Nanoparticles used to tackle stubborn oil residue in wells
US engineers have demonstrated that it is possible to use nanoparticles to extract the final drops of oil from well water, solving a longstanding problem in industry.
Oil and water are widely believed not to mix. However, the two liquids can mix effectively under certain circumstances, leading to the creation of emulsions of oil in water. This water often carries chemicals deliberately pumped into wells to push oil through cracks and pores underground and towards the surface; under this high-pressure process, some oil and water mixes to form stable emulsions.
This oil is tricky to remove with current methods, and the conundrum is known as the “produced water” problem. Engineers at Shell, which sponsored the research, told the team of Rice University engineers that the final 5 per cent of the oil remained “stubbornly emulsified” with little chance of extraction.
“Injected chemicals and natural surfactants in crude oil can oftentimes chemically stabilise the oil-water interface, leading to small droplets of oil in water which are challenging to break up,” said chemical engineer Professor Sibani Lisa Biswal, who led the study.
Biswal and her colleagues, however, were able to suggest a solution to the produced water problem which uses nanoparticles to extract most the remaining oil.
This uses a compound of magnetic iron nanoparticles and amines; the positively charged amines can help the nanoparticles find and bind to the negatively charged droplets of oil. The oil and the nanoparticles are then pulled from the solution using magnets.
The engineers tested their nanoparticle solution on lab-made emulsions with both model and crude oil. They shook the mixture of nanoparticle solution and emulsion by hand and machine, which caused the oil-water bonds to break down and oil-nanoparticle bonds to form within minutes. This technique removed more than 99 per cent of the emulsified oil, which could be separated from the water by placing a magnet beneath the test tube.
According to Biswal, the magnetic nanoparticles can also be washed with a solvent to recover the oil and then reused. Their testing demonstrated that the nanoparticle solution could be used for at least six cycles.
Now, the researchers are working on a design for an automated reactor to process produced water in bulk and recycle the nanoparticle solution.