Wellbores drilled to extract oil and gas can be dramatically reinforced with a small amount of modified graphene nanoribbons added to a polymer and microwaved, according to Rice University researchers.
The Rice labs of chemist James Tour and civil and environmental engineer Rouzbeh Shahsavari combined the nanoribbons with an oil-based thermoset polymer intended to make wells more stable and cut production costs. 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 destabilize the walls.
Results of their study appeared in the American Chemical Society journal ACS Applied Materials and Interfaces.
The researchers said that in the past, drillers have tried to plug fractures with mica, calcium carbonate, gilsonite, and asphalt to little avail because the particles are too large and the method is not efficient enough to stabilize 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 30-watt microwave was enough to cause crosslinking in the polymer that had infiltrated the sandstone, Tour says. The microwave energy needed is just a fraction of that typically used by a kitchen appliance, he says.
“This is a far more practical and cost-effective way to increase the stability of a well over a long period,” Tour says.
In the lab, the nanoribbons were functionalized — or 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 percent boost in this measurement of internal pressure, Shahsavari says. 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 says.
“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.
Lead authors of the paper are postdoctoral researcher Nam Dong Kim and graduate student Andrew Metzger, both of Rice. Co-authors are postdoctoral researchers Vahid Hejazi and Seoung-Ki Lee, graduate students Yilun Li and Ruquan Ye, alumni Jason Mann and Anton Kovalchuk and research scientist Carter Kittrell, all of Rice. Tour is the T.T. and W.F. Chao Chair in Chemistry as well as a professor of computer science and of materials science and nanoengineering. Shahsavari is an assistant professor of civil and environmental engineering and of materials science and nanoengineering.
MI-SWACO, a Schlumberger company, partially supported the research.
Source: Rice University