J.-L. Charlou et al.
88
knowledge of the processes responsible for this natural hydrogen production and
of the quantities produced is an essential starting point in the assessment of its
economic potential. This involves field characterisation together with laboratory
experimentation simulating natural conditions.
Research on Mid-Ocean Ridges
The initial objective of research is first and foremost to explore ridge segments.
Exploration may lead to the discovery of sites which are then studied in detail to
determine the geological context and the geochemistry of the fluids emitted.
The second objective is to understand the geochemical and thermodynamic processes resulting in hydrogen production. A third objective is to assess the hydrogen
flow on the active site, to evaluate the resource’s profitability and finally to study industrial recovery concepts and methods with a view to possible future exploitation.
Within the framework of mid-ocean ridge study programmes conducted by Ifremer
over the past 15 years or so, seawater interaction with basalt rock and more specifically with the deepest mantle rock (peridotites) has revealed the existence of a high
natural hydrogen flow from hydrothermal vents, associated with other hydrocarbon
gases. This natural production is an inexhaustible and sustainable energy resource.
This long-standing research, conducted mainly along the slow-spreading Mid-Atlantic
Ridge through deep-sea exploration programmes, has resulted so far in the discovery
of seven active hydrothermal sites producing large quantities of hydrogen (Fig. 5.1).
These results are the outcome of a series of research initiatives conducted successively first of all through the French-American Ridge Atlantic programme (FARA
1989–1996), then through European programmes MAST II-MARFLUX ATJ
(1994–1997), MAST III-AMORES (1997–2000), as well as bilateral French-American and French-Russian cooperation. The many surface and subsurface exploration
campaigns carried out over this period and until 2007 (Ridelente, Microsmoke, Faranaut, Diva, Flores, Iris, Serpentine, Momardream) revealed the serpentinization
process known along slow-spreading ridges and confirmed the close link between
the presence of mantle rock and the production of hydrogen and methane. Generally speaking, seawater-basalt interaction produces fluids which can have different
geochemical signatures and are generally low in hydrogen. High H 2 concentrations
can however be observed during eruptive events. Our work at the Rainbow site
(36° 14′ N-MAR) and Logatchev (13° 45′ N-MAR), located along the Mid-Atlantic
Ridge, shows a high and constant release of hydrogen from 1997 to 2007.
Recent work carried out on the ultraslow-spreading Arctic Ridge confirms the
presence of mantle rock outcrops also associated with hydrogen and methane emissions. Seawater interaction with mantle rocks, at fracture zones, is therefore a phenomenon common to slow- and ultraslow-spreading ridges. This natural chemical
process produces hydrogen (primary gas) in large quantities and inorganic hydrocarbons synthesised by catalysis (Fischer-Tropsch reactions) at high pressure and
high temperature in subcritical or supercritical conditions.
88
knowledge of the processes responsible for this natural hydrogen production and
of the quantities produced is an essential starting point in the assessment of its
economic potential. This involves field characterisation together with laboratory
experimentation simulating natural conditions.
Research on Mid-Ocean Ridges
The initial objective of research is first and foremost to explore ridge segments.
Exploration may lead to the discovery of sites which are then studied in detail to
determine the geological context and the geochemistry of the fluids emitted.
The second objective is to understand the geochemical and thermodynamic processes resulting in hydrogen production. A third objective is to assess the hydrogen
flow on the active site, to evaluate the resource’s profitability and finally to study industrial recovery concepts and methods with a view to possible future exploitation.
Within the framework of mid-ocean ridge study programmes conducted by Ifremer
over the past 15 years or so, seawater interaction with basalt rock and more specifically with the deepest mantle rock (peridotites) has revealed the existence of a high
natural hydrogen flow from hydrothermal vents, associated with other hydrocarbon
gases. This natural production is an inexhaustible and sustainable energy resource.
This long-standing research, conducted mainly along the slow-spreading Mid-Atlantic
Ridge through deep-sea exploration programmes, has resulted so far in the discovery
of seven active hydrothermal sites producing large quantities of hydrogen (Fig. 5.1).
These results are the outcome of a series of research initiatives conducted successively first of all through the French-American Ridge Atlantic programme (FARA
1989–1996), then through European programmes MAST II-MARFLUX ATJ
(1994–1997), MAST III-AMORES (1997–2000), as well as bilateral French-American and French-Russian cooperation. The many surface and subsurface exploration
campaigns carried out over this period and until 2007 (Ridelente, Microsmoke, Faranaut, Diva, Flores, Iris, Serpentine, Momardream) revealed the serpentinization
process known along slow-spreading ridges and confirmed the close link between
the presence of mantle rock and the production of hydrogen and methane. Generally speaking, seawater-basalt interaction produces fluids which can have different
geochemical signatures and are generally low in hydrogen. High H 2 concentrations
can however be observed during eruptive events. Our work at the Rainbow site
(36° 14′ N-MAR) and Logatchev (13° 45′ N-MAR), located along the Mid-Atlantic
Ridge, shows a high and constant release of hydrogen from 1997 to 2007.
Recent work carried out on the ultraslow-spreading Arctic Ridge confirms the
presence of mantle rock outcrops also associated with hydrogen and methane emissions. Seawater interaction with mantle rocks, at fracture zones, is therefore a phenomenon common to slow- and ultraslow-spreading ridges. This natural chemical
process produces hydrogen (primary gas) in large quantities and inorganic hydrocarbons synthesised by catalysis (Fischer-Tropsch reactions) at high pressure and
high temperature in subcritical or supercritical conditions.