High Risk Exploration in a Hypermature Hydrocarbon Basin: An Example from the Vienna Pull-Apart Basin, Austria

Abstract

OMV’s exploration efforts in Austria include the prospecting for new fields in units of the Alpine thrust belt below the Neogene Vienna Basin. Current exploration efforts are targeting the deep and underexplored parts of the Paleogene thrust belt with potentially large structural closures within the so-called Rhenodanubian Flysch units. Interpretation of fold-thrust structures is primarily based on new 3D seismic reflection data, which images the Paleogene nappes buried below the Neogene Vienna Basin fill and is supplemented by well data. In order to improve the understanding of the structural architecture, the results are compared to the regional structural framework of the Eastern Alps and West Carpathians to the W and NE of the Vienna Basin, respectively. Spatial seismic interpretation depicts the Rhenodanubian Flysch units being subject to three major phases of deformation during the Paleogene and Neogene: D1, Paleogene extension prior to thrusting; D2, Paleogene ~N-directed foreland propagating thrusting and subsequent Early Miocene ~N- and ~NW-directed out-of-sequence thrusting; D3, Middle and Late Miocene extension related to the formation of the Vienna pull-apart basin post-dating the thrusting episodes. Our interpretation depicts several large ~NE-trending structural closures within the deeper parts of the N-vergent Paleogene nappe stack with structural closures of up to 1000 m and areas of up to 5km². They include Paleogene turbidites, which are known dual porosity fractured reservoirs in producing fields within overlying nappes. The NE-trending structural closures result from both Paleogene N-directed thrusting and subsequent refolding of the N-vergent flysch nappes by Early Miocene NW-directed out-of-sequence thrusts. Comparison of data with the regional tectonic framework suggests that the NW-directed out-of sequence thrusts result from a local reorientation of thrusting and from basement buttressing during the Early Miocene, both being triggered by the shape and geometry of the underlying basement units. Our results highlight the exploration potential in the deeper parts of the Alpine thrust belt with target depths exceeding 3 km. Due to the complex deformation, challenging reservoir types, high formation pressures and limited amount of data, the exploration of these deep targets translates to higher geological/technical risks and uncertainties, compared to shallower, more traditional plays. However, though very challenging, the deep opportunities have the potential for finding significant resources in an already hypermature hydrocarbon basin.

Mineralogical, Bib‐sem and Petrophysical Data in Seal Rock Analysis: A Case Study From the Vienna Basin, Austria

“…Miocene sediments in the proto-Vienna Basin were deposited on top of allochthonous Alpine tectonic units which had been thrust onto autochthonous basement (Bohemian Massif and its sedimentary cover) during Paleogene to early Miocene times (Beidinger and Decker, 2016;Beidinger et al, 2019). The basin fill comprises sediments deposited during a piggy-back basin phase (early Miocene) and subsequent middle to late Miocene pull-apart and east-west extensional stages (neo-Vienna Basin; Hinsch et al, 2005).…”