Bit for drilling wells and associated drilling method

Abstract

A bit for drilling wells has a front face with radial blades having cutting elements distributed around the front face. A space for forming a core is situated at the center of the front face. A cavity is provided for evacuating the core towards a periphery of the bit. At least a portion of the cavity is situated between adjacent blades. The cavity is delimited by two lateral surfaces and a clearance surface set back with respect to the front face, and the cavity is open in a direction opposite the clearance surface. The bit may be used in methods for drilling wells and makes it possible to rapidly drill wells of great depth in all types of rock without the risk of clogging.

What is claimed is: 
     
         1 . A bit for drilling wells, comprising:
 a front face;   a plurality of radial blades provided with cutting elements, the blades being distributed around the front face;   a space for forming a core, the space being situated at the center of the front face; and   a cavity for evacuating the core towards a periphery of the bit, the cavity being situated between two adjacent of the blades and preventing any clogging inside the bit.   
     
     
         2 . A bit according to  claim 1 , wherein the radial blades are arranged on an external annular crown of the front face. 
     
     
         3 . A bit according to  claim 1 , wherein a majority of the cavity is situated between two adjacent blades, wherein the cavity is delimited by two lateral surfaces and a clearance surface, and wherein the clearance surface is set back with respect to the front face. 
     
     
         4 . A bit according to  claim 1 , further comprising drilling mud feed channels, wherein each of the channels opens onto the front face, and wherein one of the channels opens into the cavity and is suitable for facilitating the evacuation of the core towards the periphery of the bit. 
     
     
         5 . A bit according to  claim 1 , wherein the clearance surface is suitable for evacuating the core simultaneously towards the periphery and towards the rear of the bit. 
     
     
         6 . A bit according to  claim 1 , further comprising a device for breaking up the core. 
     
     
         7 . A bit according to  claim 6 , wherein the breaking device is situated in the cavity close to the center of the bit. 
     
     
         8 . A bit according to  claim 7 , wherein the breaking device is a tip made of an abrasion-resistant material. 
     
     
         9 . A bit according to  claim 8 , wherein the tip is inclined with respect to the axis of the bit. 
     
     
         10 . A bit according to  claim 1 , wherein the dimensions of the cavity are suitable for forming cylindrical cores the length of which is equal to at least twice their diameter. 
     
     
         11 . A bit according to  claim 1 , further comprising an element for radially cutting the core. 
     
     
         12 . A method for drilling wells, comprising:
 providing a bit for drilling wells, comprising:
 a front face; 
 a plurality of radial blades provided with cutting elements, the blades being distributed around the front face; 
 a space for forming a core, the space being situated at the center of the front face; and 
 a cavity for evacuating the core towards a periphery of the bit, the cavity being situated between two adjacent of the blades and preventing any clogging inside the bit; 
   forming a core at the center of the bit;   evacuating the core up through the drilling well to the ground surface; and   recovering the core.   
     
     
         13 . A method for drilling wells according to  claim 12 , further comprising analyzing the petrophysical properties of the core.