Deploying the World's Largest Bismuth Alloy Plug for Cost Effective P&A

Abstract

This paper focusses on the successful re-abandonment of a subsea well in the Gulf of Mexico using a rigless approach. The operator had already abandoned the well using conventional technology, but it was still bubbling. The objective was to re-abandon the well by setting a reliable and permanent gas tight seal in the 36" conductor. To achieve this a herculean engineering and operational feat was undertaken to design and manufacture a custom tool using record breaking volume of bismuth and thermite. The tool was deployed from a lift boat and guided into the conductor using ROV's. A timer activation mechanism initiated the thermite heater melting the bismuth alloy cast on to the outside of the tool. The bismuth alloy once molten flowed into the well filling the entire cross section of the 36" conductor. The thermite heater was then retrieved from the molten alloy leaving a solid gas tight metal to metal seal inside the conductor. Observations confirmed the success of the operation, as the bismuth alloy plug created a reliable gas tight seal, with no observed bubbles for a duration of 20 hours. By utilizing bismuth alloy technology, the complexity associated with traditional abandonment methods was eliminated, while ensuring long term reliability. The use of bismuth alloy allowed for a shorter plug length, enabling deployment in the shallow conductor without extensive workover efforts not only reducing costs but also saving time and mitigating HSE risks.