J.-L. Charlou et al.
94
1 and 2, site 8° S) currently known along the Mid-Atlantic Ridge and preliminary
calculations performed show that this gas flux is gigantic.
These questions are on the agenda and currently under debate within the international scientific community. Hard and fast answers can only be provided by
continuing to explore the deep sea, and in particular slow- and ultraslow-spreading
ridges, through the collection of field data and by seeking new sites, based on two
guiding principles: a scientific multidisciplinary approach and a long term vision.
To estimate the quantity of hydrogen that could be exploited, the natural production-migration process will also need to be understood and modelled on a large
scale. As outlined above, it is now established, mainly based on experimental simulations, that hydration of the oceanic crust generates hydrogen and, to a lesser extent, methane, by rock hydration (peridotites). However, hydrogen production does
not only depend on mineral hydration reactions, as studied in the laboratory, but
also on seawater availability and transport (fluid circulation in rock) in the fracture
area. Diffusive and advective seawater transport in the rock is not independent of
hydration reactions, as these reactions involve major variations in volume (and fracturation) and also produce heat (highly exothermic reactions). Different couplings
occur (fluid chemistry, crystal chemistry, petro-physics) whose complexity can only
be addressed by numerical modelling and appropriate changes in scale (scale of the
mineral, the fracture, large active faults, convection cell, etc.).
Similarly, we know that dihydrogen has high mobility and a high diffusive capacity, which limits its storage possibilities in the natural environment. Yet does
this imply that dihydrogen has a very short residence time in the rocks in which it
is produced? Does it migrate, carried by fluid circulation, in the form of dissolved
gas, or could dihydrogen be trapped locally in the form of gas pockets? Ultimately,
how can dihydrogen reserves be estimated based on degassing balances? Are these
reserves sufficient to consider, in the longer term, the recovery of these gases from
high temperature vents (> 350 °C) located at depths ranging from 2,000 to 4,000 m?
In quite an unexpected way, the relatively high serpentinization rates shown
through experimental work could allow industrial land-based hydrogen production
processes to be considered, using feedstocks containing Fe
2+
that are able to react
in the presence of water to form ferric phases (industrial geoinspired process). Like
natural processes, iron oxidation is accompanied by water reduction and dihydrogen production.
This example of natural dihydrogen clearly illustrates how fundamental research
geared towards the understanding of a natural phenomenon can ultimately lead to
the identification of new avenues towards applied research, with possible industrial
development prospects.
94
1 and 2, site 8° S) currently known along the Mid-Atlantic Ridge and preliminary
calculations performed show that this gas flux is gigantic.
These questions are on the agenda and currently under debate within the international scientific community. Hard and fast answers can only be provided by
continuing to explore the deep sea, and in particular slow- and ultraslow-spreading
ridges, through the collection of field data and by seeking new sites, based on two
guiding principles: a scientific multidisciplinary approach and a long term vision.
To estimate the quantity of hydrogen that could be exploited, the natural production-migration process will also need to be understood and modelled on a large
scale. As outlined above, it is now established, mainly based on experimental simulations, that hydration of the oceanic crust generates hydrogen and, to a lesser extent, methane, by rock hydration (peridotites). However, hydrogen production does
not only depend on mineral hydration reactions, as studied in the laboratory, but
also on seawater availability and transport (fluid circulation in rock) in the fracture
area. Diffusive and advective seawater transport in the rock is not independent of
hydration reactions, as these reactions involve major variations in volume (and fracturation) and also produce heat (highly exothermic reactions). Different couplings
occur (fluid chemistry, crystal chemistry, petro-physics) whose complexity can only
be addressed by numerical modelling and appropriate changes in scale (scale of the
mineral, the fracture, large active faults, convection cell, etc.).
Similarly, we know that dihydrogen has high mobility and a high diffusive capacity, which limits its storage possibilities in the natural environment. Yet does
this imply that dihydrogen has a very short residence time in the rocks in which it
is produced? Does it migrate, carried by fluid circulation, in the form of dissolved
gas, or could dihydrogen be trapped locally in the form of gas pockets? Ultimately,
how can dihydrogen reserves be estimated based on degassing balances? Are these
reserves sufficient to consider, in the longer term, the recovery of these gases from
high temperature vents (> 350 °C) located at depths ranging from 2,000 to 4,000 m?
In quite an unexpected way, the relatively high serpentinization rates shown
through experimental work could allow industrial land-based hydrogen production
processes to be considered, using feedstocks containing Fe
2+
that are able to react
in the presence of water to form ferric phases (industrial geoinspired process). Like
natural processes, iron oxidation is accompanied by water reduction and dihydrogen production.
This example of natural dihydrogen clearly illustrates how fundamental research
geared towards the understanding of a natural phenomenon can ultimately lead to
the identification of new avenues towards applied research, with possible industrial
development prospects.