Adding modified graphene nanoribbons to a polymer and then microwaving the mixture appears to reinforce wellbores drilled to extract oil and natural gas, making wells more stable and reducing production costs, Rice University researchers have discovered.

The Rice labs of chemist James Tour and civil/environmental engineer Rouzbeh Shahsavari combined a small amount of the nanoribbons with an oil-based thermoset polymer. The combination then was cured in place with low-power microwaves emanating from the drill assembly, resulting in the composite plugging microscopic fractures. The combination allowed drilling fluid to seep through and destabilize the walls.

"This is a far more practical and cost-effective way to increase the stability of a well over a long period," Tour said.

The study was published in the American Chemical Society's journal ACS Applied Materials & Interfaces. Lead authors were Rice postdoctoral researcher Nam Dong Kim and graduate student Andrew Metzger. MI-SWACO, a Schlumberger Ltd. company, partially supported the research.

In the past, oil and gas operators have attempted to plug fractures with mica, calcium carbonate, gilsonite and asphalt, but the particles are "too large and the method is not efficient enough to stabilize the wellbore," the Rice researchers said. Graphene, a form of carbon, is about 100 times stronger than the strongest steel. Graphene nanoribbons are strips of graphene that are ultra-thin, less than 50 nanometers. One nanometer is equal to one billionth of a meter.

In the lab tests, a polymer-nanoribbon mixture was placed on a sandstone block, similar to the source rock encountered in many wells. The team found that rapidly heating the graphene nanoribbons to more than 200 degrees C with a 30-watt microwave was enough to cause crosslinking in the polymer that had infiltrated the sandstone, Tour said. The microwave energy needed "is just a fraction of that typically used by a kitchen appliance." The nanoribbons were modified in the lab with polypropylene oxide to help disperse in the polymer.

"Mechanical tests on composite-reinforced sandstone showed the process increased its average strength from 5.8 to 13.3 megapascals, a 130% boost in this measurement of internal pressure," Shahsavari said. Similarly, the toughness of the composite increased by a factor of six.

"That indicates the composite can absorb about six times more energy before failure," Shahsavari said. "Mechanical testing at smaller scales via nanoindentation exhibited even more local enhancement, mainly due to the strong interaction between nanoribbons and the polymer. This, combined with the filling effect of the nanoribbon-polymer into the pore spaces of the sandstone, led to the observed enhancements."

The research suggests that a low-power microwave attachment on the drill head may allow for in-well curing of the nanoribbon-polymer solution.

Rice has been at the forefront of cutting edge energy discoveries. Two years ago a Rice team reported that amine-rich compounds were effective at capturing carbon dioxide when combined with carbon-60 molecules, also known as buckminsterfullerenes -- buckyballs (seeDaily GPIDec. 5, 2014). Buckyballs actually were discovered at Rice in 1985 by Nobel Prize laureates Richard Smalley, Robert Curl and Harold Kroto. Smalley, who died in 2005, was a leading advocate of using nanotechnology to advance energy technology.

In 2004, before the unconventional revolution led to global surpluses of oil and gas, Smalley testified before the U.S. Senate that the United States had to find ways to make energy that was "cheap" (see Daily GPIApril 24, 2004). "For worldwide peace and prosperity it needs to be cheap...We simply cannot do this with current technology. We will need revolutionary breakthroughs to even get close."