Prospects for Hydrocarbon Exploration in the Mesozoic and Paleozoic Sections of the Pannonian Basin in Hungary

Abstract

To date, exploration in the Pannonian basin of Hungary has concentrated on oil and gas believed to be derived from source rocks of the Cenozoic. In this sense, the basin is a mature hydrocarbon province. However, exploration of the Mesozoic and Paleozoic sections has just begun. These section may contain significant quantities of hydrocarbons derived from source rocks of the Mesozoic. Much of the buried basement consists of a complex system of stacked nappes composed of Mesozoic and older rocks. Basement structures from three areas are shown: (1) southwestern Hungary, where oil and gas produced from fracture zones in the crest of nappes; (2) southeastern Hungary, where thrusting occurred subsequent to Upper Cretaceous deposition; and (3) western Hungary, where thrusting occurred prior to Upper Cretaceous deposition. In general, Paleozoic-Middle Triassic rocks are overmature; however, Upper Triassic-Cretaceous rocks entered the oil-generation window during the Neogene. The heavy oils of the Zala basin were generated from organic-rich marls of the Late Triassic. In the Mecsek area, Toarcian shales are likely a good source for oil. Upper Cretaceous rocks, because of their terrestrial character, are inferred to be gas prone. Reservoir properties of Triassic and older rocks are expected to be poor, exceptmore » where fracture porosity occurs. In the Nagylengyel field, rudist limestones of Late Cretaceous contain prolific reservoirs with primary solution and fracture porosity. Although the average porosities of these reservoir rocks are relatively low (2-4%), permeabilities are >1-2 d as a result of paleokarst development.« less