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Nanoreporters tell ‘sour’ oil from ‘sweet’

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An electron microscope image shows carbon black nanoparticles modified by adding polyvinyl alcohol for downhole detection of hydrogen sulfide in oil and gas wells. The nanoreporters were created at Rice University. (Credit: Tour Group/Rice University)

Scientists at Rice University have created a nanoscale detector that checks for and reports on the presence of hydrogen sulfide in crude oil and natural gas while they’re still in the ground. The nanoreporter is based on nanometer-sized carbon material developed by a consortium of Rice labs led by chemist James Tour. Limited exposure to hydrogen sulfide causes sore throats, shortness of breath and dizziness, according to the researchers. The human nose quickly becomes desensitized to hydrogen sulfide, leading to an inability to detect higher concentrations. That can be fatal, they said. On the flip side, hydrogen sulfide is also a biologically important signaling molecule in processes that include pain and inflammation. Tour said chemists have synthesized fluorescent probes to detect it in the body. The Rice team capitalized on that work by using the probes to create downhole detectors for oil fields. Crude oil and natural gas inherently contain hydrogen sulfide, which gives off a “rotten egg” smell. Even a 1 percent trace of sulfur turns oil into what’s known as “sour crude,” which is toxic and corrodes pipelines and transportation vessels, Tour said. The extra steps required to turn the sour into “sweet” crude are costly. So it’s important to know the content of what you’re pumping out of the ground, and the earlier the better,” Tour said. Led by Rice professors Tour, Michael Wong and Mason Tomson and researcher Amy Kan, the university has pioneered efforts to gather information from oil fields through the use of nanoreporters. The nanoreporters were designed to detect and report on the presence and amount of oil in a well that might otherwise be hard to assess. Now the same team, joined by chemist Angel Martí, is employing thermally stable, soluble, highly mobile, carbon black-based nanoreporters modified to look for hydrogen sulfide and report results immediately upon their return to the surface.