Pavel, Lemberkovics_Basin Modelling
- 1. New Results of Geological and Geochemical Investigations and Basin Modelling of the Neogene Sequence, Southern Part of the Great Hungarian Plain, Hungary 1 2 Edina Pável , Viktor Lemberkovics 1 Department of Physical and Applied Geology, Eötvös Loránd University, Budapest, Hungary 2 RAG Kiha Kft., Budapest, Hungary pavel.edina1@gmail.com References Badics, B., Uhrin, A., Vető, I., Bartha, A., Sajgó, Cs, (2011): Medenceközponti földgáz-előfordulás elemzése a Makói-árokban. — Földtani Közlöny, 141, pp. 445-468. Balázs, E., Nusszer, A. (1987): Magyarország medenceterületeinek kunsági (pannóniai s. str.) emeletbeli vulkanizmusa. — MÁFI Évkönyv, 69, pp. 95-104. Haas, J., Budai, T., Csontos, L., Fodor, L., Konrád, Gy. (2010): Pre-Cenozoic geological map of Hungary, 1:500 000. — Geological Institute of Hungary, Budapest Magyar, I., Radivojević, D., Sztanó, O., Synak, R., Ujszászi, K., Pócsik, M. (2013): Progradation of the paleo-Danube shelf margin across the Pannonian Basin during the Late Miocene and Early Pliocene. — Global and Planetary Change, 103, pp. 168-173. Pepper, A. S., Corvi, P. J. (1995): Simple kinetic models of petroleum formation: oil and gas generation from kerogen. — Marine and Petroleum Geology, 12/3, 291-319. Tóth-Makk, Á., (2007): Late Miocene sequence stratigraphy of the Pannonian Basin fill (Kiskunhalas-Mélykút region, Hungary): how core, electric log and seismic data fit together? — Geologica Carpathica, 58, pp. 353–366. Acknowledgements The research was supported by the RAG Kiha Kft. We would like to express our thanks to Katalin Lőrincz, Dénes Kisfürjesi, Orsolya Sztanó, Balázs Badics, Katalin Milota, Lilla Tőkés, Ágnes Tóth-Makk, Attila Balázs, János Csizmeg and Enikő Várkonyi. Thanks Schlumberger GmbH for PetroMod 2012.1 basin modelling software. Fig.11. Maturity and migration history, potential accumulations of the study area Pepper and Corvi (1995) TII (B) Pepper and Corvi (1995) TIIIH (DE) Pepper and Corvi (1995) TII (B) Pepper and Corvi (1995) TIIIH (DE) Pepper and Corvi (1995) TIIIH (DE) 11.6 Ma 9.61 Ma 6.8 Ma present days present days Fig.10. Subsidence history of the study area 16.3 Ma 15.3 Ma 12 Ma 9.61 Ma 7.8 Ma present days 4. Subsidence history (Fig.10.) 5. Maturity and migration(Fig.11.) 6. Conclusion The results of the modelling suggest that presently the Badenian source rock is in the oil generation zone in the northern and in the northern part of the southern sub-basin. The oil generation and migration started from around 6.8 MY. The oil migrated upward along faults until the Szolnok Sandstone Formation but accumulations could not be formed yet. In the southern sub-basin significant part of the lower and middle Karpatian source rocks is in the gas generation zone, moreover the deepest parts of them reached the overmature zone. The hydrocarbon migration from the deepest part of the Karpatian source rocks started around 11.6 MY, and they started to form gas accumulations around 9.61 MY in the anticline structures of the Karpatian sandstones. Hydrocarbon gas accumulations were trapped in the Badenian carbonate formations too but no accumulations can be observed in the Pannonian sediments despite the possible upward migration along the neo-tectonic fault elements. It was concluded that one part of the southern sub-basin has either higher thermal up-heating or more deeply buried in the past than its recent structural position. The maturation of the source rock could reach the top of oil window in much shallower depths near this anomaly. Better understanding of the spatial heterogeneity of this complex geological and hydrocarbon system and the results of the basin modelling process bring new exploration perspectives for explorationists in this matured area. The subsidence history of the investigated sub- basins was significantly different. The main difference is the thickness of the Karpatian formations. While in the northern sub-basin barely 100 m thickness can be supposed; in the southern sub-basin it can reach 3500 m thickness based on our interpretation. The Miocene sediments of the southern sub-basin affected by a certain degree of inversion, which could already start during Badenian and continued in the Early Pannonian. Thickness of the Pannonian sediments is significantly different in the sub-basins too. In the southern basin the Pannonian sediments above the Pre-Pannonian formations are much thinner than in the northern basin. All of these facts made the model very complex along the 2D section. 3. Model building, parameterization In the studied area the source rocks are organic matter rich parts of the Karpatian and Badenian sediments. Based on the Hydrogen and Oxygen Index values the Badenian source rock contains type II, the Karpatian source rocks contain mainly type III kerogens (Fig.3.). During modelling the Pepper and Corvi (1995) TII (B) kinetic model has been applied in case of Badenian source rock in the southern basin, while in the northern basin TII-S(A) model has been used because of the expectedly high sulfur content of the source rock (based on oil samples, and evaporite presence). In case of Karpatian source rocks the TIIIH (DE) kinetic model has been applied. During maturation of source rocks the heat flow is one of the most important factors. The applied heat flow profiles (Fig.5.) are the results of the calibration to the measured temperature and vitrinite reflectance values in the 4 investigated wells. Fig.3. Van Krevelen diagram of Hydrogen and Oxygen Index values measured in the Badenian and Karpatian source rocks During modelling some of the input parameters were estimated, such as the eroded sediment thickness due to erosion events, the paleo water depth, the heat flow history, the role of faults during hydrocarbon migration and the original organic geochemical parameters of source rocks. Fig.5. Estimated heat flow history in the wells Fig.6. Estimated paleo water depth in the wells Fig.4. Detected eroded sediment thickness on the borehole logs of Well-2 compared to Well-1. In Well-2 on the running of log curves a sudden change can be observed between marl and silty claymarl, in Well-1 this transition is continuous Three erosion events were considered during model building. The first one happened on the boundary of Badenian and Sarmatian stages about 13 MY ago with average 50 m estimated eroded thickness.The next erosion event occurred at the end of Sarmatian time in the inverted southern sub-basin, 50-100 m eroded thickness was estimated. The third erosion event could be detected at the boundary of the Pannonian prodelta marl and silty claymarl approximately 50 m erosion is estimated based on borehole logs of Well-2 (Fig.4.). The investigated sub-basins had different evolution histories, so different paleo water depths have been determined along the section (Fig.6.). In the Pre- Pannonian ages it was estimated based on literature and paleontological investigations of wells. In Pannonian it was estimated based on calculations of decompacted sediment thicknesses. Fig.7. shows the supposed connection between paleo water depth and sediment accumulation. Fig.7. Supposed connection between paleo water depth and sediment accumulation Based on vitrinite reflectance values measured in the 4 investigated wells we could determine: the sediments in Well-2 reach the oil window in significantly shallower depths than sediments in the other wells. Compared to the Well-1 this depth difference is around 800 m (Fig.8. and Fig.9.). Fig.8. Vitrinite reflectance values measured in Well-1 and Well-2 Fig.9. Vitrinite reflectance values measured in the investigated wells 2. Seismic interpretation During seismic interpretation the Karpatian, Badenian, Sarmatian and Pannonian formations were interpreted based on drilling results of the 5 wells along the section, analogies and literature (Balázs and Nusszer, 1987; Tóth-Makk, 2007; Magyar et al., 2013). Assignment of the Karpatian source rocks was based on the TOC (Total Organic Carbon) and POT (Potential; S1+S2) contents measured in Well-4; if these values reached the good classification (TOC ≥ 1 wt%, POT ≥ 6 mg HC/g rock), we considered it as source rock. The southern sub-basin has been interpreted as a half-graben with a normal fault on its eastern edge, started to sink in the early Karpatian age. During the Badenian - early Pannonian ages this sub-basin had strong inversion phases. One of the result of this uplifting is the observed lateral facies change of Szolnok Formation from north to south. The northern sub-basin started to form later in the Badenian, and does not show significant inversion phenomena (Fig. 2.) Fig.2. Interpreted seismic section on the study area This study is focusing on a hydrocarbon exploration area in the southern part of Danube-Tisza Interfluve, Hungary. The studied sub-basins (northern and southern) formed during the syn-rift phase of the Pannonian basin development, along strike-slip zones – however under different time and geological setting. During our work a two dimensional (2D) basin model of subsidence and maturation history has been prepared for the Neogene sedimentary succession. With the help of the numerical basin modelling we were able to simulate and image the geological processes during the development of the two sedimentary sub-basins. Our goals with the current modelling were to determine the hydrocarbon potential, the time of hydrocarbon generation, the migration pathways of generated hydrocarbon and the potential accumulations. The data for the modelling was derived from 3D seismic volume, drilling results and literatures. The 2D basin model has been prepared along a selected 2D section from the 3D seismic data set (Fig.1.). 1. Introduction Fig.1. Location of the interpreted and modelled section (geological map after Haas et al., 2010)