Seismic stratigraphic units, palaeogeography and their effect on hydrocarbon distribution in the upper Neogene of the Pannonian Basin

The upper Neogene lacustrine sedimentary succession of the Pannonian Basin in Hungary was divided into 40 sequences (clinothems) by seismic stratigraphic methods. The geographic position of the clinothems reflects the gradual infilling of the basin. Different patterns of progradation, aggradation and retrogradation can be observed within the same clinothem sets along the northern shelf of Lake Pannon, demonstrating that lake level was controlled by local factors, such as tectonics and sediment supply, not solely by climate. The distribution of discovered hydrocarbon resources within the clinothems by time, by depositional environment and by geographical regions was investigated for the first time through a systematic reservoir-level analysis. The reservoir sands are increasingly younger from the northwest towards the southeast, following the progradation of the shelf. Within each region, the oldest reservoir layers appear in the deep basin, whereas the second or third reservoir peaks are associated with deltaic environments. There appear to have been no general time intervals with basin-wide reservoir peaks when sands in anomalously large quantity or with specifically good reservoir quality were deposited. The petroleum accumulation was influenced by local factors in each sub-basin, such as inherited structure, syn- and post-sedimentary deformation, sediment source and maturity, and topographic confinement.