Impact tool

Abstract

An impact tool for use in a well bore. The impact tool provides a hammer action through reciprocal movement of a cam within a spring mechanism. In an embodiment a drill bit is included to provide an impact drilling tool which requires minimum weight on bit to operate. The impact tool can therefore be run on coiled tubing and wireline.

We claim  
     
         1 . An impact tool for use in a bore hole from a surface, the impact drilling tool comprising: 
 a substantially cylindrical body having a longitudinal axis, the axis being aligned co-axially with the bore hole;    a first end, perpendicular to the longitudinal axis, having attachment means to attach the tool to a string for connection to the surface;    a second end including a working sub, the working sub including a first surface for contacting a portion of the bore hole; and    a hammer unit located between the first and second ends, the hammer unit providing a hammer action to the working sub via reciprocal movement of a cam within a spring mechanism.    
     
     
         2 . An impact tool as claimed in  claim 1  wherein the working sub is a drill bit and wherein the first surface contacts with a formation to increase depth of the bore hole.  
     
     
         3 . An impact tool as claimed in  claim 1  wherein the spring mechanism comprises at least one first spring to bias the working unit towards the cam.  
     
     
         4 . An impact tool as claimed in  claim 1  wherein the spring mechanism comprises at least one second spring located adjacent the cam to act with the cam in reciprocal motion.  
     
     
         5 . An impact tool as claimed in  claim 1  wherein the tool further comprises a drive shaft located on the longitudinal axis.  
     
     
         6 . An impact tool as claimed in  claim 5  wherein the tool further includes at least one drive key located between the cam and the drive shaft to prevent the cam rotating independently of the drive shaft while permitting the cam to move longitudinally with respect to the drive shaft.  
     
     
         7 . An impact tool as claimed in  claim 6  wherein the tool includes a second drive key located between the working sub and the drive shaft to prevent the working sub rotating independently of the drive shaft while permitting the working sub to move longitudinally with respect to the drive shaft.  
     
     
         8 . An impact tool as claimed in  claim 5  wherein the tool includes drive means, the drive means being used to rotate the drive shaft.  
     
     
         9 . An impact tool as claimed in  claim 1  wherein the cam includes a cam profile which determines number of strokes per revolution of the cam and thereby the cycle/stroke rate of the hammer unit.  
     
     
         10 . An impact tool as claimed  claim 1  wherein the tool includes a telescopic joint mounted on the longitudinal axis.  
     
     
         11 . An impact tool as claimed in  claim 1  wherein the tool includes a shear disc sub.  
     
     
         12 . An impact tool as claimed  claim 1  wherein the tool includes a release joint.  
     
     
         13 . A method of drilling a bore hole from a surface, the method comprising the steps: 
 (a) attaching an impact tool including a drill bit to a work string;    (b) running the string into a bore hole;    (c) operating the impact tool to provide a hammer action to the drill bit via a reciprocating cam within a spring mechanism; and    (d) impacting a surface of the drill bit upon a formation at a base of the bore hole.    
     
     
         14 . A method as claimed in  claim 13  wherein the work string is coiled tubing.  
     
     
         15 . A method as claimed in  claim 13  wherein the work string is a wireline.  
     
     
         16 . A method as claimed in  claim 13  wherein the method further includes the step of pumping fluid through the impact tool.  
     
     
         17 . A method as claimed in  claim 13  wherein a number of impact strokes per minute of the drill bit is set by the speed of rotation of the cam.  
     
     
         18 . A method as claimed in  claim 13  wherein the method further includes the step of steering the drill bit.