The U.S. Geological Survey has identified 2 sources of natural hydrogen, a renewable source of clean energy.
Researchers at the U.S. Geological Survey (USGS) have identified a previously overlooked potential source of clean energy that could increase the renewability and lower the carbon footprint of the nation’s energy portfolio – natural hydrogen gas trapped deep underground in rock formations. Though still requiring further study, this geologic hydrogen could provide enough clean-burning fuel to last hundreds of years if even a small fraction proves economically recoverable.
While hydrogen is expected to play an important role in future energy systems, the vast majority currently used is manufactured from natural gas, which consumes energy and releases large amounts of carbon dioxide. However, USGS scientists estimate that significant volumes of natural hydrogen gas generated within the Earth’s crust have accumulated in underground rock formations over millions of years.
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Early assessments from modeling the global resource potential show there are at least two major areas in the United States with promising geology to contain large natural hydrogen accumulations: along the Atlantic coastal plain and in central states like the Great Plains and Upper Midwest.
The Atlantic area stretches along most of the East Coast and is associated with a band of iron-rich rocks buried deep under the ocean floor, formed as the Atlantic basin opened up. Surveys confirm the iron has undergone chemical reactions with water to produce natural hydrogen that likely migrated inland towards shore trapped in sedimentary rock layers.
The central U.S. area is related to ancient rift zones like the Midcontinent Rift underlying Lake Superior about 1.1 billion years ago. Though failing to split North America, it brought vast quantities of natural hydrogen-generating iron-rich minerals closer to the surface.
Natural hydrogen forms underground through various natural processes, but researchers agree a primary mechanism is when groundwater circulates and reacts with iron-rich minerals like olivine. This causes the water to be reduced into its components—oxygen bonds to the iron, while the hydrogen gas escapes into the porous spaces within the surrounding rock.
Once formed, natural hydrogen may be consumed by certain microbes or during the formation of oil and gas deposits. However, any remaining free hydrogen can potentially migrate further and accumulate in other reservoir rocks with the right characteristics—similar to how oil and natural gas become trapped by impermeable cap rocks.
For decades, geologists assumed natural hydrogen reserves were too small to be effectively trapped. However, recent studies show the diameter of a hydrogen molecule is similar to helium, which has accumulated and been preserved in some reservoirs for over 100 million years. This suggests natural hydrogen could also be trapped for geologically long timespans under the right conditions.
USGS is incorporating all these factors into developing a “natural hydrogen system” model to understand how, where, and in what volumes hydrogen may be generated, migrated, accumulated, and preserved, borrowing from conceptual models used in petroleum geology.
If hydrogen accumulations are confirmed, finding and extracting this natural gas would use many strategies and technologies similar to current oil and gas exploration and drilling methods. However, some adjustments would be needed since hydrogen can cause embrittlement of conventional steel equipment.
Interestingly, some scientists suggest these natural hydrogen accumulations may be continually “renewable” based on the rates at which they are generated versus depleted. There are also proposals that reservoir traps may not even be needed – with hydrogen being extracted directly from source rocks currently generating it or by injecting hot water to accelerate production similar to enhanced geothermal systems.
While the potential of geologic natural hydrogen as a clean energy source is promising, significant uncertainties still need to be resolved through further investigation. The USGS is directing research efforts to map areas most prospective for hydrogen traps, develop exploration tools and strategies, reduce uncertainties around the hydrogen system components, and get better empirical data on viable, recoverable volumes.
Realizing the full potential of this resource could help the U.S. meet future energy needs with a clean, renewable source. However, many key knowledge gaps still remain to be bridged through continued scientific study before its viability can be proven.
