# Research Status of and Trends in 3D Geological Property Modeling Methods: A Review
## 2 Research on Reservoir Grid Generation Method
Second, on the one hand, the nonorthogonality of the pillar grid makes calculating conductivity during numerical simulation difficult; on the other hand, the nonorthogonality of the pillar grid affects the accuracy of the results. [PERSON] [24] proposed a grid generation method that adopts the form of a Cartesian grid at the global level and simulates the fault by truncating the hexahedron, thereby finally constructing an XY-orthogonal and locally truncated grid model. This grid can express the shape of the fault while avoiding the loss of orthogonality due to distortion, but the grid generates many polyhedral grids in models with many faults, thereby also affecting the fluid simulation operations. After analyzing the limitations of the pillar grid, [PERSON] [25] proposed a vertical stair-step grid that is more suitable for fluid simulation and experimentally demonstrated that this type of grid outperforms the pillar grid in terms of grid coarsening and fluid simulation; the author did not give the method for generating this grid. In addition, many studies have been devoted to unstructured grids. The PEBI grid is flexible and locally orthogonal, thus reducing the influence of grid orientation on the results. In 1988, [PERSON] et al. [26] proposed the implementation of the PEBI grid based on the Voronoi diagram for the numerical simulation of the reservoir grid and then improved the grid with dynamic refinement as needed [27; 28; 29]. [PERSON] of Stanford University [30; 31; 32] studied the use of the Voronoi grid, which is essentially the PEBI grid,to simulate vertical and horizontal wells and performed numerical simulation of reservoirs. Since then, scholars have successively carried out research on 3D PEBI grids along with investigation and improvement in different application environments [33; 34; 35; 36]. Additionally, many studies on PEBI grids have been published in recent years by Chinese researchers. [PERSON] [37] and [PERSON] et al. [38; 39; 40] systematically elaborated the application of PEBI grids in the numerical simulation of reservoirs. [PERSON] [41] addressed the problem of fine numerical simulation of reservoirs by adopting an idea of a hybrid grid consisting of a radial grid in the oil well area and a PEBI grid in the reservoir area. [PERSON]. [42] proposed a similar idea on hybrid grids. [PERSON] [43] and [PERSON] [44; 45; 46] studied the generation algorithm of two-dimensional (2D) PEBI grids, but did not fully address the generation algorithm of 3D PEBI grids. In general, the numerical simulation solutions of PEBI grids are not mature enough and not widely used. In addition, the research on PEBI grids is mainly for the numerical simulation of reservoirs; there are few studies on how PEBI grids are generated and maintain geological significance in geological modeling. In other words, other grids generally need to be transformed before PEBI grids can be used for the numerical simulation of reservoirs. Figure 1: Comparison of s-grid, faulted s-grid, and pillar grid (edited from [17]): (**a**) example of s-grid; (**b**) example of faulted s-grid; (**c**) example of pillar grid; (**d**) theoretical model of s-grid, faulted s-grid, and pillar grid for the processing of faults.