Two-centre rotary boring bit and method for deepening an existing well

Abstract

Two-centre rotary boring bit for boring wells, comprising, on the one hand, a pilot tool ( 1 ) comprising a body of revolution with an axial core ( 3 ) and radial blades ( 4 ) bearing cutting elements ( 5 ) and, on the other hand, an enlarging tool ( 2 ) fitted behind the pilot tool and laterally offset therefrom, the pilot tool having, on its front face, a central region ( 11 ) that has no cutting elements in order to allow the creation of a core sample ( 12 ), said central region being in communication with a cavity ( 13 ) situated between two blades ( 4 ) of the pilot tool ( 1 ) and serving to remove the core sample toward the periphery of the boring bit.

1 . Two-centre rotary boring bit for boring wells, comprising, a pilot tool comprising a body of revolution with an axial core and radial blades carrying cutting elements and, an enlarging tool located behind the pilot tool and laterally offset relative to the pilot tool, wherein the front face of the pilot tool ( 1 ) has an axial central region ( 11 ) which is devoid of cutting elements ( 5 ) for allowing the creation of an axial core sample ( 12 ), said central region being in communication with a cavity ( 13 ) located between two blades ( 4 ) of the pilot tool and serving to evacuate the core sample toward the periphery of the boring bit. 
     
     
         2 . Boring bit according to  claim 1 , wherein the cavity ( 13 ) is delimited by two blades ( 4 ) of the pilot tool ( 1 ) and a clearance surface ( 14 ) set back relative to the front face of said pilot tool. 
     
     
         3 . Boring bit according to  claim 1 , wherein the enlarging tool ( 2 ) is offset relative to the pilot tool ( 1 ), in such a way that a portion ( 9 ) of its peripheral surface is radially set back relative to the peripheral surface of the pilot tool and in that the cavity ( 13 ) of the pilot tool ( 1 ) ends up in said portion ( 9 ) of the peripheral surface of the enlarging tool. 
     
     
         4 . Boring bit according to  claim 1  wherein the enlarging tool ( 2 ) comprises a core ( 6 ) with radial blades ( 7 ) carrying cutting elements ( 8 ) and in that the cavity ( 13 ) exits between two blades ( 7 ) of the enlarging tool. 
     
     
         5 . Boring bit according to  claim 1  wherein the blades ( 4 ) of the pilot tool ( 1 ) are spiralled. 
     
     
         6 . Boring bit according to  claim 5 , wherein the blades ( 7 ) of the enlarging tools ( 1 ) are spiralled and located in the prolongation of the blades of the pilot tool. 
     
     
         7 . Boring bit according to  claim 1  wherein the pilot tool ( 1 ) further comprises a device for breaking the core sample ( 12 ). 
     
     
         8 . Boring bit according to  claim 7 , wherein the device for breaking comprises an abrasion-resistant pellet, located in the central region ( 11 ) of the pilot tool ( 1 ). 
     
     
         9 . Boring bit according to  claim 1  wherein the diameter of the central region ( 11 ) of the pilot tool ( 1 ) is adjusted so that the core sample ( 12 ) resists the lateral forces generated by the enlarging tool ( 2 ) during use of the boring bit. 
     
     
         10 . Boring bit according to  claim 1  wherein the diameter of the central region ( 11 ) of the pilot tool ( 1 ) is at least equal to the difference between the overall diameter of the enlarging tool ( 2 ) and the diameter of the pilot tool ( 1 ). 
     
     
         11 . Boring bit according to  claim 1  further comprising channels ( 10 ) for supplying drilling mud, which ends up through the front face of the pilot tool ( 1 ). 
     
     
         12 . Boring bit according to  claim 11 , wherein channels ( 16 ) for supplying drilling mud exit between the blades ( 7 ) of the enlarging tool  2 . 
     
     
         13 . Boring bit according to  claim 1  wherein the cores ( 3 ,  6 ) and the blades ( 4 ,  7 ) are made of steel and the cutting elements ( 5 ,  8 ) comprise elements made of PDC. 
     
     
         14 . (canceled) 
     
     
         15 . Method for deepening existing wells, comprising the step of implementing a two-centre boring bit in accordance with  claim 1 . 
     
     
         16 . Method according to  claim 15 , wherein the radius of the central region ( 11 ) of the pilot tool ( 1 ) of the boring bit is at least equal to the difference between the radius of the well ( 18 ) and the radius of the pilot tool ( 1 ).