THESIS BY JULIA GUÉLARD*
In the 1980s, three wells drilled by an independent prospector, Don Clarke, revealed the unexpected presence of natural molecular hydrogen (H2) in the underground of Kansas, right in the heart of the North American continent.
Since then, other continental sites have been identified, in Mali and Russia, in particular.
However, the presence of hydrogen in these intracratonic environmentsa remained unexplained, although fluid/rock interactions in the basement rock were strongly suspected of playing a role.
A new well, drilled in 2008, provided the opportunity to answer the question, by studying the three elements of the presumed rock/water/gas reactional system(1). Variable proportions of H2/CH4/N2, as well as helium, present in substantial quantities, were systematically measured at the site.
Analyses of noble gases (figure) indicate a production of H2 in the basement rocks (so-called “crustal”b), while stable C and H isotopes provide information on the consumption/production reactions between H2 and CH4, keys to the dynamic evolution of their concentrations and pressures.
The oxidation of iron(II), widely present in production waters, was identified as the trigger for the production of H2. Iron(II) is supplied by the minerals of the basement rocks (observed in surrounding wells), coming from the greenstone belt.
Therefore natural hydrogen may potentially be found on all continents, wherever these rocks are present.
This research has made it possible to identify the ingredients involved in the production of H2. Now, we need to find out which are the processes responsible for its retention inside sediments.
Future studies will aim to determine the physicochemical parameters enabling to predict the behavior of this natural hydrogen in the subsurface.
* Thesis entitled“Characterization of natural dihydrogen emanations in the intracratonic context. Example of a gas/water/rock interaction in Kansas”.
a- A craton is the stable portion of a continental area.
b- Because they are produced by the earth’s crust.
(1) - J. Guélard, V. Beaumont, V. Rouchon, F. Guyot, D. Pillot, D. Jézéquel, M. Ader, K. D. Newell, et E. Deville (2017), Natural H2 in Kansas: Deep or shallow origin? - Geochem. Geophys. Geosyst., 18, 1841–1865.
>> DOI: 10.1002/2016GC006544
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