Building 3D solid models of sedimentary stratigraphic systems from borehole data: An automatic method and case studies

3D solid models of geological structures are particularly useful to practical geological analysis and engineering design. The main difficulty raised by 3D geological modeling of sedimentary system is determining the geological genesis and geometrical boundaries of missing strata. For the lack of the comprehensive mechanism to handle missing strata, it is difficult to construct spatial geometric shapes of complicated strata with a desired accuracy in 3D utilizing the existing modeling methods. This situation limits the reliability and the practicality of the computer models. In order to construct the discontinuous geological surfaces induced by missing strata, an adapted and automatic approach for generating 3D solid models of sedimentary stratigraphic systems from borehole data, called the Borehole-Surface-Solid method, is presented. The method first utilizes the topologic dimidiate data structure to discretize borehole data into a series of scatter points, then interpolates the initial elevations of the top and bottom surfaces for each stratum, and automatically deduces the genesis of the missing strata. Subsequently, according to different geological genesis, surfaces intersecting, elevations adjusting and consistency processing are performed automatically on the missing strata's surfaces and their control surfaces. And finally, the solid model filled with 3D blocks or triangular prism meshes is built. The Borehole-Surface-Solid method has higher automaticity and stronger adaptability, and overcomes limitations of the existing modeling methods. Two concrete examples of using this method to Shanghai's construction projects show that the resulting models are natural, geologically reasonable and close to the actual stratigraphic distribution. In addition, during the implementing process, the geological laws, such as the different genesis controlling the spatial geometry of the missing strata, are converted skillfully into modeling rules that can be identified and programmed automatically by modelers, and this is helpful to promote further study on 3D modeling techniques for complex geological structures.