This report documents the initial selection of tools, modelling approaches and workflows for the various approaches to simulating subsurface dynamics of different types of High Temperature Underground Thermal Energy Storage(HT-UTES) in Work Package 2 of the HEATSTORE project. The primary focus of this report is on documenting the development of site-specific conceptual models, which paves the ground for the selection of tools, numerical approaches, and workflows. Results, validation approaches are not yet available but will be integrated into the final version of this report, due Month 35 of the project. Modelling will be performed on five sites with a High Temperature -Aquifer Thermal Energy Storage concept (HT-ATES, at Agriport A7 and Kopper Cress, Netherlands; Geneva and Berne, Switzerland; and Reykjavik, Iceland) with different high temperature water sources ranging from conventional hydrothermal deep geothermal through heated groundwater used in a geothermal power plant to waste heat from a waste incinerator. A broad variety of tools and pre-processing workflows to arrive at conceptual models is presented and reflects the different degrees of prior knowledge and maturity of the project. Process simulation will focus on heat transfer and flow with geochemical and geomechanical modelling adding important factes for some of the project. Modelling will also be applied to an advanced example of borehole thermal energy storage (BTES, French pilot project) and warm water storagae in old undergorund coal mine working (MTES, German project). Challenges here relate to a conduction-cominated storage (BTES) and the open boundaries to far-field and local groundwater flow fields (MTES). The report includes three sections on other modelling activities -assessing the HT-UTES potential in the Daish subsurface, and transferring the capabilities of advanced academic simulation tools used in HEATSTORE to other geothermal applications, i.e., constraining the nature of a high-enthalpy reservoir on the Azores and scenario modelling for superhigh-temperature resource development and utilization in Iceland.