Abstract
Numerical simulation is essential in geothermal energy development, helping to reduce subsurface uncertainty, optimize system design, and ensure regulatory compliance - critical factors given the high upfront costs and geological complexity of such projects. However, existing geothermal simulators often fall short due to limitations in geological complexity, inadequate physics, lack of engineering workflows, or restrictive licensing.
Fimbul.jl addresses these challenges as an open-source Julia package tailored for geothermal energy simulation. Built on the JutulDarcy.jl framework, it combines high-performance computing with automatic differentiation and robust numerical methods. Fimbul.jl supports a broad spectrum of geothermal applications, from aquifer and borehole thermal energy storage to conventional, enhanced, and closed-loop geothermal systems.
We demonstrate its capabilities through several case studies, including validation against a commercial simulator and digital twinning of a high-temperature aquifer thermal energy storage (HT-ATES) system.