Downhole plug with protective member

Abstract

A plug excellent in pressure resistance is provided. A downhole plug (20) includes a mandrel (1), a center element (2), at least one lip (3), and a pressure transmission means. When the center element (2) is deformed by applying a pressure of 50 MPa to the downhole plug (20) in the axial direction, a ratio (b/a) of an axial length (b) of a part where the mandrel (1) and the center element (2) are in contact with each other, to a maximum axial length (a) of the center element (2) in a cross section along the axial direction is less than 0.5.

1 . A plug for plugging a wellbore, comprising:
 a cylindrical body;   an annular elastic member configured to surround an outer peripheral surface of the cylindrical body and to be deformed under pressure;   at least one protective member configured to surround the outer peripheral surface of the cylindrical body and to prevent at least a part of the elastic member from coming into contact with the cylindrical body; and   a pair of pressure transmission means configured to sandwich the elastic member in an axial direction of the plug and to apply pressure to the elastic member in the axial direction to compress the elastic member, wherein   at least one of the protective members is integrated with one of the pressure transmission elements constituting the pressure transmission means,   one of the pressure transmission elements integrated with the protective member is in contact with an end of the elastic member and is a conical member whose outer diameter increases from an end of the cylindrical body toward the elastic member, and   when the elastic member is deformed by applying a pressure of 50 MPa to the plug in the axial direction, a ratio (b/a) of an axial length (b) of a part of the elastic member where the cylindrical body and the elastic member are in contact with each other, to a maximum axial length (a) of the elastic member in a cross section along the axial direction is less than 0.5.   
     
     
         2 . (canceled) 
     
     
         3 . (canceled) 
     
     
         4 . The plug according to  claim 1 , comprising
 a plurality of the protective members, wherein   one of the plurality of protective members is integrated with one of the pressure transmission elements constituting one of the pair of pressure transmission means, and   another one of the plurality of protective members is integrated with one of the pressure transmission elements constituting the other of the pair of pressure transmission means.   
     
     
         5 . (canceled) 
     
     
         6 . (canceled) 
     
     
         7 . (canceled) 
     
     
         8 . A plug for plugging a wellbore, comprising:
 a cylindrical body;   an annular elastic member configured to surround an outer peripheral surface of the cylindrical body and to be deformed under pressure;   at least one protective member configured to surround the outer peripheral surface of the cylindrical body and to prevent at least a part of the elastic member from coming into contact with the cylindrical body; and   a pair of pressure transmission means configured to sandwich the elastic member in an axial direction of the plug and to apply pressure to the elastic member in the axial direction to compress the elastic member, wherein   when the elastic member is deformed by applying a pressure of 50 MPa to the plug in the axial direction, an axial length (b) of a part of the elastic member where the cylindrical body and the elastic member are in contact with each other is 0.   
     
     
         9 . The plug according to  claim 8 , wherein
 the protective member is annular.