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Contributors:
  1. Ayunda Aulia Valencia

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Description: Reconstructing ancient depositional environments and sedimentary facies distributions is vital to understanding the development of petroleum systems, as well as offering insights into the wider evolution of a region. However, in many underexplored, ‘frontier’ basins the identification of sedimentary facies is only possible at sparsely located wells, which are only able to document different facies in one-dimension. This is especially problematic in petroleum-bearing basins, where we typically need to define the three-dimensional distribution and geometry of source, reservoir, and seal rocks to define a working petroleum system. However, 3D seismic reflection data are able to provide detailed imaging of the earth’s subsurface across multiple stratigraphic levels. Interrogation of these data through the analysis of seismic attributes offers the opportunity to map the geometry and distribution of different facies in three dimensions. In this study, we examine the Farsund Basin, an underexplored basin located offshore southern Norway. Despite it lying in the prolific and much-explored North Sea basin, only one well has been drilled in the basin, meaning we have a very poor understanding of its hydrocarbon resource potential. Furthermore, this E-trending basin is anomalous to the N-trending basins present regionally, having experienced a different tectonic evolution, meaning that regional depositional models may not be applicable. We undertake a seismic attribute-driven interpretation of 3D seismic reflection data to constrain the geomorphological evolution of the Farsund Basin throughout the Jurassic, thereby assessing its petroleum potential and offering broader insights into the regional tectono-stratigraphic evolution of the area. We identify a series of west-trending rivers in the Lower Jurassic, the distribution of which are controlled by syn-depositional, salt-detached faults, rather than the basement-involved faults. Subsequently, following Middle Jurassic flooding, a series of carbonate reefs, expressed as sub-circular amplitude anomalies, developed. We identify two distinct reef morphologies, which we infer represent growth in differing water depths controlled by differential compaction of sub-reef strata across underlying, inactive faults. Within the Upper Jurassic we identify numerous curvilinear features, which are arranged into discordant sets and correspond to the downdip termination of southwards-prograding deltaic clinoforms. These deltas were deposited prior to the onset of fault activity. This study highlights how seismic attribute-driven, seismic geomorphological analysis can be used to identify facies distributions and types in areas lacking well penetrations. Furthermore, the geomorphological development of such basins, inferred directly from seismic reflection data, can be related to and help constrain their hydrocarbon potential and tectono-stratigraphic evolution.

License: CC-By Attribution 4.0 International

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