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Project

GHOST DigiT

We develop digital solutions to advance geological heat storage as an eco-friendly, scalable energy storage method, reducing energy demand and supporting the green energy transition.

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Upper left: Numerical simulation of BTES systems to explore optimal system parameters from predefined templates. Upper right and middle: Simulation of high-temperature seasonal energy storage in open systems with multiple, potentially intersecting fractures allows interpretation of measured operational data to understand reservoir characteristics and support long-term planning. Bottom: Proxy model calibration for very rapid simulation of ATES systems, enabling efficient control optimization workflows.

Project Overview

GHOST DigiT is a research project focused on developing digital twin technology for geological heat storage. The project addresses how subsurface heat storage systems can be designed, monitored, and operated more efficiently using advanced numerical simulation, data integration, and optimization methods.

GHOST DigiT targets underground energy storage (UTES), including Borehole Thermal Energy Storage (BTES) and Fractured/Aquifer Thermal Energy Storage (FTES/ATES) systems, each playing an important role in seasonal energy storage and the integration of renewable heat into future energy systems. By combining physics-based simulation models with operational data, GHOST DigiT aims to reduce uncertainty and improve decision-making throughout the lifetime of such systems.

Objectives and Scope

The main objective of GHOST DigiT is to develop digital twin technologies that support both design and operation of geological heat storage systems. This includes:

  • Advancing simulation models for BTES and F/ATES at relevant spatial and temporal scales
  • Integrating observational data for calibration and continuous model updating
  • Enabling optimization of system design and operational strategies under uncertainty

The project covers the full workflow from subsurface modeling to operational decision support, with strong emphasis on methods that are scalable, robust, and applicable to real industrial and urban heat-storage systems.

Progress in Simulation Capabilities

Significant progress has been made in the development of advanced simulation capabilities for BTES and F/ATES systems. The project has extended existing geothermal simulation tools to better represent and analyse:

  • Complex borehole configurations and multi-well systems
  • Coupled heat transport and fluid flow in heterogeneous and fractured subsurface media
  • Long-term thermal evolution and interaction with groundwater systems

These developments enable more realistic modeling of both charging and discharging phases, as well as assessment of heat losses, thermal interference, and system efficiency over multiple years of operation. The resulting models are used both for system analysis and as digital twin cores in operational studies.

Digital Twins in GHOST DigiT

In GHOST DigiT, a digital twin is understood as a living, physics-based model of a geological heat storage system that is continuously informed by data. This goes beyond traditional static simulation models and includes:

  • Regular updating and calibration using operational data
  • Explicit handling of uncertainty and sensitivities
  • Use of the model as a tool for prediction, optimization, and decision support

Although the establishment of fully featured digital twins is not within the project's scope, GHOST DigiT aims to develop enabling technologies that link subsurface models with surface facilities and operational constraints, making it possible to evaluate alternative operational strategies and to support informed decisions during day-to-day operation and long-term planning.

Differentiable Simulation and Gradient-Based Methods

A key methodological innovation in GHOST DigiT is the development and use of differentiable simulation. By making the simulation models differentiable, it becomes possible to compute accurate gradients of performance metrics with respect to model parameters and control variables. This enables efficient gradient-based methods for:

  • Model calibration and data assimilation
  • Sensitivity analysis
  • Optimization of design parameters and operational strategies

These methods are especially valuable for understanding geothermal storage systems, where geological complexity often exists alongside a scarcity of detailed subsurface data.

Case Studies and Demonstrators

The methods and digital twin concepts developed in GHOST DigiT are demonstrated and validated through several real-world case studies:

  • Wesselkvartalet (Oslo): An urban BTES system used in the project to study groundwater interaction, heat leakage, and alternative operational strategies.
  • GeoTermos (Drammen): Generic and scalable BTES concepts focusing on system design, performance assessment, and coupling with surface energy systems.
  • Kvitebjørn / Skattøra (Tromsø): A full-scale seasonal geothermal storage plant used to investigate calibration versus prediction, delayed thermal response, and operational uncertainty.
  • LKAB / Kiruna-related concepts (Narvik): Large-scale industrial heat storage concepts addressing long-term storage and integration in energy-intensive industrial settings.

Together, these case studies ensure that the project developments are grounded in practical challenges and realistic operating conditions.

Scientific Outputs

GHOST DigiT has produced and continues to produce scientific outputs targeting both the geothermal and applied mathematics communities. These include:

Conference papers and peer-reviewed journal publications

Presentations at international conferences and other venues

Open and representative models, algorithms, and open-source simulation frameworks

  • Fimbul.jl – Julia-based toolbox for geothermal simulations

Other publishing

Additional information on the industrial case studies

Skattøra

Kvitebjørn Varme AS supplies the whole of Tromsøya with district heating. Ruden Energy is developing a high-temperature UTES solution (140°C) in 300 m deep wells at Tromsø, allowing heat produced in the summer to be utilized in the winter. The production of heat at Kvitebjørn Varme takes place through waste incineration with heat recovery. The project aims for a discharge capacity of 6–8 MW with a storage volume of 20 GWh. Utilizing this heat in the wintertime will further reduce demands for electric heating. The main research challenges at Skattøra are optimal plant configuration, including understanding local geology, including major faults and dominating fracture networks, and determining optimal operational conditions.

Wesselkvartalet

Wesselkvartalet is a newly constructed, mixed residential/commercial building complex in the city of Asker. It integrates a multi-reservoir, geothermal storage facility to cover its heating and cooling needs, as well as supplying stored heat in the winter to a distributed snow-melting system for the city streets. The operation of the geothermal system is complex, with three geothermal reservoirs at different depths (5, 20 and 400 m) and very different properties, and comprising more than a hundred wells, set up to provide both constant base load and rapid release of heat at occasional peak loads. The plant has now been in operation since around 2020. Current major challenges include understanding and preventing significant energy leakage (advective and diffusive), determine optimal operational conditions, best use of available data, and evaluate utility and potential of new data sources.

Fjell Skole GeoTermos

Fjell Skole GeoTermos is a borehole thermal energy storage (BTES) system located beneath the parking area of Fjell elementary school in Drammen. The system comprises 100 boreholes, each 50 meters deep, arranged in a circular pattern to store thermal energy harvested during the summer months. This stored energy is then used to heat approximately 10,000 m² of building space during the winter.

The system is designed as a closed-loop, scalable solution that minimizes climate emissions and peak electricity demand. GeoTermos has demonstrated that seasonal storage of solar energy is feasible and effective in Norway, and it has attracted international attention as a model for sustainable urban energy systems.

Narvik GeoTermos

LKAB is developing a geothermal borehole thermal energy storage system at its Narvik facility to reduce energy use and climate emissions from energy-intensive industrial processes. The system follows the same closed-loop BTES concept as the GeoTermos installation at Fjell elementary school, but is scaled and configured for industrial heat demand. Surplus heat is stored in bedrock and recovered during winter, primarily to replace oil-based heating and reduce peak electricity demand in de-icing and washing of iron-ore wagons. The system is currently under development, and forms part of LKAB’s long-term strategy to phase out fossil energy use.

Key facts

Project duration

2024 - 2027

Partners

Ruden AS, Kvitebjørn Varme AS, Seabrokers Geoenergi AS, Asplan Viak AS, Wessel Energi AS

Project type

Knowledge building project for Industry

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Project employees