Principal Investigators: Esuru Rita Okoroafor, Henry Galvis Silva, Texas A&M University
A recent Texas A&M University study marks a pioneering initiative to address the need for reliable energy storage solutions, with Underground Hydrogen Storage (UHS) emerging as a promising avenue for storing large quantities of energy to ensure stability during varying energy demands. The study titled, Investigating Alterations in Rock Properties for Underground Hydrogen Storage: A Geochemical and Geomechanical Baseline Study, was led Dr. Esuru Rita Okoroafor, Assistant Professor in the Department of Petroleum Engineering at Texas A&M University and Henry Galvis Silva, Texas A&M University doctoral student, through support by the Texas A&M Energy Institute. This was the first Texas A&M University laboratory experiment to assess the impact of hydrogen storage on different types of rocks. Research found that hydrogen results in only minor alterations in reservoir rocks (sandstone and limestone) with more relevant changes in shale rock (caprock) due to hydrogen exposure. These results demonstrate the importance of petrophysical data on screening UHS sites, site characterization, and hydrogen plume monitoring.
This seed funding resulted in a U.S. Department of Energy ULTRA-H2: Reservoir Management of Natural Hydrogen from Ultramafic Rocks project to develop a method using modeling and experimentation to determine the behavior of a large-scale geologic hydrogen reservoir based on the laboratory-scale data obtained from the preliminary study funded by the Texas A&M Energy Institute.
“By advancing our understanding of hydrogen storage, this research not only aligns with societal needs for sustainable and cleaner energy sources but also positions Texas A&M as a leader in energy research,” explains Dr. Okoroafor. “It offers significant educational opportunities, fosters innovation, supports energy security, and has the potential to stimulate economic growth, thus contributing to the university’s goals of serving the public good and addressing key societal challenges.”
UHS in saline aquifers and depleted gas reservoirs has the potential for long-term energy storage. However, numerous challenges and barriers exist that prevent this technology from becoming a widely available decarbonization solution. The UHS process comprises multiple cycles of injecting and withdrawing hydrogen gas into an underground reservoir. These cycles may elevate the risk of fracturing or failure of the seal integrity in caprock or reservoir rocks causing hydrogen to leak. Furthermore, it is crucial to assess the potential alteration of rocks caused by hydrogen exposure to understand its impact on the mechanical properties of the reservoir rock.
In the preliminary study, Dr. Okoroafor and Galvis conducted static reactivity tests on dry core samples of sandstone and limestone (possible storage rocks), and shale (possible seal rock) that were exposed to hydrogen under pressure for 30 days for shale and limestone, and 90 days for sandstone to establish a baseline of how the geomechanical properties of these rocks might change when exposed to hydrogen.
Results
Findings indicate that only the shale cores showed significant petrophysical changes with a 50% increase in porosity and 200% increase in permeability. If this is observed across different shale samples, then there will be need for further studies to determine if such increase in porosity and permeability could result in hydrogen losses from the storage rock to the seal rock. Compositional changes determined through X-ray diffraction (XRD) analysis before and after hydrogen exposure were observed in all the samples, but these changes were insignificant.
Additionally, geomechanical tests were conducted to assess how rocks were affected by high pressure. After exposure to hydrogen, the shale samples became more brittle with reduced rock strength, making it more susceptible to being fractured. The rock mechanical properties of the sandstone samples did not change significantly. The limestone samples became stiffer, making it less susceptible to deformation after exposure to hydrogen. These findings warrant further investigation at conditions typical of the subsurface, such as presence of saline water in the rock, high temperatures and high pressures.
Acknowledgments
Dr. Okoroafor and Galvis express gratitude for contributions to the project by the Texas A&M Energy Institute‘s Prof. Efstratios Pistikopoulos, University Distinguished Professor, Professor of Chemical Engineering at Texas A&M University, Institute Director, and Dow Chemical Chair, and Dr. Sean Niknezhad, Postdoctoral Research Associate, for financial contributions and laboratory facilities for the experiments; W.D. Von Gonten Labs’ Prof Bill Von Gonten and Michael Stewart for supporting petrophysics and x-ray diffraction experiments; and Texas A&M Center for Infrastructure Renewal National Corrosion and Materials Reliability Lab‘s Dr. Raymundo Case, Professor of Practice in the Department of Materials Science and Engineering, for supplying autoclave reactors and training.