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

William Bosworth,Gábor Tari

doi:10.5194/se-12-59-2021

Abstract

Abstract. Folds associated with inverted extensional faults are important exploration targets in many basins across our planet. A common cause for failure to trap hydrocarbons in inversion structures is crestal breaching or erosion of top seal. The likelihood of failure increases as the intensity of inversion grows. Inversion also decreases the amount of overburden, which can adversely affect maturation of source rocks within the underlying syn-extensional stratigraphic section. However, many rift basins are multi-phase in origin, and in some cases the various syn-rift and post-rift events are separated by multiple phases of shortening. When an inversion event is followed by a later phase of extension and subsidence, new top seals can be deposited and hydrocarbon maturation enhanced or reinitiated. These more complex rift histories can result in intra-basinal folds that have higher chances of success than single-phase inversion-related targets. In other basins, repeated inversion events can occur without significant intervening extension. This can also produce more complicated hydrocarbon maturation histories and trap geometries. Multiple phases of rifting and inversion affected numerous basins in North Africa and the Black Sea region and produced some structures that are now prolific hydrocarbon producing fields and others that failed. Understanding a basin's sequence of extensional and contractional events and the resulting complex interactions is essential to formulating successful exploration strategies in these settings.

Highlights

The concept of structural inversion has existed for over a century (Lamplugh, 1919), it was Glennie and Boegner (1981) who explicitly used this term to describe the formation of a specific structure in the southern North Sea
When an inversion event is followed by a later phase of extension and subsidence, new top seals can be deposited and hydrocarbon maturation enhanced or reinitiated
The importance of inversion tectonics to both academic researchers and industry experts was quickly recognized as shown by several subsequent seminal works (e.g. Cooper and Williams, 1989; Buchanan and Buchanan, 1995)

Summary

Introduction

The concept of structural inversion has existed for over a century (Lamplugh, 1919), it was Glennie and Boegner (1981) who explicitly used this term to describe the formation of a specific structure in the southern North Sea. Kley and Krzywiec (2020) provide a discussion of the past 30-year history of positive inversion as a structural geology concept. Positive structural inversion entails partial or even complete reversal of extensional (“normal”) offset on a fault and the formation of associated anticlines. These features are of considerable interest to oil and gas explorationists. A certain combination of these effects could either improve or degrade the pre-drill risk profile of a hydrocarbon exploration target (e.g. Macgregor, 1995; Turner and Williams, 2004; Cooper and Warren, 2010; Bevan and Moustafa, 2012; Tari et al, 2020). Failure to recognize the impact of inversion on a basin’s geologic evolution can have a disastrous impact on an exploration program

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