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Akureyri, Iceland

Gasperikova E.,Lawrence Berkeley National Laboratory | Newman G.,Lawrence Berkeley National Laboratory | Feucht D.,Lawrence Berkeley National Laboratory | Arnason K.,ISOR Iceland GeoSurvey
Transactions - Geothermal Resources Council | Year: 2011

Three-dimensional (3D) magnetotelluric (MT) inversions leading to the characterization of the electrical structure of geothermal reservoirs in a single self-consistent manner and presumably optimal accuracy and resolution are now feasible. Our work focused on two large geothermal fields - the Hengill and Krafla volcanic complexes, 200 km apart, and both known as high-temperature systems located within neo-volcanic zones of Iceland. This is the first full 3D MT inversion of Krafla MT dataset. The inverted model of electrical resistivity reveals the presence of highly resistive near surface layer, identified as unaltered porous basalt, which covers a low resistivity cap corresponding to the smectite-zeolite zone. Below this cap a more resistive zone is identified as the epidote-chlorite zone or also called the resistive core. Resistivity in the upper 1-2 km does not to correlate with lifhology but with alteration mineralogy. At the site of the IDDP well, which encountered magma at 2.1 km depth, the resistivity image shows high resistivity most likely due to epidote-chlorite geology. Just to the northwest of the well, however, an intrusive electrically conductive feature has been imaged rising from depth, and has been interpreted as a magma reservoir. A possible explanation for the magma encounter at the IDDP well is the existence of pathways or fissures connecting the magma chamber to the well. The MT response to magma pathways is not to be discernible in the data. Hengill geothermal area can be divided into two major complexes, one in the southwest and one in the northeast. The inverted model identified two low-resistivity layers. The nature of the uppermost low-resistivity layer and the increasing resistivity below is due to hydrothermal mineral alteration while the nature of the deep low-resistivity layer is not yet well understood. 3D MT inversions of Krafla and Hengill data sets showed that this approach is very promising in imaging geothermal reservoirs and that knowledge of the subsurface electrical resistivity can contribute to a better understanding of complex geothermal systems.

Armannsson H.,ISOR Iceland GeoSurvey
Applied Geochemistry | Year: 2016

Icelandic high temperature geothermal systems are considered to number thirty three, thereof three are submarine and seven subglacial. All are briefly described but the chemistry of fluids from twenty four of them is considered. The fluid in the three submarine areas and those four on land that are closest to the sea are relatively saline but to a differing extent mixed with groundwater. The rest contain dilute fluids. The fluids of the central highland systems are mostly locally derived but may in some instances be quite old whereas those in the northerly Krafla area which is inland and the Öxarfjördur area which is close to the sea appear to be a mixture of local and central highland water, but those in the inland Hengill, Geysir, Námafjall and Theistareykir areas appear to have travelled relatively long distances from the central highlands. The gas observed is magmatic except in the northerly Öxarfjördur area close to the sea where it is apparently derived from organic sediments. © 2015 Elsevier Ltd.

Gunnarsdottir M.J.,University of Iceland | Gardarsson S.M.,University of Iceland | Armannsson H.,ISOR Iceland GeoSurvey | Bartram J.,University of North Carolina at Chapel Hill
Hydrology Research | Year: 2015

Information about natural background levels (NBLs) of chemicals in source waters allows water utilities to identify trends in drinking water contamination. We estimate NBLs for chemicals in source waters for Icelandic water utilities at both national levels with all data pooled, and according to geological regime. NBLs were derived by collecting samples from 79 aquifers considered largely unimpacted by human activities. The aquifers were categorized into four geological settings that are representative of the geology of Iceland. NBLs were calculated as 90%iles of all aquifers in each setting and in all pooled. There was a statistical difference between the geological settings in 11 parameters of 37 tested. The 90%ile for nitrate for all aquifers pooled was 1.36 mg/l, indicating little anthropogenic influence on water used for public water supply in Iceland. The results were compared to the chemical status of 60 European aquifers, collected for the European Union's Sixth Framework Program Background Criteria for the Identification of Groundwater Thresholds project, revealing lower dissolved solids concentration for Icelandic groundwater than that from other parts of Europe. The explanation is likely due to high permeability of young geology settings and low population density in Iceland whereas there is a long history of agriculture and industry in most European countries. © IWA Publishing 2015.

Asmundsson R.,ISOR Iceland GeoSurvey | Asmundsson R.,Heat Research and Development | Pezard P.,Montpellier University | Sanjuan B.,Bureau de Recherches Geologiques et Minieres | And 16 more authors.
Geothermics | Year: 2014

During the early years of the Iceland Deep Drilling Project (IDDP), development of three distinctive technological and scientific approaches were formalised and then carried out until 2010 within a European funded project called HiTI (high temperature instruments for supercritical geothermal reservoir characterisation and exploitation). These approaches were: (1) development of several downhole instruments allowing them to function up to 300. °C and 400. °C, (2) identification of two new Na/Li cation ratio geothermometric relationships valid at very high temperature, (3) tracer testing with high temperature tolerant organic isomers and finally and (4) basalt rock deformation and petrophysical properties laboratory investigations at high temperature and pressure conditions. © 2013 Elsevier Ltd.

Sanjuan B.,Bureau de Recherches Geologiques et Minieres | Millot R.,Bureau de Recherches Geologiques et Minieres | Asmundsson R.,ISOR Iceland GeoSurvey | Asmundsson R.,Heat Research and Development | And 2 more authors.
Chemical Geology | Year: 2014

This work has made it possible to obtain two new Na/Li geothermometric relationships in addition to the three already known (Fouillac and Michard, 1981; Kharaka et al., 1982) and confirms that the Na/Li geothermometer, unlike the Na/K, Na/K/Ca, K/Mg and silica geothermometers, or the isotope δ18O (H2O-SO4) geothermometer, also depends on the fluid salinity and the nature of the reservoir rocks reacting with the geothermal water. One of the relationships concerns the fluids derived from seawater-basalt interaction processes existing in emerged rifts such as those of Iceland (Reykjanes, Svartsengi, and Seltjarnarnes geothermal fields) and Djibouti (Asal-Ghoubbet and Obock geothermal areas), or in numerous oceanic ridges and rises (Mid-Atlantic and Middle-Valley ridges, East Pacific rise, etc.). The best adapted Na/Li relationship for geothermal fluids discharged from emerged rifts between 0 and 365°C is:TK=920/[log(Na/Li)-1.105] (r2=0.994, n=27) where Na and Li are the aqueous concentrations of these elements given in mol/L. The other Na/Li relationship was determined using dilute waters collected from wells located in different high-temperature (200-325°C) volcanic geothermal areas of Iceland (Krafla, Námafjall, Nesjavellir and Hveragerdi). This relationship can be expressed as follows:T(K)=2002/ [log(Na/Li)+1.322] (r2=0.967, n=17).These two relationships give estimations of temperature with an uncertainty close to ±. 20. °C. The second Na/Li relationship was also successfully applied to HT dilute geothermal waters from the East African Rift (Ethiopia, Kenya).Some case studies in the literature and thermodynamic considerations suggest that the Na/Li ratios for this type of fluids could be controlled by full equilibrium reactions involving a mineral assemblage constituting at least albite, K-feldspar, quartz and clay minerals such as kaolinite, illite (or muscovite) and Li-micas. Unlike the Na/Li ratios, no thermometric relationship using Li isotopes could be determined for this type of water. However, it was noticed that δ7Li values higher than 16% are always associated with low- to medium-temperature waters. © 2014 Elsevier B.V.

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