Centralizer having atmospheric chamber for expansion in response to hydrostatic pressure

Abstract

A centralizer for use in a wellbore includes: a body for disposing around a periphery of a casing or liner string, the body having a plurality of bow springs biased toward an expanded position; a mandrel for disposing around the periphery of the casing or liner string; a piston disposed around the mandrel and movable between a locked position and a release position; a plurality of dogs, each dog mounted to or formed integrally with the respective bow spring and captured by the piston in the locked position, thereby keeping the bow springs in a retracted position; an atmospheric chamber formed between the piston and the mandrel; and a fastener for releasably connecting the piston to the mandrel in the locked position.

1 . A centralizer for use in a wellbore, comprising:
 a body for disposing around a periphery of a casing or liner string, the body having a plurality of bow springs biased toward an expanded position;   a mandrel for disposing around the periphery of the casing or liner string;   a piston disposed around the mandrel and movable between a locked position and a release position;   a plurality of dogs, each dog mounted to or formed integrally with the respective bow spring and captured by the piston in the locked position, thereby keeping the bow springs in a retracted position;   an atmospheric chamber formed between the piston and the mandrel; and   a fastener for releasably connecting the piston to the mandrel in the locked position.   
     
     
         2 . The centralizer of  claim 1 , wherein:
 an inner surface of the piston has a portion for receiving the dogs, and   an outer surface of each dog has a portion for engagement with the portion of the inner surface of the piston.   
     
     
         3 . The centralizer of  claim 2 , wherein:
 the portion of the inner surface of the piston is at least partially conical, and   the portion of the outer surface of each dog is at least partially inclined.   
     
     
         4 . The centralizer of  claim 1 , wherein:
 the body further has a pair of end rings, and   the centralizer further comprises a pair of collars, each collar mounted to the respective end ring.   
     
     
         5 . The centralizer of  claim 4 ,
 further comprising the casing or liner string; and   further comprising an anchor engaged with the periphery of the casing or liner string,   wherein the anchor is disposed between the collars.   
     
     
         6 . The centralizer of  claim 5 , wherein the mandrel abuts the anchor when the bow springs are in the retracted position. 
     
     
         7 . A method of installing a casing or liner string into a wellbore, comprising:
 forming an assembly comprising the casing or liner string and the centralizer of  claim 1  in the retracted position; and   lowering the assembly into the wellbore, wherein upon reaching an actuation depth, hydrostatic pressure exerted on the piston releases the fastener and moves the piston from the locked position to the release position, thereby freeing the dogs and allowing the bow springs to move toward the expanded position.   
     
     
         8 . A method of installing a casing or liner string into a wellbore, comprising:
 forming an assembly comprising the casing or liner string and the centralizer of  claim 1  in the retracted position;   lowering the assembly into the wellbore, wherein the centralizer remains in the retracted position; and   after lowering the assembly to a deployment depth, increasing pressure in the wellbore, wherein the increased pressure in the wellbore is exerted on the piston, thereby releasing the fastener, moving the piston from the locked position to the release position, freeing the dogs, and allowing the bow springs to move toward the expanded position.