THE oil industry, operating on a gigantic scale, might seem at first sight to have little to learn from the intricacies of medical diagnosis and therapies. Yet nanotechnology developed for medical applications could form a model for ways of exploiting oil reserves that conventional methods cannot reach.
Oilfields deemed exhausted when all the free-flowing oil has been extracted still harbour plenty of the stuff, perhaps twice as much as what has been pumped conventionally, says Iraj Ershaghi, a petroleum engineer at the University of Southern California in Los Angeles. A conservative estimate suggests that the remaining oil in old US fields amounts to “at least 360 billion barrels”, he says.
That oil is clinging to the grains in the sedimentary rock, like the greasy residue on a frying pan, or confined to small porous structures in the rock away from the main oil trap. That makes pinpointing it challenging and extracting it tricky, according to Sean Murphy, manager of the Advanced Energy Consortium (AEC) at the University of Texas at Austin, backed by 10 oil and gas companies.
Current techniques to locate oil include drilling core samples, which provide a detailed map of the bedrock within a very small area, and using seismic imaging to make a general map of the whole field. The results are reminiscent of the kind of information doctors get when probing the body using biopsies and X-ray scans, respectively.
In medical imaging, nanoparticles coated with antibodies can latch onto tumour cells, offering a new way to highlight their presence. Murphy says nanotechnology could also help to locate oil pockets within oilfields and improve the efficiency of oil recovery. Since 2008, the AEC has invested $30 million into researching these applications.
The first step towards fully exploiting old oilfields is to establish precisely where the remaining oil is, so that extraction can focus on those locations. Oil companies already flush water through old oilfields to try to recover some of the stubborn residues, and James Tour at Rice University in Houston, Texas, thinks sprinkling the water with nanoparticles could help identify exactly where the oil lies. He has devised nanoparticles with a layer of water-soluble polymers to prevent the nanoparticles clumping together, ensuring they do not become too large to get inside pores in the rock as the water carrying them is pumped through. The nanoparticles are also coated with hydrocarbon-loving compounds that can be stripped away by oil if the nanoparticles encounter significant deposits. “If you get the nanoparticle back and it has none of these chemicals, then you’ll know it has seen a lot of oil below,” he says.
Tour’s nanoparticles are carried along by the flow of water, but Ayusman Sen at Pennsylvania State University in University Park is trying to develop nanoparticles that don’t need to be pumped under pressure. Instead they spread through the naturally occurring brine in an oilfield and into the porous rock to locate oil. Previous studies have shown that something as simple as an acid-doped oil droplet floating on an alkaline solution can move if the solution becomes more alkaline in a certain direction. This gradient causes the edges of the droplet to leach acid into the solution at slightly different rates, effectively driving it on. Sen’s nanoparticles will move by exploiting the saline gradient between the fresh water in which they are pumped and the brine in the oilfield. They will also be coated with a chemical that is attracted to hydrocarbons, meaning they “will actively move around and ‘look’ for oil”, he says.
Nanoparticles attached to a tumour in the body can signal their presence by changing the wavelength of the light reflected when an infrared laser is shone at the affected tissue, but that’s not possible from deep within an oilfield. Once Sen’s nanoparticles have powered themselves away from the fresh water in which they arrived, they are essentially impossible to recover. They cannot report back on their findings.
Tour’s nanoparticles stay close to areas from where they can be pumped out, but all they can tell us is whether they encountered oil. What is needed is a way to backtrack and figure out where the nanoparticles were in the reservoir when they saw the oil, says Murphy – and that is not yet possible.
While much remains to be done to refine these techniques, if the location of the oil is already known, then nanotechnology could make its extraction more efficient. Oil companies already add detergent to the water flushed into old wells. Inside the rock pores, the detergent frees oil from the surface of individual grains and forms an emulsion, which can be recovered and broken down to extract the oil. The process is of limited effectiveness, however, if little of the detergent makes it into the oil-filled pores.
Once again, the answer might lie in borrowing ideas from medical nanotech. The pharmaceutical industry is experimenting with the delivery of anti-cancer drugs using nanocapsules that only release their contents on contact with a cancerous cell. This avoids flooding healthy tissue with drugs that are both potent and expensive. Jenn-Tai Liang, a petroleum engineer at the University of Kansas in Lawrence, is pursuing a similar idea using nanocapsules filled with detergent. He says they have two advantages: they are small enough to penetrate the tiny pores, and they only release their detergent in the presence of oil.
Although still in the early stages of development, nanotechnology could yet have a big future in oil exploration.