Newcastle University researchers are heading an EPSRC-funded research to mitigate the problem of bacteria in subsea oil deposits.
Sulphate-reducing bacteria are said to thrive in oxygen-free, watery environments. With the ability to lie dormant for very long periods, sulphate-reducing bacteria take in sulphates but release toxic, corrosive hydrogen sulphide (H2S) when they are activated. Known as ‘reservoir souring’, this increases the oil’s sulphur content, which reduces its market value.
Hydrogen sulphide is also highly toxic, posing a potential hazard to workers on offshore platforms, while its corrosiveness can damage pipelines and rigs.
Working with a range of private sector, public sector and academic partners from the UK and overseas, the Newcastle-led team is considering a number of easy-to-implement, cost-cutting measures, such as adjusting the water temperature used during oil production.
As part of its work to understand how sulphate-reducing bacteria become activated in oil reservoirs, the team is investigating the widespread practice of pumping seawater into an oil reservoir to reduce temperatures and make extraction easier but which poses problems from a reservoir souring perspective.
Research lead Dr Casey Hubert, a Visiting Professor at Newcastle University from Canada’s University of Calgary, said: “Seawater is rich in sulphates, which sulphate-reducing bacteria use for their metabolism. Our results suggest that warming the injected seawater, so that the temperatures in a hot reservoir drop down to say 70°C rather than 50°C, could prevent sulphate-reducing bacteria activity without significantly affecting the oil extraction process.”
One method currently used by the offshore industry to mitigate the impact of sulphate-reducing bacteria in oil reservoirs is to inject nitrates to stimulate the growth of another type of bacteria that out-compete sulphate-reducing bacteria for food. The Newcastle-led team also see major potential here to improve current practice.
“We’re working on ways to predict more accurately the nitrate dose that will be needed in any particular context, taking precise local conditions into account”, Dr Hubert said.
“Adjusting the nitrate dose offers ways to better manage corrosion risks associated with reservoir souring and in some cases could cut costs if lower doses could be used. Our aim is to work with industry so that the nitrate souring control technique is understood thoroughly and sees widespread use.”
Image credits and content: The Engineer