Researchers at NETL and the University of California San Diego have completed a series of studies that found hydrogen — a low-carbon fuel with tremendous potential to help the United States meet its climate change goals — can be stored in the subsurface without significantly altering the layer of protective shale caprock, which seals the storage reservoir and prevents the migration of the gas.

“These initial studies suggest that the extent of reactions activated by hydrogen with caprock is minor under the temperature and pressure conditions that would represent underground hydrogen storage,” the researchers wrote in their paper, “Initial Laboratory Measurements Probing Hydrogen Interactions with Eagle Ford Shale and Pyrite: Potential Implications for Subsurface Hydrogen Storage.”

Published by the American Chemical Society in The Journal of Physical Chemistry, the paper noted that hydrogen is emerging as a clean fuel option for transportation, electricity generation and manufacturing applications. Furthermore, large-scale hydrogen storage will be required as the nation transitions to a virtually carbon- and emissions-free economy.

Domestic, large-volume underground hydrogen storage has been demonstrated safe and effective only in salt dome structures or caverns. However, not all regions have the proper geological prerequisites for energy storage in salt formations, making it imperative to develop alternative safe, large-scale geologic storage sites across the United States.

Storage reservoirs contain three different components: (1) wells for injection and withdrawal of hydrogen, (2) porous rock where that gas is stored and (3) nonporous seal caprock (usually shale). The researchers examined the interactions of hydrogen with formation fluids and shale mineralogy to determine if there was any change in morphology and composition under reservoir conditions. Significant changes could compromise hydrogen storage security.

For their experiments, the researchers used shale from the Western Gulf Basin in south Texas. The samples contained significant concentrations of other materials, including clay, pyrite, dolomite and gypsum. The work was supported by the U.S. Department of Energy, Office of Fossil Energy and Carbon Management through the Subsurface Hydrogen Assessment, Storage, and Technology Acceleration (SHASTA) project.

To understand hydrogen reactivity with shale caprock and begin to address impacts on long-term hydrogen storage, the shale samples were exposed to hydrogen, nitrogen and water under simulated subsurface storage conditions (50 °C and pressurized to 1500 pounds per square inch absolute) for a duration of three to eight weeks. 

The researchers found that exposure of the shale to hydrogen gas alone did not result in any chemical alterations to the shale or any changes in the surface morphology. Exposure of shale to both hydrogen and water and nitrogen and water resulted in changes to the surface morphology as a result of gypsum dissolution and reprecipitation, indicating that hydrogen is not necessary to promote these changes.

“We believe this is the first experimental, peer-reviewed paper to examine the impact of hydrogen on shale caprock. The results show that there are few, if any, reactions. This bodes well for hydrogen storage as a whole and represents a step forward in the development of an economy driven by clean-burning hydrogen fuel,” said NETL Angela Goodman, the study’s corresponding author.

NETL researchers Barbara Kutchko, Deepak Tapriyal and Meghan Brandi served as study authors. Also serving as authors were University of California San Diego researchers Deborah Kim, Samantha Townsley and Vicki Grassian.

NETL is a U.S. Department of Energy national laboratory that drives innovation and delivers solutions for a clean and secure energy future. By leveraging its highly skilled innovators and state-of-the-art research facilities, NETL is advancing carbon management and resource sustainability technologies to enable environmental sustainability for all Americans.