Asphaltenes—sometimes called the “cholesterol of petroleum” due to the way they clog pipelines—are a poorly understood fraction of petroleum. But with asphaltene-rich sources such as oil sands and heavy oils gaining importance, researchers are focusing more on a molecular-level understanding of the complex material, according to the cover story in the current issue of Chemical & Engineering News, ACS’ weekly newsmagazine.
|Asphaltene and waxes clogging a crude oil pipeline. Source: London Centre for Nanotechnology. Click to enlarge.|
Asphaltenes are a complex mixture that is thought to be rich in aromatic and heterocyclic compounds, and they have a tremendous effect on the physical properties of crude oil.
“The way the viscosity of crude oil depends on asphaltene content is almost legendary,” says Andrew E. Pomerantz of Schlumberger-Doll Research Center, in Cambridge, Mass., an oil-field services company that specializes in characterizing oil reservoirs. “Viscosity depends more than exponentially on asphaltene content.”
In refining, asphaltenes clog pipes, which can be cleaned. In underground reservoirs, the high viscosity asphaltenes can clog underground rocks, impeding oil extraction. One of the goals of seeking a better understanding of the chemical nature of asphaltenes is to improve oil recovery.
“Enhanced oil recovery is going to loom as a more important player in the oil business,” Mullins says, because current extraction techniques often leave 70% of a field’s oil in the ground. “If you could get even a minor fraction of that stuff out, it’s a lot of oil,” he says, and better compositional and spectroscopic data could help.
...One way to improve recovery is to change the wettability of the rock in the geologic formation surrounding the oil. “If the rock is oil-wet, it holds on to the oil and won’t give it up,” Mullins says. “Enhanced oil recovery comes down to surface science, and the asphaltenes are key players.” If you don’t know the molecular structure, you won’t be able to optimize recovery as effectively, he notes. And as Pomerantz says, “We get a lot of energy from oil, and we’re moving to oil sources that are asphaltene-rich, where these issues are only going to become more important.”
Digging into Asphaltenes, C&EN