Researchers from the University of Houston, the Texas Center for Superconductivity at UH and Southwest Petroleum University in Chengdu, China, have come up with a graphene-based method to boost oil recovery, by achieving 15% tertiary oil recovery at a low cost, without the significant volume of chemicals used in most commercial fluids.
The scientists came up with a graphene-based Janus amphiphilic nanosheets – a solution that is is effective at a concentration of just 0.01%, reportedly meeting or exceeding the performance of both conventional and other nanotechnology-based fluids. The low concentration and high efficiency in boosting tertiary oil recovery make the nanofluid both more environmentally friendly and less expensive than options now on the market. Janus nanoparticles have at least two physical properties, allowing different chemical reactions on the same particle.
Estimations are that as much as 75% of recoverable reserves may be left after producers capture hydrocarbons that naturally rise to the surface or are pumped out mechanically, followed by a secondary recovery process using water or gas injection. Traditional “tertiary” recovery involves injecting a chemical mix into the well and can recover between 10% and 20%, according to the researchers. But the large volume of chemicals used in tertiary oil recovery has raised concerns about potential environmental damage.
This is why the results of this work, showing a simple nanofluid flooding (containing only nanoparticles) at low concentration (0.01 wt% or less), show great potential from the environmental and economic perspective.
Previously developed simple nanofluids recover less than 5% of the oil when used at a 0.01% concentration, the scientists reported. That forces oil producers to choose between a higher nanoparticle concentration – adding to the cost – or mixing with polymers or surfactants. In contrast, they describe recovering 15.2% of the oil using their new and simple nanofluid at that concentration – comparable to chemical methods and about three times more efficient than other nanofluids.
According to the researchers, when the graphene-based fluid meets with the brine/oil mixture in the reservoir, the nanosheets in the fluid spontaneously go to the interface, reducing interfacial tension and helping the oil flow toward the production well. “When it is injected, the solution helps detach the oil from the rock surface”. Under certain hydrodynamic conditions, the graphene-based fluid forms a strong elastic and recoverable film at the oil and water interface, instead of forming an emulsion.
Researchers said the difference is due to the asymmetric property of the 2D material. Nanoparticles are usually either hydrophobic – water-repelling, like oil – or hydrophilic, but this material is both Janus and also strictly amphiphilic.