A Physical Stratigraphic Hierarchy for Deep-Water Slope System Reservoirs 1: Super Sequences to Complexes

Steve Flint¹, David Hodgson¹, Anthony Sprague², and Darren Box^2
1The University of Liverpool, Liverpool, United Kingdom
²ExxonMobil Upstream Research Company, Houston, TX

Over a wide range of temporal and spatial scales deep-water clastic deposits are organized and predictable. This is in conflict with traditional models where deepwater slope channel-levee systems are envisaged to evolve from episodic, short duration turbidity currents generating disordered stratigraphic patterns. Extensive outcrop-based studies of well-exposed Permian slope deposits in the Karoo Basin, South Africa, have enhanced the development of a hierarchical approach to the prediction of the spatial and temporal partitioning of reservoir and non-reservoir facies, architecture and geometry at seismic to sub-seismic scales across a range of depositional environments. Here, the evolution of a range of reservoir and seal configurations through a stratigraphic section of 1.3 km thickness is discussed, from initial starved basin floor to upper slope deposits (the lowstand “systems tract” of a supersequence).

Slope channel-fills (storey sets), channel complexes and complex sets are organized into 10 depositional sequences that stack into 3 composite sequences. The composite sequences (one or more related sequences) are mappable for 10s of kilometers down dip and across strike. Typically, the identification of sequences and composite sequences is more straightforward in depositional levee/overbank settings where allogenic changes in sediment supply are preserved. In axial positions, sequence boundaries represent regional changes in slope channel complex set stacking patterns, fill style, and hence connectivity across regional erosion surfaces. Complex sets are identified on the basis of one or more related complex-fill styles and stacking patterns.

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