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.

Carbon capture and storage (CCS) can help nations meet their Paris CO2 reduction commitments cost-effectively. However, lack of confidence in geologic CO2 storage security remains a barrier to CCS implementation. Here we present a numerical program that calculates CO2 storage security and leakage to the atmosphere over 10,000 years. This combines quantitative estimates of geological subsurface CO2 retention, and of surface CO2 leakage. We calculate that realistically well-regulated storage in regions with moderate well densities has a 50% probability that leakage remains below 0.0008% per year, with over 98% of the injected CO2 retained in the subsurface over 10,000 years. An unrealistic scenario, where CO2 storage is inadequately regulated, estimates that more than 78% will be retained over 10,000 years. Our modelling results suggest that geological storage of CO2 can be a secure climate change mitigation option, but we note that long-term behaviour of CO2 in the subsurface remains a key uncertainty.

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Hydrogen usage and storage may contribute to reducing greenhouse gas emissions by decarbonising heating and transport and by offering significant energy storage to balance variable renewable energy supply. Underground storage of hydrogen is established in underground salt caverns, but these have restricted geographical locations within the UK and cannot deliver the required capacity. Hydrogen storage in porous geological formations has significant potential to deliver both the capacity and local positioning. This study investigates the potential for storage of hydrogen in porous subsurface media in Scotland. We introduce for the first time the concept of the hydrogen storage play. A geological combination including reservoir, seal and trap that provides the optimum hydrogen storage reservoir conditions that will be potential targets for future pilot, and commercial, hydrogen storage projects. We investigate three conceptual hydrogen storage plays in the Midland Valley of Scotland, an area chosen primarily because it contains the most extensive onshore sedimentary deposits in Scotland, with the added benefit of being close to potential consumers in the cities of Glasgow and Edinburgh. The formations assessed are of Devonian and Carboniferous age. The Devonian storage play offers vast storage capacity but its validity is uncertain due to due to a lack of geological data. The two Carboniferous plays have less capacity but the abundant data produced by the hydrocarbon industry makes our suitability assessment of these plays relatively certain. We conclude that the Carboniferous age sedimentary deposits of the D'Arcy-Cousland Anticline and the Balgonie Anticline close to Edinburgh will make suitable hydrogen storage sites and are ideal for an early hydrogen storage research project.

Résumé -Analogues géochimiques naturels pour le stockage du dioxyde de carbone en réservoir géologique poreux profond : perspective pour le Royaume-Uni -La concentration élevée en CO 2 atmosphérique participe au réchauffement climatique. Une mesure d'atténuation consiste à capter le CO 2 émis par les centrales électriques qui utilisent des combustibles fossiles, et à le stocker dans des aquifères salins ou dans des gisements exploités d'hydrocarbures. Des projets de démonstration déjà en cours et des analyses techniques indiquent que cette mesure est viable. Le CO 2 doit rester confiné pendant au moins 10 000 ans pour que cette option technologique ait un impact climatique. En vue de fournir une évaluation solide des performances d'un site de stockage, à l'échelle de temps indiquée, une approche possible est d'étudier les accumulations naturelles de CO 2 . Celles-ci sont en particulier capables de donner des informations sur les interactions roche-CO 2 -saumure à des échelles de temps comprises entre le millier et la dizaine de millions d'années. Les champs de CO 2 naturel en mer du Nord (Brae, Miller, Magnus), situés à 4 000 m d'enfouissement et plus, ne montrent pas la néoformation des phases minérales souvent prédite par la modélisation géochimique. La calcite et les feldspaths peuvent constituer encore entre 5 et 20 % des minéraux de la roche, tandis que la dawsonite n'est pas observée. Il en est de même pour des exemples de réservoirs de grès situés dans le sud-est australien et en Arizona. Il est possible qu'un état de déséquilibre thermodynamique se soit maintenu, de sorte que les modèles existants ne sont pas capables de prédire correctement les évolutions minéralogiques réelles, sur les durées pertinentes pour la séquestration du CO 2 . Ces modèles nécessitent une meilleure calibration. Les données expérimentales, à l'échéance de quelques mois, ou celles déduites des situations de récupération assistée (CO 2 -EOR), à l'échéance de quelques dizaines années, sont en général trop courtes pour offrir toutes les calibrations nécessaires. En revanche, les analogues naturels peuvent aider à combler cette lacune. Le plateau du Colorado abrite un tel système naturel, où des gisements estimés à 100 Gm 3 de CO 2 ont pu s'accumuler, à partir de sources vocaniques d'âge inférieur à 5 Ma.

Following the landmark 2015 United Nations Paris Agreement, a growing number of countries are committing to the transition to net-zero emissions. Carbon capture and storage (CCS) has been consistently heralded to directly address emissions from the energy and industrial sectors and forms a significant component of plans to reach net-zero. However, despite the critical importance of the technology and substantial research and development to date, CCS deployment has been slow. This review examines deployment efforts over the last decade. We reveal that facility deployment must increase dramatically from current levels, and much work remains to maximize storage of CO 2 in vast subsurface reserves. Using current rates of deployment, CO 2 storage capacity by 2050 is projected to be around 700 million tons per year, just 10% of what is required. Meeting the net-zero targets via CCS ambitions seems unlikely unless worldwide coordinated efforts and rapid changes in policy take place. ll

Meeting inter-seasonal fluctuations in electricity production or demand in a system dominated by renewable energy requires the cheap, reliable and accessible storage of energy on a scale that is currently challenging to achieve. Commercially mature compressed air energy storage (CAES) could be applied to porous rocks in sedimentary basins worldwide where legacy data from hydrocarbon exploration are available, and where geographically close to renewable energy sources. Here we present a modeling approach to predict the potential for CAES in porous rocks. By combining these with an extensive geological database we provide a regional assessment of this potential for the UK.