Simple tweaks to oilfield practices could provide the offshore industry with more sustainable and cheaper solutions to the health and safety, environmental, and commercial threats posed by harmful bacteria in subsea oil deposits, according to new research in the United Kingdom.
Measures such as adjusting the water temperature used during oil production could offer a way of tackling problems linked to sulfate-reducing bacteria (SRB), the researchers explain.
The U.K. government-controlled Engineering and Physical Sciences Research Council (EPSRC) (Swindon, United Kingdom) is funding the research, which is led by Newcastle University (Newcastle upon Tyne, United Kingdom). The work involves a range of private sector, public sector, and academic partners from the United Kingdom and overseas.
Having first evolved billions of years ago, SRB thrive in oxygen-free, watery environments like those that can be found in offshore oil deposits, according to the researchers. The hydrogen sulfide (H2S) they produce, however, can increase the oil’s sulfur content and reduce its market value in a process known as “reservoir souring.” H2S is also highly toxic, posing hazards to workers on offshore platforms. Meanwhile, its corrosiveness can damage pipelines and rigs—leading to oil leaks and spills.
Some SRB can remain dormant for very long periods. As part of their work to understand how SRB 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.
“Seawater is rich in sulfates, which SRB use for their metabolism,” says Casey Hubert of the University of Calgary (Calgary, Alberta, Canada). Hubert 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,” Hubert adds.
Industry has already shown substantial interest in the research, according to the team, with additional funding secured from major companies 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 can “outcompete” SRB for food, they explain. The Newcastle-led team says it sees major potential to both improve the current practice and make it more environmentally friendly.
“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”, 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.”
Their project also aims to explore whether the presence of thermophilic bacteria on cold sea-floors might be a telling sign of the presence of oil reservoirs below. These thermophilic bacteria are known to become activated when exposed to heat, the researchers explain.
If this theory is correct, the mapping and tracking of such bacteria—which might have seeped out of the reservoirs—could be a valuable, less environmentally invasive tool for oil companies to use when seeking new reserves. This could also help to reduce the risk of unsuccessful drilling, Hubert says.
Testing of the idea is now beginning off Canada’s Atlantic coast.
“Our overall aim is to identify ways of making oil recovery more environmentally friendly,” Hubert says. “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.”