As the world looks to decarbonize, governments are promoting hydrogen, a somewhat controversial energy source, as an important component of that effort. But that means there will need to be locations to store the hydrogen, a notoriously tricky process.
Researchers at Sandia National Laboratories in Albuquerque are examining some of the possibilities for storing hydrogen and have partnered with the U.S. Department of Energy’s Subsurface Hydrogen Assessment, Storage and Technology Acceleration project.
A recent study published in the International Journal of Hydrogen Energy looks at using depleted natural gas or petroleum fields for subterranean storage. Sandia chemical engineer Tuan Ho is leading that research.
Ho said that while it is possible to store hydrogen above ground, the capacity for such storage is very small.
“If you are thinking about a future hydrogen economy where you need to store huge amounts of hydrogen, then an underground storage facility is the best way to do it because it has a very high capacity for storage,” he said.
Hydrogen has yet to gain full support from the public and some environmental advocacy groups are concerned that it might prolong the extraction of fossil fuels, as one way to isolate hydrogen is by breaking apart the methane molecules found in natural gas.
A less controversial way to obtain hydrogen is by using renewable energy sources to power electrolysis, essentially separating hydrogen atoms from water molecules. However, critics of hydrogen energy say that electrolysis uses a tremendous amount of energy that could be put to better use elsewhere.
Despite those concerns, new hydrogen projects are being proposed each year. The federal government has also created incentives and provided funding for hydrogen projects.
Underground storage is already taking place in certain areas, Don Conley, the manager for Sandia’s underground hydrogen storage work, said. For example, there are areas where hydrogen is stored inside salt caverns. But that type of storage is not available everywhere and a hydrogen economy will require a lot of storage in part because hydrogen has low energy density, Conley said.
“The problem is, salt isn’t everywhere in the US where you would want to store hydrogen so you have to come up with other clever ways to store it,” Conley said.
When it comes to subterranean storage, Conley said the geology makes all the difference. The formations have to be able to hold the hydrogen in place and not have it migrate out of the reservoir.
While he said there is still research needed into subterranean hydrogen storage, he said there’s also a lot of site-specific analysis that would need to be done before an area could be used for underground storage.
“It’s less research and really just more experimentation and testing to characterize the site,” he said.
When it comes down to storing hydrogen in the subsurface, Conley said there are two questions that potential businesses have—“am I going to lose hydrogen” and “what’s the hydrogen going to look like when it comes back.”
He said answering those questions can be site specific.
“But before you ever even get to that step, we do have more research to do,” he said.
That could include looking at how hydrogen interacts with various types of rocks and how it might mix with gas in the subsurface.
Conley said Ho’s research showed that clay-rich caprock has the potential to contain stored hydrogen in depleted gas reservoirs. He said that was the biggest surprise for him and called it a pleasant surprise. But, Conley added, more research is needed on other types of rock.
Ho published his findings on clay last year in the journal Sustainable Energy & Fuels. One reason that depleted gas reservoirs could be ideal for storing hydrogen, according to Ho’s research, is that the hydrogen doesn’t tend to travel through the watery gaps in the layers of clay. That means hydrogen is unlikely to leak out if it is placed in storage in a depleted gas reservoir.
Ho explained that his research used experimental and computational techniques—meaning he performed tests and used computer models—-to investigate how hydrogen interacts with the cap rock—a geological layer of hard, impervious stones that often overlays oil and gas deposits—as well as with the more porous sandstone in the depleted oil and gas reservoirs.
The team used samples that Ho said are representative of typical depleted oil and gas reservoirs.
Because these reservoirs contain some natural gas, there is the potential that some of the natural gas will be released during the process of injecting and removing hydrogen from storage. But, Ho said, that will likely be a small amount of methane.
One of the next steps will be to test the research in the field, though Sandia has not yet chosen a location for those tests.
“I very much would like to do a field test within the next three or four years to prove the concepts that he’s discovering in his project in an actual demonstration,” Conley said.
He said the team is “particularly pleased” with the results Ho has seen in the way hydrogen interacts with clays.
