Hydrochemical Zoning and Chemical Evolution of the Deep Upper Jurassic Thermal Groundwater Reservoir Using Water Chemical and Environmental Isotope Data

A comprehensive hydrogeological understanding of the deep Upper Jurassic carbonate aquifer, which represents an important geothermal reservoir in the South German Molasse Basin (SGMB), is crucial for improved and sustainable groundwater resource management. Water chemical data and environmental isotope analyses of D, 18O and 87Sr/86Sr were obtained from groundwater of 24 deep Upper Jurassic geothermal wells and coupled with a few analyses of noble gases (3He/4He, 40Ar/36Ar) and noble gas infiltration temperatures. Hierarchical cluster analysis revealed three major water types and allowed a hydrochemical zoning of the SGMB, while exploratory factor analyses identified the hydrogeological processes affecting the water chemical composition of the thermal water. Water types 1 and 2 are of Na-[Ca]-HCO3-Cl type, lowly mineralised and have been recharged under meteoric cold climate conditions. Both water types show 87Sr/86Sr signatures, stable water isotopes values and calculated apparent mean residence times, which suggest minor water-rock interaction within a hydraulically active flow system of the Northeastern and Southeastern Central Molasse Basin. This thermal groundwater have been most likely subglacially recharged in the south of the SGMB in close proximity to the Bavarian Alps with a delineated northwards flow direction. Highly mineralised groundwater of water type 3 (Na-Cl-HCO3 and Na-Cl) occurs in the Eastern Central Molasse Basin. In contrast to water types 1 and 2, this water type shows substantial water-rock interaction with terrestrial sediments and increasing 40Ar/36Ar ratios, which may also imply a hydraulic exchange with fossil formation waters of overlying Tertiary sediments.

Optimising the thermal use of groundwater for a decentralized heating and cooling supply in the city of Munich, Germany

<p>Shallow geothermal energy can contribute to a regenerative supply of urban heating and cooling loads and hence, reduce primary energy consumption and greenhouse gas emissions. In the city of Munich, which hosts a very productive shallow aquifer, conditions are outstanding for the thermal use of groundwater. Therefore, already more than 2800 shallow geothermal systems are installed and due to better economic incentives, numbers are rising. Thus, the future development of this already intensely used urban aquifer holds challenges to avoid conflicting uses, but also opportunities to build synergies and balance the energy budget.</p><p>However, fostering a sustainable development is only possible with knowledge about the dynamic hydraulic and thermal behaviour of the groundwater and its anthropogenic and natural influences. Currently, this information is missing on a city scale as a decision basis for the responsible growth of thermal groundwater use. As a consequence, water authorities have to become increasingly restrictive when granting licenses to cope with preventive drinking water protection. Therefore, tools for the thermal management of aquifers are needed to enable resilient decision making.</p><p>The project GEO.KW (2019-2021), funded by the German Ministry for Economic Affairs and Energy, took up this challenge and develops a flexible management and optimisation tool for the thermal use of groundwater. As pilot area for an implementation, Munich offers a dynamic and well-monitored hydrogeology. The tool’s core element is the coupling between a thermal-hydraulic groundwater model and a linear optimisation model for distributed energy systems. This interdisciplinary approach, allows us to include the heat storage potential of the aquifer and study the coverable heating and cooling demand depending on the thermal resource at high temporal and spatial resolution. The optimisation integrates all regulatory restrictions of water resource management, like temperature or extraction limits, and comparatively analyses conventional heating and cooling systems alongside with thermal groundwater use. As cost factor in the optimisation, greenhouse gas emissions and economic cost is evaluated.</p><p>The development focuses on using highly parallelised open-source codes and efficient code coupling. The numerical groundwater simulation is performed with <em>PFLOTRAN</em>, a code specifically built for scalability on supercomputers. It is coupled to the linear optimiser <em>urbs </em>through the minimally invasive coupling library <em>preCICE </em>and the simulations are performed on the <em>SuperMUC-NG</em> in Garching, Germany. Since the parallelisation of optimisation problems is not straightforward, a decomposition procedure is introduced to assure performance with high resolution models.</p><p>The optimisation tool and associated methods will also be applicable to other urban areas. Thus, it will offer the decision support for an optimised growth of thermal groundwater use to assure its contribution to emission-free and decarbonised heating and cooling of cities.</p>

Geological, geochemical and geophysical studies on the non-volcanic hot springs, Atri and Tarbalo in the Indian shield: potential unconventional renewable energy sources

<p>In the fast-growing economies around the world, the demand for energy as well as environmental concerns make geothermal energy a potential renewable energy source. Most geothermal provinces across the world have the capacity to generate enormous amounts of hydrothermal energy, and hot springs in these areas are generally associated with active volcanic or tectonic activity. With modern technical advancement, low enthalpy geothermal systems (< 100°C) are also being considered for geothermal energy production. In non-volcanic hot springs, the water temperature remains low compared to volcanic hot springs. We study two such hot springs located within Neoproterozoic granulites of the tectonically stable Eastern Ghats Belt (EGB) of the Indian shield. The source of heat for these amagmatic hot springs may either be deep-seated fracture zones, or alternative heat sources at shallow crustal levels. A combination of geological, geochemical, hydrological and geophysical techniques has been applied to characterize non-volcanic hot springs in India. The hot springs at Atri and Tarbalo are located to the south of the Mahanadi Shear Zone within the EGB. Penetrative granulite facies planar structural fabrics in rocks of the northern EGB are reoriented within an E-W striking, northerly dipping ductile shear zone that is subsequently dissected by WNW-ESE trending, sub-vertical pseudotachylite-bearing faults and fractures. Tube and dug wells around the shear zone yield both hot (~ 60°C) and cold (~ 28°C) water, sometimes spatially only 20 metres apart. Chemical analyses indicate both have distinct compositions, with hot waters rich in Na<sup>+</sup>, K<sup>+</sup> and Cl<sup>-</sup> while cold-waters have higher Ca<sup>2+</sup> and HCO<sub>3</sub><sup>-</sup> concentration. Stable isotope analyses (δ<sup>2</sup>H and δ<sup>18</sup>O) of both waters indicate that both are meteoric in origin. Tritium (<sup>3</sup>H) and <sup>14</sup>C analyses indicate that hot spring waters are much older than the non-thermal groundwater. The hot water is 17714 years old, while the non-thermal groundwater indicates modern day recharge. This suggests that both waters come from different reservoirs. VLF-electromagnetic studies indicate that water exists in isolated pockets beneath the crystalline country rocks, but also circulated through WNW-ESE trending fracture systems. Heat production studies reveal that the EGB is a high radiation zone, and some host rocks have exceptionally high heat producing element (HPE) concentrations (primarily thorium) within the minerals monazite and thorite. Hence, meteoric water is entrapped in those “perched aquifers” near HPE-rich pockets for a long duration and has sufficient time to undergo radiogenic heating, shielded from the non-thermal groundwater circulating within the fracture system. These isolated pockets act as sources for the hot springs,with HPE being the source of heat. The high HPE distribution in the crust resulting from Neoproterozoic geological events has, thus, elevated the present-day equilibrium geotherm in the EGB, forming sources for shallow-level, non-volcanic hot springs within a tectonically inactive terrane. Therefore, the hot springs in these regions, as well as the hot dry rocks of these areas can be considered as potential geothermal resources.</p>

Occurrence and flow systems of the anticline-controlled thermal groundwater near Chongqing in eastern Sichuan Basin of China

A review and assessment of earlier studies shows that the thermal groundwater near Chongqing in the eastern Sichuan Basin of China has a unique occurrence called the ‘basin-anticline outcropping’ type. Its occurrence and emergence are strongly controlled by the nearly north–south trending anticlines. The basin-anticline outcropping type groundwater is similar to that of the basin type but also has the characteristics of the outcropping type because of the anticlines. The natural hot springs in the study area exist mainly in the outcropping areas of the carbonates, in the middle and the plunging ends of the anticlines where the topography was cut by rivers. They can also rise through the overlying sandstones and form up-flow springs. Geothermal wells tapping the carbonate reservoirs on the flanks of the anticlines also produce thermal groundwater. The groundwater flow can be divided into three levels: (1) shallow circulation system with groundwater of HCO3-Ca type and low TDS discharging through normal temperature springs, (2) middle circulation system with groundwater of SO4-Ca type and TDS of 2–3 g/L discharging through hot springs and (3) deep circulation system with groundwater of Cl-Na type and high TDS discharging through hot springs or wells.

Sources of Salinization of Groundwater in the Lower Yarmouk Gorge, East of the River Jordan

In the Lower Yarmouk Gorge the chemical composition of regional, fresh to brackish, mostly thermal groundwater reveals a zonation in respect to salinization and geochemical evolution, which is seemingly controlled by the Lower Yarmouk fault (LYF) but does not strictly follow the morphological Yarmouk Gorge. South of LYF, the artesian Mukeihbeh well field region produces in its central segment groundwaters, an almost pure basaltic-rock type with a low contribution (<0.3 vol-%) of Tertiary brine, hosted in deep Cretaceous and Jurassic formations. Further distal, the contribution of limestone water increases, originating from the Ajloun Mountains in the South. North of the LYF, the Mezar wells, the springs of Hammat Gader and Ain Himma produce dominantly limestone water, which contains 0.14–3 vol-% of the Tertiary brine, and hence possesses variable salinity. The total dissolved equivalents, TDE, of solutes gained by water/rock interaction (WRI) and mixing with brine, TDEWRI+brine, amount to 10–70% of total salinity in the region comprising the Mukheibeh field, Ain Himma and Mezar 3 well; 55–70% in the springs of Hammat Gader; and 80–90% in wells Mezar 1 and 2. The type of salinization indicates that the Lower Yarmouk fault seemingly acts as the divide between the Ajloun and the Golan Heights-dominated groundwaters.

Sources of Salinization of Groundwater in the Lower Yarmouk Gorge, East of the River Jordan

In the Lower Yarmouk Gorge the chemical composition of regional, fresh to brackish, mostly thermal groundwater reveal a zonation in respect to salinization and geochemical evolution, which is seemingly controlled by the Lower Yarmouk fault (LYF) but does not strictly follow the morphological Yarmouk Gorge. South of LYF the artesian Mukeihbeh well field produces in its central segment groundwaters of almost pure basaltic-rock type with low contribution (&lt;0.3 vol-%) of Tertiary brine, hosted in deep Cretaceous and Jurassic formations. Further distal, the contribution of limestone water increases originating from the Ajloun Mts. North of the LYF, the Mezar wells, the springs of Hammat Gader and Ain Himma produce dominantly limestone water, which contains 0.14-3 vol-% of the Tertiary brine and possess hence variable salinity. The total dissolved equivalents of solutes gained by water/rock interaction (WRI) and mixing with brine, TDE(WRI+brine), amounts to 10-70 % in the region comprising the Mukheibeh field, Ain Himma and Mezar 3 well, to 55-70 % in the springs of Hammat Gader, and to 80-90 % in wells Mezar 1 and 2. The type of salinization indicates that the Lower Yarmouk fault seemingly acts as the divide between the Ajloun and the Golan Heigths dominated groundwater.

Numerical Simulation of Deep Thermal Groundwater Exploitation in the Beijing Plain Area

Thermal groundwater is relatively abundant in the deep-seated bedrock underlying the Beijing plain area. The main geothermal reservoir is composed of dolomites of the Wumishan Group of the Meso–Neoproterozic Jixian System. The thermal groundwater has been developed and utilized since the 1970s and significant declines in groundwater levels were observed. A 3D unsteady flow model of an anisotropic karst-fissure aquifer based on the equivalent continuum is used to describe the flow of thermal groundwater and heat transport. The heat transportation is described by the governing equation including convection and dispersion. The simulation of this paper aims to solve such problems as uneven distribution and thinness of the aquifer, insufficient initial monitoring data, and poor knowledge of the properties of the horizontal boundary. They are solved by considering vertical stratification of the aquifer with equal thickness, replacing initial water level data by surface elevation, and choosing natural boundary far away from the exploitation areas. Through a trial–error procedure, the simulated and measured groundwater level and temperature in the simulation period are well fitted. Three exploitation schemes are proposed to predict the spatial and temporal changes in groundwater level and temperature of the thermal groundwater in the study area. The prediction results show that the reinjection can effectively slow the decline in the thermal groundwater levels. Except for the Dongnanchengqu, Xiaotangshan, and Liangxiang subgeothermal fields, the other six subgeothermal fields have the potential for further development of thermal groundwater.