Thermal Spring Discharge Research Articles

Significance of basin asymmetry and regional groundwater flow conditions in preliminary geothermal potential assessment – Implications on extensional geothermal plays

Abstract Extensional domain type geothermal plays, as fertile targets for future resource development, consist of an orogen and an adjoining sedimentary basin of asymmetric physiographic and geologic setting. Preliminary geothermal potential, i.e. prospective geothermal regions, basin-scale flow patterns, heat transfer processes, temperature distribution and appearance of thermal springs were analyzed systematically by numerical simulations in groundwater basins with special emphasis on the effects of basin asymmetry. The importance of basin-scale regional groundwater flow studies in preliminary geothermal potential assessment was demonstrated for synthetic and real-life cases. A simulated series of simplified real systems revealed the effects of anisotropy, asymmetry of the topographical driving force for groundwater flow, basin heterogeneity and basal heat flow on heat accumulation, locations of thermal spring discharge and prevailing mechanisms of heat transfer. As a new aspect in basin-scale groundwater and geothermal studies, basin asymmetry was introduced which has a critical role in discharge and accumulation patterns, thus controlling the location of basin parts bearing the highest geothermal potential. During the reconnaissance phase of geothermal exploration, these conceptual, generalized and simplified groundwater flow and heat transport models can support the identification of prospective areas and planning of shallow and deep geothermal energy utilization, also with respect to reinjection possibilities. Finally, the scope of “geothermal hydrogeology” is defined in a scientific manner for the first time.

Heat and fluid flow dynamics of a stratovolcano: The Tacaná Volcanic Complex, Mexico-Guatemala

Mexico is the world's sixth-largest geothermal energy producer. To pursue its transition to renewable energy, other potential geothermal areas are under exploration. The Tacaná hydrothermal system is one of them. In this work, we developed a preliminary 2D numerical mass and heat flow model of the natural state of the Tacaná volcano in order to gain insight into fluid and rock properties at depth. A comprehensive set of simulations was performed involving various rock permeabilities, geometries, and upper and basal boundary conditions until the simulated data matched the measured data, including spring and fumarole temperatures at the surface and thermal spring discharge. Simulation results show that the temperature structure and the phase distribution at depth are partly controlled by the permeability distribution inside the volcano together with a low topography-driven downflow and the absence of elevated fluid pressures at shallow levels. The low topography-driven recharge may be related to a low-permeability layer, whereas low fluid pressures most probably related to a relatively deep water table. The deep thermal fluid source must be connected to the San Antonio fumarolic field by a high-permeability conduit to enhance the fluid upflow and the development of a boiling zone in the uppermost part of the cone. Furthermore, our results suggest that the (almost) total absence of hydrothermal manifestation in the NE part (Guatemala) of the volcano is controlled by the tilting of the basement rocks. Our model will be used as initial conditions for the modelling of several geothermal exploitation scenarios in future work.

Fossilised geothermal surface features of the Whitianga Volcanic Centre (Miocene), Coromandel Volcanic Zone, New Zealand: Controls and characteristics

The Late Miocene Whitianga Volcanic Centre of the Coromandel Volcanic Zone, North Island, New Zealand, is host to 18 known, siliceous and intensely silicified deposits including: silicified volcanics; sediments of inferred lacustrine, fluvial and mud pool origin; siliceous hot spring deposits, or sinters; and silicic veins. Collectively these siliceous and silicified deposits indicate past geothermal activity that occurred at the Earth's surface and in the shallow subsurface. Sinters, in particular, are of interest because they are derived from deep geothermal reservoirs and precipitate from discharged thermal fluids at the intersection of the water table with the land surface. However, some siliceous and silicified features in hydrothermal paleoenvironments have been misidentified as sinters. By studying textural types, distributions, structural setting, mineral paragenesis and trace elemental composition of the siliceous and silicified deposits in the Whitianga Volcanic Centre, it is possible to differentiate sinters and identify their spring-vent source areas (100–70 °C) from more distal thermal spring discharge locations (<70 °C to ambient), extent of hydrothermal alteration, and, in places, delineate zones of epithermal upflow where AuAg mineralisation may have occurred at depth. This has important implications for the exploration of mineralised epithermal ore deposits at local to regional scales, in particular for the Hauraki Goldfield of the Coromandel Volcanic Zone.

Identification of prospective significance levels for potential geothermal fields of India

Abstract This study aims to predict prospective significance levels of potential geothermal fields already identified by Geological Survey of India (GSI) and National Geophysical Research Institute (NGRI) by field investigations. Wide range of criteria's are considered in determining the relative significance level of each geothermal field in terms of cumulative score. These criteria's include useful resource base (URBfield), Areal extent (Afield), Minimum temperature as per geothermometry (Tmin), Maximum temperature as per geothermometry (Tmax), Utilization score (USfield), Cumulative discharge of thermal springs (Q), Minimum electrical resistivity (Rmin), Maximum electrical resistivity (Rmax) and Representative reservoir temperature as per Gas thermometry (Tgas). Fuzzy Analytical Hierarchy Process (Fuzzy AHP) is used to study the dominance of each geothermal field, evaluated over the aforementioned criteria to find cumulative score. URBfield depends on possible extraction temperature of reservoir estimated by COMSOL Multiphysics® modelling and simulation software. The geothermal fields are conceptualized as shallow homogenous reservoirs with injection and extraction wells. The attributes of remaining criteria are collected from published works of NGRI and GSI. The results of this study ratify that Puga geothermal field is the most significant site among the identified potential geothermal fields, to conduct further developmental works and for commercial extraction of geothermal energy.

Functioning of natural and natural-engineering systems formation conditions and natural state of the hydrothermal system in the Valley of Geysers (Kronotsky Nature Reserve, Kamchatka)

The formation of the hydrothermal system in the Valley of Geysers is shown to be governed by a structure of radial and circular faults of above-intrusion zone of a partially melted magmatic body with an epicenter near the Upper-Geyser Field, while the hydrothermal system is shown to receive its water from elevations of +500 to +900 m abs (according to isotopic data). The catastrophic landslide of June 3, 2007, was just a stage in the general scenario of the gradual hydrothermal transformation of the inclined Geyser unit (Q34grn), building up the roof of the hydrothermal reservoir, with a gradual decline of slide resistance. The slide was triggered by the increased pressure in the hydrothermal and magmatic systems and the saturation of the Geyser unit by moisture during spring flood. According to the data of continuous regime thermohydrodynamic observations carried out in the Valley of Geysers with the use of HOBO-loggers of temperature and pressure since July 2007 to April 2010, the mean time between eruptions of Velikan geyser was 348 minutes. The intensification of precipitation input directly into the geyser pool causes a short-time increase in the time between eruptions (up to the maximum of 32 h). According to observations at the “Plotina” gage, the total estimated mean annual discharge of thermal springs (by chlorine ion) in the Valley of Geysers is 263 kg/s; the discharge of thermal springs is governed by the level of Poldprudnoe Lake and its seasonal variations exceed 40%.

Source and origin of active and fossil thermal spring systems, northern Upper Rhine Graben, Germany

Abstract Thermal water samples and related young and fossil mineralization from a geothermal system at the northern margin of the Upper Rhine Graben have been investigated by combining hydrochemistry with stable and Sr isotope geochemistry. Actively discharging thermal springs and mineralization are present in a structural zone that extends over at least 60 km along strike, with two of the main centers of hydrothermal activity being Wiesbaden and Bad Nauheim. This setting provides the rare opportunity to link the chemistry and isotopic signatures of modern thermal waters directly with fossil mineralization dating back to at least 500–800 ka. The fossil thermal spring mineralization can be classified into two major types: barite-(pyrite) fracture filling associated with laterally-extensive silicification; and barite, goethite and silica impregnation mineralization in Tertiary sediments. Additionally, carbonatic sinters occur around active springs. Strontium isotope and trace element data suggest that mixing of a hot (>100 °C), deep-sourced thermal water with cooler groundwater from shallow aquifers is responsible for present-day thermal spring discharge and fossil mineralization. The correlation between both Sr and S isotope ratios and the elevation of the barite mineralization relative to the present-day water table in Wiesbaden is explained by mixing of deep-sourced thermal water having high 87Sr/86Sr and low δ34S with shallow groundwater of lower 87Sr/86Sr and higher δ34S. The Sr isotope data demonstrate that the hot thermal waters originate from an aquifer in the Variscan crystalline basement at depths of 3–5 km. The S isotope data show that impregnation-type mineralization is strongly influenced by mixing with SO4 that has high δ34S values. The fracture style mineralization formed by cooling of the thermal waters, whereas impregnation-type mineralization precipitated by mixing with SO4-rich groundwater percolating through the sediments.

The effect of Dead Sea level fluctuations on the discharge of thermal springs

Shalev, E. and Yechieli, Y. The effect of Dead Sea level fluctuations on the dis charge of thermal springs. Isr. J. Earth Sci. 56: 19–27. Thermal springs along the Dead Sea shore have been known to exist long before the great recession of the Dead Sea of the last 40 years. This work studies a possible mechanism that drives the brine discharge along the Dead Sea shore and the effect of the lake level fluctuations on the discharge. The Goldschmidt model suggested for the discharge of the springs at the Sea of Galilee cannot explain the discharge of the springs at the Dead Sea shore. Results from numerical modeling indicate that at steady state conditions the Dead Sea brine sinks through faults, migrates across tilted blocks, and then ascends back to the Dead Sea shore with fresh groundwater. The most signifi cant change in brine discharge is caused by water level changes in the lake. A recession of the Dead Sea causes a significant increase in brine spring discharge. As the Dead Sea level drops it interrupts the steady-state conditions. Since the groundwater was in equilibrium with a higher lake level, it now flows upwards to the lower lake level, reducing the overall hydraulic head. A rise of the Dead Sea level causes a decrease or even disappearance of the thermal spring discharge. An increase in the freshwater recharge in the mountain area causes negligible changes in this brine circulation.