Journal of the Geothermal Research Society of Japan
Online ISSN : 1883-5775
Print ISSN : 0388-6735
ISSN-L : 0388-6735
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Article
  • Anna SUZUKI, Ryo HASEGAWA, Shunichi HIENUKI, Hiromi KUBOTA, Takatoshi ...
    Article type: Article
    2022 Volume 44 Issue 3 Pages 111-122
    Published: July 25, 2022
    Released on J-STAGE: January 25, 2023
    JOURNAL FREE ACCESS

    Geothermal potential area in Japan has been depopulated recently, and there have been distances between the geothermal potentials and most energy consumers living in urban areas. Since 2020, working from home (home-based telework) has spread rapidly due to the influence of the COVID-19. If some of the energy consumers work from the geothermal potential area, namely onsen areas, it would help to reduce the extra fossil fuel consumption, to reduce the environmental impact, and to save commuting costs and time. In this study, we quantitatively evaluated the advantages and feasibility of working from onsen in Naruko area, Osaki City, Miyagi Prefecture, as a case study. The environmental effects were analyzed by using the annual CO2 emissions and the costs, based on the perspective of the form of stay and the life-cycle assessments with four scenario conditions ((a) base system, (b) home-based telework in a city, (c) onsen-based telework (using hot spring only for bathing), and (d) onsen-based telework (using hot spring for bathing and heating)). Compared to the base system, the use of public baths in the onsen area can reduce CO2 emissions by about 1/3, and the use of bathing and heating by hot springs can reduce CO2 emissions by about 1/4. In the case of a short-term stay in the onsen area, the effects of reducing CO2 emission differed depending on the area where the worker is based and the season. The results indicates that some conditions of the short-term stay may results in higher CO2 emission than when nothing is done. Therefore, we expect that each of urban workers, companies, and onsen areas will change their awareness and take actions to be able to stay in the onsen area for a mid- to long-term.

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Technical Report
  • Masatoshi TSUZUKI, Tetsuomi MIYAMOTO, Naoto YAMADA, Hiroshi TANAKA, Ma ...
    Article type: Technical Report
    2022 Volume 44 Issue 3 Pages 123-135
    Published: July 25, 2022
    Released on J-STAGE: January 25, 2023
    JOURNAL FREE ACCESS

    PDC bits, which are widely used in oil and gas wells, have been generally thought to be unsuitable for geothermal wells, because the formations of geothermal fields mostly consist of hard, inhomogeneous and fractured zone, and the formation temperature is expected to be higher than oil and gas wells. In this report, the damage evaluation of the PDC bit based on the IADC dull grading system is described and compared with the structural analysis. In addition, the well logging data was analyzed to clarify the condition of the drilled formations. The PDC bit demonstrated a sufficient drilling performance in the field test, in which the drilled formations had an uniaxial compressive strength of 100 MPa or higher and were inhomogeneous and fractured under total lost circulation, and the highest formation temperature was 240 °C. Compared to a supposed case where the same formations were drilled with a conventional roller cone bit, the actual drilling rate (134 m/day) was doubled and the actual drilled interval (477 m) was more than 2.5 times, and the gauge loss was 1/16 in. or less. Furthermore, a laboratory drilling test conducted after the field demonstration revealed that the PDC bit has not reached its life and is thought to be still able to drill formations with a certain drilling rate. Several design factors of PDC bits for geothermal wells were discussed on the field demonstration and it was suggested that PDC bits have sufficient applicability to geothermal wells with appropriate bit design.

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