Simple tweaks to oilfield practice could provide the offshore industry with a more sustainable, money-saving solution to health and safety, environmental and commercial threats posed by harmful bacteria in subsea oil deposits, according to research under the Engineering and Physical Sciences Research Council (EPSRC).
Easy-to-implement, cost-cutting measures – such as adjusting the water temperature used during oil production – could offer a way of tackling problems linked to sulphate-reducing bacteria (SRB) that is greener and more effective than those currently relied on, says the EPSRC. SRB ‘breathe’ sulphates but exhale toxic, corrosive hydrogen sulphide (H2S).
The EPSRC is funding research, led by Newcastle University and working with private sector, public sector and academic partners from the UK and overseas.
First evolving billions of years ago, SRB thrive in oxygen-free, watery environments like those that can be found in offshore oil deposits. The H2S they produce, however, is a key cause of "reservoir souring," increasing the oil’s sulphur content and so reducing its market value. H2S is also highly toxic, posing a potentially deadly hazard to workers on offshore platforms, while its corrosiveness can damage pipelines and rigs, leading to oil leaks and spills.
As part of its work to understand how SRB – some of which can lie dormant for very long periods – become activated in oil reservoirs, the Newcastle-led 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.
“Seawater is rich in sulphates, which SRB use for their metabolism,” says Dr Casey Hubert of Canada’s University of Calgary, who is leading the research in his role as Visiting Professor at Newcastle University. “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 SRB activity without significantly affecting the oil extraction process.”
Industry has already shown substantial interest with additional funding secured from large supermajors in the oil and gas sector.
One method currently used by the offshore industry to mitigate the impact of SRB in oil reservoirs is to inject nitrates to stimulate the growth of another type of bacteria that out-compete SRB for food. The Newcastle-led team also see major potential here to improve current practice and make it greener.
“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 says. “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.”
The project is also exploring whether the presence of heat-loving ("thermophilic") bacteria on cold sea-floors might be a tell-tale sign of the presence of oil reservoirs below. If so, mapping and tracking the distribution of such bacteria, which might have seeped out of the reservoirs, could be a valuable, environmentally less invasive tool for oil companies to use when seeking new reserves – as well as helping to reduce the risk of unsuccessful drilling. Testing of the idea is now beginning off Canada’s Atlantic coast.
Dr Hubert concludes: “Our overall aim is to identify ways of making oil recovery more environmentally friendly. If we end up continuing to rely on fossil fuels for a few more years or decades then the imperative must be to meet our energy needs efficiently and with minimum impact on the environment.”
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