Abstract A model is presented for the generation of natural hydrogen from cratonic basement rocks and its migration into the sediments of overlying cratonic basins. It is based on the ‘discovery’ of hydrogen at Bourakebougou in the Taoudeni Basin of Mali. In the ‘Cratonic Greenstone Model’, hydrogen is generated by the serpentinization of olivine-rich, ultramafic rocks contained within Precambrian ‘greenstones’. The model requires a protolith (in greenstones), a supply of water (from groundwater), connecting faults to act as a plumbing system and an indurated sediment cover to retard hydrogen movement. Hydrogen is expelled into the overlying basin sediments, which form the host for hydrogen accumulations. The model describes a continental ‘hydrogen system’, which can form the basis for petroleum-type play-based hydrogen exploration in cratonic settings. Using play elements derived from the model, the Bourakebougou play fairway can be extended across the Taoudeni Basin >700 km northwards of the discovery.

Abstract Twenty-five years ago, a unique long-term and large-scale in situ experiment with 14 C-labelled natural organic matter (NOM) was set up at the HADES underground research facility in Mol (Belgium) to study its migration behaviour. Natural organic matter plays an important role in the mobility of various safety-relevant radionuclides, which is critical in the context of Safety & Performance Assessment (SA/PA) calculations for a possible nuclear waste repository. The objective of this work is to enlarge the confidence in current NOM transport models by validating them with the in situ experiment, which is still continued to this day. Stepwise adding more complexity to the model resulted in a 10-parameter model with which excellent fits to the data are obtained. The model considers two different fractions that are transported by advection and diffusion and can be subject to both irreversible and reversible immobilization processes. The associated fitted parameter values compare well with values determined on small-scale migration experiments. This builds confidence in the NOM transport model, which in turn contributes to the confidence in the outcome of the radionuclide migration calculations performed in the context of SA/PA. These results again highlight the incredible value of such long-running experiments at underground research facilities like HADES.

ABSTRACT Under fast-moving oceanic plates, the asthenosphere seismic B″ region becomes isolated from the convecting mantle by plate drag and acts as an advecting layer, which can serve as a long-lived source for intraplate volcanism. Geochemical enrichment of B″ can occur via infiltration by melts generated from the breakdown of serpentinite at ~200 km depth in subducting slabs. Ocean-island chains arise when melts generated within metasomatized B″ by shear melting and localized convection are released along lithospheric fractures controlled by the stress field of the plate. Intersection of metasomatized B″ with ocean-ridge systems produces oceanic plateaus. A strong anisotropy anomaly (V SH /V SV >1) at depths of ~150 km in the Pacific asthenosphere marks a metasomatized B″ domain that originated in the western paleo-Pacific basin in the Carboniferous, and that is now associated with Hawaiian volcanism. Metasomatized B″ can be trapped beneath orogenic belts during continental aggregation and tapped by edge-driven convection upon rifting to produce the correlation between intraplate volcanism and the fabric of sutures in opening ocean basins such as the Atlantic Ocean basin.

Abstract In a deep geological repository (DGR) for the long-term containment of radioactive waste, gases could be generated through a number of processes. If gas production exceeds the containment capacity of the engineered barriers or host rock, these gases could migrate through these barriers and potentially expose people and the environment to radioactivity. Expansive soils, such as bentonite-based materials, are currently the preferred choice of seal materials. Understanding the long-term performance of these seals as barriers against gas migration is an important component in the design and long-term safety assessment of a DGR. This study proposes a hydro-mechanical linear poro-elastic visco-capillary mathematical model for advective-diffusive controlled two-phase flow through a low-permeability expansive soil. It is based on the theoretical framework of poromechanics, incorporates Darcy’s Law for both the porewater and poregas, and a modified Bishop’s effective stress principle. Using the finite element method (FEM), the model was used to numerically simulate 1D flow through a low-permeability expansive soil. The results were verified against experimental results found in the current literature. Parametric studies were performed to determine the influence on the flow behaviour. Based on the results, the mathematical model looks promising and will be improved to model flow through preferential pathways.