Method and system for enhancing the performance of a well tubular expansion assembly

Abstract

The upward force exerted on an expansion cone ( 2 ), which is pulled up by a drill string ( 3 ) to expand a well tubular ( 1 ), is hydraulically enhanced by:—connecting a bottom plug ( 10 ) to a carrier body ( 11 ) below the expansion cone ( 2 );—lowering the drill string ( 3 ), cone ( 2 ), carrier body ( 11 ), bottom plug ( 10 ) and unexpanded well tubular ( 1 ) assembly into a well;—inducing the drill string ( 3 ) to pull the expansion cone ( 2 ) through a lower edge ( 13 ) of the unexpanded well tubular ( 1 ) to expand said edge ( 13 ) and to subsequently pull the bottom plug ( 10 ) into sealing engagement with the expanded edge ( 13 );—releasing the bottom plug ( 10 ) from the carrier body ( 11 );—further pulling (F 1 ) the expansion cone ( 10 ) through the well tubular ( 1 ) and simultaneously injecting fluid through the drill string ( 3 ) below the cone ( 2 ) to hydraulically increase (F 2 ) the upward force (F=F 1 +F 2 ) exerted on the expansion cone ( 2 ).

1 . A method for pulling up an expansion cone by a drill string to expand a well tubular, the method comprising:
 inserting the drill string through the unexpanded well tubular;   connecting the expansion cone to a lower end of the drill string such that the expansion cone engages a lower edge of the tubular;   connecting a bottom plug to a carrier body that is suspended below the expansion cone;   lowering the drill string, cone, bottom plug and the unexpanded well tubular into a well until an upper end of the unexpanded well tubular is co-axially arranged within a lower end of a previously installed tubular;   pulling the expansion cone by drill string pull through the lower edge of the unexpanded well tubular thereby expanding said lower edge;   inducing the carrier body to pull the bottom plug into the expanded lower edge and to seal off said lower edge;   inducing a release joint in the carrier body to release the bottom plug from the carrier body;   further pulling the expansion cone by drill string pull through at least a substantial part of the lower tubular; and   simultaneously injecting fluid through the interior of the drill string through a fluid discharge opening below the expansion cone into a space between the bottom plug and the expansion cone thereby hydraulically pushing the expansion cone through the lower tubular and increasing the upward force exerted to the expansion cone; and   
       wherein the expanded lower edge of the lower tubular has an inwardly curved shape and the bottom plug comprises:
 a sealing ring that is configured to sealingly engage said inwardly curved edge; and 
 self-locking teeth that snap into the inner surface of said inwardly curved edge when the bottom plug is pulled into the lower edge. 
 
     
     
         2 . The method of  claim 1 , wherein the fluid injection through the interior of the drill string is continued when the expansion cone is pulled through the upper end of the lower tubular into the lower end of the previously installed upper tubular. 
     
     
         3 . The method of  claim 1 , wherein the drill string pull and pressure of the fluid injected through the drill string are adjusted on the basis of a monitored longitudinal movement of the expansion cone through the well tubular and a ration between downward hydraulic force exerted on the bottom plug and upward force exerted by the expansion cone on the tubular expanded thereby. 
     
     
         4 . The method of  claim 1 , further comprising locking the upper end of the unexpanded well tubular to the previously installed tubular by a top anchor assembly and retracting the top anchor assembly when the expansion cone reaches said upper end. 
     
     
         5 . The method of  claim 1 , wherein after expansion of the well tubular the bottom plug is drilled out and the expanded well tubular forms the previously installed well tubular through which a subsequent well tubular is inserted and expanded in accordance with the method according to  claim 1 . 
     
     
         6 . The method of  claim 5 , wherein the process of expanding a subsequent well tubular, drilling out the bottom plug and expanding yet another subsequent well tubular is repeated several times to generate a Mono Diameter wellbore with a substantially constant internal diameter. 
     
     
         7 . The method of  claim 1 , wherein the expanded and previously installed well tubulars form part of a casing or liner assembly of a hydrocarbon fluid production well through which, after completion of the well, crude oil, natural gas and/or another hydrocarbon fluid is produced. 
     
     
         8 . A tubular expansion assembly, comprising:
 a drill string;   a bottom plug connectable to a carrier body below an expansion cone;   means for connecting the expansion cone to a lower end of a drill string and to pull the expansion cone by the drill string pull into a lower edge of an unexpanded well tubular thereby expanding said lower edge;   a release joint in the carrier body adapted to release the bottom plug from the carrier body when the bottom plug is pulled into the expanded lower edge of the lower tubular; and   a fluid discharge opening near a lower end of the expansion cone into for injecting fluid through the drill string and expansion cone into a space between the bottom plug and the expansion cone thereby hydraulically pushing the expansion cone through the expanding well tubular and increasing the upward force exerted the expansion cone; and   
       wherein the expanded lower edge of the well tubular has an inwardly curved shape and the bottom plug comprises:
 a sealing ring that is configured to sealingly engage said edge; and 
 self-locking teeth that snap into the inner surface of said inwardly curved edge when the bottom plug is pulled into the lower edge. 
 
     
     
         9 . Use of the tubular expansion assembly of  claim 8  in the method of  claim 1 .