Spatial data analysis and integration for regional-scale geothermal potential mapping,West Java,Indonesia

Conceptual modeling and predictive mapping of potential for geothermal resources at the regional-scale in West Java are supported by analysis of the spatial distribution of geothermal prospects and thermal springs, and their spatial associations with geologic features derived from publicly available regional-scale spatial data sets. Fry analysis shows that geothermal occurrences have regional-scale spatial distributions that are related to Quaternary volcanic centers and shallow earthquake epicenters. Spatial frequency distribution analysis shows that geothermal occurrences have strong positive spatial associations with Quaternary volcanic centers, Quaternary volcanic rocks, quasi-gravity lows, and NE-, NNW-, WNW-trending faults. These geological features, with their strong positive spatial associations with geothermal occurrences, constitute spatial recognition criteria of regional-scale geothermal potential in a study area. Application of data-driven evidential belief functions in GIS-based predictive mapping of regional-scale geothermal potential resulted in delineation of high potential zones occupying 25% of West Java, which is a substantial reduction of the search area for further exploration of geothermal resources. The predicted high potential zones delineate about 53–58% of the training geothermal areas and 94% of the validated geothermal occurrences. The results of this study demonstrate the value of regional-scale geothermal potential mapping in: (a) data-poor situations, such as West Java, and (b) regions with geotectonic environments similar to the study area.     

Geothermal energy resources and development in Iran

Interest in geothermal energy originated in Iran when James R. McNitt, a United Nations geothermal expert, visited the country in December 1974. In 1975, a contract among the Ministry of Energy, ENEL (Entes Nazionale per L’Energia Elettrica) of Italy and TB (Tehran Berkeley) of Iran was signed for geothermal exploration in the north-western part of Iran. In 1983, the result of investigations defined Sabalan, Damavand, Khoy-Maku and Sahand regions as four prospected geothermal sites in north-western Iran.From 1996 to 1999, a countrywide geothermal energy resource exploration project was carried out by Renewable Energy Organization of Iran (SUNA) and 10 more potential areas were indicated additionally.Geothermal potential site selection using Geographic Information System (GIS) was carried out in Kyushu University in 2007. The results indicated 8.8% of Iran as prospected geothermal areas in 18 fields.Sabalan as a first priority of geothermal potential regions was selected for detailed explorations. Since 1995, surface exploration and feasibility studies have been carried out and five promising areas were defined. Among those prospective areas, Northwest Sabalan geothermal filed was defined for detailed exploration to justify exploration drilling and to estimate the reservoir characteristics and capacity.From 2002 to 2004, three deep exploration wells were drilled for evaluation of subsurface geological conditions, geothermal reservoir assessment and response simulation. Two of the wells were successful and a maximum temperature of 240 °C at a depth of 3197 m was recorded. As a result of the reservoir simulation, a 55-MW power plant is projected to be installed in the Sabalan field as a first in geothermal power generation. To supply the required steam for the geothermal power plant (GPP) 17 deep production and reinjection wells are planned to be drilled this year.     

Te Kopia geothermal system (New Zealand) — the relationship between its structure and extent

The Te Kopia geothermal system is one of several high-temperature systems in the Taupo Volcanic Zone (TVZ) of New Zealand. It is located along the Paeroa Fault Zone, a major active fault system trending NE in the central TVZ. Three independent studies, i.e. resistivity survey, magnetic interpretation, and detailed topographic analysis of faults and fractures, indicate the existence of another fault system, trending NW, that also significantly influences the Te Kopia geothermal system. Results from these studies also show that, at Te Kopia, a resistivity low and hydrothermally demagnetised rocks (both are indicators of a geothermal reservoir in volcanic rocks) clearly coincide with a zone of high fault and fracture density. Hence, the Te Kopia field is a good example of the significant influence that geological structures (major fault systems) have on the extent of a geothermal reservoir, by creating zones of fractured rocks that provide permeable paths for thermal fluids.     

Aeromagnetic survey and interpretation, Ascention Island, South Atlantic Ocean

A detailed aeromagnetic survey of Ascension Island, which was completed in February and March of 1983 as part of an evaluation of the geothermal potential of the island, is described. The aeromagnetic map represents a basic data set useful for the interpretation of subsurface geology. An in situ magnetic susceptibility survey was also carried out to assist in understanding the magnetic properties of Ascension rocks and to aid in the interpretation of the aeromagnetic data. The aeromagnetic survey was interpreted using a three-dimensional numerical modeling program that computes the net magnetic field of a large number of vertically sided prisms. Multiple source bodies of complex geometry were modeled and modified until a general agreement was achieved between the observed data and the computed results. The interpretation indicates northeast- and east-trending elongate bodies of much higher apparent susceptibility than adjacent rocks. The relationship to mapped geologic features such as volcanic vents, dikes and faults suggests that these magnetic sources are zones of increased dike density and of other mafic intrusives emplaced along structures that fed the many volcanic centers. A large magnetic source on the northeastern portion of the island may be the intrusive equivalent of trachyte lavas present at the surface. A low-magnetization area, mainly north and west of Green Mountain, appears to be the most likely area for the presence of a geothermal system at moderate (1–3 km) depth.     

水热型地热资源地球化学勘探技术研究进展

地球化学勘探技术在水热型地热资源勘探中的应用研究具有较长的历史,迄今已形成了一套基于气体与元素指标的勘探技术体系,涵盖了众多技术指标,且已在世界各地诸多地热田勘探研究中获得了广泛应用。结果揭示,在预测地热田发育有利部位、估算深部热储温度以及推断地热水来源等方面,地球化学勘探技术都可发挥其特有的作用,是一种经济有效的地热勘探技术,具有良好的应用前景。但地热地球化学勘探技术也面临其自身的局限性,其应用研究不仅受地热田类型的限制,而且目前主要集中于已知地热田上方的验证性研究,技术本身的多解性也较强。因此,在地热地球化学勘探技术完善与应用研究方面,还有待进一步深化。     

Temporal and spatial distribution of local seismicity in the Chipilapa-Ahuachapán geothermal area, El Salvador

Microseismic monitoring of the Chipilapa-Ahuachapán area was carried out during August-November 1988 and October 1991–April 1992. The objective was to use the study of microearthquakes as an exploration tool to invvestigate the geothermal potential of the Chipilapa area and to evaluate the main characteristics of the seismic activity, prior to and during the exploitation tests. Since 1989, seven wells have been drilled in the area, two of which have encountered three geothermal aquifers that could be exploited for electricity generation by means of binary-cycle technology. The 1988 survey detected important, shallow and low magnitude seismic activity, located mainly south and southwest of the explored area. This activity is possibly related to the recharge zone of the Chipilapa-Ahuachapán geothermal system, located further south, beneath the Pleistocene Pacific Volcanic Chain. The 1991–1992 survey confirmed the existence of seismicity beneath the southern volcanic axis, but other important clusters of activity were recorded northward, related to the deeper structures of the Central Graben, and southwest of the Ahuachapán geothermal field, close to the 1990 hydrothermal eruption of Agua Shuca. Shallow microseismic activity also appeared along the faults limiting the Chipilapa geothermal field to the east. Although it is probable that this seismicity is due to fluid circulation in fractures, no geothermal reservoirs were intercepted by wells CHA and CH8. Moreover, no significant induced seismicity was recorded during production and injection tests.     

Geochemical exploration of the three most significant geothermal areas of Lesbos Island, Greece

Lesbos Island has several thermal manifestations linked to extensional active faults that act as channels for the ascent of deep thermal fluids.The present work describes detailed geochemical exploration aimed at evaluating the potential of the Lesbos Island geothermal resource. Exploration was carried out on the three sites (Kalloni-Stipsi, Petra-Argenos and Polichnitos) that have the most favourable hydrogeological and structural setting on the island.Hydrogeochemical data reveal the presence between Kalloni and Stipsi of a shallow thermal aquifer with temperatures below boiling point, which coincides with carbon dioxide and temperature anomalies in the overlying groundwaters. All the thermal waters in the study area have fairly similar physico-chemical features; their geochemical temperature is in the range 115–125°C. While low-medium enthalpy geothermal resources are relatively abundant in the three selected areas of Lesbos Island, the presence of a high enthalpy geothermal system is still the subject of debate.     

Developing the geothermal resources map of Iran

Geothermal exploration involves a high degree of uncertainty and financial risk, and requires reliable exploration data to constrain development decisions. The paper describes a geothermal exploration and resource identification method that is based on building a map of potential geothermal resource areas by combining geological, geochemical and geophysical datasets; it is a powerful tool for visualizing new and existing data during decision-making processes. By performing suitability analysis and geothermal area identification, and by establishing criteria to define geothermal resources with development potential, a map of Iran was constructed highlighting 18 promising areas.     

Geothermal development in Thailand

San Kampaeng and Fang geothermal areas are considered areas of interest for the exploitation of geothermal energy. The technologies of exploration and development have been studied by Thai scientists and engineers during the past four years. The first geothermal deep exploration well was drilled, in cooperation with Japan International Cooperation Agency (JICA), in the San Kampaeng geothermal area. In 1985, supplementary work is planned to define the deep structural setting in greater detail before starting to drill the next deep exploration well. In Fang geothermal area some shallow exploitation wells have been drilled to obtain fluid to feed a demonstration binary system of 120 kWe, with the technical cooperation of BRGM and GEOWATT, France. The plant will be installed next fiscal year.     

Potential for surface gas flux measurements in exploration and surface evaluation of geothermal resources

Anomalous concentrations of CO₂ and, to a lesser extent, CH₄ have been detected over many active geothermal systems. The production of these gases, and of N₂O, can be affected by both geothermal and biological processes. In this investigation, soil gas and soil-gas fluxes were measured at the Cove Fort-Sulphurdale geothermal field in Utah, which produces steam from both liquid- and vapor-dominated portions of the resource. The objectives were to determine the sources of these gases, the factors controlling their production, and the potential application to surface exploration and reservoir evaluation. Flux measurements were made in both summer and winter to evaluate and to quantify variations in seasonal noise.Carbon dioxide in soil gas, and in fluxes from the soil to the atmosphere during the summer sampling were dominated by soil respiration processes. During the winter, a geothermal component was visible. Methane fluxes were small negative values during the summer months, reflecting methanotrophic oxidation of atmospheric CH₄ and, possibly, geothermal CH₄ in the soils. Nitrous oxide in soil gas and in soil-gas fluxes to the atmosphere also varied seasonally. Surprisingly high concentrations were observed at locations directly above the steam cap. We suggest that NH₃ produced in the geothermal reservoir by the Haber reaction was seeping upward where it was biologically oxidized to NO₃⁻. This oxidation, and possible localized biological reduction of NO₃⁻ to N₂, produced moderate amounts of N₂O, averaging three times typical background flux rates and ten times background over the central portion of the geothermal area.There were higher fluxes of CO₂, CH₄ and N₂O over the steam cap and the surrounding area, relative to background values. The high flux may reflect seepage of gas along faults that intersect the more extensive liquid-dominated portion of the reservoir. Nitrous oxide measurements in soil gas and soil-gas fluxes to the atmosphere offer promise as an exploration and reservoir characterization tool.     

Reservoir engineering assessment of Dubti geothermal field,Northern Tendaho Rift,Ethiopia

Following on from surface exploration surveys performed during the 1970s and early 1980s, exploration drilling was carried out in the Tendaho Rift, in Central Afar (Ethiopia), from October 1993 to June 1995. Three deep and one shallow well were drilled in the central part of the Northern Tendaho Rift to verify the existence of a geothermal reservoir and its possible utilisation for electric power generation. The project was jointly financed by the Ethiopian Ministry of Mines and Energy and the Italian Ministry for Foreign Affairs. Project activities were performed by the Ethiopian Institute of Geological Surveys and Aquater SpA. The main reservoir engineering data discussed in this paper were collected during drilling and testing of the above four wells, three of which are located inside the Dubti Cotton Plantation, in which a promising hydrothermal area was identified by surface exploration surveys. Drilling confirmed the existence of a liquid-dominated shallow reservoir inside the Dubti Plantation, characterised by a boiling-point-for-depth temperature distribution down to about 500 m depth. The main permeable zones in the Sedimentary Sequence, which is made up of lacustrine deposits, are located in correspondence to basalt lava flow interlayerings, or at the contact between volcanic and sedimentary rocks. At depth, the basaltic lava flows that characterise the Afar Stratoid Series seem to have low permeability, with the exception of fractured zones associated with sub-vertical faults. Two different upflows of geothermal fluids have been inferred: one flow connected to the Dubti fault feeds the shallow reservoir crossed by wells TD-2 and TD-4, where a maximum temperature of 245 °C was recorded; the second flow seems to be connected with a fault located east of well TD-1, where the maximum recorded temperature was 270 °C. A schematic conceptual model of the Dubti hydrothermal area, as derived from reservoir engineering studies integrated with geological, geophysical and geochemical data, has been tested by numerical simulation, using the TOUGH2/EWASG code. Preliminary simulations, using a simple 3-D numerical model of the Dubti fault area, showed that measured temperature and pressure distribution, as well as evaluated non-condensable gas pressure at reservoir conditions, are compatible with the rise of geothermal fluid, at about 290 °C, along the sub-vertical Dubti fault from beneath the surface manifestations DB1, DB2 and DB3 located at the south-eastern end of the fault. According to the proven shallow field potential, development of this field could meet the predicted electricity requirements of Central Afar until the year 2015.     

The electricity market potential of geothermal energy: A regionally aggregative analysis

This research presents estimates of potential regional electric market shares for geothermally produced electricity in the Rocky Mountain Basin and Range Region of the western United States. A model is described which simulates the exploration for and the discovery and harnessing of electric grade geothermal energy resources during the period 1986–1995. Concurrently, electricity demand forecasts are prepared for the same period using a set of estimated electricity demand models. The two forecasts are then integrated to calculate regional electric market shares for a set of alternate electricity price futures.     

Effect of tectonics and earthquakes on geothermal activity near plate boundaries: A case study from South Iceland

We studied fracture-controlled geothermal fields in the Hreppar Rift-Jump Block (HRJB), a micro-plate bounded by two NNE rifts and the E–W transform zone of the South Iceland Seismic Zone (SISZ). Distinguishing whether the extensional rift swarm or the transform zone shear fractures host the geothermal activity is challenging. GPS mapping of 208 springs and tectonic analysis indicate that six Riedel shear fracture sets of an older transform zone in the HRJB are permeable. Northerly dextral strike-slip faults are the principal permeable faults, although the highest discharge and temperature are found at their intersections with other fracture sets. Two northerly faults from the HRJB connect to the source faults of the major 1784 and 1896 earthquakes within the active SISZ. The 1784 earthquake caused pressure changes as far north as the studied springs, indicating that earthquakes keep faults permeable over hundreds of years.     

Temperature–depth relationships based on log data from the Los Azufres geothermal field,Mexico

Equilibrium temperatures based on log data acquired during drilling stops in the Los Azufres geothermal field were used to study the relationship between temperature, depth and conductive heat flow that differentiate production from non-production areas. Temperature and thermal conductivity data from 62 geothermal wells were analyzed, displaying temperature–depth, gradient–depth, and ternary temperature–gradient–depth plots. In the ternary plot, the production wells of Los Azufres are located near the temperature vertex, where normalized temperatures are over 0.50 units, or where the temperature gradient is over 165°C/km. In addition, the temperature data were used to estimate the depth at which 600°C could be reached (5–9 km) and the regional background conductive heat flow (≈ 106 mW/m²). Estimates are also given for the conductive heat flow associated with the conductive cooling of an intrusive body (≈ 295 mW/m²), and the conductive heat flow component in low-permeability blocks inside the reservoir associated with convection in limiting open faults (from 69 to 667 mW/m²). The method applied in this study may be useful to interpret data from new geothermal areas still under exploration by comparing with the results obtained from Los Azufres.     

GIS integration model for geothermal exploration and well siting

The work involved in identifying geothermal fields can be simplified by means of a Geographical Information System (GIS), a decision-making tool used to determine the spatial association between exploration and environmental thematic maps. This methodology has been applied to part of the Sabalan geothermal field in northwestern Iran, and to the siting of exploration wells. The datasets used in the analyses consist of geological, geochemical and geophysical information. Boolean and Index Overlay knowledge-driven models were developed for site selection; the findings from these two models correlated well with the exploration data modeling. The results of the Index Overlay model were combined with those of an environmental suitability analysis for final selection of well sites. The results of exploration and environmental data modeling were combined to select and prioritize the sites of three exploratory wells in the study area.     

Thermal regime, groundwater flow and petroleum occurrences in the Cap Bon region, northeastern Tunisia

The Cap Bon region of northeastern Tunisia is part of a young continental margin that presents a thick column of sediments deposited mainly during Cretaceous and Miocene extended tectonic episodes. This sedimentary package is characterised by broad synclines alternating with NE–SW trending anticlines, and is affected by numerous NE–SW, NW–SE and E–W striking faults. Oligo-Miocene sandstones constitute the most important potential reservoir rocks in the region.The distribution of subsurface temperatures in the Cap Bon basin reflects local groundwater circulation patterns and correlates with the location of known oil and gas fields. The results of geothermal studies could therefore prove useful in the search for new hydrocarbon resources in the region. Subsurface temperatures were measured in deep oil exploration and shallow water wells. Local geothermal gradients range from 25 to 35 °C/km, showing higher values in the Korbous and Zennia areas, which correspond to zones of groundwater discharge and convergence in the Oligo-Miocene aquifer system, respectively.Analysis of thermo-hydraulic and geochemical data relative to the thermal springs in the Korbous region along the Mediterranean coast has made a useful contribution to geothermal prospecting for potential deep reservoirs. Positive geothermal gradient anomalies correspond to areas of ascending thermal waters (i.e. discharge areas), whereas negative anomalies indicate areas of infiltrating colder meteoric waters (i.e. recharge areas). The zones of convergence of upward-moving water and groundwater may be associated with petroleum occurrences.     

Evaluation of the reconnaissance results in geothermal exploration using GIS

Geographical Information System (GIS) is used to determine the spatial association between geophysical and geological evidence and production zones in a well-known geothermal field (Los Azufres, Mexico). Surface observations in Los Azufres were used to delineate areas characterized by high permeability and hot fluid transport from the reservoir: main faults, superficial fracture density, surface manifestations, contacts with the most recent rhyolite domes, and low values in the apparent resistivity surveys. Three knowledge-driven models were constructed based on a conceptual model of the field: a hydrothermal system in rough terrain with secondary permeability. Boolean, Index Overlay and Fuzzy scheme models were proposed and the results obtained show a good correlation with the location of the producing and non-producing wells that have been drilled in the field. The results obtained are useful for well siting (Boolean and Low-Risk Fuzzy models) or for planning further detailed exploration (Index Overlay and High-Risk Fuzzy models).     

First decade of geothermal development in Yangbajain field, China

The electric use of geothermal energy in China on a trial basis began in the early 1970s. Since then a total of nine small-scale pilot units, with the exception of Yangbajain, using underground thermal water for electricity generation, have been constructed in different parts of China. All of these localities are already covered by regional electric grids; these units cannot be run safely, steadily and continuously, so it is not possible to attach great importance to these miniplants. Based on their operating experience and thermodynamic and economic analyses in the present technological conditions, it appears that a geothermal water with temperature well below 100°C is favorable only to non-electric uses, except in remote areas with an extreme shortage of conventional energy sources (Liu, 1985). At present the State and local governments take only the Yangbajain geothermal field seriously. The significant achievements in Yangbajain have certainly been made possible by a number of conditions (Wu et al., 1985): a serious lack of oil and coal, and a great difficulty in developing the Xizang hydropower resources, for which an enormous capital investment is evidently needed; hydrothermal resources are present all over the Xizang plateau, usually at relatively shallow depths and consequently more convenient for exploration and exploitation; a willingness on the part of geothermal experts from the hinterlands of China to explore this new energy resource. In addition, the scientific significance of the geothermal phenomena in Xizang Plateau is of considerable interest to many geoscientists and engineers.     

Takigami geothermal system, northeastern Kyushu, Japan

The Takigami geothermal reservoir is bounded by a system of faults and fractures oriented along two main directions, north to south and east to west. The Noine fault has a large vertical displacement and trends north to south, dividing the subsurface characteristics of resistivity, permeability, temperature and reservoir depth. The Takigami geothermal fluid has a near neutral pH and is of the Na–Cl type, with a chloride content ranging from 400 to 600 ppm. The southwestern part of the area has the highest subsurface temperature, up to 250°C. The deep fluid originates from the southwest, and flow is mainly to the north and partly to the east along faults and fractures, decreasing in temperature with increasing lateral flow.     

Geothermal energy potential and utilization in Turkey

The regional distribution of the geothermal energy potential in Turkey, recent surveys, and utilization areas are described. The present and future roles of geothermal energy and their economic aspects are discussed. The implications of geothermal energy exploration and utilization are noted. Recommendations are made to expand geothermal-energy development.