Three-Dimensional Geologic Modeling Of The Pohang Basin Distributed In Haedo-Dong, Nam-Gu, Pohang-Si, Korea

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.