Geothermal Simulation Using MRST

Thermal energy from medium to high-enthalpy aquifers is an appealing energy resource: it is renewable, always on, and, at least in principle, available anywhere on the planet. Moreover, and perhaps equally important, aquifers are excellent candidates for flexible large-scale energy storage. This is imperative in order to transition from a mostly fossil-based energy supply to a mixture of renewable energy from multiple temporal resources (e.g., solar and wind power). Efficient utilization of geothermal heat requires a solid knowledge of the local subsurface situation and reservoir properties, including factors such as energy efficiency, storage capacity, economical aspects (e.g., drilling and operational costs), and compliance with legal regulations. This complexity can only be properly understood through numerical simulations. However, state-of-the-art numerical simulation tools for geothermal applications are somewhat lagging behind simulation technology for other subsurface applications (especially for oil and gas), even though they describe systems governed by the same physical principles. In this work, we present a module for geothermal simulation in the open-source MATLAB Reservoir Simulation Toolbox (MRST). The implementation is based on the industry standard finite volume discretization with single-point upstream evaluation and two-point flux approximation, and can therefore benefit from powerful solvers widely used by the reservoir simulation community. Moreover, the module can be integrated with well-established functionality from petroleum applications that are already part of MRST, such as optimal well control, inverse modelling, and uncertainty quantification, and apply it to real geomodels using complex fluid physics. We demonstrate the applicability of the module on a number of cases, ranging from simple conceptual tests, to realistic high-temperature aquifer thermal energy storage (HT-ATES) systems with industry-grade complexity.