Ingo Sass

• Dr.
• Professor (Full) at Technical University of Darmstadt

This paper reviews the current research on aquifer thermal energy storage (ATES) and mine thermal energy storage (MTES) in Germany providing descriptions of 3 low-temperature ATES (LT-ATES), 8 high-temperature ATES (HT-ATES), and 2 MTES research sites. While the overview reveals a diverse field of investigations spanning various spatial scales, res...

This paper reports more than 500 newly measured values of the dynamic viscosity of pure and mixed sodium chloride (NaCl) and calcium chloride (CaCl 2 ) aqueous solutions of which about half are unique. The data were acquired with a commercial rolling ball viscometer at ambient pressure, temperatures between 293 and 353 K, concentrations up to 6.0 m...

To date, most geothermal projects in Germany have focused on deep geothermal systems, while resources at intermediate depths have only been explored to a small extend. However, medium-depth geothermal systems have a high potential for heat generation, even in areas previously considered less favorable for deep geothermal energy, and could make a si...

This study, from Turan et al. (2024), aims to quantify the untapped geothermal potential of the Cornubian Batholith for power generation and direct heat use. Recent fieldwork, laboratory measurements and petrophysical characterization have produced a new dataset, including subsurface samples from the production well of the United Downs Project, a d...

This study reports on newly acquired density data of synthetically prepared pure and mixed NaCl and CaCl 2 aqueous solutions that span a wide range of geothermally encountered concentrations and mixing ratios. The analytical data are provided for the temperature range of 293–353 K at ambient pressure. For the reproduction of that data, PHREESCALE w...

Die Geothermie kann einen bedeutenden Beitrag zur Defossilisierung der Wärmeerzeugung in Deutschland leisten, die noch immer zu rund zwei Drittel auf fossilen Energieträgern basiert. Die vorliegende STUDIE nimmt die Geothermie im Kontext der Wärmeversorgung in urbanen Räumen in den Blick und betrachtet deren Voraussetzungen und Möglichkeiten, aber...

Space heating applications account for a high share of global greenhouse gas emissions. To increase the renewable share of heat generation, seasonal thermal energy storage (STES) can be used to make thermal energy from fluctuating renewable sources available in times of high demand. A popular STES technology is pit thermal energy storage (PTES), wh...

The storage of energy from renewable energy sources in the form of hydrogen (H2) is seen as a promising way to balance seasonal fluctuations in supply and demand. Hydrogen can be produced using excess electricity and stored temporarily in geological formations. Salt caverns, depleted oil and gas reservoirs and deep saline aquifers have been propose...

Geothermal energy could play a pivotal role in decarbonisation as it can provide clean, constant base-load energy which is weather independent. With a growing demand for clean energy and improved energy security, geothermal resources must be quantified to reduce exploration risk. This study aims to quantify the untapped resource-potential of the Co...

TRANSGEO is a regional development project that aims to explore the potential for producing sustainable geothermal energy from abandoned oil and gas wells in central Europe. Composed of 11 partner organizations and 10 associated partners in 5 countries, TRANSGEO is developing a Transnational Strategy and Action Plan to address this technical and ec...

For efficient and economically viable heat storage solutions, and to enhance their integration into the energy mix for the heat supply of district heating networks, assessing and optimizing the potential of sedimentary reservoirs for high-temperature Aquifer Thermal Energy Storage (ATES) is a key aspect. The PotAMMO project (BMBF, PtJ, FKZ: 03G091...

GeoLaB (Geothermal Laboratory in the Crystalline Basement) started in the beginning of 2023 to plan and build an underground geoscientific laboratory in a fractured crystalline basement. One of the potential selected sites is the Odenwald complex (Hessen, Germany) due to its geology (fractured crystalline basement) and petrology (Tromm granite). Co...

The influence of deep and regional geological structures is becoming increasingly important in superhot geothermal systems due to their proximity to the transition between brittleness and ductility. In the Los Humeros geothermal field in Mexico, where subsurface fluids reach temperatures of over 350 °C, the surface structures resulting from the col...

Medium-Deep Borehole Thermal Energy Storage (M D-BTES) systems are a promising technology for sustainable and efficient seasonal thermal energy storage and district heating distribution. These innovative systems are designed to store excess thermal energy e.g. generated from renewable sources in the subsurface using borehole heat exchangers (BHE) a...

The use of intermittent renewable energy sources is of great importance for reducing greenhouse gas emissions. Medium-deep borehole thermal energy storage systems (MD-BTES) represent an economic solution. At the Technical University of Darmstadt, Germany, an MD-BTES consisting of three 750 m deep borehole heat exchangers was constructed as a demons...

Outcrop analogue studies are of high priority as they allow the interpretation of geophysical surveys, minimizing the exploration risk, reliable predictions of reservoir properties and drawing conclusions on expected discharge, before drilling in a cost-wise way. Detailed knowledge of the petrophysical properties and petrographical characteristics...

The Sahinkalesi, a volcanic dome located NNE of Hasandag, Türkiye exhibits anomalous heat flow value, geothermal gradient and the Curie point depth is located at very shallow depth in this region. Our investigation indicates presence of super-critical thermal regime (378 °C) at about 4 km depth and the MT analysis indicate shallow magma chamber at...

This numerical study delves into the dynamic interaction between reservoir heterogeneity and its impact on the dual objectives of geothermal energy extraction and CO2 sequestration. Employing finite element models, this research scrutinizes the effects of variable porosity, permeability, and capillary entry pressures on fluid dynamics and thermal p...

The fracture network largely determines the efficiency of heat extraction from fractured geothermal reservoirs. Fracture openings are influenced by thermo-poroelastic stresses during cold fluid flow, with the interplay between fracture length and fracture opening regulating heat transfer. The lack of field data concerning fluctuating fracture openi...

Until now, the majority of geothermal projects in Germany have focused on deep geothermal systems, while resources at intermediate depths have been little explored. However, intermediate-depth geothermal systems possess a high potential for heat generation, even in areas previously considered less favorable for geothermal energy utilization, and th...

Challenges for geosciences with societal relevance include the use of crystalline geothermal reservoirs for the energy transition as well as final disposal. Crystalline rocks, along with clay and salt, are being considered as host rocks in the ongoing search for a suitable site for a nuclear waste repository in Germany. Currently, there is no exist...

Heat storage in crystalline basement rocks is a promising technology because it can provide a reliable source of heat and help to increase the efficiency of energy systems, and reduce greenhouse gas emissions. BTES systems work by circulating water in multiple borehole heat exchangers (BHE). However, BTES systems can be expensive to install, as the...

District heating grids (DHG) face the problem of seasonal variability and peak demands, e.g., there is a high demand for heat in winter and a low demand in summer. Operators of district heating networks and energy suppliers are therefore seeking solutions to store heat and access it at peak times, thus reducing the use of carbon-emitting heat sourc...

To increase fluid flow and thus obtain higher heat production from a geothermal well, chemical stimulation can be performed in their open-hole sections. Through chemical stimulation, fracture zone permeability in the vicinity of the borehole can be enhanced which results in higher fluid connectivity from the well to the reservoir fracture network....

Fracture networks linked to the brittle deformation of rocks are often hosts of fluid flows or geomechanical discontinuities which are important to model for rock mass stability analyses, reservoir assessment or storage capacity evaluation. However, the fractures can be mapped only poorly by subsurface geophysics or borehole imagery. 1D scan lines...

A regional assessment of the potential for geothermal heat production, power generation and also heat storage requires an evaluation of the heat in place and its recharge. Both are controlled by the flow properties and natural fluid flow through the reservoir at the present day, which must be thoroughly analysed based on the understanding and model...

Heat storage is a promising technology because it can provide a reliable heat source and help increase energy system efficiency and reduce greenhouse gas emissions. Aquifer thermal energy storage (ATES) and borehole thermal energy storage (BTES) systems work by circulating fluids with seasonal or shorter periodicity (in closed or open loop systems)...

Globally, the largest geothermal resources are linked to the crystalline basement, which could be exploited using Enhanced Geothermal Systems (EGS). The planned underground laboratory GeoLaB aims to facilitate the large-scale application of EGS technologies by performing in-situ high-flowrate experiments on fault zones. The Tromm Granite at the nor...

Against the background of climate change and the geopolitical situation, the worldwide pressure mounts to reduce the dependence on fossil fuels and to accelerate the energy transition as quickly as possible. Geothermal technologies have a key role to play in supplying and storing heat. The greatest, yet untapped geothermal potential lies in the cry...

The possibility of impure carbon dioxide (CO 2) sequestration can reduce the cost of these projects and facilitate their widespread adoption. Despite this, there are a limited number of studies that address impure CO 2 sequestration aspects. In this study, we examine the convection-diffusion process of the CO 2-nitrogen (N 2) mixture dissolution in...

Deep geothermal energy represents an essential component of the future energy supply because the resources greatly exceed the demand, and the base load capability can compensate for temporal fluctuations in wind and solar power. By far, the largest amount of heat is contained in the crystalline basement, accessible almost everywhere through deep dr...

Porosity and permeability alteration due to the thermo-poro-elastic stress field disturbance from the cold fluid injection is a deciding factor for longer, more economic, and safer heat extraction from an enhanced geothermal system (EGS). In the Soultz-sous-Forêts geothermal system, faulted zones are the main flow paths, and the resulting porosity–...

Intensive graduate courses in geothermal energy have traditionally been the remit of nations with a long tradition of high temperature geothermal utilization: Iceland, Italy, Japan, and New Zealand. In addition, El Salvador has had a Spanish language Geothermal Diploma Course for Latin America since 2010, courses in Indonesia, taught in Indonesian,...

Crystalline rocks from Mid-German Crystalline High show significant potential for geothermal exploitation and heat storage, thanks to the favorable intrinsic petrophysical rock and reservoir properties. However, the success of a heat-exchanger facility relies on the proper estimation of the hydraulic and heat transfer properties of the targeted res...

Solutions for seasonal underground thermal energy storage (UTES) systems are essential to use the full potential of fluctuating renewable energy sources. Crystalline rocks with high thermal conductivity and heat capacity show large potentials for such heat storage purposes. The efficient and economic operation of such a system relies heavily on a p...

In recent years, several studies have shown that geothermal resources considerably exceed the current energy demand in Germany. The by far largest share is attributed to the crystalline basement, which generally exhibits very high temperatures and is practically available in unlimited quantities. In the tectonically active Upper Rhine Graben (URG),...

Abstract Hydrothermal alteration is a common process in active geothermal systems and can significantly change the physiochemical properties of rocks. To improve reservoir assessment and modeling of high-temperature geothermal resources linked to active volcanic settings, a detailed understanding of the reservoir is needed. The Los Humeros Volcanic...

Solutions for seasonal energy storage systems are essential for the reliable use of fluctuating renewable energy sources. As part of the research project SKEWS, a medium deep borehole thermal energy storage system with a depth of 750 m is under construction at Campus Lichtwiese in Darmstadt, Germany, to demonstrate this innovative technology. Prior...

Deep geothermal energy represents a key element of future renewable energy production due to its base load capability and the almost inexhaustible resource base. Especially with regard to heat supply, this technology offers a huge potential for carbon saving. One of the main targets of geothermal projects in Central Europe is the Upper Rhine Graben...

The United Downs Deep Geothermal Project (UDDGP) is designed to utilize a presumably permeable steep dipping fault damage zone (constituting the hydrothermal reservoir in a very low permeability granitic host rock) for fluid circulation and heat extraction between an injection well at 2.2 km depth (UD−2) and a production well at 5 km depth (UD−1)....

Geothermal energy is an infinite energy source for the present human society. Energy extraction from the deep subsurface requires engineering using a working fluid that circulates between well doublet. Due to its thermal properties, CO2 is an ideal option as a heat transfer fluid. By using CO2, working fluid loss is an advantage compared to other w...

Deep saline aquifers are one of the best options for large-scale and long-term hydrogen storage. Predicting the diffusion coefficient of hydrogen molecules at the conditions of saline aquifers is critical for modelling hydrogen storage. The diffusion coefficient of hydrogen molecules in chloride brine with different cations ($\mathrm{Na}^+$, $\math...

Porosity and permeability alteration due to the thermo-poro-elastic stress field disturbance from the cold fluid injection is a deciding factor for longer, economic and safer heat extraction from an enhanced geothermal system (EGS). In the Soultz-sous-For\^ets geothermal system, faulted zones are the main flow paths and the resulting porosity-perme...

The crystalline basement is considered a ubiquitous and almost inexhaustible source of geothermal energy in the Upper Rhine Graben (URG) and other regions worldwide. The hydraulic properties of the basement, which are one of the key factors in the productivity of geothermal power plants, are primarily controlled by hydraulically active faults and f...

As renewable energy, geothermal can contribute substantially to the energy transition. To generate electricity or to harvest heat, high-saline fluids are tapped by wells of a few kilometres and extracted from hydrothermal reservoirs. After the heat exchanger units have been passed by, these fluids are reinjected into the reservoir. Due to the press...

This work presents the estimation of the CO2eq emissions of the geothermal power station in Los Humeros, Mexico. The calculation takes the emissions of the CO2 contained on the extracted geothermal brine plus the CO2 footprint by the power station construction. The carbon footprint estimation is based on technical reports generated by the owner com...

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 du...

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 Darm...

Integration of borehole heat exchangers (BHE) into district heating (DH) should be supported by numerical simulations to ensure efficient operation. Co-simulation allows for the use of dedicated software for above and below ground sub-models, facilitating the use of detailed 3D geological models. This paper presents a methodology for coupling DH mo...

A fractured reservoir can support and sustain long-term geothermal energy extraction operations. The process of injecting cold water to extract hot water from a fractured reservoir result in thermal and poroelastic stress alteration in the rock matrix and the fracture. The thermo-hydro-mechanical (THM) processes govern the efficiency of an enhanced...

Geothermal energy has the potential to support direct heat usage and electricity generation at a low carbon footprint. Using carbon dioxide (CO2) as a heat transfer fluid can allow us to achieve a negative carbon energy solution. This study assess the geothermal energy extraction potential from a discretely fractured reservoir using CO2. The geothe...

Borehole heat exchanger (BHE) arrays represent a key technology for the future provision of sustainable building heating and cooling energy. They are either used as pure geothermal systems only extracting heating energy from the subsurface or they are also used to store excess heat from solar thermal collectors or waste heat from cooling applicatio...

Abstract The Los Humeros Volcanic Complex has been characterized as a suitable target for developing a super-hot geothermal system (> 350 °C). For the interpretation of geophysical data, the development and parametrization of numerical geological models, an extensive outcrop analogue study was performed to characterize all relevant key units from t...

Fracture network is a crucial element to address in any model of the thermo-hydro-mechanical behaviour of a reservoir rock. This study aims to provide quantified datasets and a further understanding of the critical parameters of the fracture network pattern in crystalline rocks. In the Northern Upper Rhine Graben, such rock units are targeted for m...

A hydrothermal doublet system was drilled in a fault-related granitic reservoir in Cornwall. It targets the Porthtowan Fault Zone (PTF), which transects the Carnmenellis granite, one of the onshore plutons of the Cornubian Batholith in SW England. At 5058 m depth (TVD, 5275 m MD) up to 190 °C were reached in the dedicated production well. The injec...

Well placement in a given geological setting for a fractured geothermal reservoir is necessary for enhanced geothermal operations. High computational cost associated with the framework of fully coupled thermo-hydraulic-mechanical (THM) processes in a fractured reservoir simulation makes the well positioning a missing point in developing a field-sca...

Land subsidence due to groundwater extraction is a serious issue in Mekong Delta Vietnam, especially when it combines with the sea level rise. Various models were established to study the problem. Usually, two steps models are used. First, the groundwater models are solved to obtain changes in the water table resulting in changes in effective stres...

The increasing decentralization of electrical energy production as well as an increasing number of fluctuating regenerative energy sources require significant investments in grid expansion. Among other assessments, an exact prediction of the thermal behavior of the cable environment is necessary to be able to design cable routes both technically an...

Borehole heat exchanger arrays have become a common implement for the utilization of thermal energy in the soil. Building these facilities is expensive, especially the drilling of boreholes, into which closed-pipe heat exchangers are inserted. Therefore, cost-reducing drilling methods are common practice, which can produce inaccuracies of varying d...

A large share of the primary energy is consumed to provide space heating. Geothermal energy offers a regenerative alternative. For reasons of efficiency and environmental protection, it is important to ensure the system integrity of a borehole heat exchanger (BHE). Previous investigations have focused on the individual components of the BHE or on t...

The deep geothermal energy project at Soultz-sous-Forêts is located in the Upper Rhine Graben, France. As part of the Multidisciplinary and multi-contact demonstration of EGS exploration and Exploitation Techniques and potentials (MEET) project, this study aimed to evaluate the possibility of extracting higher amounts of energy from the existing in...

To prevent accelerated thermal aging or insulation faults in cable systems due to overheating, the current carrying capacity is usually limited by specific conductor temperatures. As the heat produced during the operation of underground cables has to be dissipated to the environment, the actual current carrying capacity of a power cable system is p...

The crystalline basement is considered a ubiquitous and almost inexhaustible source of geothermal energy in the Upper Rhine Graben and other regions worldwide. The hydraulic properties of the basement, which are one of the key factors for the productivity of geothermal power plants, are primarily controlled by hydraulically active faults and fractu...

The composition of mineral, thermal or deep groundwaters is of interest for several geotechnical applications, such as drinking-water supply, spas or geothermal energy. Verified and reliable knowledge of temperature, pH, hydrochemical composition and other parameters is crucial to extract fluids with as few technical problems as possible and exploi...

Engineering an Enhanced Geothermal System (EGS) requires a proper understanding of the fracture network properties from small to large scales in order to create a reliable geological model for reservoir simulations. As deterministic identification of all fractures in a reservoir is practically impossible, stochastic approaches known as Discrete Fra...

Well placement optimization in a given geological setting for a fractured geothermal reservoir is a prerequisite for enhanced geothermal operations. High computational cost associated in the framework of fully coupled thermo-hydraulic-mechanical (THM) processes in a fractured reservoir simulation, makes the well positioning as a missing point in de...

The deep geothermal industrial project at Soultz-sous-Forêts is located in the Upper Rhine Graben, France. As part of the MEET project, this study aims to evaluate the possibility of extracting higher amounts of energy from the existing industrial infrastructure. To achieve this objective, the effect of reinjecting fluid at lower temperature than t...

The Upper Rhine Graben (URG) is a target area for deep geothermal and heat storage projects, as petrophysical and hydraulic properties of the faulted crystalline basement rocks, and the temperature field comprise a high geothermal potential (Soultz-sous-Forêts, Landau, Insheim, Rittershoffen). However, there is a lack of knowledge on the multi-scal...

Solutions for seasonal energy storage systems are an essential component for the reliable use of fluctuating renewable energy sources and to bridge the gap between abundant heat availability from renewable sources in summer and an increased heat demand in winter. As a part of the research project ’solar crystalline borehole thermal energy storage s...

In the northern Upper Rhine Graben (URG), the crystalline basement constitutes an attractive target for deep geothermal exploitation due to the favourable reservoir temperatures and abundance of natural fractures and large-scale faults. Consequently, especially the upper, hydrothermally altered part is already successfully used for heat and power g...

This presentation included a summary of the work performed within the framework of the MalVonian project so far.

For an accurate multiscale property modelling of fractured crystalline geothermal reservoirs, an enhanced characterisation of the geometrical features and variability of the fracture network properties is an essential prerequisite. Combining regional digital elevation model analysis and local outcrop investigation, the study comprises the character...

Grouting materials for borehole heat exchangers often contain rheological additives. Typically, swelling clays are added to benefit from their thixotropic behavior, helping to adjust the stability and flowability of the grouting suspension. Clay compounds without swelling clay minerals but with similar control effects in case of suspension stabilit...

Geothermal energy has the potential to support direct heat usage and electricity generation at low carbon footprint. Using CO2 as heat transfer fluid can allow us to achieve negative carbon energy solution. In this study, geothermal energy extraction potential from a discretely fractured reservoir using CO2 is assessed. Geothermal energy extraction...

A discretely fractured reservoir has the capability to support and sustain long term geothermal energy extraction operations. The process of injecting cold water to extract hot water from a fracture reservoir results in thermal and poroelastic stresses in the rock matrix. Therefore, these thermo-hydro-mechanical (THM) mechanisms govern the efficien...

The composition of mineral, thermal or deep groundwaters is of interest for several geotechnical applications, such as drinking water supply, spas or geothermal energy. A verified and reliable knowledge of temperature, pH, hydrochemical composition and other parameters is crucial to extract fluids with as few technical problems as possible and expl...