A ground stress detection method and system based on a finite fault network

Abstract

The application discloses a kind of ground stress detection method and detection system based on limited fault network, and detection method steps include: obtaining first model, the first model is the fitting stratum model of the region to be detected;Obtain first data, the first data is the data of fault plane in the region to be detected;According to the first data, construct fault plane in the first model, obtain second model;Second model is handled using triangular grid network, and based on the first data, establish fault contact surface in the model after processing, and contact friction is established to the fault contact surface, obtain ground stress model;Under the constraint of the ground stress model, and based on the first data, calculate, obtain the ground stress of the region to be detected;The beneficial effects of the application can reflect the distribution of ground stress field near non-continuous non-penetrating fault plane, while realizing the accurate detection of ground stress.

Description

Technical Field

[0001] This invention relates to the field of geostress detection technology, and more specifically, to a geostress detection method and system based on a finite fault network. Background Technology

[0002] In recent years, shale gas has become an important area of ​​natural gas exploration and development in my country. Exploration studies of shale gas have shown that shale reservoirs are characterized by self-generation and self-storage, low porosity, ultra-low permeability, and well-developed natural fractures. Generally, they lack natural production capacity and require hydraulic fracturing to achieve economical development. Whether analyzing the propagation patterns of hydraulic fractures or making decisions and designs for fracturing and perforation schemes, the crucial parameter of in-situ stress is essential. The accuracy of in-situ stress state measurements and the realism of in-situ stress prediction models directly affect the final effect of hydraulic fracturing. Therefore, the importance of in-situ stress research in the shale gas exploration and development process is self-evident.

[0003] In existing technologies, numerical simulation software has advantages such as simple operation, fast calculation, and small workload. Therefore, the measurement of geostress is usually carried out by numerical simulation. Using computer numerical simulation can provide an optimal location for geostress evaluation, thereby reducing testing time and cost. However, when using these methods to measure geostress, the models used are small in scale, and the faults are mostly large through faults, which makes it difficult to reflect the geostress field distribution near discontinuous and non-through fault groups.

[0004] In view of the above, this application is hereby submitted. Summary of the Invention

[0005] The technical problem to be solved by the present invention is that the existing technology cannot reflect the long-term distribution of in-situ stress near discontinuous and non-penetrating fault groups. The purpose is to provide an in-situ stress detection method and system based on a finite fault network, which can directly reflect the in-situ stress field in the vicinity of discontinuous and non-penetrating faults.

[0006] This invention is achieved through the following technical solution:

[0007] This invention provides a method for detecting geostress based on a finite fault network. The method includes the following steps:

[0008] Obtain the first model, which is a fitted stratigraphic model of the area to be detected;

[0009] Acquire first data, which is the data of the fault plane in the area to be detected;

[0010] Based on the first data, a fault plane is constructed in the first model to obtain a second model;

[0011] The second model is processed using a triangular mesh network, and based on the first data, a fault contact surface is established in the processed model, and contact friction is established on the fault contact surface to obtain a geostress model.

[0012] Under the constraints of the geostress model and based on the first data, the geostress of the area to be detected is obtained.

[0013] Traditionally, geostress measurement is typically performed using numerical simulation methods, simulating geostress within a computer. This method can pinpoint the optimal geostress location, reducing testing time and costs. However, when using this method, the constructed models are small, and the faults are often large, penetrating faults, making it difficult to reflect the geostress field distribution near discontinuous, non-penetrating fault groups. This invention provides a geostress detection method based on a finite fault network. By processing the model through a triangular mesh network and constructing fault contact surfaces within the mesh model, this method can reflect the geostress field distribution near discontinuous, non-penetrating fault surfaces while achieving accurate geostress detection.

[0014] Preferably, the method for constructing the first model includes:

[0015] Obtain second data of the stress region to be detected, wherein the second data is the fault rock mechanical parameters of the stress region to be detected;

[0016] Based on the second data, a geometric model corresponding to the stress region to be detected is constructed using a proportional scaling method to obtain the first model.

[0017] Preferably, the second data includes the topography, size, elastic modulus, Poisson's ratio, subsurface density, and gravitational acceleration data of the area to be tested for geostress.

[0018] Preferably, the first data includes the structural location of the fault, the fault horizon, the fault length, the fault dip, and the fault dip angle.

[0019] Preferably, the specific sub-steps for obtaining the geostress model include:

[0020] The second model is divided into a mesh model using a triangular mesh network;

[0021] Based on the first data, a fault contact surface is generated in the mesh model to obtain a fault mesh model;

[0022] A tangential contact is set at the fault contact surface, and a corresponding friction coefficient is set on the tangential contact to obtain a geostress model.

[0023] Preferably, when processing the second model through a triangular mesh network, the established mesh is a triangular mesh, and the mesh density between the meshes ranges from 10 to 200.

[0024] Defined as grid density, which is the number of grid nodes on each boundary line (also called seeding), generally ranging from 50 to 200. Preferably, the constraint of the geostress model is specifically: displacement constraint on each boundary of the geostress model.

[0025] Preferably, the specific calculation expression of the geostress is as follows:

[0026] σ=DBδ

[0027] D is the elastic matrix; B is the geometric matrix; σ is the geostress; and δ is the nodal displacement.

[0028] Preferably, the specific expression for the nodal displacement is:

[0029] Kδ=F g +F u

[0030] K is the element stiffness matrix; Fg is the overall load array of self-weight stress; Fu is the load array of structural stress.

[0031] The present invention also provides a geostress detection system based on a finite fault network. The detection system includes a model acquisition module, a data acquisition module, a first model construction module, a second model construction module, and a geostress calculation module.

[0032] The model acquisition module is used to acquire a first model, which is a fitted stratigraphic model of the area to be detected.

[0033] The data acquisition module is used to acquire first data, which is the data of the fault plane in the area to be detected;

[0034] The first model construction module is used to construct a fault plane in the first model based on the first data to obtain a second model;

[0035] The second model construction module is used to process the second model using a triangular mesh network, and based on the first data, to establish a fault contact surface in the processed model, and to establish contact friction on the fault contact surface to obtain a geostress model.

[0036] The geostress calculation module is used to calculate, under the constraints of the geostress model and based on the first data, the geostress of the area to be detected.

[0037] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0038] This invention provides a ground stress detection method and system based on a finite fault network. By processing the model through a triangular mesh network and constructing a fault contact surface in the mesh model, the method can reflect the distribution of the ground stress field near discontinuous and non-penetrating fault surfaces, while achieving accurate detection of ground stress. Attached Figure Description

[0039] To more clearly illustrate the technical solutions of the exemplary embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly described below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0040] Figure 1 Schematic diagram of the detection method

[0041] Figure 2 Schematic diagram of the detection system

[0042] Figure 3 Schematic diagram of the first model

[0043] Figure 4 Schematic diagram of the mesh model

[0044] Figure 5 Schematic diagram of fault mesh model

[0045] Figure 6 Schematic diagram of geostress model Detailed Implementation

[0046] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the embodiments and accompanying drawings. The illustrative embodiments and descriptions of the present invention are only used to explain the present invention and are not intended to limit the present invention.

[0047] In the following description, numerous specific details are set forth in order to provide a thorough understanding of the invention. However, it will be apparent to those skilled in the art that these specific details are not necessary to practice the invention. In other embodiments, well-known structures, circuits, materials, or methods have not been specifically described in order to avoid obscuring the invention.

[0048] Throughout this specification, references to "an embodiment," "an example," or "an example" mean that a particular feature, structure, or characteristic described in connection with that embodiment or example is included in at least one embodiment of the present invention. Therefore, the phrases "an embodiment," "an example," "an example," or "an example" appearing in various places throughout the specification do not necessarily refer to the same embodiment or example. Furthermore, specific features, structures, or characteristics can be combined in one or more embodiments or examples in any suitable combination and / or sub-combination. Moreover, those skilled in the art will understand that the illustrations provided herein are for illustrative purposes and are not necessarily drawn to scale. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0049] In the description of this invention, the terms "front", "rear", "left", "right", "up", "down", "vertical", "horizontal", "high", "low", "inner", and "outer" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limiting the scope of protection of this invention.

[0050] Example 1

[0051] This embodiment discloses a geostress detection method based on a finite fault network. In this embodiment, a triangular mesh network method is used to process the constructed geometric model, and fault contact surfaces are constructed within the mesh model. Discontinuous, non-penetrating fault surfaces are displayed in the model, and the corresponding geostress distribution can be calculated. The specific method process is as follows: Figure 1 As shown, the detection method steps include:

[0052] S1: Obtain the first model, which is a fitted stratigraphic model of the area to be detected;

[0053] In step S1, the first model established is a geometric model of the strata constructed based on the size of the area to be detected and the state of the geological layers. The strata model is a simplified expression and comprehensive explanation of the composition, structure, and spatiotemporal existence of the strata entity; therefore, the established first model can intuitively reflect the strata situation of the area to be detected. In this embodiment, the first model is a hexahedral solid model, such as... Figure 3 As shown;

[0054] The method for constructing the first model includes:

[0055] Obtain second data of the stress region to be detected, wherein the second data is the fault rock mechanical parameters of the stress region to be detected;

[0056] Based on the second data, a geometric model corresponding to the stress region to be detected is constructed using a proportional scaling method to obtain the first model.

[0057] The second data includes the topography, size, elastic modulus, Poisson's ratio, subsurface density, and gravitational acceleration data of the area to be tested for geostress.

[0058] In this step, a common non-penetrating surface is removed from the geological body to simulate a fault plane. Mechanical properties of the strata and fault rocks are assigned: the elastic modulus is set between 30-45 GPa, increasing linearly with depth; Poisson's ratio is set to 0.23; and the formation density is set to 2500–2700 kg / m³. 3 The value is generally taken as 2516 kg / m³. 3 The acceleration due to gravity is 9.81 m / s². 2 These two values ​​are used to calculate the equilibrium stress. The stress calculation process involves three analysis steps: the initial analysis step, the stress equilibrium analysis step, and the mirror force analysis step. In the stress equilibrium analysis step, the gravity action mode is selected, requiring the setting of formation density and gravitational acceleration, as well as the corresponding displacement and boundary conditions.

[0059] S2: Acquire first data, which is the data of the fault plane in the area to be detected;

[0060] The first data includes the structural location of the fault, the fault horizon, the fault length, the fault dip, and the fault dip angle.

[0061] In step 2, the first data takes the eastern wing of the Yanggao Temple structure of Yangshen 11 as an example. The fault position is Wufengdi, the fault length is 20.36km, the fault dips westward, and the fault dip angle is 75-80°.

[0062] S3: Based on the first data, construct the fault plane in the first model to obtain the second model;

[0063] In step S3, based on the data obtained in step S2, the coordinates of the fault plane are obtained according to the principle of proportional scaling and by constructing a corresponding coordinate system. Based on the coordinates, the corresponding fault plane is constructed in the first model.

[0064] S4: The second model is processed using a triangular mesh network, and based on the first data, a fault contact surface is established in the processed model, and contact friction is established on the fault contact surface to obtain a geostress model;

[0065] In step S4, the second model is divided into a mesh block model, such as... Figure 4 As shown, the geometric model is divided into a finite element model composed of three-dimensional ten-node tetrahedral elements; the required fault geometry model is constructed as a joint to prepare for the subsequent setting of fault contact friction.

[0066] The specific sub-steps for obtaining the geostress model include:

[0067] The second model is divided into a mesh model using a triangular mesh network. In this embodiment, the more meshes in the constructed mesh model, the more accurate the final calculated ground stress. Therefore, the spacing between the meshes needs to be adjusted accordingly. Thus, when processing the second model using a triangular mesh network, the established mesh is a triangular mesh, and the spacing between the meshes is defined as the mesh density, which is the number of mesh nodes on each boundary line (also called seeding), generally ranging from 10 to 200.

[0068] Based on the first data, a fault contact surface is generated in the mesh model to obtain a fault mesh model;

[0069] The generated fault mesh model is as follows: Figure 5 As shown, the coordinates of the fault plane endpoints in the mesh model are obtained based on the actual fault plane area in the area to be detected. The corresponding points are marked in the mesh model, and then the points are connected to each other. After the connection, a fault plane can be obtained directly, which is the constructed fault contact surface. In the fault mesh model, the specific location of the fault can be reflected intuitively, and non-continuous and non-penetrating fault planes can be displayed.

[0070] Numerous discontinuous and non-penetrating faults are treated as three-dimensional discontinuous rectangular planes with no thickness. Taking a single fault as an example, its position in the strata is determined based on field-measured fault data. First, a reference surface is established in the model. Then, the geometric area of ​​the fault is defined according to its relative size in the strata, thereby determining the coordinates of the four endpoints of the fault rectangular plane. The location of the fault and fault group is uniquely determined by the coordinates of the four spatial vertices of the matrix. The resulting geometric model has a faster calculation speed and higher modeling efficiency in subsequent finite element analysis.

[0071] A tangential contact is established at the fault contact surface, and a corresponding friction coefficient is set on the tangential contact to obtain a geostress model, such as... Figure 6 As shown.

[0072] Specific facility methods:

[0073] Export the fault mesh model as a fixed-format file and import it back into the finite element software; then use the crack function in the interaction module to generate the fault contact surface.

[0074] The principle is to simulate the contact friction of a fault by generating two sets containing different numbers of units. The specific steps are as follows:

[0075] First, select the entire element set set-1 from the fault plane and name it Surf-a. Then, subtract the elements from set-1 and name the subset set-b. Set the two Surf elements to frictional contact and use the penalty stiffness algorithm, which allows elastic slip deformation, with the friction coefficient set to 0.6.

[0076] S5: Under the constraints of the geostress model and based on the first data, the geostress of the area to be detected is obtained.

[0077] The constraints of the geostress model are specifically: displacement constraints are applied to each boundary of the geostress model.

[0078] The six boundary surfaces of the model are defined as X1, X2, Y1, Y2, Z1, and Z2. Set the displacement values ​​of Step-2 for the right boundary X1 surface and the front boundary Y1 surface of the model (set specific values ​​as required). The normal displacement of the boundary surfaces X2, Y2, Z1, and Z2 is constrained to 0. No displacement constraint is set for the Z1 surface (upper boundary surface).

[0079] The mode and magnitude of boundary loads are crucial for inversion analysis of the geostress field. In numerical simulation, the vertical gravity field can be achieved using the unit weight of the strata, while the superposition of the horizontal tectonic stress field is simulated by setting appropriate boundary conditions and computational models. The far-field boundary tectonic action can be considered as the superposition of two basic tectonic states: horizontal compression or tension along the X and Y directions; and uniform shear deformation within the horizontal plane.

[0080] The process of trial boundary conditions is as follows: apply a set of compressive and shear forces, solve the model, extract the magnitudes of the three principal stresses at the known well point locations and the direction of the maximum horizontal principal stress, and compare them with the results obtained from hydraulic fracturing data and acoustic emission tests. If the comparison results are within the allowable error range, the boundary conditions are considered to be true formation boundary conditions; otherwise, modify the boundary conditions and recalculate until the error requirements are met.

[0081] The specific calculation expression for the aforementioned geostress is as follows:

[0082] σ=DBδ

[0083] D is the elastic matrix; B is the geometric matrix; σ is the geostress; and δ is the nodal displacement.

[0084] The specific expression for the nodal displacement is:

[0085] Kδ=F g +F u

[0086] K is the element stiffness matrix; Fg is the overall load array of self-weight stress; Fu is the load array of structural stress.

[0087] The calculated ground stress can be optimized using measured values ​​from several points. The specific optimization method is as follows:

[0088] Suppose there are N measured stress values ​​σ1(j), σ2(j), σ3(j) at points within the model domain. These values ​​are assigned corresponding weight coefficients ω1(j), ω2(j), ω3(j) according to the number of measurements and their reliability. Solving this problem using a specific structural stress parameter T (a determined F) yields stress values ​​σ′1(j), σ′2(j), σ′3(j). T is considered as a point of variation in m-dimensional space, i.e.: T = T(T1, T2, T3, ..., T m Then the sum of squared differences (fitting criterion) between σ(j) and σ1(j) is:

[0089]

[0090] Using the magnitude of E(k) as a criterion for evaluating whether T conforms to reality, we can find T that satisfies the optimization condition as follows:

[0091]

[0092] The constraints are as follows:

[0093] 0≤T i ≤maxσ1(j)

[0094] The stress and stress direction are obtained by solving the above mechanical equations.

[0095] This embodiment discloses a ground stress detection system based on a finite fault network. By processing the model through a triangular mesh network and constructing a fault contact surface in the mesh model, it can reflect the distribution of the ground stress field near discontinuous and non-penetrating fault planes and achieve accurate detection of ground stress.

[0096] Example 2

[0097] This embodiment discloses a geostress detection system based on a finite fault network. This embodiment aims to implement the detection method described in Embodiment 1. Figure 2As shown, the detection system includes a model acquisition module, a data acquisition module, a first model construction module, a second model construction module, and a ground stress calculation module;

[0098] The model acquisition module is used to acquire a first model, which is a fitted stratigraphic model of the area to be detected.

[0099] The data acquisition module is used to acquire first data, which is the data of the fault plane in the area to be detected;

[0100] The first model construction module is used to construct a fault plane in the first model based on the first data to obtain a second model;

[0101] The second model construction module is used to process the second model using a triangular mesh network, and based on the first data, to establish a fault contact surface in the processed model, and to establish contact friction on the fault contact surface to obtain a geostress model.

[0102] The geostress calculation module is used to calculate, under the constraints of the geostress model and based on the first data, the geostress of the area to be detected.

[0103] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. 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 method for detecting geostress based on a finite fault network, characterized in that, The detection method steps include: Obtain the first model, which is a fitted stratigraphic model of the area to be detected; Acquire first data, which is the data of the fault plane in the area to be detected; Based on the first data, a fault plane is constructed in the first model to obtain a second model; The second model is processed using a triangular mesh network, and based on the first data, a fault contact surface is established in the processed model, and contact friction is established on the fault contact surface to obtain a geostress model. Under the constraints of the geostress model and based on the first data, the geostress of the area to be detected is obtained; The method for constructing the first model includes: Acquire the second data of the stress region to be detected, wherein the second data is the fault rock mechanical parameters of the stress region to be detected; Based on the second data, a geometric model corresponding to the stress region to be detected is constructed according to the proportional scaling method to obtain the first model; The second data includes the topography, size, elastic modulus, Poisson's ratio, subsurface density, and gravitational acceleration data of the area to be tested for geostress. The first data includes the structural location of the fault, the fault horizon, the fault length, the fault dip, and the fault dip angle; The specific sub-steps for obtaining the geostress model include: The second model is divided into a mesh model using a triangular mesh network; Based on the first data, a fault contact surface is generated in the mesh model to obtain a fault mesh model; A tangential contact is set at the fault contact surface, and a corresponding friction coefficient is set on the tangential contact to obtain a geostress model; The specific calculation expression for the geostress is as follows: ； D is the elasticity matrix; B is the geometric matrix. δ represents the ground stress, and δ represents the nodal displacement. The specific expression for the nodal displacement is: ； K is the element stiffness matrix; Fg is the overall load array of self-weight stress; Fu is the load array of structural stress.

2. The geostress detection method based on a finite fault network according to claim 1, characterized in that, When processing the second model using a triangular mesh network, the mesh is a triangular mesh, and the mesh density between the meshes ranges from 10 to 200.

3. The geostress detection method based on a finite fault network according to claim 1, characterized in that, The constraints of the geostress model are specifically: displacement constraints are applied to each boundary of the geostress model.

4. A geostress detection system based on a finite fault network, characterized in that, To implement the method as described in claim 1, the detection system includes a model acquisition module, a data acquisition module, a first model construction module, a second model construction module, and a ground stress calculation module; The model acquisition module is used to acquire a first model, which is a fitted stratigraphic model of the area to be detected. The data acquisition module is used to acquire first data, which is the data of the fault plane in the area to be detected; The first model construction module is used to construct a fault plane in the first model based on the first data to obtain a second model; The second model construction module is used to process the second model using a triangular mesh network, and based on the first data, to establish a fault contact surface in the processed model, and to establish contact friction on the fault contact surface to obtain a geostress model. The geostress calculation module is used to calculate, under the constraints of the geostress model and based on the first data, the geostress of the area to be detected.

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