A three-dimensional multi-fault geological modeling method suitable for finite element numerical simulation

Abstract

The present invention provides a three-dimensional multiple complex fault geological modeling method suitable for finite element numerical simulation. The three-dimensional multiple complex fault geological modeling method suitable for finite element numerical simulation includes the following steps: faults are modeled separately, and their corresponding geometric models are constructed using the point cloud data of each fault, including processing multiple triangular facets into whole facets, and optimizing the geometric topological structure of the whole facets; using the crust1.0 crustal model to establish a lithospheric structure layering model, and fusing the fault model with the crust1.0 stratum model to construct a geological model of multiple complex faults. The three-dimensional multiple complex fault geological modeling method suitable for finite element numerical simulation provided by the present invention has the advantages of fully considering the geometric information of a single fault and the relationship between multiple faults during the modeling process, reducing the errors in model size and position brought about during the modeling process, and fully considering the spatial differences of model materials.

Description

Technical Field

[0001] The present invention relates to the technical field of fault geological models, and in particular to a three-dimensional multi-complex fault geological modeling method suitable for finite element numerical simulation. Background Art

[0002] Earthquakes occur when stress accumulates in active fault zones within the seismogenic layers of the Earth's crustal lithosphere under tectonic activity, reaching a critical state and leading to sudden instability and rupture. Leveraging limited existing observational data, we construct a complex three-dimensional numerical model of fault zones, simulating the earthquake development process and mechanisms, and assessing the hazard characteristics of potential destructive earthquakes in the future.

[0003] Existing numerical models of crustal lithospheric fault zones are also gradually developing and improving. Most current models are two-dimensional plane strain or plane stress models. These models account for multiple fault zones and their strike characteristics, but ignore the changes in fault dip at depth and the stratified structure of the lithosphere. Some three-dimensional models use fixed fault dips and planes at fixed depths as the stratified interfaces of the lithosphere, ignoring the geometric complexity of faults and lithosphere structure. This patent integrates existing data and technological advantages to establish a complex three-dimensional numerical model of fault zones to accurately assess seismic hazard.

[0004] The prior art discloses a three-dimensional viscoelastic modeling method containing fractures based on a public database of the lithosphere. The purpose is to more accurately reflect the multi-layered undulating characteristics and layered viscoelastic characteristics of the lithosphere, and to unify lithosphere spatial modeling, numerical simulation, and data sharing. A method for establishing a three-dimensional viscoelastic model of the lithosphere containing large fracture zones based on a public database of the earth's spheres is provided.

[0005] However, its disadvantages are:

[0006] 1. The considered fault geometry is too simple, and the fault strike and dip information is oversimplified, which will affect the accuracy of the ground stress simulation results;

[0007] 2. Due to its geometric complexity, the constructed model can only be divided into tetrahedral meshes in the upper crust, and cannot be divided into hexahedral elements. It may not be suitable for some finite element simulation software;

[0008] The prior art also discloses a method for modeling the mechanical properties of rocks within the fracture zone of a shale reservoir. The purpose of the method is to address the defects of the prior art mentioned above and to provide a method for finely modeling the mechanical properties of rocks within the fracture zone based on the fine characterization of the internal structure of the fracture zone of a shale reservoir, combined with rock mechanics testing and transverse isotropy theory adapted to shale reservoirs.

[0009] However, its disadvantages are:

[0010] 1. Single fault modeling lacks the contact relationship and mutual influence between multiple faults;

[0011] 2. It is not a systematic geological modeling. The single fault model does not take into account the surrounding rock and sedimentary layers.

[0012] Therefore, it is necessary to provide a new three-dimensional multi-fault geological modeling method suitable for finite element numerical simulation to solve the above technical problems. Summary of the Invention

[0013] The technical problem solved by the present invention is to provide a three-dimensional multi-complex fault geological modeling method suitable for finite element numerical simulation, which fully considers the geometric information of a single fault and the relationship between multiple faults during the modeling process, reduces the errors in model size and position caused by the modeling process, and fully considers the spatial differences of model materials.

[0014] To solve the above technical problems, the present invention provides a three-dimensional multi-fault geological modeling method suitable for finite element numerical simulation, which includes the following steps:

[0015] Faults are modeled individually, using the point cloud data for each fault to construct its corresponding geometric model. This involves processing multiple triangular facets into a global facet, optimizing the geometric topology of the global facet, and preparing for the subsequent hexahedral meshing. Hexahedral meshes have certain advantages in addressing fault rupture mechanisms, seismic hazards, and numerical simulation accuracy.

[0016] The layered model of the lithosphere structure - the construction of the crust1.0 model;

[0017] Construction of the fusion of fault model and crust1.0 stratigraphic model;

[0018] Model block segmentation;

[0019] Construction of material model.

[0020] Preferably, the separate fault modeling includes processing of complex faults containing detachment layers, processing of fault cross-overlapping, processing of fault splicing, fault completion, and processing of fault contact.

[0021] Preferably, the layered model of the lithosphere structure - the crust model 1.0 includes three interfaces: the bottom surface of the upper crust, the bottom surface of the middle crust and the bottom surface of the lower crust.

[0022] Preferably, the fault model is fused with the crust1.0 stratum model to delete the faults that pass through the interface and stretch and complete the faults that do not pass through the interface according to whether they pass through the interface.

[0023] Preferably, the model block segmentation is to cut and partition the model according to the corresponding plate interpretation results after fault modeling.

[0024] Preferably, the material model uses public seismic wave data to calculate rock material parameters, and assigns the material parameters to each finite element grid, converts the local coordinates of the study area model into geodetic coordinates, uses the geodetic coordinates of known faults as reference points, and translates the entire model until the corresponding points of the model are matched with the reference points; obtains the intercepts of the model in the horizontal and vertical coordinates, and calculates the geodetic coordinate values of each node on the model, uses the coordinate conversion formula to convert the geodetic coordinates of the study area model into longitude and latitude coordinates based on the WGS84 ellipsoid, and constructs a model coordinate database for matching the crust1.0 model and obtaining the basic mechanical material parameters of the study area model.

[0025] Preferably, the coordinate transformation adopts the formula:

[0026]

[0027] in: a is the major semi-axis of the WGS84 ellipsoid, b is the minor semi-axis of the WGS84 ellipsoid, and N is the radius;

[0028] The calculation formula of the effective viscosity coefficient of rock at each node in the experimental field is as follows:

[0029]

[0030] where τ creep is the strength of the study area at a certain temperature and strain rate, ε is the strain rate, T is the absolute temperature, R is the universal gas constant, A, n, E * The rheological constant of a specific rock obtained from rock experiments;

[0031] The node coordinates of the model study area model are interpolated into the rheological model results of the China Earthquake Science Experimental Field using the interpolation method to obtain the node rheological parameters of the study area model; the obtained study area node parameter database is traversed unit by unit, and the mechanical parameters and rheological parameter database of each center of the model are calculated and obtained through the node-unit file; and the database values are assigned to the 3D network model units.

[0032] Compared with related technologies, the three-dimensional multi-fault geological modeling method suitable for finite element numerical simulation provided by the present invention has the following beneficial effects:

[0033] The present invention provides a three-dimensional multi-fault geological modeling method suitable for finite element numerical simulation. The fault model constructed using data from the China Earthquake Science Experimental Field has a geometric form that is more realistic. The geometric information of a single fault and the relationships between multiple faults (contact, cutting, etc.) are fully considered during the modeling process. The lithosphere layering model considers the differences in data from various layers of the crust in the coordinate system according to the different scale ranges of the model, and considers the shape of the earth (ellipsoid) during the coordinate conversion process to reduce errors in model size and position caused by the modeling process. The material model assigns rock material parameters calculated from seismic wave velocity data (Vp, Vs) to each unit of the finite element model, fully considering the spatial differences in the model material. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 A flow chart of mid-surface optimization for a three-dimensional multi-fault geological modeling method suitable for finite element numerical simulation provided by the present invention;

[0035] Figure 2 A schematic diagram of processing a triangular facet into a whole facet in the three-dimensional multi-fault geological modeling method suitable for finite element numerical simulation provided by the present invention;

[0036] Figure 3 A method for processing complex faults containing detachment layers in a three-dimensional multi-complex fault geological modeling method suitable for finite element numerical simulation provided by the present invention;

[0037] Figure 4 A schematic diagram of fault intersections in a three-dimensional multi-complex fault geological modeling method suitable for finite element numerical simulation provided by the present invention;

[0038] Figure 5 A schematic diagram of fault splicing in a three-dimensional multi-complex fault geological modeling method suitable for finite element numerical simulation provided by the present invention;

[0039] Figure 6 A schematic diagram of fault completion in the three-dimensional multi-complex fault geological modeling method applicable to finite element numerical simulation provided by the present invention;

[0040] Figure 7 A schematic diagram of a mid-crustal layer model for a three-dimensional multi-complex fault geological modeling method suitable for finite element numerical simulation provided by the present invention;

[0041] Figure 8 A schematic diagram of a middle block model of a three-dimensional multi-complex fault geological modeling method suitable for finite element numerical simulation provided by the present invention. DETAILED DESCRIPTION

[0042] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0043] Please refer to Figure 1-8 ,in, Figure 1 A flow chart of mid-surface optimization for a three-dimensional multi-fault geological modeling method suitable for finite element numerical simulation provided by the present invention; Figure 2 A schematic diagram of processing a triangular facet into a whole facet in the three-dimensional multi-fault geological modeling method suitable for finite element numerical simulation provided by the present invention; Figure 3 A method for processing complex faults containing detachment layers in a three-dimensional multi-complex fault geological modeling method suitable for finite element numerical simulation provided by the present invention; Figure 4 A schematic diagram of fault intersections in a three-dimensional multi-complex fault geological modeling method suitable for finite element numerical simulation provided by the present invention; Figure 5 A schematic diagram of fault splicing in a three-dimensional multi-complex fault geological modeling method suitable for finite element numerical simulation provided by the present invention; Figure 6 A schematic diagram of fault completion in the three-dimensional multi-complex fault geological modeling method applicable to finite element numerical simulation provided by the present invention; Figure 7 A schematic diagram of a mid-crustal layer model for a three-dimensional multi-complex fault geological modeling method suitable for finite element numerical simulation provided by the present invention; Figure 8 A schematic diagram of a block model in a three-dimensional multi-complex fault geological modeling method suitable for finite element numerical simulation provided by the present invention. The three-dimensional multi-complex fault geological modeling method suitable for finite element numerical simulation includes: (1) modeling each fault separately, using the point cloud data of each fault to construct its corresponding geometric model;

[0044] Import the fault point cloud data for sampling. The sampling principle should consider the grid size required for the actual numerical model calculation accuracy. Random sampling or grid sampling can be used according to the data type and source. Then convert the point cloud data into triangular facets in Geomagic software. At this time, the fault is just a fault plane with no thickness. Moreover, the fault plane has problems such as short edges, spikes, and voids. The fault plane surface needs to be optimized. The processing flow is shown in Figure 1 In common numerical models, the fault thickness is generally set to 2 km, so the surface needs to be stretched. At this time, the fault surface is a volume model with thickness.

[0045] Processing multiple triangular faces into whole faces is also a necessary step in the modeling process ( Figure 2 ), many problems such as fault rupture mechanism, earthquake risk and numerical simulation calculation accuracy (the calculation accuracy of tetrahedral units is lower than that of hexahedral units) require the use of hexahedral meshes. The directly generated triangular face topology structure will affect the subsequent hexahedral mesh division.

[0046] The method for handling complex faults with detachment layers, such as the Yingxiu-Beichuan fault, has a detachment layer at the interface between the upper and middle crust. Due to its geometric complexity, low-angle faults cannot meet the requirements of hexahedral meshes or high-quality tetrahedral meshes. If the size constraint of the finite element unit is 5km*5km and the thickness of the fault is 2km, then the low-angle fault should be handled according to this size, and the horizontal detachment layer of fault 1 should be extended upward by 2km ( Figure 3 a), and simplify the fault surface into a plane and the curve into a straight line ( Figure 3 c).

[0047] Faults overlap. Some faults may have been interpreted by different people at different times, so the interpreted fault geometries may overlap and intersect (e.g. Figure 4 Fault-2 and Fault-3) require some faults to be deleted and simplified. The principle of deletion and simplification is to fully consider the existing geological knowledge and retain as many non-intersecting faults as possible.

[0048] Fault splicing. Some fault zones are large in area and are composed of multiple faults. However, the faults in the fault zone are interpreted in segments and regions. Therefore, there are gaps in the fault zone that should be continuous. The gaps in the fault zone should be connected according to the fault properties on both sides. For example, the Maowen-Wenchuan fault and the Yingxiu Beichuan fault are two independent faults, and there is a small partition between the faults. These two faults are two important faults in the Longmenshan fault zone. In some geological understandings and published numerical models, it is believed that these two faults are continuous and there is no partition. Therefore, when we build the model, we need to connect them according to the geometric characteristics (dip and strike) of the adjacent faults (such as Figure 5 shown).

[0049] Fault completion and fault contact: The Yingxiu-Beichuan fault has only a shallow part in the northeastern section (the part with a relatively large fault dip angle). From the analysis of the tectonic mechanism, the Yingxiu-Beichuan fault in the northeastern section should be caused by the slip layer of the Jiangyou-Guanxian fault. Therefore, in the modeling, the Yingxiu-Beichuan fault is extended downward in the northeastern section and contacts the horizontal slip layer of the Jiangyou-Guanxian fault. The fault completion stretching method is to extend downward according to the dip change trend of the upper fault until it contacts another fault (such as Figure 6 shown).

[0050] (2) Layered model of lithosphere structure, crust1.0 crust model, a total of three interfaces: the bottom of the upper crust, the bottom of the middle crust, the bottom of the lower crust (Moho surface) (such as Figure 7(As shown). Based on the latitude and longitude range of the model area, point cloud data from the Crust1.0 program is extracted. The resulting data is depth data based on these latitude and longitude coordinates. However, our models are typically in a rectangular coordinate system, so the crustal model based on these latitude and longitude coordinates needs to be converted to a direct coordinate system. The Earth is an ellipsoid, and when the model scale is large, the converted model is not equidistant. This problem is addressed by selecting the distance (km) per unit longitude corresponding to the model's intermediate dimension as the east-west conversion ratio for the entire model. This ensures that the resulting crustal model matches the fault model.

[0051] (3) The fault model is integrated with the crust1.0 stratigraphic model. Because there is a deviation between the fault data and the crust1.0 data, it is necessary to consider whether the fault passes through the interface (such as the bottom of the upper crust). Faults that pass through the interface should be deleted, and those that do not pass through should be stretched and supplemented.

[0052] (4) Model block segmentation: After fault modeling, the model needs to be segmented according to the corresponding plate interpretation results (such as Figure 8 shown).

[0053] (5) Material model: Use public seismic wave data (such as the crust1.0 model and the China Earthquake Science Experimental Site model) to calculate rock material parameters and assign the material parameters to each finite element mesh. The local coordinates of the study area model are converted to geodetic coordinates. Using the geodetic coordinates of the known fault as the reference point, the entire model is translated until the corresponding points of the model are matched with the reference point. The intercepts of the model in the horizontal and vertical coordinates are obtained, and the geodetic coordinate values of each node on the model are calculated. Using the coordinate conversion formula, the geodetic coordinates of the study area model (B, L, H) are converted to longitude and latitude coordinates (X, Y, Z) based on the WGS84 ellipsoid, and a model coordinate database is constructed to match the crust1.0 model and obtain the basic mechanical material parameters of the study area model.

[0054] The formula used for coordinate transformation is:

[0055]

[0056] in: a is the semi-major axis of the WGS84 ellipsoid, b is the semi-minor axis of the WGS84 ellipsoid, and N is the radius.

[0057] The calculation formula of the effective viscosity coefficient of rock at each node in the experimental field is as follows:

[0058]

[0059] where τ creepis the strength of the study area at a certain temperature and strain rate in the flexible domain, ε is the strain rate, T is the absolute temperature, R is the universal gas constant, A, n, E * is the rheological constant of a specific rock obtained from rock experiments.

[0060] Using interpolation methods, the nodal coordinates of the model study area are interpolated into the rheological model results of the China Earthquake Science Experimental Field to obtain the nodal rheological parameters of the study area model. A cell traversal is performed on the obtained study area node parameter database. The mechanical and rheological parameter databases for each model center are calculated using the node-cell file. The database values are then assigned.

[0061] The sampling principle of fault data in the present invention is to consider the grid size required for the calculation accuracy of the actual numerical model. Random sampling or grid sampling can be used according to the data type and source. The established fault model is a thick body model rather than a fault surface. Generally, the thickness of the fault is set to 2km. In order to ensure the geometric accuracy of the fault and to be able to perform grid division, the fault surface needs to be optimized to deal with the problems of short edges, spikes, and voids on the fault surface. In order to adapt to the division of hexahedral units, multiple triangular facets need to be processed into whole facets. Complex faults containing slip layers need to be geometrically modified near the low angle of the fault. Appropriate face cutting and auxiliary lines are conducive to the successful division of the grid and the generation of high-quality finite element units. Faults that overlap in space should be cropped and deleted. The principle of deletion and simplification is to fully consider the existing geological knowledge and retain non-crossing faults as much as possible. Faults with gaps should be When performing splicing (or connection), the fault properties (depth, strike, dip) on both sides of the gap must be considered during splicing, and the spliced faults must ensure the continuity and integrity of the entire fault zone; when the faults are in contact in space, the faults must be completed, extended, trimmed, and other operations must be performed based on their geological significance; a layered model of the lithospheric structure is established using a public crustal model (such as crust1.0 and China Earthquake Science Experimental Field data), and the shape of the earth must be considered when performing coordinate transformation on the obtained crustal layer data; the fault model is integrated with the crust1.0 stratigraphic model, and because there is a deviation between the fault data and the crust1.0 data, it is necessary to consider whether the fault runs through the interface (such as the bottom of the upper crust); public seismic wave data (such as the crust1.0 model and the China Earthquake Science Experimental Field model) are used to calculate the rock material parameters, and the material parameters are assigned to each finite element mesh and the 3D network model unit.

[0062] This technique fully considers existing geophysical observation data and constructs a fault geometry model through inverse modeling based on publicly available point cloud data from the China Earthquake Administration's Earthquake Science Experimental Site. This model fully accounts for spatial variations in fault strike and dip (e.g., slip zones within the fault zone and fault contacts) without compromising the model's geological significance or computational accuracy. CRUST1.0 global sediment thickness data is then used to construct a layered model of the lithospheric structure. This modeling process considers coordinate transformations between different coordinate systems (from longitude and latitude to rectangular coordinates) and the integration of the lithospheric layer model with the fault model. The finite element model generated by this geometric model is still only suitable for tetrahedral elements. For some fault rupture mechanisms and seismic hazard issues, hexahedral elements are a better choice. Therefore, the existing lithospheric fault zone model requires geometric repair and meshing. Finally, publicly available seismic wave data from the study area (e.g., the CRUST1.0 model and the China Earthquake Science Experimental Site model) are used to calculate rock material parameters and assign these material parameters to each finite element mesh.

[0063] Compared with related technologies, the three-dimensional multi-fault geological modeling method suitable for finite element numerical simulation provided by the present invention has the following beneficial effects:

[0064] The present invention provides a three-dimensional multi-fault geological modeling method suitable for finite element numerical simulation. The fault model constructed using data from the China Earthquake Science Experimental Field has a geometric form that is more realistic. The geometric information of a single fault and the relationships between multiple faults (contact, cutting, etc.) are fully considered during the modeling process. The lithosphere layering model considers the differences in data from various layers of the crust in the coordinate system according to the different scale ranges of the model, and considers the shape of the earth (ellipsoid) during the coordinate conversion process to reduce errors in model size and position caused by the modeling process. The material model assigns rock material parameters calculated from seismic wave velocity data (Vp, Vs) to each unit of the finite element model, fully considering the spatial differences in the model material.

[0065] The above descriptions are merely embodiments of the present invention and are not intended to limit the patent scope of the present invention. Any equivalent structure or equivalent process transformation made using the contents of the present invention description and drawings, or directly or indirectly applied in other related technical fields, are also included in the patent protection scope of the present invention.

Claims

1. A three-dimensional multi-fault geological modeling method suitable for finite element numerical simulation, characterized in that: The following steps are involved: Faults are modeled individually, and their corresponding geometric models are constructed using the point cloud data of each fault. This involves processing multiple triangular facets into a global facet, optimizing the geometric topology of the global facet, and preparing for the subsequent hexahedral meshing. The hexahedral mesh has certain advantages in addressing fault rupture mechanisms, seismic hazards, and numerical simulation accuracy. The layered model of the lithosphere structure - the construction of the crust1.0 model; Construction of the fusion of fault model and crust1.0 stratigraphic model; Model block segmentation; Construction of material models; The material model uses publicly available seismic wave data to calculate rock material parameters and assigns the material parameters to each finite element grid. The local coordinates of the study area model are converted to geodetic coordinates. The geodetic coordinates of known faults are used as reference points to translate the entire model until the corresponding points of the model are matched with the reference points. The intercepts of the model in the horizontal and vertical coordinates are obtained, and the geodetic coordinate values of each node on the model are calculated. The coordinate conversion formula is used to convert the geodetic coordinates of the study area model into longitude and latitude coordinates based on the WGS84 ellipsoid, and a model coordinate database is constructed for matching the crust1.0 model and obtaining the basic mechanical material parameters of the study area model. The formula used for the coordinate transformation is: in: a is the major semi-axis of the WGS84 ellipsoid, b is the minor semi-axis of the WGS84 ellipsoid, and N is the radius; The calculation formula of the effective viscosity coefficient of rock at each node in the experimental field is as follows: where τ creep is the strength of the flexible domain under a certain temperature and strain rate in the study area, ε is the strain rate, T is the absolute temperature, R is the universal gas constant, A, n, E * The rheological constant of a specific rock obtained from rock experiments; The node coordinates of the model study area model are interpolated into the rheological model results of the China Earthquake Science Experimental Field using the interpolation method to obtain the node rheological parameters of the study area model; the obtained study area node parameter database is traversed unit by unit, and the mechanical parameters and rheological parameter database of each center of the model are calculated and obtained through the node-unit file; and the database values are assigned to the 3D network model units.

2. The three-dimensional multi-fault geological modeling method suitable for finite element numerical simulation according to claim 1, characterized in that: The individual fault modeling includes processing of complex faults containing detachment layers, processing of fault cross-overlapping, processing of fault splicing, processing of fault completion, and processing of fault contact.

3. The three-dimensional multi-fault geological modeling method suitable for finite element numerical simulation according to claim 1, characterized in that: The layered model of the lithosphere structure - the crust model 1.0 includes three interfaces: the bottom surface of the upper crust, the bottom surface of the middle crust and the bottom surface of the lower crust.

4. The three-dimensional multi-fault geological modeling method suitable for finite element numerical simulation according to claim 1, characterized in that: The fault model is fused with the crust1.0 stratum model, and the faults that penetrate the interface are deleted, and the faults that do not penetrate the interface are stretched and supplemented.

5. The three-dimensional multi-fault geological modeling method suitable for finite element numerical simulation according to claim 1, characterized in that: The model block segmentation is to cut and partition the model according to the corresponding plate interpretation results after fault modeling.

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