Inversion tectonics: a brief petroleum industry perspective

Abstract

Abstract. Inverted structures provide traps for petroleum exploration, typically four-way structural closures. As to the degree of inversion, based on a large number of worldwide examples seen in various basins, the most preferred petroleum exploration targets are mild to moderate inversion structures, defined by the location of the null points. In these instances, the closures have a relatively small vertical amplitude but are simple in a map-view sense and well imaged on seismic reflection data. Also, the closures typically cluster above the extensional depocenters which tend to contain source rocks providing petroleum charge during and after the inversion. Cases for strong or total inversion are generally not that common and typically are not considered as ideal exploration prospects, mostly due to breaching and seismic imaging challenges associated with the trap(s) formed early on in the process of inversion. Also, migration may become tortuous due to the structural complexity or the source rock units may be uplifted above the hydrocarbon generation window, effectively terminating the charge once the inversion has occurred. Cases of inversion tectonics can be grouped into two main modes. A structure develops in Mode I inversion if the syn-rift succession in the preexisting extensional basin unit is thicker than its post-rift cover including the pre- and syn-inversion part of it. In contrast, a structure evolves in Mode II inversion if the opposite syn- versus post-rift sequence thickness ratio can be observed. These two modes have different impacts on the petroleum system elements in any given inversion structure. Mode I inversion tends to develop in failed intracontinental rifts and proximal passive margins, and Mode II structures are associated with back-arc basins and distal parts of passive margins. For any particular structure the evidence for inversion is typically provided by subsurface data sets such as reflection seismic and well data. However, in many cases the deeper segments of the structure are either poorly imaged by the seismic data and/or have not been penetrated by exploration wells. In these cases the interpretation in terms of inversion has to rely on the regional understanding of the basin evolution with evidence for an early phase of crustal extension by normal faulting.

Hydrocarbon accumulation in basins with multiple phases of extension and inversion: examples from the Western Desert (Egypt) and the western Black Sea

“…The Sudak folded belt offshore Crimea (Tari and Simmons, 2018) formed during the Miocene (Stovba et al, 2009(Stovba et al, , 2013(Stovba et al, , 2017Sheremet et al, 2016a, b) in multiple stages (Fig. 3).…”

“…The Black Sea is classically divided into two separate basins -the western and eastern Black Sea basins (WBSB and EBSB) -with the divide formed by the Andrusov and Tari and Simmons (2018). Location is shown in Fig.…”

“…Whereas the Maykop sequence overall is dominated by shales (Fig. 9), as in the rest of the Black Sea (Tari and Simmons, 2018), there are reservoir quality deepwater sandstones in it, as in the Krymska field (Fig. 13) and in the undeveloped Subbotina oil discovery south of the Kerch Peninsula (Fig.…”

“…Figure8. Simplified structural map of the Black Sea modified fromTari and Simmons (2018). Location is shown in Fig.1.…”

Modes of Oblique Inversion: A Case Study From the Cretaceous Fold and Thrust Belt of the Western Transdanubian Range (TR), West Hungary

“…The European Alps are the result of two orogenic event (Figure 1), where the Cretaceous (Eolapine) formation of the Austroalpine nappe‐system was overprinted by the Cenozoic collision of these Adria derived units and the European margin (Schmid et al., 2004). Inversion of former rifted margins is a widely known phenomenon in the Cenozoic evolution of the Alpine orogeny (e.g., Boutoux et al., 2014; Butler et al., 2006; Granado et al., 2017; Tari et al., 2020; Ustaszewski & Schmid, 2006). However, the role of structural inheritance during the Cretaceous formation of the Austroalpine nappes (Eoalpine orogeny) is much less studied.…”