Researchers from the Norwegian University of Science and Technology’s Department of Geoscience and Petroleum are eyeing bismuth alloys as a safer and less expensive solution for the plugging of oil and gas wells.

As an alternative to the cement plugs currently used to plug abandoned oil and gas wells — but that can develop leaks over time due to corrosion, thereby becoming a significant source of greenhouse gas emissions — impermeable bismuth alloys are showing promise for plugging these end-of-life oil wells.

Because cement can crack and lose its seal in the high pressure, high temperature environments of oil and gas wells and because cement shrinks as it cures, subsequently encouraging the formation of little pores, pathways for hydrocarbons to migrate to the surface tend to develop.

However, bismuth — which is unlikely to crack and will instead expand as it solidifies — maintains its integrity over time. The researchers added that bismuth outperformed cement during hydraulic "push-out" tests and leakage tests with nitrogen gas, finding that bismuth alloy plugs had higher resistance to applied pressure and reduced gas migration versus cement plugs.

Further, the rapid hardening time of bismuth alloys ensure reduced installation times, the researchers added.

"Reduced installation time reduces the rig time, which in turn reduces costs….One other aspect of bismuth alloy plugs is that they have the potential to be deployed riglessly, meaning that without the necessity of having a rig in place. This will in turn cut on costs drastically, as most of the costs offshore come from the 'rig-rental' costs."

The findings are detailed in the article “Development of bismuth-based solutions for well plugging and abandonment: A review,” which appears in the journal Petroleum Research,