Time domain electromagnetic spacetime dual-gradient resistivity imaging method and computer device

Abstract

The application relates to a time-domain electromagnetic space-time double-gradient resistivity imaging method, device, computer equipment, computer readable storage medium and computer program product. The method comprises the following steps: acquiring transient electromagnetic method data to be processed, wherein the data to be processed comprises electric field component attenuation data of m*n measuring points, and a far zone condition is met between the m*n measuring points and a long wire source; acquiring a spatial gradient expression of apparent resistivity and a time gradient expression of apparent resistivity; performing finite difference fusion based on the spatial gradient expression of resistivity and the time gradient expression of apparent resistivity to obtain a gradient resistivity expression; and generating a resistivity distribution map of a subsurface medium according to the data to be processed and the gradient resistivity expression. The abnormal body boundary description accuracy is improved.

Description

Technical Field

[0001] This application relates to the field of transient electromagnetic exploration technology, and in particular to a time-domain electromagnetic spatiotemporal dual-gradient resistivity imaging method, apparatus, computer equipment, computer-readable storage medium, and computer program product. Background Technology

[0002] Transient electromagnetic resistivity imaging typically relies on the eddy current diffusion velocity and radius generated by transient electromagnetics to perform time-depth conversion, and uses the time-varying apparent resistivity curve to perform Bostick-like inversion to calculate resistivity, thereby achieving resistivity-depth anomaly imaging.

[0003] Traditional transient electromagnetic apparent resistivity imaging methods, which are based on early or late apparent resistivity formulas for direct imaging, can quickly reflect the underground electrical structure, but are limited by shadowing effects and insufficient resolution, making it difficult to accurately characterize the boundaries of anomalies. Summary of the Invention

[0004] Therefore, it is necessary to provide a time-domain electromagnetic spatiotemporal dual-gradient resistivity imaging method, apparatus, computer equipment, computer-readable storage medium, and computer program product that can accurately characterize the boundaries of anomalous bodies, addressing the aforementioned technical problems.

[0005] In a first aspect, this application provides a time-domain electromagnetic spatiotemporal dual-gradient resistivity imaging method, including: Acquire the transient electromagnetic method data to be processed, the data to be processed includes electric field component attenuation data of m×n measuring points, and the m×n measuring points and the long conductor source satisfy the far-field condition; Obtain the spatial gradient expression and the temporal gradient expression of apparent resistivity, and perform finite difference fusion based on the spatial gradient expression and the temporal gradient expression of apparent resistivity to obtain the gradient resistivity expression; Based on the data to be processed and the gradient resistivity expression, a resistivity distribution map of the underground medium is generated.

[0006] In one embodiment, the m×n measuring points constitute n measuring lines, each measuring line includes m measuring points, and the measuring lines are parallel to the long conductor source; The acquisition of the data to be processed by the transient electromagnetic method includes: Acquire transient electromagnetic response data for each measuring point within a predetermined time range. The transient electromagnetic response data includes data on the decay of electric field components parallel to the long conductor source generated by induced eddy currents in the medium below the measuring point over time. The transient electromagnetic response data is converted into a preset format to obtain preset format data; A digital filter is used to suppress noise at a specific frequency in the preset format data to obtain denoised data; multiple periodic signals in the denoised data are shifted and superimposed to obtain preprocessed data, and the preprocessed data of all measurement points constitute the data to be processed.

[0007] In one embodiment, the step of obtaining the apparent resistivity spatial gradient expression includes: Obtain the mathematical expression for the electric field component at the measuring point when the emitted waveform of the long conductor source is a lower step; determine the early apparent resistivity expression based on the mathematical expression of the electric field component. The expression for the change in transverse resistivity is determined based on the early apparent resistivity expression, which characterizes the difference in apparent resistivity between two adjacent measuring points on the same measuring line. Obtain the spatial gradient expression of the electric field, and fuse the expression for the change in transverse resistivity and the expression for the spatial gradient of the electric field to obtain the spatial gradient expression of the apparent resistivity.

[0008] In one embodiment, the step of obtaining the apparent resistivity time gradient expression includes: Obtain the mathematical expression for the electric field component at the measuring point when the emitted waveform of the long conductor source is a lower step; determine the early apparent resistivity expression formula based on the mathematical expression of the electric field component. Obtain the electric field time gradient expressions for the same measuring point at the current time and the previous time, and fuse the early apparent resistivity expression formula and the electric field time gradient expression to obtain the apparent resistivity time gradient expression.

[0009] In one embodiment, the mathematical expression for the electric field component at the measuring point when the emitted waveform of the long conductor source is the following: Among them, E x Let I be the electric field component, dl be the emission current, and dl be the length of the electric dipole source, and u = μ0 is the vacuum conductivity, ρ is the resistivity, t is the observation time, and r is the transmit / receive distance; It is a probability function; The early apparent resistivity expression formula is as follows: The expression for the change in transverse resistivity is: Where i, j, and k are the measurement line, measurement point, and time sequence number, respectively. In the entire transceiver system, the difference in transmission distance between adjacent measurement points is negligible compared to the total transmission distance. r j -rj-1 ≈ 0 ; =Idl; The expression for the spatial gradient of the electric field is: in, The distance between adjacent measuring points on the measuring line; The expression for the apparent resistivity spatial gradient is: .

[0010] In one embodiment, the electric field time gradient expression is: Where Ex is the electric field component, and i, j, and k are the measurement line, measurement point, and time sequence number, respectively; The expression for the apparent resistivity time gradient is: ; Where r is the transmit / receive distance. =Idl, where I is the emission current and dl is the length of the electric dipole source.

[0011] In one embodiment, the gradient resistivity expression is: in, The apparent resistivity value at the reference point can be approximated using drilling data or rock physics data. Indicates survey line i Upper L Each measuring point j L exist t K Gradient resistivity at time t ρ gradient .

[0012] Thirdly, this application also provides a computer device, including a memory and a processor, wherein the memory stores a computer program, and the processor executes the computer program to implement the above-described time-domain electromagnetic spatiotemporal dual-gradient resistivity imaging method.

[0013] Fourthly, this application also provides a computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the above-described time-domain electromagnetic spatiotemporal dual-gradient resistivity imaging method.

[0014] Fifthly, this application also provides a computer program product, including a computer program that, when executed by a processor, implements the above-described time-domain electromagnetic spatiotemporal dual-gradient resistivity imaging method.

[0015] The aforementioned temporal electromagnetic spatiotemporal dual-gradient resistivity imaging method, apparatus, computer equipment, computer-readable storage medium, and computer program product acquire data to be processed using transient electromagnetic methods. This data includes electric field component attenuation data from m×n measuring points, where the m×n measuring points and the long conductor source satisfy far-field conditions. The method acquires the apparent resistivity spatial gradient expression and the apparent resistivity temporal gradient expression, performs finite-difference fusion based on these expressions to obtain the gradient resistivity expression, and generates a resistivity distribution map of the subsurface medium based on the data to be processed and the gradient resistivity expression. By calculating the derivative relationship of apparent resistivity with respect to the electric field component direction, it overcomes surface static offset and improves the lateral resolution of anomalies. Furthermore, by calculating the derivative relationship of apparent resistivity with respect to the electric field in the time direction, it achieves the conversion between the time derivative and depth, improving the resolution of anomalies in the depth direction. Moreover, the above method does not require iterative inversion, has fast imaging speed, good stability, and strong timeliness. It can provide important parameters for qualitative and quantitative interpretation of massive data acquired by time-domain electromagnetic arrays in the field, and also provide a good initial model for high-precision inversion. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of this application or related technologies, the drawings used in the description of the embodiments of this application or related technologies will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 This is a framework diagram of a temporal electromagnetic spatiotemporal dual gradient resistivity imaging method in one embodiment; Figure 2 This is a schematic diagram of the layout of the transmitter and receiver in one embodiment; Figure 3 This is a flowchart illustrating a temporal electromagnetic spatiotemporal dual-gradient resistivity imaging method in one embodiment. Figure 1 ; Figure 4 This is a flowchart illustrating a temporal electromagnetic spatiotemporal dual-gradient resistivity imaging method in one embodiment. Figure 2 ; Figure 5 This is a schematic diagram of a single anomaly body model in one embodiment; Figure 6 This is a schematic diagram of the apparent resistivity pseudo-section of a single low-resistivity anomalous volume in one embodiment. Figure 7 This is a schematic diagram of a dual-abnormality model in one embodiment; Figure 8This is a schematic diagram of a pseudo-profile of the apparent resistivity of two anomalous volumes in one embodiment; Figure 9 This is an example of an apparent resistivity plane diagram during multi-stage fracturing in one embodiment; Figure 10 This is an internal structural diagram of a computer device in one embodiment. Detailed Implementation

[0018] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0019] The time-domain electromagnetic spatiotemporal dual-gradient resistivity imaging method provided in this application can be applied to, for example... Figure 1 In the framework shown, Figure 1 The framework shown includes: a transmitter, a receiver, a server, and a visualization terminal. The receiver has a built-in SD card.

[0020] The execution subject and timing relationship involved in the time-domain electromagnetic spatiotemporal dual-gradient resistivity imaging method provided in this application embodiment are shown in Table 1. Referring to Table 1, the time-domain electromagnetic spatiotemporal dual-gradient resistivity imaging method provided in this application embodiment includes 5 processing stages: Table 1 The first processing stage is data acquisition, which is performed by the transmitter and receiver. A schematic diagram of the transmitter and receiver layout can be found here. Figure 2 As shown, Figure 2 In the diagram, AB represents the transmitting source, and the area formed by the black dots is the measurement network range. Each black dot is a measurement point, and each measurement point is equipped with a receiver. Figure 2 A line parallel to AB and connecting m measuring points is called a measuring line. Figure 2 The illustration uses only the first side line, line1, as an example. Figure 2 It contains n survey lines. The line spacing refers to the distance between two adjacent survey lines, and the point spacing refers to the distance between two adjacent survey points on the same survey line. Both the line spacing and the point spacing can be flexibly set according to the actual situation. For example, both the line spacing and the point spacing can be set to 50m.

[0021] The second processing stage is data transmission. The transmitter emits a bipolar square wave current with a duty cycle of 50%. Each receiver collects transient electromagnetic response data within a predetermined time range and stores the collected data in an SD card. Users can use this SD card to upload the data collected by the receiver to the server.

[0022] The third processing stage is preprocessing. The server preprocesses the data collected by each receiver to obtain the data to be processed by the transient electromagnetic method. For details, please refer to the following description.

[0023] The fourth processing stage is gradient calculation. The server performs gradient calculation based on the data to be processed and generates a resistivity distribution map of the underground medium based on the gradient calculation results.

[0024] The fifth processing stage is imaging output. The server transmits the generated resistivity distribution map to the visualization terminal, which displays the resistivity distribution map for geological interpretation.

[0025] In one exemplary embodiment, such as Figure 3 As shown, a time-domain electromagnetic spatiotemporal dual-gradient resistivity imaging method is provided. This time-domain electromagnetic spatiotemporal dual-gradient resistivity imaging method is a server processing procedure, and includes the following steps 302 to 306. Wherein: Step 302: Obtain the data to be processed by the transient electromagnetic method. The data to be processed includes the electric field component attenuation data of m×n measuring points. The m×n measuring points and the long conductor source meet the far-field condition.

[0026] As described above, the server receives transient electromagnetic response data within a predetermined time range collected by each receiver. This embodiment uses m×n measurement points, each equipped with a receiver. The transient electromagnetic response data collected by the receiver within the predetermined time range can also be understood as the transient electromagnetic response data of the measurement point where the receiver is located within the predetermined time range. Therefore, the server can receive m×n transient electromagnetic response data points within the predetermined time range, i.e., m×n sets of independent transient electromagnetic response data.

[0027] For each measurement point, the server can perform format conversion, noise suppression and other processing on the transient electromagnetic response data within a predetermined time range to obtain the electric field component attenuation data of that measurement point. The electric field component attenuation data of m×n measurement points constitute the data to be processed by the transient electromagnetic method.

[0028] Among them, see Figure 2 As shown, m×n measuring points constitute n measuring lines, and each measuring line includes m measuring points. The electromagnetic mechanism used in this embodiment is a transient electromagnetic method based on electric dipole source excitation. When the transmitting source is a long conductor source, the transmitting and receiving distance ( Figure 2 As shown r j The judgment is made by requiring that the distance be greater than the skin depth threshold (usually 3-5 times the skin depth) determined by the earth resistivity and the observation time, so as to meet the far-field conditions; when the transmission and reception distance is greater than this threshold, the long conductor source can be equivalently determined as an electric dipole source.

[0029] By substituting the data to be processed into the gradient resistivity expression, the gradient resistivity of each measuring point at each time step can be obtained. Finally, a resistivity distribution map of the subsurface medium can be generated based on this gradient resistivity. The method for obtaining the gradient resistivity expression is described below.

[0030] Step 304: Obtain the spatial gradient expression and the temporal gradient expression of apparent resistivity. Perform finite difference fusion based on the spatial gradient expression and the temporal gradient expression of apparent resistivity to obtain the gradient resistivity expression.

[0031] The apparent resistivity spatial gradient expression characterizes the spatial gradient of apparent resistivity. The apparent resistivity temporal gradient expression characterizes the temporal gradient of apparent resistivity. After obtaining the gradient expressions of apparent resistivity in these two dimensions, finite difference fusion is performed to obtain the gradient resistivity expression.

[0032] Step 306: Generate a resistivity distribution map of the underground medium based on the data to be processed and the gradient resistivity expression.

[0033] By substituting the data to be processed into the gradient resistivity expression, the gradient resistivity of each measuring point at each time can be obtained. Finally, a resistivity distribution map of the underground medium can be generated based on the gradient resistivity.

[0034] In the above embodiments, the data to be processed by the transient electromagnetic method is acquired. This data includes electric field component attenuation data from m×n measuring points, where the m×n measuring points and the long conductor source satisfy the far-field condition. The spatial and temporal gradient expressions of apparent resistivity are obtained. Finite-difference fusion is performed based on these expressions to obtain a gradient resistivity expression. A resistivity distribution map of the subsurface medium is generated according to the data to be processed and the gradient resistivity expression. By calculating the derivative of apparent resistivity with respect to the electric field component direction, surface static offset is overcome, improving the lateral resolution of anomalies. Furthermore, by calculating the derivative of apparent resistivity with respect to the electric field time direction, the conversion between the time derivative and depth is achieved, improving the depth-direction resolution of anomalies. Moreover, the above method does not require iterative inversion, has fast imaging speed, good stability, and strong timeliness. It can provide important parameters for the qualitative and quantitative interpretation of massive data acquired by time-domain electromagnetic arrays in the field, and also provides a good initial model for high-precision inversion.

[0035] In some embodiments, see Figure 2 As shown, m×n measuring points constitute n measuring lines, each measuring line includes m measuring points, and the measuring lines are parallel to the long conductor source; the process of acquiring the data to be processed by the transient electromagnetic method includes the following steps: Acquire transient electromagnetic response data for each measuring point within a predetermined time range. The transient electromagnetic response data includes data on the decay of electric field components parallel to the long conductor source generated by induced eddy currents in the medium below the measuring point over time. Convert the raw acquired data into a preset format to obtain preset format data. Use a digital filter to suppress noise of specific frequencies in the preset format data to obtain denoised data. Shift and superimpose multiple periodic signals in the denoised data to obtain preprocessed data. The preprocessed data from all measuring points constitute the data to be processed.

[0036] Optionally, the transmitter uses a long conductor source to emit a bipolar square wave current with a duty cycle of 50%, which is transmitted through... Figure 2 The multi-channel receiver (m×n channels) shown collects transient electromagnetic response data within a predetermined time range. Each receiver will collect a set of transient electromagnetic response data, which can also be referred to as the transient electromagnetic response data of the measurement point where the corresponding receiver is located within the predetermined time range.

[0037] For each measuring point, the transient electromagnetic response data of that measuring point within a predetermined time range includes: the data of the electric field component Ex generated by the induced eddy current in the medium below the measuring point, which is parallel to the direction of the emission source (direction of the long conductor source), decaying over time.

[0038] Specifically, transient electromagnetic response data manifests as a series of time-delay gates and their corresponding electric field values. For example, the early electric field value at 0.01 ms reflects information about shallow low-resistivity bodies, while the late electric field value at 0.1 s reveals deep electrical structures. Here, the electric field value refers to the value of the electric field component Ex, which is particularly sensitive to well-conducting underground targets and is a key basis for inverting underground three-dimensional electrical structures, especially for delineating low-resistivity anomalies.

[0039] Optionally, the receiver can store the acquired transient electromagnetic response data in an SD card and use the SD card to transmit the transient electromagnetic response data to the server. Alternatively, the receiver supports wireless transmission and can wirelessly transmit the transient electromagnetic response data to the server. This application embodiment does not limit the transmission method.

[0040] For a transient electromagnetic exploration area containing m×n measuring points, such as Figure 2For example, the server receives m×n sets of independent transient electromagnetic response (EMI) data. For each set of EMI data, a standard processing procedure is performed: first, the EMI data is unpacked and converted to the server's internal format to obtain preset format data; then, a digital filter is used to suppress interference noise at specific frequencies such as power frequency in the preset format data to obtain denoised data; finally, multiple periodic signals in the denoised data are shifted and superimposed to suppress random noise and improve the signal-to-noise ratio, thus obtaining preprocessed data. After the above processing, each measuring point finally obtains a set of time-discrete electric field component Ex attenuation data representing its geoelectric characteristics. Plotting this data on a time-amplitude coordinate system yields a unique, high-quality electric field attenuation curve for that measuring point. The preprocessed data corresponding to each of the m×n sets of independent EMI data constitutes the data to be processed.

[0041] Specifically, as described above, the transmitter emits a bipolar square wave current with a 50% duty cycle, thus the emitted current exhibits periodicity. The aforementioned translation and superposition process can include: aligning the data collected in each cycle with its transmission off-time as the starting point (synchronizing and aligning the signals of each cycle to lay the foundation for coherent superposition); and adding all the aligned data at the corresponding sampling points (observation times) (utilizing signal coherence to suppress noise randomness), resulting in a smooth transient electromagnetic attenuation curve with a significantly improved signal-to-noise ratio.

[0042] In the above embodiments, after the server receives the transient electromagnetic response data of each measuring point within a predetermined time range, it preprocesses the data to improve the signal-to-noise ratio, thereby improving the accuracy of subsequent resistivity imaging.

[0043] In some embodiments, the step of obtaining the apparent resistivity spatial gradient expression includes: A mathematical expression for the electric field component at the measuring point when the emitted waveform of the long conductor source is a lower step is obtained; an early apparent resistivity expression formula is determined based on the mathematical expression of the electric field component; a transverse resistivity change expression is determined based on the early apparent resistivity expression formula, the transverse resistivity change expression representing the difference in apparent resistivity between two adjacent measuring points on the same measuring line; an electric field spatial gradient expression is obtained, and the transverse resistivity change expression and the electric field spatial gradient expression are fused to obtain the apparent resistivity spatial gradient expression.

[0044] This application relates to transient electromagnetic sounding using a long conductor source, based on the principle of transient electromagnetic sounding excited by a horizontal electric dipole source at the ground surface. When the length of the long conductor source is much smaller than the transmit / receive distance, it is considered an electric dipole source. That is, when the transmit / receive distance is greater than the skin depth threshold (usually 3-5 times the skin depth) determined by the earth resistivity and observation time, the long conductor source is equivalently determined as an electric dipole source. When the transmitted waveform of the long conductor source is a lower step, the time-domain horizontal electric field component E at the measurement point... x The mathematical expression is: (1) In the formula, E x The electric field component in the data to be processed is represented by I; the emission current is the current supplied to the long conductor source during field data acquisition; dl is the length of the electric dipole source; u = μ0 is the vacuum conductivity, ρ is the resistivity; t is the observation time, for example, if the predetermined duration is 0.0001s to 1s, t is a certain time point within that range; r is the transmit / receive distance. Let be a probability function.

[0045] Due to the complexity of formula (1), it is mathematically impossible to obtain an analytical result of the apparent resistivity within the observation period. The conventional approach is to use a segmented method, dividing the apparent resistivity into early and late apparent resistivity. When considering the early apparent resistivity or the far-field region, we have: (2) Substituting formula (2) into formula (1) yields the expression for the early apparent resistivity of the transient electromagnetic field of the electric dipole source: (3) Based on the aforementioned early apparent resistivity expression, the expression for the change in transverse resistivity can be determined as follows: (4) In the formula, i, j, and k are the survey line, survey point, and time sequence number, respectively. This indicates that the j-th measuring point on the i-th measuring line is at the th position. The change in transverse resistivity at any given time. In the entire transceiver system, the difference in transmit / receive distance between adjacent measuring points on the same measuring line is negligible compared to the transmit / receive distance itself. Therefore... r j -r j-1 ≈ 0 , =Idl, it can be seen from formula (4) that the transverse resistivity changes The difference in apparent resistivity between two adjacent measuring points on the same measuring line is represented by the difference in apparent resistivity at the j-th measuring point on the i-th measuring line. The resistivity at time t is related to the (j-1)th measuring point on the i-th measuring line at time t. The difference in resistivity at any given time.

[0046] Define the measuring point j on the measuring line i. t Spatial gradient of electric field at time t for: (5) in, This indicates that the measuring point j on the measuring line i is... t The electric field components at time t, This indicates that the measuring point j-1 on measuring line i is at... t The electric field components at time t. It represents the distance between adjacent measuring points on the measuring line; that is, the distance between the j-th measuring point on the i-th measuring line and the (j-1)-th measuring point on the i-th measuring line.

[0047] Substituting equation (5) into equation (4), we obtain the expression for the spatial gradient of apparent resistivity: (6) The above embodiments provide a method for obtaining the spatial gradient expression of apparent resistivity. By calculating the derivative relationship between apparent resistivity and electric field component direction, the static offset of the surface layer is overcome and the lateral resolution of the anomalous body is improved.

[0048] In some embodiments, the step of obtaining the apparent resistivity time gradient expression includes: Obtain the mathematical expression of the electric field component at the measuring point when the emitted waveform of the long conductor source is a step below; determine the early apparent resistivity expression formula based on the mathematical expression of the electric field component; obtain the electric field time gradient expression of the same measuring point at the current time and the previous time; fuse the early apparent resistivity expression formula and the electric field time gradient expression to obtain the apparent resistivity time gradient expression.

[0049] Optionally, the mathematical expression of the electric field component at the measuring point when the long conductor source emits a waveform that is lowered by a step, and the process of obtaining the early apparent resistivity expression formula can be found in the aforementioned embodiments, and will not be repeated here.

[0050] The electric field time gradient expression for the same measuring point at the current time and the previous time can be: In the formula, This indicates that the measuring point j on the measuring line i is... t The electric field components at time t, This indicates that the measuring point j on the measuring line i is... t The electric field components at time t. i, j, and k are the measurement line, measurement point, and time sequence number, respectively. It should be noted that in the embodiments of this application, some parameters in some formulas may be used in other formulas. These parameters have the same meaning and can be used interchangeably.

[0051] Among them, observation time t and t The logarithmic form is used because the amplitude of the transient electromagnetic response spans multiple orders of magnitude from its early to late stages, whereas a simple linear time difference t... k -t k-1 This can lead to large differences in calculation results between early and late stages, which is not conducive to uniformly analyzing decay characteristics across the entire time series. However, defining the apparent decay rate parameter under the logarithmic time coordinate can not only conform to the physical law of power-law decay of electromagnetic fields, but also achieve normalization processing of data across orders of magnitude.

[0052] By fusing the early apparent resistivity expression formula and the electric field time gradient expression, the apparent resistivity time gradient expression can be obtained as follows: (7) The above embodiments provide a method for obtaining the expression for the apparent resistivity time gradient. By calculating the derivative relationship between apparent resistivity and electric field in the time direction, the conversion between the time derivative and depth is realized, thereby improving the resolution of anomalies in the depth direction.

[0053] In some embodiments, after obtaining the spatial gradient expression for resistivity and the temporal gradient expression for apparent resistivity, in order to simultaneously constrain the transverse and longitudinal resistivity, the spatiotemporal joint resistivity change formula can be derived by combining formulas (6) and (7): Finally, based on the finite difference principle, the survey line is obtained along the survey line and in chronological order. i Upper L Each measuring point j L exist t K Gradient resistivity at time t ρ gradient for: in, The apparent resistivity value at the reference point can be approximately obtained from drilling data or rock physics data. Where k = 1, 2, 3... K, l = 1, 2, 3... L.

[0054] In some embodiments, as described above, after preprocessing, each measuring point ultimately obtains a set of time-discrete electric field component attenuation data representing its geoelectric characteristics, for example, t The electric field component at time t is E x1， t The electric field component at time t is E x2 , ... t The electric field component at time t is E xk， ... t The electric field component at time t is E xn。 E x1 E x2 ...E xk ...E xn The resistivity decreases sequentially. Based on this data, the gradient resistivity at any given time can be obtained for each measuring point using the above gradient resistivity expression. In the embodiments of this application, "time" and "observation time" have the same meaning.

[0055] Specifically, for any measuring point, after obtaining the gradient resistivity at each time step, the time step is converted into depth using the skin depth calculation formula. With a certain measuring line as the horizontal axis and depth as the vertical axis, the gradient resistivity is marked at the corresponding position in the coordinate system. The Kriging interpolation method is used to interpolate the offline gradient resistivity in the coordinate system into a regular grid. Then, the gradient resistivity in the coordinate system is converted into grayscale values, thus obtaining the resistivity distribution map of the subsurface medium, which is sometimes referred to as the imaging result in this embodiment. Grayscale values ​​are only one example; a color image can also be used, and this embodiment does not limit this.

[0056] For any given measuring point, after obtaining the gradient resistivity at each time step, Kriging interpolation is used to interpolate these discrete gradient resistivity values ​​into a regular grid. Color mapping technology is applied to convert the resistivity values ​​into a pseudo-color image, resulting in a resistivity distribution map of the subsurface medium, typically using a red-blue transition color system, where red represents high resistivity and blue represents low resistivity. Thresholding is used to identify anomalous boundaries. Standardized result maps, such as planar contour maps, are generated.

[0057] In some embodiments, see Figure 4As shown, the overall workflow of the temporal electromagnetic spatiotemporal dual-gradient resistivity imaging method is presented. First, external equipment (receiver) acquires data. Then, the server preprocesses the data acquired by the receiver and determines whether the far-field conditions are met. If met, an early apparent resistivity expression is obtained. Based on the early apparent resistivity expression, the spatial gradient expression and temporal gradient expression of resistivity are obtained. Finite-difference fusion is performed based on the spatial gradient expression and the temporal gradient expression of resistivity to obtain the gradient resistivity expression. Based on the preprocessed data, the gradient resistivity is calculated using this gradient resistivity expression. Finally, the calculated gradient resistivity is imaged. The temporal electromagnetic spatiotemporal dual-gradient resistivity imaging method is an efficient geophysical exploration technique that combines spatial and temporal gradients. It can be used to quickly identify the electrical distribution and boundary characteristics of subsurface anomalies. Based on the three-dimensional high-density spatiotemporal array acquisition characteristics of existing temporal electromagnetic acquisition technology, resistivity is calculated by jointly using lateral spatial gradients and longitudinal temporal gradients. This method improves the lateral and longitudinal resolution of the temporal electromagnetic method, suppresses the static migration effect, achieves rapid on-site imaging, and has good timeliness.

[0058] The temporal electromagnetic spatiotemporal dual-gradient resistivity imaging method provided in this application has significant technical effects and advantages compared with the prior art. First, regarding the accuracy of anomalous body boundary identification, model verification shows that the boundary identification error of the dual-gradient method provided in this application is smaller than that of the traditional apparent resistivity imaging method, thus improving accuracy. Figure 5 A single anomaly model provided for embodiments of this application. The effects are compared. Figure 6 Left imaging results and Figure 6 The imaging results on the right were verified. Figure 6 This is a pseudo-profile of the apparent resistivity of a single low-resistivity anomaly. Figure 6 The image on the left is the imaging result obtained using the method of the embodiments of this application. Figure 6 The image on the right shows the imaging results obtained using traditional methods. The boundaries of the true anomalies, marked by dashed boxes, closely match the gradient extremum regions. The imaging results of this embodiment meet expectations, and the boundary recognition performance is superior to traditional apparent resistivity imaging. Secondly, in terms of data processing efficiency, traditional inversion methods require hours to days of computation, while the imaging method of this embodiment can complete data processing and image generation in just minutes, improving efficiency by two orders of magnitude. This advantage stems from the computational process based directly on gradient calculation rather than iterative inversion.

[0059] Furthermore, regarding adaptability to complex geological conditions, embodiments of this application provide, as follows: Figure 7The dual-anomaly model shown is used to simulate imaging effects under complex geological conditions. Based on the sensitivity of electromagnetic methods to low-resistivity anomalies, dual low-resistivity and low-high-resistivity anomalies are placed separately. Traditional methods struggle to distinguish adjacent anomalies spaced 200m apart, while the method in this embodiment can clearly differentiate them (see...). Figure 8 This effect was verified by setting up models with different resistivity combinations (low resistance, high resistance, double high resistance, etc.). Figure 8 This is a pseudo-profile of the apparent resistivity of a dual-anomaly volume (imaging result). The top, middle, and bottom sections represent dual low resistivity, low high resistivity, and dual high resistivity, respectively. The imaging results are applicable to the electromagnetic field, showing better imaging effects on low-resistivity volumes, and can be further analyzed based on the parameter Δρ. zx It can identify low-to-high resistance anomaly boundaries.

[0060] At the engineering application level, the embodiments of this application do not require expensive high-performance computing equipment; they can be achieved using only conventional electromagnetic exploration equipment and specialized algorithms, significantly reducing equipment costs. These technical effects are verified by uniformly adopting the skin depth formula (t in milliseconds) as the evaluation standard and comparing it with traditional methods under the same model parameters, ensuring the objectivity of the evaluation. The comprehensive advantages of the embodiments of this application make them promising for applications in mineral exploration, hydrological surveys, and other fields.

[0061] The embodiments of this application provide a spatiotemporal dual-gradient resistivity imaging method applicable to time-domain electromagnetic exploration in hydraulic fracturing monitoring. Traditional resistivity imaging methods have the following shortcomings in hydraulic fracturing monitoring in complex geological areas such as Chongqing: the fracturing section boundary is blurred, making it difficult to distinguish the fracturing influence range; the response characteristics of low-resistivity anomalies are not significant, leading to large errors in judging the fracturing fluid diffusion range; and real-time performance is insufficient, making it impossible to dynamically track the fracturing process. The embodiments of this application can adopt the following technical solutions: a) using a 4km long conductor source and such... Figure 9 The measurement network layout shown allows for transient electromagnetic measurements to be performed in stages before and after fracturing; b) Measurement points are set up according to a preset grid to collect potential difference data, with a sampling interval of ≤1ms to ensure the integrity of the transient field signal; c) Real-time imaging maps are generated by fusing dual-gradient data, and the fracturing-affected zone (such as Δρ) is highlighted through threshold segmentation. zx Positive and negative transition boundaries). Figure 9 This is a planar diagram of apparent resistivity during multi-stage fracturing. It shows the original apparent resistivity, the dual-gradient apparent resistivity, and Δρ. zx And the changes in apparent resistivity before and after 42-stage fracturing. It can determine the fracturing progress and fracturing range in real time. Verification shows that, compared with the original method, the method of this application embodiment has the following advantages: a) Boundary clarity: Dual gradient imaging (with attached...) Figure 9 - Top right) Compared to the original method (attached) Figure 9 - Top left) Significantly improves the resolution of the fracturing section boundary, clearly distinguishing the fracturing and unfracturing areas. b) Anomaly response: (See attached image) Figure 9 Δρ on the lower left zx The graph shows an initial positive trend followed by a negative trend along the eastward direction near section 42 of the fracturing, consistent with the attached... Figure 5 The boundary delineation of the low-resistivity anomaly indicates that the area near the 42nd fracturing stage is low-resistivity, consistent with the actual fracturing situation. c) Dynamic monitoring: Imaging of the difference in apparent resistivity before and after the 42nd fracturing stage (attached). Figure 9 The lower right section shows that the fracturing termination area and the unfracturing area have different change response characteristics, which can be used to divide the fracturing area and achieve real-time monitoring of the fracturing situation.

[0062] It should be understood that although the steps in the flowcharts of the embodiments described above are shown sequentially according to the arrows, these steps are not necessarily executed in the order indicated by the arrows. Unless explicitly stated herein, there is no strict order restriction on the execution of these steps, and they can be executed in other orders. Moreover, at least some steps in the flowcharts of the embodiments described above may include multiple steps or multiple stages. These steps or stages are not necessarily completed at the same time, but can be executed at different times. The execution order of these steps or stages is not necessarily sequential, but can be performed alternately or in turn with other steps or at least some of the steps or stages of other steps.

[0063] Based on the same inventive concept, this application also provides a resistivity imaging device for implementing the aforementioned time-domain electromagnetic spatiotemporal dual-gradient resistivity imaging method. The solution provided by this device is similar to the implementation described in the above method; therefore, the specific limitations in one or more resistivity imaging device embodiments provided below can be found in the above-described limitations of the time-domain electromagnetic spatiotemporal dual-gradient resistivity imaging method, and will not be repeated here.

[0064] In one exemplary embodiment, a time-domain electromagnetic spatiotemporal dual-gradient resistivity imaging device is provided, comprising: The acquisition module is used to acquire the data to be processed by the transient electromagnetic method. The data to be processed includes the attenuation data of electric field components at m×n measurement points, and the m×n measurement points and the long conductor source meet the far-field condition.

[0065] The fusion module is used to obtain the spatial gradient expression and the temporal gradient expression of apparent resistivity, and to perform finite difference fusion based on the spatial gradient expression and the temporal gradient expression of apparent resistivity to obtain the gradient resistivity expression.

[0066] The generation module is used to generate a resistivity distribution map of the underground medium based on the data to be processed and the gradient resistivity expression.

[0067] In some embodiments, the acquisition module is configured to acquire transient electromagnetic response data of each measuring point within a predetermined time range, wherein the transient electromagnetic response data includes data on the electric field component parallel to the long conductor source generated by induced eddy currents in the medium below the measuring point, which decays over time; convert the transient electromagnetic response data into a preset format to obtain preset format data; use a digital filter to suppress noise of a specific frequency in the preset format data to obtain denoised data; and shift and superimpose multiple periodic signals in the denoised data to obtain preprocessed data, wherein the preprocessed data of all measuring points constitute the data to be processed.

[0068] In some embodiments, the fusion module is configured to: acquire a mathematical expression for the electric field component at the measuring point when the emitted waveform of the long conductor source is a lower step; determine an early apparent resistivity expression based on the mathematical expression for the electric field component; determine a transverse resistivity change expression based on the early apparent resistivity expression, wherein the transverse resistivity change expression characterizes the difference in apparent resistivity between two adjacent measuring points on the same measuring line; acquire an electric field spatial gradient expression; and fuse the transverse resistivity change expression and the electric field spatial gradient expression to obtain an apparent resistivity spatial gradient expression.

[0069] In some embodiments, the fusion module is configured to obtain a mathematical expression for the electric field component at the measuring point when the emitted waveform of the long conductor source is a step below; determine an early apparent resistivity expression formula based on the mathematical expression of the electric field component; obtain the electric field time gradient expression at the same measuring point at the current time and the previous time; and fuse the early apparent resistivity expression formula and the electric field time gradient expression to obtain an apparent resistivity time gradient expression.

[0070] In some embodiments, the mathematical expression for the electric field component at the measuring point when the emitted waveform of the long conductor source is the following: Among them, E x Let I be the electric field component, dl be the emission current, and dl be the length of the electric dipole source, and u = μ0 is the vacuum conductivity, ρ is the resistivity, t is the observation time, and r is the transmit / receive distance; It is a probability function; The early apparent resistivity expression formula is as follows: The expression for the change in transverse resistivity is: Where i, j, and k are the measurement line, measurement point, and time sequence number, respectively. In the entire transceiver system, the difference in transmission distance between adjacent measurement points is negligible compared to the total transmission distance. r j-r j-1 ≈ 0 ; =Idl; The expression for the spatial gradient of the electric field is: in, The distance between adjacent measuring points on the measuring line; The expression for the apparent resistivity spatial gradient is: .

[0071] In some embodiments, the electric field time gradient expression is: Where Ex is the electric field component, and i, j, and k are the measurement line, measurement point, and time sequence number, respectively; The expression for the apparent resistivity time gradient is: ; Where r is the transmit / receive distance. =Idl, where I is the current and dl is the length of the electric dipole source.

[0072] In some embodiments, the gradient resistivity expression is: in, The apparent resistivity value at the reference point can be approximated using drilling data or rock physics data. Indicates survey line i Upper L Each measuring point j L exist t K Gradient resistivity at time t ρ gradient .

[0073] Each module in the aforementioned time-domain electromagnetic spatiotemporal dual-gradient resistivity imaging device can be implemented entirely or partially through software, hardware, or a combination thereof. These modules can be embedded in the processor of a computer device in hardware form or independent of it, or stored in the memory of a computer device in software form, so that the processor can call and execute the operations corresponding to each module.

[0074] In one exemplary embodiment, a computer device is provided, which may be a server, and its internal structure diagram may be as follows: Figure 10As shown, this computer device includes a processor, memory, input / output (I / O) interfaces, and a communication interface. The processor, memory, and I / O interfaces are connected via a system bus, and the communication interface is also connected to the system bus via the I / O interfaces. The processor provides computational and control capabilities. The memory includes non-volatile storage media and internal memory. The non-volatile storage media stores the operating system, computer programs, and a database. The internal memory provides the environment for the operation of the operating system and computer programs stored in the non-volatile storage media. The database stores data to be processed. The I / O interfaces are used for exchanging information between the processor and external devices. The communication interface is used for communication with external terminals via a network connection. When the computer program is executed by the processor, it implements a time-domain electromagnetic spatiotemporal dual-gradient resistivity imaging method.

[0075] Those skilled in the art will understand that Figure 10 The structure shown is merely a block diagram of a portion of the structure related to the present application and does not constitute a limitation on the computer device to which the present application is applied. Specific computer devices may include more or fewer components than those shown in the figure, or combine certain components, or have different component arrangements.

[0076] In one embodiment, a computer device is also provided, including a memory and a processor, wherein the memory stores a computer program, and the processor executes the computer program to implement the steps in the above method embodiments.

[0077] In one embodiment, a computer-readable storage medium is provided having a computer program stored thereon that, when executed by a processor, implements the steps in the above method embodiments.

[0078] In one embodiment, a computer program product is provided, including a computer program that, when executed by a processor, implements the steps in the above method embodiments.

[0079] Those skilled in the art will understand that all or part of the processes in the methods of the above embodiments can be implemented by a computer program instructing related hardware. The computer program can be stored in a non-volatile computer-readable storage medium, and when executed, it can include the processes of the embodiments of the above methods. Any references to memory, databases, or other media used in the embodiments provided in this application can include at least one of non-volatile memory and volatile memory. Non-volatile memory can include read-only memory (ROM), magnetic tape, floppy disk, flash memory, optical memory, high-density embedded non-volatile memory, resistive random access memory (ReRAM), magnetic random access memory (MRAM), ferroelectric random access memory (FRAM), phase change memory (PCM), graphene memory, etc. Volatile memory can include random access memory (RAM) or external cache memory, etc. By way of illustration and not limitation, RAM can take many forms, such as Static Random Access Memory (SRAM) or Dynamic Random Access Memory (DRAM). The databases involved in the embodiments provided in this application may include at least one type of relational database and non-relational database. Non-relational databases may include, but are not limited to, blockchain-based distributed databases. The processors involved in the embodiments provided in this application may be general-purpose processors, central processing units, graphics processing units, digital signal processors, programmable logic devices, quantum computing-based data processing logic devices, artificial intelligence (AI) processors, etc., and are not limited to these.

[0080] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this application.

[0081] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of this patent application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this application should be determined by the appended claims.

Claims

1. A time-domain electromagnetic spatiotemporal dual-gradient resistivity imaging method, characterized in that, The method includes: Acquire the transient electromagnetic method data to be processed, the data to be processed includes electric field component attenuation data of m×n measuring points, and the m×n measuring points and the long conductor source satisfy the far-field condition; Obtain the spatial gradient expression and the temporal gradient expression of apparent resistivity, and perform finite difference fusion based on the spatial gradient expression and the temporal gradient expression of apparent resistivity to obtain the gradient resistivity expression; Based on the data to be processed and the gradient resistivity expression, a resistivity distribution map of the underground medium is generated.

2. The method according to claim 1, characterized in that, The m×n measuring points constitute n measuring lines, each measuring line includes m measuring points, and the measuring lines are parallel to the long conductor source; The acquisition of the data to be processed by the transient electromagnetic method includes: Acquire transient electromagnetic response data for each measuring point within a predetermined time range. The transient electromagnetic response data includes data on the decay of electric field components parallel to the long conductor source generated by induced eddy currents in the medium below the measuring point over time. The transient electromagnetic response data is converted into a preset format to obtain preset format data; A digital filter is used to suppress noise at a specific frequency in the preset format data to obtain denoised data; multiple periodic signals in the denoised data are shifted and superimposed to obtain preprocessed data, and the preprocessed data of all measurement points constitute the data to be processed.

3. The method according to claim 1, characterized in that, The steps for obtaining the spatial gradient expression of apparent resistivity include: Obtain the mathematical expression for the electric field component at the measuring point when the emitted waveform of the long conductor source is a lower step; determine the early apparent resistivity expression based on the mathematical expression of the electric field component. The expression for the change in transverse resistivity is determined based on the early apparent resistivity expression, which characterizes the difference in apparent resistivity between two adjacent measuring points on the same measuring line. Obtain the spatial gradient expression of the electric field, and fuse the expression for the change in transverse resistivity and the expression for the spatial gradient of the electric field to obtain the spatial gradient expression of the apparent resistivity.

4. The method according to claim 1, characterized in that, The steps for obtaining the expression for the apparent resistivity time gradient include: Obtain the mathematical expression for the electric field component at the measuring point when the emitted waveform of the long conductor source is a lower step; determine the early apparent resistivity expression formula based on the mathematical expression of the electric field component. Obtain the electric field time gradient expressions for the same measuring point at the current time and the previous time, and fuse the early apparent resistivity expression formula and the electric field time gradient expression to obtain the apparent resistivity time gradient expression.

5. The method according to claim 3, characterized in that, The mathematical expression for the electric field component at the measuring point when the emitted waveform of the long conductive wire source is the following: Among them, E x Let I be the electric field component, dl be the emission current, and dl be the length of the electric dipole source, and u = μ0 is the vacuum conductivity, ρ is the resistivity, t is the observation time, and r is the transmit / receive distance; It is a probability function; The early apparent resistivity expression formula is as follows: The expression for the change in transverse resistivity is: Where i, j, and k are the measurement line, measurement point, and time sequence number, respectively. In the entire transceiver system, the difference in transmission distance between adjacent measurement points is negligible compared to the total transmission distance. r j -r j-1 ≈ 0 ; =Idl; The expression for the spatial gradient of the electric field is: in, The distance between adjacent measuring points on the measuring line; The expression for the apparent resistivity spatial gradient is: 。 6. The method according to claim 4, characterized in that, The expression for the electric field time gradient is: Where Ex is the electric field component, and i, j, and k are the measurement line, measurement point, and time sequence number, respectively; The expression for the apparent resistivity time gradient is: ； Where r is the transmit / receive distance. =Idl, where I is the emission current and dl is the length of the electric dipole source.

7. The method according to claim 1, characterized in that, The expression for gradient resistivity is: in, The apparent resistivity value at the reference point can be approximated using drilling data or rock physics data. Indicates survey line i Upper L Each measuring point j L exist t K Gradient resistivity at time t ρ gradient .

8. A computer device comprising a memory and a processor, wherein the memory stores a computer program, characterized in that, When the processor executes the computer program, it implements the steps of the method according to any one of claims 1 to 7.

9. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the computer program is executed by a processor, it implements the steps of the method according to any one of claims 1 to 7.

10. A computer program product, comprising a computer program, characterized in that, When the computer program is executed by a processor, it implements the steps of the method according to any one of claims 1 to 7.

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