Researchers from Saudi Arabia have analyzed the prospects of geological storage of carbon dioxide in salty water-bearing horizons known as aquifers. This approach is considered one of the most promising ways of reducing greenhouse gas emissions.
Aquifers are deep porous rocks filled with salt water which is not suited for drinking or agriculture. They are widespread around the world and have great potential for storing CO₂. At depths greater than 800 meters, carbon dioxide is in a supercritical state, in the form of a dense gas or liquid. In this form, it easily penetrates pores and can be retained in subsoil in a variety of ways: by dissolving in brine (solubility trapping), by entering into chemical reactions with rocks and forming solid minerals (mineralization), by being retained in pores due to capillary forces or by accumulating under impermeable layers of rocks.
After studying these mechanisms, the researchers from the King Fahd University of Petroleum and Minerals have proposed an unusual solution: the use of CO₂ nanobubbles to improve storage efficiency. This refers to gas bubbles with a diameter of less than one micrometer. Unlike ordinary bubbles, they do not float to the surface and do not burst quickly. Due to extremely low buoyancy and the Brownian motion, nanobubbles remain in the liquid for a long time and can evenly penetrate the porous structure of the rock. Their high surface area helps CO₂ rapidly dissolve in brine and activates chemical reactions with minerals. Moreover, the use of nanobubbles can reduce the need for preliminary gas compression, making the injection process cheaper.
However, the technology is still in the early stages of research. Most of the experiments were conducted in laboratory conditions with purified water, whereas CO₂ interacts with multicomponent salt solutions in real aquifers. It is also not entirely clear how nanobubbles behave under the high pressure and temperature characteristic of deep underground formations. Another issue is the high cost of the experiments absent government subsidies.
Nevertheless, the researchers are confident in the great potential of nanobubbles for CO₂ storage, calling on the scientific community to cooperate and proposing to develop uniform evaluation standards, strengthen data exchange between laboratories and begin the first pilot field tests.
