As time runs out to keep global warming from causing catastrophic damage, organizations such as the United Nations are calling for urgently scaling up the technology to trap and store carbon dioxide.
To have an impact, huge amounts of carbon dioxide will have to be captured and injected underground into rock formations. But the long-term effectiveness and reliability of this process remain unclear.
To assess the fate of large-scale storage underground, scientists at Stanford University have turned to a tiny device. It’s called a lab-on-chip, or a microfluidic device, and is commonly used to study the physics and chemistry of materials on a microscopic scale. By putting a tiny sliver of shale rock into the device, the researchers are now using it to study how rocks react and change when exposed to gases and acids.
The findings, published in the journal Proceedings of the National Academy of Sciences, should help researchers assess the fate of carbon dioxide and other gases and wastes stored in specific geological sites.
Carbon capture and storage is on the rise around the world, with 30 large projects operating already, and at least three times as many planned. Most of these projects lock away the greenhouse gas in saline aquifers or in oil and gas wells.
Injecting into rock formations “can lead to complex geochemical reactions, some of which may cause dramatic structural changes in the rock that are hard to predict,” said Ilenia Battiato, a professor of energy resources engineering at Stanford who led the new study.
Scientists have typically used computer simulations to predict these changes. But these models don’t always get the precise mechanics right. In reality, some reactions don’t last for more than a second, while others can continue for years. Plus, the formation of various minerals from ongoing chemical reactions, and the changes in the shape and chemistry of rock surfaces all affect the reactions.
For a direct, real-time understanding of this geochemical reaction evolution, the Stanford team took eight rock samples from the Marcellus shale in West Virginia and the Wolfcamp shale in Texas. After cutting and polishing the rock slivers into tiny bits, they enclosed them in a glass chamber, and injected acid solutions into the chamber through small inlets.
Each rock sample contained different amounts of reactive carbonate minerals. The researchers used high-speed cameras and microscopes to observe how chemical reactions dissolved and rearranged the minerals at microscopic scale and sub-second speeds.
No current technologies can provide the detailed look at these rock-chemical interaction that this lab-on-a-chip setup provides, the researchers say. Scientists could use the knowledge gained from such microfluidic studies to improve the prediction accuracy of carbon storage models.
Source: Bowen Ling et al. Probing multiscale dissolution dynamics in natural rocks through microfluidics and compositional analysis. PNAS, 2022.
