Three-dimensional fracturing stress field evolution characterization method and system based on mining effects

Abstract

The invention discloses a three-dimensional fracturing stress field evolution characterization method and system based on mining effect. The evolution characterization method comprises the following steps: constructing and transforming a three-dimensional mining stress tensor: numerically simulating mining on a mining face, extracting mining stress components in a target research area, constructing a three-dimensional second-order stress tensor, and calculating principal stress scalars and principal directions; continuously and smoothly transforming mining principal stresses: constructing a three-dimensional six-direction principal direction matrix, then constructing a principal stress inner product matrix, calculating a rotation matrix and obtaining a continuous and smooth evolution trajectory of the principal stress directions; reproducing the spatiotemporal mining stress field: assigning a spatial mining stress field to a fracturing model in the form of a predefined field, and assigning a temporal mining stress field to the fracturing model in the form of a dynamic load boundary; constructing and transforming a three-dimensional fracturing stress tensor: numerically simulating mine fracturing under mining action, extracting and calculating fracturing principal stresses, and characterizing and analyzing the evolution law of the fracturing stress field under the action of the mining stress field.

Description

Technical Field

[0001] The present invention relates to the field of mine fracturing, and in particular to a method and system for characterizing the evolution of a three-dimensional fracturing stress field based on mining effects. Background Art

[0002] Fracturing has a wide range of applications in mines. For example, in coal mines, coal mining often faces problems such as hard roof, low-permeability coal seams, and hard coal seams. Hard roof is prone to roof collapse accidents, gas extraction efficiency in low-permeability coal seams is low, and hard coal seams are not conducive to top coal caving. These problems can be solved to a certain extent by fracturing. Fracturing can cut off the roof to achieve the purpose of pressure relief, increase the permeability of the coal body to improve the permeability, and crack the coal body to improve the caving of the top coal. In non-coal mines, when mining hard rocks, fracturing can be used to break up hard rock, reduce the difficulty and cost of blasting operations, and improve production efficiency.

[0003] Hydraulic fracturing in mines usually needs to solve engineering problems in a specified spatial location. Therefore, the expansion direction of the hydraulic fracturing cracks is crucial. Studies have shown that the expansion direction of hydraulic fracturing cracks is affected by the distribution of principal stresses in the hydraulic fracturing environment. Stress disturbances will be formed during mining, and stress concentration areas will be formed around the mining space. As the mining operation proceeds, the mining stress will migrate dynamically. In engineering, the areas that require hydraulic fracturing are generally within the influence range of mining stress. Therefore, the spatiotemporal evolution of the mining stress field will affect the distribution of the hydraulic fracturing stress field, and then affect the expansion direction of the hydraulic fracturing cracks.

[0004] In addition, current research on the expansion direction of hydraulic fractures mainly focuses on the design of parameters such as ground stress difference, fracturing fluid conditions, perforation azimuth, perforation length, and number of perforations. The research objects are mostly fracture morphology, and the effect of the dynamically changing mining stress field on the hydraulic fracture stress field is rarely considered. This patent focuses on studying the interaction between the mining stress field and the hydraulic fracture stress field, and accurately characterizing the distribution characteristics of the pressure stress field. It aims to reasonably design hydraulic fracture parameters according to the dynamic distribution and evolution law of the mining stress field, thereby assisting in controlling the expansion direction of the fractures. Summary of the invention

[0005] In response to the problems and needs raised above, this solution proposes a three-dimensional fracturing stress field evolution characterization method and system based on mining effects. Due to the adoption of the following technical features, the above technical objectives can be achieved and many other technical effects can be brought about.

[0006] One object of the present invention is to propose a method for characterizing the evolution of a three-dimensional fracturing stress field based on mining effects, comprising the following steps:

[0007] S10, construct and transform three-dimensional mining stress tensor: perform numerical simulation on mining face mining, extract mining stress components in the target study area, construct three-dimensional second-order stress tensor, and calculate principal stress scalars and principal directions;

[0008] S20, continuous and smooth transformation of dynamic principal stress: construct a three-dimensional six-direction principal direction matrix, then construct the principal stress inner product matrix, calculate the rotation matrix and obtain the continuous and smooth evolution trajectory of the principal stress direction;

[0009] S30, reproducing the spatiotemporal mining stress field: assigning the spatial mining stress field to the fracturing model in the form of a predefined field, and assigning the temporal mining stress field to the fracturing model in the form of a dynamic load boundary;

[0010] S40. Construct and transform three-dimensional fracturing stress tensor: perform numerical simulation on mine fracturing under mining action, extract and calculate the principal fracturing stress, characterize and analyze the evolution law of the fracturing stress field under the action of mining stress field.

[0011] In an example of the present invention, in step S10, constructing a three-dimensional second-order stress tensor and calculating the principal stress scalar and the principal direction specifically include the following steps:

[0012] The mining stress components include: 3 normal stresses and 3 shear stresses, and a 3×3 second-order stress tensor is constructed according to the symmetry of the shear stress. The stress tensor is then decomposed using the eigenvalue method to calculate the principal stress scalar and its corresponding principal direction; wherein the mining stress components are obtained at the unit integration points.

[0013] In an example of the present invention, in step S20, continuously and smoothly transforming the mining principal stress specifically includes the following steps:

[0014] Using the three principal stresses of maximum principal stress, intermediate principal stress and minimum principal stress, based on the symmetry of the six directions of front-back, left-right and top-bottom of a point, the principal stress and the principal stress in the opposite direction are spliced ​​to construct a three-dimensional six-direction principal direction matrix H, that is, H = [V1, -V1, V2, -V2, V3, -V3];

[0015] Perform an inner product operation on two adjacent three-dimensional six-direction main direction matrices, that is, M = H1·H2, to obtain the main direction inner product matrix M;

[0016] The inner product matrix is ​​decomposed to calculate the rotation matrix R between the two three-dimensional six-direction matrices, that is, R = U × V T , U and V are the left singular matrix and right singular matrix after eigenvalue decomposition of the inner product matrix, respectively;

[0017] The three-dimensional rotation matrix in the Lie group space is transformed into the Lie algebra space through logarithmic mapping, that is, r=log(R). After linear interpolation in the Lie algebra space, it is transformed into the Lie group space through exponential mapping R'=log(r') to obtain the continuous and smooth evolution trajectory of the main direction.

[0018] In an example of the present invention, in step S30, assigning the spatial mining stress field to the fracturing model in the form of a predefined field specifically includes: assigning the mining stress tensors of each unit to the units in the fracturing area in batches to realize the predefined stress field.

[0019] In one example of the present invention, in step S30, assigning a time-series mining stress field to the fracturing model in the form of a dynamic load boundary specifically includes: setting a predefined field in the mining stress space, and calculating a dynamic load function based on the continuously evolving principal stress trajectory, and then applying the mining stress to the fracturing model as a dynamic load.

[0020] In an example of the present invention, step S40 specifically includes the following steps:

[0021] Firstly, numerical simulation of fracturing under mining action is carried out, and the fracturing stress components at the unit integration points are extracted. The principal stress scalars and principal directions of the fracturing are calculated by eigenvalue decomposition, and the three-dimensional six-direction principal direction matrix of the fracturing stress field is constructed. Then, the inner product matrix and rotation matrix of the fracturing principal stress are calculated in turn. Finally, the continuous and smooth evolution trajectory of the principal direction of the fracturing is calculated by Lie group and Lie algebra. Finally, the influence of the mining stress field on the evolution of the fracturing stress field is analyzed, and the expansion law of the cracks is further analyzed based on the fracturing stress field.

[0022] Another object of the present invention is to propose an evolution characterization system of the three-dimensional fracturing stress field evolution characterization method based on mining effects as described above, comprising:

[0023] The mining stress tensor construction and transformation module is configured to perform numerical simulation on mining face mining, extract mining stress components in the target study area, construct a three-dimensional second-order stress tensor, and calculate the principal stress scalars and principal directions;

[0024] The principal stress continuous smooth transformation module is configured to construct a three-dimensional six-direction principal direction matrix, then construct the principal stress inner product matrix, calculate the rotation matrix and obtain the continuous smooth evolution trajectory of the principal stress direction;

[0025] A mining stress field spatiotemporal reproduction module, configured to assign a spatial mining stress field to the fracturing model in the form of a predefined field, and to assign a temporal mining stress field to the fracturing model in the form of a dynamic load boundary;

[0026] The three-dimensional fracturing stress tensor construction and transformation module is configured to perform numerical simulation on mine fracturing under mining action, extract and calculate the principal stress of fracturing, and characterize and analyze the evolution law of fracturing stress field under the action of mining stress field.

[0027] In one example of the present invention, the mining stress tensor construction and transformation module includes:

[0028] A second-order stress tensor construction unit is used to construct a 3×3 second-order stress tensor according to the symmetry of shear stress; wherein the mining stress components include: 3 normal stresses and 3 shear stresses;

[0029] The principal stress calculation unit is configured to calculate the principal stress scalar and its corresponding principal direction by using the eigenvalue decomposition method for the stress tensor; wherein the dynamic stress component is obtained from the unit integration point.

[0030] In one example of the present invention, the mining principal stress continuous smooth transformation module includes:

[0031] The three-dimensional six-direction matrix construction unit is configured to use the three principal stresses of the maximum principal stress, the intermediate principal stress and the minimum principal stress, based on the symmetry of the six directions of front and back, left and right, and top and bottom of a point, to splice the principal stresses and the principal stresses in the opposite directions to construct a three-dimensional six-direction principal direction matrix H, that is, H = [V1, -V1, V2, -V2, V3, -V3];

[0032] The main direction inner product matrix calculation unit is configured to perform an inner product operation on two adjacent three-dimensional six-directional main direction matrices, that is, M=H1·H2, to obtain a main direction inner product matrix M;

[0033] A rotation matrix calculation unit is configured to perform a singular value decomposition of the inner product matrix to calculate a rotation matrix R between two three-dimensional six-direction main direction matrices, that is, R = U × V T , U and V are the left singular matrix and right singular matrix after eigenvalue decomposition of the inner product matrix, respectively;

[0034] The trajectory smoothing evolution unit is configured to transform the three-dimensional rotation matrix in the Lie group space into the Lie algebraic space through logarithmic mapping, i.e., r=log(R), and after linear interpolation in the Lie algebraic space, transform it into the Lie group space through exponential mapping R'=log(r') to obtain a continuous smooth evolution trajectory of the main direction.

[0035] Another object of the present invention is to provide a computer-readable storage medium having a computer program stored thereon, wherein when the computer program is executed by a processor, the method for characterizing the evolution of a fracturing stress field as described in any one of the above is implemented.

[0036] The outstanding beneficial effects compared with the prior art are as follows:

[0037] The present invention proposes a method for simulating the spatiotemporal evolution of a fracturing stress field based on a coal mining stress field, transforms the macroscopic mining stress into a three-dimensional principal stress state at each integral point, obtains continuous principal direction evolution characteristics through an inner product matrix and a rotation matrix, and combines the principal stress scalar to assign the spatial distribution characteristics and temporal evolution of the mining stress field to a fracturing model. After extracting the principal stress state at each position in the fracturing stress field, the three-dimensional principal stress states in the mining stress field and the fracturing stress field are compared, and the interaction law between the mining stress field and the fracturing stress field is analyzed, thereby achieving the visualization of the principal stress evolution in the mining stress field and the fracturing stress field and the effect of a refined study of the interaction between the two.

[0038] The best embodiment for carrying out the present invention will be described in more detail below with reference to the accompanying drawings so that the features and advantages of the present invention can be easily understood. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings of the embodiments of the present invention, wherein the drawings are only used to illustrate some embodiments of the present invention, but not to limit all embodiments of the present invention thereto.

[0040] Figure 1 A flow chart of simulating the spatiotemporal evolution of a fracturing stress field under mining action according to an embodiment of the present invention;

[0041] Figure 2 is a three-dimensional main direction evolution trajectory according to an embodiment of the present invention;

[0042] Figure 3 It is a schematic diagram for comparative analysis of the fracturing stress field and the mining stress field according to an embodiment of the present invention. DETAILED DESCRIPTION

[0043] In order to make the purpose, technical solution and advantages of the technical solution of the present invention clearer, the technical solution of the embodiment of the present invention will be clearly and completely described in conjunction with the drawings of specific embodiments of the present invention. The same figure marks in the drawings represent the same parts. It should be noted that the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the described embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0044] Unless otherwise defined, the technical terms or scientific terms used herein shall have the usual meanings understood by persons of ordinary skill in the field to which the present invention belongs. The words "first", "second" and similar words used in the patent application specification and claims of the present invention do not indicate any order, quantity or importance, but are only used to distinguish different components. Similarly, words such as "one" or "one" do not necessarily indicate a quantity limitation. Words such as "include" or "comprise" mean that the elements or objects appearing before the word include the elements or objects listed after the word and their equivalents, without excluding other elements or objects. Words such as "connect" or "connected" are not limited to physical or mechanical connections, but may include electrical connections, whether direct or indirect. "Up", "down", "left", "right" and the like are only used to indicate relative positional relationships. When the absolute position of the described object changes, the relative positional relationship may also change accordingly.

[0045] According to the first aspect of the present invention, a three-dimensional fracturing stress field evolution characterization method based on mining effects is as follows: Figure 1 As shown, the following steps are included:

[0046] S10, construct and transform three-dimensional mining stress tensor: perform numerical simulation on mining face mining, extract mining stress components in the target study area, construct three-dimensional second-order stress tensor, and calculate principal stress scalars and principal directions;

[0047] S20, continuous and smooth transformation of dynamic principal stress: construct a three-dimensional six-direction principal direction matrix, then construct the principal stress inner product matrix, calculate the rotation matrix and obtain the continuous and smooth evolution trajectory of the principal stress direction;

[0048] S30, reproducing the spatiotemporal mining stress field: assigning the spatial mining stress field to the fracturing model in the form of a predefined field, and assigning the temporal mining stress field to the fracturing model in the form of a dynamic load boundary;

[0049] S40. Construct and transform three-dimensional fracturing stress tensor: perform numerical simulation on mine fracturing under mining action, extract and calculate the principal fracturing stress, characterize and analyze the evolution law of the fracturing stress field under the action of mining stress field.

[0050] The present invention proposes a method for simulating the spatiotemporal evolution of a fracturing stress field based on a coal mining stress field, transforms the macroscopic mining stress into a three-dimensional principal stress state at each integral point, obtains continuous principal direction evolution characteristics through an inner product matrix and a rotation matrix, and combines the principal stress scalar to assign the spatial distribution characteristics and temporal evolution of the mining stress field to a fracturing model. After extracting the principal stress state at each position in the fracturing stress field, the three-dimensional principal stress states in the mining stress field and the fracturing stress field are compared, and the interaction law between the mining stress field and the fracturing stress field is analyzed, thereby achieving the visualization of the principal stress evolution in the mining stress field and the fracturing stress field and the effect of a refined study of the interaction between the two.

[0051] In an example of the present invention, in step S10, constructing a three-dimensional second-order stress tensor and calculating the principal stress scalar and the principal direction specifically include the following steps:

[0052] The mining stress components include: 3 normal stresses and 3 shear stresses, and a 3×3 second-order stress tensor is constructed according to the symmetry of the shear stress. The stress tensor is then decomposed using the eigenvalue method to calculate the principal stress scalar and its corresponding principal direction; wherein the mining stress components are obtained at the unit integration points.

[0053] For example, the mining stress components need to be obtained from the unit integration points rather than the nodes; the mining stress components include three normal stresses (σ 11 ,σ 22 ,σ 33 ) and three shear stresses (τ 12 ,τ 13 ,τ 23 ), and then construct a 3×3 second-order stress tensor based on the symmetry of shear stress, that is, Then the stress tensor is decomposed using the eigenvalue method, that is, Ax = λx and B = V -1 AV, calculate the principal stress scalar (λ i ) and its corresponding main direction (V i ).

[0054] In an example of the present invention, in step S20, continuously and smoothly transforming the mining principal stress specifically includes the following steps:

[0055] Using the three principal stresses of maximum principal stress, intermediate principal stress and minimum principal stress, based on the symmetry of the six directions of front-back, left-right and top-bottom of a point, the principal stress and the principal stress in the opposite direction are spliced ​​to construct a three-dimensional six-direction principal direction matrix H, that is, H = [V1, -V1, V2, -V2, V3, -V3];

[0056] Perform an inner product operation on two adjacent three-dimensional six-direction main direction matrices, that is, M = H1·H2, to obtain the main direction inner product matrix M;

[0057] The inner product matrix is ​​decomposed to calculate the rotation matrix R between the two three-dimensional six-direction matrices, that is, R = U × V T , U and V are the left singular matrix and right singular matrix after eigenvalue decomposition of the inner product matrix, respectively;

[0058] The three-dimensional rotation matrix in the Lie group space is transformed into the Lie algebra space through logarithmic mapping, that is, r=log(R). After linear interpolation in the Lie algebra space, it is transformed into the Lie group space through exponential mapping R'=log(r') to obtain the continuous and smooth evolution trajectory of the main direction.

[0059] In an example of the present invention, in step S30, assigning the spatial mining stress field to the fracturing model in the form of a predefined field specifically includes: assigning the mining stress tensors of each unit to the units in the fracturing area in batches to realize the predefined stress field.

[0060] In one example of the present invention, in step S30, assigning a time-series mining stress field to the fracturing model in the form of a dynamic load boundary specifically includes: setting a predefined field in the mining stress space, and calculating a dynamic load function based on the continuously evolving principal stress trajectory, and then applying the mining stress to the fracturing model as a dynamic load.

[0061] That is to say, reproducing the spatiotemporal mining stress field includes: establishing a fracturing model and assigning the mining stress field. When studying the influence of the spatial distribution of mining stress on the fracturing stress field, the mining stress tensors of each unit are batch-assigned to the units in the fracturing area to realize the predefined stress field. When studying the influence of the temporal evolution of the mining stress field on the fracturing stress field, in addition to setting the predefined field of the mining stress space, it is also necessary to calculate the dynamic load function according to the continuously evolving principal stress trajectory, and then apply the mining stress to the fracturing model as a dynamic load.

[0062] In an example of the present invention, step S40 specifically includes the following steps:

[0063] Firstly, numerical simulation of fracturing under mining action is carried out to extract the fracturing stress components at the unit integration points, and the fracturing principal stress scalar (λ i ') and the main direction (V i '), construct a three-dimensional six-direction matrix of the fracturing stress field, and then calculate the inner product matrix and rotation matrix of the fracturing principal stress in turn. Finally, the continuous and smooth evolution trajectory of the fracturing principal direction is calculated by Lie group and Lie algebra. Finally, the influence of the mining stress field on the evolution of the fracturing stress field is analyzed, and the expansion law of the cracks is further analyzed based on the fracturing stress field.

[0064] It is worth noting that matters not covered by the present invention are well-known technologies.

[0065] According to the second aspect of the present invention, an evolution characterization system of the above-mentioned three-dimensional fracturing stress field evolution characterization method based on mining effects comprises:

[0066] The mining stress tensor construction and transformation module is configured to perform numerical simulation on mining face mining, extract mining stress components in the target study area, construct a three-dimensional second-order stress tensor, and calculate the principal stress scalars and principal directions;

[0067] The principal stress continuous smooth transformation module is configured to construct a three-dimensional six-direction principal direction matrix, then construct the principal stress inner product matrix, calculate the rotation matrix and obtain the continuous smooth evolution trajectory of the principal stress direction;

[0068] A mining stress field spatiotemporal reproduction module, configured to assign a spatial mining stress field to the fracturing model in the form of a predefined field, and to assign a temporal mining stress field to the fracturing model in the form of a dynamic load boundary;

[0069] The three-dimensional fracturing stress tensor construction and transformation module is configured to perform numerical simulation on mine fracturing under mining action, extract and calculate the principal stress of fracturing, and characterize and analyze the evolution law of fracturing stress field under the action of mining stress field.

[0070] The present invention proposes a spatiotemporal evolution simulation system of a fracturing stress field based on a coal mine mining stress field, transforms the macroscopic mining stress into a three-dimensional principal stress state at each integral point, obtains continuous principal direction evolution characteristics through an inner product matrix and a rotation matrix, and combines the principal stress scalar to assign the spatial distribution characteristics and temporal evolution of the mining stress field to a fracturing model. After extracting the principal stress state at each position in the fracturing stress field, the three-dimensional principal stress states in the mining stress field and the fracturing stress field are compared, and the interaction law between the mining stress field and the fracturing stress field is analyzed, thereby realizing the visualization of the principal stress evolution in the mining stress field and the fracturing stress field and the effect of refined research on the interaction between the two.

[0071] In one example of the present invention, the mining stress tensor construction and transformation module includes:

[0072] A second-order stress tensor construction unit is used to construct a 3×3 second-order stress tensor according to the symmetry of shear stress; wherein the mining stress components include: 3 normal stresses and 3 shear stresses;

[0073] The principal stress calculation unit is configured to calculate the principal stress scalar and its corresponding principal direction by using the eigenvalue decomposition method for the stress tensor; wherein the dynamic stress component is obtained from the unit integration point.

[0074] In one example of the present invention, the mining principal stress continuous smooth transformation module includes:

[0075] The three-dimensional six-direction matrix construction unit is configured to use the three principal stresses of the maximum principal stress, the intermediate principal stress and the minimum principal stress, based on the symmetry of the six directions of front and back, left and right, and top and bottom of a point, to splice the principal stresses and the principal stresses in the opposite directions to construct a three-dimensional six-direction principal direction matrix H, that is, H = [V1, -V1, V2, -V2, V3, -V3];

[0076] The main direction inner product matrix calculation unit is configured to perform an inner product operation on two adjacent three-dimensional six-directional main direction matrices, that is, M=H1·H2, to obtain a main direction inner product matrix M;

[0077] A rotation matrix calculation unit is configured to perform a singular value decomposition of the inner product matrix to calculate a rotation matrix R between two three-dimensional six-direction main direction matrices, that is, R = U × V T , U and V are the left singular matrix and right singular matrix after eigenvalue decomposition of the inner product matrix, respectively;

[0078] The trajectory smoothing evolution unit is configured to transform the three-dimensional rotation matrix in the Lie group space into the Lie algebraic space through logarithmic mapping, i.e., r=log(R), and after linear interpolation in the Lie algebraic space, transform it into the Lie group space through exponential mapping R'=log(r') to obtain a continuous smooth evolution trajectory of the main direction.

[0079] According to a third aspect of the present invention, a computer-readable storage medium stores a computer program, and when the computer program is executed by a processor, the method for characterizing the evolution of a fracturing stress field as described in any one of the above is implemented.

[0080] The specific process of a three-dimensional fracturing stress field evolution characterization method based on mining effects is as follows: Figure 1 As shown:

[0081] Take coal mining as an example ,

[0082] Step 1: Establish a mining face with a length, width, and height of 300m, 100m, and 3m respectively in ABAQUS, and set a 50m coal pillar around it. Carry out a series of modeling work such as assigning material properties and dividing the grid, and add keywords to record the unit integration points. After the mining simulation is completed, the coordinates of the integration points in the target study area and their corresponding stress components (S 11 ,S 22 ,S 33 ,S 12 ,S 13 ,S 23 ), then construct the stress tensor, and obtain the three principal stress scalars (λ1, λ2, λ3) and the principal directions (V1, V2, V3) through eigenvalue decomposition.

[0083] Step 2: At each integration point, the three principal stresses of maximum principal stress, intermediate principal stress and minimum principal stress are used. Based on the symmetry of six directions (front and back, left and right, up and down) of a point, the principal stress in the opposite direction takes a negative value, and the three principal stresses are spliced ​​to construct a three-dimensional six-direction principal direction matrix; the inner product operation is performed on two adjacent three-dimensional six-direction principal direction matrices to obtain the principal stress inner product matrix; then the inner product matrix is ​​singularly decomposed to calculate the rotation matrix between the two three-dimensional six-direction principal direction matrices, and the rotation matrix is ​​transformed into the Lie algebra space through logarithmic mapping for interpolation, and then mapped back to the Lie group space to obtain the continuous and smooth evolution trajectory of the principal stress direction, such as Figure 2 shown.

[0084] Step 3, in the mining model, the area 50m ahead of the rotating working face is used as the fracturing simulation area, and the mining stress field is applied in the fracturing model. When studying the influence of the spatial distribution of mining stress on the fracturing stress field, in the predefined stress field in ABAQUS, the mining stress tensor of each unit is batch-assigned to each unit in the fracturing area through Python secondary development; when studying the influence of the time-series evolution of the mining stress field on the fracturing stress field, in addition to setting the predefined field of mining stress space, it is also necessary to calculate the distribution function of the load according to the continuously evolving principal stress trajectory through the Fortran subroutine, and apply the mining stress to the boundary of the fracturing model as a dynamic load.

[0085] Step 4: After applying the mining stress field, carry out numerical simulation of fracturing under mining action, and then extract the fracturing stress component (S 11 ',S 22 ',S 33 ',S 12 ',S 13 ',S 23 '), calculate the principal stress scalar (σ1', σ2', σ3') and principal direction (V1', V2', V3') of the fracturing stress field by eigenvalue decomposition, construct the three-dimensional six-direction principal direction matrix of the fracturing stress field according to the principal direction, and then calculate the inner product matrix and rotation matrix of the fracturing principal stress in turn, and then calculate the continuous and smooth evolution trajectory of the principal stress direction of the fracturing by Lie group and Lie algebra, analyze the influence of the mining stress field on the evolution of the fracturing stress field, and further analyze the expansion law of the crack based on the fracturing stress field, such as Figure 3 shown.

[0086] Through the above steps, the continuous evolution of the mining stress field and the pressure stress field can be achieved. There is a large stress change in the stress concentration area. The fracture tip stress field causes the transformation of the principal stress vector of the surrounding mining stress. The mining stress field that evolves in time and space also affects the evolution of the fracturing crack stress field.

[0087] The above describes in detail an exemplary implementation of a three-dimensional fracturing stress field evolution characterization method and system based on mining mining effects proposed in the present invention with reference to a preferred embodiment. However, those skilled in the art will appreciate that, without departing from the concept of the present invention, various modifications and variations can be made to the above-mentioned specific embodiments, and various technical features and structures proposed in the present invention can be combined in various ways without exceeding the protection scope of the present invention, which is determined by the attached claims.

Claims

1. A method for characterizing the evolution of three-dimensional fracturing stress field based on mining effects, characterized in that: The steps include: S10, construct and transform three-dimensional mining stress tensor: perform numerical simulation on mining face mining, extract mining stress components in the target study area, construct three-dimensional second-order stress tensor, and calculate principal stress scalars and principal directions; S20, continuously and smoothly transforming the principal stress: constructing a three-dimensional six-direction principal direction matrix, then constructing a principal stress inner product matrix, calculating the rotation matrix and obtaining a continuous and smooth evolution trajectory of the principal stress direction; wherein, continuously and smoothly transforming the principal stress specifically includes the following steps: Using the three principal stresses of maximum principal stress, intermediate principal stress and minimum principal stress, based on the symmetry of the six directions of front and back, left and right, and up and down, the three-dimensional six-direction principal direction matrix is ​​constructed by splicing the principal stress and the principal stress in the opposite direction. H ,Right now H =[ V 1,- V 1, V 2,- V 2, V 3,- V 3]; Perform the inner product operation on two adjacent three-dimensional six-direction main direction matrices, that is, M = H 1. H 2. Get the main direction inner product matrix M ; Decompose the inner product matrix singular value to compute the rotation matrix between two three-dimensional six-direction matrices R ,Right now R = U × V T , U and V They are the left singular matrix and the right singular matrix after the eigenvalue decomposition of the inner product matrix; The three-dimensional rotation matrix in the Lie group space is transformed into the Lie algebra space through logarithmic mapping, that is r =log( R ), after linear interpolation in Lie algebraic space, and then through exponential mapping R’ =log( r’ ) is converted into Lie group space to obtain the continuous and smooth evolution trajectory of the main direction; S30, reproducing the spatiotemporal mining stress field: assigning the spatial mining stress field to the fracturing model in the form of a predefined field, and assigning the temporal mining stress field to the fracturing model in the form of a dynamic load boundary; S40. Construct and transform three-dimensional fracturing stress tensor: perform numerical simulation on mine fracturing under mining action, extract and calculate the principal fracturing stress, characterize and analyze the evolution law of the fracturing stress field under the action of mining stress field.

2. The method for characterizing the evolution of three-dimensional fracturing stress field based on mining effects according to claim 1 is characterized in that: In step S10, constructing a three-dimensional second-order stress tensor and calculating the principal stress scalar and the principal direction specifically includes the following steps: The mining stress components include: 3 normal stresses and 3 shear stresses, and a 3×3 second-order stress tensor is constructed according to the symmetry of the shear stress. The stress tensor is then decomposed using the eigenvalue method to calculate the principal stress scalar and its corresponding principal direction; wherein the mining stress components are obtained at the unit integration points.

3. The method for characterizing the evolution of three-dimensional fracturing stress field based on mining effects according to claim 1 is characterized in that: In step S30, assigning the spatial mining stress field to the fracturing model in the form of a predefined field specifically includes: assigning the mining stress tensors of each unit to the units in the fracturing area in batches to realize the predefined stress field.

4. The method for characterizing the evolution of three-dimensional fracturing stress field based on mining effects according to claim 1 is characterized in that: In step S30, assigning a time-series mining stress field to the fracturing model in the form of a dynamic load boundary specifically includes: setting a predefined field in the mining stress space, and calculating a dynamic load function according to the continuously evolving principal stress trajectory, and then applying the mining stress to the fracturing model as a dynamic load.

5. The method for characterizing the evolution of three-dimensional fracturing stress field based on mining effects according to claim 1 is characterized in that: The step S40 specifically includes the following steps: Firstly, numerical simulation of fracturing under mining action is carried out, and the fracturing stress components at the unit integration points are extracted. The principal stress scalars and principal directions of the fracturing are calculated by eigenvalue decomposition, and the three-dimensional six-direction principal direction matrix of the fracturing stress field is constructed. Then, the inner product matrix and rotation matrix of the fracturing principal stress are calculated in turn. Finally, the continuous and smooth evolution trajectory of the principal direction of the fracturing is calculated by Lie group and Lie algebra. Finally, the influence of the mining stress field on the evolution of the fracturing stress field is analyzed, and the expansion law of the cracks is further analyzed based on the fracturing stress field.

6. An evolution characterization system of a three-dimensional fracturing stress field evolution characterization method based on mining effects as claimed in any one of claims 1 to 5, characterized in that: include: The mining stress tensor construction and transformation module is configured to perform numerical simulation on mining face mining, extract mining stress components in the target study area, construct a three-dimensional second-order stress tensor, and calculate the principal stress scalars and principal directions; The mining principal stress continuous and smooth transformation module is configured to construct a three-dimensional six-direction principal direction matrix, then construct a principal stress inner product matrix, calculate the rotation matrix and obtain a continuous and smooth evolution trajectory of the principal stress direction; wherein the mining principal stress continuous and smooth transformation module includes: The three-dimensional six-way matrix construction unit is configured to use the three principal stresses of the maximum principal stress, the intermediate principal stress and the minimum principal stress, and to construct a three-dimensional six-way principal direction matrix by splicing the principal stress and the principal stress in the opposite direction based on the symmetry of the six directions of front and back, left and right, and up and down of a point. H ,Right now H =[ V 1, - V 1, V 2, - V 2, V 3, - V 3]; The main direction inner product matrix calculation unit is configured to perform inner product operation on two adjacent three-dimensional six-way main direction matrices, that is, M = H 1. H 2. Get the main direction inner product matrix M ; A rotation matrix calculation unit configured to perform a singular value decomposition of the inner product matrix to calculate a rotation matrix between two three-dimensional six-direction principal direction matrices R ,Right now R = U × V T , U and V They are the left singular matrix and the right singular matrix after the eigenvalue decomposition of the inner product matrix; The trajectory smoothing evolution unit is configured to transform the three-dimensional rotation matrix in the Lie group space into the Lie algebra space through logarithmic mapping, that is, r =log( R ), after linear interpolation in Lie algebraic space, and then through exponential mapping R’ =log( r’ ) is converted into Lie group space to obtain the continuous and smooth evolution trajectory of the main direction; A mining stress field spatiotemporal reproduction module, configured to assign a spatial mining stress field to the fracturing model in the form of a predefined field, and to assign a temporal mining stress field to the fracturing model in the form of a dynamic load boundary; The three-dimensional fracturing stress tensor construction and transformation module is configured to perform numerical simulation on mine fracturing under mining action, extract and calculate the principal stress of fracturing, and characterize and analyze the evolution law of fracturing stress field under the action of mining stress field.

7. The evolution characterization system of the three-dimensional fracturing stress field evolution characterization method based on mining effects according to claim 6 is characterized in that: The mining stress tensor construction and transformation module includes: A second-order stress tensor construction unit is used to construct a 3×3 second-order stress tensor according to the symmetry of shear stress; wherein the mining stress components include: 3 normal stresses and 3 shear stresses; The principal stress calculation unit is configured to calculate the principal stress scalar and its corresponding principal direction by using the eigenvalue decomposition method for the stress tensor; wherein the dynamic stress component is obtained from the unit integration point.

8. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the computer program is executed by a processor, the method for characterizing the evolution of a fracturing stress field as claimed in any one of claims 1 to 5 is implemented.

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