Carbon dioxide is a powerful gas—it can make soft drinks fizzy, refrigerate in the form of dry ice, and even put out raging fires. As the most abundant greenhouse gas in the atmosphere, however, it’s also the leading cause of climate change. That’s why scientists and engineers are looking to capture produced carbon dioxide from anthropogenic sources, primarily industrial, and put to use it elsewhere, following a mitigation strategy called Carbon Capture, Utilization, and Storage (CCUS).

One way to utilize carbon dioxide is for unconventional oil extraction. By injecting it underground, residual oil can be extracted from depleted reservoirs. But this is not without potential risk. Because carbon dioxide is a good solvent for organic compounds, it can pick up certain hazardous compounds from these reservoirs, which can then find their way into groundwater.

This is the risk that Civil and Environmental Engineering’s Athanasios Karamalidis, Greg Lowry, and Aniela Burant set out to address in their research, “Measurement and Modeling of Setschenow Constants for Selected Hydrophilic Compounds in NaCl and CaCl2 Simulated Carbon Storage Brines,” published in the Accounts of Chemical Research special issue, “Chemistry of Geologic Carbon Storage.” A better understanding of the solubility of hydrophilic organic compounds in concentrated brines has provided models that more accurately predict the solubility of potentially harmful compounds. These models can then be used to predict the behaviors of organic compounds in related oil and gas activities, such as hydraulic fracturing, which also produce large quantities of brine.

We extended all the boundaries of what we know about organic compounds, whether they’re hydrophilic or hydrophobic.

Athanasios Karamalidis, Associate Research Professor, Civil and Environmental Engineering, Carnegie Mellon University

“Now, if we have a good estimate for the solubility in brine or supercritical CO2, we can plug it into our models and get a sense of how a compound might migrate, solubilize, or dissolve in the presence of supercritical carbon dioxide,” says Karamalidis. “We extended all the boundaries of what we know about organic compound solubility in high saline waters, whether they’re hydrophilic or hydrophobic.”

The team continues to work on understanding the behavior of organic compounds in brines and expand to other fields of research.  When it comes to fracking and shale gas operations, the use of biocides—organic compound additives—has always presented a major problem; despite being an essential part of fracking fluids, many biocides are also toxic to humans.

“We try to create an umbrella effort for understanding how organic compounds, either derived from oil reservoirs or added as biocides, behave in underground conditions,” says Karamalidis. “And the reason for doing that is that we want to propose greener, more efficient organic biocides and fracking chemicals for the oil and gas industry that are also environmentally friendly.”

Understanding the subsurface behavior of these compounds in a quantifiable, systematic way can expedite any effort in implementation. With climate change at the forefront of environmental concerns, this research marks a significant step in complementing conventional industrial practices and helping the development of greener technologies for CCUS.