Drag block assembly

Abstract

Disclosed is a drag block assembly for use with a downhole tool in a subterranean well, such as packers or bridge plugs. The drag block assembly comprises a generally cylindrically shaped sleeve and a block element. The block element is mounted to the sleeve such that it can radially slide. The block element is outwardly biased from the sleeve by an electromagnetic element.

What is claimed is: 
     
         1 . A drag block assembly for a downhole tool comprising:
 a generally cylindrically shaped sleeve; and   a block element mounted to said sleeve, such that said block element can radially slide, and wherein said block element is outwardly biased from said sleeve by an electromagnetic element.   
     
     
         2 . The drag block assembly of  claim 1 , wherein said electromagnetic element comprises a first magnetic member mounted to said sleeve and a second magnetic member mounted to said block element, and wherein said first magnetic member and second magnetic member have magnetization aligned such that they repel each other. 
     
     
         3 . The drag block of  claim 2 , wherein said first magnetic member and said second magnetic member have a magnetization sufficient to provide a spring-like action to said block element and generate a drag force between said block element and a casing of a wellbore when said drag block assembly is introduce into said casing. 
     
     
         4 . The drag block assembly of  claim 1 , wherein:
 said sleeve has an outer surface, an array of longitudinally disposed slots disposed around said outer surface, and an inner surface at the bottom of each slot;   said block element has an elongated block-like body with a casing-wall-contacting outer surface and a bottom surface; and   there are a plurality of said block elements, each said slot has one of said block elements mounted in said slot such that said casing-wall-contacting outer surface protrudes through said slot, and said bottom surface faces said inner surface of said sleeve.   
     
     
         5 . The drag block assembly of  claim 4 , wherein:
 said sleeve further comprises a wall extending from said inner surface to said outer surface in each slot; and   said block has an elastic member extending around its periphery, such that said elastic member contacts said wall to block debris from entering into a space between said inner surface and said bottom surface.   
     
     
         6 . The drag block assembly of  claim 4 , wherein said drag block is radially moveable within said slot. 
     
     
         7 . The drag block assembly of  claim 6 , wherein said electromagnetic element comprises a plurality of first magnetic members and a plurality of second magnetic members, said inner surface of each said slot has one of said first magnetic members mounted thereto, said bottom surface of each block element has one of said second magnetic members mounted thereto, and wherein said first magnetic member and said second magnetic member have magnetization aligned such that they repel each other to thus outwardly bias said drag block element in said slot. 
     
     
         8 . The drag block assembly of  claim 4 , wherein said block element has a first lateral end having a first flange extending lengthwise therefrom and a second lateral end having a second flange extending lengthwise therefrom and wherein said first flange is retained by a retaining ring disposed about said outer surface of said sleeve and said second flange being retained by a tab connected to said sleeve wherein said block is thus mounted in and retained from moving out of said slot. 
     
     
         9 . The drag block assembly of  claim 8 , wherein said drag block is radially moveable within said slot. 
     
     
         10 . The drag block assembly of  claim 9 , wherein:
 said sleeve further comprises a wall extending from said inner surface to said outer surface in each slot; and   said block has an elastic member extending around its periphery such that said elastic member contacts said wall to block debris from entering into a space between said inner surface and said bottom surface.   
     
     
         11 . The drag block assembly of  claim 10 , wherein said electromagnetic element comprises a plurality of first magnetic members and a plurality of second magnetic members, said inner surface of each said slot has one of said first magnetic members mounted thereto, said bottom surface of each block element has one of said second magnetic members mounted thereto, and wherein said first magnetic member and said second magnetic member have magnetization aligned such that they repel each other to thus outwardly bias said drag block element in said slot. 
     
     
         12 . The drag block of  claim 11 , wherein said first magnetic member and said second magnetic member have a magnetization sufficient to provide a spring-like action to said block element and generate a drag force between said block element and a casing of a wellbore when said drag block assembly is introduce into said casing. 
     
     
         13 . A method of centering a downhole tool with drag friction comprising:
 (a) connecting a drag block assembly to said downhole tool, said drag block assembly having a generally cylindrically shaped sleeve and a plurality of block elements mounted to said sleeve such that they can radially slide;   (b) biasing each said block element outwardly from said sleeve by an electromagnetic element; and   (c) placing said downhole tool into a casing in a wellbore such that a casing-wall-contacting outer surface of each block elements presses outward on the casing thus centering the downhole tool in the casing and creating drag friction.   
     
     
         14 . The method of  claim 13 , wherein said electromagnetic element comprises a plurality of first magnetic member mounted to said sleeve and a plurality of second magnetic member, wherein said first magnetic members are mounted to said sleeve, each said block element has one of said second magnetic members mounted thereto, and said first magnetic member and second magnetic member have magnetization aligned such that they repel each other. 
     
     
         15 . The method of  14 , wherein said first magnetic member and said second magnetic member have a magnetization sufficient to provide a spring-like action to said block element and generate a drag force between said block element and said casing when said drag block assembly is introduce into said casing. 
     
     
         16 . The method of  claim 15 , wherein:
 said sleeve comprises an outer surface, an array of longitudinally disposed slots having a bottom and disposed around said outer surface, and an inner surface at said bottom of each slot;   each said block element comprises an elongated block-like body with a casing-wall-contacting outer surface and a bottom surface; and   each said slot has one of said block elements mounted in said slot such that said casing-wall-contacting outer surface protrudes through said slot, and said bottom surface faces said inner surface of said sleeve.   
     
     
         17 . The method of  claim 16 , wherein:
 said sleeve further comprises a wall extending from said inner surface to said outer surface in each slot; and   said block has an elastic member extending around its periphery such that said elastic member contacts said wall to block debris form entering into a space between said inner surface and said bottom surface.   
     
     
         18 . The method of  claim 17 , wherein said electromagnetic element comprises a plurality of first magnetic members and a plurality of second magnetic members, said inner surface of each said slot having one of said first magnetic members mounted thereto, said bottom surface of each said drag block element having one of said second magnetic members mounted thereto, and wherein said first magnetic member and said second magnetic member have magnetization aligned such that they repel each other to thus outwardly bias said drag block element in said slot. 
     
     
         19 . The method of  claim 18 , wherein said drag block is radially moveable within said slot.