Tunnel and Underground Space (터널과지하공간)

Korean Society for Rock Mechanics and Rock Engineering (한국암반공학회)
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Report on Extended Leak-Off Test Conducted During Drilling Large Diameter Borehole

국내 대구경 시추공 굴진 중 Extended Leak-Off Test 수행 사례 보고

  • Jo, Yeonguk (Deep Subsurface Storage and Disposal Research Center, Geology Division, Korea Institute of Geoscience and Mineral Resources) ;
  • Song, Yoonho (Deep Subsurface Storage and Disposal Research Center, Geology Division, Korea Institute of Geoscience and Mineral Resources) ;
  • Park, Sehyeok (Deep Subsurface Storage and Disposal Research Center, Geology Division, Korea Institute of Geoscience and Mineral Resources) ;
  • Kim, Myung Sun (Deep Subsurface Storage and Disposal Research Center, Geology Division, Korea Institute of Geoscience and Mineral Resources) ;
  • Park, In-Hwa (Deep Subsurface Storage and Disposal Research Center, Geology Division, Korea Institute of Geoscience and Mineral Resources) ;
  • Lee, Changhyun (Deep Subsurface Storage and Disposal Research Center, Geology Division, Korea Institute of Geoscience and Mineral Resources)
  • 조영욱 (한국지질자원연구원 국토지질연구본부 심층처분환경연구센터) ;
  • 송윤호 (한국지질자원연구원 국토지질연구본부 심층처분환경연구센터) ;
  • 박세혁 (한국지질자원연구원 국토지질연구본부 심층처분환경연구센터) ;
  • 김명선 (한국지질자원연구원 국토지질연구본부 심층처분환경연구센터) ;
  • 박인화 (한국지질자원연구원 국토지질연구본부 심층처분환경연구센터) ;
  • 이창현 (한국지질자원연구원 국토지질연구본부 심층처분환경연구센터)
  • Received : 2022.09.26
  • Accepted : 2022.10.17
  • Published : 2022.10.31
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Abstract

We report results of Extended Leak-Off Test (XLOT) conducted in a large diameter borehole, which is drilled for installation of deep borehole geophysical monitoring system to monitor micro-earthquakes and fault behavior of major fault zones in the southeastern Korean Peninsula. The borehole was planned to secure a final diameter of 200 mm (or more) at a depth of ~1 km, with 12" diameter wellbore to intermediate depths, and 7-7/8" (~200 mm) to the bottom hole depth. We drilled first the 12" borehole to approximately 504 m deep and installed American Petroleum Institute standard 8-5/8" casing, then annulus between the casing and bedrock was fully cemented. XLOT was carried out for several purposes such as confirming casing and cementing integrity, measuring rock stress states. To that end, we drilled additional 4 m long open hole interval to directly inject water and pressurize into the rock mass using the upper API casings. During the XLOT, flow rates and interval pressures were recorded in real time. Based on the logs we tried to analyze hydraulic conductivity of the test interval.

본 고에서는 한반도 동남권에 분포하는 주요 단층대에 대한 장기 거동 및 미소진동 관찰을 목적으로 하는 시추공 기반 심부 복합지구물리 모니터링 시스템 구축의 일환으로 수행된 대구경 시추공 굴착 현장에서 이루어진 Extended Leak-Off Test (XLOT)에 대한 내용 및 결과를 보고한다. 다양한 시추공 센서 설치를 위한 모니터링공의 굴착은 ~1 km 깊이에서 최종 구경 200 mm 이상을 확보하는 것을 목표로 하여, 중간 깊이까지 12" 구경의 시추공 굴진 및 케이싱 설치, 이후 최종 심도까지 7-7/8" 구경의 시추공을 굴진하는 것으로 설계되었다. 현장 여건에 맞추어 약 504 m 깊이까지 12" 구경의 시추공이 굴착되었으며, API 규격의 8-5/8" 케이싱을 설치하고 배면과 암반 간의 틈새(annulus)에 대한 세멘팅 작업을 수행하였다. 이후 하부 구간 굴진(7-7/8")에 앞서 세멘팅 건정성 확인 및 암반 응력 측정 등을 목적으로 XLOT를 수행하였다. 약 4 m 길이의 나공 구간(open hole)을 확보하고, 상부에 설치된 케이싱을 이용해 물을 주입하여 시험 심도의 암반을 가압하였다. XLOT 수행 과정에서 주입 유량에 따른 시험 구간 내 압력 변화 양상을 실시간 모니터링 하였으며, 이 자료들을 일부 활용하여 현장 시추공 조건에서의 암반 투수율을 해석하였다.

Keywords

Acknowledgement

본 연구는 한국지질자원연구원 기본사업 '한반도 동남권 지진·단층 활동 평가를 위한 심부 복합지구물리 모니터링 시스템 구축' 과제(GP2018-009)의 일환으로 작성되었음을 밝힌다. 현장 시험 준비 및 수행 과정에 도움을 주신 동남권 심부 복합지구물리 관측소 구축 용역 사업 (주)테라이지-(주)어스이엔지 컨소시엄 및 연구원 내외 관계자들께 감사드린다.

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