September 28, 2022

A small device could help store carbon on a large scale

As time is running out to stop global warming from causing catastrophic damage, organizations such as the United Nations are calling for an urgent scale-up of technology to trap and store carbon dioxide.

To have an impact, huge amounts of carbon dioxide will need to be captured and injected underground into rock formations. But the long-term effectiveness and reliability of this process remains uncertain.

To assess the fate of large-scale underground storage, Stanford University scientists turned to a tiny device. It’s called a lab-on-a-chip, or 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, researchers are now using it to study how rocks react and change when exposed to gases and acids.

The results, published in the journal Proceedings of the National Academy of Sciencesshould help researchers assess the fate of carbon dioxide and other gases and wastes stored at specific geological sites.

Carbon capture and storage is on the rise globally, with 30 major projects already underway and at least three times as many planned. Most of these projects trap greenhouse gases in saline aquifers or in oil and gas wells.

Injection into rock formations “can lead to complex geochemical reactions, some of which can cause dramatic structural changes in rock that are difficult to predict,” said Ilenia Battiato, a Stanford energy resources engineering professor who has led the new study.

Scientists have typically used computer simulations to predict these changes. But these models don’t always get the right precise mechanics. In fact, some reactions don’t last more than a second, while others can last for years. Additionally, the formation of various minerals from ongoing chemical reactions and changes in the shape and chemistry of rock surfaces all affect reactions.

For a direct, real-time understanding of the progress of this geochemical reaction, the Stanford team collected eight rock samples from the Marcellus Shale in West Virginia and the Wolfcamp Shale in Texas. After cutting and polishing the rock shards into tiny pieces of sand, 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 minerals on a microscopic scale and at sub-second speeds.

According to the researchers, no current technology can provide the detailed insight into these rock-chemistry interactions that this lab-on-chip setup provides. Scientists could use the insights gained from these microfluidic studies to improve the accuracy of carbon storage model predictions.

Source: Bowen Ling et al. Probing multi-scale dissolution dynamics in natural rocks using microfluidics and compositional analysis. PNAS2022.