ALBERT

Description: Die im Norddeutschen Becken vorkommenden hochsalinaren, heißen Tiefenwässer besitzen ein beträchtliches Wärmepotential, das bisher in Neustadt-Glewe, Neubrandenburg und Waren zur Energiegewinnung genutzt wird. Das Ziel der vorliegenden Arbeit bestand zum einen darin, die Herkunft und die Genese dieser Solen und der in ihnen gelösten Stoffe zu rekonstruieren. Ein zweiter Schwerpunkt bestand in der Ermittlung geochemischer Parameter, die für einen problemlosen Langzeitbetrieb geothermischer Anlagen und somit für deren Wirtschaftlichkeit von Bedeutung sind. Die untersuchten Solen stammten aus Aquiferen, die durch fünf Bohrungen (Neubrandenburg, Waren, Rheinsberg, Neustadt-Glewe, Hamburg-Allermöhe) in Tiefen von 1250 bis 3250 m (54 bis l28°C) erschlossen wurden. Alle untersuchten Na-Cl-Solen wurden aus Sandsteinaquiferen des Keuper (Contorta!Postera-Schichten) gefördert, für die mit zunehmender Tiefe steigende TDS-Gehalte (134 bis 224 g/1) charakteristisch sind. Die Zusammensetzung der gelösten Feststoffe blieb über einen Zeitraum von 3 Jahren konstant. Die Br/CJ-Verhältnisse der Solen sind kleiner als in eingedampftem Meerwasser. Dies und 811B-Werte von +23.8 %o bis +36.3 %o indizieren die Herkunft des Salzgehaltes durch Auflösung/Laugung von Salzen. Das Gas-Wasser-Volumenverhältnis in Proben geothermisch genutzter Solen liegt bei max. 1:10. Die Gasphase wird von C02, N2 und CH4 dominiert, wobei der Gehalt an C02 und CH4 mit der Tiefe zunimmt. Als Spurengase treten He, Ar, H2 und weitere Kohlenwasserstoffe auf (jeweils 〈1 Vol.-%). Die Gasphase des Thermalwassers Neustadt-Giewe zeigte über einen Zeitraum von 2 Jahren keine Änderung in ihrer Zusammensetzung. Periodische Schwankungen in sehr kleinen Konzentrationsbereichen während einer mehrtägigen Gasmeßkampagne korrelieren mit den Erdgezeiten. Die N2-Ar-He-Verhältnisse zeigen, daß es sich um tiefzirkulierende Oberflächenwässer handelt. Untermauert wird diese Interpretation durch die sehr niedrigen 3HefHe-Verhältnisse (R!Ra:S;O.Ol), die keine Mantelheliumkomponente anzeigen, sowie die gegenüber Luft (295.5) leicht erhöhten 40 Ar/36 Ar-Verhältnisse von bis zu 367.5. He-Akkumulationsalter als scheinbare Verweildauer der Solen von 20 bis 50 Ma wurden berechnet. Das Tiefenwasser von NeustadtGiewe besaß gegenüber den anderen Lokationen erhöhte Kohlenwasserstoffgehalte. Die 813C1,2,3- Werte weisen auf thermogenetische Kohlenwasserstoffe und auf ein marines Ausgangsmaterial mit einer Reife, die einer Vitrinitreflektion von etwa 1.2 % entspricht, hin. Die Herkunft aus Corgreichen Zechstein-Sedimenten ist wahrscheinlich, organisches Material des wesentlich tiefer liegenden Karbons scheidet als Quelle aus. Die 8180- und öD-Werte der Wässer zeigen an, daß meteorisches Wasser bei der Genese eine bedeutende Rolle gespielt hat. Die ermittelte isatopische Zusammensetzung der meteorischen Komponente weicht von heutigen Niederschlagswässern ab und weist einen letztmaligen Kontakt mit der Atmosphäre zu einer Zeit deutlich wärmeren Klimas als das heutige nach. Die in einem Thermalwasser vorhandenen Gase können die technologische Eignung der Sole und den Betrieb einer geothermischen Anlage maßgeblich beinflussen (Scaling, Auftreten brennbarer Gase, Entlösung von Gasen). Bei Vorhandensein Corg-reicher Sedimente nimmt die Wahrscheinlichkeit des Auftretens brennbarer Gase in Wässern aus größerer Tiefe, die durch ihre höhere Temperatur wirtschaftlicher sind, zu. Um die Entgasung eines Tiefenwassers innerhalb einer Anlage zu verhindem und somit Scaling und unkontrolliertes Entgasen zu minimieren, wurde anhand Literaturdaten exemplarisch für den Thermalwasserkreislauf der Anlage Neustadt-Giewe (Sole mit den höchsten Gasgehalten) ein Mindestanlagendruck berechnet. Danach sind etwa 2 bar ausreichend, um ein Entgasen der Sole zu verhindern; Strömungseffekte erfordern jedoch eine Erhöhung des Anlagendrucks auf etwa 4 bar. Die zeitliche Konstanz in der Zusammensetzung der gelösten Feststoffe und der Gasphase über einen Zeitraum von 2 bzw. 3 Jahren zeugt von einer relativ großen räumlichen Homogenität der Aquifere, wodurch der Betrieb der Anlagen durch Änderungen in der chemischen Zusammensetzung der Solen kaum gefährdet zu sein scheint. Die Ergebnisse der vorliegenden Arbeit haben gezeigt, daß sowohl bei der hydrodynamischen Vorerkundung als auch während des Betriebes eines geothermischen Heizwerkes die genaue Kenntnis der Gasmengen und der Gaszusammensetzung von entscheidender Bedeutung ist.

Description: Deep seated hydrothermal brines in the North German Basin have a considerable heat potential, which is currently used for geothermal energy recovery in Neustadt-Glewe, Neubrandenburg and Waren. One aim of this study was to reconstruct the origin of these brines and their dissolved substances. Another goalwas to determine geochemical parameters which are critically influence the long-term operation, and hence the econornic viability of geothermal plants. The brines come from aquifers which have been accessed by 5 boreholes (Neubrandenburg, Waren, Rheinsberg, Neustadt-Glewe, Hamburg-Allermöhe) in depths from 1250 to 3250 m (54 to 128 °C). All investigated Na-Cl-brines were produced from sandstone aquifers of the Keuper (Contorta!Postera layers). Typically, TDS-values (134 to 224 g/1) increase with depth. The compositions of the dissolved solids were constant during 3 years. The Br/Cl ratios of the brines are lower than evaporated sea water. This, and 811B-values of +23.8 %o up to +36.3 %o indicate dissolution/leaching of salt as the origin of the salt content. The gas-water volume ratio of samples from brines used for geothermal energy recovery are less than around 1:10. The gas phase is dorninated by C02, N2 and C~ with higher C02- and C~ contents with increasing depths. He, Ar, H2 and other hydrocarbons exist as traces ( 〈1 vol.% each). The gas phase of the thermal water from Neustadt-Giewe showed no changes in its composition during 2 years. Small · periodical variations in the concentrations obtained from gas monitaring over several days correlate with the earth tides. The N2-Ar-He ratios show that the waters are deep-circulating meteoric waters. This interpretation is supported by very low 3HefHe ratios (R!Ra:S;O.Ol), which show no mantle helium, and 40 ArP6 Ar ratios up to 367.5, which are slightly enhanced compared to air (295.5). He accumulation ages, taken as the apparent residence time of the brines, were calculated to be 20 to 50 Ma. Compared to the other locations the formation water from Neustadt-Giewe contained enhanced hydrocarbon contents. The 813C1,2,3 values point to thermogenic hydrocarbons and to a marine source rock with a maturity corresponding to about 1.2 % vitrinite reflectivity. An origin from Corg-rich Zechstein sediments seems probable, organic material from significantly deeper-seated Carboniferous formations can be ruled out. The 8180 and ÖD values of the waters confirm that meteoric water played an important role in the brine genesis. The determined isotopic composition of the meteoric component deviates from recent precipitation and indicates a last contact with the atmosphere at a time when climate conditions were significantly warmer than today. Gases dissolved in thermal waters can significantly affect both the technological suitability of a brine and the operation of a geothermal heat plant (scaling, degassing, occurence of flammable gases). If Corg-rich sedimentary rocks occur, the probability of the occurence of flammable gases increases in waters from larger depths, which are more economic due to their higher temperature. The pressure needed to prevent degassing inside a plant and thus to rninirnize scaling and uncontrolled degassing was calculated for the example of the thermal water cycle at Neustadt-Giewe (brine with the highest gas content). About 2 bars are sufficient to prevent degassing; however, flow effects require increasing the pressure up to about 4 bars. The constant composition of both the dissolved solids and gases over a period of 2 to 3 years is a sign of a relatively large spatial uniformity of the aquifers. Therefore the continuous operation of the plants seems unlikely to be endangered by a change in the chernical composition of the brines. The results of this study have shown that during the hydrodynarnic reconnaissance as weil as during the operation of a geothermal heat plant, precise knowlegde of the gas concentration is of essential importance.

Description: Receiver function analysis is routinely used to isolates P-to-S converted waves from a complex of earthquake recordings s as to explore crustal and upper mantle structures and to infer possible geodynamic processes within the Earth. In the last several years the number of deployments of portable seismic arrays has been greatly increased. The conventional receiver function method, which stacks receiver functions at a single station, is not suitable for such a large amount of data. In this thesis modifications of the receiver function method have been made. Techniques of reflection seismology have been introduced into the receiver function analysis. Modified receiver function method has been successfully applied to the seismological data acquired in Tibet and the Central Andes. In these two Earth"s largest and highest plateaus, data of many available seismic broadband and short-period experiments have been collected. In Tibet, data of the INDEPTH II and GEDEPTH I experiments in southern Tibet and the PASSCAL 91/92 experiment across the central Tibetan Plateau have been combined. A Total number of about 50 stations were distributed roughly in a NNE directed profile. More than 900 receiver functions have been obtained. In the Central Andes, more than 200 stations have been deployed within the experiments of PISCO, CINCA, ANCORP, PUNA and KDS of the project of the SFB 267, and the BANJO and SEDA broadband arrays of the PASSCAL experiments. More than 640 teleseismic receiver functions have been obtained. Results are summarized in the following. (1) Crustal thicknesses under the two plateaus are reliably determined by Teleseismic receiver functions. P-to-S converted waves at the Moho are clearly seen under the Tibetan plateau and under Central Andean plateau. In southern Tibet the Moho is 75-80 km deep. In northern Tibet it becomes shallower to a depth of 55-60 km. In the Central Andes, the continental Moho is 65-70 km deep beneath the Andean Plateau (it appears to be 15 km shallower beneath Puna than beneath Altiplano). The Moho abruptly reduces its depth beneath the eastern edge of the Eastern Cordillera (65-64.5°W) and remains 45-50 km depth in the Sub Andes. Further east there is another abrupt reduction of Moho depth between the Sub Andes and the Chaco Plain. The Moho is 30-35 km beneath the Chaco Plain. (2) Evidence of crustal-scale underthrusting is found in Tibet as well as in the Andes. The INDEPTH data clearly show an intra-crustal phase at a depth of 50-60 km in the southern Tibet. This conversion boundary is probably the evidence of the underthrust Indian crust. In the Andean data a more than 300 km west-dipping intra-crustal converter evidently marks the boundary of the underthrust Brazilian shield crust. This boundary exists across the entire Altiplano and Puna plateau from 20 km depth below the Eastern Cordillera to 40 km depth below the Western Cordillera and the Precordillera. In both plateaus, most of the thickened crust, if not all, can be attributed to the crustal-scale underthrusting. (3) Plate boundaries are found to a depth of about 250 km between the Indian and the Asian lithospheric mantle and to a depth of about 120 km between the Nazca plate and the South American plate. However, the nature of these boundaries is different. In the Central Andes, the plate boundary is interpreted as the oceanic Moho of the Nazca plate, above which a 10 km layer of oceanic crust with lower seismic velocity suggests that the gabbroic rocks do not completely transform to eclogite until a depth of 120 km. Most of the intermediate depth seismicity stops at the same depth, suggesting a relation with phase transformation. In Tibet the observed plate boundary of the two lithosperic mantles probably reflects the temperature difference between the two plates. The cold Indian mantle is subducted under the warm Asian mantle. The Temperature difference can be as high as 500.700 ° resulting in large seismic velocity contrast. (4) Interesting variations have been found in the upper mantle discontinuities which are related to the plate collision and subduction processes. In Tibet, the 410 km discontinuity is clearly seen in its globally average depth in the south, and is disturbed and becomes complicated in the north. The 660 km discontinuity is continuously displayed throughout the Tibetan profile. Similarly, in the Central Andes, the 410 km discontinuity is not imaged coherently, which is obviously attributed to the subduction complexity of the phase transformation of the mantle rocks. It is interesting to see that the 660 km discontinuity is depressed by about 30-40 km in the region of the cold Nazca slab, which corresponds to a temperature reduction of 300-600° within the slab.