Evolution of gases associated with rift opening, natural hydrogen and others. Case of the East African Rift

• Main Author: Pasquet, Gabriel
• Other Authors: Laboratoire des Fluides Complexes et leurs Réservoirs (LFCR), TOTAL FINA ELF-Université de Pau et des Pays de l'Adour (UPPA)-Centre National de la Recherche Scientifique (CNRS), Université de Pau et des Pays de l'Adour, Isabelle Moretti
• Format: Doctoral or Postdoctoral Thesis
• Language: French
• Published: HAL CCSD 2022
• Subjects: Hydrogen; Gas; Rift; East African Rift; Hydrogène; Gaz; Rift est-Africain; [SDU.STU.AG]Sciences of the Universe [physics]/Earth Sciences/Applied geology; Mid-Atlantic Ridge; Iceland
• Online Access: https://theses.hal.science/tel-04329560; https://theses.hal.science/tel-04329560/document; https://theses.hal.science/tel-04329560/file/thesispasquet.pdf

Hydrogen is becoming an increasingly key part of the global energy mix, researches are progressing. The production techniques are diverse, ranging from polluting but economical means, such as the CH4 vapocracking, to the clean but expensive (water electrolysis) or even renewable and potentially cheaper natural hydrogen (H2). This thesis is based on the primary need to build a global database of natural H2 rich areas and to understand its origin. The link between geothermal potential and H2 resources will also be discussed.Oceanic ridges are known to host H2 emissions from hydrothermal vents. In a similar geological context, onshore, what is the generation of H2 at the initiation of rifts and then ridges, such as in Iceland where the presence of a plume lead to the emersion of the mid-Atlantic ridge. The Afar Depression, also marked by the presence of a hot spot, is composed of three opening branches: the southern Red Sea, the western end of the Gulf of Aden and the northern end of the Ethiopian Rift. This large system allows comparison of gases emitted from a rift that is still continental (Southern Ethiopian) to those from an oceanic zone (Asal Rift in the Republic of Djibouti).During two field missions in the Republic of Djibouti and Ethiopia, numerous sites were sampled - hydrothermal sites, volcanoes, fumaroles and active faults - both in continental crust at the initial stage of rifting and in oceanic crust. Unfortunately, Covid and the war in Ethiopia have limited these field acquisitions.Our results show the presence of H2 in both oceanic and continental domains, but in rather low percentages (< 3%). At the surface, H2 concentration increases with proximity to the axial zone of the rift or to an active volcanic centre. Active faults allow a rapid migration path between the magma chamber and the surface. Thus, fumaroles often have a mantle signature. This signature of degassing is marked at the surface by a small variation in H2 concentration over time, unlike the emissions described in cratons. The ...