Small changes with regard to oilfield practice could enable the offshore industry to gain a more sustainable solution to environmental and commercial threats posed by harmful bacteria in subsea oil deposits, according to new research.
A research led by Newcastle University and funded by the Engineering and Physical Sciences Research Council (EPSRC) is exploring ways to address the problems associated to a kind of bacteria that reduces sulphate in offshore oil deposits.
Thriving in oxygen-free, watery environments, the sulphate-reducing bacteria can lie dormant for long periods but when they get activated, they breathe sulphates and exhale toxic, corrosive hydrogen sulphide (H2S).
Called ‘reservoir souring’, the bacteria boosts the oil’s sulphur content, thereby reducing its value in the oil market.
As well as being toxic for workers on offshore platforms, hydrogen sulphide is corrosive, causing damage to pipelines and rigs, leading to oil leaks and spills.
Along with a range of private sector, public sector and academic partners from the UK and overseas, the Newcastle-led team is exploring cost-effective measures, such as adjustment of water temperature used during oil production.
The team is also looking at the popular practice of pumping seawater into an oil reservoir to reduce temperatures and make extraction easier. However, this approach poses problems from a reservoir souring perspective.
Canada’s University of Calgary’s visiting professor to Newcastle University and research lead Dr Casey Hubert 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.”
Currently, a method used by the offshore industry to reduce the impact of sulphate-reducing bacteria in oil reservoirs is to inject nitrates. This injection leads to growth of another type of bacteria that out-compete sulphate-reducing bacteria for food.
The research team also finds potential here to improve current practice and make it greener.
Dr Hubert said: "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.
"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 looking at whether the presence of thermophilic bacteria on cold seafloors might be a sign of the presence of oil reservoirs below. If so, tracking of such bacteria could be valuable as it would be an environmentally-less invasive tool for oil companies seeking new reserves.
Testing of this idea has begun off Canada’s Atlantic coast.
Image: Sulphate-reducing bacteria thrive in oxygen-free, watery environments. Photo: courtesy of Newcastle University.