Drill bit

Abstract

The present invention provides a drill bit ( 1 ), and a method for its manufacture, that is suitable for use within a casing drilling process. The drill bit ( 1 ) comprises a monolithic body ( 5, 6, 8 ) made from bronze, e.g. aluminium bronze or nickel aluminium bronze, and a relatively hard material mounted thereon. The hard material may comprise polycrystalline diamond (PDC), tungsten carbide or cubic boron nitride. In one embodiment the monolithic body comprises a crown ( 6 ) and a plurality of cutting members ( 5 ). The hard material may be mounted directly on the crown or, alternatively, on the cutting members ( 5 ). The described drill bit ( 1 ) facilitates the drilling of hard rock formations while still being capable of being drilled through by a standard oilfield drill bit.

1 . A drill bit suitable for drilling a casing in a well bore, the drill bit comprising a monolithic body made from bronze and one or more areas of a relatively hard material mounted on the monolithic body so as to provide a cutter suitable for cutting earth or rock. 
     
     
         2 . The drill bit as claimed in  claim 1  wherein the monolithic body exhibits a yield strength of at least 45,000 psi. 
     
     
         3 . The drill bit as claimed in  claim 1  wherein the monolithic body exhibits yield strength of at least 60,000 psi. 
     
     
         4 . The drill bit as claimed in  claim 1  wherein the monolithic body is formed from an aluminium bronze. 
     
     
         5 . The drill bit as claimed in  claim 1  wherein the monolithic body is formed from a nickel-aluminium bronze. 
     
     
         6 . The drill bit as claimed in  claim 1  wherein the monolithic body comprises a crown. 
     
     
         7 . The drill bit as claimed in  claim 6  wherein the crown comprises one or more flow by areas. 
     
     
         8 . The drill bit as claimed in  claim 6  wherein the crown comprises a mechanical connecter suitable for attaching the drill bit to a drill string. 
     
     
         9 . The drill bit as claimed in  claim 1  wherein the monolithic body comprises one or more cutting members. 
     
     
         10 . The drill bit as claimed in  claim 9  wherein the one or more cutting members comprise a gauge pad. 
     
     
         11 . The drill bit as claimed in  claim 10  wherein every gauge pad comprises one or more recesses suitable for receiving gauge inserts. 
     
     
         12 . The drill bit as claimed in  claim 6  wherein the relatively hard material is mounted on the crown. 
     
     
         13 . The drill bit as claimed in  claim 9  wherein the relatively hard material is mounted on the leading edge of the one or more cutting members. 
     
     
         14 . The drill bit as claimed in  claim 1  wherein the relatively hard material comprise one or more preformed cutters mounted within recesses. 
     
     
         15 . The drill bit as claimed in  claim 1  wherein the relatively hard material comprises polycrystalline diamond. 
     
     
         16 . The drill bit as claimed in  claim 1  wherein the relatively hard material comprises tungsten carbide. 
     
     
         17 . The drill bit as claimed in  claim 1  wherein the relatively hard material comprises cubic boron nitride. 
     
     
         18 . A method of manufacturing a drill bit suitable for drilling a casing in a well bore, the method comprising:
 casting a bronze so as to form a monolithic body;   heat treating the cast bronze;   mounting a relatively hard material on the monolithic body so as to provide a means for cutting earth or rock.   
     
     
         19 . The method of manufacturing a drill bit as claimed in  claim 18  wherein the casting of the monolithic body comprises casting a crown. 
     
     
         20 . The method of manufacturing a drill bit as claimed in  claim 19  wherein the casting of the crown comprises the formation of one or more flow by areas. 
     
     
         21 . The method of manufacturing a drill bit as claimed in  claim 18  wherein the casting of the monolithic body comprising casting one or more cutting members. 
     
     
         22 . The method of manufacturing a drill bit as claimed in  claim 21  wherein the casting of the one or more cutting members comprises casting of a gauge pad. 
     
     
         23 . The method of manufacturing a drill bit as claimed in  claim 22  wherein the casting of the gauge pad comprises casting one or more recesses suitable for receiving gauge inserts. 
     
     
         24 . The method of manufacturing a drill bit as claimed in  claim 18  wherein the casting of a bronze comprises casting an aluminium bronze or a nickel aluminium bronze. 
     
     
         25 . The method of manufacturing a drill bit as claimed in  claim 18  wherein the casting of the bronze comprises a casting method selected from the group comprising sand casting, centrifugal casting, continuous casting, permanent mould casting and plaster casting. 
     
     
         26 . The method of manufacturing a drill bit as claimed in  claim 18  wherein the heat treating of the cast bronze provides the monolithic body with a yield strength of at least 45,000 psi. 
     
     
         27 . The method of manufacturing a drill bit as claimed in  claim 18  wherein the heat treating of the cast bronze provides the monolithic body with a yield strength of at least 60,000 psi. 
     
     
         28 . The method of manufacturing a drill bit as claimed in  claim 18  wherein the mounting of the relatively hard material on the monolithic body comprises the formation of one or more recesses. 
     
     
         29 . The method of manufacturing a drill bit as claimed in  claim 28  wherein the one or more recesses are formed on a leading edge of one or more cutting members. 
     
     
         30 . The method of manufacturing a drill bit as claimed in  claim 28  wherein the one or more recesses are formed on a crown. 
     
     
         31 . The method of manufacturing a drill bit as claimed in  claim 28  wherein the mounting the relatively hard material on the monolithic body comprises attaching preformed cutters within the one or more recesses. 
     
     
         32 . The method of manufacturing a drill bit as claimed in  claim 31  wherein attaching the preformed cutters comprises brazing the cutters within the one or more recesses. 
     
     
         33 . The method of manufacturing a drill bit as claimed in  claim 18  wherein the method further comprises forming a mechanical connection on the heat treated monolithic body.