Ingrid Stober

Water-Rock Interaction

Preface. Groundwater -- field and experimental studies. Groundwater Evolution in an Arid Coastal Region of the Sultanate of Oman based on Geochemical and Isotopic Tracers C.E. Weyhenmeyer. A combined isotopic tool box for the investigation of water-rock interaction: An overview of Sr, B, O, H isotopes and U-series in deep groundwaters from the Vienne granitoid (France) P. Negrel, et al. Water-rock reaction experiments with Black Forest gneiss and granite K. Bucher, I. Stober. The distribution of rare earth elements and yttrium in water-rock interactions: field observations and experiments P. Moller. Hydrothermal and volcanic settings. A case study of gas-water-rock interaction in a volcanic aquifer: the south-western flank of Mt. Etna (Sicily) A. Aiuppa, et al. Modelling chemical brine-rock interaction in geothermal reservoirs M. Kuhn, et al. Mineral deposits. Water-rock reactions in a barite-fluorite underground mine, Black Forest (Germany) I. Stober, et al. Extensional Veins and Pb-Zn Mineralisation in basement rocks: The role of penetration of formation brines S. Gleeson, B. Yardley. Experimental studies. Interaction of polysilicic and monosilicic acid with mineral surfaces M. Dietzel.

Deep groundwater in the crystalline basement of the Black Forest region

Two major types of groundwater can be readily distinguished in the Variscian crystalline basement of the Black Forest in S–W Germany. Saline thermal water utilized in spas has its origin in 3–4 km deep reservoirs and developed its composition by 3 component mixing of surface freshwater, saltwater (of ultimately marine origin) and a water–rock reaction component. In contrast to the thermal water, CO2-rich mineral water, tapped and bottled from many wells in the Black Forest, has low salinities but a TDS distribution similar to that of thermal water. It developed its chemical composition entirely by reaction of CO2-rich water with the gneissic or granitic aquifer rock matrix. Particularly important is the contribution of various plagioclase dissolution and weathering reactions that may, at some locations, involve precipitation and dissolution of secondary calcite. Sodium/Ca ratios of water and of rock forming plagioclase in the basement rocks suggests that plagioclase weathering is strongly incongruent. Calcium is released to the water, whereas Na remains fixed to the albite feldspar component. The major element composition of 192 water samples used in this study also indicates a clear vertical stratification of the type of water chemistry; Ca–HCO3 near the surface, Na–Ca–HCO3–SO4 at intermediate depth and Na–Ca–Cl at great depth. The mean permeability of Black Forest granite is about K=10−6 m/s; it is significantly lower in gneisses (gneiss: mean K=5×10−8 m/s) leading to focused flow through granite. Highly permeable fracture and fault zones, particularly in granite, are utilized by high-TDS saline deep groundwater as ascent channels and flow paths. Although spatially closely associated, the topography driven upwelling system of saline deep water and the near-surface flow system of CO2-rich mineral waters are hydraulically and chemically unconnected.

Hydrogeology of crystalline rocks

Preface. 1. Water Conducting Features in Crystalline Rocks. Geological and hydraulic properties of water-conducting features in crystalline rocks M. Mazurek. Feldspars as microtextural markers of fluid flow I. Parsons, M.R. Lee. 2. Hydraulic Properties of Crystalline Rocks. Hydraulic properties of the Upper Continental Crust: data from the Urach 3 geothermal well I. Stober, K. Bucher. In-situ petrohydraulic parameters from tidal and barometric analysis of fluid level variations in deep wells: Some results from KTB K. Schulze, et al. The role of water-conducting features in the Swiss concept for the disposal of high-level radioactive waste M. Mazurek, et al. The scaling of hydraulic properties in granitic rocks D. Schulze-Makuch, P. Malik. 3. Hydrochemical Properties of Water in Crystalline Rocks. The composition of groundwater in the Continental crystalline crust K. Bucher, I. Stober. Evolution of fluid circulation in the Rhine graben: Constraints from the chemistry of present fluids L. Aquilina, et al. Occurrence and origin of Cl-rich amphibole and biotite in the Earths crust - implications for fluid composition and evolution K. Kullerud. Rare earth elements and yttrium as geochemical indicators of the source of mineral and thermal waters P. Moller. 4. Microbial Processes in Crystalline Rocks. The hydrogen driven intra-terrestrial biosphere and its influence on the hydrochemical conditions in crystalline bedrock aquifers K. Pedersen. Ancient microbial activity in crystalline bedrock - results from stable isotope analyses E.-L. Tullborg.

The Composition of Groundwater in the Continental Crystalline Crust

The composition of water stored in the crystalline rocks (basement) of the upper continental crust has in general four components: i) a surface water component derived from rain, snow and other precipitation, ii) a seawater component derived from modern or fossil seawater, iii) an imported component from ongoing magmatic or metamorphic reactions elsewhere in the crust, and iv) a contribution from the reactions between water and the local rock matrix.

Chemical evolution of thermal waters from limestone aquifers of the Southern Upper Rhine Valley

Thermal spas in the Upper Rhine Graben recover their waters mainly from two different limestone aquifers, Hauptrogenstein (Middle Jurassic) and Muschelkalk (Middle Triassic). The thermal waters are heated along anomalous high thermal gradients in the Tertiary rift valley. The highest well head temperature is about 40°C in Hauptrogenstein wells and 60°C in Muschelkalk wells. Mineralization (TDS) is up to 5 g/kg in Hauptrogenstein and as high as 17 g/kg in the Muschelkalk aquifer. About 300 chemical analyses from 13 wells were used in this study. Compositional relationships between major chemical components (Na/Cl, K/Cl, Mg/Cl, SO4/Cl, Cl/Br and Na/Br) suggest that thermal water from the Hauptrogenstein originates from mixing of 3 components: (a) meteoric water, (b) fossil seawater (residual formation water) and (c) a third component that resulted from water–rock reaction. The total amount of dissolved solids and the water type from the deeper Muschelkalk aquifer depends on the depth of the aquifer at the well location. The chemical characteristics of the thermal water indicate that water composition is derived mainly from water–rock interaction.

Researchers study conductivity of crystalline rock in proposed radioactive waste site

The crystalline basement of the Black Forest is under consideration as a possible repository for radioactive waste. Crystalline rock has traditionally been considered impermeable, even though very deep wells such as the Kola well in the former Soviet Union have been found to contain open, water-filled fissures at more than 12,000 m depth. In 1995, researchers investigated the conductivity of the Black Forest crystalline rock and the chemical properties of the water within [Stober, 1995] and found that the crystalline basement is more permeable than once thought. Hydrogeologic evidence revealed the presence of several thermal and mineral water springs in the crystalline rocks, suggesting that the region may be especially poorly suited for the radioactive waste repository.

Permeabilities and Chemical Properties of Water in Crystalline Rocks of the Black Forest, Germany

Investigations were carried out to determine the hydraulic and hydrochemical properties of crystalline rocks in the Black Forest of Germany and neighbouring regions. Rock permeabilities (K) were determined to a depth of 3500 m. These parameters range from K = 3.5 × 10-10 ms-1 to K = 8.7 × 10-5 ms-1; and can increase up to an order of magnitude which is typical for porous aquifers. It is shown that on an average, granites are more pervious than gneisses and only the permeabilities of gneisses decrease with depth. The geochemistry of natural waters in crystalline rocks is not constant, but varies with depth and location. The concentration increases with depth and the water-type changes from a Ca–-Na–-HCO 3-type (or Na–-Ca–-HCO3–-) at shallow depths to a Na–-Cl-type at greater depths. Thermal springs are found only in granitic rocks with on average higher permeabilities than in gneisses. Thermal waters are welling up in valleys at the bottom of steep mountains. The chemical composition of thermal spring water is identical to that of water found at greater depths. Using geothermometers it is found, that the depth of the deposits of thermal spring water in the crystalline basement rocks of the Black Forest is some 1000 m below the surface. The topographic relief in the mountains induces a deep circulation of infiltrating rain-water with an upwelling as thermal springs in the valleys.

Water-rock reaction experiments with Black Forest gneiss and granite

Five characteristic samples of crystalline rocks of the Black Forest basement, three gneisses from the Kinzig Valley and two granites (Triberg & Barhalde) from the Variscan basement of the Central Black Forest have been experimentally reacted with water in a batch reactor under a series of different experimental conditions in order to better understand the composition and evolution of groundwater in the crystalline basement.

Geothermal Energy Resources

In physics, energy is the ability of a physical system to do work on other physical systems. There are many different forms of energy including mechanical (potential, kinetic), thermal, electric, chemical and nuclear energy. Thermal energy can be understood as the random motion of atoms and molecules.

Hydraulic Properties of the Upper Continental Crust: data from the Urach 3 geothermal well

The 4500m deep research borehole at Urach (South Germany) has been extensively used for hydraulic testing of the crystalline basement. The data permit a general interpretation of the hydraulic properties of crystalline continental upper crust. The typical granitic and gneissic basement contains an interconnected fluid-filled fracture system and behaves hydraulically like a confined fractured aquifer. Thus standard hydraulic well-tests can be used in the basement. The conclusions are based on data from the central part of the upper crust and are, therefore, believed to be characteristic and significant for the brittle upper continental crust in general.