A fully integrated reservoir modelling approach aiming for the best conditioned static model for an underground gas storage facility (UGSF) in a complex structural and depositional setting is presented. The Nussdorf UGSF is a depleted gas field characterized by typical deep-water depositional environment settings including sediment mass-flow systems being shed off the emerging Alpine thrust front during the Neogene. The key challenge in assessing this specific storage performance is the communication within the individual stacked sandstone layers, as well as determining the existing cross-flow between such layers through wells and due to juxtaposition across faults. Highly heterogeneous reservoir facies, representing thin-layered, stacked sandy fans embedded in marly shale, were realized by joining object-based and Gaussian simulations constrained by a gross depositional environment model. Modelling known pressure communication across intrareservoir faults required fault throws to be adjusted at scales below the limit of seismic resolution. Scoping simulation runs on a best-guess model led to a full back-loop of the geological modelling. Several loops revealed that iterations limited to property realizations were insufficient, requiring additional modifications of the structural model. Only via this expensive approach could a geologically consistent and ‘fit for purpose’ reservoir model for the UGSF be achieved.