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Thesis by Valentine Combaudon : « Mécanismes et quantification de la génération d’hydrogène naturel en contexte intracratonique : le cas du Mid-Rift System (Kansas, USA) » (Natural hydrogen generation mechanisms and quantification in an intracratonic context: the Midcontinent Rift System (Kansas, USA).

For the last ten years or so, geologists have been fascinated by the natural hydrogen (H2) emitted within “cratons”, in the heart of continents. While its presence in subsurface has been identified in many places around the globe, it remains to be ascertained whether the use of this decarbonized energy source is likely to be economically viable. To answer this question and then identify the drilling sites with the greatest potential, large-scale quantification of this resource requires the use of modelling.

Moreover, while the origin and quantity of H2 emitted from the seafloor has been largely understood for decades, the potential of the various minerals in cratonic rocks to produce it, via water-rock interaction reactions, remains unknown. Questions about the source of H2 is nonetheless essential in order to assess the corresponding resource.

This PhD research set about examining the issue, taking as its subject the North American Midcontinent Rift System (MRS) composed of ancient rocks (over 1 billion years old) and extending over thousands of kilometers. The study of these rocks was based on a multi-scale approach (from nm to cm) for which an analytical workflow was developed (Figure 1), based on different observation techniques: microscopy for phase identification, synchrotron for chemical speciation and µ-tomography for estimating volumes of altered minerals [1]. The application of these imaging techniques to various rocks in the Kansas basement, south of the rift, has made it possible to quantify the potential of the geological formations in place to produce natural hydrogen by quantifying the reduced iron in minerals, as well as to estimate the resources already produced via the quantification of oxidized iron.

Figure 1
Figure 1: Analytical workflow used to quantify H2 potential
from a multi-scale rock study.

The implementation of this workflow has enabled the identification of the H2 source rock and the complete characterization of the “hydrogen system” in the southern part of the rift [2] (Figure 2). In addition to this source rock (or generating rock), the reservoir rock and then the cap rock are found above, and it appears that the production of this decarbonized resource remains active there, even though the rocks in question are far older than the oil reservoirs, where fossil hydrocarbons are produced.

Figure 2
Figure 2: Characterization of the Hydrogen system in the southern part of the rift, in the Kansas Precambrian basement.

Finally, the same characterization was conducted for the northern part of the rift, in Minnesota where active surface hydrogen production occurs at the outcrop of Precambrian rocks. This characterization made it possible to identify new H2 production and consumption markers, in the form of volatile fatty acids, in hyper-basic and highly chemically reduced waters [3]. Such compounds result from the biological consumption of H2, or from its chemical reactivity with inorganic carbon such as CO2.

The knowledge acquired during this research, as well as the analysis protocols developed, have been integrated into IFPEN’s commercial solutions aimed at identifying and characterizing exploration zones. The protocols are now being used to study other emitting sites, with the aim of producing numerical models for predicting potential subsurface resources in the very near future.

 

References:

  1. Combaudon, V., Sissmann, O., Bernard, S., Viennet, J. C., Megevand, V., Le Guillou, C., Guélard, J., Martinez, I., Guyot, F., Derluyn, H. & Deville, E., Are the Fe-rich-clay veins in the igneous rock of the Kansas (USA) Precambrian crust of magmatic origin, (2024). Lithos, 474, 107583.
    >> https://doi.org/10.1016/j.lithos.2024.107583
        

  2. Combaudon, V., Centrella S., Kularatne, K., Sissmann, O., Sénéchal, P., Deville, E. & Derluyn, H., Mass transfer study of a fayalite-bearing gabbro from the Kansas Precambrian basement (USA) and implications for natural hydrogen generation, in review at Chemical Geology.
        

  3. Combaudon, V., Sissmann, O., Guelard, J., Noirez, S., Derluyn, H., & Deville, E. Investigating reduced and alkaline fluids degassing CH4-H2-He with high concentrations of formate and acetate in iron-rich Precambrian shield rocks, in review at International Journal of Hydrogen Energy.

       

Scientific contact: olivier.sissmann@ifpen.fr

>> ISSUE 56 OF SCIENCE@IFPEN