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1.
A model to explain the behaviour of the Sulphur Springs geothermal field has been derived from downhole temperature records in the exploration boreholes. The model incorporates a main reservoir at 1 – 1.5 km depth, intersected by steeply inclined fissures which carry steam and gas to the well bores, and to the natural fumaroles. A substantial decline in the gas content of the steam could have serious consequences where the fissures are utilised as conduits between the boreholes and the deep reservoir. Further development of the field should concentrate on the fissures around 300 m or on the reservoir itself around 1000 – 1500 m.  相似文献   

2.
On the basis of a geological - volcanological - geophysical survey, integrated with petrological and geochronological data, a structural model, including a shallow magmatic body, was defined for the Ribeira Grande area, Sao Miguel island (Azores). Two series of production tests were carried out in the Pico Vermelho 1 and Ribeira Grande 1 wells, which led to a preliminary definition of the deep fluid circulation. The data obtained from these studies were used to reconstruct a preliminary model of the Ribeira Grande geothermal field.  相似文献   

3.
Based on geological and geothermal knowledge of the Travale geothermal field, a mathematical model is proposed for the heat transfer from the top of the reservoir to the soil surface.Consistency between observed and calculated temperatures demonstrates that the heat is transferred by conduction and that the established temperature field depends essentially on the temperature at the top of the reservoir and its slope.  相似文献   

4.
The distribution of the Na-K-Ca index values in the geothermal aquifer of Cerro Prieto indicates a probable cold-water recharge in the northern and western parts of the present producing field. In the central part of the field, the distribution of Na-K-Ca values is very irregular, due to the effect of percolation or the vertical descending flow of colder waters caused by apparent over-exploitation.The large area with indices varying between 0·5 and 0·7 to the east, southeast, and south of the field confirm the presence of hotter geothermal waters than those observed in the present producing field. The limits of this hot aquifer have not yet been determined toward the east and southeast.The temperature distribution in the Cerro Prieto aquifer confirms the conclusions reached using the Na-K-Ca index. The maximum temperature calculated was in well M-53 (350°C) and the minimum was in M-9 (250°C), when wells M-6 and M-1A, which have lower temperatures, are not taken into account.The chloride distribution in the aquifer confirms the recharge of colder, less saline waters in the northern and western parts of the field. It was surprising to find that the chloride content in the aquifer was lower in the eastern part (M-53) than in the present field, even though the temperature is higher. Another interesting fact is the extremely low chloride content found in well M-101, with temperatures around 290°C.The distribution of potassium and silica in the aquifer was not as useful for the interpretation of fluid movement as originally expected. Discrepancies were found with respect to the interpretations based on the Na - K - Ca index and the chloride content.In regard to the changes in the Na - K - Ca index, in temperature, and in chloride content during the exploitation of the field, a gradual increase in Na - K - Ca index values was observed in wells with high and low enthalpy. In exceptional cases these values decrease or remain constant. This increase in the index has represented a 10 to 20°C temperature decrease with respect to the original values existing at the beginning of the exploitation of the field (1973). The chloride content in the aquifer has decreased at different rates, from 670 mg/l per year in M-26 to 371 mg/1 per year in well M-42, even though in some wells (M-20) it has increased and in others (M-5) it has remained almost constant.In order to decrease the rate of temperature and pressure reduction in the present producing field, it is recommended that production of low enthalpy wells be suspended and be replaced by new wells located in the periphery of the field, preferably to the southwest and northeast. Thus, the production area would at least be doubled, in an attempt to avoid the percolation or vertical flow, which is apparently causing the cooling of the reservoir.Another measure, which could help prevent a rapid drawdown, is to exploit the deeper hot aquifers that apparently exist in the center of the field. This would first have to be confirmed by an exploratory well or by deepening one of the present wells.  相似文献   

5.
6.
Preliminary isotopic studies of Cerro Prieto geothermal fluids and earlier studies of Mexicali Valley ground waters suggest local recharge of the geothermal system from the area immediately to the west. Oxygen isotope exchange of water with reservoir rock minerals at temperatures increasing with depth has produced fluids with oxygen-18 contents increasing with depth, and pressure drawdown in the southeastern part of the field has allowed lower oxygen-18 fluids to invade the production aquifer from above. The contents of tritium and carbon-14 in the fluid suggest only that the age of the fluid is between 50 and 10,000 years. The isotopic compositions of carbon and sulfur are consistent with a magmatic origin of these elements but a mixed sedimentary-organic origin appears more likely for carbon and is also possible for sulfur. Investigations of the isotopic compositions of geothermal and cold ground waters continue and are being expanded as fluids become available and as separation and analysis methods are improved.  相似文献   

7.
In October 1981 the AAMT method was tested in the geothermal field of Travale. This method is based on the MT method, but uses artificial EM fields excited by a transmitter some kilometres from the receiving station. The transmitter consists of a switch mode amplifier for the lower frequency band (< 300 Hz) and six stacked linear amplifiers for the high frequency band. Maximum output is about 5 kW. For measurement of the very small EM field at the receiver the correlation technique is used to obtain best noise rejection. Interpretation of measured data is done by model calculations with the help of a near field theory. Cagniard's theory is found to be applicable only for high frequencies (i.e. short periods). The final result is a three-layer model in good agreement with known geology and resistivity models from other authors.  相似文献   

8.
Crack extension caused by a shut-down operation in production wells (build-up test) in Takinoue (Kakkonda) geothermal power plant, Iwate Prefecture, Japan, has been successfully measured by an acceleration-sensitive long-distance acoustic emission measurement technique. The distribution and activity of subsurface cracks in a geothermal reservoir can be determined by the combined procedure of the pressure build-up test and AE measurements. The feasibility and importance of the measurements are demonstrated by AE data and their interpretation.  相似文献   

9.
Wells in the Dixie Valley geothermal field of central Nevada intercept a fracture-dominated hydrothermal system at depths of 2.5 to 3 km. The reservoir water is a dilute sodium-bicarbonate-chloride type solution thought to be in equilibrium with quartz, calcite, chlorite, and albite. Fluid sampling and chemical analysis of production during an early flow test gave remarkably low calcium concentrations. Thermodynamic calculations of mineral stability in the presence of the reservoir water indicate that five times the amount of calcium measured in fluid reaching the surface is actually in solution in the reservoir fluid. Approximately 80 percent of the calcium is lost as calcium carbonate scale on the well casing before the fluid reaches the surface. The results of thermodynamic calculations compare well with the scale-volume measurements of Benoit (1989).  相似文献   

10.
A fluid inclusion study of the hydrothermal minerals in two breccias from two wells in the Bagnore geothermal field (Italy) has provided information on the evolution of the fluids, and has also demonstrated that fluid inclusions can be utilized as geothermometers in this geothermal field. Both breccias come from reservoir zones: one (Bagnore 3bis (Bg 3bis)) was cored at a depth of 3111 m below ground level (b.g.l.), whereas the other (Bagnore 22 (Bg 22)) was ejected during a blow-out, probably from a fractured zone present between 2200 and 2300 m b.g.l. The hydrothermal cement of the breccias is mostly made up of quartz, K-feldspar, Na-rich plagioclase, calcite, chlorite and illite. Fluid inclusion studies were carried out on quartz (Bg 3bis and Bg 22 breccias) and adularia (Bg 22 breccia). Three types of fluid inclusions were recognized in the Bg 3bis breccia. Type I (liquid-rich) inclusions trapped an aqueous fluid with a CO2 concentration (1.7–2.7 mol/kg) that is significantly higher than present-day fluids (0.5 mol/kg). Type II (liquid-rich) inclusions formed after type I, and trapped a fluid with less CO2 (0.6–1.0 mol/kg). Type III (vapor-rich) coexist with type I inclusions, and record an early fluid circulation under boiling conditions. The decrease of the CO2 (and total gas) concentrations from type I inclusions to type II inclusions, and on to present-day conditions can be related to boiling with gas loss and/or mixing. Only one type of fluid inclusion (type II), with moderate CO2 concentration (0.7–0.3 mol/kg), was found in the Bg 22 breccia. Boiling and/or mixing explain the variation of the CO2 content in the Bg 22 reservoir fluid from inclusion formation to modern CO2 concentration (0.3 mol/kg). The absence of any type I inclusions in Bg 22 breccia may be related to non-uniform CO2 concentrations in different parts of the field. Present-day temperatures (295±10 °C for Bg 3bis and 320±10 °C for Bg 22) are close or equal to fluid inclusion average total homogenization temperatures (around 290 °C for Bg 3bis and 320 °C for Bg 22), suggesting that fluid inclusions can be useful for estimating local temperatures when direct measurements are not available or dubious.  相似文献   

11.
The Yanaizu-Nishiyama geothermal field, also known as Okuaizu, supports a 65 MWe geothermal power station. It is located in the western part of Fukushima Prefecture, northeast Japan. This field is characterised by rhyolitic volcanism of about 0.3–0.2 Ma that formed Sunagohara volcano. Drillcore geology indicates that volcanism began with a caldera-forming eruption in the center of this field, creating a 2-km-diameter funnel-shaped caldera. Subsequently, a fault-bounded block including this caldera subsided to form a 5-km-wide lake that accumulated lake sediments. Post-caldera volcanism formed lava domes and intrusions within the lake, and deposited ash-flow tuffs in and around the lake. The hydrothermal system of this field is strongly controlled by subvertical faults that have no relation to the volcanism. The principal production zone occurs at a depth of 1.0–2.6 km within fractured Neogene formations along two northwest-trending faults to the southeast of the caldera. These faults also formed fracture zones in the lake sediments, but there was no apparent offset of the sediments. Stratigraphic studies suggest that post-caldera activities of Sunagohara volcano have migrated southeastward to the present high-temperature zone. The source magma of Sunagohara volcano may contribute to the thermal potential of this field.  相似文献   

12.
The Hatchobaru power plant Unit No. 1 (55 MW) has been operating since 1977 and Unit No. 2 (55 MW) since 1990. The mean capacity factor of the power plant has reached about 90%. Considering that the long-term operation of the plant, over 30 years for Unit No. 1 and nearly 20 years for Unit No. 2, has been maintained with such a high capacity factor, sustainable development in terms of economic production has been achieved. To maintain a stable operation, systematic reservoir monitoring and reservoir simulation studies have been conducted. The monitoring of changes in reservoir pressure, temperature and gravity indicates that the reservoir is currently approaching a stable state. Results of a simulation study suggest that the sustainable power output of the Hatchobaru reservoir is approximately 120 MW, and each productive fault has the capacity to produce enough steam to generate from 11 to 55 MW. Therefore, it would be possible to maintain the rated power output of 110 MW by optimizing well alignments so that the mass production can be kept within the sustainable productivity of each fault, and the injected water does not cool the production zones.  相似文献   

13.
A three dimensional numerical model of the northwest (NW) Sabalan geothermal system was developed on the basis of the designed conceptual model from available field data. A numerical model of the reservoir was expressed with a grid system of a rectangular prism of 12 km × 8 km with 4.6 km height, giving a total area of 96 km2. The model has 14 horizontal layers ranging in thickness between 100 m to 1000 m extending from a maximum of 3600 to −1000 m a.s.l. Fifteen rock types were used in the model to assign different horizontal permeabilities from 5.0 × 10−18 to 4.0 × 10−13 m2 based on the conceptual model.Natural state modeling of the reservoir was performed, and the results indicated good agreements with measured temperature and pressure in wells. Numerical simulations were conducted for predicting reservoir performances by allocating production and reinjection wells at specified locations. Three different exploitation scenarios were examined for sustainability of reservoir for the next 30 years. Effects of reinjection location and required number of makeup wells to maintain the specified fluid production were evaluated. The results showed that reinjecting at Site B, immediate adjacent to production zone, is most effective for pressure maintenance of the system.On the base of existing data and assumptions the reservoir can sustain producing fluid equivalent to 50 MWe of electricity for more than 30 years. The reservoir can produce the maximum amount of fluids equivalent to 90-100 MWe for only 5 years, but the production capacity decreases to 50 MWe after 20 years of operation because of pressure and enthalpy drop. The reservoir can sustain 50 MWe over 100 years that can be defined as a sustainable production level of the field.  相似文献   

14.
G. Geri  I. Marson  A. Rossi  B. Toro 《Geothermics》1982,11(3):153-161
The results of precise levelling measurements on a specially constructed network of benchmarks in the Travale geothermal area (Tuscany, Italy) revealed the subsidence of the central part of this area, at an average rate of 20 mm/year in the period 1978 – 1980. Two sets of gravity measurements over the same time-interval, using two Lacoste — Romberg gravimeters, have an average standard error of 2–4 μGal for the main network, and 4–8 μGal for the auxiliary network. The observed g variations fall within the error range in most of the stations. The variations noted in the stations in the south-western area of the field clearly fall outside the confidence interval, and cannot entirely be attributed to changes in elevation.An absolute gravity station was set up at Palazzo at Piano (Siena), where measurements were made by the IMGC absolute gravimeter, to detect any long-term gravity variations induced by geodynamic events.  相似文献   

15.
The low-temperature geothermal field of Nea Kessani, located in NE Greece, is characterized by a thermal reservoir made up of arkosic sandstones. The temperature distribution at depth, inferred from exploratory and productive wells, indicates that hot fluids rising from depth enter the arkosic reservoir in a restricted area of the field and flow towards local thermal springs. Well production tests have revealed the presence of hydrogeological boundaries within the arkosic reservoir.The geochemical characteristics of the thermal waters, which have an NaCl/HCO3 composition and salinity varying between 5 and 6 g/L, indicate that these waters undergo conductive cooling within the reservoir. No admixture of waters from the aquifers in the cover has been observed. The slight chemical differences existing between the thermal waters are probably caused by CO2, which represents about two thirds by volume of the discharged fluid. This CO2, as indicated by its isotopic composition, could originate from decomposition of marbles of the Paleozoic basement underlying the arkosic reservoir and may also affect the isotopic composition of the thermal waters, which exhibit an interesting positive oxygen shift. However, such a shift could also be the result of water-rock exchange processes at low temperatures, since the water feeding the field comes from a regional circulation which, as indicated by its deuterium content, has recharge areas on the Rhodope Chain. Alternatively, the shift could be attributed to the contribution of a deep-seated high-temperature geothermal reservoir, but a present there is no evidence of high-temperature resources in the region. A maximum temperature of 110°C has been estimated by quartz geothermometry.The physical, chemical and hydrogeological data available so far have permitted us to formulate a fluid circulation model for the Nea Kessani geothermal field.  相似文献   

16.
Some deep wells (1400–3000 m) have been drilled into the volcanic system of the Sabatini Mts., north of Rome, in search of high enthalpy geothermal fluids.Baccano caldera has formed over a carbonate structural high with a Quaternary volcanic cover, on the inside of a large graben that developed from the Upper Miocene and is characterized by a strong positive thermal anomaly. A spatially irregular Neogenic neoautochthon cycle, an allochthonous flysch complex (‘Sicilidi’ s.l.) and a Meso-Cenozoic ‘basal’ carbonate sequence were recognized in the sediments crossed by these wells below the volcanic cover. The observed structural setting can be correlated to that of analogous outcropping structures (Mt. Soratte) and shows a tensional tectonic phase overlying an older, mainly compressional phase.The stratigraphic and mineralogic analyses revealed important differences in the Trias, which is mainly calcareous in the western sector of the area and anhydritic in the eastern: the two facies at present seem to be tectonically brought closer to one another.The isotopic analyses all show values comparable to those of the sedimentary carbonate host rocks, suggesting limited circulation of the hydrothermal fluids. 18O/16O analyses on specimens in the most restrictive locations next to interfaces show a relatively larger extent of isotopic exchange with aqueous fluids.Fluid circulation, which is mainly extinct, seems to belong to a closed system. Two types of circulation have been recognized: the first of these is connected to the stratigraphic discontinuities (especially at the contact between the allochthonous flysch complex and the basal carbonate sequence) and is characterized by mainly K-feldspar and Sulphide-Sulphate mineralizations; the second circulation is tied to the fracture systems and is particularly widespread in the pyroclastic cover where it appears in the form of sulphate- and carbonate-rich dykes. This system seems to have undergone a mixing with surface waters.  相似文献   

17.
Commercial production of electricity from the Tiwi geothermal system began in 1979. In 1982, Tiwi became the world's first water-dominated system to produce more than 160 MWe. Today the field supplies about 11% of Luzon's electricity. Initially, the reservoir was single-phase liquid with a small, shallow steam zone on the east side. Temperature reversals in the first wells showed the east to be an outflow zone. As production began, reservoir pressure declined, two-phase conditions developed, and groundwater entered the reservoir from the east. As many production wells cooled, brine production increased and generation decreased from about 280 MWe in 1983 to about 190 MWe in 1986. Improvements to surface facilities and new wells drilled farther west raised generation to about 280 MWe by mid-1993. Separated brine was first injected into the reservoir, but this lowered steam production; injection is now outside the field.  相似文献   

18.
Alfina geothermal field is made up of a gas-cap (CO2) overlying an almost closed aquifer. The wells drilled in the highest part of the reservoir produce gas while the others either produce hot water or are sterile.During the first production tests the analysis of pressure and water-levels showed that the gas-water interface had risen. This was later confirmed when a gas-producing well began carrying water.This paper attempts to explain field behaviour by means of simple calculations and assuming an idealized geological structure.This study gives an estimation of the average porosity and initial gas in place.  相似文献   

19.
Prospecting for geothermal reservoirs by geophysical methods has proved to be a challenge in recent years. In the case of Nestos geothermal field, considered to be a blind field (no surface manifestation), the geological and geophysical data were studied and intercorrelated. The geophysical results from SP, gravity, and VES data were compared with basement morphology and tectonics, as well as with the high temperatures measured in the area of main geothermal interest. As a result, the highly conductive subsurface zone and high temperatures observed on the ground surface were closely associated with a specific fracturing system. The latter was successfully mapped by the SP method. The SP method also defined certain fracture zones which, being highly electrically polarized, are hypothesized as future geothermal targets.All existing geophysical data have been re-evaluated, along with the SP data acquired over the geothermal field, and compared with the thermal contour maps and regional tectonics of the area.A deep borehole, drilled earlier in the area of the geothermal field, detected high temperatures in the basement (115°C), but very low flowrate of the geothermal fluids. According to the results of this study, this is due to the fact that the borehole was located outside the area of the main fracture zones of geothermal interest.  相似文献   

20.
Tokaanu–Waihi geothermal field is situated near the southern end of the Taupo Volcanic Zone, New Zealand. Neutral chloride thermal waters discharge at Tokaanu and Waihi in the north of the field on flat land between the andesite volcanoes Tihia and Kakaramea and the shore of Lake Taupo, while steam-heated thermal features occur at Hipaua on the northern flanks of Kakaramea. Electrical resistivity surveys have been made over the field using several different measurement techniques. In the north of the field where roads and tracks allow vehicle access, resistivity profiling using Schlumberger arrays with electrode spacings (AB/2) of 500 m and 1000 m show that Tokaanu, Waihi and Hipaua all lie within a continuous region of low apparent resistivity (5–20 Ωm) and are thus part of the same geothermal system. Along the eastern edge of the system there is a sharp transition to apparent resistivities greater than 100 Ωm in the cold surrounding region. Surveys on Lake Taupo using an equatorial bipole-bipole electrode array towed behind boats (spacing equivalent to AB/2=500 m) found that the low resistivity zone extends offshore by about 1 km. The steep, bush-clad, southern part of the field was surveyed with magnetotelluric (MT) resistivity measurements using both naturally occurring signals and the 50 Hz radiation from the power wires as sources. These measurements found low resistivities over the north-eastern slopes and around the summits of Tihia and Kakaramea, indicating thermal activity. However, the measurements were too widely spaced to allow the field boundary to be clearly delineated. Interpretation of the resistivity and other data suggests that the Tokaanu–Waihi thermal waters rise nearly vertically from a source deep beneath the elevated southwestern part of the field to the water table. These waters then flow north to discharge at the surface near Lake Taupo. Neighbouring geothermal systems, which occur at Tongariro about 18 km south of Tokaanu–Waihi, and at Motuoapa about 10 km to the northeast, are separated from the Tokaanu–Waihi field by high resistivity ground. This suggests that the thermal fluids discharging at the three fields do not have a common source, as has been suggested previously.  相似文献   

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