A UK firm has developed a new method for sealing abandoned oil wells using an innovative plug device and simulation models.

BiSN Technologies say they can design bespoke plugging solutions for any of the millions of abandoned wells currently in existence.

When a well reaches its economic limit and production no longer covers operating costs, it is ‘plugged’ and abandoned. The method currently used by the industry (in place since the 1950s) basically entails putting in a steel bridge plug in the outer production casing and pouring in cement.

The recent leak at Total’s Elgin site highlights weaknesses associated with the ‘plug and abandon’ method according to BiSN.

Their technology development began with studies of sulphate reducing bacteria present in oil wells which produce acid that attacks concrete and steel.

‘We came up with an alloy that’s not attacked by H2S [hydrogen sulphide],’ Paul Carragher, BiSN’s Director told The Engineer.  

‘We melt the alloy down in situ, and because the alloy runs like water and has a very thin consistency when it melts, it goes into any nooks and crannies and corrosion pits in the casing, then when it solidifies it expands to create a seal – very much like a cork and wine bottle.’

The tool has been developed with the help of the Virtual Engineering Centre – a Liverpool University led partnership established to provide innovative solutions to industry challenges.

A simulation shows how the alloy melts and solidifies in the well and demonstrates the integrity of the seal. The simulation has been validated with experimental data and is adaptable to both oil and gas applications, onshore and offshore.

‘There’s lots of different sizes of wells and there’s also different types of casings and we can put all those different parameters in and specify a plug for the particular well; and we can also say it’s good according to our models - up to to say 50,000 PSI - and we can change the length of tool to increase the pressure,’ Carragher said.