Modelling of Geological Basins is typically based on integration of deep seismic and borehole data. In order to have systematically arranged data needed for the interpretation and modelling, it requires establishment of a basic Interactive Interpretation and Data Correlation Sys-tem (IIDCS). The establishment of a basic Interactive Interpretation and Data Correlation System (IIDCS) at the Croatian Geological Survey is one of the main goals of the GeoTwinn project. GeoTwinn is a Horizon 2020 project intended and designed to twin the Croatian Geological Survey (HGI-CGS) with two world-leading geoscience research insti-tutes; the Geological Survey of Denmark and Greenland (GEUS) and the British Geological Survey of the United Kingdom Research and Innovation (BGS-UKRI), leading to significantly strengthen HGI-CGS’s research collabo-ration (http://projects.hgi-cgs.hr/geotwinn/). GeoTwinn project consists four Work Packages (WPs); (1) 3D geo-logical surveying and modelling, (2) advanced groundwater flow and contaminant transport modelling, (3) geological hazards, and (4) geothermal energy.The IIDCS is built primarily for the GeoTwinn project, and will be used for the interpretation of geophysical and geological data, the advanced reservoir modelling, and fi-nally, for building an Initial 3D reservoir-properties model for the greater Zagreb area. It is also the intention of Geo-Twinn to use the IIDCS for introducing the digital storage, organization and management of all kinds of geophysical, geological and petrophysical data available at the Croatian Geological Survey.Geological modelling of the greater Zagreb area and its deep geothermal aquifer is the main objective of WP1. The model is to be used for modelling of geochemical processes, and fluid and heat flow modelling in the WP4. Zagreb geothermal aquifer is situated inside Triassic do-lostones and dolomitic limestones, and Badenian bioclas-tic limestones of the Vrapče formation. Well data shows that geothermal aquifer lays in depths between (approx.) 800 to 900 meters, and seismic data shows very com-plex structural and stratigraphic relations. The bottom and the base of aquifer were mapped using Halliburton Landmark DecisionSpace Geoscience software, and the data was stored into the Interpretation and Data Cor-relation System (IIDCS) using Halliburton Landmark OpenWorks database.