Natural Hydrogen Generation from Phanerozoic Sedimentary Siderite

Siderite (FeCO3) is an iron carbonate present in Archean and Neoproterozoic Banded Iron Formations (BIFs) as well as in much more recent sedimentary basins. Due to its high iron content, it could be part of H2 systems, and we have quantified its potential as a H2-generating rock and its kinetics from samples from the Llanos Basin in Colombia and from the Solimões Basin in Brazil. The H2 potential of natural siderite-rich Cenozoic formations was measured with a Hydrogen-Eval pyrolyzer, where the H2 yield depends linearly on the siderite content of the rock. It reaches 3.5 mol/kg for a sample containing 50% of siderite. The siderite is known to be unstable and to decompose at relatively low temperatures, between 100 and 200 °C. These results suggest that sedimentary siderite could be an additional potential H2-generating rock, through oxido-reduction, with an active H2 generation window between 3 and 6 km. In sedimentary basin at these depths, reservoirs and traps are likely to be present, and the porosity could be ideal for accumulation. Strong external water supply through hydrodynamics will promote H2 generation, but the dehydration of rocks such as clays will also enable it through local water supply.