Stijene donjeg i srednjeg miocena, u istočnom dijelu Dravske depresije karakterizira složena geološka građa kao posljedica njihova formiranja unutar kontinentalnog riftnog sustava te naknadnih tektonskih procesa. Cilj disertacije je predstaviti procjenu potencijala geološkog uskladištenja CO2 temeljenu na tektonostratigrafskoj interpretaciji unutar istočnog dijela Dravske depresije. U tu svrhu kartirani su rasjedi, granice sekvencija, distribucija seizmofacijesa, analizirani su seizmički atributi, litofacijesi i sadržaj planktonskih foraminifera na uzorcima stijena. Zatim su procijenjene vrijednosti poroznosti na temelju karotažnih mjerenja, konstruirane se karate temperature, tlaka i gustoće CO2 u ležišnim uvjetima, kao i facijesni i petrofizikalni modeli interpretiranih sekvencija kako bi se izračunao teoretski kapacitet geološkog uskladištenja CO2. Definirano je osam litofacijesa koji su korelirani s interpretiranim seizmofacijesima u okoliše aluvijalne lepeze, lepezne delte, plitkomorske okoliše i dubokovodne okoliše. Sin-riftna tektonika je predstavljena višefaznom aktivnosti, koja se može prikazati tektonostratigrafskim sekvencijama prvog do trećeg reda, pri čemu je glavnina ekstenzije ostvarena po ekstenzijskim strukturama tipa ekstenzijskog detachmenta. Kolektorske stijene unutar rane sin-riftne faze predstavljene su litofacijesima okoliša aluvijalne lepeze i lepezne delte u obliku kanalnih formi i pješčanih tijela vrlo ograničenog prostiranja, dok su u naslagama kasne sin-riftne faze predstavljene litofacijesima priobalnih okoliša, lepezne delte i debritnih tokova na rasjednim padinama. Kapaciteti uskladištenja CO2 kreću se u rasponu od 6 kg/m3. Regionalni izolator za ove duboke slane vodonosnike predstavljen je panonskim laporima formacija „Croatica“ i „Medvedski breg“.
|Abstract (english)|| |
Lower and Middle Miocene rocks in the eastern part of the Drava Depression, between Podravska Slatina and Bizovac are characterized by complex geology resulting from their formation within the continental rift system and subsequent tectonic processes. Assessing the geological storage potential of carbon dioxide in such rocks therefore requires a complex approach to the analysis of seismic and well data. The aim of this dissertation is to present an assessment of the potential of geological storage of carbon dioxide based on tectonostratigraphic interpretation of the Early and Middle Miocene depositional succession in the research area between Podravska Slatina and Bizovac within the eastern part of the Drava Depression. In this study, complex geological setting represented by both lateral and vertical changes posed a issue in the correlations of the Early and Middle Miocene units that did not consider simultaneous fault activity. That is why, in this thesis special attention is given to the influence of fault activity and its role on sediment infill and its stratigraphic affiliation. For that purpose detailed tectonostratigraphic interpretation within sequence stratigraphy was performed (e.g. structural analysis of fault planes, interpretation of sequence boundaries, seismofacies distribution, and seismic attributes of RMS amplitude and RSM variance). Conventional geological methods included lithofacies reconstruction and paleontological analysis of planktonic foraminifera. In order to determine the petrophysical properties, a multimineral assessment of porosity was performed based on well log measurements. The final steps was to map the temperature, pressure and density of carbon dioxide at reservoir conditions complementary with the facies and petrophysical model for interpreted sequences. This additionally enabled numerical estimate of the CO2 geological storage capacity at the observed locations. Thickness distribution of the Lower and Middle Miocene rocks show the existence of several main depocenters located within the interpreted syn-rift structures of Krčenik, Magadenovac, Marjanci, Klokočevci and Hrkanovci. Detailed tectonostratigraphic analysis was made only in the northern part of the study area with reliable seismic data covering the Krčenik, Magadenovac and Marjanci depocenters. Syn-rift tectonics is characterized with multiphase activity where the majority of the extension was accommodated by extensional structures in the hangingwall of the extension detachment type. In the hangingwall of the extensional detachment structures, the syn-rift half-graben, graben, basin sag and supradetachment basins were formed together with numerous normal faults. Extensional detachments most likely represent inherited structures reactivated during the syn-rift phase. Interpreted extensional detachments Dravica and Miholjački Poreč can be spatially connected into the system of the main NE marginal Drava Depression extension fault, that delimitated the entire area of deposition during the syn-rift. Based on petrographic-sedimentological analysis, eight lithofacies were defined: Lithofacies of carbonate breccias and conglomerates (A), Lithofacies of polymictic breccia, conglomerates, sandstones and siltstones (B), Lithofacies of siltstones and silty limestones (C), Volcanic lithofacies (E), Lithofacies of marls intercalated with calcarenite and calcirudite (F), Lithofacies of polymictic breccia, conglomerate, sandstone, siltstone and silty micrite (G), Lithofacies of micritic limestone (H). These lithofacies are grouped into two associations, one representing deposits associated with predominantly continental environments and the other associated with marine environments. Within these lithofacies associations, alluvial fan environments, fan deltas, shallow-water environments, and deep-sea environments have been interpreted. Based on the interpretation of seismic data, it was possible to map the rift tectonostratigraphic sequences (RS). A first-order syn-rift sequence, which represents the entire syn-rift infill, can be divided into higher-order sequences associated with major normal fault structures. In the study area, considering the tectonic and sedimentary conditions, the second-order sequences can be distinguished into spatially separated sequences. These second-order sequences are associated with either continental deposition conditions, formed during extension onset - early rift phase, or with marine conditions, formed during a larger magnitude of extension - late rift phase. Here, second-order sequences of the early syn-rift phase were mapped, RS-Čret Viljevski (which is additionally divided into three third-order sequences) in the western part of the study area, and RS-Malinovac and RS-Števkovica in the eastern part of the study area. During the late rift phase, in the western part of the study area, due to the extension along the Dravica detachment, the second-order sequence RS-Dravica was formed and divided into two third-order sequences (RS-Dravica-1 and RS-Dravica-2). At the same time, in the eastern part of the study area, due to the extension along the Miholjački Poreč detachment a second-order sequence RS-Miholjački Poreč was formed, which is also divided into two third-order sequences (RS-Miholjački Poreč-1 and RS-Miholjački Poreč-2). Interpreted sequences of early rift phase are correlated with Lower Miocene. The interpreted sequences of the late rift phase correspond to the M5 and M6 zones of the Middle Miocene planktonic foraminifera. Mapping of seismofacies, lithofacies analysis and paleostructural reconstruction within each interpreted sequence enabled interpretation of the distribution of the environment, the location of potential reservoir rocks and the construction of a facies model. Within the early syn-rift phase, i.e. the Early Miocene, the reservoir rocks are represented by lithofacies A and B of the alluvial fan and fan delta respectively, which are in form of channels and sand bodies of a very limited distribution. Potential Middle Miocene reservoirs within the late syn-rift phase deposits are represented by lithofacies A, B, E, and G of coastal environments, fan deltas, and debris flow deposits of fault slopes. The regional seal for the deep saline aquifers of the Lower and Middle Miocene is represented by the Pannonian marls of the “Croatica” and “Medvedski breg” formations. Their thicknesses are variable, but suitable above the zones of interpreted reservoir rocks. Within the syn-rift infill, the lithofacies H may pose a local seal if potential reservoir rocks are located in their base. The calculated specific CO2 storage capacity in the collector rocks range up to 6 kg/m3. The PhD research presented here characterize a viable methodology for regional assessment of the potential of geological storage of CO2 in syn-rift rocks within the continental (passive) rift system. Due to the complexity of the sediment infill, as well as the structural relations of the syn-rift basin, various well data and reliable seismic data are needed, as well as the knowledge of their lithological composition. The methodological approach presented here involves interpretation of seismostratigraphic surfaces that represent rift tectonostratigraphic boundaries that can be correlated to the tectonic activity of the marginal normal faults. Mapping of seismofacies, analysis of lithofacies and analysis of paleostructural relationships within the interpreted sequence enables the interpretation of the distribution of the environment, the location of potential reservoir rocks and the construction of a facies model. In a complex lithological conditions, the method of multimineral inverse porosity estimation enables the estimation of porosity on well data, necessary for the construction of a petrophysical model. Together with the calculated values of carbon dioxide density, in reservoir conditions, it is possible to determine the theoretical storage capacity.