Structural Inversions in Western Hungary and Eastern Slovenia and Their Impact on Hydrocarbon Trapping and Reservoir Quality

Abstract

The first major oil field discovered in Hungary, Budafa, is an inverted anticline found based on surface dip measurements in the western Pannonian Basin in the 1930's. Surface anticlines were known in this area for a long time as they were referred to as the “Sava Folds” after a local river crossing the border zone between Hungary, Slovenia and Croatia. As this particular exploration play was relatively simple, i.e. E-W trending anticlines with relatively shallow Pliocene to Miocene clastic reservoir targets, all these prospects were drilled up as early as in the 1940's and all of them are essentially depleted by now. Current exploration efforts are focusing on the deeper parts of these anticlines where reservoir quality prediction and imaging of viable traps are the main challenges. As most of these anticlines are the products of Late Pannonian (Pliocene) inversion of Middle Miocene syn-rift half-grabens, the proper structural understanding of the core of the anticlines is critical. Recently acquired 3D seismic reflection data over the Lovaszi-Petisovci gas field complex, which straddles the Hungarian-Slovenian border, is used as the critical new data for a case study to illustrate the nature of positive structural inversion in the western Pannonian Basin. The 3D seismic data were also used to find sweets spots in the tight sandstone reservoirs within the inverted Miocene deposits. Whereas the Sava Folds, including Lovaszi-Petisovci anticlines, have map-view dimensions on the scale of 10s of kilometers, the Transdanubian Central Range of western Hungary has also experienced inversion and significant neotectonic uplift during the Quaternary, but at much larger wavelength of about 100s km. The kinematics of this large-scale inversion and its impact on the hydrocarbon exploration potential are poorly understood at present. On the scale of the entire Pannonian Basin, the inverted structures are concentrated at the western margin of the basin gradually propagating eastwards into the basin since the Late Pliocene. The inversions are driven by the ongoing shortening in the broader area, including the Alps, between the Adriatic promontory of Africa and the European plate.

AAPG Datapages/Search and Discovery Article #90194 © 2014 International Conference & Exhibition, Istanbul, Turkey, September 14-17, 2014