting element being at least partially conical, and a crest portion of the third cutting element extending beyond the cutting plane by a distance up to about 70% of a total height of the third cutting element as measured from the bit face.   
     
     
         12 . The percussion drill bit of  claim 11 , a radius of curvature of the crest portion of the third cutting element being less than a radius of curvature of the crest portions of the first and second cutting elements. 
     
     
         13 . The percussion drill bit of  claim 12 , a ratio of the radius of curvature of the crest portion of the third cutting element to a diameter of the third cutting element being between about 0.12:1 and about 0.30:1 and a ratio of a radius of curvature of the crest portion of the first and second cutting elements to a diameter of the first and second cutting elements being between about 0.4:1 and about 0.7:1. 
     
     
         14 . The percussion drill bit of  claim 11 , at least one of the first, second, or third cutting elements comprising diamond. 
     
     
         15 . The percussion drill bit of  claim 11 , the outer circumferential row being a gage row. 
     
     
         16 . A method for drilling a borehole, comprising:
 running a percussion hammer drill bit into a borehole, the percussion hammer drill bit including:
 a bit body having a bit face; 
 first and second cutting elements on the bit face and defining a cutting plane in tangential contact with a crest portion of the first cutting element and a crest portion of the second cutting element; and 
 a third cutting element on the bit face and positioned at least partially between the first and second cutting elements, the third cutting element being at least partially conical and a crest portion of the third cutting element being offset from the cutting plane; and 
   contacting a formation with the first, second, and third cutting elements to extend the borehole.   
     
     
         17 . The method of  claim 16 , wherein contacting the formation comprises:
 moving the bit body back and forth axially within the borehole; and   indexing the bit body about a longitudinal axis extending therethrough.   
     
     
         18 . The method of  claim 16 , wherein the first and second cutting elements are:
 in a same circumferential gage row on the bit face; or   in different circumferential rows on the bit face.   
     
     
         19 . The method of  claim 16 , wherein the crest portion of the third cutting element extends beyond the cutting plane by a distance up to about 70% of a total height of the third coning element as measured from the bit face. 
     
     
         20 . The method of  claim 16 , wherein the crest portion of the third cutting element is below the cutting plane by a distance up to about 25% of a total height of the third cutting element as measured from the bit face.