--> Forward Stratigraphic Modelling of Deep-Sea Sedimentary Environments: Predicting Facies Distribution in Salt Tectonics Context

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Forward Stratigraphic Modelling of Deep-Sea Sedimentary Environments: Predicting Facies Distribution in Salt Tectonics Context

Abstract

Abstract

Deep-sea sedimentary environments represent the ultimate frontier for hydrocarbons exploration as they are associated to many technical and scientific challenges. Even if the understanding of such environments has substantially increased during the last decades supported by advances in seismic imaging techniques and deep-sea drilling, reproducing the dynamic evolution of these systems is still a major defy. The use of innovative diffusion-based forward stratigraphic modelling approaches allows the reproduction of deep-sea sedimentary systems evolution under dynamic subsidence and uplift conditions. The modelling principles mimic the transport and sedimentation of sedimentary packages through time steps of tens of thousands of years or more along a continuously evolving basin-surface of hundreds of square kilometers. These sedimentary packages are transported along the system by diffusion following dynamic waterflow pathways and gravity driven creeping. Two sediment sources were used in the model: (1) a mix between lithic fine-grained sands as well as shale particles and (2) a mix between fine-grained quartz-rich sand particles and shales. Vertical uplift and subsidence were set as a proxy for syn-sedimentary salt kinetics, which directly impact on the basin geometry. A full 4D-grid resulted from the forward stratigraphic model showing the distribution of sandstone and shale packages through time. As two mineralogically different sources have been included in the model (lithic versus quarzitic sand), it was possible to determine the preferential sediment transport route and distal accumulation related to these sources. Such results provide valuable information on the impact of the primary source composition on the reservoir quality prediction previous to any diagenetic overprint. Lithology content in cells was consequently combined with calculated environmental parameters in order to generate a sedimentary facies grid evidencing the distribution of amalgamated channel infill, overbank, stacked lobes and shales. Alternative scenarios underlining the non-uniqueness of geological models were also generated by multi-realization loops permitting to consider the spectrum of variability linked to autocyclic processes (i.e channel avulsions). The Forward stratigraphic modelling approach constitutes a powerful tool for predicting facies distribution in deep-sea sedimentary systems and thus a valuable contribution for reducing risks in next exploration targets.