ERE5.4

Geothermal energy and thermal energy storages can significantly reduce the consumption of fossil energy resources by storing large amounts of heat in the subsurface, which is especially valuable when dealing with fluctuating renewable energy sources. Crystalline rocks with low hydraulic conductivity are a suitable target for such storage systems due to reduced convective heat losses. In the frame of the research project SKEWS (Seasonal Crystalline Borehole Thermal Energy Storage), a medium deep borehole thermal energy storage demonstrator with four 750 m deep borehole heat exchangers will be built at the Technical University of Darmstadt, Germany. In the preparation phase of this project, an extensive geophysical, petrophysical and structural dataset is gathered for the characterization of the project site’s subsurface.

This multi-disciplinary dataset is used for the creation of a first-order finite element method (FEM) model of the storage reservoir for thermo-hydraulic modelling. The input data includes a large petrophysical dataset for crystalline rocks and a stress-dependent Discrete Fracture Network (DFN) for the hydraulic characterization of the fractured granodioritic basement rock. For numerical analysis of the storage operation cycles, a novel co-simulation approach, using the FEM suite FEFLOW and the Modelica library MoSDH, is used to consider the interconnection between the subsurface heat-exchangers and the surface heating grid. This approach allows for detailed FEM modelling of the subsurface, while being able to take the complexity of the surface heating network into account at the same time. The model will be updated continuously by additional data during the building process of the pilot and the following experiments, to generate a highly detailed and validated numerical model of a heat storage system in a granodioritic reservoir. Ultimately, the presented workflow can serve for the accurate prediction of the performance of upscaled systems and therefore support a well-founded design process of this novel storage technology.

How to cite: Seib, L., Bossennec, C., Julian, F., Bastian, W., Frey, M., and Sass, I.: Numerical modeling of a granodioritic MD-BTES test-site, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4198, https://doi.org/10.5194/egusphere-egu22-4198, 2022.

Efficient thermal energy storage concepts are key for achieving the ambitious international climate targets. Implemented in thermal energy networks with a high contribution made by volatile renewable energy sources, large-scale applications for sensible heat and cold storage are favourable. They compensate for short-term fluctuations in the energy demand profiles, and they enable solar energy harvested in summer to be recovered for use in winter. Especially when pre-existing infrastructure facilities (e.g., basin installations from disused industrial, water treatment, and stormwater retention facilities) are reused as framework structures for thermal energy storage devices, environmental boundary conditions are often adverse. This is, for example, due to interference with near-subsurface aquifers or due to a suboptimal geometry of the given storage structure. For identifying strengths and weaknesses of a storage facility, and for technological optimization, simulation of thermal processes is vital. By this, the role of subsurface heterogeneity and slowly evolving transient thermal conditions in the storage device as well as in the ambient ground can be analysed. Thus, different degrees of utilisation, potential lateral energy losses or gains, and ultimately the economic viabilities of potential solutions can be evaluated. Most of the existing modelling applications do not address these issues in full detail. In fact, previous studies revealed that originally predicted efficiencies and amortization periods are often not achieved. This can be attributed to insufficiently represented boundary conditions (e.g., steady and uniform ambient temperatures at all exterior storage interfaces) or to rigorous simplifications by symmetric modelling techniques (no possibility to implement asymmetric processes, e.g., groundwater flow in surrounding subsurface).

In our study, we use a new numerical model to represent hydrogeological processes around ground-based thermal storage devices at high resolution and in different respects. In a series of generic scenarios, we focus on fundamental parameters of groundwater and environmental conditions, such as different groundwater levels and flow velocities, and we inspect the influence of various thermophysical (thermal conductivity/storage capacity) and hydraulic material parameters (e.g., porosity, permeability). With these, we analyse effects on storage utilisation rates, thermal losses, and temperature conditions in the surrounding area. Finally, we provide insight into previously neglected influencing factors and offer improvement strategies for the planning and implementation of large-scale, closed, seasonal thermal energy storage systems.

How to cite: Bott, C. and Bayer, P.: Modelling environmental interactions of large-scale, closed seasonal thermal energy storage systems, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-856, https://doi.org/10.5194/egusphere-egu22-856, 2022.

Crustal deformation allows us to monitor and understand critical properties of exploited geothermal systems around the world. The Hellisheiði high-temperature geothermal field (in 2011: 303MW_e and 133MW_th) in SW Iceland has been previously studied using Global Navigation Satellite Systems (GNSS) and Interferometry Synthetic Aperture Radar (InSAR) data between 2011 and 2015. These studies characterized the subsidence rate related to the extraction of fluids in the Hellisheiði area, as well as a 4-month uplift at the start of injection of geothermal fluids in the Húsmúli area. This uplift was accompanied by significant seismicity culminating with two M_L >3.5 earthquakes felt in the surrounding region.

We carry out further analysis of GNSS and InSAR data between 2011 and 2019 that show a total of three uplift events, separated by periods of subsidence or little deformation in the Húsmúli area. The deformation episodes seem to correlate with heightened seismic activity despite the continued decrease of injected mass flow rate in the original injection boreholes.

Here we use a finite element poroelastic model (COMSOL Multiphysics) to relate the extraction and injection of the adjacent Hellisheiði and Húsmúli areas to the ground deformation within the same time span. We assume that the boreholes can be represented by three point-injector sources: one of negative mass flow rate in Hellisheiði, and two of positive mass flow rates in (west and east) Húsmúli. The three sources are necessary to explain the deformation observed between 2011 and 2019. The poroelastic model presents insights into the temporal response of geothermal systems from extraction/injection, changes in exploitations and variability in permeability all of which induce heightened strain and stress in the fractured Húsmúli region. We investigate if poroelastic effects may be responsible for triggering transient earthquake swarms and to what degree poroelasiticy can explain the spatially and temporally complex uplift and subsidence. We suggest this study offers new insights into the Hellisheiði geothermal system that are transferable to geothermal systems around the world.

How to cite: Ducrocq, C., Heimisson, E. R., Geirsson, H., Árnadóttir, T., Axelsson, G., Hjörleifsdóttir, V., and Drouin, V.: Temporal deformation in the Hellisheiði geothermal field and its adjacent Húsmúli injection field explained by poroelastic modelling, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-531, https://doi.org/10.5194/egusphere-egu22-531, 2022.

Aquitard hydraulic properties are notoriously difficult to assess, yet accurate aquitard hydraulic conductivity estimates are critical to quantify recharge and discharge to and from semi-confined aquifer systems via hydraulic head gradients. Such flux quantification is required to evaluate the risks of aquifer exploitation by groundwater abstraction and aquifer vulnerability to surface contamination. In this study, we consider a regionally important aquitard and compare existing hydraulic conductivity estimates obtained through traditional methods to those inferred from long-term hydraulic head monitoring and thermally-derived vertical groundwater fluxes (0.04--0.25 m/y). We estimate the fluxes using numerical modeling to analyse the propagation of decadal climate signals into temperature-depth profiles and fitting the simulated and observed inflection point depths (minimum temperature). Results reveal that climate-disturbed temperature-depth profiles paired with multi-level head data can yield accurate vertical fluxes and aquitard hydraulic conductivities. This approach for characterizing groundwater systems and quantifying flows to and from sedimentary aquifers is more efficient but yields results that are comparable to conventional methods.

How to cite: Bense, V., Kruijssen, T., van der Ploeg, M., and Kurylyk, B.: Inferring aquitard hydraulic conductivity using transient temperature-depth profiles impacted by ground surface warming, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3659, https://doi.org/10.5194/egusphere-egu22-3659, 2022.

The storage of low-temperature heat in the near surface underground is already widely used worldwide, whereas only little attempts of storing of higher temperatures have been made so far. However, this can become increasingly important in the heat transition strategy by contributing with this technology to medium and peak load supply. Previous works have demonstrated that a large part of the required thermal energy can be efficiently stored in former oil reservoirs in Tertiary sediments of the URG. The advantage of using depleted oil reservoirs as HT-ATES is that they have a lower overall project risk due to the knowledge of the subsurface from the exploration history and that the geological and geophysical data, which are mostly available, allow a more reliable forecast of efficiency and development costs.

KIT in Karlsruhe has now planned the "Deepstor" HT-ATES research infrastructure for its Northern Campus. The site is adjacent to the former Leopoldshafen oil field and can draw on a large amount of data from boreholes for assessment prior to drilling. The targeted reservoirs is the several meters in thickness consisting of fine-grained calcareous sandstones from the Oligocene Froidfontaine Formation at a depth of approx. 1,300 meters.

The baseline of this study is the interpretation of petrophysical data such as resistivity-, sonic-, gamma and SP-logs to derive hydrogeological and geothermal parameters in 15 deep wells in vicinity of the planned drilling site. An integrated data analysis is performed with simulations to gain a quantitative understanding of the fluid and heat flow of the HT-ATES site and to predict the storage and recuperation capacity. Poro-perm values from core material are used to calibrate the results. The aim is a statistically based assessment of the storage site for planning and cost estimation of the research infrastructure.

This work should provide further insights for the future development of geothermal heat storage and enable the integration of a HT-ATES in the KIT campus.

How to cite: Steiner, U., Ang, N., Bauer, F., and Schill, E.: Characterization of Oligocene Oil Reservoir Sandstones for High Temperature Aquifer Thermal Energy Storage (HT-ATES) in the Upper Rhine Graben (URG), SW Germany, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5084, https://doi.org/10.5194/egusphere-egu22-5084, 2022.

Under natural conditions the thermal signature at the Earth´s surface equilibrates with the geothermal heat flux. Given that downward propagation of heat by conduction and advection is magnitudes lower than the daily and seasonal variation at the surface, these short-phased patterns impart a dampened and long-phased temperature response in the shallow subsurface. While climate change manifests in temperature trends that correlate at decade scale this signature is integrated by the slow heat transfer in gradual subsurface warming. In many places land use and small scale anthropogenic structures overprint the thermal response of the subsurface to climate change at the surface. In our contribution we present evidence of subsurface warming in natural and anthropogenic settings for different case studies in Central Europe. Repeated temperature depth logs reveal that in natural environments shallow subsurface temperature rise is trailing when compared to the rise in surface temperature and diminishes towards greater depths (e.g. +0.35 K per decate at the surface, +0.28 at 20 m, and +0.09 at 60 m below ground level for 32 wells in Bavaria). While in general a coherent pattern is found for different locations in natural environments, site-specific trends have a high spread (e.g. +0.36±0.44 K per decade for 227 wells in Austria) and temperature can also be dependent on vertical or lateral groundwater flow in the region. In built-up areas temperature rise in the subsurface is characterised by a higher variance and often exceeds the rise of surface temperature. Especially in dense urban areas ground temperature is elevated indicating local extreme temperature rises that are magnitudes higher than temperature rise at the surface. The high variance originates partially from the scarcity of reliable and long-term monitoring. Monitoring data typically lacks either depth or time resolution as temperature is either continously logged at a single-depth, erratically measured as depth profile, or measured at the surface during groundwater quality measurements.

How to cite: Bayer, P., Benz, S. A., Menberg, K., Blum, P., Noethen, M., and Hemmerle, H.: Subsurface warming trends in response to climate change and local heat sources in Central Europe, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5610, https://doi.org/10.5194/egusphere-egu22-5610, 2022.

The use of shallow geothermal energy (SGE) resources in oceanic volcanic environments entails additional challenges when compared to continental sedimentary/plutonic settings. The efficiency of shallow geothermal heat exchangers heavily depends on the geology and hydrogeology of the terrain where are placed. Volcanic rocks in small oceanic islands (<5,000 km²) are the result of volcanism, erosion, and tectonic collapse. All these processes conform highly heterogeneous formations with complex hydrogeology whose thermal response to shallow geothermal systems requires a good understanding of heat transfer in such environments. The SAGE4CAN project will concentrate on SGE resource assessment taking into account heterogeneity characteristic of volcanic formations, both at local and insular scale. To this end, the Canary Islands are selected as representative volcanic oceanic islands, to define SGE implementation barriers including but not limited to (1) heterogeneities of thermal properties intrinsic to volcanic formations (volcanic dikes, red layers, landslides, etc.), (2) heat advection in the context of complex groundwater flow in the unsaturated (dominate in midlands and highlands) as well as in the saturated medium (coast), (3) enhanced geothermal gradients, (4) transient effects of urban and volcanic activity, (5) heating and cooling demand, (6) shallow geothermal energy installations design and optimization, as well as (7) energy transition strategies in energy-dependent islands. The SGE4CAN project will investigate novel approaches to overcome such boundary conditions of oceanic volcanic islands in the estimation of the renewability of the resources, developing novel procedures to conduct cost-efficient and open-access Thermal Response Tests (TRTs), investigate the performance of existent SGE systems, assessing environmental impacts associated with SGE use. The knowledge generated from this project will be used on its final stage to identify adequate strategies for the integration of SGE into heating and cooling policies and action plans, as well as to raise awareness about the technology so that it gets recognition.

How to cite: García-Gil, A., Santamarta, J. C., Mejías Moreno, M., Baquedano, C., Garrido Schneider, E., Alonso Sánchez, T., Rey Ronco, M. Á., Sánchez-Navarro, J. Á., Marazuela, M. Á., Andreu Gallego, A., and Tiscar Cervero, J. M.: The SAGE4CAN project: The use of shallow geothermal energy from oceanic volcanic islands, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5795, https://doi.org/10.5194/egusphere-egu22-5795, 2022.

High Temperature - Aquifer Thermal Energy Storage (HT-ATES) offers a promising opportunity for climate-neutral heat supply in urban areas due to their high storage capacity and the possibility of direct integration into the regional district heating system. The assessment of the storage potential of HT-ATES requires reliable numerical models of the corresponding storage formation. To analyse the potential of the Lower Muschelkalk (Middle Triassic) as HT-ATES horizon, an unstructured 3D finite element model of the natural gas storage facility in Berlin/Spandau was developed. At this site, two porous layers (average porosity of 22 %) of oolithic grainstones characterize the target formation with a total thickness of about 30 m and a natural reservoir temperature of 32 °C in a depth of 535 m below ground surface. Beside lab analysis of core samples and fluid samples from the site, slug-withdrawal tests were performed in summer 2021 to identify hydraulic key parameters for the numerical simulations. The results indicate a productivity between 0.5 and 1.2 l/s/bar with reservoir permeability between 250 and 700 mD allowing maximum flow rates between 55 and 135 m³/h. In this study, we present a complete workflow from geological characterisation, lab analysis and field testing to detailed numerical HT-ATES simulations. Furthermore, we compare the storage potential based on different data sources such as solar heating systems and district heating networks. First results from the numerical simulations with storage volumes between 15,000 m³ (solar heating system) and 400,000 m³ (district heating system) show promising mean efficiency values between 60 % and 90 % within 25 years of operation. The hydraulic tests and the underlying numerical simulations indicate that the Lower Muschelkalk is suitable for HT-ATES.

How to cite: Wenzlaff, C., Winterleitner, G., Virchow, L., Regenspurg, S., Thielke, C., and Blöcher, G.: Assessing the geological potential of the Lower Muschelkalk as High Temperature - Aquifer Thermal Energy Storage (HT-ATES) horizon in Berlin (Germany), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7500, https://doi.org/10.5194/egusphere-egu22-7500, 2022.

Geothermal energy and thermal energy storage are essential components in balancing a decarbonated future energy supply. The north-eastern shoulder of the Upper Rhine Graben (URG), with its Variscan basement belonging to the Mid-German Crystalline High, is a potential target area for heat storage projects. Ganodioritic units in the city area of Darmstadt provide suitable thermo-mechanical properties to implement a Medium Deep Borehole heat exchanger Thermal Energy Storage (MD-BTES). This study focuses on the structural architecture of such crystalline units, representing a heterogeneous fracture and fault network. An approach combining geophysical characterisation and the analysis of surface fracture network analogue is performed to quantify the dimensions and topology of such a fracture network in the subsurface.

Two 2D seismic profiles helped to characterise the deep subsurface structures of the BTES demo site area and to localise the boundaries between the unweathered basement, the weathered basement, and the overlying sedimentary layers. The weathered basement and Permian volcano-sedimentary and Quaternary fluviatile units build the near-surface groundwater aquifer. This shallow aquifer requires a detailed investigation, performed through electrical resistivity mapping, near-surface S-wave refraction seismic survey, ground-penetrating radar lines and radon emanations profiles, combined with shallow geotechnical drillings. Selected surface analogues are located in the northern Odenwald Massif, the most extensive outcropping section of the Mid-German Crystalline High. The first analogue is a pit located 150 m apart from the BTES demo site. The second is the Mainzer Berg quarry in the Sprendlinger Horst, at a 12 km westbound distance, which belongs to Variscan granodioritic and granitic units with similar properties. Derived from these analogues, the fracture length distribution follows the power-law with an exponent about -2. The main relevant orientations identified are trending N030°E -N040°E, N090°E -N100°E, N120°E -N130°E and N165°E, with an overall fracture density of 3.06 frac.m^-1 for the demo site subsurface. Additionally, the connectivity of the fracture network is heterogeneous due to clustering. Such clustering also affects weathered horizons, which constitute the near-surface groundwater aquifer.

These fracture network properties are then implemented into sub-surface semi-artificial discrete fracture network (DFN) models to quantify at the first-order the flow properties of such heat storage rocks. This approach allows a successful characterisation of the BTES site, improves the local reservoir model accuracy and ensures an optimal assessment of the storage system behaviour.

How to cite: Bossennec, C., Seib, L., Frey, M., Burschil, T., Buness, A. H., Welsch, B., and Sass, I.: Geophysical and structural characterisation of a granodioritic MD-BTES test-site, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-734, https://doi.org/10.5194/egusphere-egu22-734, 2022.

The formation of free gas bubbles (degassing) is a major issue during production of geothermal fluids. These often contain substantial amounts of dissolved gasses, such as CO₂, CH₄ and N₂. Lower pressures in the region surrounding the production well can cause dissolved gas to come out of the solution. This can have detrimental effects on the production and generally on the operation, such as corrosion of the facilities or reduced water production as the gas limits the space where the water can flow. This study aims to improve the understanding of the conditions under which free gas nucleates, including determination of the bubble point pressure and temperature and the rate at which bubbles form during depressurization.

The focus of this study is on CO₂ degassing from high salinity brines. We report a series of well-controlled depressurization experiments in a pressure cell that allows for visual monitoring of the degassing process. The cell is filled with brine saturated with dissolved CO₂ at high pressure and temperature. The pressure within the cell can be reduced in a reproducible manner thus allowing for repeatable experiments. A high-speed camera paired with a uniform LED light source is used to record the degassing process. The pressure in the cell is monitored using a transducer synchronized with the camera. The resulting images were analysed using an in-house MATLAB code, which allows for determination of the bubble point pressure and rate of bubble formation. Experiments were performed at high pressure (up to 200 bar) and temperature (up to 200 °C) using a fixed CO₂ concentration of 200 mmol/L (i.e. 8.8 g/L). Two saline brine solutions are used to assess the influence of the salt concentration on the bubble nucleation process: a low salinity (1 M NaCl) and a high salinity (1.5 M CaCl₂ + 2 M NaCl) solution.

A model based on the geochemical software PHREEQC was also developed to predict the solubility of CO₂ in high salinity geothermal brines. This model allows for simulating the degassing behaviour at the same conditions as those used in the experiments. From these simulations, the theoretical bubble point pressure and temperature can be estimated along with the rate of gas exsolution during a depressurization process. As there are several alternative equation-of-states for CO₂ in solution with brines, a comparative matching of the depressurization experiments with individual formulations is presented.

How to cite: Boeije, C., Weinzierl, W., Zitha, P., and Pluymakers, A.: Degassing kinetics of high salinity geothermal fluids, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9212, https://doi.org/10.5194/egusphere-egu22-9212, 2022.

In conjunction with a deep geothermal project which is being implemented on the TU Delft campus in the Netherlands, a high temperature aquifer thermal energy storage (HT-ATES) is being considered. An initial feasibility study suggests that this could significantly reduce CO₂ emissions from heating and be financially beneficial. As part of the research associated with the implementation of the geothermal well, a 500 m deep monitoring and exploration well has been drilled to further investigate two target layers for HT-ATES and to allow for scientific records before, during and after the production phase of the geothermal project. With this drilling, the potential for HT-ATES of multiple layers is investigated by means of innovative exploration methods. An extensive set of downhole geophysical logging tools was used, many cores from both consolidated and unconsolidated layers were taken and a pumping test was carried out in the deepest layer. This work presents an initial overview of the work carried out and provides insights into the initial results of this innovative exploration drilling. The Delft geothermal project is therefore a great example of a beneficial interplay of economic and societal interest (i.e. city heating, CO₂-neutral campus) and scientific innovation.

How to cite: Vardon, P., Bloemendal, M., Beernink, S., Hartog, N., Barnhoorn, A., Schmiedel, T., Abels, H., and Laumann, S.: Exploration of high temperature aquifer thermal energy storage in Delft (The Netherlands), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12929, https://doi.org/10.5194/egusphere-egu22-12929, 2022.

Fracture surface topography exhibits long-range spatial correlations resulting in a heterogeneous aperture field. This leads to the formation, within fracture planes, of preferential flow channels controlling flow and transport processes. We have investigated numerically the influence of the statistical properties of the aperture field and upscaled hydraulic behavior on heat transport in rough rock fractures with realistic geometries. Similarly to the rough fracture's hydraulic behaviour, we find that its heat transport behaviour deviates from the conventional parallel plate fracture model with increasing fracture closure and/or decreasing correlation length.  We demonstrate that the advancement of the thermal front is typically slower in rough fractures compared to smooth fractures having the same mechanical aperture. In contrast with previous studies that neglect temporal and spatial temperature variations in the rock matrix, we find that the thermal behavior of a rough-walled fracture can, under field-relevant conditions, be predicted from a parallel plate model with an aperture equal to the rough fracture's effective hydraulic aperture. The practical implication of our finding is that thermal exchanges at the scale of a single fracture is controlled by the effective hydraulic transmissivity. Provided that thermal properties of the host rock are known, this implies that (1) geothermal efficiency can be computed at field sites using hydraulic characterization alone, and predicted using well-known low-dimensional hydraulic parameterizations in terms of effective hydraulic properties and (2) heat tracer tests are reliable for inferring effective fracture transmissivity.

How to cite: Klepikova, M., Méheust, Y., Roques, C., and Linde, N.: Heat transport by flow through rough rock fractures, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9263, https://doi.org/10.5194/egusphere-egu22-9263, 2022.

Understanding of subsurface flow and transport is of major interest supporting optimal design for several societal relevant technologies, such as waste disposals, geothermal or groundwater production facilities. To advance measurement and modeling techniques and refine them for practical applications, we further developed the fractured aquifer test site Rock Garden at the Martin Luther University Halle. The Rock Garden test site is situated beneath the courtyard of the Faculty of Natural Sciences III and is 60 m x 60 m in size. Fractured Rotliegend series of conglomerates, sand- and siltstones are investigated at the site by 6 drillings. A central borehole (B3) is 40 m in depth and developed as an open borehole between 15 m - 40 m below surface. Five boreholes are developed as groundwater observation wells of about 20 m depth and are equipped with filter screens between 10 m - 20 m below surface. Natural groundwater levels are on average about 3 m below surface and vary about 0.5 m around this value. The average gradient varies as a function of time between 0.3 % and 0.5 %, direction east northeast. A first pumping test in B3 unraveled hydraulic connection to all of the five surrounding boreholes. The effective transmissivities are of the order of 10^-5 m²/s and storativities are of the order of 10^-4. To understand hydraulically active fractures or fracture zones and their connection to the rock matrix at the Rock Garden site, a first flowmeter experiment was performed in well B3. Under natural conditions no flowmeter signals have been detected suggesting vertical ambient flow to be smaller than 7 cm/min. Under pumping conditions, the flowmeter signals suggest diffuse horizontal inflow from conglomerate lenses (about 80 % of the total inflow) and discrete horizontal inflow from fractures in clay and siltstones (about 20 % of the total inflow). To characterize these fractured and porous zones in detail, we plan performing hydraulic and tracer tomography at the Rock Garden test site in the near future.

How to cite: Englert, A. and Bayer, P.: Rock Garden test site – hydraulics in porous fractured media, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9562, https://doi.org/10.5194/egusphere-egu22-9562, 2022.

Aquifer Thermal Energy Storage (ATES) has significant potential to provide large-scale seasonal cooling and heating in the built environment, offering a low-carbon alternative to fossil fuels. To deliver safe and sustainable ATES deployments, accurate numerical modelling tools must be used to predict flow and heat transport in the targeted aquifers. However, numerical simulation of ATES systems is very challenging, due to the associated high computational cost of capturing fluid flow and heat transport at a high resolution and importance of accurately modelling complex geological heterogeneity.

Here, we present a novel approach to simulate ATES, based on the use of surface-based geologic models (SBGM), a double control-volume finite element method, and unstructured tetrahedral meshes with dynamic mesh optimisation (DMO). Previous use of DMO for a range of porous media flow applications has allowed an important reduction in the cost of numerical simulations. DMO allows the resolution of the mesh to vary over time and space to satisfy a user-defined solution precision for selected fields, refining where the solution fields are complex and coarsening elsewhere. SBGM allows accurate representation of complex geological heterogeneity and efficient application of DMO, essential for accurate simulation of ATES without excessive computational cost. 

We demonstrate application of these methods in two low-temperature ATES scenarios: a homogeneous aquifer, and a heterogeneous fluvial aquifer containing meandering, channelised sandbodies separated by mudstones. For both cases, cold and warm water are injected alternatively over 6-month periods via a well doublet. We demonstrate that DMO reduces the required number of mesh elements by a factor of up to 22 and simulation time by a factor of up to 15, whilst maintaining the same accuracy as an equivalent fixed mesh. DMO significantly reduces the computational cost of ATES simulations in both homogeneous and heterogeneous aquifers. This offers significant advantages compared to conventional methods in assessing the impact of uncertain geologic heterogeneity on ATES operation and efficiency, and in optimising individual and multiple ATES deployments.

How to cite: Regnier, G., Salinas, P., Jacquemyn, C., and Jackson, M. D.: Numerical modelling of Aquifer Thermal Energy Storage systems with Surface-Based Geologic modelling and Dynamic Mesh Optimisation, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11934, https://doi.org/10.5194/egusphere-egu22-11934, 2022.