— Tiny sensors coated with the wonder-material graphene and powered by flowing water could expedite the discovery of oil and natural gas reserves, according to university researchers supported by the energy industry.
The idea is to plop the sensors into the water injected down exploration wells where they can then move sideways through cracks and crevices in the Earth in search of hydrocarbons. The electricity generated by the flow of water would allow the sensors to relay their findings to the surface.
"The oil companies realized that in order to more efficiently explore for oil, they need to have some way to investigate what's going on between the wells," Nikhil Koratkar, who led the research at Rensselaer Polytechnic Institute in Troy, New York, told me today.
Currently, oil wells are drilled vertically. This means companies know what's happening at well A and well B, but don't know what happening in the spaces between them. They could drill hundreds of wells, but that gets expensive. Better to drill a few wells and use a new technology to explore laterally.
Armed with $1 million from the oil-industry backed Advanced Energy Consortium to work on a solution, Koratkar, an expert in nanostructured materials and devices, is trying to figure out how to power oil-seeking sensors small enough to fit through pores in the rock.
"When you get down to less than a micron, you can't use a battery, you can't use a normal source of power," he said.
The solution from his team is to coat teeny tiny sensors in graphene, a Nobel Prize worthy crystalline material made with a single layer of carbon atoms that is flexible, stretchy, and can be wrapped around any type of sensor.
Graphene meets water
In lab experiments, Koratkar's team found that a 15 micron by 30 micron sheet of graphene plopped into flowing water generated 85 nanowatts of power. The voltage is generated by friction between ions that stick to the surface of graphene and are pushed along by the fluid flow.
"That friction causes these ions to stick slip, stick slip," he explained. The interaction of these ions with free electrons on the graphene generates harvestable electricity.
For this to work, "there's got to be ions in the water and these ions have to stick to the surface of the graphene," Krotkar noted, emphasing that pure water won't work. In his team's experiments, they added hydrogen chloride to the water.
The lab results were reported in online Tuesday in the journal Nano Letters.
In the field, oil companies may need to add chemicals to the water they use, which if the controversy over fracking in the natural gas sector is any guide could raise eyebrows. Krotkar said oil companies often pump seawater into their wells and that water may contain existing ions that will do the trick.
For now, the electricity generation potential has been demonstrated in the lab. Out in the field, these sensors will need to get their data up to the surface, a difficult task since the power generated is only sufficient send a signal a few inches.
"Once you send these sensors in there, it is very difficult to get them back out. So you got to send them in, sense the data, and relay this back to the surface," he said. "And that, right now, is a huge challenge."
He envisions the deployment of an army of the sensors that relay the data one short hop at a time: sensor A to sensor B, then B to C, and so on.
Another challenge is designing a sensor to detect oil that is powered by the flow of water since oil and water don't mix. "The moment you hit the oil-water interface, we don't know what's going to happen," Krotkar said.
It's possible, he noted, that the sensors could detect gases or changes in the water chemistry before the oil is encountered.
Krotkar's research is oil industry focused, but he said the findings should apply wherever there is a natural motion of a fluid, such as the coming and going of tides. "If you could place a surface in contact with moving water, then one could harvest small amounts of energy," he said.
The potential of harvesting tidal energy, for now at least, is limited to the micro and nano scales, Krotkar noted. The material is one atom thick and its electricity harvesting potential is lost once even a few layers of graphene are stacked together, which seems necessary for the structural integrity of larger pieces.
"Now it might be possible to grow a 1 meter by 1 meter graphene film, but that gets more and more challenging. I don't know how scalable it is," he said, dashing hopes of tidal flats lined with graphene sheets harvesting enough electricity to power homes on the shore.
Instead, he said, outside of oil exploration, the technology could find applications such as self-powered microbots, microsubmarines, even sensors injected into the bloodstream.
"Anytime you go really small, that's where this becomes feasible," he said.
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John Roach is a contributing writer for msnbc.com.