Journal of the Geological Society of Korea (지질학회지)

The Geological Society of Korea (대한지질학회)
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Three-dimensional geologic modeling of the Pohang Basin distributed in Haedo-Dong, Nam-Gu, Pohang-Si, Korea

한국 포항시 남구 해도동 일대에 분포하는 포항분지의 삼차원 지질 모델링

  • Ahn, Hae-Sung (School of Earth and Environmental Sciences, Seoul National University) ;
  • Park, Jai-Yong (School of Earth and Environmental Sciences, Seoul National University) ;
  • Kim, Jun-Mo (School of Earth and Environmental Sciences, Seoul National University) ;
  • Kim, Jeong-Chan (Geologic Environment Research Division, Korea Institute of Geoscience and Mineral Resources)
  • 안해성 (서울대학교 지구환경과학부) ;
  • 박재용 (서울대학교 지구환경과학부) ;
  • 김준모 (서울대학교 지구환경과학부) ;
  • 김정찬 (한국지질자원연구원 지구환경연구본부)
  • Received : 2014.10.28
  • Accepted : 2015.01.28
  • Published : 2015.02.28
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Abstract

A series of three-dimensional geologic modeling is performed using a three-dimensional geologic model to characterize quantitatively and visualize realistically distributions of geologic formations and lithofacies in the Pohang Basin distributed in Haedo-Dong, Nam-Gu, Pohang-Si, Korea. First, three-dimensional structural modeling is performed using the digital elevation model (DEM) data with the geologic map, the eight borehole data with the geologic formation boundaries, and the discrete smooth interpolation (DSI) method. Second, three-dimensional grid modeling is performed based on the geologic formation boundaries of the three-dimensional structural model. Third, the three-dimensional geologic formation modeling is performed by integrating the three-dimensional structural model and three-dimensional grid model. Fourth, three-dimensional lithofacies modeling is performed for the Tertiary (Neogene Miocene) marine sediments (Hakrim Formation, Hunghae Formation, Idong Formation, Duho Formation) using the six borehole data with the lithofacies. An optimal theoretical variogram is selected through the variogram analyses, and the sequential indicator simulation (SIS) and truncated Gaussian simulation (TGS), which are kinds of conditional simulations, are then performed respectively. The results of the conditional simulations show that mudstone is overwhelmingly distributed compared with sandstone similarly to the actual deep borehole data, and sandstone has excellent extension (connectivity) in the horizontal direction rather than the vertical direction. In addition, the results of the truncated Gaussian simulation show that the distribution of sandstone and its extension in the horizontal direction is localized near the boreholes compared with those of the sequential indicator simulation. On the other hand, the results of the sequential indicator simulation are more similar to the statistical analyses results of the actual deep borehole data compared with those of the truncated Gaussian simulation. As a result, the three-dimensional lithofacies model using the sequential indicator simulation show higher reliability than that using the truncated Gaussian simulation in terms of statistics. Finally, cross validation is performed to identify the most influential borehole among the six deep boreholes. Its results show that the borehole PY-2 is most influential in the three-dimensional lithofacies modeling performed in this study. This arises because the borehole PY-2 is located closest at the center of the three-dimensional geologic modeling domain. The three-dimensional geologic modeling technology presented in this study and its results can be usefully applied in quantitative characterization and realistic visualization of deep geologic formations for energy and resources exploration, geothermal energy development, geologic radioactive waste disposal, and geologic carbon dioxide storage.

한국 포항시 남구 해도동에 분포하는 포항분지 내 지층 및 암상 분포를 정량적으로 특성화하고 사실적으로 가시화하기 위하여 삼차원 지질 모델링 기술을 이용한 일련의 삼차원 지질 모델링을 수행하였다. 첫 번째로 지표 지질도가 반영된 수치 표고 모델 자료 및 지층 경계면 정보 시추 자료 8개를 사용하여 불연속 평활 보간법을 이용한 삼차원 구조 모델링을 수행하였다. 두 번째로 삼차원 구조 모델의 지층 경계면에 기초하여 삼차원 격자 모델링을 수행하였다. 세 번째로 삼차원 구조 모델과 격자 모델을 중합하는 삼차원 지층 모델링을 수행하였다. 네 번째로 암상 정보 시추 자료 6개를 사용하여 사암과 이암이 혼재되어 있는 제3기(신신생기 마이오세) 해성 퇴적층(학림층, 흥해층, 이동층, 두호층)에 대해서만 삼차원 암상 모델링을 수행하였다. 우선 베리오그램 분석을 통하여 최적의 이론적 베리오그램을 선정하였으며, 이를 사용하여 조건부 시뮬레이션 기법의 일종인 순차 지시 시뮬레이션 및 절단 가우시안 시뮬레이션을 각각 수행하였다. 실제 대심도 시추공 자료와 마찬가지로 조건부 시뮬레이션 결과에서도 이암이 사암에 비해서 압도적으로 많이 분포하며, 사암이 수직 방향보다는 주로 수평 방향으로 우수한 연장성을 가진다. 또한 순차 지시 시뮬레이션 결과에 비해서 절단 가우시안 시뮬레이션 결과에서 사암의 분포 및 수평 방향의 연장성이 시추공 주변에서만 국한된다. 한편 절단 가우시안 시뮬레이션 결과에 비해서 순차 지시 시뮬레이션 결과가 실제 대심도 시추공 자료의 통계 분석 결과와 보다 더 유사하다. 따라서 전반적으로 순차 지시 시뮬레이션을 사용한 삼차원 암상 모델이 절단 가우시안 시뮬레이션을 사용한 삼차원 암상 모델보다 통계학적 측면에서 좀 더 높은 신뢰성을 나타낸다. 마지막으로 삼차원 암상 모델링에 사용된 6개의 대심도 시추공 중에서 영향력이 가장 큰 시추공을 파악하기 위해서 교차 검증을 수행하였다. 그 결과는 시추공 PY-2가 본 연구에서 수행된 삼차원 암상 모델링에서 가장 영향력이 큼을 보여준다. 이는 시추공 PY-2가 삼차원 지질 모델링 영역 중앙에 가장 가깝게 위치하기 때문이다. 이와 같이 본 연구를 통해서 제시된 삼차원 지질 모델링 기술과 삼차원 지질 모델링 결과들은 향후 에너지자원 탐사, 지열 에너지 개발, 방사성 폐기물 지층 처분 및 이산화탄소 지중 저장 등의 목적으로 심부 지층을 정량적으로 특성화하고 사실적으로 가시화하는 데에 매우 유용하게 활용될 수 있을 것으로 기대된다.

Keywords

Acknowledgement

Supported by : 한국에너지기술평가원, 한국연구재단

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