Potential of CO2 storage opportunities and the role of natural CO2 reservoirs in the Pannonian Basin

One of the key elements to achieve a low-carbon and sustainable future is to utilize the porous media in the subsurface. Carbon dioxide capture, utilization and storage is a promising way to use the subsurface and reduce anthropogenic greenhouse gas emissions, especially carbon dioxide. The Pannonian Basin, shared by Central-Eastern European countries, is one of the most prospective areas of onshore CO₂ geological storage in Europe. Late Miocene sedimentary rocks of the Pannonian Basin offer significant potential for storing large gas volumes. Storage potential assessment focused on two major groups of geological structures: depleted hydrocarbon reservoirs and saline aquifers. The CO₂ storage capacity of the potential fields was estimated based on volumetric parameters. The total CO₂ storage capacity of the depleted hydrocarbon fields is estimated to be ~97 Mt whereas in deep saline reservoirs is estimated to fall ~760 Mt. The reservoir rock with the highest storage potential consists of turbiditic sandstone, which is widespread and has regional extent in the Pannonian Basin.
The mechanisms of storage and the effect of CO₂ on porous rock still raises questions. Natural CO₂ occurrences have developed in similar geological structures to hydrocarbon reservoirs and represent a unique opportunity to study and understand the long-term fate of CO₂ in reservoir structures. Core samples from natural CO₂ reservoirs were investigated by detailed modal, textural and geochemical analysis. With isotope geochemistry (stable C, O and H isotopes in carbonates) and geochemical modeling (with PHREEQC) tools, we aim to shed light on which carbonates precipitated as a response to CO₂ flooding, and to estimate the mineral interactions on geological time scale (Falus et al., 2025).