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1.
The bottom of the magnetized crust determined from the spectral analysis of magnetic anomaly is interpreted as a level of the Curie point isotherm. A spectral analysis technique was used to estimate the depth of the magnetic anomalies sources (Curie point depth analysis) of the eastern shore of the Gulf of Suez, Egypt. The depth to the tops and centers of the magnetic anomalies are calculated by azimuthally averaged power spectrum method for the whole area. The results obtained suggests from this study showed that the average depth to the top of the crustal block ranges between 1.15 and 1.9 km, whereas the average depth to the center of the deepest crustal block ranges between 9.1 and 12.7 km. Curie point depths in the study area range between 14.5 km in the northwestern part of the study area and 26 km in the southeastern part of the study area. The results imply a high geothermal gradient (34.7 °C/km) and corresponding high heat flow value (72.87 mW/m2) in the northwestern part of the study area. The southeastern part of the study area displays a low geothermal gradient (24.26 °C/km) and low heat flow value (50.9 mW/m2). These results are consistent with the existence of the possible promising geothermal reservoir in the eastern shore of the Gulf of Suez especially at Hammam Faraun area.  相似文献   

2.
The Curie point depth map of Eastern Iran was constituted from spectral analysis of the aeromagnetic data. The reduction to pole (RTP) was applied to the magnetic anomaly data. The Curie point depth values from 165 overlapping blocks, 100 × 100 km in size, have been estimated. The Curie point depth method provides a relationship between the 2-D FFT power spectrum of the magnetic anomalies and the depth of magnetic sources by transforming the spatial data into the frequency domain. The centroid and top depth of the magnetic sources (respectively Z0 and Zt) is calculated from radially averaged log power spectrum for each block. Finally, the Curie point depth of Eastern Iran is obtained by Zb = 2Z0–Zt. The highest value of 24 km is located in eastern and western boundaries of the Lut block, and the lowest value of 12 km is located at north of study area. The shallow depths in the Curie-point depth map are well correlated with the young volcanic areas and geothermal potential fields. Geothermal gradient ranging from 24 to 45°C/km. The deduced thermal structure in eastern Iran has a relationship with orogenic collapse associated with delamination of thickened lithospheric root between the Lut and Afghan continental blocks.  相似文献   

3.
The geothermal structure beneath of the Barramiya?CRed Sea coast area of the Central Eastern Desert of Egypt has been determined using Curie point depth (CPD), which is temperature-dependent. The CPD and the surface heat flow (q) maps of such area are estimated by analyzing aeromagnetic data. Such data are low-pass-filtered and analyzed to estimate the magnetic bottom using the centroid method. The heat flow map reflects the geothermic nature of the region. However, it is suggested that the shallow Curie point temperature depth pattern depends on the tectonic regime and morphology, which continues eastwards through the Red Sea. Particularly, the coastal regions are characterized by high heat flow (83.6?mW/m2) and shallow Curie depth (22.5?km), whereas the western portion of the studied area has a lower heat flow (<50?mW/m2) and deeper Curie depth (~40?km). In addition to its bordering to the Red Sea margin, such high heat flow anomaly is associated with the increased earthquake swarms activity in the Abu Dabbab area. El-Hady (1993) attributed the swarm activity to the geothermal evolution. Also, the heat flow pattern is correlatable by the numerous results of shallow borehole temperature measurements as reported by Morgan and Swanberg (1979). A significant low heat flow extending in the northeast?Csouthwest direction, which is associated with NE?CSW large areal extent negative Bouguer gravity anomaly and NE/SW-trending belt of the deep CPD region, seems to be directly related to the surface outcrops of Precambrian older granitoids of the mountainous range of that trend.  相似文献   

4.
The geothermal regime beneath the Barramiya-Red Sea coast area of the Central Eastern Desert of Egypt has been determined by using the Curie point depth, which is temperature dependent. This study is based on the analysis of aeromagnetic data. The depth to the tops and centroid of the magnetic anomalies are calculated by power spectrum method for the whole area. The result of this investigation indicates, two new maps of the Curie point depth (CPD) and the surface heat flow (q) maps of the study area. The coastal regions are characterized by high heat flow (83.6 mW/m2), due to the geothermic nature of the region, and shallow Curie depth (22.5 km), where (CPD) depends on the tectonic regime and morphology in the eastern part of the area. The western portion of the studied area has a lower heat flow (<50 mW/m2) and deeper Curie depth (∼40 km), due to the existence of a large areal extent of negative Bouguer anomaly in the NE-SW direction. In addition to its bordering to the Red Sea margin, such high heat flow anomaly is associated with the increased earthquake swarms activity in the Abu Dabbab area.  相似文献   

5.
Deep onshore Mesozoic basins have favourable geothermal aquifers at depth comprising basal Permo-Triassic sandstones. The principal basins are the Wessex and Worcester (southern England), Cheshire (northwest England), Eastern England, Larne and Lough Neagh (Northern Ireland). Measured temperatures are up to 80 °C and could reach 100 °C in the deepest parts of some of the basins. Porosity and permeability data from depth are limited, but values high enough to allow adequate yields have been measured in many of the basins. Productive sandstones vary from a few tens of metres to hundreds of metres thick resulting in productive transmissivities. The estimated heat in place (Inferred Geothermal Resource) has been calculated as 201?×?1018 to 328?×?1018 J. New heat demand maps illustrate that many of the centres of high heat use are coincident with Upper Palaeozoic basins. Within the Carboniferous and Devonian there are thick sequences of deeply buried arenaceous deposits. Some productive local aquifers occur at shallow depth, but most depend on fissure flow that is anticipated to diminish rapidly with depth. The exception may be the Carboniferous Limestone where warm springs and a pronounced thermal anomaly in Eastern England demonstrate groundwater flow at depth, possibly along pathways of many kilometers.  相似文献   

6.
An updated analysis of geothermal data from the highland area of eastern Brazil has been carried out and the characteristics of regional variations in geothermal gradients and heat flow examined. The database employed includes results of geothermal measurements at 45 localities. The results indicate that the Salvador craton and the adjacent metamorphic fold belts northeastern parts of the study area are characterized by geothermal gradients in the range of 6–17°C/km. The estimated heat flow values fall in the range of 28–53 mW/m2, with low values in the cratonic area relative to the fold belts. On the other hand, the São Francisco craton and the intracratonic São Francisco sedimentary basin in the southwestern parts are characterized by relatively higher gradient values, in the range of 14–42°C/km, with the corresponding heat flow values falling in the range of 36–89 mW/m2. Maps of regional variations indicate that high heat flow anomaly in the São Francisco craton is limited to areas of sedimentary cover, to the west of the Espinhaço mountain belt. Crustal thermal models have been developed to examine the implications of the observed intracratonic variations in heat flow. The thermal models take into consideration variation of thermal conductivity with temperature as well as change of radiogenic heat generation with depth. Vertical distributions of seismic velocities were used in obtaining estimates of radiogenic heat production in crustal layers. Crustal temperatures are calculated based on a procedure that makes simultaneous use of the Kirchoff and Generalized Integral Transforms, providing thereby analytical solutions in 2D and 3D geometry. The results point to temperature variations of up to 300°C at the Moho depth, between the northern Salvador and southern São Francisco cratons. There are indications that differences in rheological properties, related to thermal field, are responsible for the contrasting styles of deformation patterns in the adjacent metamorphic fold belts.  相似文献   

7.
This study focuses on the water and gas chemistry of the northeastern Algerian thermal waters. The helium gas was used to detect the origin of the geothermal fluid. In the Guelma Basin, the heat flow map shows an anomaly of 120 ± 20 mW/m2 linked to the highly conductive Triassic extrusion. The chemical database reveals the existence of three water types, Ca-SO4/Na-Cl, which are related to evaporites and rich in halite and gypsum minerals. The third type is Ca (Na)-HCO3, which mostly characterizes the carbonated Tellian sector. The origin of thermal waters using a gas-mixing model indicates a meteoric origin, except for the El Biban hot spring (W10), which shows a He/Ar ratio of 0.213, thus suggesting the presence of batholith. The helium distribution map indicates a lower 3He/4He ratio between 0 Ra and 0.04 Ra in the W10 and W15 samples, which is compatible with the crustal ratio. Reservoir temperatures estimated by silica geothermometers give temperatures less than 133 °C. The geothermal conceptual model suggests that a geothermal system was developed by the deep penetration of infiltrated cold waters to a depth of 2.5 km and then heated by a conductive heat source (batholith for El Biban case). The thermal waters rise up to the surface through the deep-seated fractures. During their ascension, they are mixed with shallow cold groundwater, which increase the Mg content and cause the immature classification of the water samples.  相似文献   

8.
The Gulf of Suez is characterized by the presence of many hot springs and deep thermal wells scattered around its coastal areas. So it is considered one of the promised geothermal areas in Egypt. In this study, the main emphasis is to investigate the geothermal potential around the Gulf of Suez using the available logging and geothermometer datasets. The temperature profiles and well logging data of some hot springs and deep wells around or within the coastal area of the Gulf of Suez are used in this study. The temperature profiles are analyzed and some important thermophysical properties are estimated (geothermal gradient, thermal conductivity, heat flow, and specific heat capacity). Such analysis revealed that a medium to high geothermal gradient (22.0–30°C/Km) is given for the Gulf of Suez as a whole, with some spots of much higher gradient in the order of 35.0–44°C/Km (Ras Fanar and Hammam Faraun areas). The compiled thermal plots show that the thick evaporites and rock salt lithology, which is a major constituent in this area, attain the highest thermal conductivity (>3.10 W/m/K) and heat flow (>90 mW/m2) and the lowest specific heat capacity (<0.30 J/kg/K). The available gamma ray and the natural gamma ray spectroscopy logs are used to conduct a radioactive-based heat generation study using the characteristic radioactive nature of some elements like; 238U, 235U, 232Th, and of the isotope of 40K. A good linearity is observed between the heat production (A in microwatt per cubic meter) and the gamma ray (API) along a wide range of datasets (0–150 API) in all wells. The heat production factor increases in the carbonate lithology (up to 3.20?μW/m3) and is proportional to the shale volume. A geothermometer-based study is used to estimate the subsurface formation temperature and heat flow from the geochemical analysis of some water samples collected from the studied hot springs. The estimated thermal parameters are in harmony with the regional thermal regime concluded form logging data. A thermal basin growth study, in relation to the clay diagenesis is conducted concerning the thermal effects that take place with depth giving rise to another clay mineral (illite). Furthermore, a number of 2D thermal–burial history diagrams are constructed for the complied sections of some of the studied areas to show the vertical distribution of the estimated petrothermal properties. A reserve evaluation study is carried out to estimate the economic geothermal capacity of these hot springs to be used as alternative clean source for possible energy production (electricity) and other low-temperature purposes.  相似文献   

9.
This study investigates the characteristics of geothermal water in 10 geothermal fields in Beijing. The relationships between the deuterium excess parameter (d) and temperature, depth, age of geothermal groundwater, groundwater flow field, and Eh were investigated using geothermal groundwater samples. Results showed that (1) the average d value of geothermal water is 5.4, whereas that of the groundwater in normal temperature is 6.04. The differences are induced by the oxygen isotope exchange during the water–rock interaction, which may be more easily completed in geothermal water than in cold groundwater. (2) The d value increases remarkably with the age of the geothermal groundwater. The d value increases from 11.2 to 14.6 when the age of the geothermal water is 12,760 ± 130 a and 38,960 ± 630 a, respectively. Moreover, the isotope heat exchange for composition of the hydrogen and oxygen isotopes in the geothermal groundwater proceeds sufficiently with time. (3) The d value decreases from 5.72 to 3.03 when the depth increases from 125.13 to 3221 m. Generally, in the same area, the d value decreases with depth because the temperature is increasing. (4) The d value of the groundwater gradually reduces from the northern recharge area to the southern discharge area. The average d value is 7.31 in the northern recharge area and 5.68 in the middle Beijing Depression, whereas the d value in the southern area of Fengheying is ?9.20. The larger difference in d values between the recharge and discharge areas is due to the slower velocity of underwater flow, which induces longer time for oxygen exchange. (5) The relationship between the d and Eh is complex. When Eh is <200 mV, the d value of the geothermal water decreases with the decrease in Eh. When Eh is higher than 200 mV, the d value increases slightly with the decrease in Eh. The study of the characteristics of deuterium excess parameters for geothermal water could provide a scientific isotopic evidence for assessment and exploitation measures in geothermal groundwater systems.  相似文献   

10.
The Upper Carboniferous, coal-bearing sequence of the Intrasudetic Basin (SW Poland) includes coals ranging from high-volatile bituminous to anthracitic rank. The lowest values of reflectance are recorded around the basin margins (0.6% R0 max), the highest ones appear in the center of the basin (exceeding 4% R0 max). Reflectance gradients are very high, reaching 0.6%/100 m in the centre of the basin.A comparison of the isoreflectance maps for three lithostratigraphical units—the Walbrzych, Bialy Kamien and Zacler Formations, with the present-day burial depth and the depth of burial during the Westphalian B/C—indicates that there is a strong relationship between reflectance and the sediment cover during the Westphalian B/C, particularly in the vicinity of Walbrzych and Lubawka. This suggests that the increase in coal rank is related to the increase in cover which permitted the temperature to build-up to high values.In the eastern and central parts of the basin and the Nowa Ruda area, higher reflectance than that derived from burial depth is observed which is believed to result from higher heat flow from the basement. The volcanic rocks of the Intrasudetic Basin appear to have little effect on coal rank and are not considered to be a significant contributor to the heat flow of the region.During coalification, the oldest Westphalian coal seams were buried to about 700 m and the youngest seams of the Walbrzych Formation to 900 m. Around the basin margins the coals had reached their present-day rank by the Westphalian B/C and in the central part probably by the end of the Stephanian. Most effective coalification took place during the Westphalian A,B occupying a period of less than 20 million years. The coalification temperature is calculated to be 160–170°C with a geothermal gradient of 8–10°C/100 m. These geothermal conditions support the suggestion of a volcanic origin for the Intrasudetic Basin.  相似文献   

11.
Tauranga low-temperature geothermal system (New Zealand) has been used for the last 40 years for direct uses including space heating, bathing and greenhouses. Warm-water springs in the area are between 22 and 39 °C, with well temperatures up to 67 °C at 750 m depth. A heat and fluid flow model of the system is used to determine reservoir properties and assess thermal potential. The model covers 130 km by 70 km to 2 km depth, and was calibrated against temperatures measured in 17 wells. Modelling shows that to maintain the observed primarily conductive heat flow regime, bulk permeability is ≤2.5?×?10?14 m2 in sedimentary cover and ≤1?×?10?16 m2 in the underlying volcanic rocks. The preferred model (R 2?=?0.9) corresponds to thermal conductivities of 1.25 and 1.8 W/m2 for sedimentary and volcanic rocks, respectively, and maximum heat flux of 350 mW/m2. The total surface heat flow is 258 MW over 2,200 km2. Heat flux is highest under Tauranga City, which may be related to inferred geology. Model simulations give insights into rock properties and the dynamics of heat flow in this low-temperature geothermal system, and provide a basis to estimate the effects of extracting hot fluid.  相似文献   

12.
Guangdong Province in Southeast China is noted for its numerous geothermal resources due to tectonic episodes, mainly occurred during the Cretaceous. The surface heat flow and geothermal gradient are the most direct ways to understand the temperature of the Earth. However, geothermal resources are poorly utilized in Guangdong Province due to limited numbers of boreholes and surficial hydrothermal fluids. To improve the understanding of underground temperature distribution in Guangdong Province, we have applied power-density spectral analysis to aeromagnetic anomaly data to calculate the depth of the Curie isothermal surface. Upward continuation is applied and tested to the magnetic data. The calculated Curie isotherm is between 18.5 km and 25 km below surface. The fluctuation in the depth range reflects lateral thermal perturbations in the Guangdong crust. In particular, the eastern, northern, western and coastline areas of the province have a relatively shallow Curie isotherm. By comparing the surface heat flow, geothermal gradient, distribution of Mesozoic granite-volcanic rocks, and natural hot springs, we conclude that during Mesozoic, magmatism exerted great influence on the deep thermal state of Guangdong Province. A shallow Curie isotherm surface, as well as numerous natural hot springs and high heat flow,show clear signatures of shallow heat sources.  相似文献   

13.
Understanding the thermal distribution within the crust and rheology of the earth’s lithosphere requires the knowledge of the Depth to the Bottom of Magnetic Sources (DBMS). This depth is an important parameter in this regard, which can be derived from aeromagnetic data and can be used as a representation for temperature at depth where heat flow values can be evaluated. In this work, high-resolution aeromagnetic (HRAM) data of part of Chad Basin (covering about 80% of the entire basin), an area bounded by eastings 769,000 and 1,049,900 mE and northings 1,200,000 and 1,500,000 mN, were divided into 25 overlapping blocks and each block was analyzed using spectral fractal analysis method. The spectral analysis method was used to obtain the Depth to the Top of Magnetic Source (DTMS), centroid depth, and DBMS. From the calculated DBMS, the geothermal gradient and heat flow parameters were evaluated and the result obtained shows that DBMS varies between 18.18 and 43.64 km. Also the geothermal gradient was found to be varying between 13.29 and 31.90 °C/km and heat flow parameters vary between 33.23 and 79.76 mW/m2, respectively. The heat distribution of this area is one of the key parameters responsible for various geodynamic processes; therefore, this work is important for numerically understanding the thermal distribution in Chad Basin, Nigeria since rock rheologies depend on temperature, which is a function of depth.  相似文献   

14.
Tulsishyam thermal springs are located in the Saurashtra region of Gujarat, India with discharge temperatures varying from 39 to 42 °C. The pH of these thermal springs varies from 7.1 to 7.4, indicating neutral character. Though these thermal springs propagate through the near surface layer of Deccan basalt, detailed geochemical analysis of the thermal waters using Piper diagram suggests that the water is interacting with the granitic basement rock. Silica and cation geothermometry estimates have reservoir temperature in the range of 138 to 207 °C categorizing it into a low to moderate enthalpy geothermal system. Furthermore, the area has high heat flow values of 53–90 mW/m2 because of shallow Moho depth. The prevailing conditions suggest that the geothermal energy can potentially be exploited through an enhanced geothermal system (EGS). The study also indicates different mineral phases that may precipitate out of water during exploitation of geothermal energy and it should be taken into account while designing an EGS for the area.  相似文献   

15.
Increased seismicity and occurrences of hot springs having surface temperature of 36–58 °C are observed in the central part of India (74–81° E, 20–25° N), where the NE trending Middle Proterozoic Aravalli Mobile Belt meets the ENE trending Satpura Mobile Belt. Earlier Deep Seismic Sounding (DSS) studies along Thuadara-Sendhwa-Sindad profile in the area has showed Mesozoic Sediments up to around 4 km depth covered by Deccan Trap and the Moho depth with a boundary velocity (Pn) of 8.2 km/s. In the present study, surface heat flow of 48 ± 4 mW m?2 has been estimated based on Pn velocity, which agrees with the value of heat flow of 52 ± 4 mW m?2 based on Curie point isotherms estimates. The calculated temperature-depth profile shows temperature of 80–120 °C at the basement, which is equivalent to oil window temperature in Mesozoic sediments and around 570–635 °C at Moho depth of 38–43 km and the thermal lithosphere is about 110 km thick, which is comparatively higher than those of adjoining regions. The present study reveals the brittle–ductile transition zone at 14–41 km depth (temperature around 250–600 °C) where earthquake nucleation takes place.  相似文献   

16.
Niutuozhen geothermal field is located in the Jizhong graben, belonging to the northern part of Bohai Bay Basin in North China. Chemical and isotopic analyses were carried out on 14 samples of the geothermal fluids discharged from Neogene Minghuazhen (Nm), Guantao (Ng), and Jixianian Wumishan (Jxw) formations. The δ2H and δ18O in water, δ13C in CH4, δ13C in CO2, and 3He/4He ratio in the gases were analyzed in combination with chemical analyses on the fluids in the Niutuozhen geothermal field. The chemical and isotopic compositions indicate a meteoric origin of the thermal waters. The reservoir temperatures estimated by chemical geothermometry are in the range between 60 and 108 °C. The results show that the gases are made up mainly by N2 (18.20–97.42 vol%), CH4 (0.02–60.95 vol%), and CO2 (0.17–25.14 vol%), with relatively high He composition (up to 0.52 vol%). The chemical and isotopic compositions of the gas samples suggest the meteoric origin of N2, predominant crustal origins of CH4, CO2, and He. The mantle-derived He contributions are calculated to be from 5 to 8% based on a crust–mantle binary mixing model. The deep temperatures in the Jxw reservoir were evaluated based on gas isotope geothermometry to be in the range from 141 to 165 °C. The mantle-derived heat fraction in the surface heat flow is estimated to be in the range of 48–51% based on 3He/4He ratios.  相似文献   

17.
Geothermal springs are some of the most obvious indicators of the existence of high-temperature geothermal resources in the subsurface. However, geothermal springs can also occur in areas of low average subsurface temperatures, which makes it difficult to assess exploitable zones. To address this problem, this study quantitatively analyzes the conditions associated with the formation of geothermal springs in fault zones, and numerically investigates the implications that outflow temperature and discharge rate from geothermal springs have on the geothermal background in the subsurface. It is concluded that the temperature of geothermal springs in fault zones is mainly controlled by the recharge rate from the country rock and the hydraulic conductivity in the fault damage zone. Importantly, the topography of the fault trace on the land surface plays an important role in determining the thermal temperature. In fault zones with a permeability higher than 1 mD and a lateral recharge rate from the country rock higher than 1 m3/day, convection plays a dominant role in the heat transport rather than thermal conduction. The geothermal springs do not necessarily occur in the place having an abnormal geothermal background (with the temperature at certain depth exceeding the temperature inferred by the global average continental geothermal gradient of 30 °C/km). Assuming a constant temperature (90 °C here, to represent a normal geothermal background in the subsurface at a depth of 3,000 m), the conditions required for the occurrence of geothermal springs were quantitatively determined.  相似文献   

18.
Geothermal water is plentiful in Changbai Mountain region, northeastern China, due to the volcanic activities and widespread faults. For the exploration of geothermal resources, this study uses quartz and cation geothermometer to estimate the temperatures of the geothermal reservoir and uses the tubular models to evaluate the thermal gradient. The hydrogeochemical characteristics of the geothermal resources were also evaluated by hydrogeochemical analysis. The results showed that the geothermal reservoir temperatures of the four major thermal springs in Changbai Mountain region range from 72 to 169 °C. The average geothermal reservoir temperatures of Jinjiang hot springs, Changbai hot springs I, Xianrenqiao hot springs, and Changbai hot springs II are 129.25, 169, 89, and 73.67 °C, respectively. The geothermal gradient values of the four major thermal springs have different characteristics. The geothermal gradient values of Jinjiang hot springs and Changbai hot springs I are 4.6 and 3.1 °C/100 m, respectively. The geothermal gradient values of Xianrenqiao thermal springs and Changbai thermal springs II are both lower than 1.5 °C/100 m, with the values of 1.1 and 1.4 °C/100 m. And the geothermal gradients are influenced by Changbai Mountain Tianchi volcano. In addition, the water chemical analyses showed that the geothermal water types are HCO3-Na with higher concentrations of Na+, Cl?, SO4 2?, TDS, and HCO3 ? than the non-thermal waters, which suggested a deep and long water cycle of the thermal water, and therefore a sufficient water-rock interaction.  相似文献   

19.
Exploration of Perth's geothermal potential has been performed by the Western Australian Geothermal Centre of Excellence (WAGCoE). Detailed vertical temperature and gamma ray logging of 17 Western Australia Department of Water's (DoW) Artesian Monitoring (AM) wells was completed throughout the Perth Metropolitan Area (PMA). In addition, temperature logs from 53 DoW AM wells measured in the 1980s were digitised into LAS format. The logged data are available in the WAGCoE Data Catalogue.

Analysis of the gamma ray logs yielded the first estimates of radiogenic heat production in Perth Basin formations. Values by formation ranged between 0.24 and 1.065 μW m?3. The temperature logs provide a picture of true formation temperatures within shallow sediments in the Perth Basin. A three-dimensional model of the temperature distribution was used to produce maps of temperature at depth and on the top of the Yarragadee aquifer.

The temperature data were interpreted with a one-dimensional conductive heat model. Significant differences between the model and the observations was indicative of heat moving via non-conductive mechanisms, such as advection or convection. Evidence of non-conductive or advective heat flow is demonstrated in most formations in the region, with significant effects in the aquifers. Average conductive geothermal gradients range from 13°C km?1 to 39°C km?1, with sandstone formations exhibiting average gradients of approximately 25°C km?1, while insulating silt/shale formations show higher average gradients of over 30°C km?1.

To produce preliminary heat flow estimates, temperature gradients were combined with thermal conductivities measured elsewhere. The geometric mean heat flow estimates range between 64 mW m?2 to 91 mW m?2, with the standard deviation of the arithmetic mean heat flow ranging between 15 and 23 mW m?2.

The study characterises the shallow temperature regime in the Perth Metropolitan Area, which is of direct relevance towards developing commercial geothermal projects.  相似文献   

20.
《Applied Geochemistry》2005,20(1):23-39
Hydrothermal alteration at Los Azufres geothermal field is mostly propylitic with a progressive dehydration with depth and temperature increase. Argillic and advanced argillic zones overlie the propylitic zone owing to the activity of gases in the system. The deepest fluid inclusions (proto-fluid) are liquid-rich with low salinity, with NaCl dominant fluid type and ice melting temperatures (Tmi) near zero (0 °C), and salinities of 0.8 wt% NaCl equivalent. The homogenization temperature (Th)  = 325 ± 5 °C. The boiling zone shows Th = ±300 °C and apparent salinities between 1 and 4.9 wt% NaCl equivalent, implying a vaporization process and a very important participation of non-condensable gases (NCGs), mostly CO2. Positive clathrate melting temperatures (fusion) with Th = 150 °C are observed in the upper part of the geothermal reservoir (from 0 to 700 m depth). These could well be the evidence of a high gas concentration. The current water produced at the geothermal wells is NaCl rich (geothermal brine) and is fully equilibrated with the host rock at temperatures between T = 300 and 340 °C. The hot spring waters are acid-sulfate, indicating that they are derived from meteoric water heated by geothermal steam. The NCGs related to the steam dominant zone are composed mostly of CO2 (80–98% of all the gases). The gases represent between 2 and 9 wt% of the total mass of the fluid of the reservoir.The authors interpret the evolution of this system as deep liquid water boiling when ascending through fractures connected to the surface. Boiling is caused by a drop of pressure, which favors an increase in the steam phase within the brine ascending towards the surface. During this ascent, the fluid becomes steam-dominant in the shallowest zone, and mixes with meteoric water in perched aquifers. Stable isotope compositions (δ18O–δD) of the geothermal brine indicate mixing between meteoric water and a minor magmatic component. The enrichment in δ18O is due to the rock–water interaction at relatively high temperatures. δ13C stable isotope data show a magmatic source with a minor meteoric contribution for CO2. The initial isotopic value δ34SRES = −2.3‰, which implies a magmatic source. More negative values are observed for shallow pyrite and range from δ34S (FeS2) = −4‰ to −4.9‰, indicating boiling. The same fractionation tendencies are observed for fluids in the reservoir from results for δ18O.  相似文献   

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