Drilling apparatus

Abstract

Drilling apparatus comprises a cutting structure defined by a percussive action cutte ( 42 ) and at least one other cutter. The percussive action cutter is adapted to be urged in a drilling direct ion by hydraulic pressure force, while the other cutter ( 43 ) is urged in a drilling direction by mechanical force.

1 . Drilling apparatus comprising a cutting structure defined by at least one percussive action cutter and at least one other cutter, the at least one percussive action cutter being adapted to be urged in a drilling direction by hydraulic pressure force.  
   
   
       2 . The apparatus of  claim 1 , wherein a plurality of percussive action cutters are provided.  
   
   
       3 . The apparatus of  claim 1 , wherein the at least one other cutter comprises a roller cone.  
   
   
       4 . The apparatus of  claim 1 , wherein the at least one other cutter comprises a plurality of roller cones.  
   
   
       5 . The apparatus of  claim 1 , wherein the at least one other cutter comprises a fixed cutter.  
   
   
       6 . The apparatus of  claim 1 , wherein the at least one other cutter comprises a plurality of fixed cutters.  
   
   
       7 . The apparatus of  claim 5 , wherein the fixed cutter is a PDC cutter.  
   
   
       8 . The apparatus of  claim 1 , wherein, in use, the at least one other cutter is adapted to support at least the majority of mechanical weight applied to the apparatus.  
   
   
       9 . The apparatus of  claim 1 , further including means for creating a percussive force and means for transferring the resulting percussive force to the at least one percussive action cutter.  
   
   
       10 . The apparatus of  claim 9 , wherein said means for creating a percussive force comprises a hammer tool.  
   
   
       11 . The apparatus of  claim 10 , wherein the means for transferring the resulting percussive force to the at least one percussive action cutter comprises an anvil.  
   
   
       12 . The apparatus of  claim 10 , wherein the hammer tool is hydraulically actuated.  
   
   
       13 . The apparatus of  claim 1 , wherein the percussive action cutter defines a flow restriction, such that hydraulic fluid flowing therethrough experiences a pressure drop, and thus creates a pressure force on the cutter.  
   
   
       14 . The apparatus of  claim 13 , wherein the restriction comprises at least one jetting nozzle.  
   
   
       15 . The apparatus of  claim 14 , wherein the flow restriction is provided in combination with a piston area defined by the percussive action cutter.  
   
   
       16 . The apparatus of  claim 15 , wherein the piston area serves as an anvil.  
   
   
       17 . The apparatus of  claim 1 , further comprising a hydraulically actuated hammer tool defining a fluid pressure responsive piston area of dimensions comparable to the cutting area of the at least one percussive action cutter.  
   
   
       18 . The apparatus of  claim 17 , wherein the hammer tool is at least as large as the cutting area of the at least one percussive action cutter.  
   
   
       19 . The apparatus of  claim 1 , wherein there is a degree of overlap in the area swept by the cutting surface of the at least one percussive action cutter and the at least one other cutter.  
   
   
       20 . The apparatus of  claim 1 , wherein a percussive action cutter is located to cut a central portion of a bore.  
   
   
       21 . The apparatus of  claim 1 , wherein at least one percussive action cutter has a cutting face located forwards of the cutting face of the at least one other cutter.  
   
   
       22 . The apparatus of  claim 21 , wherein said at least one percussive action cutter includes laterally directed drilling fluid outlets ahead of the at least one other cutter.  
   
   
       23 . The apparatus of  claim 1 , wherein the at least one percussive action cutter is retractable or removable.  
   
   
       24 . The apparatus of  claim 1 , wherein the at least one percussive action cutter is axially moveable relative to the at least one other cutter.  
   
   
       25 . The apparatus of  claim 24 , wherein movement of the at least one percussive action cutter beyond a predetermined relative axial position is operator detectable.  
   
   
       26 . The apparatus of  claim 25 , wherein movement of the at least one percussive action cutter beyond a predetermined relative axial position at least restricts fluid flow through a fluid port.  
   
   
       27 . The apparatus of  claim 25 , wherein said movement corresponds to said at least one other cutter cutting ahead of said at least one percussive action cutter.  
   
   
       28 . The apparatus of  claim 25 , wherein forward movement of the at least one percussive action cutter beyond a predetermined axial position relative to the at least one other cutter corresponds to said at least one percussive action cutter having cut ahead of said at least one other cutter.  
   
   
       29 . The apparatus of  claim 28 , further comprising means responsive to said forward movement of the at least one percussive action cutter, said means being effective to at least reduce the percussive action of said at least one cutters in response to said forward movement.  
   
   
       30 . The apparatus of  claim 24 , wherein the at least one percussive action cutter is normally retracted from a fully extended configuration.  
   
   
       31 . The apparatus of  claim 30 , wherein the at least one percussive action cutter is spring biassed towards the normally retracted position.  
   
   
       32 . The apparatus of  claim 1 , wherein the at least one percussive action cutter comprises a mounting member in sliding sealing contact with a bore defined by a supporting body, whereby fluid pressure in the bore creates a pressure force acting on the cutter.  
   
   
       33 . The apparatus of  claim 1 , wherein the apparatus is in the form of a shoe.  
   
   
       34 . A drilling method comprising the steps: 
 providing drilling apparatus comprising a cutting structure defined by at least one percussive action cutter and at least one other cutter; and    urging the least one percussive action cutter in a drilling direction by hydraulic pressure force while urging the at least one other cutter in a drilling direction by mechanical force.