Natural hydrogen and cratons

The race for finding natural hydrogen has begun a few years after the discover of remarkable volumes of the gas in Mali and the publication of an increasing number of technical reports and scientific papers demonstrating its existence either in the subsurface or associated with surface seeps. Besides allowing important advances on the understanding of the geological elements and processes involved in the natural hydrogen generation, migration, and, perhaps, accumulation, it has culminated in one important question for its exploration: which are the best geological settings to find economic accumulations of hydrogen??

In a recent presentation at the HNAT Summit , I have discussed how cratons comprise some of the most interesting settings to find economic accumulations or fields to produce natural hydrogen. Cratons correspond to the core of continents that contain the oldest known rocks and a geological record with ages spanning from more than 4 billions to a few millions years ago. Most of the known geologic hydrogen occurrences described so far are located within cratons. Comprising abnormally thick and cold lithospheric domains, these settings contain a wide range of possible hydrogen sources that include Archean to Paleoproterozoic ultramafic, mafic and other iron-rich rocks of greenstone belt successions and Lake Superior-type deposits. Ancient granites and other radiogenic nuclide-rich igneous assemblages of the basement are also potential drivers for radiolytic reactions, which may also produce helium through time. Basement units of cratons are typically covered by ancient to modern sedimentary rocks preserved within intracratonic depocenters. These successions may contain different types of conventional to unconventional reservoirs, associated or not with Phanerozoic mafic dikes and sills. Known cases revealed that the latter can play a double role in the hydrogen system, both as sources and seals or permeability barriers. The long tectonic history of cratons, on the other hand, culminated with the development of a variable set of structures and deep- to shallow-seated faults that together comprise potential migration pathways and natural hydrogen plays. Interestingly, cratons underlie lowland areas that host the largest acquifers and hydrographic basins of the world. It makes them well drained domains with enough water to infiltrate react with iron-rich sources and produce the natural hydrogen over the geological time.

It is difficult to precise the future of the hydrogen exploration. However, it is clear that the future of this natural resource is intrinsically linked to the ancient cratonic core of the continents. In fact, the only known area that produce natural hydrogen so far is located within an African craton, the Taodeni craton, while the recent achievements the Gold Hydrogens’ Ramsay project in Australia is within the Gawler craton. ?It makes this geological setting even more prolific to explore… Anyway, there is still much work to be done. One of them is to define the most prolific types of [intracratonic] plays to discover and produce natural hydrogen. In the last two years, we have achieved advances on the subject through combined efforts. Meanwhile, interesting exploratory areas have emerged in Brazil, Africa, Australia, North America and Colombia.. Let’s see what will happen!

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