Reactive transport experiments of coupled carbonation and serpentinization in a natural serpentinite. Implication for hydrogen production and carbon geological storage

Serpentinization and carbonation of ultramafic formations is a ubiquitous phenomenon, which deeply influences the biogeochemical cycles water, hydrogen, carbon... while supporting particular biosphere around oceanic hydrothermal vents. Carbonation peridotites other mafic rocks also hot topic in current energy landscape as engineered sequestration mineral CO2 these could help reduce atmospheric emissions cope with climate change. In this study, we present two reactive percolation experiments performed on natural serpentinite dredged from ultraslow South-West Indian Oceanic Ridge. The cores (length 3-4 cm dia. 5.6 mm) were subjected for about 10 days to continuous injection NaHCO3-saturated brine at respectively 160{\deg}C 280{\deg}C. Petrographic petrophysical results well outlet fluid compositions compared numerical batch simulations PHREEQC open software allowing reconstruct mineralogical evolution both cores. most striking observation fast dramatic decrease permeability principally due precipitation carbonates. On contrary, serpentine was found be less impacting it precipitates low-flow zones, out main paths. total, 5.6% total injected retained core, same time, hydrogen consistently produced recovered H2 corresponding 0.8% maximum possible. global behavior interpreted result an interplay between interacting spatio-temporal lengthscales controlled by Damkohler number.