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1.
Integrated geophysical surveys were performed in two sites, Fossa di Fuardo and Terme di San Calogero in Lipari Island, Southern Italy with the intent of the exploration of low-enthalpy geothermal fluids. Both sites show strong geochemical and geologic evidences of hydrothermal activity. The geophysical methods consist of two microgravimetric surveys, two 2D geoelectric profiles, a seismic reflection profile and a five seismic refraction profiles. The seismic methods allowed us to locate the main subsurface seismic discontinuities and to evaluate their geometrical relationships. The gravity field was used to constraint the seismic discontinuities, while the electric prospecting let discriminate more conductive areas, which could correspond to an increase in thermal fluid circulation in the investigated sites.The results obtained by the different geophysical methods are in good agreement and permit the definition of a reliable geo-structural model of the subsurface setting of the two investigated areas. A low-enthalpy geothermal reservoir constituted by a permeable pyroclastic and lava sequence underlying two shallow impermeable formations was found at Fossa del Fuardo. The reservoir is intersected by some sub-vertical faults/fractures that probably play an important role in convoying the thermal water up to the surface. At the other site, Terme di S. Calogero, the geophysical surveys showed that an intense circulation of fluids affects the subsurface of the area. This circulation concentrates along a ENE-trending fault located at a little distance from the thermal resort. The hot fluids may upraise along the fault if the width of the ascent area is smaller than 20 m.  相似文献   

2.
Summary
A ground-water study carried out in the Serowe area of eastern Botswana between 1985–1988 has provided the opportunity to evaluate the role of a multiparameter low-level airborne geophysical survey in a hydrogeological investigation. The survey included magnetic, VLF (very low frequency), and coaxial EM (electromagnetic) measurements. In total, 7,500 line kilometers were flown over an area of 3,300 km2 with a nominal ground clearance of 20 m and a line spacing of 400 m.
The main aquifer, the Ntane Sandstone Formation (Karoo age), is confined between mudstones below and basalt above, and is broken into a series of graben and horst structures by numerous E-W striking faults. All bedrock, however, is completely masked by a 20–60 m thick overburden of sands, calcretes, silcretes, and sandstones known collectively as the Kalahari beds.
Airborne magnetic and VLF geophysical surveys have been used to penetrate this masking cover. Images and stacked profiles obtained from the survey revealed structural and geological features of major hydrogeological significance. This provided the information necessary for the formulation of a conceptual model.
The results helped guide the subsequent exploration drilling program in an efficient and effective manner, cutting down the need for extensive ground surveys. The investigation confirmed the availability of a 35,000 m3/day resource, sustainable for a 25-year period. Highest yields were obtained from fracture zones associated with VLF anomalies. Potential wellfields were identified in confined sections of the aquifer, with production boreholes to be sited, where possible, on fractures associated with VLF anomalies.  相似文献   

3.
Correlation of geophysical data collected using the NMR method in the Negev Desert, Israel, with hydrogeological data from nearby observation wells is presented. The experiment was conducted near Kibbutz Revivim in the Besor drainage system (Fig. 1). The objective of the survey was to detect groundwater layers in the Quaternary cover filling and Eocene fractured aquifers down to a depth of 100 m. The experiment was performed using a combination of two different geophysical techniques, namely the NMR and time domain electromagnetic (TDEM) methods. The geophysical results were verified by measuring the water level in three observation wells, two of which were drilled several months after the geophysical survey was carried out.The water level measured in these follow-up observation wells shortly after drilling did not coincide with the geophysical data. However, it settled over a period of time and finally stabilized at a depth very similar to that obtained from the NMR measurements. This phenomenon is caused by the fractured nature of the phreatic aquifer. Since the flow of water in such aquifers is confined by the fractures, the appearance of water in the well during or shortly after drilling is determined solely by the intersection of the well and the fracture. Our experiments showed that geophysical measurements in fractured phreatic aquifers may have a distinct advantage over direct borehole measurements, since the former average the depth to the water table over large areas (several thousand square meters) while the latter are limited by the area of the borehole cross-section (several tens of square centimeters).  相似文献   

4.
Bathymetric and gravity surveys were carried out from 1988 to 1994, in the Gulf of Naples (Southern Italy) to offshore extend the already existing Bouguer anomaly map. In order to improve the knowledge of the structural setting beneath the active Neapolitan volcanoes (Vesuvio, Campi Flegrei and Ischia), 862 stations were surveyed within the isobath of 400 m; at the same time, and about 2000 on-land gravity values were also collected. A new Bouguer anomaly map spanning the whole volcanic region was drawn from the final data set. Gravity anomalies were referred to the new absolute gravity station in Naples and computed according to 1980 Geodetic Reference System. Finally, a density value of 2200 kg/m3 was used in the computation of the Bouguer and terrain effects. We carried out the inversion of the gravity anomalies adopting a 2.5-D modelling along selected profiles crossing the investigated area. The interpretative models were constrained to data obtained from deep wells and other geophysical investigations.  相似文献   

5.
Traditional numerical methods for the delineation of wellhead protection areas span deterministic and probabilistic approaches. They provide time-related capture zones. However, none of the existing approaches identifies the groundwater contribution areas related to each source or sink. In this work, the worthiness of the so-called double delineation approach was extended. This task was achieved by simple postprocessing of its dual outputs leading to a highly efficient screening tool. In the particular context of geothermal resources management through the well doublets of the Dogger aquifer in the Paris Basin (France), the approach was extended to forecast the compositional heat breakthrough at production wells. Hence, cold-water breakthrough and temperature decline in production wells are timely assessed in low-enthalpy geothermal reservoirs. The method quantifies how groundwater volumes are moving through space and time between any couple of source and sink. It provides unprecedented tools advancing the enhanced understanding of water resources systems functioning. It is highly recommended to implement the presented concepts in the current and future generations of community groundwater models.  相似文献   

6.
In this paper the main results from the implementation and interpretation of a geophysical survey carried out in Chalkidiki (Northern Greece) are presented. The objective of the geophysical survey was to study the general geological conditions of the area (stratigraphy and tectonism) and to focus on the hydrogeological behaviour of the geological formations in the area. The ultimate target was to point out the most promising locations for the successful construction of hydro wells. Since direct hydrogeological information was not available, three different geophysical techniques were applied in order to follow a step by step approach to the exploration of the study area. Firstly, the Very Low Frequency (VLF) electromagnetic method was applied since the majority of the area was dominated by the formation of ophiolites and water flow was possibly expected only in fractured zones at a relatively small depth. Secondly, at the locations of the conductive zones detected by the VLF survey additional Electrical Resistivity Tomography (ERT) sections at different scales were measured to provide more detailed information about the geometrical characteristics of them. Finally, Self-Potential (SP) measurements along the same profiles were conducted in order to provide supplementary information concerning the nature of the conductive zones such as the possible relation with electrokinetic sources. The combined interpretation of the geophysical data proved very efficient for deciding the most promising locations for the construction of hydro wells.  相似文献   

7.
A high resolution geophysical survey was carried out on the Pont De Coq, a medieval stone arch bridge located in Normandy (France) in 2011 and 2012. Two complementary methods are used: Electrical Resistivity Tomography (ERT) and Ground PenetratingRadar (GPR). They allow to evaluate the structural state of the bridge and to characterize the subsurface around and beneath the bridge. An excellent correlation is obtained between the geophysical methods and the geological data obtained around the bridge. In order to improve the restitution of the geophysical data, an advanced photogrammetric method is performed, providing a high resolution 3D Digital Terrain Model (DTM) of the Pont de Coq. The advanced photogrammetry enhances the presentation of the GPR and ERT data. This approach is an easy-to-use, rapid and cost-effective tool for stakeholders. Finally, it is a promising and original method for improved interpretations of future geophysical surveys.  相似文献   

8.
In 1979 and 1980, 535 magnetotelluric soundings using a frequency range of 1700 Hz-8 Hz were performed on the island of Réunion for geothermal exploration.Few direct hot-water discharges were observed. Consequently, geophysical methods, particularly the audiomagnetotelluric method, were used extensively. Favourable geological conditions for this method were encountered and the results, which were controlled using classical electrical methods on test areas, suggest an unusual distribution of resistivities for lava flows situated above suspected geothermal areas. These layers progressively decrease in resistivity down to a very conductive layer. In areas where these conductive layers were nearest the surface, detailed studies were carried out showing a close correlation between decreasing resistivity and increasing hydrothermal alteration. In addition, gradient wells reveal high geothermal gradients in such areas. The conductive layers revealed by audiomagnetotelluric soundings seem to correlate with thermal effects creating progressive hydrothermal alteration from an inferred hot-water reservoir up toward the surface.  相似文献   

9.
Norikura Volcano has not been active during the last 10,000 years in spite of the activity of the surrounding volcanic mountains. To study past volcanic activities, geological studies were carried out extensively. However, quite a few geophysical investigations were conducted to contribute to volcanology. Our objective is to detect the present subsurface structure of Norikura Volcano and to define volcanic stratifications. In the vicinity of Norikura Volcano, geothermal fields are still active. Subsurface volcanic rocks in this area have been exposed to geothermal activity and altered. To comprehend volcanic stratifications of Norikura and geothermal activity, we conducted audio frequency magneto-telluric (AMT) surveys around Norikura Volcano. AMT survey is useful in clearly defining the resistivity structure related to volcanic regions. The AMT data were acquired over a frequency range 10 Hz–10 kHz. Decomposition analysis was applied to the tensor impedance data. Subsequently, apparent resistivity and phase data were inverted using a two-dimensional magneto-telluric (MT) inversion and a model of Norikura was derived. The final model manifests that the surface resistors are in agreement with andesite lava or dacite lava. As for the deeper structure, a horizontal conductor is situated above resistive basements. The alteration of the conductor was weak, while basement rocks were strongly altered and/or heated through the thermal activity. The existence of these layers seems to indicate the degree of thermal activity of Norikura Volcano.  相似文献   

10.
Magnetotelluric (MT) and ground magnetic surveys were conducted on the Mahallat geothermal field situated in Markazi province, central Iran, as a primary part of the explorations and developments of a geothermal energy investigation program in the region. Mahallat region has the greatest geothermal fields in Iran. MT survey was performed in November 2011 on an 8 km profile crossing the hot springs with a total of 17 stations. The 2D inversion of the determinant MT data was performed using a 2D inversion routine based on the Occam approach. The 2D resistivity model obtained from the determinant data shows a low resistivity zone at 800-2000 m depth and a higher resistivity zone above the low resistivity zone, interpreted as geothermal reservoir and cap rock, respectively. It also revealed two major concealed faults which are acting as preferential paths for the circulation of hydrothermal fluids. To obtain more geophysical evidence, a ground magnetic survey with 5000 stations was also performed over an area of 200 km2 around the MT profile. Magnetic measurements show a main positive anomaly of about +1000 nT over the study area, which could be interpreted as an intrusive body with the high magnetic susceptibility (i.e. mafic and ultramafic rocks) into the sedimentary host rocks. We interpret the body as the heat source of the geothermal system. Structural index and depth estimation of the anomaly indicate that the intrusive body is similar to a cylinder extending from about one kilometer depth down to greater depths. The results of MT and magnetic investigations indicate a geothermal reservoir which proves the preliminary geological observations to a great extent.  相似文献   

11.
Magnetotelluric surveys were conducted to investigate the structure in the El Hito Anticline in the southern Loranca Basin, Spain. The structure of this anticline is partly known from nearby data (geological cross sections, geological maps, well-logs) from vintage geophysical and geological basin-scale surveys. Unfortunately, these surveys do not have the appropriate resolution to determine certain characteristics of the anticline accurately, such as the thickness or geometry of geological units. To address this deficiency, magnetotelluric data were acquired at 51 sites along three profiles to image the electrical resistivity of the anticline. To identify a geologically reasonable resistivity model, a conceptual model based on previous geological and geophysical information (cross sections and well-log data) was generated. Several inversions were performed using the conceptual model, which played a key role in the interpretation of the magnetotelluric data, and the construction of a suitable initial model was essential in producing geologically meaningful models. Using these results, we obtained 2-D resistivity models that provide information on the main geological units and structures. We also performed sensitivity tests to understand the morphology and structure of the resistive basement better. The results indicate the presence of basement highs that show different structural styles for the basement and its cover, and an increase in the basement depth towards the south. The final 2-D resistivity models provide new information regarding the structure of the anticline and demonstrate a clear correlation between the main geological units and resistivity, as well as correlations with mapped surface faults.  相似文献   

12.
The paper deals with hydraulic problems, arising with the development of geothermal deep ground-water flow. It begins with a brief comment upon the most important principles of flow, regarding the influence of temperature of water. Further it is explained what kind of hydraulic investigations on deep boreholes are necessary and how they have to be done.Finally, it will be reported about hydraulic investigations on particular geothermal water resources in Austria. Results of a pumping test, made at a deep well and lasting 15 months, show that by thermohydraulic investigations, particularly in connexion with geophysical measurements, fundamental statements can be made about available geothermal resources of the earth's crust for the technical planning and economic working of a geothermal energy production plant. The paper ends with a brief report about experiences made with the first geothermal heat supply plant that has been installed in Austria (Waltersdorf/East Styria).  相似文献   

13.
The Antinaco-Los Colorados valley is a wide N–S tectonic depression, located between the Sa. de Velazco and the Sa. de Famatina, both ranges belonging to the Sierras Pampeanas thick-skinned deformation province in Argentina. From previously reported magnetotelluric (MT) data, it is known that the thickness of the sedimentary sequences may reach up to 8 km in the central zone of this basin. In particular, the Quaternary-to-recent alluvial filling contains an aquifer complex of great importance for this semiarid zone providing water for irrigation and also for human consumption. To obtain information about the electrical structure of the alluvial cover, 17 vertical electric soundings were carried out along an E–W traverse profile extending from one side of the valley to the other. A geoelectrical model is proposed taking into account complementary hydrogeological and geophysical information. In this model, the various layers which could contain fresh water are identified and the level of the water table inferred from the model is almost coincident with that observed from existing wells in the surveyed zone.  相似文献   

14.
In recent times, velocity surveys at marine well locations have been performed using non-explosive energy sources such as air-guns and gas guns. In addition, surveys in land wells have been successfully carried out using a modified version of the air-gun. This paper illustrates some of the characteristics of these devices and compares the data obtained from typical surveys with conventional dynamite surveys. Since data obtained from well velocity surveys using non-explosive sources are now commonly recorded on tape, they lend themself to further digital processing and interpretation techniques that were not previously so conveniently available. Some examples of these processes, e.g. the examination of attenuation, frequency and energy content of the recorded well geophone signals, are given in the paper. Examples of some other digital processes, using calibrated Acoustic logs, whether recorded digitally in the field or subsequently converted from analogue recordings, are also given in the paper. These include the construction of an Acoustic log in the vertical axis from logs obtained in deviated wells.  相似文献   

15.
This paper deals with the design, acquisition and processing of vertical seismic profiling data collected in 2016 at the directional Thônex-01 geothermal well, drilled in 1993 in the Geneva Canton (Switzerland). The aim of the study was to obtain additional information from existing-abandoned well for downhole geophysical characterization of potential geothermal reservoirs in the Geneva area. The main results obtained by this study allowed an improved subsurface image by multi-offset acquisitions near and around the deviated well. Specifically we were able to (1) improve the velocity model of the Geneva Basin, which, at present, is only constrained by one unique deep exploration well, located at the south-west of the basin, far away from the study area; (2) image the transition between the Tertiary Molasse siliciclastic sediments and the Mesozoic carbonates; (3) define an acquisition strategy for future vertical seismic profiling surveys in support of the geothermal exploration campaigns in the area. This study has demonstrated the value of vertical seismic profiling method for the refinement of the subsurface geology at local scale, and its usefulness to assist the planning of second well associated with geothermal doublets.  相似文献   

16.
Accurate estimation of aquifer parameters, especially from crystalline hard rock area, assumes a special significance for management of groundwater resources. The aquifer parameters are usually estimated through pumping tests carried out on water wells. While it may be costly and time consuming for carrying out pumping tests at a number of sites, the application of geophysical methods in combination with hydro-geochemical information proves to be potential and cost effective to estimate aquifer parameters. Here a method to estimate aquifer parameters such as hydraulic conductivity, formation factor, porosity and transmissivity is presented by utilizing electrical conductivity values analysed via hydro-geochemical analysis of existing wells and the respective vertical electrical sounding (VES) points of Sindhudurg district, western Maharashtra, India. Further, prior to interpolating the distribution of aquifer parameters of the study area, variogram modelling was carried out using data driven techniques of kriging, automatic relevance determination based Bayesian neural networks (ARD-BNN) and adaptive neuro-fuzzy neural networks (ANFIS). In total, four variogram model fitting techniques such as spherical, exponential, ARD-BNN and ANFIS were compared. According to the obtained results, the spherical variogram model in interpolating transmissivity, ARD-BNN variogram model in interpolating porosity, exponential variogram model in interpolating aquifer thickness and ANFIS variogram model in interpolating hydraulic conductivity outperformed rest of the variogram models. Accordingly, the accurate aquifer parameters maps of the study area were produced by using the best variogram model. The present results suggest that there are relatively high value of hydraulic conductivity, porosity and transmissivity at Parule, Mogarne, Kudal, and Zarap, which would be useful to characterize the aquifer system over western Maharashtra.  相似文献   

17.
There is a clear correlation between the principal areas of current geothermal development and the seismically active boundaries of the moving segments of lithosphere defined by the plate tectonic models of the Earth. The tectonic position of Egypt in the northeastern corner of African continent suggests that the most important areas for geothermal exploration are in the region where a cluster of hot springs with varied temperatures was located around the Gulf of Suez. Gravity and magnetotelluric surveys were made in the area of Hammam Faraun hot spring, which represents the most promising area for geothermal development in Egypt. These surveys were carried out for the purpose of eliciting the origin of Hammam Faraun hot spring. The results of the analyses and interpretations of these data show that the heat source of the hot spring is due to uplift of hot basement rock. This uplift may cause deep circulation and heating of the undergroundwater.  相似文献   

18.
Structurally bound upwelling and outflowing hot fluids in the city of Wiesbaden suggest an interesting geothermal potential at the northern margin of the permo‐carboniferous Saar–Nahe basin, Germany. The Saar–Nahe basin in the Wiesbaden area was previously not a target for intensive geophysical prospecting of the deep underground. We present an exploration concept to investigate potential geothermal reservoirs near Wiesbaden for heat and power production. The acquired geophysical exploration data give new insights into the local geometry and internal structure of the Saar–Nahe basin. The exploration combines a wide range of methods, including the analysis of data, a dense grid gravity survey, as well as two‐dimensional and three‐dimensional seismic surveys. The resulting data, which for the first time reveal the deep structure of the Mainz and Saar–Nahe basins near Wiesbaden down to a depth of c. 4,000 m, show that the Saar–Nahe basin is strongly segmented and contains deep‐reaching active faults. Combining these information with numerical models of the stresses in the fault system and of the temperature distribution in the exploration area, a promising drilling target has been identified, which promise high permeability at a low risk of induced or triggered seismicity.  相似文献   

19.
The productivity and the water quality of coastal aquifers can be highly heterogeneous in a complex environment. The characterization of these aquifers can be improved by hydrogeological and complementary geophysical surveys. Such an integrated approach is developed in a non-consolidated coastal aquifer in Myanmar (previously named Burma).A preliminary hydrogeological survey is conducted to know better the targeted aquifers. Then, 25 sites are selected to characterize aquifers through borehole drillings and pumping tests implementation. In the same sites, magnetic resonance soundings (MRS) and vertical electrical soundings (VES) are carried out. Geophysical results are compared to hydrogeological data, and geophysical parameters are used to characterize aquifers using conversion equations. Finally, combining the analysis of technical and economical impacts of geophysics, a methodology is proposed to characterize non-consolidated coastal aquifers.Depth and thickness of saturated zone is determined by means of MRS in 68% of the sites (evaluated with 34 soundings). The average accuracy of confined storativity estimated with MRS is ± 6% (evaluated over 7 pumping tests) whereas the average accuracy of transmissivity estimation with MRS is ± 45% (evaluated using 15 pumping tests). To reduce uncertainty in VES interpretation, the aquifer geometry estimated with MRS is used as a fixed parameter in VES inversion. The accuracy of groundwater electrical conductivity evaluation from 15 VES is enough to estimate the risk of water salinity. In addition, the maximum depth of penetration of the MRS depends on the rocks' electrical resistivity and is between 20 and 80 m at the study area.  相似文献   

20.
In order to investigate aquifers, several geophysical surveys have been carried out in the Baril area of the southern flank of Piton de la Fournaise volcano on Reunion in the Indian Ocean using audiomagnetotelluric (AMT), very-low-frequency (VLF) and self-potential (SP) methods. We present the results with emphasis on a comparison between SP data and the findings of geoelectric surveys. AMT soundings have indicated, from the surface downward, three layers: (i) resistive volcanic rocks, (ii) an intermediate resistivity layer, and (iii) a conductive basement attributed to a seawater-bearing aquifer. VLF measurements allow the mapping of the first layer apparent resistivity, and therefore its bottom, when the true resistivity is supposed to be isotropic and homogenous. When this assumption does not hold, only the SP method permits the mapping of this bottom. Because of the good agreement between the SP and electromagnetic results, we propose the SP method as the first tool that should be used in studying shallow hydrogeological structures in volcanic areas.  相似文献   

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