Synthetic seismic model of a Permian biosiliceous carbonate – carbonate depositional system (Spitsbergen, Svalbard Archipelago)

The non-unique correspondence between seismic and subsurface geology is a fundamental problem when interpreting seismic data sets. Synthetic seismic models of outcrop analogs are commonly constructed to cover the gap between the small-scale outcrop observations and low-resolution seismic data. The Permian biosiliceous carbonate – carbonate sediments on Spitsbergen are characterized by a wide variability in lithologies and microfacies determining the petrophysical properties (e.g., porosity, acoustic properties) that consequently complicate seismic interpretation. This study uses 1D and 2D synthetic seismic modelling techniques (at different resolutions) to gain an understanding of how seismic reflectors are expressed with respect to the sediment distribution, aiming to facilitate real seismic interpretation. In the study area, nine microfacies were defined that were used to produce a geological model displaying small-scale microfacies variations within a well-defined sequence stratigraphic framework. Laboratory derived petrophysical properties (Vp, ρBulk and AI) were assigned to each predefined microfacies body in the geological models in order to construct acoustic impedance models that were used to produce synthetic seismograms. The appearance of the seismic reflectors in the synthetic seismic profiles is primarily controlled by changes in mineral composition and link to spatial microfacies distributions within the depositional sequences. Differences in acoustic impedance and the origin of synthetic seismic reflections within a single microfacies type are mainly caused by porosity contrasts (varying between 5 and 20%) and diagenetic modifications such as chertification and cementation. This detailed information cannot be derived from the low-frequency seismograms (25–100 Hz) resulting in changes in seismic expression when seismic resolution diminishes. Comparison with time equivalent, real and synthetic seismic data of the Finnmark Platform reveals similarities with the synthetic seismic reflection patterns of Spitsbergen. In both areas, the pronounced seismic traces follow abrupt microfacies transitions, which are coherent with cycle boundaries and timelines.