Traditional methods of oil recovery call for flooding well formations with water, but often as much as two-thirds of the oil is left behind through this process. Carbon dioxide is more efficient for oil recovery because it dissolves into oil and reduces its viscosity, but that approach also has problems.
For starters, formations are not uniform. Areas and layers that allow oil to pass through easily are interspersed with areas and layers that are less permeable. Injected CO2 flows through areas of high permeability but leaves a lot of oil unswept in areas of low permeability, says Baojun Bai, the Lester Birbeck Endowed Professor of Geosciences and Geological and Petroleum Engineering. The differences in viscosity between the injected CO2 and oil can cause the CO2 to seep through finger-like channels in the formation; the carbon dioxide that’s produced reduces the efficiency of the greenhouse gas storage in formations.
Bai hopes to solve these problems by using small particle gels — ranging in size from a nanometer to a few millimeters — that can be stable under reservoir temperatures for more than a year.
“Injecting particle gels into CO2 flooding formations is a win-win method because particle gels can not only help increase oil recovery, but they also can help keep CO2 contained in the formation and thus increase greenhouse CO2 storage efficiency,” Bai says. “Storing the carbon dioxide underground is environmentally friendly because it keeps the gas out of the atmosphere.”