Eliminating Gas Migration During Well Abandonment in Offshore Australia

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.