Well construction and completion

Abstract

A well sealing system includes a tailipipe set in a wellbore casing, the annular space between the tailpipe and the casing being sealed by a packer comprising at least two annular seals, and the internal diameter of the tailpipe being sealed by at least two internal seals. Disclosed are also an apparatus and a method for providing a casing in a bore hole for a well an offshore location, comprising the steps of: a) fabricating a casing in a location remote from the offshore well location; b) floating the casing to the location; c) orienting the casing to a substantially vertical position; d) lowering in a drilling assembly; e) operating a drill bit included in the drilling assembly to drill a borehole; f) lowering the casing into the bore hole as required.

1 . A well sealing system including a tailpipe set in a wellbore casing, the annular space between the tailpipe and the casing being sealed by a packer comprising at least two annular seals, and the internal diameter of the tailpipe being sealed by at least two internal seals, so that the wellbore above the tailpipe and the wellbore below the tailpipe are separated by two layers of seals. 
   
   
       2 . A well sealing system according to  claim 1  wherein tubing extends from the surface of the wellbore to the tailpipe, and the two internal seals are deployed down this tubing. 
   
   
       3 . A well sealing system according to  claim 1  wherein the two internal seals engage with a profile in the internal diameter of the tailpipe. 
   
   
       4 . A well sealing system according to  claim 2 , wherein the tubing is disengaged after the internal seals have been deployed. 
   
   
       5 . A well sealing system according to  claim 1  wherein the internal seals are removable. 
   
   
       6 . A length of casing for installation in a wellbore, the casing including a dynamic seal which seals the annulus between the outer diameter of the length of casing and the inner diameter of any previously installed conductor or casing lengths. 
   
   
       7 . A length of casing according to  claim 6 , wherein the dynamic seal includes a disengagable part that can release from the length of casing for installation to engage with the annulus between two previously installed casing lengths. 
   
   
       8 . A length of casing according to  claim 7 , wherein the dynamic seal includes a non-disengagable part that remains on the length of casing being lowered after the disengagable part has been released, the non-disengagable part continuing to seal the annulus between the length of casing being lowered and a previously installed casing length. 
   
   
       9 . A method of providing a casing a bore hole for a well an offshore location, comprising the steps of a) fabricating a casing in a location remote from the offshore well location b) floating the casing to the location c) orienting the casing to a substantially vertical position d) lowering in a drilling assembly e) operating a drill bit included in the drilling assembly to drill a borehole f) lowering the casing into the bore hole as required. 
   
   
       10 . A method according to  claim 9  wherein the drilling assembly is lowered simultaneously with the casing. 
   
   
       11 . A method according to  claim 9  wherein a bore hole pressure control means is lowered onto the bore hole after the casing is introduced to the bore hole. 
   
   
       12 . A method according to  claim 9  wherein an umbilical having a flowpath is included in fluid communication with the bore hole. 
   
   
       13 . A method according to  claim 9  wherein after the casing is lowered in the bore hole to its final position, a cement plug is formed at the bottom of the casing before the drilling assembly is removed from the bore hole. 
   
   
       14 . A method according to  claim 9  wherein a subsequent casing is provided at the sea bed in the same manner, the subsequent casing having an outer diameter smaller than that of the inner diameter of the previous said casing, the subsequent casing being lowered through the previous casing. 
   
   
       15 . A casing installation system comprising a casing supported by flotation means, and a first ship for towing the casing, and an orientation means for orienting the casing vertically. 
   
   
       16 . A casing installation system according to  claim 15  wherein the casing is supported between a first ship and a second ship during orientation. 
   
   
       17 . A casing installation system according to  claim 16  wherein a control system including one or more rotatable grips are attached to the casing to hold the casing while it is orientated. 
   
   
       18 . A casing installation system according to  claim 15  wherein a drilling assembly is provided that is insertable within the casing. 
   
   
       19 . A casing installation system according to  claim 15  wherein a sealing means is provided for sealing the bore hole from the surrounding environment.