Interpretation of Geophysical Well Logs from Deep Geothermal Borehole in Pohang

포항 심부 지열 시추공에 대한 물리검층 자료해석

  • Hwang, Se-Ho (Groundwater & Geothermal Resource Division, Korea Institute of Geoscience & Mineral Resources) ;
  • Park, In-Hwa (Groundwater & Geothermal Resource Division, Korea Institute of Geoscience & Mineral Resources) ;
  • Song, Yoon-Ho (Groundwater & Geothermal Resource Division, Korea Institute of Geoscience & Mineral Resources)
  • 황세호 (한국지질자원연구원 지하수지열연구부) ;
  • 박인화 (한국지질자원연구원 지하수지열연구부) ;
  • 송윤호 (한국지질자원연구원 지하수지열연구부)
  • Published : 2007.11.30

Abstract

Various geophysical well logs have been made along the four deep wells in Pohang, Gyeongbuk. The primary focus of geophysical well loggings was to improve understanding the subsurface geologic structure, to evaluate in situ physical properties, and to estimate aquifer production zones using fluid temperature and conductivity gradient logs. Especially natural gamma logs interpreted with core logs of borehole BH-1 were useful to discriminate the lithology and to determine the lithologic sequences and boundaries consisting of semi-consolidated Tertiary sediments and intrusive rocks such as basic dyke and Cretaceous sediments. Cross-plot of physical properties inferred from geophysical well logs were used to identify rock types such as Cretaceous sandstone and mudstone, Tertiary sediments, rhyolite, and basic dyke. The temperature log indicated $82.51^{\circ}C$ at the depth of 1,981.3 meters in borehole BH-4. However, considering the temperature of borehole BH-2 measured under stable condition, we expect the temperature at the depth in borehole BH-4, if it is measured in stable condition, to be about 5 or $6^{\circ}C$ higher. Several permeable fractures also have been identified from temperature and conductivity gradient logs, and cutting logs.

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