As the oil sector increasingly turns to cost-saving technologies to boost oil recovery, researchers at the University of Houston (UH) and China’s Southwest Petroleum University say they have discovered a nanotechnology-based solution capable of recovering more oil from onshore and offshore fields.
The solution: graphene-based Janus amphiphilic nanosheets.
Researchers were able to achieve 15% tertiary oil recovery using a nanofluid of graphene-based amphiphilic nanosheets that are effective at low concentrations, only 0.01%, making it both economical and environmentally friendly.
“Our nanosheets, or nanofluid, is not just good for geological conditions. It also is good for other applications above ground—oil spill cleanup,” Zhifeng Ren, the MD Anderson chair professor of the UH physics department and lead author on a paper describing the work, told Hart Energy.
The findings were unveiled during a time of increasing focus on technology by oil and gas companies looking for cheaper ways to safely unlock hydrocarbons amid a commodity price recovery.
Typically, only about 10% of a reservoir’s original oil in place is recovered during primary recovery, according to the U.S. Department of Energy’s Office of Fossil Fuels. Secondary recovery techniques, which usually involve water or gas injection, can increase the percentage to between 20% and 40%, while tertiary methods “offer prospects for ultimately producing 30% to 60%, or more, of the reservoir's original oil in place.”
As part of the lab experiment, four man-made sandstone rock cores, each with different physical properties, were tested in flooding equipment. The process involved:
- Cleaning the rock cores;
- Saturating cores with brine;
- Establishing initial brine water and oil saturation by oil injection until no more brine water was produced;
- Brine water flooding until no more oil, or 100% water cut, was produced; and
- Nanofluid flooding until no more oil was extracted, researchers said. The total injection volume of nanofluid for each flooding test was 3x to 4x the pore volume.
“We found that in a saline environment, the nanosheets spontaneously approach the oil-water interface, reducing the interfacial tension,” enabling oil to flow to the production well, according to the researchers’ paper. “Furthermore, we found that a solid-like film forms with strong hydrodynamic power. The firm rapidly separates oil and water for slug-like oil displacement.”
With one of the rock cores, researchers recovered 15.2% of the oil using the nanofluid.
“When it is injected, the solution helps detach the oil from the rock surface,” Ren said in a UH news release. 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, he added.
Researchers pointed out that the oil recovery factor is below 5% with other simple nanofluids when used at the same 0.01% concentration. This, as pointed out in the release, could force oil producers to spend more money to increase the nanoparticle concentration or mix in polymers or surfactants. Cost and lower commodity prices were among the reasons the project was pursued, Ren said.
“Our results provide a novel nanofluid flooding method for tertiary oil recovery that is comparable to the sophisticated chemical methods,” they said. “We anticipate that this work will bring simple nanofluid flooding at low concentration to the stage of oil field practice, which could result in oil being recovered in a more environmentally friendly and cost-effective manner.”
But much work still lies ahead. The method has not been field tested, and it is unknown how much it would cost per well compared to other EOR methods and other simple nanofluids. However, Ren said the price won’t be too high mainly because the process is simple and less fluid is used than other methods.
“Our next step is working to further optimize the process, try to reduce costs further and we need to make a larger quantity so that if we work with a company to do a field test we have enough quantity to do a field test,” Ren said.
Others researchers who participated in the project included Ching-Wu (Paul) Chu, chief scientist at the Texas Center for Superconductivity at UH; graduate students Dan Luo and Yuan Liu; researchers Feng Wang and Feng Cao; and Richard C. Willson, professor of chemical and biomolecular engineering. The team also included researchers from Southwest Petroleum University in Chengdu, China: Jingyi Zhu, Xiaogang Li and Zhaozhong Yang.
Velda Addison can be reached at vaddison@hartenergy.com.