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Now showing items 1 - 16 of 22

  • Developing the geothermal resources map of Iran

    Yousefi, Hossein   Noorollahi, Younes   Ehara, Sachio   Itoi, Ryuichi   Yousefi, Amin   Fujimitsu, Yasuhiro   Nishijima, Jun   Sasaki, Kyuro  

    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. (C) 2009 Elsevier Ltd. All rights reserved.
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  • Numerical model of the hydrothermal system beneath Unzen Volcano, Japan

    Fujimitsu, Yasuhiro   Ehara, Sachio   Oki, Ryosuke   Kanou, Ryohei  

    Drilling of the volcanic conduit in the Unzen Scientific Drilling Project (USDP) was completed in 2004. Some conduit materials of the 1990-95 eruption were encountered at the bottom of Well USDP-4 (150 m below sea level), and a bottom temperature of about 200 degrees C was estimated using logging data, although before drilling a temperature of about 700 degrees C had been inferred. Accordingly, conduit cooling from the initial temperature (850 degrees C) to the estimated temperature (about 200 degrees C) was evaluated by numerical simulation. The drilling provides constraints for the numerical model. The drilling indicates that the N-S width of the conduit of the latest eruption is 20 to 30 m and that it occupies a zone of about 300 m, which includes conduits of past eruptions. The process of cooling in the conduit, from an initial temperature of 850 degrees C in 1995 (the end of the eruption) to 200 degrees C in 2004 (completion of the conduit drilling), was replicated in models with permeabilities of I and 10 mdarcys. This result demonstrates that a highly permeable volcanic body surrounding a small conduit is required to explain the estimated bottom temperature. Our study also aimed to use a numerical simulation to construct a comprehensive hydrothermal model beneath Unzen Volcano. There are four large geothermal systems in the Shimabara Peninsula (Obama hot springs, Unzen fumarolic field, Shimabara hot springs and the West Unzen High Temperature Body [WUHTB]). Three pressure sources ("Sources A", "B" and "C" from shallow to the deep) were determined by geodetic data during the 1990-95 eruption. Source C is located at about 8 km deep at WUHTB, and is considered to be a magma body. We attempted to explain the existence of the four geothermal systems from the large-scale structures (the topography of the Shimabara Peninsula and Unzen Graben) and the various heat sources. We first set a heat source around Source C and changed its position and size. This numerical model produced the upflow zones at the Obama and Shimabara hot springs and WUHTB; however, the Unzen fumarolic field became a recharge area. This result indicates that another heat source is required to explain the Unzen fumarolic field and that two heat sources beneath WUHTB and the Unzen fumarolic field are involved in the formation of the four hydrothermal systems in the Shimabara Peninsula. (C) 2008 Elsevier B.V. All rights reserved.
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  • Evaluation of subsurface thermal environmental change caused by a ground-coupled heat pump system

    Fujimitsu, Yasuhiro   Fukuoka, Koichiro   Ehara, Sachio   Takeshita, Hiroto   Abe, Fuminori  

    The authors have been conducting demonstration and performance assessment of the ground-coupled hear pump (GCHP) system optimized for the air conditioning system of an experimental house in the artificial island in Fukuoka City, Japan, since 2005 to evaluate the subsurface thermal environmental changes caused by heat exchange with the ground The authors monitored the underground temperature and groundwater level in some observation wells around the heat exchanging well, and performed numerical simulation of the underground temperature change with a groundwater simulator "FEFLOW" The simulation result for a 20-year operation by using the numerical model, which had replicated the measured heat exchange rate during the 40-day heating operation from 15 December 2006, predicted that the cumulative increase or decrease of subsurface temperature will not be seen Therefore, it is thought that there is little impact to the subsurface thermal environment around this GCHP system (C) 2009 Elsevier B V All rights reserved
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  • Geological and engineering features of developing ultra-high-temperature geothermal systems in the world

    Okamoto, Kyosuke   Asanuma, Hiroshi   Ishibashi, Takuya   Yamaya, Yusuke   Saishu, Hanae   Yanagisawa, Norio   Mogi, Toru   Tsuchiya, Noriyoshi   Okamoto, Atsushi   Naganawa, Shigemi   Ogawa, Yasuo   Ishitsuka, Kazuya   Fujimitsu, Yasuhiro   Kitamura, Keigo   Kajiwara, Tatsuya   Horimoto, Seiki   Shimada, Kuniaki  

    It has been suggested that a large amount of crustal fluid is trapped at a supercritical state within intrusive rocks beneath volcanoes or calderas near the mountain ranges of northeastern Japan. If we could extract and use these crustal fluids, we could expect to achieve a high level of energy productivity. We have collated field data on high-temperature geothermal areas of the world, used these to produce simple models of their geothermal systems, and then explored their features in terms of the amount of potential power generation. For example, a potential of around 0.1 GW per reservoir over 30 years is expected in northeastern Japan if we consider supercritical reservoirs extending to a 5 km depth.
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  • Analysis of gravity data to delineate structural features controlling the Eburru geothermal system in Kenya

    Maithya, Justus   Fujimitsu, Yasuhiro   Nishijima, Jun  

    The gravity modeling of the Eburru was conducted in an attempt to delineate geological structures controlling the geothermal system and estimate the geothermal reservoir extent. A total of 375 data points were used and a Bouguer density of 2.27 g/cm(3) to generate a complete Bouguer anomaly map of the area. Gravity data were separated into regional and residual components to enhance the structural features from the sedimentary and basement rocks in the study area. The gravity data were analyzed using gradient interpretation techniques for edge detection, such as horizontal derivative and an improved normalized horizontal tilt angle. For carrying out the three-dimensional (3-D) modeling, a volume of 12 x 13 km and 5 km deep was selected. The model was constrained using the estimated densities of cuttings obtained from the drilled wells. This study presents the interpretation results of various gravity anomaly maps and 3-D inversion model. Interpretation of horizontal derivative and improved normalized horizontal tilt angle of gravity data indicate the existence of high gradient anomalies. The anomaly maps were used to identify several faults that compared well with the mapped faults. The 3-D model revealed a dense body interpreted as the geothermal reservoir with a volume of about 3.0 km(3) and an average block density value of 2.45 g/cm(3). The dense body which is a fractured zone overlies a high density body likely to be the heat source responsible for heating the reservoir. There appears to be a close relationship between the faults system and the geothermal reservoir. These faults serve as fluid pathways from deeper parts to shallow regions. The results obtained from this study will lead to an improved understanding of the geothermal system in the study area and aid the future geothermal exploration of the field.
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  • Monitoring Hot Spring Aquifer Using Repeat Hybrid Micro-gravity Measurements in Beppu Geothermal Field,Japan

    Naritomi, Kento   Sofyan, Yayan   Ohsawa, Shinji   Fujimitsu, Yasuhiro  

    Repeat hybrid micro-gravity measurements were conducted to detect the gravity change caused by hot spring water production around Beppu in eastern Kyushu, Japan. An A10 #017 absolute gravimeter (Micro-g LaCoste) and a CG-5 #549 gravimeter (Scintrex) were used for this study in intervals of three to four months at eight gravity stations. According to the results obtained with the absolute gravimetry, a gravity change of up to 33 mu gal was detected at the Beppu Geothermal Research Laboratory (BGRL) reference station. The observed absolute gravity was compared with the groundwater level, and there was a good correlation between the gravity changes and the groundwater level changes. Based on the precipitation, groundwater level, and soil character, the effect of the water content changes in the unsaturated zone was estimated precisely by using a Gwater-1D. This calculation can explain that the gravity seasonal changes were caused by the groundwater level changes. After removal of noise effects (e.g., tidal movement, precipitation, and shallow groundwater level changes), the residual gravity changes, which were measured by the relative gravimeter, were subdivided into two types of responses. Gravity changes up to 90 mu gal were observed from April 2014 to July 2015. After that, gravity became stable, except for small seasonal changes.
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  • Monitoring Thermal Activity of the Beppu Geothermal Area in Japan Using Multisource Satellite Thermal Infrared Data

    Mia, Md. Bodruddoza   Fujimitsu, Yasuhiro   Nishijima, Jun  

    The Beppu geothermal area, one of the largest spa resorts on the northeast Kyushu Island of Japan, is fed by hydrothermal fluids beneath the volcanic center of Mt. Garan and Mt. Tsurumi in the west. We explored the thermal status of the Beppu geothermal area using nighttime multisource satellite thermal infrared data (TIR) from the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) and Landsat 8 thermal infrared scanner (TIRS) to monitor heat loss from 2009 to 2017. We also assessed heat loss from Mt. Garan fumaroles to investigate a relationship between them. The normalized differential vegetation index (NDVI) threshold method of spectral emissivity, the split-window algorithm for land surface temperature (LST), and the Stefan-Boltzmann equation for radiative heat flux (RHF) were used to estimate heat loss in this study. Total heat loss increased by about a 35% trend overall from 2009 to 2015 and then declined about 33-42% in 2017 in both the Beppu geothermal area and Mt. Garan fumaroles overall. The higher thermal anomalies were found in 2015 mostly in the southeastern coastal area of the Beppu geothermal region. The highest thermal anomaly was obtained in 2011 and the lowest in 2017 within the Mt. Garan fumaroles. The areas with a higher range of RHF values were recorded in 2015 in both study areas. Finally, the results show similar patterns of heat loss and thermal anomalies in both the Beppu geothermal area and Mt. Garan fumaroles, indicating a closely connected geothermal system overall. This suggests that nighttime TIR data are effective for monitoring the thermal status of the Beppu geothermal area.
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  • Monitoring Thermal Activity of the Beppu Geothermal Area in Japan Using Multisource Satellite Thermal Infrared Data

    Mia, Md.   Fujimitsu, Yasuhiro   Nishijima, Jun  

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  • Mapping hydrothermal altered mineral deposits using Landsat 7 ETM+ image in and around Kuju volcano, Kyushu, Japan

    Mia, Md Bodruddoza   Fujimitsu, Yasuhiro  

    To evaluate the conventional methods for mapping hydrothermal altered deposits by using Landsat 7 ETM+ image in and around Kuju volcano is the prime target of our study. The Kuju volcano is a mountainous composite which consists of hornblende-andesite lava domes and associated lava flows. We used the colour composite, band ratio, principal component analysis, least square fitting and reference spectra analysis methods. The colour composite and band ratio methods showed very clearly the hydrothermal altered deposits of clay minerals, iron oxides and ferric oxides around the fumaroles. The principal component analysis using the Crosta technique also enabled us to represent undoubtedly the altered hydroxyl and iron-oxide mineral deposits of this region concentrating around the fumaroles. Least square fitting method illustrated the goethite, hematite and clay alteration region. Finally the target detection method for reference spectral analysis by using ENVI 4.3 detected the representative hydrothermal altered minerals around Kuju volcano fumaroles area. Therefore, all the methods showed high efficiency for mapping hydrothermal altered deposits especially iron-oxide minerals such as hematite, goethite and jarosite, which are alteration products of hydrothermal sulfides around the fumaroles.
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  • Monitoring heat losses using Landsat ETM plus thermal infrared data - a case study at Kuju fumarolic area in Japan

    Mia, Md. Bodruddoza   Fujimitsu, Yasuhiro  

    To monitor heat losses using Landsat 7 thermal infrared data from 2002 to 2010 within the active fumarolic region of Kuju volcano in Japan, we used the Stefan-Boltzmann equation for radiative heat flux (RHF) estimation. Heat discharge rate (HDR) was calculated by using the relationship coefficient of RHF and HDR, obtained from two previous studies. The highest total RHF was found to be about 57.7 MW in 2002 and the lowest was about 21.1 MW in 2010. We found the highest HDR, of about 384.5 MW, in 2002 and the lowest, of about 140.8 MW, in 2010. The RHF anomalous areas were showing a declining trend during our study period. The relationship between the land surface temperature (LST) above ambient and RHF was, as expected, in a strong correlation for each result during our study period. Overall, our study was able to delineate the declining trend of heat losses that supports a previous study of similar declining trend of HDR using steam maximum diameter method from the active fumarolic region of Kuju volcano.
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  • Analysis and interpretation of magnetotelluric data in characterization of geothermal resource in Eburru geothermal field,Kenya

    Maithya, Justus   Fujimitsu, Yasuhiro  

    The magnetotelluric method (MT) is an essential geophysical method for the exploration of geothermal systems. In this study, the MT method was used to assess the extent of the geothermal resource in Eburru geothermal field, Kenya, with the aim of delineating the electrical conductivity structure of the area. Dimensionality analyses demonstrated that the MT data could be interpreted using two-dimensional approaches, but some localized 3-D effects were detected. A 2-D MT inversion was performed to generate resistivity models of Eburru geothermal field. Given its ability to recover complex resistivity models for the ground, three dimensional (3-D) MT inversion was also carried out, and a joint interpretation made from the 2-D and 3-D models. Both inversion approaches gave similar results and revealed a low resistivity layer (< 10 Omega m) interpreted as clay cap, and an intermediate resistivity beneath interpreted as a geothermal reservoir immediately below the low resistivity. The sequence here infers the presence of geological structures controlling the geothermal system. The resistivity profiles analyzed revealed a structure of low resistivity (< 10 Omega m) interpreted as the fluid pathway. This structure trend an S-N direction which is consistent with the faults orientation in the field and serves as a conducting channel for transporting heat from the heat source to the shallow region approximately 2 km above sea level.
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  • Analysis and interpretation of magnetotelluric data in characterization of geothermal resource in Eburru geothermal field, Kenya

    Maithya, Justus   Fujimitsu, Yasuhiro  

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  • Monitoring Heat Losses Using Landsat ETM plus Thermal Infrared Data: a Case Study in Unzen Geothermal Field, Kyushu, Japan

    Mia, Md. Bodruddoza   Bromley, Chris J.   Fujimitsu, Yasuhiro  

    The Unzen geothermal field, our study area, is situated in the Shimabara Peninsula of Kyushu Island in Japan and is an area of active fumaroles.. Our prime objectives were (1) to estimate radiative heat flux (RHF), (2) to calculate approximately the heat discharge rate (HDR) using the relationship of RHF with the total heat loss derived from two geothermal field studies, and (3) finally, to monitor RHF as well as HDR in our study area using seven sets of Landsat 7 ETM + images from 2000 to 2009. We used the normalized differential vegetation index (NDVI) method for spectral emissivity estimation, the mono-window algorithm for land surface temperature (LST), and the Stefan-Boltzmann equation analyzing those satellite TIR images for RHF. We estimated that the maximum RHF was about 251 W/m(2) in 2005 and minimum was about 27 W/m(2) in 2001. The highest total RHF was about 39.1 MW in 2005 and lowest was about 12 MW in 2001 in our study region. We discovered that the estimated RHF was about 15.7 % of HDR from our studies. We applied this percentage to estimate HDR in Unzen geothermal area. The monitoring results showed a single fold trend of HDR from 2000 to 2009 with highest about 252 MW in 2005 and lowest about 78 MW in 2001. In conclusion, TIR remote sensing is thought as the best option for monitoring heat losses from fumaroles with high efficiency and low cost.
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  • Estimation and monitoring heat discharge rates using Landsat ETM+ thermal infrared data: a case study in Unzen geothermal field, Kyushu, Japan

    Mia, Md. Bodruddoza   Fujimitsu, Yasuhiro   Bromley, Chris J.  

    The Unzen geothermal field, our study area is active fumaroles, situated in Shimabara Peninsula of Kyushu Island in Japan. Our prime objectives were (1) to estimate radiative heat flux (RHF), (2) to calculate approximately heat discharge rate (HDR) using the relationship of radiative heat flux with the total heat loss derived from two geothermal field studies and (3) finally, to monitor RHF as well as HDR in our study area using seven sets of Landsat 7 ETM+ images from 2000 to 2009. We used the NDVI (Normalized differential vegetation index) method for spectral emissivity estimation, the mono-window algorithm for land surface temperature (LST) and the Stefan-Boltzmann equation analyzing those satellite TIR images for RHF. We obtained a desired strong correlation of LST above ambient with RHF using random samples. We estimated that the maximum RHF was about 251 W/m(2) in 2005 and minimum was about 27 W/m(2) in 2001. The highest total RHF was about 39.1 MW in 2005 and lowest was about 12 MW in 2001 in our study region. We discovered that the estimated RHF was about 15.7 % of HDR from our studies. We applied this percentage to estimate heat discharge rate in Unzen geothermal area. The monitoring results showed a single fold trend of HDR from 2000 to 2009 with highest about 252 MW in 2005 and lowest about 78 MW in 2001. In conclusion, TIR remote sensing is thought as the best option for monitoring heat losses from fumaroles with high efficiency and low cost.
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  • Geological structures controlling the placement and geometry of heat sources within the Menengai geothermal field,Kenya as evidenced by gravity study

    Kanda, Isaack   Fujimitsu, Yasuhiro   Nishijima, Jun  

    Menengai volcano is one of the late Quaternary caldera volcanoes formed on a massive shield in the inner-trough of the Kenya rift valley, associated with a high thermal gradient resulting from shallow magmatic intrusion. While drilling of geothermal wells in Menengai area proved the existence of exploitable steam, the complexity of its geological setup has led to various technical setbacks where sited well targets turned out to be unproductive. These challenges were attributed partly to the lack of adequate knowledge to delineate the depth and lateral extent of heat sources. The present work attempts to understand the geological structures that appear control the placement and geometry of heat sources within the Menengai geothermal field. This study utilizes the sensitivity of gravity data to deep structures resolution to determine a three-dimensional (3-D) inversion model. A total of 1823 gravity points were used in generating the Bouguer anomaly, using a Bouguer density of 2.23 g/cm(3). The model was constrained using estimated densities of drill hole cutting recovered from the geothermal wells. The resultant model was then interpreted together with surface manifestations, geology, and geological structures. Lineament structures were extracted from satellite images and used to enrich the geological structures. The model showed a close relationship between faults and inferred geometry of subsurface volcanic complexes displayed as discrete dike-like bodies in the near-surface environment. The structural system controlling the extent of the dense trachytic body of Olrongai is distinct, but for the caldera, some inference can be made from the results of this study. These faults are interpreted as the feeder dikes of the dense syenitic intrusives, that are hosted within the trachytic formation, and believed to be the heat source for the geothermal system. These structures act as conduits of magma to shallow levels, supplying the much-needed heat to the geothermal reservoir.
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  • Geological structures controlling the placement and geometry of heat sources within the Menengai geothermal field, Kenya as evidenced by gravity study

    Kanda, Isaack   Fujimitsu, Yasuhiro   Nishijima, Jun  

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