Journal of the Geothermal Research Society of Japan
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Volume 26 , Issue 1
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  • Hiroaki NIITSUMA
    Volume 26 (2004) Issue 1 Pages 1-10
    Released: August 07, 2009
    JOURNALS FREE ACCESS
    This paper presents a concept of “EIMY; Energy In My Yard”, which proposes that local energy demands should be met from an optimum combination of local, renewable sources to the maximum degree that technical and economic considerations permit. Shortfalls and surpluses in local energy production would be accommodated through an interface with the national grid. The various kinds of renewable energy could play within the EIMY framework, according to their nature, ubiquity, and capacity. Integrated renewable energy systems have considerable advantage over independent utilization of renewable resources. A computer simulation for a rural area in Japan shows that an integrated renewable energy system with an optimum combination of resources can decrease not only CO2 emission but also the cost, even though the installation and operating costs were assigned at current market rates, without weighting for advantages such as low CO2 emission in the simulation. Problems to realize EIMY are also discussed.
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  • Tetsuya SHOJI
    Volume 26 (2004) Issue 1 Pages 11-24
    Released: August 07, 2009
    JOURNALS FREE ACCESS
    Temperature data in the Yanaidzu-Nishiyama geothermal field have been analyzed statistically in order to reveal general trends of temperature profiles and to estimate deep level temperatures from shallow level temperature profiles. Applied regression functions are (1)T=T0+b·√d+c·d(3-coefficient power function), (2)T=T0+b·√d-d0+c·(d-d0)(4-coefficient power function), (3) T = T∞ [1- exp { - b (d-d0) }] (exponential function), and (4) T = T0 + b·1n (d-d0) (logarithmic function), where d is depth, T is temperature, and b, c, d0 and T0 (and T∞) are constants. Equation (2) is the best for regression of the total data of each well, but the worst for estimation of deep level temperatures. In contrast, Equation (4) is the best for the estimation, though the advantage is small for Equations (1) and (3). This fact suggests that these three functions are applicable for reducing a general trend when geostatistics is applied for underground temperatures. It is possible to estimate temperatures ahead 500 m and 1000 m within errors of 50°C and 100°C, respectively, when Equation (4) is applied for temperature data more than 500 m in depth.
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  • Hisashi JOTAKI, Keisuke USHIJIMA
    Volume 26 (2004) Issue 1 Pages 25-38
    Released: August 07, 2009
    JOURNALS FREE ACCESS
    Directional drilling is an important technology to explore and develop for geothermal energy and many geothermal wells are completed by directional drilling at Takigami geothermal field. Especially, many directional wells of the No. 2 reinjection site are drilled for the E.W fault from an early stage of exploration to a development and an operation stage. This paper reports the optimization of well casing program and directional drilling technique based on geological and drilling data analysis of each stage. At Takigami geothermal field, the conventional directional drilling technique (a combination of magnetic single shot survey and Low-torque Down Hole Motor) was applied for directional wells in exploration stage before 1990. On the other hands, the steerable drilling technique (a combination of MWD and High-torque Steerable Down Hole Motor) became widespread in geothermal fields after 1994 and this technique was applied for directional wells during a development and an operation stage. The steerable drilling produces an accurate directional control of a well trajectory and a long deviated directional well. Moreover, the steerable drilling shortens drilling progress by reducing directional survey time and increasing penetration rate in comparison with the conventional directional drilling. Finally, the cost reduction of drilling operation is achieved by the steerable drilling at Takigami geothermal field.
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  • Hikari FUJII, Takashi ISHIKAMI, Kazuo OHSHIMA, Yasushi KANEKO
    Volume 26 (2004) Issue 1 Pages 39-57
    Released: August 07, 2009
    JOURNALS FREE ACCESS
    In this paper, snow-melting tests and numerical simulations were conducted to develop the procedures in improving the designs and operating conditions of snow-melting systems using Ground-Coupled Heat Pump (GCHP) systems. Snow-melting tests, conducted in Akita City, Japan, showed the improvement of snow-melting efficiencies with the use of thermal-conductive sand between the interlocking blocks on the surface of pavements and the snow-melting pipes for circulating heat medium. A 3D numerical simulation model was developed for the prediction of temperature behavior in the snow-melting sites. The 3D numerical simulation model was combined with temperature behavior prediction model of heat exchange wells and the performance curves of heat pumps to develop a snow-melting systems model. Optimization calculations were conducted using the snow-melting system model to improve snow-melting efficiencies, while minimizing total power consumption of the system.
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