Subterranean Storage of Hydrogen
“You want the hydrogen to stay where you inject it,” Tuan said. “You don’t want it to migrate away from the storage zone and get lost. That’s just a waste of money, which is a big concern for any storage facility.”
Tuan’s collaborators at the University of Oklahoma used experiments to study how hydrogen interacts with samples of sandstone and shale. They found that hydrogen does not stay inside sandstone after it is pumped out, but up to 10% of the adsorbed gas got stuck inside the shale sample, Tuan said. These results were confirmed by Tuan’s computer simulations.
Taking a closer look at a specific type of clay that is common in the shale around oil and gas reservoirs, Tuan conducted computer simulations of the molecular interactions between layers of montmorillonite clay, water and hydrogen. He found that hydrogen does not prefer to go into the watery gaps between mineral layers of that kind of clay.
This means that the loss of hydrogen in clay due to getting stuck or moving through it would be tiny, Tuan said. This is quite positive for underground storage of hydrogen. These findings on clay were published last year in the journal Sustainable Energy and Fuels.
Additional absorption experiments are being conducted at Stevens Institute of Technology and the University of Oklahoma to confirm the molecular simulation results, Tuan said.
Risks of contamination?
Using both experiments and simulation, Tuan’s team found that residual natural gas can be released from the rock into the hydrogen when hydrogen is injected into a depleted natural gas reservoir. This means that when the hydrogen is removed for use, it will contain a small amount of natural gas, Tuan said.
“That’s not terrible because natural gas still has energy, but it contains carbon, so when this hydrogen is burned, it will produce a small amount of carbon dioxide,” Tuan said. “It’s something we need to be aware of.”
Tuan’s team, principally Sandia postdoctoral researcher Aditya Choudhary, is currently studying the effects of hydrogen on a depleted oil reservoir and how leftover oil might contaminate or interact with hydrogen gas using both molecular simulations and experiments.
The findings from Tuan’s research can be used to inform and guide large field-scale tests of underground hydrogen storage, said Don, who also manages Sandia’s portion of DOE Office of Fossil Energy and Carbon Management’s Subsurface Hydrogen Assessment, Storage, and Technology Acceleration project. The project plans to conduct such a field-scale test in the future to demonstrate the feasibility of depleted oil and natural gas reservoirs for hydrogen storage, he added.
Additional research is needed to understand how microorganisms and other chemicals in depleted petroleum reservoirs might interact with stored hydrogen, Tuan said.
“If we want to create a hydrogen economy, we really need widely distributed means of storing large quantities of hydrogen,” Don said. “Storage in salt is excellent where it exists, but it can’t be the sole option. So, we’re turning to depleted oil and gas reservoirs and aquifers as more geologically distributed means of storing large quantities of hydrogen. It’s all in the name of decarbonizing the energy sector.”
Mollie Rappe is Senior Corporate Communications Specialist at Sandia National Laboratories. The article was originally posted to the website of Sandia Labs.
