Tertiary Subsurface Facies, Source Rocks and Hydrocarbon Reservoirs in the SW Part of the Pannonian Basin (Northern Croatia and South-Western Hungary)

摘要

The Neogene sedimentary successions of the Drava, Sava and Slavonija–Srijem depressions in the SW part of the Pannonian Basin System are built up of three 2nd order megacycles separated by four major erosional unconformities. The first megacycle contains terrestrial to marine syn-rift and early post-rift sediments of Early to Mid-Miocene age. The second is built up of Late Miocene Lake Pannon deposits, while the third contains those sediments which were deposited in the remnants of Lake Pannon and in the subsequent fluvial systems, in areas of continuous subsidence associated with basin inversion from the Pliocene onwards. Most of the petroleum source rocks and reservoir rocks are of Miocene age and were formed during the first and second depositional megacycle. Conditions for the accumulation and preservation of large quantities of marine and terrigenous organic matter were most favourable during the Badenian, Sarmatian and Early Pannonian, in deep basin settings, partly associated with rifting. The generation of hydrocarbons was promoted by relatively high geothermal gradients during the initial and subsequent thermal subsidence. Various sedimentary environments produced deposits with good reservoir characteristics: e.g. fault-related talus breccia (mainly Lower Miocene), reefs (mainly Badenian), coastal, shallow marine (Karpatian, Badenian) and deltaic (Pannonian–Pontian) sand bodies or turbiditic sand lobes (mainly Pannonian). The hydrocarbon (HC) migration paths were often provided by the major unconformities bounding the three megacycles, as well as by faults, particularly around the basement highs.