cement factory
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There is a challenge of making sure that carbon dioxide stays in the ground when it is injected.

Climate models have predicted for a long time that extreme heat waves of the sort experienced by millions of people this summer would become more common at the levels of planet-warming gases in Earth's atmosphere. As emissions and temperatures continue to rise, there is growing scientific consensus that countries will need to actively remove and manage CO 2 for the world to avoid warming beyond the threshold of 1.5 degrees.

CO 2 is injected into rock formations to keep carbon out of the atmosphere. There are still questions that need to be answered.

Minerals dissolve in a 3 mm square sample of Marcellus shale during the injection of acid. Dynamic flow and reactive transport experiments are performed by using a fluorescent microscopy technique, which allows for clear images to be captured every 100 microseconds. Credit: Ling et al. 2022, Proceedings of the National Academy of Sciences / Stanford University

"Injecting carbon dioxide in storage 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, the study's primary investigator.

Reactions to something.

Earth scientists have been trying to predict how injections of CO 2 or other fluids will affect a rock formation with simulations.

Existing models don't reliably predict the interplay and full consequences of geochemical reactions, which often produce tighter seals by plugging pathways with dissolved minerals, but can also lead to cracks and wormholes that can allow buried carbon dioxide to affect drinking water or escape to the atmosphere. There are many reactions. They control the effectiveness of the seal.

The wide range of time and spatial scales is one of the chief modeling challenges. Reactions can last for months or even years. As reactions progress, the evolving mix and concentration of various minerals in any given patch of rock, and changes to the geometry and chemistry of the rock surface, influence fluid chemistry, which in turn affects fracture and possible pathways for leaks

There's a lab on a chip.

Scientists refer to a "lab on a chip" when describing the new solution. It's called a "rock on a chip" because the technology involves putting a small piece of rock into a cell.

The researchers used rock samples from West Virginia and Texas to demonstrate their invention. They cut and polished the bits of rock that were no bigger than a few grains of sand. The samples were put into a chamber with two small inlets that could be used to inject acid solutions. They used high-speed cameras and microscopes to watch how chemical reactions cause individual mineral grains in the samples to dissolution.

The idea of miniaturizing research that once required large labs cuts across Earth sciences, biomedicine, chemistry, and other fields. You can describe it better if you can see it. He said that the observations have a connection with the ability to assess and design for safety. No current technologies approach the level of detail possible with this new device, which is why geologists are able to examine rocks under a microscope.

Maximizing for safety.

The role of carbon removal in government plans for addressing climate change and the hundreds of millions of dollars now flowing to the technology from private investors make it a matter of growing importance. Projects that remove CO 2 directly from the atmosphere are only in pilot scale. More than 100 projects in development worldwide and the U.S. government are examples of those that catch emissions at the source.

Some carbon storage plans don't bury carbon underground. It is possible that geological storage could be made more stable and secure with the new technology. To make good predictions about what's going to happen once you inject CO 2, researchers need to incorporate this knowledge in their models.

The same platform will be used by Battiato and colleagues to study the reactions triggered by injections of waste water from oil production, desalination plants, and industry. Although underground hydrogen storage is often cited as a promising solution to ensure safe storage of the highly flammable gas at large scale, testing it out at even pilot scale will require better screening tools and understanding of biogeochemical reactions.

More information: Probing multiscale dissolution dynamics in natural rocks through microfluidics and compositional analysis, Proceedings of the National Academy of Sciences, 2022. doi.org/10.1073/pnas.2122520119 Journal information: Proceedings of the National Academy of Sciences