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The changes in the energy sector after the Paris agreement and the establishment of the Green Deal, pressed the governments to embrace new measures to reduce greenhouse gas emissions. Among them, is the replacement of fossil fuels by renewable energy sources or carbon-neutral alternative means, such as green hydrogen. As the European Commission approved green hydrogen as a clean fuel, the interest in investments and dedicated action plans related to its production and storage has significantly increased. Hydrogen storage is feasible in aboveground infrastructures as well as in underground constructions. Proper geological environments for underground hydrogen storage are porous media and rock cavities. Porous media are separated in depleted hydrocarbon reservoirs and aquifers, while rock cavities are subdivided into hard rock caverns, salt caverns, and abandoned mines. Depending on the storage option, various technological requirements are mandatory, influencing the required capital cost. Although the selection of the optimum storage technology is site depending, the techno-economical appraisal of the available underground storage options featured the porous media as the most economically attractive option. Depleted hydrocarbon reservoirs were of high interest as site characterisation and cavern mining are omitted due to pre-existing infrastructure, followed by aquifers, where hydrogen storage requires a much simpler construction. Research on data analytics and machine learning tools will open avenues for consolidated knowledge of geological storage technologies.
During the last years, the European Union set the lines for a cleaner energy sector. As the need for energy resources with minimum environmental impact increases, the focus of researchers turned to green hydrogen, which is considered a clean fuel. Ways for its production and storage are under investigation. The storage of hydrogen can be feasible in above-ground infrastructures as well as in underground constructions. For the underground hydrogen storage specific geological environments are required. Two main categories are preferred, the geological formations with high porosity, known as porous media, and the cavities created in hard rocks. These categories are further divided into subcategories where different technological requirements are mandatory, influencing the required capital cost. The selection of optimum storage technology is site-dependent, however, the most economically attractive option based on the techno-economic appraisal of the available technologies is the porous media. This category is subdivided into depleted hydrocarbon reservoirs and aquifers, where the first one constitutes the most attractive option due to the pre-existing infrastructure and the already available site characterization. Further research on data analysis and machine learning tools will create a common understanding of the needs and requirements of hydrogen geological storage.
RESUMO
Background: It is widely acknowledged that carbon dioxide (CO 2), a greenhouse gas, is largely responsible for climatic changes that can lead to warming or cooling in various places. This disturbs natural processes, creating instability and fragility of natural and social ecosystems. To combat climate change, without compromising technology advancements and maintaining production costs at acceptable levels, carbon capture and storage (CCS) technologies can be deployed to advance a non-disruptive energy transition. Capturing CO 2 from industrial processes such as thermoelectric power stations, refineries, and cement factories and storing it in geological mediums is becoming a mature technology. Part of the Mesohellenic Basin, situated in Greek territory, is proposed as a potential area for CO 2 storage in saline aquifers. This follows work previously done in the StrategyCCUS project, funded by the EU. The work is progressing under the Pilot Strategy, funded by the EU. Methods: The current investigation includes geomechanical and petrophysical methods to characterise sedimentary formations for their potential to hold CO 2 underground. Results: Samples were found to have both low porosity and permeability while the corresponding uniaxial strength for the Tsotyli formation was 22 MPa, for Eptechori 35 MPa and Pentalofo 74 MPa. Conclusions: The samples investigated indicate the potential to act as cap-rocks due to low porosity and permeability, but fluid pressure within the rock should remain within specified limits; otherwise, the rock may easily fracture and result in CO 2 leakage or/and deform to allow the flow of CO 2. Further investigation is needed to identify reservoir rocks as well more sampling to allow for statistically significant results.
RESUMO
Nuclear magnetic resonance (NMR) (H1) transverse relaxation measurements were carried out on 37x70-mm cylindrical mineral/organic composites to determine and monitor the porosity evolution. Porosity is related, in principle, to the stability of such materials in geotechnical applications, for example, engineering foundations. The specimens represented novel formulations of mixed "wastes" containing coarse screened mineral, digested sewage sludge, quicklime, and pulverized fuel ash mixed and compacted together to form mechanically competent material. The measurements on a selected formulation indicated initially low porosity (<12%) that becomes lower over 6 months ( approximately 8%) due to pozzolanic reactions occurring. A relaxation time cutoff of 1.5 ms between "bound" and 'mobile' pore water much lower than sandstones (33 ms) was observed. The results confirmed that the NMR method allows a more reliable assessment of porosity and pore-size evolution.
