Three-dimensional geological modeling

With the increasing demand for resources around the world and the increasing attention paid to geological and environmental problems, research institutions in various countries gradually turn their attention to improving resource support capacity and alleviating environmental pressure, which requires a more detailed and better understanding of underground space. It is this growing social demand and the remarkable technological progress in geographic information system (GIS), digital mapping, data storage and analysis, and visualization technology that directly promotes the transformation from traditional two-dimensional geological mapping to three-dimensional geological mapping (also known as three-dimensional geological modeling).

Three-dimensional geological map is an extension of traditional two-dimensional geological map to three-dimensional. These maps can describe the depth, thickness and material properties of underground superimposed strata in three-dimensional space. The output result is a fully attributed and digitized 3D model created through geological interpretation and strict application of original data, geological knowledge and statistical methods.

Two-dimensional and three-dimensional output results are classified according to similar geological structural units, and presented according to a certain proportion and resolution for specific purposes and the needs of related institutions. The three-dimensional geological model completed by three-dimensional mapping can provide information for customers who need to solve geoscience problems, because: ① the completed three-dimensional geological map can explain and describe complex geological conditions in an understandable format and various map views; (2) When new information is available, various derivative diagrams or explanatory diagrams can be made and updated; ③ According to the specific needs of the earth resource information, publish and customize it according to the needs of customers (Berg et al., 20 1 1).

Second, the scope of application and application examples

At present, scientists of USGS use 3D/4D tools to do the following work: ① Visualize and interpret geological information; ② Verify the data; ③ Verify their explanations and models. Examples of three-dimensional geological mapping include the description of underground space oriented to resource evaluation, such as the description of aquifers in the central United States, and the input parameters of process models, such as earthquakes in the western United States. At the same time, USGS hopes to expand its 3D/4D processing capacity by developing new 3D/4D tools and frameworks and improving and using existing technologies more effectively, so as to monitor, interpret and distribute natural resource information.

Geological Survey of Canada has integrated 3D geological mapping into all its work. However, the demand for three-dimensional geological mapping in groundwater research has not completely changed from the traditional geological survey. The concept of basin analysis is the basis of three-dimensional geological mapping by Canadian Geological Survey. Under this framework, the work focuses on data collection and understanding of the geological history of the basin. Basin analysis has been used as a commonly used three-dimensional research method in groundwater research projects. Subsequent data processing, interpolation and visualization in GIS software still depend on the complexity of geography and geology, research objectives and needs.

The three-dimensional geological model of the British Geological Survey is called LithoFrame. It represents the extension of geological map from 2D to 3D (table 1). The core of the concept of LithoFrame is that models with different resolutions correspond to each other, forming a seamless transition from a general national model to a detailed field model.

Table 1 Main characteristics of lithograph resolution

Note: the scale of lithofarame:1m is 1: 1 ten thousand; 250 is1:250,000; 50 is1:50000; 10 is1:10,000.

The three-dimensional modeling of the French Geological Survey mainly involves three areas: public services, international cooperation projects and scientific research activities carried out in cooperation with many partners and customers:

1) Public services: EU, French-speaking countries, regional governments and city authorities;

2) International projects: private companies and foreign governments;

3) Research: laboratories and cooperative universities.

The main application fields of three-dimensional modeling activities of the French Geological Survey are geological survey, aquifer protection and management, urban geology, earthquake risk assessment, civil engineering, carbon capture and storage research, geothermal potential, mineral resources exploitation and post-harvest assessment.

ArcGIS, Gocad, EarthVision, 3D GeoModeller, GI3D, Multilayer-GDM and Banlangen are the most commonly used software packages for foreign geological survey institutions to create 3D geological maps and models. Among them, GSI3 D, 3D GeoModeller and Multilayer-GDM were developed by geological survey institutions and customized according to their geological mapping and modeling requirements. Many other software packages are also used in some modeling workflows of geological survey institutions, including GIS, statistical analysis, seismic depth conversion, visualization and attribute modeling software.

Three. sources of information

Berg R C, Mathers S J, etc. Overview of 3D geological mapping and modeling in current geological survey institutions. Notice of Illinois Geological Survey, 104