Article written by Dr. Albert Harutyunyan.
The role of hydrogen in the global energy transition is becoming more and more indisputable as deposits of natural hydrogen (H2) attract attention as a potentially clean, abundant source of energy. Nevertheless, the genesis and accumulation of natural hydrogen remain controversial.
One area that deserves close attention is the dehydration of serpentinized rocks, which may contain untapped potential for hydrogen generation. This article examines this concept’s scientific nuances and feasibility and suggests directions for future research.
Formation of hydrogen by dehydration of serpentinized rocks
The dehydration of serpentinized rocks has been identified as a probable source of natural hydrogen. Serpentinization, the chemical alteration of ultramafic rocks of the upper mantle by infiltration water, has been well documented to generate hydrogen in the platform regions of the oceanic crust. However, a less studied additional process, deserpentinization, occurs under elevated temperature and pressure, potentially releasing significant amounts of hydrogen. At the depths of the earth’s crust, at various pressures, when a temperature of 450-500 °C is reached, water is released from serpentinized rocks, and under high thermobaric conditions, it is hydrolyzed into hydrogen and oxygen. Oxygen oxidizes some metals, and hydrogen promotes the formation of hydrocarbons and other compounds. Laboratory studies simulate these conditions, demonstrating the release of water on a scale of tens of thousands of cubic kilometers per rock mass. Despite these results, scaling laboratory results to geological conditions raises questions about the reproducibility and consistency of hydrogen yield.
Ways of accumulation and formation of reservoirs
The migration of hydrogen and related compounds from deep sources of the Earth’s crust to storage reservoirs is crucial for the viability of natural hydrogen. The low density and high hydrogen diffusivity make it challenging to retain it during upward migration. According to the dehydration model, geza geofluids and hydrocarbons migrate through deep faults, becoming enriched in various elements before accumulating in fractured rocks of the crystalline basement and in porous sedimentary layers. Field data from regions such as Mali, where natural hydrogen seeps have been documented, provide a basis for optimism. However, comprehensive geophysical and geochemical studies are needed to confirm whether such accumulations can be reliably predicted using the criteria outlined for hydrocarbon and diamond exploration. Key factors include the presence of surface depressions, deep faults, volcanism, ophiolite structures, seismic velocity inversions, and magnetic telluric anomalies, all characteristic of deposits of hydrogen, hydrocarbons, and diamonds.
Comparative Analysis of Hydrogen, Hydrocarbon, and Diamond Genesis
The parallels between hydrogen, hydrocarbon, and diamond formation underscore the importance of a unified conceptual framework. The release of hydrogen during dehydration coincides with ultra-high pressures and temperatures conducive to diamond genesis from carbon-rich substrates. This raises intriguing questions about the competitive or cooperative nature of these processes. For instance, can hydrogen and hydrocarbons coexist in economically significant quantities without one pathway dominating?
The Mali hydrogen field provides a case study for comparative analysis. The inversion of seismic wave velocities and density contrasts observed there align with the proposed criteria. Similar observations in hydrocarbon-rich regions suggest that natural hydrogen exploration may benefit from the methodologies employed in oil and gas prospecting.
Challenges and Economic Considerations
Despite its promise, the deserpentinization model faces substantial challenges. Hydrogen’s reactivity with surrounding minerals and fluids reduces its free-state availability, while the economics of extraction remain uncertain. Unlike hydrocarbons, which are energetically dense and established in global markets, hydrogen’s viability depends on cost-effective capture and transport. Field validation of hydrogen reservoirs is crucial to assessing whether extraction can compete with alternative hydrogen production methods, such as electrolysis or microbial pathways.
Furthermore, geological heterogeneity complicates predictions. Regions rich in serpentinized rocks, such as mid-ocean ridges, have not yielded substantial hydrogen reservoirs, raising questions about the broader applicability of the deserpentinization model. Comparative analyses with abiotic and biotic hydrocarbon models are necessary to refine predictive tools and identify promising exploration targets.
Refining Exploration Criteria
The proposed criteria for identifying natural hydrogen deposits mirror those used for hydrocarbons and diamonds, emphasizing deep faults, geophysical anomalies, and associated geofluids. However, hydrogen-specific refinements are needed. For instance, detecting hydrogen seepage through near-surface geochemical surveys or measuring isotope ratios in fluids could provide direct evidence of hydrogen presence.
Innovations in geophysical techniques, such as high-resolution seismic imaging and magnetic telluric sounding, offer tools for delineating potential reservoirs. Incorporating these technologies into existing frameworks can enhance the precision of exploration efforts. Collaborative field studies in known hydrogen-bearing regions, such as Mali, and potential sites in the Lesser Caucasus could provide critical insights.
Concluding Synthesis
The dehydration of serpentinized rocks represents a compelling avenue for natural hydrogen generation, with implications for scientific understanding and energy exploration. However, rigorous field validation and economic analysis are essential to transition from concept to application. By refining exploration criteria, integrating advanced geophysical techniques, and fostering international collaboration, the potential of natural hydrogen can be systematically evaluated and harnessed for a sustainable energy future.
