AAPG Middle East Region Geoscience Technology Workshop, Rift Basin Evolution and Exploration

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Hyperextended Rifted Margins: The Lessons Learnt and their Implications for Future Exploration


Research by academic consortiums and petroleum companies using field analogues, numerical modelling and a wealth of new wells and high-resolution seismic data has not only enhanced our understanding of the formation of deep water rifted margins but resulted also in a paradigm shift. The most fundamental learning in deep water exploration is that the lessons learnt in the proximal domain cannot simply be applied to the distal domain. Indeed, numerous examples have shown that classical depth-uniform thinning models calibrated at proximal margins cannot predict the thermal regime and subsidence history of distal margins. Thus, unravelling the processes relating to extreme crustal thinning, magma production and breakup is fundamental to understand the play elements of this new and distinct play fairway. Adoption of the new learnings on the distal domain, in particular on its lithology, rheology and the impact of hydrothermal and/or magmatic fluids is necessary to become predictive and to develop play-based exploration workflows. However, the development of new concepts to explore distal margins critically depends on the access to pertinent geological and geophysical data sets, which remain a key problem at many rifted margins. At present, little is known about the depositional environments, sedimentary facies and magmatic systems, the kinematics and age of structures and the subsidence and thermal history of deep-water, distal rifted margins. The latest results of the rifted margin research show that most rifted margins evolve through three main deformation stages: an initial/diffuse stage, a necking/localizing stage and a breakup stage. Defining and mapping such stages and the related structures, stratigraphic and magmatic sequences is crucial to evaluate the play elements for each of these domains, in particular in the presence of voluminous magmatic additions or syn-extensional salt. Key questions that emerge from recent studies are: 1) how does the architectural variability of the continental crust control the thermal regime and subsidence history of distal domains, and 2) can the magmatic and thermal evolution of hyperextended systems be predicted based on ß-factors as done in classical depth uniform models or do we need other approaches? Finding answers to these questions, however, is at present limited by the poor understanding of the processes controlling the late stages of rifted margin formation. In particular the assessment of deep-seated mantle processes and their control on surface processes, the role of fluids (siliceous and aqueous) and the impact of inheritance (compositional, structural and thermal) is necessary to reach a better geological understanding and develop, implement and calibrate new quantitative models. In this presentation I will re-evaluate some of the challenges in understanding and explore distal margins, present new conceptual ideas and discuss their potential for the evaluation of petroleum systems in these frontier areas. The aim is to review some of the preconceived ideas on potential plays and prompt us to rethink the existing concepts. Although deep water rifted margins may be complex, the understanding of these complexities may evidence potential future plays in distal domains.