Three-dimensional crustal stress prediction method based on structure size deformation and numerical simulation

Abstract

The invention discloses a three-dimensional crustal stress prediction method based on structure size deformation and numerical simulation. The method specifically comprises the following steps: S100, a first stage: constructing large deformation simulation; comprising the following steps: S110, establishing a three-dimensional frame model by using depth domain horizon data according to a seismic interpretation result; s120, setting a constitutive model and a strain softening mode; s130, stratum mechanical parameters are set; s140, setting a boundary condition; s150, setting speed boundary loading; s160, carrying out numerical calculation, comparing strain distribution in a simulation result with fault distribution obtained through geological exploration, and checking the correctness of a large-deformation simulation result of the structure; s200, in the second stage, small strain simulation is constructed, the simulation result in the first stage serves as an initial model, and speed boundary loading is modified into stress boundary loading; carrying out numerical calculation, and comparing stress distribution of a simulation result with an actual measurement result; according to the method, the model constraint degree is increased, and the reliability of a three-dimensional crustal stress prediction result can be improved.

Description

Technical Field

[0001] This invention relates to the field of geological exploration technology, specifically a three-dimensional geostress prediction method based on structural deformation and numerical simulation. Background Technology

[0002] In-situ stress is a natural stress stored in the Earth's rock strata, typically including vertical stress caused by the gravity of the rock layers and tectonic stress caused by geological deformation. The variation of stress state with a spatial point is called the in-situ stress field. The influence of in-situ stress is widespread in human activities: for example, in oil and gas well fracturing, in-situ stress constrains the spatial distribution of fractures; in tunnel excavation, high-stress sections pose a risk of rockburst, thus endangering engineering safety; and in natural earthquake prediction, seismic gaps with high in-situ stress are key monitoring areas. Therefore, accurate measurement and prediction of in-situ stress are crucial for these projects.

[0003] Precise stress measurements can be obtained at specific locations using methods such as hydraulic fracturing, borehole stress relief, and acoustic emission. However, for complex tectonic deformation zones, the results from a few measurement points are far from reflecting the stress field characteristics of the entire three-dimensional space. Therefore, engineers attempt to use the "hard data" from these measurement points as constraints to predict the three-dimensional stress distribution through numerical simulation techniques. Common numerical simulation methods include the finite element method, finite difference method, discrete element method, boundary element method, and variational method. However, regardless of the method used, current simulation techniques generally do not consider the long-term tectonic deformation process, using only the results of long-term tectonic deformation as the initial geological model for numerical simulation. Modeling by tectonic partitioning and embedded fracture weak zones, then applying stress boundaries, and obtaining the three-dimensional stress field distribution based on stress equilibrium calculations is a method of small-strain numerical simulation, feasible for regions with relatively simple tectonic deformation. However, for regions with complex tectonic deformation, especially those since the Quaternary period, with numerous fractures of different levels, geometric attitudes, and mechanical states, geological modeling struggles to handle these complex deformations. Furthermore, stress and strain are closely related, and the tectonic deformation history since the Quaternary period profoundly influences the current stress field distribution.

[0004] In the prior art, patent CN117272728A provides a method for predicting the three-dimensional geostress field in complex tectonic zones. It proposes pre-constructing a three-dimensional geological mechanical model and calculating the dynamic rock mechanical elastic parameters corresponding to small layers based on well logging data. Then, a stress field prediction is established, and finally, the finite element method is used to perform an overall geostress field inversion calculation. While this method has some effectiveness in simulating large macroscopic deformations, it cannot effectively address the issue of combining it with small strain scales.

[0005] Based on the above situation, we propose a three-dimensional geostress prediction method based on structural deformation and numerical simulation. The method generates faults and stress fields through numerical calculation. Compared with conventional small-strain numerical simulation, which only obtains stress field results, the simulation method proposed in this invention has more sufficient constraints. Summary of the Invention

[0006] The purpose of this invention is to provide a three-dimensional geostress prediction method based on structural deformation and numerical simulation. By performing numerical calculations in two stages, namely large structural deformation numerical simulation and small strain numerical simulation, the model constraints are increased, thereby improving the reliability of the three-dimensional geostress prediction results.

[0007] This invention is implemented as follows: a three-dimensional geostress prediction method based on structural deformation and numerical simulation, comprising the following steps:

[0008] S100, Phase 1: Simulation of large deformation of structures;

[0009] Specifically, the steps include the following:

[0010] S110. Based on the seismic interpretation results, a three-dimensional framework model is established using depth domain layer data.

[0011] S120, Define the constitutive model and strain softening method;

[0012] S130, Set formation mechanical parameters;

[0013] S140, Set boundary conditions;

[0014] S150, Set the speed boundary load, including the magnitude and direction of the speed;

[0015] S160. Perform numerical calculations and compare the strain distribution in the simulation results with the fault distribution obtained through geological exploration to verify the correctness of the large structural deformation simulation results.

[0016] S200, Second Stage: Constructing Small Strain Simulations;

[0017] Specifically, the steps include the following:

[0018] S210. Using the simulation results of the first stage as the initial model for this stage, the velocity boundary loading is modified to the stress boundary loading.

[0019] S220. Perform numerical calculations and compare the stress distribution of the simulation results with the measured results.

[0020] Furthermore, in step S120, the constitutive model includes an elastic constitutive model, a Mohr-Coulomb elastoplastic constitutive model, and a Berg creep constitutive model.

[0021] Furthermore, in step S120, the strain softening method is used to reduce the mechanical strength of the rock layer as the strain increases, including a decrease in the internal friction angle.

[0022] Furthermore, in step S130, the method of setting the formation mechanics parameters includes based on drilling lithology, core mechanics experiments, and empirical value ranges.

[0023] Furthermore, in step S130, when the constitutive model is a Mohr-Coulomb elastoplastic constitutive model, the formation mechanical parameters include density, Young's modulus, Poisson's ratio, internal friction angle, cohesion, tensile strength, tangential stiffness, and normal stiffness.

[0024] Furthermore, in step S140, the boundary conditions include three types: fixed, sliding, and free.

[0025] Furthermore, in step S210, the stress boundary loading includes normal stress and / or shear stress, as well as stress magnitude and stress direction.

[0026] Compared with existing technologies, the advantages of this invention are: it generates both faults and in-situ stresses in the simulation. Compared with traditional simple small-strain simulations, it solves the problem of only simulating and predicting large deformation strain levels while ignoring the role of small strain levels. It also overcomes the difficulties in establishing initial models for complex structural regions and the problem of oversimplification due to manually set faults. Therefore, it increases the model's constraint, which helps improve the reliability of three-dimensional in-situ stress prediction results. Attached Figure Description

[0027] Figure 1 This is a flowchart illustrating a three-dimensional geostress prediction method based on structural deformation and numerical simulation provided by the present invention.

[0028] Figure 2 This is the initial model setup diagram;

[0029] Figure 3 This is a speed boundary loading settings diagram;

[0030] Figure 4 (a) is the strain and stress field simulation of velocity boundary loading - the cumulative maximum shear strain diagram of left-side sliding 30m;

[0031] Figure 4 (b) is the strain and stress field simulation of velocity boundary loading - the cumulative maximum shear strain diagram of left-side sliding 60m;

[0032] Figure 4 (c) is the stress field distribution under velocity boundary loading simulation - leftward sliding 60m;

[0033] Figure 5 This is a diagram showing the stress boundary loading settings;

[0034] Figure 6 (a) is the cumulative maximum shear strain diagram after sliding 60m to the left and then being subjected to stress boundary loading;

[0035] Figure 6 (b) shows the stress field distribution after sliding 60m to the left and then applying stress boundary loading. Detailed Implementation

[0036] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0037] The following description, in conjunction with the accompanying drawings and specific embodiments, provides further details:

[0038] A three-dimensional geostress prediction method based on tectonic deformation and numerical simulation is proposed. The entire process is divided into two stages: large tectonic deformation simulation and small tectonic strain simulation. The process steps are as follows: Figure 1 As shown.

[0039] Phase 1: Simulation of Large Deformation

[0040] (1) Based on the seismic interpretation results, a three-dimensional framework model is established using depth domain layer data. For example... Figure 2 As shown, a geological model with dimensions of 10km x 10km x 0.5km was constructed. Vertically, it was divided into an upper 400m thick caprock and a lower 100m thick basement. The caprock was further subdivided into an upper 360m thick hard layer and a lower 40m thick soft layer. This example did not use depth-domain seismic horizon control for stratification, but more detailed models could be used.

[0041] (2) Set constitutive models and strain softening methods. Commonly used constitutive models include elastic constitutive, Mohr-Coulomb elastoplastic constitutive, and Berg creep constitutive. Strain softening methods usually set the mechanical strength of the rock layer to decrease as the strain increases, such as reducing the internal friction angle.

[0042] This example uses a Mohr-Coulomb elastoplastic constitutive model. Strain softening is set in the hard cap layer, and the softening method is as follows: when the cumulative maximum shear strain is less than 0.025, the internal friction angle of the simulated material is 40°; when the cumulative maximum shear strain is greater than 0.03, the internal friction angle of the simulated material decreases to 35°; when the cumulative maximum shear strain is between 0.025 and 0.03, the internal friction angle of the simulated material decreases linearly according to the following formula.

[0043]

[0044] In the formula, θ is the internal friction angle of the simulated material, and ε is the cumulative maximum shear strain of the model.

[0045] (3) Based on drilling lithology, core mechanics experiments, and empirical value ranges, formation mechanical parameters are set. These parameters depend on the selected constitutive model. Taking the Mohr-Coulomb constitutive model as an example, the formation mechanical parameters include density, Young's modulus, Poisson's ratio, internal friction angle, cohesion, tensile strength, tangential stiffness, and normal stiffness. The formation mechanical parameters in this example are shown in Table 1.

[0046] Table 1. Formation Mechanical Parameters

[0047]

[0048]

[0049] (4) Set boundary conditions, including three types: fixed, sliding, and free. In this example, the base is fixed in the Z direction, the east and west sides of the cap layer are fixed in the X direction, the north and south sides are fixed in the Y direction, and the upper surface is a free interface.

[0050] (5) Set the velocity boundary load, including the magnitude and direction of the velocity. For example... Figure 3 As shown, a northwest-southwest velocity of 0.001 m / step is applied to the north block on both the east and west sides of the basement and caprock. This is the loading method for a left-lateral strike-slip structure.

[0051] (6) Numerical calculations are performed, and the strain distribution in the simulation results is compared with the fault distribution obtained through geological exploration to verify the correctness of the large structural deformation simulation results. For example... Figure 4 As shown, left-hand strike-slip faults with a strike-slip depth of 30m and 60m produced shear strain zones of different intensities. The left-hand strike-slip condition generated a right-hand en echelon fault, and the simulation results are consistent with the theoretical strike-slip model. Each model stage simultaneously generates a corresponding stress field (…). Figure 4 c).

[0052] Phase Two: Constructing Small-Strain Simulations

[0053] (7) Using the simulation results from the first stage as the initial model for this stage, the velocity boundary loading is modified to stress boundary loading, including the type of normal stress or shear stress, stress magnitude, and stress direction. For example... Figure 5 As shown, the velocity loading is removed, and stress loading is added to the western boundary of the caprock. The stress is 1.5 times the static rock pressure at the corresponding depth, and the material is squeezed from west to east along the X direction.

[0054] (8) Numerical calculations are performed, and the stress distribution of the simulation results is compared with the measured results. For example... Figure 6 As shown, the second stage is a small strain simulation, so the cumulative maximum shear strain diagram is not significantly different from the simulation results of the first stage, but the stress field is significantly different from the results of the previous stage.

[0055] This invention predicts three-dimensional geostress distribution through two stages: large deformation simulation and small strain simulation. The first stage generates faults through numerical calculations. These faults vary in scale, geometric orientation, and mechanical state in three-dimensional space, providing a more refined model than traditional manually constructed fault models. The second stage uses the refined simulation results from the first stage as the initial model to conduct conventional small strain simulations. The obtained geostress is compared with measured geostress. By experimenting with different stress boundary parameters, it is hoped that results can be obtained that closely match measured geostress and have predictive significance in areas beyond the measured points.

[0056] This invention generates both faults and in-situ stresses in the simulation. Compared to traditional simulations that only simulate and predict large deformation strain levels while ignoring the effects of small strain levels, it overcomes the difficulties in establishing initial models for complex tectonic zones and the problem of oversimplification due to manually defined faults. Therefore, it increases the model's constraint level, which helps improve the reliability of three-dimensional in-situ stress prediction results.

[0057] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention can have various modifications and variations. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A three-dimensional geostress prediction method based on structural deformation and numerical simulation, characterized in that, Includes the following steps: S100, Phase 1: Simulation of large deformation of structures; Specifically, the steps include the following: S110. Based on the seismic interpretation results, a three-dimensional framework model is established using depth domain layer data. S120, Define the constitutive model and strain softening method; S130, Set formation mechanical parameters; S140, Set boundary conditions; S150, Set the speed boundary load, including the magnitude and direction of the speed; S160. Perform numerical calculations and compare the strain distribution in the simulation results with the fault distribution obtained through geological exploration to verify the correctness of the large structural deformation simulation results. S200, Second Stage: Constructing Small Strain Simulations; Specifically, the steps include the following: S210. Using the simulation results of the first stage as the initial model for this stage, the velocity boundary loading is modified to the stress boundary loading. S220. Perform numerical calculations and compare the stress distribution of the simulation results with the measured results.

2. The three-dimensional geostress prediction method based on structural deformation and numerical simulation according to claim 1, characterized in that, In step S120, the constitutive model includes an elastic constitutive model, a Mohr-Coulomb elastoplastic constitutive model, and a Berg creep constitutive model.

3. The three-dimensional geostress prediction method based on structural deformation and numerical simulation according to claim 2, characterized in that, In step S120, the strain softening method is used to reduce the mechanical strength of the rock layer as the strain increases, including a decrease in the internal friction angle.

4. The three-dimensional geostress prediction method based on structural deformation and numerical simulation according to claim 1, characterized in that, In step S130, the method of setting the formation mechanics parameters includes based on drilling lithology, core mechanics experiments, and empirical value ranges.

5. The three-dimensional geostress prediction method based on structural deformation and numerical simulation according to claim 4, characterized in that, In step S130, when the constitutive model is a Mohr-Coulomb elastoplastic constitutive model, the formation mechanical parameters include density, Young's modulus, Poisson's ratio, internal friction angle, cohesion, tensile strength, tangential stiffness, and normal stiffness.

6. The three-dimensional geostress prediction method based on structural deformation and numerical simulation according to claim 1, characterized in that, In step S140, the boundary conditions include three types: fixed, sliding, and free.

7. The three-dimensional geostress prediction method based on structural deformation and numerical simulation according to claim 1, characterized in that, In step S210, the stress boundary loading includes normal stress and / or shear stress, as well as stress magnitude and stress direction.

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