A Julia-Based Computational Framework for Combined Geothermal and Natural Gas Production in Mature Sandstone Reservoirs

The combined use of geothermal energy extraction and conventional natural gas production represents a promising approach to improve subsurface energy utilization during the energy transition. Mature gas reservoirs offer the potential to supply geothermal heat to nearby communities while extending hydrocarbon recovery through reuse of existing infrastructure. This study investigates combined geothermal–natural gas production in mature sandstone reservoirs, focusing on the Middle Buntsandstein Formation in Northwest Germany. A new computational framework is developed in the Julia programming language, incorporating two-phase flow, gas compressibility, and coupled heat transport. The framework exploits modern Julia features such as automatic differentiation, flexible finite-volume discretization, and multithreading based parallelization to efficiently simulate large-scale reservoir systems. Numerical simulations over a 30-year production period assess the influence of reservoir geometry, stratigraphy, and well configuration on thermal and water breakthrough behavior. Horizontal, anticlinal, and inclined reservoir settings can be evaluated to identify favorable production strategies. Work in progress investigates, if combined geothermal production can enhance cumulative gas recovery compared to conventional scenarios, primarily due to delayed water breakthrough. The framework provides a flexible basis for assessing combined subsurface energy systems while highlighting remaining limitations and directions for future development.