The crystalline basement is considered a ubiquitous and almost inexhaustible source of geothermal... more 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 fractures. While the most accurate in situ information about the general fracture network is obtained from image logs of deep boreholes, such data are generally sparse, costly and thus often not openly accessible. To circumvent this problem, an outcrop analogue study with interdisciplinary geoscientific methods was conducted in the Tromm Granite, located in the southern Odenwald at the northeastern margin of the URG. Using LiDAR scanning, the key characteristics of the fracture network were extracted in a total of five outcrops, additionally complemented by lineament analysis of two different digital elevation models. Based on this, discrete fracture network (DFN) models were developed to calculate equivalent permeability tensors under assumed reservoir conditions. The influence of different parameters, such as fracture orientation, density, aperture and mineralization was investigated. In addition, extensive gravity and radon measurements were carried out in the study area, allowing for more precise localization of fault zones with naturally increased porosity and permeability. Gravity anomalies served as input data for a stochastic density inversion, through which areas of increased open porosity were identified. A laterally heterogeneous fracture network characterizes the Tromm Granite, with the highest natural permeabilities expected at the pluton margin, due to the influence of large shear and fault zones.
Well placement in a given geological setting for a fractured geothermal reservoir is necessary fo... more 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-scale investigation. To enhance the knowledge of well placement for different working fluids, we present the importance of this topic by examining different injection-production well (doublet) positions in a given fracture network using coupled THM numerical simulations. Results of this study are examined through the thermal breakthrough time, mass flux, and the energy extraction potential to assess the impact of well position in a twodimensional reservoir framework. Almost ten times the difference between the final amount of heat extraction is observed for different well positions but with the same well spacing and geological characteristics. Furthermore, the stress field is a strong function of well position that is important concerning the possibility of high-stress development. The objective of this work is to exemplify the importance of fracture connectivity and density near the wellbores, and from the simulated cases, it is sufficient to understand this for both the working fluids. Based on the result, the production well position search in the future will be reduced to the high-density fracture area, and it will make the optimization process according to the THM mechanism computationally efficient and economical.
Seasonal thermal energy storage in medium deep borehole heat exchanger arrays is a very promising... more Seasonal thermal energy storage in medium deep borehole heat exchanger arrays is a very promising technology for increasing the share of sustainable heat sources in district heating grids, while minimizing the thermal impact on shallow aquifers. However, the integration of a medium deep borehole thermal energy storage system is highly dependent on its interaction with other heating components in the grid. Furthermore, the construction of medium deep borehole heat exchangers is accompanied by additional environmental burdens and large capital expenditures (CAPEX). Hence, their contribution for the mitigation of greenhouse gas emissions as well as the financial implications induced by medium deep borehole thermal energy storage systems are not quantified yet. In order to pursue these questions, an economic and environmental assessment tool has been developed, which is based on a life cycle approach (Welsch et al. 2018, Welsch 2019). It is able to consider different district heat gener...
The Canadian province of Alberta has the highest per capita CO2-equivalent emissions in Canada, p... more The Canadian province of Alberta has the highest per capita CO2-equivalent emissions in Canada, predominantly due to the industrial burning of coal for the generation of electricity and mining operations in the oil sand deposits. The use of Alberta’s geothermal potential could reduce CO2 emissions significantly by substituting at least some fossil fuels. Relatively little is known about the potential for geothermal energy utilization in Alberta despite of a number of geothermal studies conducted over several decades. To assess the geothermal reservoir potential, detailed knowledge of the thermoand petrophysical rock properties is needed. We conducted an analogue study that compared a number of rock properties from the Devonian Southesk-Cairn Carbonate Complex and of the Rimbey-Meadowbrook Reef Trend with selected outcrop samples from stratigraphically correlative outcrops in the Rocky Mountains. Samples from the Leduc and Nisku formations were analyzed for thermal conductivity, ther...
The utilization of medium deep borehole heat exchangers (BHEs) as seasonal thermal energy storage... more The utilization of medium deep borehole heat exchangers (BHEs) as seasonal thermal energy storages is expected to have benefits compared to shallow BHE storages. Medium deep borehole thermal energy storages (MD-BTES) have almost no impact on shallow groundwater resources and require less floor space. As no such system is put into practice so far, the efficiencies, the amount of heat that can be stored or extracted and the fluid temperatures that can be achieved by MD-BTES are unknown. Therefore, 200 different models of MD-BTES were compared, using FEFLOW for modeling the heat transport processes in the BHEs and in the underground. The influence of different parameters on the storage performance was studied by varying the BHE length, the number of BHEs and the spacing between the BHEs. A simplified underground model was assumed and a simplified operation procedure was applied over a period of 30 years of storage operation. Depending on the storage design, storage efficiencies of more...
In a fault-related deep granitic reservoir located in Redruth, Cornwall (UK), a geothermal double... more In a fault-related deep granitic reservoir located in Redruth, Cornwall (UK), a geothermal doublet-system (United Downs Deep Geothermal Power Project, UDDGP) was completed in June 2019. The development of the geothermal resource of the high-heat-producing granites beneath SW England (Cotton et al., 2020), is the major goal of UDDGP. In the production well UD-1 with a depth of 5275 m (MD), up to 190°C have been measured. The doublet-system (UD-1 and the injection well UD-2 with a depth of 2393 m MD) is aligned vertically, so that both wells penetrate the large-scale Porthtowan Fault Zone (PTF), acting as the geothermal reservoir linking the wells. The PTF is located in the Carnmenellis Granite, the largest onshore pluton of the Cornubian Batholith. An in depth understanding of the geothermal reservoir is needed to create a basis for reservoir modelling and to allow for an adequate configuration and dimensioning of the geothermal system including the geothermal power plant. Within the scope of the EU funded MEET project (EU-H2020, GA no. 792037), which aims to support and develop new technologies, approaches and potentials for exploration and exploitation of enhanced geothermal systems (EGS), 20 side wall cores (SWCs) were obtained in UD-1 at selected depths between 4200 m MD and 4900 m MD to petrographically and petrophysically analyze the granitic reservoir rock. The rock characterization laboratory workflow includes petrophysical measurements followed by a mineralogical and geochemical analysis to define and characterize the properties and composition of the relevant granite types and fracture and fault zones. The cores were analyzed for particle and bulk density, porosity, permeability, thermal conductivity, thermal diffusivity including calculated heat capacity and ultra-sonic wave velocities. Thin sections were analyzed for mineralogical composition and texture, intensity of hydrothermal alteration, fractures and the general condition of the rock. Furthermore, XRD, ESEM, XRF and ICP-MS analyses were performed to provide information about the mineral assemblage, bulk geochemistry and the resulting radiogenic heat production. For the preparation of a reservoir-scale chemical stimulation, acidification experiments under in-situ conditions (150°C and 17.5 MPa) were conducted by Core Flooding Tests (CFTs) on seven selected SWCs using customized acid systems for stimulation of granitic rocks (Lummer et al., 2018). The CFTs resemble the planned chemical stimulation of the reservoir and is an experiment for the evaluation of the effectiveness of a potential chemical treatment of the reservoir rock to reach sufficiently high flow rates to allow for an economic productivity. The SWCs consist to major parts of hydrothermally-altered granite, so that the results of the experiments can be transferred to altered faults zones and fractures of the PTF. According to the XRD results, the Carnmenellis granite can be classified as monzogranite, while the altered SWCs are plotting as quartz-rich granitoides, monzogranites, granodiorites, and even as tonalities and quartz diorites/ -gabbros/ -anorthosites (according to Streckeisen) for the highly altered samples. The XRF results suggest a more uniform composition so that the samples plot in the granite, granodiorite, quartz monzonite and only one highly altered sample in foid monzodiorite field of the TAS diagram. The CFT results show a high efficiency of the customized acid system with resulting permeability enhancement factors between 2 and up to >100, depending on the initial permeability of the specimens and dissolution of secondary minerals during the experiments. Provided material of this dataset: - D5.5_Appendix_3_P32MEET data table: overview of the samples, petrophysical measurements (including derived calculated parameters), results of XRD, XRF, ICP-MS, thin sections and core flooding test - Characterisation of the 20 Side wall core samples with macroscopic and microscopic description including photos (PDFs) - Photos of the 20 Side wall core thin sections (ZIP data file and list of inventory) - Additional photos from the Side wall cores before and after the CFTs (ZIP data file and list of inventory) - Excel table with ESEM data and material - Excel table with and detailed CFTs data and material Acknowledgments: The present work was put into practice at the Technical University in Darmstadt, at the Institute of Applied Geosciences, Department of Geothermal Science and Technology within the framework of the projects MEET and the United Downs Deep Geothermal Power Project in Cornwall, UK. We thank the laboratory stuff and the project partners related to MEET/ UDDGP, to mention B. Lédesert, D. Scheuvens, J. Reinecker, R. Petschick and R. Shail.V1.
A regional assessment of the potential for geothermal heat production, power generation and also ... more 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 modelling of the architecture of deep reservoirs. In the Upper Rhine Graben, well known for its vast geothermal potential, a characterization of the structural organization at the basin scale and an understanding of mass and heat transfer are, therefore, useful for correctly estimating the technical and economic potential for geothermal energy. The distribution of the resources can be quantified based on the basin analysis approach. This is classically used for hydrocarbon resources and is applied in this study to predict the geothermal fluid-flow paths. The role of faults and their hydraulic regime on temperature field heterogeneities is investigated. Several scenarios with or without rift basin internal faults and various transmissivity ranges along these faults are analysed and compared. The measured temperature field is used for the calibration of the different model scenarios results. The scenario with the most significant role for internal faults as fluid-flow pathways in the western Upper Rhine Graben is the one that provides the most accurate reproduction of the temperature field. Such output highlights the importance of quantifying the hydraulic behaviour of faults and associated fracture networks in space and time. Supplementary material: dataset containing geometry, facies distribution and main results of scenario 4 is available at https://doi.org/10.6084/m9.figshare.c.6628506
This article is an open access article distributed under the terms and conditions of the Creative... more This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY
The crystalline basement is considered a ubiquitous and almost inexhaustible source of geothermal... more 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 fractures. While the most accurate in situ information about the general fracture network is obtained from image logs of deep boreholes, such data are generally sparse, costly and thus often not openly accessible. To circumvent this problem, an outcrop analogue study with interdisciplinary geoscientific methods was conducted in the Tromm Granite, located in the southern Odenwald at the northeastern margin of the URG. Using LiDAR scanning, the key characteristics of the fracture network were extracted in a total of five outcrops, additionally complemented by lineament analysis of two different digital elevation models. Based on this, discrete fracture network (DFN) models were developed to calculate equivalent permeability tensors under assumed reservoir conditions. The influence of different parameters, such as fracture orientation, density, aperture and mineralization was investigated. In addition, extensive gravity and radon measurements were carried out in the study area, allowing for more precise localization of fault zones with naturally increased porosity and permeability. Gravity anomalies served as input data for a stochastic density inversion, through which areas of increased open porosity were identified. A laterally heterogeneous fracture network characterizes the Tromm Granite, with the highest natural permeabilities expected at the pluton margin, due to the influence of large shear and fault zones.
Well placement in a given geological setting for a fractured geothermal reservoir is necessary fo... more 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-scale investigation. To enhance the knowledge of well placement for different working fluids, we present the importance of this topic by examining different injection-production well (doublet) positions in a given fracture network using coupled THM numerical simulations. Results of this study are examined through the thermal breakthrough time, mass flux, and the energy extraction potential to assess the impact of well position in a twodimensional reservoir framework. Almost ten times the difference between the final amount of heat extraction is observed for different well positions but with the same well spacing and geological characteristics. Furthermore, the stress field is a strong function of well position that is important concerning the possibility of high-stress development. The objective of this work is to exemplify the importance of fracture connectivity and density near the wellbores, and from the simulated cases, it is sufficient to understand this for both the working fluids. Based on the result, the production well position search in the future will be reduced to the high-density fracture area, and it will make the optimization process according to the THM mechanism computationally efficient and economical.
Seasonal thermal energy storage in medium deep borehole heat exchanger arrays is a very promising... more Seasonal thermal energy storage in medium deep borehole heat exchanger arrays is a very promising technology for increasing the share of sustainable heat sources in district heating grids, while minimizing the thermal impact on shallow aquifers. However, the integration of a medium deep borehole thermal energy storage system is highly dependent on its interaction with other heating components in the grid. Furthermore, the construction of medium deep borehole heat exchangers is accompanied by additional environmental burdens and large capital expenditures (CAPEX). Hence, their contribution for the mitigation of greenhouse gas emissions as well as the financial implications induced by medium deep borehole thermal energy storage systems are not quantified yet. In order to pursue these questions, an economic and environmental assessment tool has been developed, which is based on a life cycle approach (Welsch et al. 2018, Welsch 2019). It is able to consider different district heat gener...
The Canadian province of Alberta has the highest per capita CO2-equivalent emissions in Canada, p... more The Canadian province of Alberta has the highest per capita CO2-equivalent emissions in Canada, predominantly due to the industrial burning of coal for the generation of electricity and mining operations in the oil sand deposits. The use of Alberta’s geothermal potential could reduce CO2 emissions significantly by substituting at least some fossil fuels. Relatively little is known about the potential for geothermal energy utilization in Alberta despite of a number of geothermal studies conducted over several decades. To assess the geothermal reservoir potential, detailed knowledge of the thermoand petrophysical rock properties is needed. We conducted an analogue study that compared a number of rock properties from the Devonian Southesk-Cairn Carbonate Complex and of the Rimbey-Meadowbrook Reef Trend with selected outcrop samples from stratigraphically correlative outcrops in the Rocky Mountains. Samples from the Leduc and Nisku formations were analyzed for thermal conductivity, ther...
The utilization of medium deep borehole heat exchangers (BHEs) as seasonal thermal energy storage... more The utilization of medium deep borehole heat exchangers (BHEs) as seasonal thermal energy storages is expected to have benefits compared to shallow BHE storages. Medium deep borehole thermal energy storages (MD-BTES) have almost no impact on shallow groundwater resources and require less floor space. As no such system is put into practice so far, the efficiencies, the amount of heat that can be stored or extracted and the fluid temperatures that can be achieved by MD-BTES are unknown. Therefore, 200 different models of MD-BTES were compared, using FEFLOW for modeling the heat transport processes in the BHEs and in the underground. The influence of different parameters on the storage performance was studied by varying the BHE length, the number of BHEs and the spacing between the BHEs. A simplified underground model was assumed and a simplified operation procedure was applied over a period of 30 years of storage operation. Depending on the storage design, storage efficiencies of more...
In a fault-related deep granitic reservoir located in Redruth, Cornwall (UK), a geothermal double... more In a fault-related deep granitic reservoir located in Redruth, Cornwall (UK), a geothermal doublet-system (United Downs Deep Geothermal Power Project, UDDGP) was completed in June 2019. The development of the geothermal resource of the high-heat-producing granites beneath SW England (Cotton et al., 2020), is the major goal of UDDGP. In the production well UD-1 with a depth of 5275 m (MD), up to 190°C have been measured. The doublet-system (UD-1 and the injection well UD-2 with a depth of 2393 m MD) is aligned vertically, so that both wells penetrate the large-scale Porthtowan Fault Zone (PTF), acting as the geothermal reservoir linking the wells. The PTF is located in the Carnmenellis Granite, the largest onshore pluton of the Cornubian Batholith. An in depth understanding of the geothermal reservoir is needed to create a basis for reservoir modelling and to allow for an adequate configuration and dimensioning of the geothermal system including the geothermal power plant. Within the scope of the EU funded MEET project (EU-H2020, GA no. 792037), which aims to support and develop new technologies, approaches and potentials for exploration and exploitation of enhanced geothermal systems (EGS), 20 side wall cores (SWCs) were obtained in UD-1 at selected depths between 4200 m MD and 4900 m MD to petrographically and petrophysically analyze the granitic reservoir rock. The rock characterization laboratory workflow includes petrophysical measurements followed by a mineralogical and geochemical analysis to define and characterize the properties and composition of the relevant granite types and fracture and fault zones. The cores were analyzed for particle and bulk density, porosity, permeability, thermal conductivity, thermal diffusivity including calculated heat capacity and ultra-sonic wave velocities. Thin sections were analyzed for mineralogical composition and texture, intensity of hydrothermal alteration, fractures and the general condition of the rock. Furthermore, XRD, ESEM, XRF and ICP-MS analyses were performed to provide information about the mineral assemblage, bulk geochemistry and the resulting radiogenic heat production. For the preparation of a reservoir-scale chemical stimulation, acidification experiments under in-situ conditions (150°C and 17.5 MPa) were conducted by Core Flooding Tests (CFTs) on seven selected SWCs using customized acid systems for stimulation of granitic rocks (Lummer et al., 2018). The CFTs resemble the planned chemical stimulation of the reservoir and is an experiment for the evaluation of the effectiveness of a potential chemical treatment of the reservoir rock to reach sufficiently high flow rates to allow for an economic productivity. The SWCs consist to major parts of hydrothermally-altered granite, so that the results of the experiments can be transferred to altered faults zones and fractures of the PTF. According to the XRD results, the Carnmenellis granite can be classified as monzogranite, while the altered SWCs are plotting as quartz-rich granitoides, monzogranites, granodiorites, and even as tonalities and quartz diorites/ -gabbros/ -anorthosites (according to Streckeisen) for the highly altered samples. The XRF results suggest a more uniform composition so that the samples plot in the granite, granodiorite, quartz monzonite and only one highly altered sample in foid monzodiorite field of the TAS diagram. The CFT results show a high efficiency of the customized acid system with resulting permeability enhancement factors between 2 and up to >100, depending on the initial permeability of the specimens and dissolution of secondary minerals during the experiments. Provided material of this dataset: - D5.5_Appendix_3_P32MEET data table: overview of the samples, petrophysical measurements (including derived calculated parameters), results of XRD, XRF, ICP-MS, thin sections and core flooding test - Characterisation of the 20 Side wall core samples with macroscopic and microscopic description including photos (PDFs) - Photos of the 20 Side wall core thin sections (ZIP data file and list of inventory) - Additional photos from the Side wall cores before and after the CFTs (ZIP data file and list of inventory) - Excel table with ESEM data and material - Excel table with and detailed CFTs data and material Acknowledgments: The present work was put into practice at the Technical University in Darmstadt, at the Institute of Applied Geosciences, Department of Geothermal Science and Technology within the framework of the projects MEET and the United Downs Deep Geothermal Power Project in Cornwall, UK. We thank the laboratory stuff and the project partners related to MEET/ UDDGP, to mention B. Lédesert, D. Scheuvens, J. Reinecker, R. Petschick and R. Shail.V1.
A regional assessment of the potential for geothermal heat production, power generation and also ... more 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 modelling of the architecture of deep reservoirs. In the Upper Rhine Graben, well known for its vast geothermal potential, a characterization of the structural organization at the basin scale and an understanding of mass and heat transfer are, therefore, useful for correctly estimating the technical and economic potential for geothermal energy. The distribution of the resources can be quantified based on the basin analysis approach. This is classically used for hydrocarbon resources and is applied in this study to predict the geothermal fluid-flow paths. The role of faults and their hydraulic regime on temperature field heterogeneities is investigated. Several scenarios with or without rift basin internal faults and various transmissivity ranges along these faults are analysed and compared. The measured temperature field is used for the calibration of the different model scenarios results. The scenario with the most significant role for internal faults as fluid-flow pathways in the western Upper Rhine Graben is the one that provides the most accurate reproduction of the temperature field. Such output highlights the importance of quantifying the hydraulic behaviour of faults and associated fracture networks in space and time. Supplementary material: dataset containing geometry, facies distribution and main results of scenario 4 is available at https://doi.org/10.6084/m9.figshare.c.6628506
This article is an open access article distributed under the terms and conditions of the Creative... more This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY
Uploads
Papers by Kristian Bär