Eliminating Gas Migration During Well Abandonment in Offshore Australia

Well Abandonment with Wel-lok™ STC

Statistics

Location:
Australia
Environment:
Offshore
Deviation:
Depth:
874'
Downhole Pressure:
434psi
Differential Pressure:
500psi
Temperature:
35ºC
Setting ID:
8.535"
Restriction:
8.379"
Sealing ID:
12.415"

Identification of problem

After a successful first campaign in Australia, BiSN’s Wel-lok™ technology was chosen to address gas migration in a 20 well offshore P&A campaign. For each well, the operator has chosen to set 2 BiSN plugs, one around 900’ and the second around 300’. This is to ensure all potential gas producing zones are addressed and will be permanently abandoned.

Issues to overcome

The production casing by surface casing annulus was cemented with gas flowing through the channeled cement. To achieve a bismuth seal in the annulus, section milling was required. 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. This is done by pulling the heater out of the bismuth alloy when all of the alloy is liquid. Since the plugs were set shallow in the wells, the time to remove the heaters was shorter than on a deeper set plug due to the alloy cooling faster.

Application

On each of the wells and at both setting depths, a section milled window is being cut in the 9 5/8” production casing out to the 13 3/8” surface casing and a Wel-lok™ STC with removable heater is being set inside the window.

Outcomes/Conclusion

Each of these wells are currently being monitored until all wells are plugged before casings are cut and removed to complete the permanent abandonment.

About the application

The Wel-lok™ STC (Seal Through Casing) has been developed to achieve a gas tight V0 seal well annuli that cannot be achieved by traditional cement balance plugs. Run on electric line, this tool does not need surface pumping equipment to circulate the alloy in place. Due to its viscosity and density, once melted the liquid alloy will flow with gravity into the annulus. When it cools below its melting point it solidifies, expands and creates a gas tight seal across the entire wellbore. The entire process, from melting to solidification, takes place in minutes and the seal is ready to test within an hour.

Seal Through Casing - BiSN
Seal Through Casing - BiSN
Seal Through Casing - BiSN
Seal Through Casing - BiSN

How it works…

The Wel-lok™ STC (Seal Through Casing) has been developed to achieve a gas tight V0 seal well annuli that cannot be achieved by traditional cement balance plugs.

Get in touch and find a
permanent solution for your well

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