Cartographic modeling of discontinuous layered geological bodies

If the dip angle of the fault is large and the plane structure of the stratum interface in the modeling range is similar, the mapping modeling method can also be used. The idea of mapping modeling of discontinuous layered geological bodies is as follows: firstly, draw fault tracks on a group of parallel horizontal sections, and divide each fault track into two tracks corresponding to the upper and lower walls; Select one from the horizontal section group as the standard section, and divide the standard section into triangular or quadrilateral grids with the constraints of fault trajectory and boundary line to form a standard plane grid; Taking the boundary lines and fault lines on other horizontal sections as constraints, the standard plane grids are mapped to other horizontal sections to obtain several horizontal section grids with the same grid structure. Connect the corresponding nodes on all adjacent horizontal cross-section grids with line segments to form a node trajectory network; According to the fault cutting situation, the original stratigraphic interface is simulated in each block, and the intersection operation between the node trace network and the original stratigraphic interface is carried out to generate the stratigraphic interface; The fault traces on the interface of adjacent strata are connected with the corresponding nodes on the boundary line to form strata, and several strata form a solid model. The specific steps are as follows:

(1) Select a group of horizontal geological sections with different elevations, draw fault traces respectively, and connect the traces of the same fault on adjacent sections to form a fault interface.

(2) Select a standard horizontal geological section, and triangulate or quadrangle it with fault trace and boundary line as constraints to form a standard plane grid.

(3) Using the plane mapping deformation method, one section in the horizontal geological section group is selected in turn, and the standard plane grid is deformed with the fault trace and boundary line of the section as constraints to form the plane grid of the section. In this way, a group of horizontal geological sections with the same grid structure and reflecting the fault trajectory can be obtained. Connect the corresponding nodes on all adjacent horizontal geological sections with line segments to obtain the node trace network.

(4) According to the fault cutting situation, the model is divided into different fault blocks, and the original sampling data is used to simulate the original stratum interface in each fault block.

(5) Select a fault block in turn, and use the node trace in the fault block to intersect with each original stratum interface, and the intersection point obtained is the grid node corresponding to the stratum interface. These nodes are combined with the topological structure of standard plane grid to form stratum interface.

(6) The boundary lines and fault traces of adjacent horizontal geological sections are correspondingly connected to form the lateral interface and fault interface of the model, thus forming a closed solid model.

7.3.3.2 structural fault system

Drawing horizontal geological profiles with different elevations is a means to reflect the spatial characteristics of faults. On the horizontal geological profile, faults are represented by traces. If the traces of the same fault are connected on different horizontal geological sections, a fault plane is formed. The collection of all fault planes constitutes a fault system (Figure 7. 13). For convenience, a certain number of equidistant horizontal geological sections can be selected according to the geometry of fault plane.

Fig. 7. 13 Fault system constructed by parallel horizontal geological sections

In order to ensure the reasonable connection between the upper and lower wall fault blocks of the fault, the fault is regarded as a thin sheet composed of double-layer curved surfaces, and the thickness of the thin sheet is about equal to the horizontal fault distance of the fault. According to this method, the fault trace on the same horizontal geological section can be split into two curves, and the number of nodes on these two curves is exactly the same as the order of nodes. The fission of intersecting lines is actually realized by the fission of nodes on intersecting lines. When modeling, each node can be divided into node groups with the same coordinates and different node numbers, and then the coordinates of each node in the node group can be adjusted appropriately according to the thickness of the fault slice. As shown in Figure 7. 14, when a node is on the fault trace, it splits into two nodes; When a node is the intersection of two fault trajectories, it can be divided into three or four. Fig. 7. 14(a) indicates that the nodes are on a fault line, fig. 7. 14(b) indicates that two fault lines intersect in a "d" shape, and fig. 7. 14(c) indicates that two fault lines intersect in an "x" shape.

Fig. 7. Split of14 fault trajectory

Construction of plane grid of horizontal geological section in 7.3.3.3

Firstly, a standard section is selected from a group of horizontal geological sections, and a standard plane grid H0 is formed by triangulation or quadrilateral with the fault trace and boundary line on the section as constraints. Then, a section Hi is selected from the horizontal section group in turn, and the standard plane grid is deformed with the fault trace and boundary line of Hi as fixed constraints to obtain the plane grid of Hi. Although the geometric shapes of Hi and H0 are different, their grids are completely corresponding, that is to say, the grid nodes of Hi and H0 are in one-to-one correspondence, and the grid cells are also in one-to-one correspondence.

DSI method and direct method can be used for deformation calculation. This deformation is similar to the elastic deformation of materials. When the boundary of the material changes, the interior of the material changes accordingly to adapt to the boundary deformation. The following describes the deformation method by taking the horizontal segment Hi as an example. In the deformation calculation, firstly, the nodes on H0 fault trajectory and boundary line are mapped to the fault trajectory and boundary line on Hi in turn. Then, with the nodes of fault trajectory and boundary line on Hi as fixed constraints, the plane mesh deformation with topology preservation is carried out by DSI method or direct method.

After the horizontal geological section grids are formed one by one according to the above method, a group of plane grids with different geometric shapes but the same structure are obtained. The node trace network can be formed by connecting the corresponding nodes of all adjacent parts with line segments.

7.3.3.4 simulates stratigraphic interface.

Faults divide the model into several independent fault blocks B={Bk|k=0, …, m}(m is the number of independent fault blocks in the model), and the stratum interface in each fault block should be simulated separately. The algorithm process of stratum interface simulation is as follows:

(1) Select the fault block Bk from the fault block set, take the maximum projection range of the fault block Bk on the horizontal plane as the reference plane, and create the original interface set sk={ski|i=0, ..., n}(i is the serial number of stratum interface, and n is the number of stratum layers) by using the mapping modeling method of continuous layered geological bodies.

(2) Select the interface ski from the original interface set, calculate the intersection points of all node traces in the fault block Bk and ski, form an intersection point set Nki, select different original stratum interfaces in turn, and repeat this process, and the intersection set Nk={Nkii=0, ..., n} will be obtained.

(3) Select different fault blocks in turn and repeat steps 1) and 2) to obtain the intersection of all original stratigraphic interfaces in all fault blocks, where N={Nk|k= 1, ..., m}.

(4) Select the nodes belonging to the same layer interface Si from N to form a set Gi={Nkik=0,.., m}, and replace the corresponding nodes of the standard plane grid H0 with nodes in the node set gi, so that H0 becomes Si. Repeated execution of this process can form stratum interface set S.

Connection of 7.3.3.5 side boundary

After the simulation of stratum interface is completed, the stratum can be formed by directly connecting the boundary line of adjacent stratum interface with the corresponding nodes on the fault boundary line, and then the solid model can be formed. In addition, because each fault boundary includes upper and lower walls, the relationship between fault boundary and fault block should be considered when connecting strata, and the part between upper and lower wall boundaries has nothing to do with strata in fault block, so fault attributes should be given.