Carbon sequestration will pose great engineering challenges

Climate change is upon us and in order to mitigate its worst effects in the coming decades we’ll need to do two things: stop pumping further CO2 into the atmosphere and suck out some of the carbon already there.

Yet the idea of carbon storage has received comparatively little attention when it comes to its challenges, which is what a team of researchers in the United States has set out to remedy by trying to work out the lifecycle costs of new carbon storage infrastructure.

Specifically, they wanted to know how managing and disposing of high salinity brines, a by-product of efficient underground carbon sequestration, could be done cost-effectively.

Storing sequestered carbon in CO2 reservoirs underground safely to minimize subsurface pressure accumulation, including the elimination of excess brine from the surface, will require plenty of energy and could be a costly undertaking, the researchers explain.

“Designing massive new infrastructure systems for geological carbon storage with an appreciation for how they intersect with other engineering challenges — in this case the difficulty of managing high salinity brines — will be critical to maximizing the carbon benefits and reducing the system costs,” explains Meagan Mauter, an associate professor of Civil and Environmental Engineering at Stanford University who was an author of a new study.

Brine is concentrated salt water that is extracted from underground reservoirs in order to increase carbon dioxide storage capacity and minimize earthquake risk. For their study the researchers decided to focus on the treatment of brine associated with storing carbon from coal-fired power plants because they are the largest sources of carbon dioxide in the U.S.

“Saline reservoirs are the most likely storage places for captured carbon dioxide because they are large and ubiquitous, but the extracted brines have an average salt concentration that is nearly three times higher than seawater,” the scientists say.

“These brines will either need to be disposed of via deep well injection or desalinated for beneficial reuse,” they explain. “Pumping it underground — an approach that has been used for oil and gas industry wastewater — has been linked to increased earthquake frequency and has led to significant public backlash. But desalinating the brines is significantly more costly and energy intensive due, in part, to the efficiency limits of thermal desalination technologies. It’s an essential, complex step with a potentially huge price tag.”

To maximize their carbon reduction benefits and reduce costs, large-scale carbon storage systems will need to be designed very efficiently by engineers. “There are water-related implications for most deep decarbonization pathways,”  Mauter says. “The key is understanding these constraints in sufficient detail to design around them or develop engineering solutions that mitigate their impact.”