Milling Tool

Abstract

A milling tool for enlarging portions of a wellbore. The milling tool includes a housing that defines a central bore along its length. A piston is moveably disposed within the central bore, and axial movement of the piston moves support arms radially outwardly from the housing. The support arms carry milling blades for enlarging portions of a wellbore.

What is claimed is: 
     
         1 . A milling tool comprising:
 a housing defining a central bore along its length;   a piston moveably disposed within the bore between a first position and a second position;   a support arm that is moveable radially outwardly from the housing when the piston is moved to the second position; and   a milling blade affixed to the support arm and having at least one milling cutter for milling a surrounding portion of wellbore.   
     
     
         2 . The milling tool of  claim 1  wherein there are three milling blades affixed to the support arm. 
     
     
         3 . The milling tool of  claim 1  further comprising:
 a piston chamber formed within the bore; and 
 the piston having an enlarged diameter piston portion that resides within the piston chamber. 
 
     
     
         4 . The milling tool of  claim 3  wherein the piston is moved from the first position to the second position by fluid pressure upon the enlarged diameter piston portion. 
     
     
         5 . The milling tool of  claim 4  wherein fluid is flowed through an axial flow passage formed within the piston to enter the piston chamber. 
     
     
         6 . The milling tool of  claim 1  wherein the milling blade has a length that is at least one-fifth of the length of the housing. 
     
     
         7 . The milling tool of  claim 1  wherein there are three support arms. 
     
     
         8 . The milling tool of  claim 3  further comprising a compressible spring that biases the enlarged diameter piston portion axially such that the piston is biased toward the first position. 
     
     
         9 . A milling assembly for enlarging a portion of a wellbore, the milling assembly comprising:
 a running string having a central flowbore defined along its length;   a milling tool affixed to the running string, the milling tool comprising:
 a housing defining a central bore along its length; 
 a piston moveably disposed within the bore between a first position and a second position; 
 a support arm that is moveable radially outwardly from the housing when the piston is moved to the second position; and 
 a milling blade affixed to the support arm and having at least one milling cutter for milling a surrounding portion of wellbore. 
   
     
     
         10 . The milling assembly of  claim 9  wherein there are three milling blades affixed to the support arm. 
     
     
         11 . The milling assembly of  claim 9  further comprising:
 a piston chamber formed within the bore; and 
 the piston having an enlarged diameter piston portion that resides within the piston chamber. 
 
     
     
         12 . The milling assembly of  claim 11  wherein the piston is moved from the first position to the second position by fluid pressure upon the enlarged diameter piston portion. 
     
     
         13 . The milling assembly of  claim 12  wherein fluid is flowed through an axial flow passage formed within the piston to enter the piston chamber. 
     
     
         14 . The milling assembly of  claim 9  wherein the milling blade has a length that is at least one-fifth of the length of the housing. 
     
     
         15 . The milling assembly of  claim 9  wherein there are three support arms. 
     
     
         16 . The milling assembly of  claim 11  further comprising a compressible spring that biases the enlarged diameter piston portion axially such that the piston is biased toward the first position.