Time-shifting magnetotelluric three-dimensional inversion imaging method and equipment based on non-structural finite element

Abstract

The invention provides a time-shifting magnetotelluric three-dimensional inversion imaging method and device based on a non-structural finite element, and the method comprises the steps: building a core geological structure model of a research region, and not carrying out the modeling of a peripheral boundary; exporting a grid file and an area information file after core area modeling; importing the grid file and the regional information file into a program with a user interface, and expanding the model data of the boundary region; detecting and identifying different grid areas, selecting a predetermined area, and assigning resistivity and subdivision grid density parameters; performing grid encryption subdivision to generate a grid data file required in a forward and reverse modeling process; carrying out parallel calculation on the multi-frequency forward modeling program and the multi-frequency inversion program; subtraction is carried out on the three-dimensional inversion result, and the electrical property change characteristics of the fractured area are determined.

Description

Technical Field

[0001] The embodiments of the present invention relate to the field of geophysical exploration technology, and in particular to a time-lapse magnetotelluric three-dimensional inversion imaging method and device based on non-structural finite elements. Background Art

[0002] With the development of unconventional oil and gas resources (such as shale gas and tight oil and gas), fracturing technology has been widely used as a key means to increase reservoir permeability. However, accurately identifying and monitoring the spatial distribution and boundary changes of fracturing zones has become a technical challenge in oil and gas field development. Geophysical monitoring is widely used in oil and gas reservoir exploration and development. Time-lapse electromagnetic monitoring technology, which can effectively obtain reservoir fluid properties, has become an important auxiliary means of microseismic reservoir monitoring. Magnetotellurics (MT) is one of the most mature technologies. Traditional MT monitoring focuses on static resistivity inversion, while time-lapse MT (TLMT) technology can capture the temporal changes in subsurface resistivity, making it suitable for studying dynamic processes such as fluid injection. Early studies mostly used one-dimensional and two-dimensional inversion methods, but these technologies have difficulty accurately describing resistivity changes under complex three-dimensional geological conditions. Most studies have focused on near-surface observations, and their interpretation of deep formation dynamics is insufficient. Summary of the Invention

[0003] In view of the above problems existing in the prior art, an embodiment of the present invention provides a time-lapse magnetotelluric three-dimensional inversion imaging method and device based on non-structural finite element.

[0004] In the first aspect, an embodiment of the present invention provides a time-lapse magnetotelluric three-dimensional inversion imaging method based on non-structural finite elements, comprising: establishing a core geological structure model of the study area without modeling the outer boundary; exporting a grid file and a regional information file after modeling the core area; importing the grid file and the regional information file into a program with a user interface, and expanding the model data of the boundary area; detecting and identifying different grid areas, selecting a predetermined area and assigning resistivity and grid density parameters; performing grid encryption and generation of a grid data file required in the forward and inversion process; performing parallel calculations on a multi-frequency forward program and a multi-frequency inversion program; and subtracting the three-dimensional inversion results to determine the electrical change characteristics of the fracturing area.

[0005] Based on the contents of the above method embodiments, the time-lapse magnetotelluric three-dimensional inversion imaging method based on non-structural finite elements provided in the embodiments of the present invention establishes a core geological structure model of the study area without modeling the outer boundary, including: only modeling the core geological structure to reduce model smoothing and computing resource consumption caused by large boundaries.

[0006] Based on the contents of the above-mentioned method embodiment, the time-lapse magnetotelluric three-dimensional inversion imaging method based on unstructured finite elements provided in the embodiment of the present invention, the grid file and regional information file after the core area modeling are exported, including: the exported regional information file and grid file both contain domain units, boundary units, edge units, vertex units and geometric entity information.

[0007] Based on the contents of the above-mentioned method embodiments, the time-lapse magnetotelluric three-dimensional inversion imaging method based on non-structured finite elements provided in the embodiments of the present invention imports the grid file and the regional information file into a program with a user interface, and expands the model data of the boundary area, including: identifying the boundary of a predetermined core area according to the imported grid file and the regional information file, and expanding the boundary area according to predetermined boundary size parameters, supplementing the unestablished boundary area, and ensuring the predetermined grid accuracy of the predetermined core area.

[0008] Based on the contents of the above-mentioned method embodiments, the time-lapse magnetotelluric three-dimensional inversion imaging method based on non-structured finite elements provided in the embodiments of the present invention, wherein different grid areas are detected and identified, a predetermined area is selected, and resistivity and grid density parameters are assigned, including: identifying an upper boundary area and a lower boundary area, where the upper boundary is the sky area in the forward model, and the lower boundary is the boundary surrounding rock area in the forward model, assigning resistivity to the sky area and the boundary surrounding rock area, and the smaller the grid subdivision value, the finer the subdivision.

[0009] Based on the contents of the above method embodiments, the time-lapse magnetotelluric three-dimensional inversion imaging method based on unstructured finite elements provided in the embodiments of the present invention, wherein the multi-frequency forward modeling program and the multi-frequency inversion program are parallel calculated, includes: during forward modeling, parallel calculation of multiple frequencies is performed using the parallelization instructions of the shared memory parallel programming OpenMP, and during inversion, parallel calculation of the part requiring frequency calculation is performed, with the number of logical processors of the central processing unit (CPU) being the number of frequencies for parallel calculation.

[0010] Based on the content of the above method embodiment, the time-lapse magnetotelluric 3D inversion imaging method based on unstructured finite elements provided in the embodiment of the present invention, wherein the 3D inversion result is subtracted to determine the electrical property change characteristics of the fracturing area, includes: during forward modeling, using apparent resistivity for subtraction: in, is the difference in apparent resistivity; is the apparent resistivity after forward modeling; T n is any moment after fracturing; T0 is the moment before fracturing; n is the time point; during inversion, the resistivity values ​​of the same grid cells in the inversion results are directly subtracted: Where m is the inversion result, which is represented by a three-dimensional tetrahedral grid, and each grid is assigned the resistivity value after inversion; Δm is the resistivity difference of the same grid cell in the inversion result.

[0011] In the second aspect, an embodiment of the present invention provides a time-lapse magnetotelluric three-dimensional inversion imaging device based on non-structural finite elements, including: a first main module, used to establish a core geological structure model of the study area without modeling the outer boundary; a second main module, used to export the grid file and regional information file after the core area modeling; a third main module, used to import the grid file and regional information file into a program with a user interface, and expand the model data of the boundary area; a fourth main module, used to detect and identify different grid areas, select a predetermined area and assign resistivity and grid density parameters; a fifth main module, used to perform grid encryption and generate grid data files required in the forward and inversion process; a sixth main module, used to realize parallel calculation of a multi-frequency forward program and a multi-frequency inversion program; a seventh main module, used to realize subtraction of the three-dimensional inversion results and determine the electrical change characteristics of the fracturing area.

[0012] In a third aspect, an embodiment of the present invention provides an electronic device, including:

[0013] At least one processor, at least one memory and a communication interface; wherein,

[0014] The processor, memory and communication interface communicate with each other;

[0015] The memory stores program instructions that can be executed by the processor, and the processor calls the program instructions to execute the time-lapse magnetotelluric three-dimensional inversion imaging method based on non-structured finite elements provided by any one of the various implementation methods of the first aspect.

[0016] In a fourth aspect, an embodiment of the present invention provides a non-transitory computer-readable storage medium, which stores computer instructions, and the computer instructions enable a computer to execute the time-lapse magnetotelluric three-dimensional inversion imaging method based on non-structured finite elements provided by any one of the various implementation methods of the first aspect.

[0017] The time-lapse magnetotelluric three-dimensional inversion imaging method and equipment based on non-structural finite elements provided in the embodiments of the present invention combine the non-structural finite element method to simplify the modeling process and accurately capture the resistivity changes of deep formations under complex three-dimensional geology; subtract the three-dimensional inversion results to highlight the electrical change characteristics of the fracturing area, clearly characterize the boundaries, and enhance the ability to evaluate the fracturing effect; introduce parallel computing technology to improve the efficiency of three-dimensional forward modeling and inversion, accelerate the calculation process, and provide an efficient and accurate technical means for monitoring the fracturing area. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, a brief introduction will be given below to the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0019] Figure 1 A schematic flow chart of a time-lapse magnetotelluric three-dimensional inversion imaging method based on unstructured finite elements provided in an embodiment of the present invention;

[0020] Figure 2 A schematic structural diagram of a time-lapse magnetotelluric three-dimensional inversion imaging device based on non-structural finite elements provided in an embodiment of the present invention;

[0021] Figure 3 A schematic diagram of the physical structure of an electronic device provided by an embodiment of the present invention;

[0022] Figure 4 A schematic diagram of core area modeling provided by an embodiment of the present invention;

[0023] Figure 5 A schematic diagram of an exported area information data file provided in an embodiment of the present invention;

[0024] Figure 6 A schematic diagram of exporting a grid data file provided by an embodiment of the present invention;

[0025] Figure 7 A schematic diagram of setting the grid range size of boundary conditions provided in an embodiment of the present invention;

[0026] Figure 8 A schematic diagram of setting regional grid resistivity and segmentation values ​​provided in an embodiment of the present invention;

[0027] Figure 9 Schematic diagram of the five files required to complete forward and inversion provided by an embodiment of the present invention;

[0028] Figure 10 A schematic diagram comparing the calculation process before and after the forward parallel optimization provided by an embodiment of the present invention;

[0029] Figure 11 A schematic diagram comparing the calculation process before and after the inversion parallel optimization provided by an embodiment of the present invention;

[0030] Figure 12 A schematic diagram of the use of the forward modeling result data difference software provided in an embodiment of the present invention;

[0031] Figure 13A schematic diagram of the use of the inversion result data difference software provided in an embodiment of the present invention;

[0032] Figure 14 A schematic diagram of the original modeling effect provided by an embodiment of the present invention;

[0033] Figure 15 A schematic diagram of the y=0 section mesh after mesh segmentation without boundary modeling provided in an embodiment of the present invention;

[0034] Figure 16 A schematic diagram of the y=0 section mesh after mesh segmentation for boundary range modeling provided by an embodiment of the present invention;

[0035] Figure 17 Schematic diagram of the x=0 slice and the z=1000m slice of the forward formation model at time T1 provided by an embodiment of the present invention;

[0036] Figure 18 Schematic diagram of the x=0 slice and the z=1000m slice of the forward formation model at time T2 provided by an embodiment of the present invention;

[0037] Figure 19 Schematic diagram of the x=0 slice and the z=1000m slice of the forward formation model at time T3 provided by an embodiment of the present invention;

[0038] Figure 20 ρ at time T1, T2, and T3 provided in the embodiment of the present invention xy , ρ yx Schematic diagram of the drawing;

[0039] Figure 21 ρ at time T1 provided in the embodiment of the present invention xy , ρ yx Schematic diagram of the comparison between the resulting image and the processed image;

[0040] Figure 22 ρ at time T2 provided in the embodiment of the present invention xy , ρ yx Schematic diagram of the comparison between the resulting image and the processed image;

[0041] Figure 23 ρ at time T3 provided in the embodiment of the present invention xy , ρ yx Schematic diagram of the comparison between the resulting image and the processed image;

[0042] Figure 24 A schematic diagram comparing the inversion image at time T1 provided by an embodiment of the present invention and the inversion image after processing;

[0043] Figure 25A schematic diagram comparing the inversion image at time T2 provided by an embodiment of the present invention and the inversion image after processing;

[0044] Figure 26 A schematic diagram comparing the inversion image at time T3 provided by an embodiment of the present invention and the inversion image after processing;

[0045] Figure 27 Schematic diagram of tetrahedral unit nodes and edges provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0046] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention. In addition, the technical features in the various embodiments or single embodiments provided by the present invention can be combined with each other arbitrarily to form a feasible technical solution. This combination is not subject to the constraints of the sequence of steps and / or structural composition mode, but must be based on the ability of ordinary technicians in this field to implement it. When the combination of technical solutions is mutually contradictory or cannot be implemented, it should be considered that this combination of technical solutions does not exist and is not within the scope of protection required by the present invention. If there are step numbers in the following embodiments, they are only set for the convenience of explanation and description, and the order between the steps is not limited in any way. The execution order of each step in the embodiment can be adaptively adjusted according to the understanding of those skilled in the art.

[0047] The embodiment of the present invention provides a time-lapse magnetotelluric three-dimensional inversion imaging method based on non-structural finite element, see Figure 1 The method includes: establishing a core geological structure model of the study area without modeling the outer boundary; exporting a grid file and a regional information file after the core area modeling; importing the grid file and the regional information file into a program with a user interface to expand the model data of the boundary area; detecting and identifying different grid areas, selecting a predetermined area and assigning resistivity and grid density parameters; performing grid densification to generate a grid data file required in the forward and inversion process; performing parallel calculations on a multi-frequency forward modeling program and a multi-frequency inversion program; and subtracting the three-dimensional inversion results to determine the electrical property change characteristics of the fracturing area.

[0048] The forward modeling process is based on the unstructured finite element method:

[0049] 1) Governing equations

[0050] For the 3D MT forward modeling, assuming the time harmonic factor is eiωt , and ignoring the displacement current, the vector Helmholtz equation satisfied by the electric field is:

[0051]

[0052] Where, To find the curl, E is the electric field strength, ω is the angular frequency, μ is the magnetic permeability, and σ is the electrical conductivity.

[0053] 2) Non-structural finite element method

[0054] The weak form of the finite element method obtained by using the Galerkin method for equation (1) is:

[0055]

[0056] Where Ω is the discrete region, φ is the unstructured tetrahedral vector basis function, and v is the volume.

[0057] Tetrahedral mesh and corresponding vector basis functions are used for discretization, and the discrete region Ω is divided into a finite number of non-overlapping tetrahedral elements. Figure 27 The local node and edge numbering for the tetrahedral elements is shown.

[0058] Finite dimensional function Substituting into the above formula (2) we can get:

[0059]

[0060] Among them E h is the approximate solution of the finite element method, E i is the electric field value on the edge of the unit, is the conductivity tensor, and M is the number of edges in the computational domain Ω. After imposing the Dirichlet boundary conditions, we can obtain a large set of complex linear equations:

[0061] KE=b#(4)

[0062] Where K is the finite element unit matrix and b is the right-hand side term related to the boundary conditions.

[0063] Based on the content of the above method embodiment, as an optional embodiment, the time-lapse magnetotelluric three-dimensional inversion imaging method based on non-structural finite elements provided in the embodiment of the present invention establishes a core geological structure model of the study area without modeling the peripheral boundary, including: only modeling the core geological structure to reduce model smoothing and computing resource consumption caused by large boundaries. Figure 4 As shown in Figure 3, the key to establishing a core geological structure model of the study area is not to model the outer boundaries in order to avoid model smoothing and computing resource consumption caused by large boundaries.

[0064] Based on the content of the above method embodiment, as an optional embodiment, the time-lapse magnetotelluric three-dimensional inversion imaging method based on non-structured finite elements provided in the embodiment of the present invention, the mesh file and regional information file after the core area modeling are exported, including: the exported regional information file and mesh file both contain domain units, boundary units, edge units, vertex units and geometric entity information. After completing the core area modeling, the mesh file and regional information file are exported as follows Figure 5 and Figure 6 shown.

[0065] Based on the content of the above method embodiment, as an optional embodiment, the time-lapse magnetotelluric three-dimensional inversion imaging method based on non-structural finite elements provided in the embodiment of the present invention, the grid file and the regional information file are imported into a program with a user interface, and the model data of the boundary area is expanded, including: according to the imported grid file and regional information file, the boundary of the predetermined core area is identified, and the boundary area is expanded according to the predetermined boundary size parameters, and the unestablished boundary area is supplemented to ensure the predetermined grid accuracy of the predetermined core area. Figure 7 As shown, these two files are imported into a self-made program with a UI interface for mesh data processing. The program will automatically process and expand the model data in the boundary area, supplement the unestablished large boundary area, and maintain the fine mesh quality in the core area.

[0066] Based on the content of the above method embodiment, as an optional embodiment, the time-lapse magnetotelluric three-dimensional inversion imaging method based on non-structured finite elements provided in the embodiment of the present invention, the detection and identification of different grid areas, the selection of predetermined areas and the assignment of resistivity and grid density parameters include: identifying the upper boundary area and the lower boundary area, the upper boundary is the sky area in the forward model, the lower boundary is the boundary surrounding rock area in the forward model, the resistivity is assigned to the sky area and the boundary surrounding rock area, and the smaller the grid subdivision value, the finer the subdivision.

[0067] like Figure 8 As shown in the figure, the program automatically detects and identifies different grid areas, requiring the user to select specific areas and assign resistivity and grid density parameters to ensure that different geological units obtain appropriate electrical parameters and grid density. The upper boundary generally represents the sky area in the forward model, and the lower boundary represents the surrounding rock area of ​​the forward initial model. The program will ask the user whether to perform grid refinement, thereby generating five grid data files required in the forward or inversion process, such as Figure 9 shown.

[0068] Based on the content of the above method embodiment, as an optional embodiment, the time-lapse magnetotelluric three-dimensional inversion imaging method based on unstructured finite elements provided in the embodiment of the present invention, the parallel calculation of the multi-frequency forward program and the multi-frequency inversion program includes: using the parallelization instructions of the shared memory parallel programming OpenMP to parallelly calculate multiple frequencies during forward modeling, and parallelizing the parts that require frequency calculation during inversion, and the number of logical processors of the central processing unit CPU is the number of frequencies for parallel calculation.

[0069] Forward part such as Figure 10 As shown in the figure: Multiple frequencies will generate separate results, so they do not interfere with each other. At this time, the parallelization instructions of OpenMP can be used to perform multi-frequency parallelism to speed up the calculation. Among them, n is the number of frequencies. Generally, the number of logical processors of the CPU is the maximum number of simultaneous parallel frequencies. Figure 11 As shown: the inversion part has multiple parts, and the parts that require frequency calculation are performed in parallel, followed by subsequent calculations.

[0070] Based on the content of the above method embodiment, as an optional embodiment, the time-lapse magnetotelluric 3D inversion imaging method based on unstructured finite elements provided in the embodiment of the present invention, wherein subtracting the 3D inversion results to determine the electrical property change characteristics of the fracturing area includes: using apparent resistivity for subtraction during forward modeling: in, is the difference in apparent resistivity; is the apparent resistivity after forward modeling; T n is any moment after fracturing; T0 is the moment before fracturing; n is the time point; during inversion, the resistivity values ​​of the same grid cells in the inversion results are directly subtracted: Where m is the inversion result, which is represented by a three-dimensional tetrahedral grid, and each grid is assigned the resistivity value after inversion; Δm is the resistivity difference of the same grid cell in the inversion result.

[0071] Before the fracturing construction, the baseline geophysical observation data is obtained, and the electromagnetic forward calculation and inversion calculation are performed on the data to obtain the apparent resistivity and underground resistivity model before fracturing. After the fracturing construction is completed, the monitoring data is collected again under the same measuring points and parameter conditions, and the forward modeling and inversion are performed in the same way to obtain the apparent resistivity and underground resistivity model after fracturing. Subsequently, the apparent resistivity data before and after fracturing are subtracted to obtain the apparent resistivity change value; the underground resistivity model before and after fracturing is subtracted to obtain the resistivity change value. Finally, by analyzing the difference distribution of apparent resistivity and resistivity, the changes in the underground medium in the fracturing area and the evaluation of the fracturing effect are realized. For forward modeling, the apparent resistivity is used to make a difference such as For inversion, the resistivity values ​​of the same grid cells in the inversion result model are directly subtracted as shown in Δm.

[0072] Forward part such as Figure 12 As shown, through the data processing software, you can directly make a difference and split the data of different frequencies into different data files. First, select forward processing at the top of the software interface; select the forward file (forward data file after fracturing) and the background file (forward data file before fracturing), select the processing method to calculate the difference, and click Process data. The processed data will be placed in the folder to which the forward file belongs (a folder named after the forward file will be generated). In the inversion part, select Inversion processing at the top of the interface, select the first file and the second file respectively, and then click Process inversion data. The new data file will be placed in the folder of the original file as shown below. Figure 13 shown.

[0073] The embodiment of the present invention provides a time-lapse magnetotelluric three-dimensional inversion imaging method based on non-structured finite elements. It combines the non-structured finite element method to simplify the modeling process and accurately capture the resistivity changes of deep formations under complex three-dimensional geology. It also subtracts the three-dimensional inversion results to highlight the electrical change characteristics of the fracturing area, clearly characterize the boundaries, and enhance the ability to evaluate the fracturing effect. It introduces parallel computing technology to improve the efficiency of three-dimensional forward modeling and inversion, accelerate the calculation process, and provide an efficient and accurate technical means for monitoring the fracturing area.

[0074] To solve the technical limitations of smoothing extremely fine model details when processing large-scale models, the model comparison between the traditional process and the results of this method is used to demonstrate the advantages of this method. Figures 14 to 16 As shown. By comparison, it was found that the modeling mesh without boundary processing would have better effect, and the processing was more appropriate in some details. After comparison, it was also found that in the forward calculation, with the same number of 369,640 grids, the same number of 121 measurement points, and the same 9 frequencies, the time consumed before parallelization was 132.280 seconds, while after parallelization, the time consumed was 40.685 seconds. This is a reduction of approximately 225% in time consumption. With the same number of 369,640 grids; the same number of 121 measurement points; and the same 21 frequencies, the time consumed before parallelization was 309.174 seconds, while after parallelization, the time consumed was 66.309 seconds. This is a reduction of approximately 366% in time consumption.

[0075] Meanwhile, in the inversion calculation, with the same five frequencies, 121 measurement points, and 337,755 cells, the time taken for ten inversion runs was 2792.700 seconds before parallelization and 1594.492 seconds after parallelization, a reduction of approximately 75%.

[0076] For the same 21 frequencies, 289 measurement points, and 316,161 cells, the time taken for ten inversion runs was 35,340.576 seconds before parallelization and 2,779.601 seconds after parallelization, a reduction of approximately 1,171%. This indicates that the greater the number of frequencies, the greater the improvement in inversion and forward modeling speed.

[0077] In order to demonstrate the difference calculation of the inversion results before and after fracturing to better explain the changes in the fracturing range boundary, three layers of rock models with different resistivity are used here. From top to bottom, the first layer is 400 meters thick and has a resistivity of 200 ohm-meters; the second layer is 1300 meters thick and has a resistivity of 100 ohm-meters; the third layer is 800 meters thick and has a resistivity of 800 ohm-meters. In this formation simulation, different cubes are modeled to represent the fracturing range at different times. They are cubes with side lengths of 600 meters, 800 meters, and 1000 meters respectively. The specific models are as follows: Figures 17 to 19 After the forward modeling, the forward modeling of the model at three time points is shown in the figure below. Figure 20 At the same time, the model before fracturing (i.e. the model without abnormal body) is forward modeled using The processed image is easier to distinguish the fracturing area. Figures 21 to 23 Then the same model is inverted and the same method is used. Here, the boundary of the changed area is more obvious through the comparison of three-dimensional slices in the z direction, such as Figures 24 to 26 shown.

[0078] The implementation basis of each embodiment of the present invention is achieved through programmed processing by a device with a processor function (i.e., software). Therefore, in engineering practice, the technical solutions and functions of each embodiment of the present invention can be encapsulated into various modules. Based on this reality, on the basis of the above embodiments, an embodiment of the present invention provides a time-lapse magnetotelluric three-dimensional inversion imaging device based on non-structured finite elements, which is used to execute the time-lapse magnetotelluric three-dimensional inversion imaging method based on non-structured finite elements in the above method embodiment. See Figure 2The device includes: a first main module, which is used to establish a core geological structure model of the study area without modeling the outer boundary; a second main module, which is used to export the grid file and regional information file after the core area modeling; a third main module, which is used to import the grid file and regional information file into a program with a user interface and expand the model data of the boundary area; a fourth main module, which is used to detect and identify different grid areas, select a predetermined area and assign resistivity and grid density parameters; a fifth main module, which is used to perform grid encryption and generate grid data files required in the forward and inversion process; a sixth main module, which is used to realize parallel calculation of a multi-frequency forward program and a multi-frequency inversion program; and a seventh main module, which is used to perform subtraction of three-dimensional inversion results and determine the electrical change characteristics of the fracturing area.

[0079] The embodiment of the present invention provides a time-lapse magnetotelluric three-dimensional inversion imaging device based on non-structural finite elements, which adopts Figure 2 Several modules in it are combined with the non-structural finite element method to simplify the modeling process and accurately capture the resistivity changes of deep formations under complex three-dimensional geology; the three-dimensional inversion results are subtracted to highlight the electrical change characteristics of the fracturing area, clearly characterize the boundaries, and enhance the ability to evaluate the fracturing effect; the introduction of parallel computing technology improves the efficiency of three-dimensional forward modeling and inversion, accelerates the calculation process, and provides an efficient and accurate technical means for fracturing area monitoring.

[0080] It should be noted that the device in the device embodiment provided by the present invention can be used to implement the method in the above-mentioned method embodiment as well as the method in other method embodiments provided by the present invention. The only difference is that the corresponding functional module (i.e., software) is set. The principle is basically the same as the principle of the above-mentioned device embodiment provided by the present invention. As long as those skilled in the art refer to the specific technical solutions in other method embodiments on the basis of the above-mentioned device embodiment, obtain the corresponding technical means and the technical solutions composed of these technical means by combining technical features, and ensure the practicality of the technical solutions, they can improve the device in the above-mentioned device embodiment to obtain the corresponding device class embodiment (i.e., software) for implementing the methods in other method class embodiments. For example:

[0081] Based on the content of the above-mentioned device embodiment, as an optional embodiment, the time-lapse magnetotelluric three-dimensional inversion imaging device based on non-structural finite elements provided in the embodiment of the present invention also includes: a first submodule, which is used to implement the establishment of the core geological structure model of the study area without modeling the outer boundary, including: only modeling the core geological structure to reduce model smoothing and computing resource consumption caused by large boundaries.

[0082] Based on the content of the above-mentioned device embodiment, as an optional embodiment, the time-lapse magnetotelluric three-dimensional inversion imaging device based on non-structured finite elements provided in the embodiment of the present invention also includes: a second sub-module, used to realize the grid file and regional information file after exporting the core area modeling, including: the exported regional information file and grid file both contain domain units, boundary units, edge units, vertex units and geometric entity information.

[0083] Based on the content of the above-mentioned device embodiment, as an optional embodiment, the time-lapse magnetotelluric three-dimensional inversion imaging device based on non-structural finite elements provided in the embodiment of the present invention also includes: a third sub-module, used to realize the importing of the grid file and the regional information file into a program with a user interface, and expand the model data of the boundary area, including: identifying the boundary of the predetermined core area according to the imported grid file and regional information file, and expanding the boundary area according to the predetermined boundary size parameters, supplementing the unestablished boundary area, and ensuring the predetermined grid accuracy of the predetermined core area.

[0084] Based on the content of the above-mentioned device embodiment, as an optional embodiment, the time-lapse magnetotelluric three-dimensional inversion imaging device based on non-structural finite elements provided in the embodiment of the present invention further includes: a fourth submodule, used to realize the detection and identification of different grid areas, select a predetermined area and assign resistivity and grid density parameters, including: identifying the upper boundary area and the lower boundary area, the upper boundary is the sky area in the forward model, and the lower boundary is the boundary surrounding rock area in the forward model, assigning resistivity to the sky area and the boundary surrounding rock area, and the smaller the grid subdivision value, the finer the subdivision.

[0085] Based on the content of the above-mentioned device embodiment, as an optional embodiment, the time-lapse magnetotelluric three-dimensional inversion imaging device based on unstructured finite elements provided in the embodiment of the present invention further includes: a fifth submodule, used to realize the parallel calculation of the multi-frequency forward modeling program and the multi-frequency inversion program, including: using the parallelization instructions of the shared memory parallel programming OpenMP to perform parallel calculation of multiple frequencies during forward modeling, and performing parallel calculation of the parts that require frequency calculation during inversion, and the number of logical processors of the central processing unit CPU is the number of frequencies for parallel calculation.

[0086] Based on the content of the above device embodiment, as an optional embodiment, the time-lapse magnetotelluric three-dimensional inversion imaging device based on non-structural finite elements provided in the embodiment of the present invention further includes: a sixth submodule for implementing the subtraction of the three-dimensional inversion results to determine the electrical change characteristics of the fracturing area, including: using apparent resistivity for subtraction during forward modeling: in, is the difference in apparent resistivity; is the apparent resistivity after forward modeling; Tn is any moment after fracturing; T0 is the moment before fracturing; n is the time point; during inversion, the resistivity values ​​of the same grid cells in the inversion results are directly subtracted: Where m is the inversion result, which is represented by a three-dimensional tetrahedral grid, and each grid is assigned the resistivity value after inversion; Δm is the resistivity difference of the same grid cell in the inversion result.

[0087] The method of the embodiment of the present invention is implemented by electronic devices, so it is necessary to introduce the relevant electronic devices. Based on this purpose, the embodiment of the present invention provides an electronic device, such as Figure 3 As shown, the electronic device includes: at least one processor, a communications interface, at least one memory, and a communications bus, wherein the at least one processor, the communications interface, and the at least one memory communicate with each other via the communications bus. The at least one processor can call logic instructions in the at least one memory to execute all or part of the steps of the methods provided in the aforementioned method embodiments.

[0088] In addition, the logic instructions in the at least one memory mentioned above can be implemented in the form of a software functional unit and can be stored in a computer-readable storage medium when sold or used as an independent product. Based on this understanding, the technical solution of the present invention, or the part that contributes to the prior art, or the part of the technical solution, can be embodied in the form of a software product. The computer software product is stored in a storage medium and includes several instructions for enabling a computer device (which can be a personal computer, server, or network device, etc.) to execute all or part of the steps of the method described in each method embodiment of the present invention. The aforementioned storage medium includes: various media that can store program codes, such as a USB flash drive, a mobile hard disk, a read-only memory (ROM), a random access memory (RAM), a magnetic disk or an optical disk.

[0089] The device embodiments described above are merely illustrative. The units described as separate components may or may not be physically separate, and the components shown as units may or may not be physical units, i.e., they may be located in one location or distributed across multiple network units. Some or all of the modules may be selected based on actual needs to achieve the objectives of the present embodiment. Persons of ordinary skill in the art will be able to understand and implement the present invention without inventive effort.

[0090] Through the description of the above embodiments, those skilled in the art can clearly understand that each embodiment can be implemented by means of software plus a necessary general hardware platform, and of course can also be implemented by hardware. Based on this understanding, the essence of the above technical solution or the part that contributes to the existing technology can be embodied in the form of a software product. This computer software product can be stored in a computer-readable storage medium, such as ROM / RAM, a magnetic disk, an optical disk, etc., and includes a number of instructions for enabling a computer device (which can be a personal computer, a server, or a network device, etc.) to execute the methods described in each embodiment or some parts of the embodiment.

[0091] The flowcharts and block diagrams in the accompanying drawings show the possible architectures, functions and operations of the systems, methods and computer program products according to multiple embodiments of the present invention. Based on this understanding, each box in the flowchart or block diagram can represent a module, program segment or part of the code, and the module, program segment or part of the code contains one or more executable instructions for implementing the specified logical function. It should also be noted that in some alternative implementations, the functions marked in the box can also occur in an order different from that marked in the accompanying drawings. For example, two consecutive boxes can actually be executed substantially in parallel, or sometimes in the opposite order, depending on the functions involved. It should also be noted that each box in the block diagram and / or flowchart, and the combination of boxes in the block diagram and / or flowchart, can be implemented with a dedicated hardware-based system that performs the specified function or action, or can be implemented with a combination of dedicated hardware and computer instructions.

[0092] It should be noted that the terms "include", "comprising" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device that includes a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, the elements defined by the sentence "include..." do not exclude the presence of other identical elements in the process, method, article or device that includes the elements. Any "predetermined threshold", "preset threshold" or similar expressions that do not indicate a specific value can be determined by a person of ordinary skill in the art through simple experiments or corresponding debugging.

[0093] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A time-lapse magnetotelluric three-dimensional inversion imaging method based on unstructured finite elements, characterized in that: include: Establish a core geological structure model of the study area without modeling the outer boundaries; Export the mesh file and regional information file after core area modeling; Importing the grid file and the region information file into a program with a user interface to expand the model data of the boundary region; Detect and identify different grid areas, select predetermined areas and assign resistivity and grid density parameters; perform grid densification and generate grid data files required in the forward and inversion process; The multi-frequency forward modeling program and the multi-frequency inversion program are calculated in parallel; the three-dimensional inversion results are subtracted to determine the electrical property change characteristics of the fracturing area.

2. The time-lapse magnetotelluric three-dimensional inversion imaging method based on unstructured finite element according to claim 1, characterized in that: The core geological structure model of the study area is established without modeling the outer boundary, including: only modeling the core geological structure to reduce model smoothing and computing resource consumption caused by large boundaries.

3. The time-lapse magnetotelluric three-dimensional inversion imaging method based on unstructured finite element according to claim 2, characterized in that: The mesh file and the region information file after the core region modeling are exported, including: the exported region information file and mesh file both contain domain units, boundary units, edge units, vertex units and geometric entity information.

4. The time-lapse magnetotelluric three-dimensional inversion imaging method based on unstructured finite element according to claim 3, characterized in that: The method of importing the grid file and the region information file into a program with a user interface and expanding the model data of the boundary area includes: identifying the boundary of a predetermined core area according to the imported grid file and the region information file, and expanding the boundary area according to predetermined boundary size parameters, supplementing the unestablished boundary area, and ensuring the predetermined grid accuracy of the predetermined core area.

5. The time-lapse magnetotelluric three-dimensional inversion imaging method based on unstructured finite element according to claim 4, characterized in that: The detecting and identifying different grid areas, selecting a predetermined area, and assigning resistivity and grid density parameters include: identifying an upper boundary area and a lower boundary area, where the upper boundary is a sky area in a forward model, and the lower boundary is a boundary surrounding rock area in the forward model, assigning resistivity to the sky area and the boundary surrounding rock area, and the smaller the grid division value, the finer the division.

6. The time-lapse magnetotelluric three-dimensional inversion imaging method based on unstructured finite element according to claim 5, characterized in that: The parallel calculation of the multi-frequency forward program and the multi-frequency inversion program includes: using the parallelization instructions of the shared memory parallel programming OpenMP to parallelly calculate multiple frequencies during forward modeling, and parallelizing the parts that require frequency calculation during inversion, with the number of logical processors of the central processing unit CPU being the number of frequencies for parallel calculation.

7. The time-lapse magnetotelluric three-dimensional inversion imaging method based on unstructured finite element according to claim 6, characterized in that: The subtraction of the three-dimensional inversion results to determine the electrical property change characteristics of the fracturing area includes: in the forward modeling, using the apparent resistivity for subtraction: in, is the difference in apparent resistivity; is the apparent resistivity after forward modeling; T n is any moment after fracturing; T0 is the moment before fracturing; n is the time point; during inversion, the resistivity values ​​of the same grid cells in the inversion results are directly subtracted: Where m is the inversion result, which is represented by a three-dimensional tetrahedral grid, and each grid is assigned the resistivity value after inversion; Δm is the resistivity difference of the same grid cell in the inversion result.

8. A time-lapse magnetotelluric three-dimensional inversion imaging device based on unstructured finite elements, characterized in that: include: The first main module is used to establish the core geological structure model of the study area without modeling the outer boundaries; The second main module is used to export the mesh file and regional information file after the core area modeling; The third main module is used to import the grid file and the regional information file into a program with a user interface to expand the model data of the boundary area; the fourth main module is used to detect and identify different grid areas, select a predetermined area and assign resistivity and grid density parameters; the fifth main module is used to perform grid encryption and generate the grid data files required in the forward and inversion process; The sixth main module is used to realize parallel calculation of the multi-frequency forward program and the multi-frequency inversion program; the seventh main module is used to realize the difference of the three-dimensional inversion results to determine the electrical change characteristics of the fracturing area.

9. An electronic device, characterized in that: include: At least one processor, at least one memory and a communication interface; wherein, The processor, memory and communication interface communicate with each other; The memory stores program instructions that can be executed by the processor, and the processor calls the program instructions to execute the method according to any one of claims 1 to 7.

10. A non-transitory computer-readable storage medium, characterized in that The non-transitory computer-readable storage medium stores computer instructions, which cause a computer to execute the method of any one of claims 1 to 7.

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