National Low Carbon Day | Geological Hydrogen: A Green Energy Treasure Hidden Deep Underground

Today is National Low Carbon Day. With the rapid development of human society, the demand for energy is increasing. However, traditional fossil energy such as coal, oil, and natural gas will produce a large amount of carbon dioxide during combustion, exacerbating global warming. Therefore, the search for clean, renewable, and low-carbon energy has become the focus of global attention. Among them, geological hydrogen, as an emerging clean energy, has gradually entered people's field of vision.

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01The “Rainbow Family” of Hydrogen

Hydrogen is one of the most common elements in the universe and is found almost everywhere. Hydrogen is colorless, odorless and highly flammable, and usually requires a certain amount of energy to separate it from other compounds such as water ( H₂O ), methane (CH₄ ) and ammonia ( NH₃ ) . In industry, there are many ways to prepare hydrogen, which can be mainly divided into three types: gray hydrogen, blue hydrogen and green hydrogen, depending on the production method .

Gray hydrogen is hydrogen produced by the combustion or processing of fossil fuels (oil, natural gas, coal, etc.). The production technology of this type of hydrogen is mature and the cost is relatively low. It currently still occupies a dominant position in global hydrogen production. The disadvantage is that it is accompanied by a large amount of greenhouse gas emissions such as carbon dioxide during the preparation process, so it is not a clean energy.

Burning natural gas (Source: Wikipedia)

Blue hydrogen also comes from fossil fuels, but unlike gray hydrogen, blue hydrogen captures and stores the released carbon dioxide during its preparation to reduce greenhouse gas emissions. Therefore, compared with gray hydrogen, blue hydrogen is more environmentally friendly. However, this type of hydrogen can only be regarded as a transitional clean energy solution, after all, its production still relies on fossil fuels.

Post-combustion carbon capture technology (Source: Wikipedia common)

Green hydrogen is hydrogen produced by electrolyzing water with renewable energy sources such as solar energy and wind energy . The entire production process does not emit any greenhouse gases, so it is considered the most environmentally friendly and sustainable type of hydrogen. Although the current production cost is relatively high, with the continuous advancement of technology, green hydrogen is expected to occupy an important position in the future energy system .

Green hydrogen renewable energy production pipeline - Green hydrogen for clean electricity solar and wind turbine facilities ( copyright image of the library, reprinting may cause copyright disputes )

In addition to the above three types, the Victoria Hydrogen Center of Swinburne University of Technology in Australia has even further divided hydrogen into yellow hydrogen, brown hydrogen, turquoise hydrogen, pink hydrogen, and white hydrogen. These eight types of hydrogen from different sources are named after colorful colors, forming a wonderful "rainbow family".

What is even more surprising is that the terms gold hydrogen and natural hydrogen have recently emerged. What type of hydrogen are these?

02 Unlimited potential of geological hydrogen

In fact, the so-called white hydrogen, golden hydrogen, and natural hydrogen are all the protagonists of our discussion today - geological hydrogen , which is a naturally generated hydrogen resource in nature. In 1987, in the Republic of Mali in the interior of West Africa, an oil and gas field exploration company encountered an accident while drilling in the ancient village of Brakeb. The borehole exploded due to the continuous release of flammable gas. After the accident, the borehole was sealed. In 2012, when engineers opened the borehole again, they were surprised to find that it was still emitting flammable gas. After testing, it was found that the hydrogen content was as high as 98%.

Subsequently, the locals installed a generator and built a simple hydrogen power station. What is even more surprising is that after more than ten years of discharge, there is no sign of gas pressure reduction in the borehole, which indicates that hydrogen is being continuously produced and replenished deep underground. Geologists believe that this discovery may be epoch-making, not only breaking the traditional concept that " pure hydrogen is almost impossible to exist near the surface of the earth ", but also drawing people's attention to the development of geological hydrogen.

How is geological hydrogen produced? Geologists believe that geological hydrogen is the result of the interaction between groundwater and iron-rich rocks in the mantle . When groundwater encounters iron-rich rocks under high temperature and pressure, a chemical reaction occurs. For example, water reacts with olivine to become another mineral, serpentine , while releasing hydrogen .

Olivine is a magnesium-iron silicate mineral , usually emerald green or olive green , sometimes light yellow or gray-green , and is named after the color of olives. In the eyes of geologists, olivine is not rare. It is found all over the earth. Olivine and its variants account for more than 50% of the mantle material on the earth, and almost all kinds of extrusive rocks on the earth contain olivine. It is precisely because of the widespread distribution of olivine underground that unique natural conditions are created for the formation of geological hydrogen.

Olivine crystals that have been eroded from lava rock ( Source: Wikipedia )

According to media reports, French scientists have confirmed the formation principle of geological hydrogen through experiments and found that adding catalysts can significantly accelerate the production of hydrogen. Scientists placed water, olivine and aluminum oxide (catalyst) in a tiny pressure cooker called a diamond pressure chamber ( the tiny space inside is about the width of a pencil lead ), and successfully obtained hydrogen after 24 hours of reaction at a high temperature of 200 ℃ to 300 ℃ and a high pressure of 2000 Pa . The experimental results show that the catalyst aluminum oxide can accelerate the natural formation process of geological hydrogen by 7 to 50 times . This new formula for rapid production of hydrogen in large quantities is expected to promote the development and widespread application of geological hydrogen.

03Geological Hydrogen Gold Rush

Many scholars see "geological hydrogen" as an extraordinary opportunity. The reason is that the generation process of geological hydrogen has little impact on the environment, the development process is not only cleaner and cheaper than blue hydrogen or green hydrogen , but also has huge reserves , indicating that it has great potential and application value in the future energy development field.

Relevant data show that the current global demand for hydrogen energy is about 94 million tons per year , and it is expected that by 2050, the global demand for hydrogen energy will increase to 10 times the current level . A study by the United States Geological Survey shows that there are up to 5 trillion tons of hydrogen resources underground in the world . Although most of them cannot be mined with current technology, even obtaining a small part of them will be enough to meet humanity's hydrogen needs for centuries.

Scholars have keenly noticed the development prospects of geological hydrogen, and more and more energy companies have begun to launch geological hydrogen research projects, setting off a "gold rush". The American magazine Science even listed "the discovery of natural hydrogen sources below the surface" as one of the top ten scientific breakthroughs in 2023.

In recent years, many countries have reported cases of geological hydrogen discovery. For example, in May 2023, high-concentration geological hydrogen with reserves of up to 46 million tons was discovered in the Lorraine Basin in France. This may be the largest geological hydrogen deposit in the world to date ; in October 2023, Australia drilled its first geological hydrogen well in South Australia and found that the gas contained a high concentration of hydrogen of up to 73.3% at a depth of 240 meters underground. However, the commercial feasibility of this geological hydrogen field still needs further evaluation. It is expected to be put into trial production by the end of 2024.

However, the exploration and development of geological hydrogen still faces multiple challenges. The first task is to find rich deposits through scientific methods ; secondly, it is necessary to explore effective methods (such as water injection, rock heating, etc.) to stimulate the hydrogen production reaction in underground rock formations and improve the efficiency of hydrogen production to meet the needs of commercial mining; thirdly, the development process also needs to consider how to ensure that the flammable and explosive, large-volume hydrogen can be safely transported from the production site to the use site , and many other problems need to be solved, such as gas compression, chemical synthesis , and pipeline construction .

The “rainbow family” of hydrogen

(Image source: https://www.swinburne.edu.au/news/2022/05/the-colours-of-hydrogen-explained/)

Peridot (Photo: Ma Zhifei)

High-quality peridot is also a beautiful gemstone (Photo: Ma Zhifei)

Serpentine. Under certain temperature and pressure conditions, olivine can be altered and transformed into serpentine through hydrothermal treatment. (Photo: Ma Zhifei)

Serpentine (Photography: Ma Zhifei)

Author: Ma Zhifei, a popular science writer and member of the Beijing Science Writers Association, has written more than 10 popular science books, including "A Dream of Red Mansions" and "Glass Earth". He has won the Ministry of Natural Resources' Excellent Popular Science Book Award, the Wu Dayou Popular Science Book Award, and the China Natural Resources Writers Association's "China Gem Literature Award" Popular Science Works Award.

Reviewer: Li Ruixia, Vice President and Researcher of Sinopec New Star (Beijing) New Energy Research Institute, National Geothermal Center

Produced by: Science Popularization China

Produced by: China Science and Technology Press Co., Ltd., China Science and Technology Publishing House (Beijing) Digital Media Co., Ltd.