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3-D Sequence Stratigraphic Modelling of Shallow Marine Systems in Syn- to Post-rift Settings

Abstract

The North Sea hydrocarbon province is mature and hence exploration is increasingly focussed on stratigraphic and combination traps in syn- and early post-rift successions. These systems are active during thermal subsidence and marine transgression and preserve a complicated depositional architecture that is challenging to predict with conventional sequence stratigraphic models. Despite the advances of sequence stratigraphic theory there remains a lack of understanding of the interplay of the major controls (tectonic displacement, eustatic sea level and sediment supply) in three dimensions, particularly in regard to supply-driven sequences. A solid understanding would facilitate identification of reservoirs, and prediction of their geometry and calibre in syn- and post-rift settings, where elucidating the interplay of these controls is critical. We address this challenge with a novel, geometric, 3D sequence stratigraphic model that integrates tectonic constraints to sequence stratigraphy and considers both along-strike and down-dip variability in facies distribution on a fault segment-scale. The model generates a 3D accommodation surface in the hangingwall of a normal fault and applies an algorithm for potential sediment accumulation for the setting. Stacking patterns and systems tracts are predicted in time and space for a given set of controls and work is being undertaken to invert the model for potential prediction of facies distribution in the inter-well space in the subsurface and inter-log space in outcrop. Tests of the model are based upon a number of scenarios observed in 3D seismic, well and core data from the Central North Sea, with a focus on Upper Jurassic-Early Cretaceous, shallow-marine environments. Exhumed systems from modern rifts are analysed as analogues (e.g. Gulf of Corinth, Greece). Results demonstrate the along-strike and down-dip variability of sequence architectures in a number of real scenarios, and demonstrate a diachronous (time-transgressive) nature to sequence boundaries and other ‘correlatable’ key surfaces. The results from the model and field examples challenge classic sequence stratigraphic theory that such surfaces can be used as correlation horizons across a basin, which has direct implications for static reservoir model generation and hydrocarbon volume and production rate predictions.