Downhole Tubular Section Mill

Abstract

A casing section mill has a main body with cut-outs to accommodate casing section mill blades mounted thereon, and stabilizer inserts mounted in the cut-outs below the blades. The stabilizer inserts yield an outer diameter substantially the same as the drift inner diameter of the casing being milled, thereby providing positive centralization and stabilization of the blades. The casing section mill may be rotated by a downhole positioned positive displacement motor in the drillstring, by drillstring rotation from the surface, or a combination of downhole positive displacement motor and drillstring rotation.

We claim: 
     
         1 . A casing section mill, comprising:
 an elongated main body having upper and lower ends and a central bore through an uphole section thereof, with a means for connecting said upper end to a drillstring, said main body further comprising a pair of elongated cutouts extending to a position proximal said lower end;   a piston slidably disposed in said central bore, said piston movable in response to fluid flow through said central bore of said main body;   a pair of blades rotatably disposed in said main body, said blades comprising heel sections, wherein said piston bears on said heel sections in response to fluid passage through said bore of said main body, moving said blades from a first, retracted position to a second, extended position to engage a casing string for cutting or milling;   a plurality of stabilizer inserts removably mounted in a lower or downhole portion of said elongated cutouts, in a downhole direction from said blades, said stabilizer inserts sized to yield an outer diameter across said mounted stabilizer inserts substantially equal to the inner drift diameter of the casing string being cut or milled.   
     
     
         2 . The casing section mill of  claim 1 , wherein said blades comprise elongated cutters having multiple hardened inserts therein. 
     
     
         3 . The casing section mill of  claim 2 , wherein said stabilizer inserts comprise elongated inserts with an upper end positioned proximal said blades when said blades are in their first, retracted position, and a lower end extending substantially to a lower or downhole end of same main body, and wherein said lower end of said stabilizer inserts comprise tapered profiles to aid in movement downhole in a wellbore. 
     
     
         4 . An assembly for milling casing in a wellbore, comprising:
 a drillstring comprising a bottomhole assembly, said bottomhole assembly comprising:
 a casing section mill, said casing section mill comprising: an elongated main body having upper and lower ends and a central bore therethrough, said main body further comprising a plurality of elongated cutouts extending to a position proximal said lower end; 
 a piston slidably disposed in said central bore, said piston movable in response to fluid flow through said central bore of said main body; 
 a pair of blades rotatably disposed in said main body, said blades comprising heel sections, wherein said piston bears on said heel sections in response to fluid passage through said bore of said main body, moving said blades from a first, retracted position to a second, extended position to engage a casing string for cutting or milling; 
 a plurality of stabilizer inserts removably mounted in a lower or downhole portion of said elongated cutouts, in a downhole direction from said blades, said stabilizer inserts sized to yield an outer diameter across said mounted stabilizer inserts substantially equal to the inner drift diameter of the casing string being cut or milled; and 
   a positive displacement motor disposed in an uphole position from said casing section mill, whereby rotation of said positive displacement motor due to fluid flow results in rotation of said casing section mill.   
     
     
         5 . The casing section mill of  claim 4 , wherein said stabilizer inserts comprise elongated inserts with an upper end positioned proximal said blades when said blades are in their first, retracted position, and a lower end extending substantially to a lower or downhole end of same main body, and wherein said lower end of said stabilizer inserts comprise tapered profiles to aid in movement downhole in a wellbore. 
     
     
         6 . A method of milling casing, comprising the steps of:
 a) providing a casing section mill, comprising:
 an elongated main body having upper and lower ends and a central bore through an uphole section thereof, with a means for connecting said upper end to a drillstring, said main body further comprising a pair of elongated cutouts extending to a position proximal said lower end; 
 a piston slidably disposed in said central bore, said piston movable in response to fluid flow through said central bore of said main body; 
 a pair of blades rotatably disposed in said main body, said blades comprising heel sections, wherein said piston bears on said heel sections in response to fluid passage through said bore of said main body, moving said blades from a first, retracted position to a second, extended position to engage a casing string for cutting or milling; 
 a plurality of stabilizer inserts removably mounted in a lower or downhole portion of said elongated cutouts, in a downhole direction from said blades, said stabilizer inserts sized to yield an outer diameter across said mounted stabilizer inserts substantially equal to the inner drift diameter of the casing string being cut or milled; 
   b) running said casing section mill downhole into a wellbore, on a drillstring;   c) positioning said casing section mill within a section of casing to be milled; and   d) commencing fluid flow through said drillstring, said positive displacement motor and said casing section mill, thereby extending said blades and engaging said blades with said casing string and rotating said casing section mill.   
     
     
         7 . The method of  claim 6 , comprising the further step of:
 e) rotating said drillstring from the surface, resulting in a rotational speed of said casing section mill from the combination of said positive displacement motor and said drillstring rotation.   
     
     
         8 . The method of  claim 7 , comprising the further step of:
 f) monitoring torque readings on said drillstring.