Hydrogen plays a leading role in achieving a future with net zero greenhouse gas emissions. The present challenge is producing green hydrogen to cover the fuel demands of transportation and industry to gain independence from fossil fuels. This review’s goal is to critically demonstrate the existing methods of biomass treatment and assess their ability to scale up. Biomass is an excellent hydrogen carrier and biomass-derived processes are the main target for hydrogen production as they provide an innovative pathway to green hydrogen production. Comparing the existing processes, thermochemical treatment is found to be far more evolved than biological or electrochemical treatment, especially with regard to scaling prospects.

As industry moves from fossil fuels to green energy, substituting hydrocarbons with hydrogen as an energy carrier seems promising. Hydrogen can be stored in salt caverns, depleted hydrocarbon fields, and saline aquifers. Among other criteria, these storage solutions must ensure storage safety and prevent leakage. The ability of a caprock to prevent fluid from flowing out of the reservoir is, thus, of utmost importance. In this review, the main factors influencing fluid flow are examined. These are the wettability of the caprock formation, the interfacial tension (IFT) between the rock and the gas or liquid phases, and the ability of gases to diffuse through it. To achieve effective sealing, the caprock formation should possess low porosity, a disconnected or highly complicated pore system, low permeability, and remain strongly water-wet regardless of pressure and temperature conditions. In addition, it must exhibit low rock–liquid IFT, while presenting high rock–gas and liquid–gas IFT. Finally, the effective diffusion coefficient should be the lowest possible. Among all of the currently reviewed formations and minerals, the evaporites, low-organic-content shales, mudstones, muscovite, clays, and anhydrite have been identified as highly effective caprocks, offering excellent sealing capabilities and preventing hydrogen leakages.

The definition of pre-Messinian source rocks in the eastern Mediterranean is of paramount importance for hydrocarbon exploration because of the ability of salt to act as a high-quality seal rock. This research evaluates the organic geochemical features of the Upper Miocene (Tortonian—Messinian) sedimentary succession onshore Crete Island, Greece. The study employs original (Messinian, Agios Myron Fm) and published (Tortonian, Viannos Fm, Skinias Fm, Moulia Fm, and Messinian Ploutis section) results from organic geochemical analyses of mudstone samples. One hundred and one samples were examined using standard organic geochemistry methodology (Rock-Eval II and VI-TOC) to define the origin, type, and degree of organic matter maturity. The data indicate that the studied samples have poor to fair gas-prone source rock potential. These possible source rock units have not experienced great temperatures during burial, and, thus, their organic matter is thermally immature. The sub-salt (Tortonian—Messinian) source rock units are likely to be of higher thermal maturity in the western and eastern south Cretan trenches because of tectonic subsidence and a thicker sedimentary overburden. Several traps can grow in these regions, associated with normal faults, rotated blocks and unconformities (both below and above the unconformities). This research provides a basis for the further evaluation of the hydrocarbon potential in Crete Island. It is an area that shares geological similarities with the surrounding regions that contain proven reserves and is of crucial economic and strategic importance.

Neogene deposits in southern central Crete vary significantly in facies on a small scale due to synsedimentary tectonic resulting in block faulting. Integrated subsections from the Psalida, Mires and Kourtiani Kefala proved to be three suitable sequences for biostratigraphic studies based on calcareous and siliceous phytoplankton associations. Seven bioevents were used to determine the subzonal boundaries. They are in stratigraphical order: Last Occurence (LO) of , equivalent to the top of subzone CN8a (Lower Tortonian), First Occurence (FO) of , equivalent to the subzone CN8b (Lower Tortonian), Common Occurrence (CO), although rare, of the / group, equivalent to the base of subzone CN9a (Upper Tortonian), FO of , equivalent to subzone CN9bA (Lower Messinian) and the diatom biozone as well as the silicofl agellate biozone , FO of , equivalent to biozone CN9bB (Lower Messinian), FO of as well as LO of , (uppermost Zanclean – lowest Piacenzian), equivalent to subzones CN11b–CN12aA, CO of , and of (Lower Piacenzian), equivalent to subzone CN12aB, which correspond to the diatom biozone and the silicoflagellate subzone . Two sedimentation cycles are recognized for development of the Messara Basin. The first cycle starts in Lower Tortonian and lasts to the Lower Messinian (CN8a to CN9bB), while after the desiccation of Mediterranean follows the second one from the Upper Zanclean to the Lower Piacenzian (CN11b to CN12aB). No more marine Neogene sediments are recorded in Messara. German Die neogenen Ablagerungen im südlichen Zentralkreta zeigen markante fazielle Unterschiede auf schmalem Raum infolge synsedimentärer Tektonik, welche die Gegend zu einem Tafelbruchblock geformt hat. Vereinheitlichte Subprofile von Psalida, Mires und Kourtiani Kefala zeigen drei geeignete Sequenzen für biostratigrafische Studien, die sich sowohl auf kalkigen wie auch auf kieselige Phytoplankton-Vergesellschaftungen stützen. Zur Biostratigrafie und zur Abgrenzung der (Sub)Biozonen wurden sieben Biohorizonte ausgewählt. Sie sind in stratigrafischer Reihe: letztes Vorkommen (LO) von Discoaster bollii, äquivalent zum oberen Teil der Subzone CN8a (Unteres Torton), erstes Vorkommen (FO) von Discoaster loeblichii, äquivalent zur Subzone CN8b (Unter-Torton), gemeinsames Vorkommen (CO), wenn auch selten, der Gruppe Discoaster berggrenii / Discoaster quinqueramus, äquivalent des basalen Teils der Subzone CN9a (Oberes Torton), FO von Amaurolithus primus, äquivalent zur Subzone CN9bA (Unteres Messin) sowie die Diatomeen-Biozone Nitzschia miocenica und die Silicoflagellaten-Biozone Distephanus speculum minutus, FO von Amaurolithus delicatus, äquivalent zur Biozone CN9bB (Unter-Messin), FO von Discoaster asymmentricus sowie LO von Reticulofenestra pseudoumbilica; (oberstes Zanclium–basales Piacenzium), äquivalent zu den Subzonen CN11b–CN12aA, CO von Discoaster pentaradiatus, Discoaster surculus und Discoaster tamalis (unter Piacenzium), äquivalent zur Subzone CN12aB, welche den Biozonen Nitzschia jouseae (Diatomeen) und Distephanus boliviensis boliviensis entspricht. Zwei Sedimentationszyklen wurden für die geologische Entwicklung der Messara festgestellt. Der erste beginnt im unteren Torton und dauert bis zum Unteren Messin (CN8a bis CN9bB). Nach der Messinischen Salinitätskrise im Mittelmeer beginnt im Laufe des Unteren Pliozäns (Ober-Zanklium) der zweite Zyklus und endet im Mittelpliozän (Unter-Piacentium; CN11b bis CN12aB). Nach Beendigung des zweiten Sedimentationszyklus wurde in Messara nicht mehr marines Neogen nachgewiesen.