Damage to the historic town of Staufen (Germany) caused by geothermal drillings through anhydrite-bearing formations

Shallow geothermal systems for the heating and cooling of buildings will play an important role in the future renewable energy supply. Especially in dense settlements the geother­mal energy utilization for facility heating and cooling is very promising. Therefore, it is important to analyse the damage to Staufen im Breisgau (Germany). In September of 2007, seven geothermal borehole heat exchanger (BHE) drillings were per­formed in a small square directly adjacent to the 16th century town hall in the centre of the town. These led to enormous structural damage to buildings as a function of four different geological parameters: artesian groundwater, two interacting karst formations, strong tectonization, and a swellable anhy­drite formation. Some weeks after termination of the well con­struction, uplift started, and recently (March 2010) reached a magnitude of approximately 26 cm. Actually, some 250 build­ings (March 2010) are involved; showing cracks, tilting, and other effects of the differential swelling movements beneath the foundations. Surface uplifts with rate up to 10 mm/month have been determined using high-resolution spaceborne radar data and radarinterferometric techniques. These amplitudes correlate with data from benchmarks of terrestrial geodetic surveyng. Besides the uplift due to the swelling processes, fu­ture problems could arise from the fact that the gypsum formed from the swelled anhydrite is soluble in water. Thus, sinkholes and other karst related phenomena may occur

Results of a reference-date measurement of 153 springs and creeks within the Tuxbach catchment area, Tyrol, Austria

The Tuxertal (Tux Valley) is located in the Eastern Alps in Tyrol, Austria and is drained by the Tuxbach (Tux Creek). The catchment area comprises 135 km², with the Olperer (3,476 m) as the highest elevation point and the confluence of the Tuxbach into the Zemmbach at Gstan (645 m) as lowest point. Geologically, the Tuxertal belongs to the north-western edge of the Tauern Window and therefore exhibits a complex petrographic and tectonic structure. In the Tuxertal, small cooperatives or private owners organise the drinking water supply and operate nearby springs. These springs are mostly fed by small catchment areas. Due to the complex geology groundwater quality can differ on a small scale. The crystalline rocks can cause an exceedance of critical values defined in Austria’s drinking water ordinance (BMSG 2001), especially with respect to heavy metal concentrations. Another challenge for drinking water supply is to find springs with sufficient discharge rates, resilient to modifications induced by climate change. A regional overview of the groundwater quality and quantity is crucial to identify the most suitable springs and to replace springs with elevated metal concentrations or insufficient discharge. A reference-date measurement, covering the whole Tuxertal, served to compile hydrochemical data and to provide decision-makers with adequate information to ensure a reliable drinking water supply. During 21 and 31 August 2018 a total number of 147 springs and 6 creeks were sampled. With this publication we provide the results of the reference-date measurement as .xlsx and .csv file.V1.

COUPLED MEASUREMENTS OF THERMOPYSICAL AND HYDRAULICAL PROPERTIES OF UNSATURATED AND UNCONSOLIDATED ROCKS

ABSTRACT Thermal conductivity and diffusivity as well as the hydraulic properties of unconsolidated rocks are the most important parameters required to quantify subsurface conductive and convective heat transfer. Soil mechanical and mineralogical constraints such as thermal conductivity of the individual grain fractions, the bulk dry density and the pressures remain constant. On the other hand, temperature and water content in the unsaturated zone are highly variable in time and space. The variations of the ratio between the gas phase and the water phase occupying the pore space has a varying thermal insulating effect due to the low thermal conductivity of air. In addition, the unsaturated hydraulic conductivity is a function of the water content of unconsolidated rocks. The air in the pore space reduces the effective conductive cross-sectional area, which leads to a decrease in hydraulic conductivity. Increasing drainage induces negative pore pressure (suction) and due to the hysteresis in drainage and irrigation thus the local water distribution is changed. Presented herein is the implementation of a newly developed thermal conductivity and thermal diffusivity meter for the integrated investigation of soil mechanics, hydraulic and geothermal properties of unconsolidated rocks. Patent applications are pending. Furthermore an evaporation test was developed and columnar drainage experiments with continuously conducted measurement of water content, pore pressure, and thermal conductivity at different levels of the column. To simultaneously measure the hydraulic properties as well as the unsaturated thermal conductivity they are equipped with a full-space line (heat) source. In these experiments many different unconsolidated rocks are examined in order to provide the respective parameters for a new capillary tension/ thermal conductivity function analogue to the existing capillary tension/ water content functions

Numerical simulation of a comparative study on heat extraction from Soultz-sous-For\^ets geothermal field using supercritical carbon dioxide and water as a working fluid

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 working fluids. This study developed a field-scale hydro-thermal model to examine the heat extraction potential from Soultz-sous-For\^ets with CO2 as the working fluid. Results are compared for the same scenario with water as the working fluid. A better understanding of the heat extraction mechanism is established by considering the reservoir response and the wellbore heat exchange. Sensitivity analyses are performed for different injection temperatures and flow rates for 50 years. Results show that the wellbore effect is multiple times higher than the reservoir response to the production temperature. Furthermore, lowering the injection temperature eventuates to a smaller temperature reduction at the subsurface, enhancing the overall heat extraction potential with a minor impact on thermal breakthrough. The cold region developed around the injection wellbore may affect the production fluid temperature due to its proximity to the production wellbore. To reach higher heat extraction efficiency, it is essential to use sufficient wellbore spacing. CO2 can be used as working fluid for over 50 years as it does not show significant thermal breakthrough and temperature plume evolution in the reservoir under studied conditions. CO2 shows lower temperature reduction for all injection rates and temperatures for 50 years of operation.Comment: 17 pages, 8 figure

Magnetic Susceptibility of Rock Samples of the Northern Upper Rhine Graben Region and Adjacent Areas

We present here a comprehensive dataset on the magnetic susceptibility of the main geologic units in and adjacent to the northern Upper Rhine Graben. It represents a complement to the PetroPhysical Property Database (P³) of Bär et al. (2020) and thus follows the database structure as described there. The magnetic susceptibility is a unitless physical quantity that describes how magnetizable a material (e.g. rocks) is. It is the ratio between the magnetic field strength H and induced magnetization M. Besides the remanence, the susceptibility of geological formations decisively influences the amplitude of crustal magnetic anomalies. This parameter depends mainly on the proportion of iron-rich minerals such as magnetite and hematite in the total rock volume. Therefore, mafic rocks usually exhibit the highest susceptibilities, but variations of several orders of magnitude within the same lithology are possible. The northern URG region is characterized by several distinct elongated magnetic anomalies associated with the high susceptibility of magmatic complexes in the crystalline basement and in particular in the Mid-German Crystalline High. The basement represents an important reservoir for geothermal projects due to the very high temperatures. Detailed geological modelling of this horizon is thus being performed within the BMWi funded Hessen 3D 2.0 project (Bär et al. 2016) and the Interreg NWE project DGE-ROLLOUT (www.nweurope.eu/DGE-Rollout). Since very deep boreholes and seismic profiles are sparse, magnetic anomalies provide important insights about the structure and composition of the basement. For realistic modelling of these anomalies, an extensive investigation of the magnetic susceptibility in the model units was required. The analyzed rock samples, mostly derived from abandoned and active quarries as well as natural and other artificial outcrops, were provided by the Institut für Steinkonservierung Mainz e.V. The majority of the in total 430 samples were collected in the Odenwald. Additional sample locations are in the Saar-Nahe Basin, the Palatinate, the Vogelsberg and the Rhenish Massif. Apart from outcrop samples, the susceptibility was measured on 24 core plugs from the three wells Weiterstadt 1, Stockstadt 33R and Worms 3. The measurements were carried out at about 20 °C with the SM-30 handheld device from ZH instruments and were usually repeated three times for each sample, but the number may vary depending on the heterogeneity and size of the samples. The results of the susceptibility measurements are shown in Fig. 1. The values range from about -2.4e-5 to 0.07 [SI]. The susceptibility of the post-Variscan units is generally very small, meaning that their effect on the crustal magnetic field can be neglected. This excludes the Permo-Carboniferous and Tertiary volcanic and volcano-sedimentary horizons, which are likely sources of stronger anomalies in the Saar-Nahe Basin, the northernmost URG and the Sprendlinger Horst. The highest susceptibility values were measured in gabbros of the Frankenstein complex. The dataset is a supplement to another publication (Frey et al. 2020, subm.) that presents the results of the joint inversion of gravity and magnetic data in the northern Upper Rhine Graben. The measured magnetic susceptibilities were a key input for this study.V1.

New Methods for Determining the Thermophysical and Hydraulical Properties of Unsaturated and Unconsolidated Rocks

ABSTRACT The heat conductivity and diffusivity as well as the hydraulic properties of unconsolidated rocks are important parameters to quantify the conductive and convective heat transfer in the subsurface. Depending on the type and way of installation of an underground heat exchanger system the involved soil undergoes compaction, change in saturation e.g.. The most soil properties will be changed somehow, just the grain size distribution remains constant. In the operation phase the temperature and saturation are variable in time and space. The change in the ratios of the gas phase and water phase in the subsoil affects the themo-physical performance. The hydraulic conductivity of soils is a non-linear function on the water content. The heat capacity of unconsolidated rocks can be calculated from the heat capacities of the individual components and their volume fractions. In contrast, there is no linear dependence of the thermal conductivity and the water content. Established computational models provide approximations for the thermal conductivity as a function of water content and other constraints such as temperature. However, for the additional determination of convective transport behavior, the unsaturated hydraulic conductivity and water retention function, largely dependent on the tortuosity of the pore space, have to be determined simultaneously. Here, for the integrated study of soil mechanics, hydraulic and geothermal properties of unconsolidated rocks, a heat and temperature conductivity meter has been developed and patented. The device allows measurements of samples either under constant pressure of up to 7.6 Mpa which means soil compaction can be varied stepwise or it can be driven at a constant sample volume. The treatment temperatures of the soil samples can be varied from -10 to +80 ° C. Additionally to the parameters such as temperature, pressure, volume and water content, the capillary tension is recorded during the measurement. For the simultaneous study of water transport characteristics and the unsaturated conductivity of undisturbed unconsolidated rock samples, an evaporation test has been developed. It is equipped with a full-space line source to determine the thermal conductivity. This allows the simultaneous measurement of thermal conductivity, water retention characteristics and hydraulic conductivity of a soil sample up to the air entry point of the ceramic tensiometer cap (approx. -780 hPa). The functionality of the equipment and methods has been validated and the devices were used for soil investigation in numerous projects. Determination of the design parameters of shallow geothermal systems and of the heat transfer of burried cables is thepurpose of the methods presented in this study. The data compile mathematical models for the thermo-physical parameters of soils. A mathematical function for calculating the thermal conductivity in dependence of the capillary tension is introduced here and the test results of geotechnical and geothermal soil parameters of sand, clay and silt are presented

Permeability and Thermal Conductivity Measurements of Near Surface Units at the Wairakei Geothermal Field, New Zealand

ABSTRACT Thirty one outcrop and drill core samples (to about -500 mRL) from geothermal wells from Te Mihi, western Wairakei Geothermal Field (New Zealand), have been analysed for their mineral assemblage and hydrothermal alteration, thermal conductivity, permeability, bulk rock porosity and density, as part of a study on the affect of the geological parameters on the thermal conductivity. At Wairakei, cores of Huka Falls Formation (soft, lacustrinedeposited tuff and sediments), Waiora Formation (variably consolidated, medium hard, hydrothermally altered volcanic tuff) and Karapiti Rhyolite (hard, altered rhyolite lava and breccias) were analysed from wells WK223, WK224 and WK227 (unaltered/least altered field margin); WK206, WK207, WK212, WK219 and WK247 (Te Mihi upflow zone); and WKM14, WK205, WK210, WK213 and WK221 (infield, south and east of Te Mihi). The effect of hydrothermal alteration (rank and intensity) on thermal conductivity was tested by analysing samples from the same stratigraphic units from different wells, albeit with a range of styles of hydrothermal alteration (e.g. claydominated argillic, characterised by a progression from smectite to illite-dominated clay assemblages, to propylitic). Results demonstrate a good correlation between porosity and thermal conductivity, but no clear relationship between permeability and thermal conductivity. We also compared permeability and thermal conductivity from the Wairakei Field samples with data from rocks in central Europe

Interdisciplinary fracture network characterization in the crystalline basement: a case study from the Southern Odenwald, SW Germany

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 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 and costly and thus often not openly accessible. To circumvent this problem, an outcrop analogue study was conducted with interdisciplinary geoscientific methods in the Tromm Granite, located in the southern Odenwald at the northeastern margin of the URG. Using light detection and ranging (lidar) scanning, the key characteristics of the fracture network were extracted in a total of five outcrops; these were additionally complemented by lineament analysis of two different digital elevation models (DEMs). Based on this, discrete fracture network (DFN) models were developed to calculate equivalent permeability tensors under assumed reservoir conditions. The influences of different parameters, such as fracture orientation, density, aperture and mineralization, were investigated. In addition, extensive gravity and radon measurements were carried out in the study area, allowing fault zones with naturally increased porosity and permeability to be mapped. Gravity anomalies served as input data for a stochastic density inversion, through which areas of potentially 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