Marine isolation assembly

Abstract

An isolation assembly that employs a pack-off device at an annular space between a landing string and a riser. The assembly is configured to ensure sealing off of an annular space below the pack-off device such that potentially hazardous well testing applications may safely proceed early on in completions operations. That is, in advance of any significant rig-level pressure control equipment hook-up, the pack-off device may seal off the annulus from any potential hydrocarbon leaks up the riser toward the rig. Further, where such seal holds back pressures exceeding a predetermined level, a burst element may be incorporated into the wall of the riser to allow for controlled venting therefrom.

We claim: 
     
         1 . An isolation assembly for a marine well, the assembly comprising:
 a landing string coupled to a rig above sea level and to a well head system at a seabed therebelow;   a riser disposed about said string and coupled to the rig and system; and   a pack-off device for sealable disposal in an annulus between said string and said riser.   
     
     
         2 . The assembly of  claim 1  wherein said pack-off device exceeds a rating of about 6,000 PSI relative a potential pressure differential in the annulus therebelow. 
     
     
         3 . The assembly of  claim 1  further comprising a burst element incorporated into said riser below a location of said pack-off device to allow pressurized release of hydrocarbons from within the annulus. 
     
     
         4 . The assembly of  claim 1  wherein said pack-off device is one of an inflatable device, a compressible device and a packer swab cup device. 
     
     
         5 . The assembly of  claim 1  wherein said pack-off device is located below a lubricator valve of said string and below a slip joint of said riser. 
     
     
         6 . The assembly of  claim 1  wherein said pack-off device is located adjacent the well head system. 
     
     
         7 . The assembly of  claim 6  wherein the adjacent location of said pack-off device is within less than about five feet of the system. 
     
     
         8 . The assembly of  claim 1  wherein said pack-off device comprises a sealable feed-thru for communication from the rig. 
     
     
         9 . The assembly of  claim 8  wherein said feed-thru accommodates one of an umbilical for communication to the system and a hydraulic line for inflatably effectuating the sealable disposal of said device in the annulus. 
     
     
         10 . An offshore completions equipment assembly comprising:
 a rig having a floor above a sea level;   a well head system anchored to a seabed below the rig and providing access to a well below the seabed;   a riser providing a stable channel between said rig and said system; and   a landing string disposed from said rig and through said riser to said system, said string outfitted with a pack-off device for sealing an annular space between said riser and said string at a location adjacent said system.   
     
     
         11 . The assembly of  claim 10  wherein said well head system further comprises:
 a test tree for well testing applications; and 
 a seabed control unit coupled to said tree for driving the applications as directed from a rig control unit at the rig. 
 
     
     
         12 . The assembly of  claim 11  wherein the pack-off device is configured for inflating to attain the sealing of the annular space, the assembly further comprising a hydraulic line between said seabed control unit and the pack-off device for the inflating as directed by the rig control unit. 
     
     
         13 . The assembly of  claim 10  wherein said riser comprises a burst element in a wall thereof below said pack-off device, said burst element configured to allow pressure release from the annulus upon exposure to a predetermined pressure therein. 
     
     
         14 . The assembly of  claim 13  wherein the predetermined pressure is greater than about 5,000 PSI. 
     
     
         15 . The assembly of  claim 13  further comprising an access line coupled to the wall of said riser at the location of said burst element, said access line providing an isolated pathway back to the rig. 
     
     
         16 . The assembly of  claim 15  further comprising collection equipment disposed at the rig and coupled to said access line for accommodating fluid intake therefrom. 
     
     
         17 . A method comprising:
 deploying a pack-off device on a landing string from an offshore rig through a riser anchored to a well head system at a seabed; and   sealing off an annulus between the string and the riser with the device at a location adjacently uphole of the system.   
     
     
         18 . The method of  claim 17  further comprising performing a well test application with a test tree of the system after said sealing. 
     
     
         19 . The method of  claim 17  further comprising venting pressure from the annulus below the pack-off device and through the riser. 
     
     
         20 . The method of  claim 19  wherein said venting comprises one of releasing pressure into surrounding water and releasing pressure through a line coupled to the riser and leading back to the rig.