Geological Hydrogen Storage: Geochemical Reactivity of Hydrogen with Sandstone Reservoirs

[Image: see text] The geological storage of hydrogen is necessary to enable the successful transition to a hydrogen economy and achieve net-zero emissions targets. Comprehensive investigations must be undertaken for each storage site to ensure their long-term suitability and functionality. As such, the systematic infrastructure and potential risks of large-scale hydrogen storage must be established. Herein, we conducted over 250 batch reaction experiments with different types of reservoir sandstones under conditions representative of the subsurface, reflecting expected time scales for geological hydrogen storage, to investigate potential reactions involving hydrogen. Each hydrogen experiment was paired with a hydrogen-free control under otherwise identical conditions to ensure that any observed reactions were due to the presence of hydrogen. The results conclusively reveal that there is no risk of hydrogen loss or reservoir integrity degradation due to abiotic geochemical reactions in sandstone reservoirs

Pore-scale imaging of hydrogen displacement and trapping in porous media

Hydrogen can act as an energy store to balance supply and demand in the renewable energy sector. Hydrogen storage in subsurface porous media could deliver high storage capacities but the volume of recoverable hydrogen is unknown. We imaged the displacement and capillary trapping of hydrogen by brine in a Clashach sandstone core at 2–7 MPa pore fluid pressure using X-ray computed microtomography. Hydrogen saturation obtained during drainage at capillary numbers of &lt;10 −7 was ∼50% of the pore volume and independent of the pore fluid pressure. Hydrogen recovery during secondary imbibition at a capillary number of 2.4 × 10 −6 systematically decreased with pressure, with 80%, 78% and 57% of the initial hydrogen recovered at 2, 5 and 7 MPa, respectively. Injection of brine at increasing capillary numbers up to 9.4 × 10 −6 increased hydrogen recovery. Based on these results, we recommend more shallow, lower pressure sites for future hydrogen storage operations in porous media. </p

Enabling large-scale hydrogen storage in porous media – the scientific challenges

Expectations for energy storage are high but large-scale underground hydrogen storage in porous media (UHSP) remains largely untested. This article identifies and discusses the scientific challenges of hydrogen storage in porous media for safe and efficient large-scale energy storage to enable a global hydrogen economy. To facilitate hydrogen supply on the scales required for a zero-carbon future, it must be stored in porous geological formations, such as saline aquifers and depleted hydrocarbon reservoirs. Large-scale UHSP offers the much-needed capacity to balance inter-seasonal discrepancies between demand and supply, decouple energy generation from demand and decarbonise heating and transport, supporting decarbonisation of the entire energy system. Despite the vast opportunity provided by UHSP, the maturity is considered low and as such UHSP is associated with several uncertainties and challenges. Here, the safety and economic impacts triggered by poorly understood key processes are identified, such as the formation of corrosive hydrogen sulfide gas, hydrogen loss due to the activity of microbes or permeability changes due to geochemical interactions impacting on the predictability of hydrogen flow through porous media. The wide range of scientific challenges facing UHSP are outlined to improve procedures and workflows for the hydrogen storage cycle, from site selection to storage site operation. Multidisciplinary research, including reservoir engineering, chemistry, geology and microbiology, more complex than required for CH4 or CO2 storage is required in order to implement the safe, efficient and much needed large-scale commercial deployment of UHSP.This work was stimulated by the GEO*8 Workshop on “Hydrogen Storage in Porous Media”, November 2019 at the GFZ in Potsdam (Germany). NH, AH, ET, KE, MW and SH are funded by the Engineering and Physical Sciences Research Council (EPSRC) funded research project “HyStorPor” (grant number EP/S027815/1). JA is funded by the Spanish MICINN (Juan de la Cierva fellowship-IJC2018-036074-I). JM is co-funded by EU INTERREG V project RES-TMO (Ref: 4726 / 6.3). COH acknowledges funding by the Federal Ministry of Education and Research (BMBF, Germany) in the context of project H2_ReacT (03G0870C).Peer reviewe

Microbial risk assessment for underground hydrogen storage in porous rocks

Geological hydrogen storage, e.g. in depleted gas fields (DGF), can overcome imbalances between supply and demand in the renewable energy sector and facilitate the transition to a low carbon emissions society. A range of subsurface microorganisms utilise hydrogen, which may have important implications for hydrogen recovery, clogging and corrosion. We gathered temperature and salinity data for 75 DGF on the UK continental shelf and mapped their suitability for hydrogen storage in terms of the risk of adverse microbial effects, based on a novel collection of microbial growth constraints. Data on wind and solar operational capacities as well as offshore gas and condensate pipeline infrastructure were overlaid on the microbial risk categorization to optimize geographical centers of green hydrogen production, transport infrastructure and underground storage. We recommend storing hydrogen in 9 DGF that are at no microbial risk due to temperatures > 122 °C, or in the 35 low-risk DGF with temperatures > 90 °C. We recommend against utilising high-risk DGF with temperatures < 55 °C (9 DGF). Alignment with centers for renewable energy production and out-of-use pipelines suitable for repurposing to transport hydrogen suggests that no-risk and low-risk DGF in the Southern North Sea are the most suitable candidates for hydrogen storage. Our results advise site selection choices in geological hydrogen storage in the UK. Our methodology is applicable to any underground porous rock system globally.We would like to express our gratitude to the National Data repository for making the data available that enabled this research. Dr Edlmann, Dr Hassanpouryouzband and Dr Thaysen were supported by funding from the Engineering and Physical Sciences Research Council (EPSRC) [Grant Number EP/S027815/1] (HyStorPor Project) and from the Fuel Cells and Hydrogen 2 Joint Undertaking (now Clean Hydrogen Partnership) under grant agreement No 101006632. This Joint Undertaking receives support from the European Union’s Horizon 2020 research and innovation program, Hydrogen Europe and Hydrogen Europe Research. Dr Slabon was funded by UK Research and Innovation as part of the EPSRC and NERC Industrial CDT for Offshore Renewable Energy (IDCORE), Grant number EP/S023933/1.Peer reviewe

Hydrogen wettability and capillary pressure in Clashach sandstone for underground hydrogen storage

Hydrogen (H2) can support the transition to net-zero carbon (C) emissions by facilitating increased renewable energy use by acting as an energy store to balance supply and demand. Underground H2 storage in porous media is investigated due to its high capacity and economical price. An important unknown in underground porous media H2 storage is the volume of recoverable H2 which is partly controlled by the H2 wettability. Current H2 contact angle data in sandstone systems span large ranges and fall short of clarifying if H2 wettability changes with pressure.We computed novel in-situ receding and advancing contact angles for the H2-brine-Clashach sandstone system at pore fluid pressures of 2–7 MPa and for nitrogen (N2)-brine-Clashach sandstone at 5 MPa, based on X-ray microtomography images of gas displacement and trapping in Clashach sandstone. A centrifuge analysis of the capillary pressure (Pc) at varying water saturations was conducted for N2. The H2 Pc curve was derived from the N2 Pc, the N2 wettability measurements, and existing information on the density differential between brine and H2 and N2, and the interfacial tensions of these gases.The results show no change of the H2-brine-Clashach sandstone contact angles within the examined pressure range, with mean receding (drainage) and advancing (imbibition) contact angles of 61° ± 24–26° and 58° ± 20–22°, respectively, at all pore fluid pressures, indicating a water-wet rock and implying that based on the wettability alone, no decrease in H2 recovery with increasing pressure (i.e. reservoir depth) is expected. While residual trapping was consistent with trapping in water-wet systems, the observed increase in residual trapping at 7 MPa requires further investigation. Alignment with other wettability studies in sandstone systems indicates that for contact angles around 60–70°, wettability may not always be the main control for the H2 saturation in the pore space but that H2 dissolution and channeling events may significantly affect those parameters. Further, contact angle measurements in artificial systems significantly underestimate in-situ contact angles as provided by this study, highlighting the need for microtomography-based wettability investigations. We found relatively low irreducible water saturations of 12.6–14.0 % at H2 Pc of 0.43 MPa, suggesting a favorable H2 relative permeability in Clashach and high H2 storage capacity. Our results provide detailed insights into the controls on H2 displacement and capillary trapping as well as crucial input parameters for the modelling and design of H2 storage operations in porous media

Hydrogen recovery from porous media decreases with brine injection pressure and increases with brine flow rate

Zero carbon energy generation from renewable sources can reduce climate change by mitigating carbon emissions. A major challenge of renewable energy generation is the imbalance between supply and demand. To overcome the energy imbalances, subsurface storage of hydrogen in porous mediais suggested as a large-scale and economic solution, yet its mechanisms are not fully understood. Important unknowns are the effect of the high migration potential of the small and mobile hydrogen molecule and the volume of recoverable hydrogen.We conducted non-steady state, cyclic hydrogen and brine injection experiments at 2-7 MPa and flow rates of 2-80 µl min-1 using water-wet Clashach sandstone cylinders of 4.7 mm diameter and 53-57 mm length (Clashach composition: ~96 wt.% quartz, 2% K-feldspar, 1% calcite, 1% ankerite). Two sets of experiments were performed using our new transparent flow-cell designed for x-ray computed microtomography: 1) Experiments using a laboratory x-ray source (University of Edinburgh) imaged the flow, displacement and capillary trapping of hydrogen by brine as a function of saturation after primary drainage and secondary imbibition. 2) Experiments using synchrotron radiation (Diamond Light Source, I12-JEEP tomography beamline) captured time-resolved hydrogen and brine flow and displacement processes. Pressure and mass flow measurements across the experimental apparatus complemented the microtomography volumes in both sets of experiments.Results from a water-wet rock show that hydrogen behaves as a non-wetting phase and sits in the centre of the pore bodies, while residual brine sits in corners and pore throats. Hydrogen saturation in the pore volume is independent of the injection pressure and increases with increasing hydrogen/brine injection ratio up to ~50% saturation at 100 % hydrogen. Capillary trapping of hydrogen during brine imbibition occurs via snap off and is greatest at higher brine injection pressures, with 10 %, 12% and 21% hydrogen trapped at 2, 5 and 7 MPa, respectively. Higher brine flow rates reduce capillary trapping and increase hydrogen recovery at any given injection pressure. Based on these results, future hydrogen storage operations should inject 100% hydrogen and manage the reservoir pressure to avoid high pressures and minimize capillary trapping of hydrogen during brine reinjection.Ongoing analysis of time-resolved experimental data will provide further insight into the critical pore-scale processes that ultimately influence the potential for geological hydrogen storage and recovery

Pore-scale imaging of hydrogen displacement and trapping in porous media

Hydrogen can act as an energy store to balance supply and demand in the renewable energy sector. Hydrogen storage in subsurface porous media could deliver high storage capacities but the volume of recoverable hydrogen is unknown. We imaged the displacement and capillary trapping of hydrogen by brine in a Clashach sandstone core at 2–7 MPa pore fluid pressure using X-ray computed microtomography. Hydrogen saturation obtained during drainage at capillary numbers of &lt;10 −7 was ∼50% of the pore volume and independent of the pore fluid pressure. Hydrogen recovery during secondary imbibition at a capillary number of 2.4 × 10 −6 systematically decreased with pressure, with 80%, 78% and 57% of the initial hydrogen recovered at 2, 5 and 7 MPa, respectively. Injection of brine at increasing capillary numbers up to 9.4 × 10 −6 increased hydrogen recovery. Based on these results, we recommend more shallow, lower pressure sites for future hydrogen storage operations in porous media. </p