Researchers think they may have found an attractive and simpler method to remove oil from produced water at drilling sites using magnetic nanoparticles, a technique that could be used both onshore and in the offshore.

In a study published in theJournal of Nanoparticle Research, engineering researchers at the Cockrell School of Engineering at the University of Texas at Austin (UT) said the new technique may improve water treatment for oil and natural gas production, more efficiently clean up oil spills, and potentially remove lead from drinking water.

"This new technique is really aimed at removing that little bit of oil in that water that needs to be removed before you can consider it treated," said UT's Saebom Ko, who was lead author. Ko, a research associate in the Department of Petroleum and Geosystems Engineering, said, "The advantage of employing magnetic nanoparticles is that the small oil droplets that attach to the nanoparticles are much more quickly separated from water than traditional physical separation processes because magnetic force can be orders of magnitude larger than gravitation."

Nanotechnology's use in the oil and gas industry is not new. The energy industry for years has partnered with scientists at some of the nation's leading universities to advance game-changing technology. Rice University in Houston has been at the forefront for several oil and gas breakthroughs involving nanotechnology research. Last year Rice researchers discovered that adding modified graphene nanoribbons to a polymer and then microwaving the mixture appeared to reinforce drilled wellbores.

Nanoparticles, of different sizes and at different concentrations, can be coated with different chemicals, including polymers, for use in a wide array of applications and industries. Their versatility inspired the UT team to explore how they might be applied to oil production to reduce the environmental footprint and increase drilling efficiency, both onshore and offshore.

Researchers believe the nanoparticle breakthrough could be used to treat freshwater used in hydraulic fracturing (fracking) and to help clean drinking water.

Production methods currently used separate about 95% of the oil from produced water but they leave behind small oil droplets that are difficult to extract, which makes water treatment and disposal more challenging and environmentally risky, the researchers said.

Ko's team included Hugh Daigle, a petroleum and geosystems engineering professor, as well biomedical engineering professor Thomas Milner and researcher Chun Huh.

The team designed surface coatings to create magnetic nanoparticles that could be used to remove oil using high gradient magnetic separation. The technique previously had been successfully used in mining operations to remove metals and in the food industry to remove toxic particles.

The UT design advanced surface coatings for nanoparticles able to adhere to oil droplets using electrostatic force. Basically, the positively charged magnetic nanoparticles latch on to the negatively charged oil droplets through electrostatic attractive force, "similar to how a dust-trapping cloth picks up dust," researchers said.

The process, which takes seconds in laboratory tests, also could happen in reverse: if the target substances have positive surface charges, the magnetic nanoparticles could be coated with negatively charged polymers to attract the target.

"It's a simple idea," Daigle said. "We are leveraging the magnetic properties of these nanoparticles to get them to stick to the oil droplets and essentially magnetize the oil droplets so they can be pulled out with a magnet."

The flexibility of magnetic nanoparticles and the relative ease of the technique have motivated the team to consider different applications.

"The applications can extend far beyond the oilfield because, with an appropriate surface coating design, you can take your magnetic core and coat it with whatever chemical you choose on the outside to stick to the target and pull it out with a magnet," Daigle said.

Researchers are envisioning designs that use the nanoparticles to clean up oil spills in the ocean. They also are exploring how magnetic nanoparticles may be used to remove led and other contaminants from drinking water. Plans are to test some ideas this summer.

Specifically for the oil and gas industry, the team is working on a treatment system that would have capacity to rapidly handle high volumes of oil and water, which would be crucial for onshore and offshore drilling sites.

"We are currently developing a chemical-free regeneration process to reuse nanoparticles," Ko said. "Other regeneration methods use chemicals to extract the oil, resulting in production of other hazardous waste. We believe that by recycling and reusing nanoparticles, it could not only reduce operational costs, but it could be an environmentally friendly process that reduces hazardous waste."

Funding for the tests was provided by Maersk Oil and UT's Nanoparticles for Subsurface Engineering Industrial Affiliates Program.