Along-Strike Prediction of Syn-Rift Fan Delta Architecture With Field, Subsurface and Numerical Modeling Investigations

Abstract

Syn-rift successions are attractive plays in many mature and frontier basins, but the interaction of normal faulting, and along-strike variation in shallow water processes and supply results in complicated depositional architectures that make the subsurface distribution of reservoirs and seals difficult to predict. Here, we integrate field, numerical, and subsurface approaches to address: 1) the along-strike variability and interplay of accommodation and sediment supply, and 2) the quantification of sequence stratigraphic interpretations in syn-rift settings. Field data and UAV photogrammetry-based 3D outcrop models are analysed from two adjacent and contemporaneous, Early-Middle Pleistocene, syn-rift fan-deltas, onshore the Gulf of Corinth, Greece. The deltas are situated 6 km apart in the hangingwall of a single normal fault, with one positioned near the fault centre (Kerinitis) and one near the fault tip (Selinous). By comparing the two systems, we quantify estimates of lake level, subsidence and sedimentation rates. Field data is input into the 3D sequence stratigraphic forward model ‘Syn-Strat’ to assess the impact of along-strike, down-dip and temporal (3D) variation of controls on the nature of stacking and formation of stratal surfaces. Varying the relative magnitude of subsidence to eustasy and different subsidence and sedimentation regimes through time provides the first quantitative insight into how the diachroneity of stratigraphic surfaces changes around a fault block. ‘Syn-Strat’ and a unit thickness extrapolation technique are also used to dissociate base level change from tectonic subsidence in the preserved stratigraphic record and reduce uncertainties in interpretation. Interfan areas, away from sediment sources, are occupied by reworking of marginal deposits and preserve a markedly different depositional architecture to fan axes. The evolution of the Kerinitis-Selinous interfan area reveals stratigraphic response to net subsidence followed by net uplift regimes, as a result of northward migration of fault activity and death of the normal fault controlling the two deltas. Our quantitative approach to the prediction of syn-rift stacking patterns and time transgressive surfaces is applicable to other rift basins to help reduce uncertainty during reservoir appraisal. Implications for stratigraphic pinchout assessment, connectivity analysis and cross-hole correlations are demonstrated with 3D reflection seismic and well data (North Sea).

AAPG Datapages/Search and Discovery Article #90350 © 2019 AAPG Annual Convention and Exhibition, San Antonio, Texas, May 19-22, 2019