Graphene nanoribbons help to plug gaps in wellbores

Oil and gas companies could cut costs by reinforcing wellbores with modified graphene nanoribbons that are added to a polymer and then microwaved.

This is the claim of Rice University chemist James Tour and civil and environmental engineer Rouzbeh Shahsavari, who’ve combined the nanoribbons with an oil-based thermoset polymer intended to make wells more stable.

Credit: Nam Dong Kim/Rice University
Credit: Nam Dong Kim/Rice University

According to Rice, when cured in place with low-power microwaves emanating from the drill assembly, the composite would plug the microscopic fractures that allow drilling fluid to seep through and destabilise the walls.

Results of their study have appeared in ACS Applied Materials and Interfaces.

The researchers said that drillers have formerly tried to plug fractures with mica, calcium carbonate, gilsonite and asphalt with limited success because the particles are too large and the method is not efficient enough to stabilise the wellbore.

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

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

In the lab, the nanoribbons were modified with polypropylene oxide to aid their dispersal 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 per cent 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," he 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 researchers suggested a low-power microwave attachment on the drill head would allow for in-well curing of the nanoribbon-polymer solution.