Researchers at Rice University have shown that adding modified graphene nanoribbons to a polymer and then microwaving the mixture appears to reinforce wellbores drilled to extract oil and natural gas, which can make wells more stable and reduce production costs.
The team 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.
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. 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. Similarly, the toughness of the composite increased by a factor of six. According to the team, that indicates the composite can absorb about six times more energy before failure. 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.
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. They stated that this GNR-based method is a far more practical and cost-effective way to increase the stability of a well over a long period.