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1.
A geothermal field producing dry steam or high temperature water is a trap for convection currents generated in an aquifer of high permeability and of sufficient thickness by a deep heat source. A basic implication of this concept is, that a geothermal field requires a cap-rock of more or less impermeable rocks above the producing aquifer. In Larderello, Monte Amiata, and Salton Sea geothermal fields, a clearly reconnaissable tight formation overlies the producing zone and limits the upward movements of the convection currents. In other fields,i.e. The Geysers (California), Wairakei and Waiotapu (New Zealand) we do not know a geologically well defined cap-rock formation, presenting a large difference in permeability in comparison with the reservoir formation. The hot water circulating in a hydrothermal system without a cap-rock can produce deposits and rock alteration in proper places along the flow paths. The tracture and pore filling and any other permeability reducing factors increase resistance to the water circulation: those processes can originate an effective cap-rock. By such processes a hydrothermal system can become a self-sealed geothermal field. The silica deposition is probably the main self-sealing process. In fact, 1) silica is very common. 2) it is available with almost no limitation, 3) its deposition is strictly related to temperature changes, and 4) it is likely to produce very effective patterns of deposition. Where an unlimited CO2 supply is available at depth, the calcium carbonate deposition appears to be a noticeable sealing process, which is controlled by pressure, at relatively shallow depth. In other cases CaCO3 precipitation should not be an important factor in the self-sealing of geothermal fields. Argillization appears to be an important shallow process. It is especially effective in the acid environment of many thermal shows, thus determining their migration and/or extinction. According to our analysis and to present evidence those three self-sealing processes are the most important ones. In The Geysers Field, the wells penetrated the same formation, the Franciscan graywackes, from top to bottom. The Franciscan Formation has a very low primary permeability; secondary or fissure permeability is at the contrary very high. It is evident that there is no recognizable cap-rock in the accepted sense of petroleum geology. The wells produce superheated steam; the producing zone begins at 300 m depth or so; the quantity of steam increases with the thickness of the producing zone penetrated by the holes. Beginning in 1964, the wells have been drilled with air as circulating medium. No steam or water has been observed in the top few hundreds meters drilled: we can safely conclude that the graywackes are impervious in the upper section of the holes. Cores and cuttings show frequent fissures filled with silica in different mineral forms and hydrothermally altered rocks are common. In the Geysers area, hot springs, steam vents, carbon dioxide and hydrogen sulphide fumaroles are numerous, and wide zones of rocks, altered by past hydrothermal activity, are prominent features. As usual in many hyperthermal areas, also in The Geysers the manifestations of surface heat change frequently in place, in size, and in fluids discharge. The filling of rock fissures by mineral deposition seems the simplest and most natural explanation of the place changes of the individual springs. The active faults continually generate new fissures, limit the sealing action, and account for the persistent surface thermal activity of the area. The composition of the waters from the hot springs at The Geysers has been re-considered, in comparison with both surface waters and natural steam. The hot springs mainly originate by natural steam condensation, as Allen and Day stated in 1927. This conclusion is now strenghtened and extended: the perched water table producing hot springs at The Geysers is purely condensed steam. Practically all its characteristics can be explained by this condition alone. Separation from other shallow water bodies is extremely sharp. Let us sumarize: the impermeability of the upper section of the holes is demonstrated by the lack of fluids in the Sulphur Bank area, whereas the geochemistry of the hot springs compared with shallow waters indicates that similar conditions occur in the Geysers and Little Geysers areas. Furthermore, silica and other fissure-filling processes occur all over the region, as well as argillization of graywackes. We conclude that:
- a)a cap-rock exists in The Geysers Field; this fact readily explains the production of dry steam; 相似文献
2.
R. W. Rex 《Bulletin of Volcanology》1973,37(3):461-462
The Imperial Valley is a major rift valley characterized by unusually high heat flow and large quantities of water in storage in the thick fill of alluvium provided by the sediments of the delta of the Colorado River. The inventory of hot water appears to be sufliciently large that if used for water desalination it might add several million acreleet of new water to the resources of the lower Colorado River basin. This distilled water would serve to lower river salinity and provide extra water to help meet the U. S. — Mexico treaty commitments. A major fraction of water desalination costs lie in the cost of energy and are related to desalination technology which is directly related to water chemistry. The discovery of low salinity geothermal waters in the Imperial Valley opened th possibility for a major breakthrough in lowered water desalination costs. We have tried to develop a broad understanding of the origins of the waters of the Imperial Valley and how natural recharge occurs. The chemical composition of the waters of the central portion of Imperial Valley basin waters, while not that of present surface flow of the rivers, nevertheless does have a close affinity to Colorado River water. No sea water seems to be present in the valley although marine sediments appear to occur on basement on West Mesa and on basement to the east in Arizona south of Yuma. Low salinity waters dominate the basin hydrology and waters as saline or more saline than sea water appear to be restricted to the immediate area of the Salton Sea. The isotope work of T. Coplen makes it possible to determine the relative contribution of precipitation runoff from California watersheds and from Colorado River water. Both sources are significant. The Colorado River water in aquifers from 100–400 m appears to have been entrapped from a relatively homogeneous basin which was subject to substantial evaporation. Its original source was snow melt water from the Colorado River. Five types of waters, none of them sea water, were recognized by their salt geochemistry. Bromide/chloride data are particularly effective in resolving different types of water masses. The bromide/chloride data agree with the isotope data and identify rainfall and precipitation runoff from the high mountains to the west. Modern Colorado River water is easily recognized by its salts and two types of ancient Colorado River waters from previous lake stage are proposed on the basis of the bromide/chloride data. One old lake occurring during the pluvial stage associated with the last Ice Age is proposed to account for much of the water in artesian aquifers. Another younger lake stage, possibly with Lake Cahuilla affinities is also suggested. Mountain runoff waters can be distinguished in the subsurface by their relatively lower salinity and high bicarbonate concentration, and their heavy isotopic composition. Revised fluid reserve calculations based on additional porosity data continue to show that the low salinity water resources of the Imperial Valley may exceed two billion acre-feet. The oceanic plate tectonic model is modified in the Imperial Valley by the evidence of a series of complex blocks with the generation of both tensional and compressional features in the valley. Major strike slip faults dominate the tectonic fabric but conjugate features increase complexity by a large degree and a major amount of work will be needed before any geologically sound structural models can be generated. Xenoliths within the obsidians at the volcanoes at the south end of the Salton Sea provide samples of the basement under the Imperial Valley. These xenoliths include partially remelted granitic rocks, fragments of basalt, greenschist, and baked shale and sandstone. This is taken as evidence that the basement in the valley consists in part of partially remelted granite. This would render basement plastic and readily deformed. The source of the heat is suggested to be derived from basalt that comes into the basement and deeper sediments from below. This upward movement of basalt along a spreading zone is the continental equivalent to a sea floor spreading area. In the continental case the insulating blanket of wet sediment retains the heat and appears to produce a major geothermal resource. The geothermal resources of the Imperial Valley are the aggregate of the thermal energy of the large inventory of subsurface water heated by the complex mix of intrusive phenomena. The net result is to generate a polygenetic geothermal resource of very large dimensions. 相似文献
3.
Natural hot spring waters ascending rapidly to the surface become supersaturated with respect to quartz because of rapid cooling, separation of steam and sluggish deposition of quartz and other crystallineSiO 2 phases. Large amounts of silica are likely to be deposited in hot spring systems only after the solubility of amorphous silica has been exceeded. Cristobalite and chaleedony probably form in hot spring systems only by the crystallization of previously deposited silica gel rather than by direct deposition from solution. Experimental data indicate that the solubilit of quartz in water rises with increasing temperature along the vapor pressure curve to a maximum value of 725 ppm at 330°C. However, the maximum amount of silica likely, to occur in hot spring systems where quartz precipitates at depth is appreciably greater. Steam formation during adiabatic cooling of a water quickly brought to the surface from 330°C at depth might leave the silica in the remaining liquid concentrated to about 1150 to 1400 ppm. Under such conditions, amorphous silica might precipitate (probably as a colloidal suspension) after the water cooled below about 200°C to 250°C. Waters initially in equilibrium with quartz at a temperature less than 210°C probably will precipitate amorphous silica in channelways underground only when and where large quantities of steam separate from the waters as a result of sudden decreases in pressure or hydrostatic head. Above 150° to 200°C amorphous silica and volcanic glass can contribute very large quantities of silica to the solution. However, at these temperatures in natural systems they are eventually converted to crystalline phases. Thus, control of dissolved silica at depth is likely to be relatively short lived in respect to the ages of most hot spring systems. The dissolved-silica content of 90 hot spring waters from Yellowstone National Park was measured colorimetrically in the field immediately after collection. Comparison with laboratory studies on the solubility of amorphous silica indicates that many waters in «alkaline» springs are markedly undersaturated with silica with respect to amorphous silica at the temperatures of the pools. Thus, the dissolved silica content of these waters cannot be accounted for by equilibria with amorphous silica. Rather, silica appears to be controlled by the dissolution, deposition, or alteration of other silica-bearing phases at depth. Furthermore, many springs now have compositions essentially identical (with respect to all components) to those determined in 1888, indicating that either equilibrium or steady state conditions have prevailed at depth for a long time. Veins of fine-grained quartz were found in drill core from the Upper Basin, and it is reasonable to assume that quartz controlled the quantity of silica in solution in those places of deposition. Possibly the silica content of the surface waters might allow an estimate of the temperatures at which these waters were last in equilibrium with quartz at depth. Assuming adiabatic cooling along the vapor pressure curve and correcting for steam formation, quartz solubility data compared with natural water analyses suggests that underground temperatures approach 205°C in the Upper Geyser Basin of Yellowstone. In the Norris Geyser Basin, underground temperatures of 245°C are suggested. 相似文献
4.
5.
G. Heiken B. Crowe T. McGetchin F. West J. Eichelberger D. Bartram R. Peterson K. Wohletz 《Bulletin of Volcanology》1980,43(2):383-395
From August to October, 1976, La Soufrière de Guadeloupe was observed, and recorded with an automated sequence camera and numerous handheld cameras. During the period of observation, the nature of volcanic activity ranged from mild steam emission to moderately energetic phreatic eruptions. Background fumarolic activity (steam emission) was characterized by the emission of generally tephra-free steam clouds 50 to 150 m above the summit. The clouds rose buoyantly above the vent and were blown downwind at prevailing wind velocities. Phreatic eruptions were well-documented on September 22, October 2, and October 4. In the latter two eruptions, small bursts of tephra-laden steam erupted at intervals of 30 to 45 min, and rose from 350 to 500 m above the summit. In the largest observed eruption, that of October 2, the steam and tephra cloud rose to a maximum height of 600 to 650 m in 20 min. A white vapor cloud and a medium gray, tephra-laden cloud were erupted simultaneously from the summit vent and both were surrounded by a vapor collar: the clouds were thoroughly mixed within 1 km downwind of the summit. The concurrent growth of clouds from separate vents (summit and flank) implies a common source. Simultaneous eruption of tephra-free and tephra-laden clouds from the same vent is puzzling and implies: (i) lateral changes in the degree of alteration of dome rocks along the elongate vent, hence erodability of the dome lavas, or (ii) differences in the gas velocities. These «mixed» clouds moved westward, downwind and downslope as a density current, along the watersheds of the R. Noire and R. des Pères with an approximate velocity of 10 to 25 m/sec. Upon reaching the sea the clouds continued to move forward, but at a decreased velocity, and spread laterally, having left behind the restrictions of valley walls. A thin gray veneer of moist tephra, ranging from several cm thick near the dome to less than 1 mm thick several km downwind, was deposited along a narrow corridor southwest of the summit. Tephra from the phreatic eruptions consisted mostly of hydrothermally altered lithic, mineral, and glass fragments derived from dome lavas; no fresh (juvenile) pyroclasts were present in the tephra. Absence of juvenile tephra at La Soufrière supports the view that activity was due to groundwater circulating in a vapor-dominated geothermal system, probably driven by a shallow heat source. At La Soufrière, most vapor-dominated systems are located in elevated areas of groundwater recharge where groundwater movement is downward and outward. The sporadic phreatic eruptions may be related to the rate of recharge of meteoric waters within the dome, the decrease in pore pressure during fortnightly tidal minimums or both. Whatever the triggering mechanism, vapor-dominated fluids eroded vent walls during phreatic eruptions and carried out fine-grained, hydrothermally altered, pre-existing dome material as tephra. 相似文献
6.
J. Rogers 《Bulletin of Volcanology》1966,29(1):173-175
The temperatures at which melting begins of three New Zealand greywackes and two argillites were determined as a function of water pressure up to 3000 atmospheres. The purpose of these experiments was to provide data possibly relevant to the genesis of the North Island ignimbrites and for comparison with the experiments ofBowen andTuttle (1958) on the melting temperatures of granites and the ternary minimum system (NaAlSi3O8 — KAlSi3O8 — SiO2 — H2O). Powdered samples of the rocks were heated in unsealed silver tubes in cold seal bombs, the water pressure being measured on a Bourdon gauge and applied during heating. Temperature control was ± 5°C. Twelve days was the longest heating period, most being for 24 hours, which was sufficient for apparent reaction. At the end of an experiment, the pressure was released, and the sample quickly cooled by removal from the bomb. The samples were crushed and examined by X-ray diffraction and the petrographic microscope. The PT curve for the beginning of melting of the greywackes and argillites is very close toBowen andTuttle’s for granites and the ternary minimum to 1000 atmospheres water pressure. Above this pressure the greywackes melt at slightly higher temperatures than on the granite curve with the argillites a little higher still. These observations are similar to those reported for shales byWyllie andTuttle 1960, 1961, for greywackes byWinkler andvon Platen 1961, and pelitic sediments byWyart andSabatier, 1959. The amount of anatectic melt increases rapidly above the temperature of initial melting and is inversely related to the quartz present in the greywackes. The partially melted products were often notably vesicular. Cordierite, mullite, hypersthene, scapolite and mica were identified in the X-ray diffractograms as coexisting with the melt. These experiments are in agreement with published work in showing that the quartz and alkali feldspars of granites, shales and arkosic sediments can in the presence of water react and begin to melt at 20–25 kilometres depth in the earth assuming a geothermal gradient of 30°C/km. The melt is granitic or granodioritic in composition. 相似文献
7.
Geothermal data analysis at the high-temperature hydrothermal area in Western Sichuan 总被引：2，自引：0，他引：2
Jian Zhang WuYang Li XianChun Tang Jiao Tian YingChun Wang Qi Guo ZhongHe Pang 《中国科学:地球科学(英文版)》2017,60(8):1507-1521
The western Sichuan hydrothermal area is located at the northeastern margin of the eastern syntaxis of the Qinghai-Tibet Plateau, which is also the eastern end of the Mediterranean-Himalayan geothermal activity zone. There are 248 warm or hot springs in this area, and 11 have temperatures beyond the local boiling temperature. Most of these hot springs are distributed along the Jinshajiang, Dege-Xiangcheng, Ganzi-Litang, and Xianshuihe faults, forming a NW-SE hydrothermal belt. A geothermal analysis of this high-temperature hydrothermal area is an important basis for understanding the deep geodynamic process of the eastern syntaxis of the Qinghai-Tibet Plateau. In addition, this study offers an a priori view to utilize geothermal resources, which is important in both scientific research and application. We use gravity, magnetic, seismic, and helium isotope data to analyze the crust-mantle heat flow ratio and deep geothermal structure. The results show that the background terrestrial heat flow descends from southwest to northeast. The crustal heat ratio is not more than 60%. The high temperature hydrothermal active is related to crustal dynamics processes. Along the Batang-Litang-Kangding line, the Moho depth increases eastward, which is consistent with the changing Qc/Qm(crustal/mantle heat flow) ratio trend. The geoid in the hydrothermal zone is 4–6 km higher than the surroundings, forming a local "platform". The NW-SE striking local tensile stress zone and uplift structure in the upper and middle crust corresponds with the surface hydrothermal active zone. There is an average Curie Point Depth(CPD) of 19.5–22.5 km in Batang, Litang, and Kangding. The local shear-wave(S-wave) velocity is relatively low in the middle and lower crust. The S-wave shows a low velocity trap(Vs3.2 km s.1) at 15–30 km, which is considered a high-temperature partial melting magma, the crustal source of the hydrothermal active zone. We conclude that the hydrothermal system in this area can be divided into Batang-type and Kangding-type, both of which rely on a crustal heating cycle of atmospheric precipitation and surface water along the fracture zone. The heat is derived from the middle and lower crust: groundwater penetrates the deep faults bringing geothermal energy back to the surface and forming high-temperature springs. 相似文献
8.
F. Barberi H. Bizouard R. Clocchiatti N. Metrich R. Santacroce A. Sbrana 《Bulletin of Volcanology》1981,44(3):295-315
The volcanic history of Somma-Vesuvius indicates that salic products compatible with an origin by fractionation within a shallow magma chamber have been repeatedly erupted («Plinian» pumice deposits). The last two of these eruptions, (79 A.D. and 3500 B.P.) were carefully studied. Interaction with calcareous country rocks had limited importance, and all data indicate that differentiated magmas were produced by crystal-liquid fractionation within the undersaturated part of petrogeny’s residua system at about 1 kb water pressure. The solid-liquid trend indicates that the derivative magmas originated by fractionation of slightly but significantly different parental liquids. Some lavas of appropriate composition were selected as parental liquids to compute the entity of the fractionation. Results suggest that in both bases a fractionation of about 70 weight % was needed to produce liquids with the composition of the pumice. The combination of all data indicates that the two Plinian eruptions were fed by a magma chamber (3–4 km deep) having a volume of approx. 2.0–2.5 km3. The temperature of the magma that initially entered the chamber was about 1100°C, whereas the temperature of the residual liquids erupted was Plinian pumice was 800° and 850°C respectively. There is no evidence that such a magma chamber existed at Vesuvius after the 79 A.D. eruption. These results have relevant practical implications for volcanic hazard and monitoring and for geothermal energy. 相似文献
9.
Application of the silica geothermometer to over 70,000 non-thermal groundwaters from the United States has shown that there is a correlation between the average silica geotemperatures for a region (T SiO2 in °C) and the known regional heat flow (q in mW m?2) of the form: 1 $$TSiO_2 = mq + b$$ wherem andb are constants determined to be 0.67°C m2 mW?1 and 13.2°C respectively. The physical significance of ‘b’ is the mean annual air temperature. The slope ‘m’ is related to the minimum average depth to which the groundwaters may circulate. This minimum depth is estimated to be between 1.4 and 2.0 km depending on the rock type. A preliminary heat flow map based on equation (1) is presented using theT SiO2 for new estimates of regional heat flow where conventional data are lacking. Anomalously high localT SiO2 values indicate potential geothermal areas. 相似文献
10.
The volcanic centre of Monte Seda Oro, N. W. Sardinia, representative of a Cenozoic calc-alkaline andesitic suite of rocks is composed of a variety of rocks ranging from high alumina basalts to dacites. The minerals of basaltic, andesitic and dacitic rocks show only limited variation in chemical composition. The geochemical data suggest that the various rock-types are related by a crystal-liquid fractionation. Least-squate numerical calculations, using major element data, support the derivation of andesites with SiO3 content ranging from 53.8 to 59.0% from basalts having about 48.7% of SiO2 by low pressure crystal fractionation of the phenocryst phases present in these rocks. However, the origin of dacites cannot be readily explained by this mechanism. 相似文献
11.
The Soufrière volcano in Guadeloupe island delivered a phreatic eruption that commenced on July 8th, 1976 and lasted until March 1st, 1977. This eruption was similar to the 1797, 1798, 1809 and 1956 outbreaks. Phreatic activity ejected blocks derived from the fissure walls and fine pyroclasts produced by hydrothermal alteration of the old dome’s rocks. Field observations and measurements allowed the present authors to calculate the mass and energy transfer of steam and ashes: 107 tons of water (very low considering that on the mountain summit the annual precipitation is 10 tons m)2,106 m3 of ashes. The most important energy transfers was thermal: about 5 × 1020 ergs for each phreatic eruption. The total kinetic energy output was 2 × 1019 ergs for a total thermal energy output of 64 × 1020 ergs. The gases and fine pyroclasts did pollute the atmosphere, waters and soils and consequently affected the population living on the slopes of the volcano. 相似文献
12.
V. Gottini 《Bulletin of Volcanology》1970,34(2):406-413
The chemical variability of the products of contact-anatexis, completely different from the normal trend of magmatic differentiation, may be explained by the quantitative variation of gaseous transfer, according to the state of the basaltic magma which may be pyromagma or hypomagma at the contact with the surrounding sialic rocks. Therefore, two types of contact-anatexis must be distinguished: 1st.Anatexis at the contact with pyromagma. If the tectonical conditions are favourable, then the basaltic magma rises so high in the sialic crust that the gas tension overcomes the hydrostatic pressure. A gas phase will separate and cause a considerable gas transfer by which pneumatophilic substances (Na, Fe, Ti etc.) are supplied to the overlying anatectic magma. 2nd.Anatexis at the contact with hypomagma. If the rising basaltic magma cannot reach very high levels in the sialic crust, then the gas tension remains lower than the hydrostatic pressure, and the gases are molecularly dispersed within the melt. The gas transfer will be insignificant, and the anatexis is merely due to the supply of heat without any appreciable change of the chemical composition of the anatectic magma. 相似文献
13.
Grant Heiken Napoleon Ramos Wendell Duffield John Musgrave Kenneth Wohletz Sue Priest James Aldrich Wilmer Flores Alexander Ritchie Fraser Goff Dean Eppler Carlos Escobar 《Journal of Volcanology and Geothermal Research》1991,45(1-2)
The Platanares geothermal area, Departamento de Copán, Honduras, is located within a graben that is complexly faulted. The graben is bounded on the north by a highland composed of Paleozoic (?) metamorphic rocks in contact with Cretaceous - Tertiary redbeds of unknown thickness. These are unconformably overlain by Tertiary andesitic lavas, rhyolitic ignimbrites, and associated sedimentary rocks. The volcanic rocks are mostly older than 14 Ma, and thus are too old to represent the surface expression of an active crustal magma body. Thermal fluids that discharge in the area are heated during deep circulation of meteoric water along faults in a region of somewhat elevated heat flow. Geothermometry based upon the chemical composition of thermal fluids from hot springs and from geothermal gradient coreholes suggests that the reservoir equilibrated at temperatures as high as 225 to 240°C, within the Cretaceous redbed sequence. Three continuously cored geothermal gradient holes have been drilled; fluids of about 165°C have been produced from two drilled along a NW-trending fault zone, from depths of 250 to 680 m. A conductive thermal gradient of 139°C/km, at a depth of 400 m, was determined from the third well, drilled 0.6 km west of that fault zone. These data indicate that the Platanares geothermal area holds considerable promise for electrical generation by moderate- to hightemperature geothermal fluids. 相似文献
14.
Fraser Goff Jamie Gardner Rosemary Vidale Robert Charles 《Journal of Volcanology and Geothermal Research》1985,23(3-4)
Detailed geochemistry supported by geologic mapping has been used to investigate Sulphur Springs, an acid-sulfate hot spring system that issues from the western flank of the resurgent dome inside Valles Caldera. The most intense activity occurs at the intersection of faults offsetting caldera-fill deposits and post-caldera rhyolites. Three geothermal wells in the area have encountered pressures <1 MPa and temperatures of 200°C at depths of 600 to 1000 m. Hot spring and fumarole fluids may discharge at boiling temperatures with pH 1.0 and SO4 8000 mg/l. These conditions cause argillic alterations throughout a large area.Non-condensible gases consist of roughly 99% CO2 with minor amounts of H2S, H2, and CH4. Empirical gas geothermometry suggests a deep reservoir temperature of 215 to 280°C. Comparison of 13C and 18O between CaCO3 from well cuttings and CO2 from fumarole steam indicates a fractionation temperature between 200 and 300°C by decarbonation of hydrothermally altered Paleozoic limestone and vein calcite in the reservoir rocks. Tritium concentrations obtained from steam condensed in a mudpot and deep reservoir fluids (Baca #13, 278°C) are 2.1 and 1.0 T.U. respectively, suggesting the steam originates from a reservoir whose water is mostly >50 yrs old. Deuterium contents of fumarole steam, deep reservoir fluid, and local meteoric water are practically identical even though 18O contents range through 4‰, thus, precipitation on the resurgent dome of the caldera could recharge the hydrothermal system by slow percolation. From analysis of D and 18O values between fumarol steam and deep reservoir fluid, steam reaches the surface either (1) by vaporizing relatively shallow groundwater at 200°C or (2) by means of a two-stage boiling process through an intermediate level reservoir at roughly 200°C.Although many characteristics of known vapor-dominated geothermal systems are found at Sulphur Springs, fundamental differences exist in temperature and pressure of our postulated vapor-zone. We propose that the reservoir beneath Sulphur Springs is too small or too poorly confined to sustain a “true” vapor-dominated system and that the Sulphur Springs system may be a “dying” vapor-dominated system that has practically boiled itself dry. 相似文献
15.
A geochemical study of thermal and cold springs, stream waters and gas emissions has been carried out in the Mt. Amiata geothermal region.The cold springs and stream waters do not seem to have received significant contribution from hot deep fluids. On the contrary, the thermal springs present complex and not clearly quantifiable interactions with the hot fluids of the main geothermal reservoir.The liquid-dominated systems in the Mt. Amiata area, like most of the high-enthalpy geothermal fields in the world, are characterized by saline, NaCl fluids. The nature of the reservoir rock (carbonatic and anhydritic), and its widespread occurrence in central Italy, favor a regional circulation of “Ca-sulfate” thermal waters, which discharge from its outcrop areas. Waters of this kind, which have been considered recharge waters of the known geothermal fields, dilute, disperse and react with the deep geothermal fluids in the Mt. Amiata area, preventing the use of the main chemical geothermometers for prospecting purposes. The temperatures obtained from the chemical geothermometers vary widely and are generally cooler than temperatures measured in producing wells.Other thermal anomalies in central Italy, apart from those already known, might be masked by the above-mentioned circulation. A better knowledge of deep-fluid chemistry could contribute to the calibration of specific geothermometers for waters from reservoirs in carbonatic rocks. 相似文献
16.
Temperature inversions at shallow to moderate depths have been observed commonly in boreholes drilled in geothermal areas. The inversions result from thermal disequilibria generated by steam and/or hydrothermal fluids invading shallow horizontal, or sub-horizontal fractures, or permeable horizons, from a deep vertical, or sub-vertical feeder-fracture.Subsurface distribution of temperatures in Momotombo geothermal area of Nicaragua, Central America, indicates that the anomaly is generated by steam and water, convecting in a narrow feeder-fracture-zone located at the western edge of the field. The north-trending zone of the feeder-fracture is bound on the west by the area of massive, impermeable andesitic rocks, and is capped by an impermeable, approximately 300 m. thick silica-cap, which seals if from the ground surface. The thermal fluids penetrate a system of horizontal, or sub-horizontal fractures, extending east of the feeder-fracture beneath the silica cap. The flow of thermal fluids eastward through the system of the horizontal, or sub-horizontal fractures is generating a plume-like geothermal anomaly, which is expressed by the temperature inversion zone pervasive in the boreholes to the east of the feeder-fracture.A time-dependant model for a semi-infinite half-space (z > 0) in contact with a hot, well stirred, isotropic fluid flowing through an aquifer overlain by a finite space of constant thickness is solved for the data collected from the Momotombo geothermal boreholes. Curve fitting between the simulated and observed temperature/depth profiles suggests that the thermo-tectonic events which caused the present-day Momotombo hydrothermal system occurred approximately 5,500 years ago, following development of vertical, or subvertical fractures along a N5°E trending faultline. Hot fluids emerging from these fractures move eastward through a system of horizontal, or sub-horizontal fractures, with a velocity of 11 to 20 m/yr. 相似文献
17.
Runrun Zhang Xi Chen Qinbo Cheng Zhicai Zhang Peng Shi 《Stochastic Environmental Research and Risk Assessment (SERRA)》2016,30(6):1641-1657
Reservoir storage plays an important role in water supply during the dry season when precipitation is insufficient. In a watershed where the streams are controlled by reservoirs, drought occurrences depend on not only precipitation variations but also reservoir regulation. In this study, the joint dependence structure of the reservoir storage and its relevant variables of precipitation and/or upstream outflow were analyzed for two cascade reservoirs in a headwater basin of the Huaihe River, China. Correlation analysis indicates that the reservoir storage in October (the end of the wet season) depends highly on the regional precipitation at time scales of several months, e.g., 7 months for the upstream and 9 months for the downstream. Additionally, the downstream storage is correlated with outflow from the upstream reservoir at the 5-month timescale significantly. For estimation of the joint probability of pairs of the storage and its relevant variables, univariate marginal distributions and bivariate copula were appropriately selected in terms of statistical tests. The bivariate return period of \(T(X < x,Y < y)\) and \(T(X \le x,Y \ge y)\) and the conditional probability of \(P(Y \ge y|X \le x)\) were estimated by using the selected Clayton copula. The results from contour lines of the bivariate return period demonstrate that the probability of drought occurrences affected by both reservoir storage and precipitation/outflow is smaller than that by either of the variables. Meanwhile, the concurrent drought probability between precipitation and reservoir storage in the upstream is higher than that in the downstream. The estimated conditional probability offers useful information on how much the regular storage could be remained under some specified drought levels of precipitation/upstream outflow. Therefore, the results are helpful for improving the operation strategies of the cascade reservoirs for the adaptive management of drought under different climate variations. 相似文献
18.
Depressurisation of the Tauhara field due to massive withdrawal of deep chloride water from the adjacent Wairakei field for geothermal power has caused considerably hydrological and chemical changes at Tauhara. In the undisturbed state (1962), deep chloride water discharged as hot and boiling dilute chloride springs on the east and west flanks of the field (the Terrace and Spa areas, respectively), while steam from the two-phase zone of the deep system produced by absorption into near-surface groundwater, steam-heated sulphatebicarbonate waters and by mixing with chloride water, chloride-sulphate waters. By 1978–1981 the chloride waters had stopped discharging on the western flank, the steam flow towards the surface had greatly increased (by 5–10 fold) increasing the volume and temperature of the steam-heated waters, but the dilute chloride waters of the Terrace area had changed very little. Silica concentrations in the near-surface waters appear to be controlled by the solubility of amorphous silica, which is present in the surface zone rocks (e.g., Taupo pumice breccias). The increased steam flow led to enrichment in the 13O and D contents of the steam-heated waters by loss of secondary steam and enlargement of the area and intensity of steaming ground, the latter accompanied by hydrothermal eruptions in 1974 and 1981. Generation of the steam-heated waters has been modelled using mass, heat and isotope balances. The model is consistent with observed heat and cold groundwater flows and requires that a large proportion of the heat from adsorbed primary steam is released as secondary steam. Tritium contents show that the steam-heated waters have a mean residence time of 50–100 years. In the future, invasion of the deep system by cooler surface waters may reduce steam flow and lower surface aquifer temperatures. 相似文献
19.
Electrical resistivity tomography study of Taal volcano hydrothermal system, Philippines 总被引：1，自引：0，他引：1
I. Fikos G. Vargemezis J. Zlotnicki J. R. Puertollano P. B. Alanis R. C. Pigtain E. U. Villacorte G. A. Malipot Y. Sasai 《Bulletin of Volcanology》2012,74(8):1821-1831
Taal volcano (311?m in altitude) is located in The Philippines (14°N, 121°E) and since 1572 has erupted 33 times, causing more than 2,000 casualties during the most violent eruptions. In March 2010, the shallow structures in areas where present-day surface activity takes place were investigated by DC resistivity surveys. Electrical resistivity tomography (ERT) lines were performed above the two identified hydrothermal areas located on the northern flank of the volcano and in the Main Crater, respectively. Due to rough topography, deep valleys, and dense vegetation, most measurements were collected using a remote method based on a laboratory-made equipment. This allowed retrieval of information down to a depth of 250?m. ERTs results detail the outlines of the two geothermal fields defined by previous self-potential, CO2 soil degassing, ground temperature, and magnetic mapping (Harada et al. Japan Acad Sci 81:261–266, 2005; Zlotnicki et al. Bull Volcanol 71:29–49, 2009a, Phys Chem Earth 34:294–408, 2009b). Hydrothermal fluids originate mainly from inside the northern part of the Main Crater at a depth greater than the bottom of the Crater Lake, and flow upward to the ground surface. Furthermore, water from the Main Crater Lake infiltrates inside the surrounding geological formations. The hydrothermal fluids, outlined by gas releases and high temperatures, cross the crater rim and interact with the northern geothermal field located outside the Main Crater. 相似文献
20.
Geochemical studies on cold meteoric waters, post-1980 hot spring waters, fumarole emissions from the dacite dome, and volcanic rocks at Mount St. Helens (MSH) from 1985 to 1989 show that magmatic volatiles are involved in the formation of a new hydrothermal system. Hot spring waters are enriched in 18O by as much as 2 and display enrichments in D relative to cold waters. A well-defined isotopic trend is displayed by the isotopic composition of a>400°C fumarole condensate collected from the central crater in 1980 (-33 D, +6 18O), of condensate samples collected on the dome, and of cold meteoric and hot spring waters. The trend indicates that mixing occurs between local meteoric water and magmatic water degassing from the dacite dome. Between 30 and 70% magmatic water is present in the dome fumarole discharges and 10% magnatic water has been added to the waters of the hydrothermal system. Relations between Cl, SO4 and HCO3 indicate that the hot spring waters are immature volcanic waters formed by reaction of rocks with waters generated by absorption of acidic volcanic fluids. In addition, the B/Cl ratios of the spring waters are similar to the B/Cl ratios of the fumarole condensates (0.02), values of 13C in the HCO3 of the hot springs (-9.5 to-13.5) are similar to the magmatic value at MSH (-10.5), and the 3He/4He ratio, relative to air, in a hot spring water is 5.7, suggesting a magmatic origin for this component.managed by Martin Marietta Energy Systems, Inc., under contract DE-AC05-84OR21400 with the US Department of Energy 相似文献