Long-Term Storage of Carbon Dioxide in Soil Confirmed

In the ongoing battle against climate change, strategies beyond mere reduction of carbon dioxide (CO2) emissions are gaining traction, particularly Carbon Capture and Storage (CCS). This approach involves capturing CO2 either directly from the atmosphere or at its source, such as power plants, and storing it permanently underground. However, the long-term fate of this stored CO2 has remained uncertain. Recent simulations conducted by researchers at the Technical University of Vienna (TU Wien) provide new insights, demonstrating that CO2 can indeed be stored safely and indefinitely in the earth.

Marco De Paoli, a researcher at TU Wien's Institute of Fluid Mechanics and Heat Transfer, secured a EUR1.5 million ERC Starting Grant to develop methods for describing the flow of liquids through porous materials. Currently collaborating with the University of Twente in the Netherlands, De Paoli is set to initiate this ERC project at TU Wien later this year.

In complex simulations run on supercomputers, De Paoli and colleagues from Italy and the UK have extensively analyzed the interactions between CO2 and groundwater within porous rock. At significant depths, the pressure transforms CO2 into a liquid state. Despite its lower density compared to water, the liquid CO2 does not rise when injected into groundwater; instead, it dissolves, resulting in a liquid mixture that is denser than the surrounding water.

De Paoli explains that this density difference creates a compelling dynamic within the porous rock. The regions with higher CO2 concentration cause the water to sink more rapidly, enhancing the mixing process and forming a network of areas with varying CO2 saturation.

However, this phenomenon is not universally applicable. For effective storage, a relatively impermeable layer of rock is essential to allow the CO2 to accumulate before dissolving. Additionally, the underlying rock must be sufficiently porous to facilitate the downward movement of the CO2-laden water.

De Paoli emphasizes that such geological conditions are not uncommon. He cites former oil reservoirs and saline aquifers as examples, noting that Austria alone has at least six such aquifers suitable for this purpose.

The research team concluded that under the right geological conditions, CO2 can remain in the earth indefinitely. Even potential geological changes, such as earthquakes or human activities, would not disrupt this storage. From their calculations, the researchers have also developed straightforward models that can be utilized in practical applications, such as predicting CO2 flow in the ground or formulating injection strategies.

In the coming years, De Paoli aims to address further critical questions related to this research. He is particularly interested in how the rock properties may change when exposed to CO2-rich water. Specific chemical reactions could lead to the dissolution of minerals in the rock, potentially increasing the CO2 flow downward. Addressing these questions is vital for mitigating the effects of climate change effectively.