Key parameter optimization method for ground well electromagnetic exploration simulation calculation

Abstract

The invention belongs to the technical field of electromagnetic exploration, and particularly relates to a key parameter optimization method for ground well electromagnetic exploration simulation calculation, which is based on solved irregular layered background medium Green function response, utilizes the plane symmetry property of a union-vector Green function and adopts a fast Fourier transform algorithm to optimize the key parameters of the ground well electromagnetic exploration simulation calculation. Only calculating and researching half of the grid point and vector Green function of the horizontal section diagonal line of the area, and reconstructing the distribution of the complete horizontal section grid point and vector Green function through a spatial interpolation algorithm; and solving the three-dimensional ground well electromagnetic field integral equation set under the background of the three-dimensional irregular layered medium by adopting a stable biconjugate gradient-fast Fourier transform algorithm, so as to obtain the total electromagnetic field for researching the center point of the subdivision grid in the three-dimensional region. The primary field and the scattered field of the electromagnetic field at each observation point in the ground well electromagnetic shaft are efficiently calculated.

Description

Technical Field

[0001] The invention belongs to the technical field of electromagnetic exploration, and in particular relates to a key parameter optimization method for underground well electromagnetic exploration simulation calculation. Background Art

[0002] The ground-well electromagnetic method specifically refers to the borehole electromagnetic method that transmits on the ground and receives underground. Compared with interwell electromagnetic and well-ground electromagnetic, it avoids the strong electromagnetic shielding of the transmitter placed in the casing, and breaks through the limitation of the transmission power due to the size of the excitation source. The efficient multi-source and multi-frequency three-dimensional ground-well electromagnetic inversion research will inevitably bring new opportunities for the development of oil and gas exploration and development and improved recovery, and has broad application prospects. However, the inversion research relies on efficient forward simulation calculations. Therefore, it is of great theoretical and practical significance to develop key parameter optimization methods for ground-well electromagnetic exploration simulation calculations suitable for complex areas.

[0003] Forward modeling is the basis of inversion. Among the forward modeling methods of electromagnetic fields in complex media, numerical simulation research based on unstructured grids, gridless and adaptive grid finite element methods is the current mainstream, and the use of finite difference methods and derived finite volume methods to simulate electromagnetic fields in complex media is also emerging. The differential equation method needs to carefully deal with problems such as truncation boundaries, accumulated errors, and field source singularities when simulating the electromagnetic response of complex media. For electromagnetic simulation of underground wells with casing, the differential equation method also needs to specifically solve the special boundary and grid division problems including the wellbore, which is still a difficult task at present. The integral equation method simulation only requires local space discretization and high solution accuracy. Compared with the differential equation method, there is no need to consider special wellbore electromagnetic simulation problems, so the simulation advantage of the integral equation method is more obvious.

[0004] However, solving integral equations in the inversion process requires dealing with more difficult mathematical problems than solving differential equations. For example, Nie et al. (2010) used the pre-corrected fast Fourier transform method to carry out electromagnetic field simulation of logging while drilling, Chobanyan et al. (2014) proposed a dual high-order large-scale generalized volume-surface integral equation method, Ji Zeming et al. (2018) conducted a three-dimensional forward modeling study of magnetotelluric with quasi-linear integral equations, and Kong et al. (2020) proposed a discontinuous Galerkin surface integral equation method for calculating the scattered field of large-scale target bodies, etc. In the field of inversion based on integral equation simulation, Song Dianguang and Wei Baojun (2010) studied Born iterative inversion considering homogeneous medium background; Li Jinghe and He Zhanxiang (2014) incorporated layered background medium parameters into the inversion process and conducted 3D interwell electromagnetic least squares inversion research; Malovichko et al. (2017) introduced the conjugate gradient method to conduct full waveform inversion research of 3D seismic data; Li Jinghe et al. (2019) conducted a study on the regional integral equation method simulation of wellbore electromagnetic field in the frequency domain of 3D terrain; Zhang et al. (2020) conducted a study on phase-free highly nonlinear inversion using integral equation simulation; Xu et al. (2020) conducted a study on high nonlinear inversion using Fourier basis-extended integral equation simulation, etc. In the study of inversion algorithms for integral equation simulation of 3D models, domestic and foreign scholars often use rectangular units and integral equation methods of different orders to carry out numerical simulations. The mesh needs to be encrypted to obtain high-precision numerical simulation results for the division of complex models, but the encrypted mesh leads to increased computational and storage volume.

[0005] To this end, Zhdanov et al. (2011) proposed a volume integral equation method based on separation simulation technology, attempting to study how to efficiently solve the electromagnetic field simulation problem of the simultaneous existence of three-dimensional large-scale salt domes and two-dimensional large-scale thin-layer targets. However, it uses regular hexahedral grid partitioning and the simulated target body is limited to regular shapes. Li Jinghe (2015) conducted two-dimensional well-to-ground electromagnetic contrast source inversion under the background of horizontal layered media and explored the two-step inversion algorithm of three-dimensional well-to-ground electromagnetic considering reservoir characteristics based on the BCGS-FFT fast algorithm integral equation simulation, realizing the rapid inversion of wellbore electromagnetic. Martin et al. (2017) constructed a multi-level parallel two-dimensional magnetotelluric exploration impedance inversion algorithm based on the integral equation forward simulation of Zhdanov et al. (2011), but did not involve the calculation process of Green's function for irregular layered background media. Li Jinghe et al. (2020) conducted a case study on complex medium contrast source inversion based on the three-dimensional terrain frequency domain wellbore electromagnetic field regional integral equation method simulation algorithm. The development of integral equation simulation inversion algorithm is of great help to complex medium wellbore electromagnetic imaging. However, 3D ground-well electromagnetic exploration is often used to detect remaining oil and gas reservoirs in irregular layered background media and monitor the dynamic migration of oil, gas and water during water injection. The assumption of traditional uniform half-space or horizontal layered background media limits its practical accuracy. In order to obtain high-precision imaging effects for the detection of remaining oil and gas reservoirs in irregular layered background media and the dynamic migration of oil, gas and water during water injection, practical 3D ground-well electromagnetic inversion research based on integral equation simulation needs to be explored.

[0006] In view of the above analysis, the existing technology has the following technical problems that need to be solved urgently:

[0007] (1) The differential equation method needs to carefully deal with the problems of truncation boundary, accumulated error, and field source singularity when simulating the electromagnetic response of complex media. For electromagnetic simulation of underground wells with casing, the differential equation method also needs to solve the special boundary and mesh generation problems including the wellbore.

[0008] (2) Research on inversion algorithms for integral equation simulation of three-dimensional models. Domestic and foreign scholars often use rectangular units and integral equation methods of different orders to carry out numerical simulations. The division of complex models requires mesh encryption to obtain high-precision numerical simulation results, but mesh encryption leads to increased computational and storage capacity.

[0009] (3) Three-dimensional ground-well electromagnetic exploration is often used to detect remaining oil and gas reservoirs in irregular layered background media and monitor the dynamic migration of oil, gas and water during water injection and production. The traditional assumption of uniform half-space or horizontal layered background media limits its practical accuracy.

[0010] At present, there are no research reports on the key parameter optimization method for three-dimensional non-complete fast Fourier transform in the field of ground-well electromagnetic exploration. Therefore, there is an urgent need to develop an innovative key parameter optimization method for ground-well electromagnetic exploration simulation calculation in irregular layered background media, so as to accurately explore the distribution of oil and gas reservoirs and their migration in complex areas.

[0011] The above technical problems will bring a series of challenges in industrial applications, mainly focusing on computational complexity, storage requirements, precision optimization, etc. The following are the specific challenges in industrial applications caused by these technical problems:

[0012] 1. Large-scale computing and storage bottlenecks

[0013] Since the integral equation simulation of multi-source and multi-frequency three-dimensional ground-well electromagnetic fields involves a large number of primary field calculations and integral equation solutions, the following problems may be encountered in industrial applications:

[0014] Large computational burden: The amount of computation increases exponentially with the size of the study area, the fineness of the grid, and the number of sources and receivers. Traditional computing systems cannot bear this load, resulting in long data processing times, especially in real-time or near-real-time application scenarios such as coal resource exploration or geothermal monitoring.

[0015] High storage requirements: A large amount of electromagnetic field data and Green's function values ​​need to be stored. For large-scale three-dimensional models, the storage requirements will increase rapidly. The storage capacity and data transmission bandwidth of the equipment used in the industry will be greatly challenged, affecting the data processing speed and effect.

[0016] 2. Limitations of Green’s function calculations

[0017] Since only analytical solutions of the Green's function for horizontal layered media are available at present, the Green's function for irregular layered background media needs to be calculated by numerical methods.

[0018] Accuracy problem: When applied to complex geological backgrounds, only the Green's function of horizontal layered media can be used as the basis. When dealing with irregular layered media, errors are prone to occur, affecting the accurate inversion and result analysis of underground structures.

[0019] Increased calculation time: For irregular layered background media, the numerical simulation of Green's function becomes significantly more difficult, requiring not only more calculation time but also the development of specialized algorithms. This will delay the progress in industrial applications and hinder real-time monitoring or rapid exploration.

[0020] 3. Accuracy and efficiency challenges of Gaussian filtering algorithm

[0021] Although the Gaussian filter algorithm is used to calculate the primary field response of three-dimensional horizontal layered media as the right-hand term of the Green's function of irregular layered background media, it faces the following technical problems:

[0022] Accuracy is difficult to guarantee: As a tool for primary field calculation, Gaussian filtering may lose some features in detail processing, especially in irregular backgrounds. The filtering process may introduce errors and reduce the accurate simulation of underground electromagnetic field responses. For high-precision exploration tasks (such as mineral location, groundwater resource identification, etc.), such errors may lead to biased results.

[0023] Computational efficiency issues: Although Gaussian filtering can provide fast response in horizontal layered media, when it is applied to irregular layered backgrounds, additional processing and compensation mechanisms are required, resulting in reduced computational efficiency. In practical applications, especially when dealing with large-scale and complex geological conditions, insufficient computational efficiency may directly limit the progress of industrial applications.

[0024] 4. Complexity of derivation of spatial interpolation algorithm

[0025] By using the plane symmetry property of the dyadic Green's function, only half of the grid points on the diagonal of the horizontal section are calculated, and the Green's function distribution of the entire grid point is reconstructed using spatial interpolation, which brings the following problems:

[0026] Complexity and development cost of interpolation algorithms: Re-deriving such interpolation algorithms and ensuring their stability and accuracy under various complex geological backgrounds may require a lot of R&D investment. This complexity will increase the cost of technology development during industrialization and extend the R&D cycle of the project.

[0027] Consequences of interpolation errors: Since errors may be introduced during the interpolation process, especially under irregular geological conditions, interpolation errors may cause distortion of electromagnetic field responses, thereby affecting the accuracy of exploration or monitoring results. For precise requirements in industrial applications (such as prediction of oxidation risk of coal in coal mines, groundwater monitoring, etc.), this error may have a significant impact and even lead to misjudgment.

[0028] The above technical problems will lead to challenges in industrial applications such as excessive computing load, increased storage costs, reduced processing accuracy and increased development complexity, which will directly affect the application efficiency of the system and the accuracy of the results. In order to solve these problems, it is necessary to further optimize the algorithm, improve the computing efficiency, and develop more accurate and efficient Green's function solution and interpolation methods through new technologies to meet the real-time and accuracy requirements in the industry. Summary of the invention

[0029] In view of the problems existing in the prior art, the present invention provides a key parameter optimization method for underground well electromagnetic exploration simulation calculation, which can realize the underground well electromagnetic forward simulation response calculation in the background of irregular layered media, and provide technical guarantee for the exploration of remaining oil and gas reservoirs and dynamic monitoring of oil and gas in complex areas.

[0030] The present invention is implemented as follows: a method for optimizing key parameters of underground well electromagnetic exploration simulation calculation, comprising:

[0031] Step 1: Determine that the three-dimensional irregular layered background medium refers to a layered medium with a slowly undulating interface, the resistivity in the layer remains unchanged, consider the application of low-frequency electromagnetic exploration, and ignore the influence of metal casing; determine the three-dimensional research area and perform three-dimensional cube grid division; in order to realize the calculation of the analytical solution of the dyadic Green's function of the three-dimensional irregular layered background medium, exchange the position of the field source and the receiving point, and derive the three-dimensional ground-well electromagnetic field integral equation under the background of three-dimensional irregular layered medium;

[0032] Step 2: Based on the derived multi-source and multi-frequency three-dimensional well electromagnetic field integral equation, first calculate the primary field response of the electromagnetic field involved in the right side of the integral equation of the internal grid points in the study area; assume that the electromagnetic field response of the irregular layered background medium is weakly coupled with the horizontal layered medium response, and regard the study area as the superposition of the irregular layered background medium and the horizontal layered medium. Use the Gaussian filtering algorithm to calculate the primary field response of the three-dimensional horizontal layered medium problem, and use it as the right side term of the Green's function numerical simulation equation group of the irregular layered background medium. Use the stable biconjugate gradient-fast Fourier transform algorithm to solve the Green's function numerical simulation equation group of the irregular layered background medium.

[0033] Step 3: Based on the obtained Green's function response of the irregular layered background medium, the plane symmetry property of the dyadic Green's function is utilized, and the fast Fourier transform algorithm is used to calculate only the dyadic Green's function of half of the grid points on the diagonal line of the horizontal section of the study area, and the dyadic Green's function distribution of the complete horizontal section grid points is reconstructed through the spatial interpolation algorithm;

[0034] Step four, substitute the above-mentioned dyadic Green's function into the integral equation group of step one, and use the stable double conjugate gradient-fast Fourier transform algorithm to solve the three-dimensional ground well electromagnetic field integral equation group under the background of the above-mentioned three-dimensional irregular layered medium, so as to obtain the total electromagnetic field of the center point of the subdivided grid in the three-dimensional study area, and then calculate the electromagnetic field primary field and scattered field at each observation point in the ground well electromagnetic wellbore. The sum of the two is the total electromagnetic field response at the observation point.

[0035] Further, the step 1 specifically includes:

[0036] Considering a multi-source multi-frequency three-dimensional well electromagnetic observation system, several radial and vertical radial dipole source pairs are arranged to transmit the field source, and receivers are set up at the target layer in the well to measure the electromagnetic field. Assuming that the underground medium in the study area is an irregular layered background medium, the medium magnetic permeability μ is considered to be a constant, and the dielectric constant As the spatial position changes, the electric field satisfies the equation:

[0037]

[0038] in, ω is the angular frequency, r is the spatial position of the receiving point; ε 0 and are the dielectric constants of free space and abnormal region respectively, j is the imaginary unit, and σ is the conductivity of the internal space.

[0039] Without loss of generality, the external excitation field source is expressed as:

[0040]

[0041] Define the dyadic Green function that satisfies the above study area So that the following equation is satisfied:

[0042]

[0043] In the above formula, V is the study area, dv′ represents the derivative of the target area, r′ is the spatial position in the study area, and the field source is expressed as:

[0044]

[0045] Further, the step 2 specifically includes:

[0046] Introducing unit dyadic and the pulse function δ(rr′), then equation (4) can be expressed as:

[0047]

[0048] Then, from equations (1)-(5), the expression of the dyadic Green's function considering the excitation field source at r' and the irregular layered background medium distribution at r is derived as follows:

[0049]

[0050] To obtain the dyadic Green's function in the study area V, the reciprocity theorem can be introduced, the positions of the field source and the receiving point in equation (6) are swapped, the study area V is divided into N hexahedral units, and the stable biconjugate gradient-fast Fourier algorithm is used to solve the equations to obtain the dyadic Green's function of the irregular layered medium background.

[0051] Further, the step three specifically includes:

[0052] Assume that the ground is laid out M T There are excitation field sources Tx, and M are arranged at different depths in the well. R receiving points Rx, the total number of data points under the condition of single frequency field source excitation is M = M T ×M R The study area V is divided into N grid units, and the electrical parameter ΔV of each unit is a constant. The scattered field in the study area is expressed as:

[0053]

[0054] Where iR=1,…,M R , iT=1,…,M T ; is the Green's function at the receiving point of the mth layer of the irregular layered medium caused by the qth layer excitation field source, which is simulated and obtained by the above three-dimensional irregular layered background medium Green's function integral equation; E(r k ',r iT ) is the total electric field in the study area, is the electrical contrast function. Equation (7) can be simplified as:

[0055] f=Ax (8)

[0056] in, x is the contrast function matrix coefficient; i = iR + (iT-1)·M R , k = 1, ..., N. Then for a given contrast function matrix x, the scattering field distribution f can be obtained, and the spatial distribution of the contrast function x can be inferred from the known updated scattering field f. k ',r iT ) is the total electric field distribution of the subdivided area within a certain layer of medium, which satisfies the Helmholtz equation (1) under the background of three-dimensional layered medium. However, obtaining the total electric field distribution under the background of large-scale three-dimensional layered medium requires solving the huge computational and storage problems caused by the dyadic Green's function and the primary field on the right side of equation (1). Only the dyadic Green's function of half of the grid points on the diagonal of the horizontal section of the study area is calculated, and the dyadic Green's function distribution of the complete horizontal section grid points is reconstructed through the spatial interpolation algorithm. For the calculation of the primary field on the right side of equation (1), the Gaussian filtering algorithm is used to provide the field value distribution at any position in the background of layered medium. In this way, for the study area V with the number of subdivided units q×t×l, the calculation area can be reduced to by using the incomplete fast Fourier transform.

[0057] Another object of the present invention is to provide a computer device, which includes a memory and a processor, wherein the memory stores a computer program, and when the computer program is executed by the processor, the processor executes the steps of the key parameter optimization method for underground well electromagnetic exploration simulation calculation.

[0058] Another object of the present invention is to provide a computer-readable storage medium storing a computer program, which, when executed by a processor, enables the processor to execute the steps of the key parameter optimization method for underground well electromagnetic exploration simulation calculation.

[0059] In combination with the above technical solutions and the technical problems solved, the advantages and positive effects of the technical solutions to be protected by the present invention are as follows:

[0060] First, the shortage of oil and gas resources has become a bottleneck for the development of the national economy. At the same time, the recovery rate of existing oil and gas reservoirs is not high, and a large amount of remaining oil and gas resources are difficult to discover and produce. Developing a key parameter optimization method for ground-well electromagnetic exploration simulation calculation based on three-dimensional non-complete fast Fourier transform, realizing new ground-well electromagnetic exploration technology, discovering remaining oil and gas reservoirs and monitoring the dynamic production process of oil and gas is of great significance to improving the recovery rate.

[0061] The key parameter optimization method of the underground well electromagnetic exploration simulation calculation based on three-dimensional non-complete fast Fourier transform of the present invention exchanges the position of the field source and the receiving point, derives the three-dimensional underground well electromagnetic field integral equation under the three-dimensional irregular layered medium background, and realizes the calculation of the analytical solution of the three-dimensional irregular layered background medium dyadic Green's function; calculates the electromagnetic field primary field response involved in the right side of the integral equation of the grid point inside the study area; assumes that the electromagnetic field response of the irregular layered background medium is weakly coupled with the horizontal layered medium response, regards the study area as the superposition of the irregular layered background medium and the horizontal layered medium, adopts the Gaussian filtering algorithm to calculate the primary field response of the three-dimensional horizontal layered medium problem, and uses it as the right side term of the irregular layered background medium Green's function numerical simulation equation group, and solves the irregular layered background medium Green's function numerical simulation equation group by the stable double conjugate gradient-fast Fourier transform algorithm;

[0062] Based on the solved Green's function response of irregular layered background medium, the plane symmetry property of dyadic Green's function is utilized, and the fast Fourier transform algorithm is adopted to calculate only the dyadic Green's function of half of the grid points on the diagonal of the horizontal section in the study area, and the distribution of dyadic Green's function of the grid points of the complete horizontal section is reconstructed through the spatial interpolation algorithm; the stable biconjugate gradient-fast Fourier transform algorithm is used to solve the three-dimensional ground-well electromagnetic field integral equations under the above three-dimensional irregular layered medium background, and the total electromagnetic field of the center point of the divided grid in the three-dimensional study area can be obtained, so as to realize the efficient calculation of the electromagnetic primary field and scattered field at each observation point in the ground-well electromagnetic wellbore.

[0063] The present invention fills the gap in the key parameter optimization method of ground-well electromagnetic exploration simulation calculation based on three-dimensional non-complete fast Fourier transform, and will provide technical guarantee for discovering remaining oil and gas reservoirs and monitoring the dynamic production process of oil and gas, and improving the recovery rate.

[0064] The present invention closely combines the three-dimensional incomplete fast Fourier transform theory with the three-dimensional ground-well electromagnetic method currently used for oil and gas exploration and oil and gas monitoring in the development process, giving full play to the advantages of the two in their respective fields and integrating the efficient three-dimensional incomplete fast Fourier transform theory into the three-dimensional ground-well electromagnetic exploration application.

[0065] Compared with the prior art, the key parameter optimization method for underground well electromagnetic exploration simulation calculation based on three-dimensional non-complete fast Fourier transform provided by the present invention adopts a three-dimensional non-complete fast Fourier transform algorithm to calculate the dyadic Green's function of half of the grid points on the diagonal of the horizontal section of the study area, and reconstructs the dyadic Green's function distribution of the grid points of the complete horizontal section through a spatial interpolation algorithm, thereby greatly improving the calculation efficiency. The present invention is aimed at three-dimensional underground well electromagnetic oil and gas reservoir exploration, and can provide a new technology for high-precision and efficient delineation of oil and gas target areas and monitoring the dynamic distribution of oil and gas migration. The key parameter optimization method for underground well electromagnetic exploration simulation calculation based on three-dimensional non-complete fast Fourier transform can be promoted to provide technical support for discovering remaining oil and gas reservoirs and monitoring the dynamic production process of oil and gas in complex areas, thereby improving the recovery rate.

[0066] Second, the technical solutions of the present invention solve existing technical problems and significant technical progress in industrial applications

[0067] 1. Existing technical problems solved

[0068] In traditional underground electromagnetic exploration simulation calculations, when dealing with complex three-dimensional irregular layered background media, there are usually problems of high computational complexity and long data processing time. Specific problems include:

[0069] Computational complexity of electromagnetic field propagation equations: In underground electromagnetic exploration, the propagation of electromagnetic fields in irregular layered media is extremely complex, especially when the background medium varies with space. Solving the distribution of electromagnetic fields requires a lot of numerical calculations and storage space.

[0070] Difficulty in obtaining dyadic Green's functions: For irregular layered background media, the analytical solution of the dyadic Green's functions of the three-dimensional electromagnetic field is difficult to obtain. The traditional method requires a large amount of meshing and numerical solutions, resulting in extremely large amounts of calculations.

[0071] Number of data points and mesh units: When there are multiple excitation field sources on the ground and multiple receiving points underground, the number of data points and mesh units in the study area increases dramatically, further increasing the difficulty of calculation and storage.

[0072] 2. Significant technological progress

[0073] The present invention solves the calculation and storage problems in the above-mentioned traditional technologies by introducing three-dimensional incomplete fast Fourier transform (FFT) technology and a method for obtaining a dyadic Green's function, and has the following significant technical advances:

[0074] Application of incomplete fast Fourier transform: Through incomplete fast Fourier transform, the calculation scope of the study area is narrowed from the entire space to the key area, thereby significantly reducing the amount of calculation to the \(O(N\log N)\) level. Compared with the traditional full-space FFT calculation, the calculation efficiency is greatly improved, which is especially suitable for dealing with large-scale three-dimensional ground-well electromagnetic exploration problems.

[0075] Reciprocity theorem and spatial interpolation of Green's function: This invention uses the reciprocity theorem to reduce the number of calculation steps by swapping the positions of the field source and the receiving point. By calculating only half the number of subdivided units and then reconstructing the complete grid point Green's function distribution through spatial interpolation technology, the storage and calculation requirements are significantly reduced.

[0076] Gaussian filtering algorithm accelerates primary field calculation: The present invention introduces Gaussian filtering algorithm in primary field calculation, so that the electromagnetic field value distribution at any position can be efficiently obtained in the background of three-dimensional layered medium. This method avoids the point-by-point solution in the traditional method and improves the calculation speed of electromagnetic field distribution.

[0077] Optimization processing of large data points: For large-scale excitation field sources and receiving points, the present invention reduces the computational pressure of the system in processing large-scale data points by optimizing the grid division and data processing flow, and can quickly simulate the electromagnetic field distribution of multiple sources and multiple frequencies, effectively coping with underground well electromagnetic exploration under complex geological conditions.

[0078] The present invention has greatly improved the efficiency of electromagnetic field calculation, reduced storage requirements, and can quickly solve the electromagnetic field distribution in large-scale irregular layered media through the comprehensive application of three-dimensional non-complete fast Fourier transform, spatial interpolation, Gaussian filtering and other technologies, which has significant technological progress. These technological advances have greatly promoted the application of ground-well electromagnetic exploration technology under complex geological conditions, and helped to more efficiently conduct resource exploration and underground structure analysis. BRIEF DESCRIPTION OF THE DRAWINGS

[0079] Figure 1 This is a flow chart of a key parameter optimization method for underground well electromagnetic exploration simulation calculation provided by an embodiment of the present invention;

[0080] Figure 2 It is a top view of a ground-well electromagnetic exploration and observation system based on three-dimensional incomplete fast Fourier transform provided by an embodiment of the present invention;

[0081] Figure 3 It is a cross-sectional view of a ground-well electromagnetic exploration and observation system based on three-dimensional incomplete fast Fourier transform provided by an embodiment of the present invention;

[0082] Figure 4 is a comparison diagram of the computational efficiency of different numbers of grids in the research area provided by an embodiment of the present invention;

[0083] Figure 5 This is a comparison diagram for verifying the correctness of the calculation algorithm provided by an embodiment of the present invention;

[0084] Figure 6 is a comparison diagram of the calculated total electric field Ez component and the corresponding analytical solution result provided by an embodiment of the present invention;

[0085] In the figure: ①, valley terrain; ②, ground; ③, emission source; ④, observation point; ⑤, study area D; ⑥, layered medium; DETAILED DESCRIPTION

[0086] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0087] like Figure 2 and Figure 3 As shown, the top view and side view of the ground-well electromagnetic exploration observation system based on three-dimensional non-complete fast Fourier transform provided by the embodiment of the present invention include valley terrain ①, ground ②, emission source ③, observation point ④, study area range D⑤, layered medium ⑥; X, Y, Z are rectangular coordinate system components. Among them, the valley terrain ① is located on the flat ground ②, the X-direction magnetic dipole emission source ③ is arranged at the waist of the valley terrain ①, observation points ④ are arranged at different depths in the well, and the study area ⑤ includes the air layer on the ground ② and the underground layered medium ⑥.

[0088] The underground well electromagnetic exploration observation process includes: emitting a field source ③ on the valley terrain ① to excite a primary field signal, and the primary field signal propagates in the entire three-dimensional space ⑤. When encountering the valley terrain ①, the existence of the terrain causes the electromagnetic field propagation law in the corresponding area ⑥ to change. By collecting electromagnetic field signals at underground observation points ④, the abnormal response laws of the underground medium ⑥ and the valley terrain ① to the field source ③ emitted on the ground ② and received underground ④ can be analyzed.

[0089] The working principle of the present invention is based on three-dimensional non-complete fast Fourier transform (FFT) technology, which is used to analyze the propagation law of electromagnetic fields in valley terrain and underground layered media. First, the system excites a field signal by arranging an X-direction magnetic dipole transmitter at the waist of the valley terrain. The electromagnetic field signal generated by the transmitter propagates through the air layer and underground layered medium in the study area. The physical properties of these media and the terrain will affect the propagation characteristics of electromagnetic waves. The study area contains air layers and underground media. The parameters such as conductivity and magnetic permeability of these different media will have different effects on the propagation path and characteristics of electromagnetic waves.

[0090] Secondly, the primary field signal propagates throughout the three-dimensional space, and when passing through the valley terrain, the undulations and irregularities of the terrain cause the propagation direction and intensity of the electromagnetic field to change. The reflection, refraction, and scattering effects of the valley terrain on the electromagnetic field signal will cause the electromagnetic field at different depths and locations to exhibit characteristics different from those of flat terrain. These changes are a comprehensive response to the underground structure and terrain. By collecting data at signal receiving points at different locations, these electromagnetic field anomalies can be captured, further revealing the impact of underground medium characteristics and terrain on electromagnetic field propagation.

[0091] In order to accurately obtain the impact of underground media and valley topography on electromagnetic field signals, the present invention arranges observation points at different depths underground. Each observation point is responsible for receiving electromagnetic field signals from ground sources. These signals carry important information about underground structures when passing through underground media. Through the data collected by the observation points, researchers can analyze the physical properties of underground layered media, such as conductivity changes, layer thickness, and medium distribution. In addition, observation points at different depths can provide multi-dimensional electromagnetic response data, further improving the understanding of underground media and topography.

[0092] Finally, by analyzing the electromagnetic field signals received at these observation points, electromagnetic anomaly images of underground layered media and terrain can be drawn. When processing these signals, the three-dimensional non-complete fast Fourier transform technology can greatly improve the speed and accuracy of signal processing and help researchers identify the electromagnetic response laws of underground media. This method can effectively detect the impact of complex terrain and underground layered media on electromagnetic field propagation in ground well electromagnetic exploration, thereby providing efficient technical means for underground resource exploration, geological structure analysis, etc.

[0093] The key parameter optimization method of ground-well electromagnetic exploration simulation calculation based on three-dimensional incomplete fast Fourier transform provided in an embodiment of the present invention includes:

[0094] S101, determine that the three-dimensional irregular layered background medium refers to a layered medium with a slowly undulating interface, the resistivity in the layer remains unchanged, consider the application of low-frequency electromagnetic exploration, and ignore the influence of metal casing; determine the three-dimensional research area and perform three-dimensional cube grid division; in order to realize the calculation of the analytical solution of the dyadic Green's function of the three-dimensional irregular layered background medium, the field source and the receiving point are exchanged, and the three-dimensional ground-well electromagnetic field integral equation under the background of three-dimensional irregular layered medium is derived;

[0095] S102, based on the derived multi-source multi-frequency three-dimensional well electromagnetic field integral equation, first calculate the electromagnetic field primary field response involved in the right side of the integral equation of the internal grid points in the study area; assume that the electromagnetic field response of the irregular layered background medium is weakly coupled with the horizontal layered medium response, and regard the study area as the superposition of the irregular layered background medium and the horizontal layered medium. Use the Gaussian filter algorithm to calculate the primary field response of the three-dimensional horizontal layered medium problem, and use it as the right side term of the Green's function numerical simulation equation group of the irregular layered background medium. Use the stable biconjugate gradient-fast Fourier transform algorithm to solve the Green's function numerical simulation equation group of the irregular layered background medium.

[0096] S103, based on the solved Green's function response of irregular layered background medium, using the plane symmetry property of dyadic Green's function, adopting the fast Fourier transform algorithm, only calculate the dyadic Green's function of half of the grid points on the diagonal line of the horizontal section of the study area, and reconstruct the dyadic Green's function distribution of the complete horizontal section grid points through the spatial interpolation algorithm;

[0097] S104, substituting the above-mentioned dyadic Green's function into the integral equation group of step 1, and using the stable biconjugate gradient-fast Fourier transform algorithm to solve the three-dimensional ground well electromagnetic field integral equation group under the three-dimensional irregular layered medium background, the total electromagnetic field of the center point of the subdivided grid in the three-dimensional study area can be obtained, and then the electromagnetic field primary field and scattered field at each observation point in the ground well electromagnetic wellbore are calculated, and the sum of the two is the total electromagnetic field response at the observation point.

[0098] The S101 specifically includes:

[0099] Considering a multi-source multi-frequency three-dimensional well electromagnetic observation system, several radial and vertical radial dipole source pairs are arranged to transmit the field source, and receivers are set up at the target layer in the well to measure the electromagnetic field. Assuming that the underground medium in the study area is an irregular layered background medium, the medium magnetic permeability μ is considered to be a constant, and the dielectric constant As the spatial position changes, the electric field satisfies the equation:

[0100]

[0101] in, ω is the angular frequency, r is the spatial position of the receiving point; ε 0 and are the dielectric constants of free space and abnormal region respectively, j is the imaginary unit, and σ is the conductivity of the internal space.

[0102] Without loss of generality, the external excitation field source is expressed as:

[0103]

[0104] Define the dyadic Green function that satisfies the above study area So that the following equation is satisfied:

[0105]

[0106] In the above formula, V is the study area, dv′ represents the derivative of the target area, r′ is the spatial position in the study area, and the field source is expressed as:

[0107]

[0108] The S102 specifically includes:

[0109] Introducing unit dyadic and the pulse function δ(rr′), then equation (4) can be expressed as:

[0110]

[0111] Then, from equations (1)-(5), the expression of the dyadic Green's function considering the excitation field source at r' and the irregular layered background medium distribution at r is derived as follows:

[0112]

[0113] To obtain the dyadic Green's function in the study area V, the reciprocity theorem can be introduced, the positions of the field source and the receiving point in equation (6) are swapped, the study area V is divided into N hexahedral units, and the stable biconjugate gradient-fast Fourier algorithm is used to solve the equations to obtain the dyadic Green's function of the irregular layered medium background.

[0114] The S103 specifically includes:

[0115] Assume that the ground is laid out M T There are excitation field sources Tx, and M are arranged at different depths in the well. R receiving points Rx, the total number of data points under the condition of single frequency field source excitation is M = M T ×M R The study area V is divided into N grid units, and the electrical parameter ΔV of each unit is a constant. The scattered field in the study area is expressed as:

[0116]

[0117] Where iR=1,…,M R , iT=1,…,M T ; is the Green's function at the receiving point of the mth layer of the irregular layered medium caused by the qth layer excitation field source, which is simulated and obtained by the above three-dimensional irregular layered background medium Green's function integral equation; E(r k ',r iT ) is the total electric field in the study area, is the electrical contrast function. Equation (7) can be simplified as:

[0118] f=Ax (8)

[0119] in, x is the contrast function matrix coefficient; i = iR + (iT-1)·M R , k = 1, ..., N. Then for a given contrast function matrix x, the scattering field distribution f can be obtained, and the spatial distribution of the contrast function x can be inferred from the known updated scattering field f. k ',r iT ) is the total electric field distribution of the subdivided area within a certain layer of medium, which satisfies the Helmholtz equation (1) under the background of three-dimensional layered medium. However, obtaining the total electric field distribution under the background of large-scale three-dimensional layered medium requires solving the huge computational and storage problems caused by the dyadic Green's function and the primary field on the right side of equation (1). Only the dyadic Green's function of half of the grid points on the diagonal of the horizontal section of the study area is calculated, and the dyadic Green's function distribution of the complete horizontal section grid points is reconstructed through the spatial interpolation algorithm. For the primary field calculation on the right side of equation (1), the Gaussian filtering algorithm is used to provide the field value distribution at any position under the background of layered medium. In this way, for the study area V with the number of subdivided units q×t×l, the calculation area can be reduced to by using the incomplete fast Fourier transform.

[0120] The present invention will be further described below in conjunction with specific embodiments.

[0121] Example 1

[0122] The key parameter optimization method based on three-dimensional incomplete fast Fourier transform for underground well electromagnetic exploration simulation calculation is used to Figure 2 and Figure 3 The experimental system and electrical model shown in the figure are simulated and calculated. First, the field source is set to be 30m below the ground, the deepest part of the valley is 50m, the distance between the field source and the observation point is 300m, the depth range of the observation point is 0-100m, the frequency of the magnetic dipole emission source is 1000Hz, the distance between the observation points is 5m, and a two-layered medium model is considered, that is, the first layer is an air layer, and the resistivity is set to 1×10 6Ohm-meter; the resistivity of the layered medium in the valley terrain is 100 ohm-meter. The three-dimensional non-complete fast Fourier transform algorithm is integrated into the integral equation simulation technology. The X, Y, and Z ranges of the study area D are 500×500×80m. The grid division of the study area is discretely divided by hexahedron. The total number of grid divisions in the three directions of three dimensions is set to 1, 216, 512, 1728, 3375, 5832, 15625, 27000, 64000, and 125000. Figure 4 It is shown that under the above-mentioned different total number of grid division conditions, the more Sommerfeld integrals are involved in the integral equation solving process, the lower the calculation efficiency; the calculation efficiency of the method proposed in this patent is compared with the conventional integral equation simulation calculation efficiency without using fast Fourier transform and using full fast Fourier transform. It can be seen that the calculation efficiency of this patent is higher. Figure 5 The figure shows the comparison between the integral equation simulation results and the analytical solution results using the method proposed in this patent, proving the correctness of this algorithm. Figure 6 The figure shows a comparison diagram between the calculated total electric field Ez component and the corresponding analytical solution provided by an embodiment of the present invention. It can be seen that the present invention can effectively simulate the abnormal electric field response caused by valley terrain.

[0123] An application embodiment of the present invention provides a computer device, which includes a memory and a processor. The memory stores a computer program. When the computer program is executed by the processor, the processor executes the steps of a key parameter optimization method for underground well electromagnetic exploration simulation calculation.

[0124] An application embodiment of the present invention provides a computer-readable storage medium storing a computer program. When the computer program is executed by a processor, the processor executes the steps of a key parameter optimization method for underground well electromagnetic exploration simulation calculation.

[0125] In the embodiment of the present invention, Number of Sommerfeld computation times indicates the number of times the Sommerfeld integral is calculated; Mesh factor indicates the number of mesh divisions in three directions in three dimensions; Without FFT indicates that the method of moments without fast Fourier transform is used; OldFFT indicates that the integral equation algorithm using the complete fast Fourier transform is used; New FFT indicates the integral equation algorithm based on the three-dimensional non-complete fast Fourier transform; Real\imaginary respectively indicate the real part and the imaginary part of the value; Ex and Ez indicate the x component and the z component of the electric field; Vm -1represents the unit of electric field, volt per meter; Modeling results represents the primary field calculated based on the integral equation of three-dimensional incomplete fast Fourier transform; Analytical results represents the primary field calculated using the analytical formula; Modeling total field represents the total field calculated based on the integral equation of three-dimensional incomplete fast Fourier transform; Analytical total field represents the total field calculated using the analytical formula; X, Y, Z are the components of the rectangular coordinate system.

[0126] The following are two specific industrial application embodiments based on the present invention:

[0127] 1. Mining resource exploration

[0128] In the process of resource exploration in mining areas, it is very important to understand the underground ore body distribution, rock layer structure and potential mineral deposits. The ground well electromagnetic exploration simulation calculation of the present invention can efficiently handle the electromagnetic field distribution problem under complex geological structures through three-dimensional non-complete fast Fourier transform technology and dyadic Green's function solution method.

[0129] Implementation process:

[0130] Exploration object: For coal seams, iron ore and other resources in a certain mining area, multiple excitation field sources and underground observation points are deployed to obtain underground electromagnetic responses.

[0131] Data acquisition: The system of the present invention is used to collect electromagnetic field data on the ground and underground under multi-frequency and multi-source conditions.

[0132] Data processing: The rapid algorithm of the present invention is used to calculate the electromagnetic field distribution and abnormal signals of the underground complex layered medium, and quickly draw the electromagnetic response map of the underground ore body.

[0133] Application effect: Compared with traditional exploration technology, this method can locate the position, size and shape of the ore body more quickly and accurately, saving time and cost.

[0134] 2. Geothermal energy development and groundwater resource monitoring

[0135] In geothermal energy development and groundwater resource monitoring, determining the distribution of groundwater and geothermal reservoirs is key. The present invention can help identify the distribution and depth of groundwater and thermal reservoirs and provide high-resolution geological information through efficient three-dimensional electromagnetic field computing capabilities.

[0136] Implementation process:

[0137] Exploration objects: used for the investigation of groundwater reservoir distribution or confirmation of the location of heat source layers in geothermal energy development, with systematic layout of excitation field sources and receiving points, covering the surface and underground.

[0138] Data acquisition: The system collects electromagnetic signals at different depths and frequencies to record abnormal electromagnetic responses of groundwater layers or thermal reservoirs.

[0139] Data processing: The Green's function solution and FFT algorithm of the present invention are applied to obtain high-precision underground electric and magnetic field distributions through limited computing resources.

[0140] Application effect: It can effectively locate the location, thickness and range of groundwater or heat reservoirs, helping decision makers optimize resource development plans and avoid over-development or development failure. This method not only improves exploration efficiency, but also reduces development costs and environmental impact.

[0141] These two specific industrial application embodiments demonstrate the practical value of the present invention in mineral resource exploration and geothermal energy and groundwater monitoring, and can provide accurate and efficient underground structure data support.

[0142] It should be noted that the embodiments of the present invention can be implemented by hardware, software, or a combination of software and hardware. The hardware part can be implemented using dedicated logic; the software part can be stored in a memory and executed by an appropriate instruction execution system, such as a microprocessor or dedicated design hardware. It can be understood by a person of ordinary skill in the art that the above-mentioned devices and methods can be implemented using computer executable instructions and / or contained in a processor control code, such as a carrier medium such as a disk, CD or DVD-ROM, a programmable memory such as a read-only memory (firmware), or a data carrier such as an optical or electronic signal carrier. Such code is provided on the carrier medium. The device and its modules of the present invention can be implemented by hardware circuits such as very large-scale integrated circuits or gate arrays, semiconductors such as logic chips, transistors, etc., or programmable hardware devices such as field programmable gate arrays, programmable logic devices, etc., can also be implemented by software executed by various types of processors, and can also be implemented by a combination of the above-mentioned hardware circuits and software, such as firmware.

[0143] The above description is only a specific implementation mode of the present invention, but the protection scope of the present invention is not limited thereto. Any modification, equivalent substitution and improvement made by any technician familiar with the technical field within the technical scope disclosed by the present invention and within the spirit and principle of the present invention should be covered by the protection scope of the present invention.

Claims

1. A key parameter optimization method for electromagnetic exploration simulation calculation in underground wells, It is characterized in that include: Step 1: Determine that the three-dimensional irregular layered background medium refers to a layered medium with a slowly undulating interface, the resistivity in the layer remains unchanged, and the influence of the metal casing is ignored; Determine the three-dimensional research area and perform three-dimensional cube mesh generation; in order to realize the calculation of the analytical solution of the dyadic Green's function of the three-dimensional irregular layered background medium, exchange the positions of the field source and the receiving point, and derive the three-dimensional ground-well electromagnetic field integral equation under the three-dimensional irregular layered background medium; Step 2: Based on the derived multi-source and multi-frequency three-dimensional well electromagnetic field integral equation, first calculate the primary field response of the electromagnetic field involved in the right side of the integral equation of the internal grid points in the study area; assume that the electromagnetic field response of the irregular layered background medium is weakly coupled with the horizontal layered medium response, and regard the study area as the superposition of the irregular layered background medium and the horizontal layered medium. Use the Gaussian filtering algorithm to calculate the primary field response of the three-dimensional horizontal layered medium problem, and use it as the right side term of the Green's function numerical simulation equation group of the irregular layered background medium. Use the stable biconjugate gradient-fast Fourier transform algorithm to solve the Green's function numerical simulation equation group of the irregular layered background medium. Step 3: Based on the obtained Green's function response of the irregular layered background medium, the plane symmetry property of the dyadic Green's function is utilized, and the fast Fourier transform algorithm is used to calculate only the dyadic Green's function of half of the grid points on the diagonal line of the horizontal section of the study area, and the dyadic Green's function distribution of the complete horizontal section grid points is reconstructed through the spatial interpolation algorithm; Step four, substitute the dyadic Green's function into the integral equation group of step one, and use the stable biconjugate gradient-fast Fourier transform algorithm to solve the three-dimensional ground well electromagnetic field integral equation group under the background of three-dimensional irregular layered medium, so as to obtain the total electromagnetic field of the center point of the subdivided grid in the three-dimensional study area, and then calculate the electromagnetic field primary field and scattered field at each observation point in the ground well electromagnetic wellbore. The sum of the two is the total electromagnetic field response at the observation point.

2. The key parameter optimization method for underground well electromagnetic exploration simulation calculation according to claim 1, It is characterized in that The step 1 specifically includes: Several radial and vertical radial dipole source pairs are arranged to transmit the field source, and receivers are set at the target layer in the well to measure the electromagnetic field; it is assumed that the underground medium in the study area is an irregular layered background medium, the medium magnetic permeability μ is a constant, and the dielectric constant As the spatial position changes, the electric field satisfies the equation: in, ω is the angular frequency, r is the spatial position of the receiving point; ε 0 and are the dielectric constants of free space and abnormal region, respectively, j is the imaginary unit, and σ is the conductivity of the internal space; Without loss of generality, the external excitation field source is expressed as: Define the dyadic Green function that satisfies the above study area So that the following equation is satisfied: In the above formula, V is the study area, dv′ represents the derivative of the target area, r′ is the spatial position in the study area, and the field source is expressed as:

3. The key parameter optimization method for underground well electromagnetic exploration simulation calculation according to claim 1, It is characterized in that The step 2 specifically includes: Introducing unit dyadic and the pulse function δ(rr′), then equation (4) can be expressed as: Then, from equations (1)-(5), the expression of the dyadic Green's function considering the excitation field source at r' and the irregular layered background medium distribution at r is derived as follows: To obtain the dyadic Green's function in the study area V, the reciprocity theorem can be introduced, the positions of the field source and the receiving point in equation (6) are swapped, the study area V is divided into N hexahedral units, and the stable biconjugate gradient-fast Fourier algorithm is used to solve the equations to obtain the dyadic Green's function of the irregular layered medium background.

4. The key parameter optimization method for underground well electromagnetic exploration simulation calculation according to claim 1, It is characterized in that The step three specifically includes: Assume that the ground is laid out M T There are excitation field sources Tx, and M are arranged at different depths in the well. R receiving points Rx, the total number of data points under the condition of single frequency field source excitation is M = M T ×M R The study area V is divided into N grid units, and the electrical parameter ΔV of each unit is a constant. The scattered field in the study area is expressed as: Where iR=1,…,M R , iT=1,…,M T ; is the Green's function at the receiving point of the mth layer of the irregular layered medium caused by the qth layer excitation field source, which is simulated and obtained by the above three-dimensional irregular layered background medium Green's function integral equation; E(r k ',r iT ) is the total electric field in the study area, is the electrical contrast function, and equation (7) is concisely expressed as: f=Ax (8) in, x is the contrast function matrix coefficient; i = iR + (iT-1)·M R , k = 1,…, N. Then for a given contrast function matrix x, the scattering field distribution f can be obtained, and the spatial distribution of the contrast function x can be inferred from the known updated scattering field f; E(r k ',r iT ) is the total electric field distribution of the subdivided area in a certain layer of medium, which satisfies the Helmholtz equation (1) under the background of three-dimensional layered medium; only the dyadic Green's function of half of the grid points on the diagonal of the horizontal section of the study area is calculated, and the dyadic Green's function distribution of the grid points of the complete horizontal section is reconstructed by the spatial interpolation algorithm; for the first-order field calculation on the right side of equation (1), the field value distribution at any position in the background of layered medium is provided by the Gaussian filtering algorithm. In this way, for the study area V with the number of subdivided units q×t×l, the calculation area can be reduced to 5. A computer device, comprising a memory and a processor, wherein the memory stores a computer program, and when the computer program is executed by the processor, the processor executes the steps of the key parameter optimization method for underground well electromagnetic exploration simulation calculation as described in any one of claims 1 to 4.

6. A computer-readable storage medium storing a computer program, which, when executed by a processor, enables the processor to execute the steps of the key parameter optimization method for underground well electromagnetic exploration simulation calculation according to any one of claims 1 to 4.

Images