Assessing hydrogen production potential from carbonate and shale source rocks: A geochemical investigation

The global push towards achieving net-zero carbon dioxide emissions by 2050 shows the urgency of transitioning to a hydrogen-based economy, with clean hydrogen fuel emerging as a fundamental component of future energy consumption. This study explores hydrogen production from geological sources, specifically organic-rich Shale and Carbonate mudrocks, as a significant and sustainable method for natural hydrogen production. Recognizing the critical challenge posed by the interaction of hydrogen with rock-forming minerals and organic matter during production, this research emphasizes the need for a comprehensive understanding of the geochemical composition of these rock materials. To assess the feasibility and implications of utilizing organic-rich source rocks for hydrogen production, we conducted thorough analyses of source rock samples from different formations. The representatives’ samples were subjected to comprehensive analyses including Rock-Eval pyrolysis, X-ray diffraction (XRD), X-ray fluorescence (XRF), scanning electron microscope (SEM) examinations, and gas chromatography (GC) analysis of the produced gas. Our results revealed that the high total organic carbon (TOC) samples (average 14.7 %) with Type I and II kerogens yielded substantial hydrogen-rich gases, approximately 44.71 % and 36.02 % for SH-O1 and JOS samples, respectively. JOS produced slightly higher hydrocarbon gases (∼50 %) compared to SH-O1 (∼45 %), along with more H₂S (5.78 %), due to higher total sulfur content. In contrast, the SH-C1 sample, characterized by very low TOC (0.27 %), predominantly quartz and muscovite minerals (>78 %), and Type IV kerogen, produced higher CO₂ (22.09 %) and minimal hydrogen (1.27 %), highlighting the influence of mineralogical and geochemical composition. This study suggests that hydrocarbon source rocks with high organic matter content hold significant potential for maximizing energy gas recovery (>85 %, including hydrogen and hydrocarbons) through the pyrolysis of their kerogen content. These findings demonstrate the viability of hydrogen gas production from unconventional sources such as organic-rich shales, potentially impacting strategies for sustainable energy production and contributing significantly to global decarbonization efforts.