By Zak Milner
Is hydrogen a good alternative to fossil fuels?
Burning fossil fuels – oil, coal, natural gas – has released aprox. 735 billion tonnes of CO2 since the industrial revolution. CO2 is a greenhouse gas, and is the major driver of human-induced climate change. To avoid catastrophic consequences to the climate and the lives of future generations, scientists are searching for sustainable, cleaner energy sources. Hydrogen gas (H2) may be one such alternative. In contrast to fossil fuels, when hydrogen gas is combusted, no CO2 is released.
How is natural hydrogen used to generate energy?
H2 is already being produced – half of it through the process of steam-methane reforming (SMR), in which methane gas is reacted with steam at high temperatures and pressures. Water electrolysis is another major production process – hydrogen and oxygen molecules are physically broken apart using electricity.
What are the problems with current production?
SMR produces CO2 as a by-product. This can only be sustainable with low-cost storage of the CO2. Water electrolysis requires electricity. It will have to make sure that this power comes from renewable sources, and (again) there is a cost-barrier. The production cost of natural hydrogen is 2 to 10 times cheaper than both current production processes. Could naturally occurring, zero-carbon hydrogen play a role in this emerging industry?
The Malian hydrogen discovery
In 2015, natural hydrogen company Hydroma came across H2 by chance, whilst drilling to pump water for Bourakebougou, Mali. After analysis of the well Bougou-1, it was proven that the gas had a concentration of 98% pure H2. This is the purest naturally occurring hydrogen ever to have been discovered. A further 12 exploratory wells were analysed, and the size of the hydrogen field has been estimated at 8km in diameter. Since the discovery of the system, Hydroma are has used H2 to provide electricity to the local village. Some scientists believe gas generation will continue for thousands of years, sustainably decarbonising the local community.
How is natural hydrogen formed?
The process of H2 formation within the subsurface is similar to the well-understood formation of petroleum. It is hypothesised that for H2 generation to occur, there must be 1) a U/Fe rich source, 2) a reservoir rock and 3) a geological trap. Research indicates the Malian H2 is generated from deep source rocks, Archean in age. In this particular system, the H2 is then trapped and sealed in 5 reservoirs, overlain by 5 solidified lava flows.
So, what are the problems?
For many years the oil and gas industry has dismissed the existence of natural hydrogen. Nigel Smith writes, “From a geologic perspective, hydrogen has been neglected”, in his 2005 review of natural hydrogen. Oil and gas are generated from sediments rich in organic-matter, rather than ancient iron or uranium-rich rocks. The differing geological systems in which these commodities form therefore means petroleum companies have never come across economically significant concentrations of H2.
The mining industry would perhaps be more likely to come across natural hydrogen, however these companies rarely take gas compositional data. Furthermore, the explosions and other mine formation processes degasses the near-surface environment, releasing all near-surface gases into the atmosphere thus eliminating any chance to detect H2.
Natural hydrogen is very difficult to detect…
The key factor in commercialisation will be overcoming the difficulty in detection of natural hydrogen. Firstly, the hydrogen molecule is extremely small, making it very easy to escape into the atmosphere. Second, H2 is very reactive with oxidants in near surface environments and is taken up in these chemical reactions. Thirdly, H2 is consumed by microorganisms in the subsurface. Therefore, in order to detect true volumes and gas compositions of H2 we must look into drilling at depth where these factors are excluded.
Is Mali a one-off H2 discovery?
No. A recent comprehensive review of natural hydrogen reports 100s of global occurrences over 10% gas concentration. It is important to note that these are all accidental discoveries, rather than intentional ones. It is understood that wells in Eastern Siberia are flowing H2 gas at a rate of 100,000m3 per day. This provides an exciting prospect of more of these hydrogen fields to be discovered and, with further research and targeted exploration, this form of hydrogen could represent an inexhaustible source of green energy.
Image: Sophie Draper