Abstract
Three dimensional (3D) geological model is frequently used to represent the geological conditions of the subsurface. The generalized triangular prism (GTP) model designed for borehole sampling data is a spatial data model that could retain the internal connection between the three adjacent boreholes and distinguish between the bedding and cross-bedding directions, which is proper for accurate 3D geological modeling. The traditional building method cannot consider two factors: the borehole distance is usually longer than the stratigraphic thickness, and the top and the bottom surface have different accuracy at the same time. In this study, we describe the new interpolation method for the GTP 3D geological model to improve the model accuracy with sparse borehole data. Firstly, definition and calculation method of the GTP model smoothness are proposed to measure the model smoothness and accuracy degree, which are used to decide whether the GTP voxel requires interpolation. Secondly, the virtual borehole design and calculation method for the GTP voxel subdivision in terms of the GTP geometric smoothness are discussed in detail. Finally, the GTP adaptive interpolation can be performed through the GTP voxel subdivision and the geometric optimization rebuilding. This method could adaptively interpolate the existing GTP model by local updating without changing the GTP model structure, it has high efficiency compared to the classical method. In addition, the feasibility and accuracy of this method could be proven by the actual case. The study will provide a new and reliable interpolation method for the GTP model, and it is also conducive to economic geology related research.
Highlights
Because of the core problem with 3D geological modeling, the researchers have carried out many works in the fields (Mansouri et al, 2015; Hillier et al, 2021)
The generalized triangular prism (GTP) voxel is specially designed for borehole geological structures, and the stratigraphic geological model could be directly built with borehole data (Wang et al, 2015); it could retain the internal connection between the three adjacent boreholes and distinguish between the bedding and crossbedding directions
GTP interpolation approaches for improving model accuracy must be studied urgently, as the lack of an appropriate approach limits the widespread application of the GTP modeling method
Summary
The development of human activities in underground spaces has gradually intensified. A method of building a GTP voxel geological model with complex geological structures (faults, folds, lenses, and missing stratum) was proposed for a variety of solutions, and others studied the addition of virtual borehole method (Che et al, 2006) Based on these previous work, the GTP voxel could be extended from expressing geometric shapes to expressing the property field in the geological body for 4D geological interpolation (Glynn et al, 2011; Wang et al, 2017). The calculation method to measure the GTP model smoothness is designed, and it could complete the adaptive interpolation process according to the smoothness conditions, the virtual boreholes need to be added at the locations where the changes are nonsmooth, the model is optimized and rebuilt the entire automated interpolation process is rebuilt to obtain a refined GTP geological model This will be an important extension and supplement to the existing method, the proposed method is expected to expand the application scope of and expression accuracy of the GTP method, which will provide new theories and technical methods for 3D geological modeling. An example is taken to prove the method accuracy and reliability
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