Sedimentology, log analysis, and high-resolution seismic data of the P01-FA structure, located in the western part of the Netherlands sector of the North Sea, were used to assess the correlatability and connectivity of the sand bodies, to unravel the complex internal reservoir architecture, and to demonstrate the impact that different conceptual geological models driven by different correlation methods can have on the correct understanding of the subsurface. Heterogeneity of reservoir architecture and internal reservoir facies was first assessed based on a well-to-well log-based correlation, and the results were compared with a correlation based on detailed examination of an inverted seismic cube. The overall resulting reservoir architecture based on detailed seismic-supported geological and stratigraphical analysis is significantly different from the one based only on well-to-well correlation, which may, at first glance, suggest a simple layercake architecture. The new model highlights how both, the internal structural and stratigraphical framework and the distribution of reservoir facies are most likely the result of a complex interplay of erosion, sedimentation, and tectonics. Tectonics was especially active during the lower and middle part of the Upper Rotliegend Group accumulation, thus influencing the lateral continuity of individual stratigraphic units. This study also demonstrates how unravelling the internal composition of mixed aeolian-fluvial reservoirs, by detailed seismic examination, is critical to describe the reservoir heterogeneity in order to assess and predict connectivity. This is especially important in sandy reservoir containing minor reservoir elements which can create large permeability contrasts (e.g., baffles and barriers) and ultimately influence hydrocarbon flow. This study demonstrates that an integrated evaluation using detailed sedimentary facies analysis and examination of seismic inversion data can allow a better understanding of reservoir geology by reducing the subsurface uncertainties and thus the risk associated with future appraisal and development activities. Copyright © 2011 SEPM (Society for Sedimentary Geology).