Sealing Multiple Annuli During Well Abandonment in Offshore Australia

Well Abandonment with Wel-lok™ MXD

Statistics

Location:
Australia
Environment:
Offshore
Deviation:
Depth:
876'
Downhole Pressure:
428psi
Differential Pressure:
500psi
Temperature:
35ºC
Setting ID:
6.276"
Restriction:
6.151"
Sealing ID:
12.415"

Identification of problem

BiSN had been contracted for a 20 well P&A campaign to provide gas tight seals for eliminating gas migration in the annulus between 9 5/8” production casing and 13 3/8” surface casing. One well in this campaign had a different casing program but the same issue. In addition to the 9 5/8” and 13 3/8” casings, this well also had a 7” casing which was cemented in place. This required a tool that could be run inside the 7” casing and seal through a section milled window through the 9 5/8” casing and out to the 13 3/8” casing.

Issues to overcome

With the 7” casing cemented inside the 9 5/8”, the challenge was to provide a tool with a small enough OD to pass through the 7” casing and provide sufficient alloy to create a gas tight seal out to 13 3/8” casing. The client also required a solid bismuth alloy plug across the wellbore so the modified thermite heater would need to be removed, not left in the center of the plug.

Application

For this well, a window was section milled through 2 strings of casing (7” and 9 5/8”) out to 13 3/8” casing. BiSN deployed a 5.75” OD Wel-lok™ MXD that was set across this window. The MXD utilizes bailers to deploy the bismuth alloy in pellet form rather than casting the alloy onto the outside of the heater as other BiSN tools do. This allows for the maximum amount of alloy to be deployed while providing a smaller OD tool.

Outcomes/Conclusion

The Wel-lok™ MXD was successfully set and gas migration was eliminated. This well is currently being monitored until all wells on the platform are plugged. This is the largest MXD BiSN has deployed and the first multiple annuli plug.

About the application

The Wel-lok™ MXD (Maximum Drift) has been specifically developed for rigless through tubing applications. This tool has a smaller OD and higher expansion ratio than some of the other Wel-lok™ tools but uses the same technology to create metal to metal seals. Unlike conventional through tubing tools utilising a petal basket and cement or inflatable packers, the MXD™ offers a gas tight seal up with up to a 10,000 psi differential pressure rating and can be deployed in a single trip. Utilising bismuth alloy pellets, deployed inside a bailer, it eliminates restrictions of the volume of alloy that can used to create a seal.

Maximum Drift Tool - BiSN
Maximum Drift Tool - BiSN
Maximum Drift Tool - BiSN
Maximum Drift Tool - BiSN

How it works…

The Wel-lok™ MXD (Maximum Drift) has been specifically developed for rigless through tubing applications.

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