A real-time imaging method and system for transient electromagnetic data while drilling

Abstract

The present invention relates to a real-time imaging method and system for transient electromagnetic data while drilling. The method includes: S1: Collecting time-domain electromagnetic data using sensors, preprocessing the data to obtain transient electromagnetic response data; S2: Decomposing the transient electromagnetic response data into an upward field and a downward field, and retaining the upward field transient electromagnetic response data; S3: Determining the start time and time step of interpolation, and performing interpolation on the upward field transient electromagnetic response data in both spatial and temporal dimensions; S4: Calculating the temporal gradient and spatial gradient of the transient electromagnetic data; S5: Performing time-depth conversion on the measurement points with the smallest gradient change range to obtain the visual depth, and after normalizing the temporal gradient and spatial gradient, synthesizing data for imaging. The method provided by the present invention can quickly obtain the structural information of the underground structure and achieve real-time imaging.

Description

Technical Field

[0001] The present invention relates to the fields of electromagnetic imaging technology and drilling, and particularly relates to a real-time imaging method and system for transient electromagnetic data while drilling. Background Art

[0002] During the tunneling and roadway driving processes, water disasters in unfavorable water bodies are often encountered, seriously threatening the safety of personnel and equipment. Therefore, advanced detection is required during tunneling and roadway driving. The means of advanced detection include geophysical exploration methods and drilling, and both have their own advantages. Geophysical exploration methods, especially electromagnetic detection methods, have the advantages of non-destructive detection and large detection range, and can prevent problems before they occur; while the drilling method can accurately determine the occurrence state of water bodies and the positions of unfavorable water bodies. In production practice, the two methods complement each other. In recent years, in order to further improve the tunneling and roadway driving efficiency, advanced detection technology has also seen new developments, and a transient electromagnetic advanced detection technology while drilling that combines drilling with the transient electromagnetic method in geophysical exploration methods has emerged. This new type of detection technology can collect transient electromagnetic data during the drilling process.

[0003] The transient electromagnetic method (time-domain electromagnetic method) is a type of electromagnetic detection method in geophysical exploration. It is based on Faraday's law of electromagnetic induction. By artificially and repeatedly exciting electromagnetic pulse signals, and using magnetic sensors to collect electromagnetic field signals during the intervals between the transmitted pulses. When the magnetic field where the electrical medium underground undergoes a sudden change, an eddy current field, called the secondary field, will be induced. The secondary field propagates in space and is received by the sensor. Due to the differences in the electrical properties of underground media, the intensities of the induced eddy currents generated are different, and the attenuation speeds of the induced fields are also different. Therefore, information such as the conductivity of the medium can be inferred by analyzing the attenuation characteristics of the secondary field received by the sensor. Since fluids often exhibit good conductivity, the transient electromagnetic method is widely used in the advanced detection of tunnels and roadways.

[0004] Traditional transient electromagnetic advanced detection is often carried out separately from drilling. It is necessary to process and interpret the transient electromagnetic observation data before continuing the tunneling. This requires first observing the data and then performing inversion processing, so the construction efficiency is greatly delayed. The data processing and interpretation technology of transient electromagnetic has become a difficult point restricting the construction progress.

[0005] At present, there are mainly two techniques for processing and interpreting time-domain electromagnetic data. One is the qualitative apparent resistivity imaging method, and the other is the quantitative inversion method. Among them, the apparent resistivity method is a fast approximate imaging method. It approximately obtains the abnormal distribution of relative high and low resistances by assuming that the diffusion velocity of electromagnetic waves and the underground are a uniform half-space model. This method is fast, but it is a qualitative method and often has false anomalies. The other method is the inversion method, which can perform one-dimensional, two-dimensional, and three-dimensional inversions for time-domain observation data of different dimensions. Although many articles and patents have been published on two-dimensional and three-dimensional forward and inversion techniques, the application cases of two-dimensional and three-dimensional inversions are still extremely rare in practice. The reason is that the maturity of two-dimensional and three-dimensional inversion techniques is still not high, and efficiency is a major problem. Therefore, at present, the main method for processing time-domain electromagnetic data is one-dimensional inversion. The object of one-dimensional inversion is the data of a single measurement point. It assumes that the formation below the measurement point is layered, and continuously iteratively solves the model parameters closest to the measured data through an optimization algorithm. It is a quantitative data processing method. However, since the one-dimensional inversion method regards each measurement point as a layered model, the one-dimensional inversion ignores the three-dimensional properties of the real underground medium, and such approximations often bring many problems, and even the inversion results are false anomalies.

[0006] For the new type of transient electromagnetic detection equipment while drilling, the acquisition of transient electromagnetic data progresses as the drill pipe advances. This requires that the transient electromagnetic data can be processed and interpreted in real time. This poses a great challenge to the interpretation accuracy and calculation speed of traditional transient electromagnetic data. Summary of the Invention

[0007] To solve the above technical problems, the present invention provides a real-time imaging method and system for transient electromagnetic data while drilling.

[0008] The technical solution of the present invention is: A real-time imaging method for transient electromagnetic data while drilling, comprising:

[0009] Step S1: Use a sensor to collect time-domain electromagnetic data, perform preprocessing on it, and obtain transient electromagnetic response data;

[0010] Step S2: Decompose the transient electromagnetic response data into an upward field and a downward field, and retain the upward field transient electromagnetic response data;

[0011] Step S3: Determine the start time and time step of interpolation, and perform interpolation in the spatial and time dimensions on the upward field transient electromagnetic response data;

[0012] Step S4: Calculate the time gradient and spatial gradient of the transient electromagnetic data. The gradients include two-dimensional gradients and three-dimensional gradients. Among them, the two-dimensional gradients calculate the gradients with respect to the measuring point spacing and time of the sensor respectively, and the three-dimensional gradients calculate the gradient with respect to time and calculate the two-dimensional gradient for the spatial dimension;

[0013] Step S5: Perform time-depth conversion on the measuring point with the smallest gradient change range to obtain the visual depth, and after normalizing the time gradient and spatial gradient, synthesize data imaging.

[0014] Compared with the prior art, the present invention has the following advantages:

[0015] The present invention discloses a real-time imaging method for transient electromagnetic data while drilling, which can be applied to transient electromagnetic data while drilling to perform structural imaging on the transient electromagnetic data. The method provided by the present invention does not require iteration, can quickly obtain the structural information of the underground structure, and realizes real-time imaging. In addition, the imaging method proposed by the present invention can be applied to two-dimensional and three-dimensional data. Description of the Drawings

[0016] Figure 1 It is a schematic diagram of a borehole model in an embodiment of the present invention;

[0017] Figure 2 It is a flowchart of a real-time imaging method for transient electromagnetic data while drilling in an embodiment of the present invention;

[0018] Figure 3 It is a schematic diagram of the result after processing by using seven-point smoothing and trace smoothing in an embodiment of the present invention;

[0019] Figure 4 It is the imaging result with the reference point as the background field in an embodiment of the present invention;

[0020] Figure 5 It is the imaging result with a homogeneous half-space as the background field in an embodiment of the present invention;

[0021] Figure 6 It is a structural block diagram of a real-time imaging system for transient electromagnetic data while drilling in an embodiment of the present invention. Detailed Embodiments

[0022] The present invention provides a real-time imaging method for transient electromagnetic data while drilling, which can quickly obtain the structural information of the underground structure and realize real-time imaging.

[0023] In order to make the objectives, technical solutions and advantages of the present invention clearer, the following further elaborates on the present invention through specific embodiments and in conjunction with the drawings.

[0024] Embodiment 1

[0025] The embodiments of the present invention adopt a mature three-dimensional forward finite element time domain program to simulate the theoretical data measured in the borehole. The borehole model is as follows: Figure 1 As shown in the figure: There are two vertical plate-like bodies below the borehole. The two plate-like bodies are exactly the same. The resistivity of the plate-like body is 5 Ωm, and the resistivity of the half-space background is 200 Ωm. The top of the plate-like body is 20 m away from the ground. The thickness of the plate-like body in the x direction is 20 m, and the extension in the y direction is 50 m. The drilling distance of the borehole is 300 m, and the starting coordinate is (-150, 0, 0). There are 61 measuring points in total, and the point spacing is 5 m.

[0026] As Figure 2 shown, a real-time imaging method for transient electromagnetic data while drilling provided by the embodiments of the present invention includes the following steps:

[0027] Step S1: Use a sensor to collect time-domain electromagnetic data, and perform preprocessing on it to obtain transient electromagnetic response data;

[0028] Step S2: Decompose the transient electromagnetic response data into an upward field and a downward field, and retain the transient electromagnetic response data of the upward field;

[0029] Step S3: Determine the start time and time step of interpolation, and perform interpolation on the transient electromagnetic response data of the upward field in the spatial and time dimensions;

[0030] Step S4: Calculate the time gradient and spatial gradient of the transient electromagnetic data. The gradient includes: the gradient includes a two-dimensional gradient and a three-dimensional gradient. Among them, the two-dimensional gradient calculates the gradient with respect to the measuring point spacing and time of the sensor respectively, and the three-dimensional gradient calculates the gradient with respect to time and calculates the two-dimensional gradient in the spatial dimension;

[0031] Step S5: Perform time-depth conversion on the measuring point with the smallest gradient change range to obtain the visual depth, and after normalizing the time gradient and spatial gradient, synthesize data imaging.

[0032] In one embodiment, the above step S1: Use a sensor to collect time-domain electromagnetic data, and perform preprocessing on it to obtain transient electromagnetic response data, specifically including:

[0033] Step S11: Manually remove bad points and abnormal data from the time-domain electromagnetic data;

[0034] Step S12: Use wavelet denoising method to remove random noise;

[0035] Step S13: Use a five-point or seven-point filtering method to smooth the time-domain electromagnetic data;

[0036] Step S14: Then use the trace smoothing method to smooth the jump point data between traces;

[0037] The embodiments of the present invention perform processing using seven-point smoothing and trace smoothing. The result after smoothing is as shown in Figure 3 shown;

[0038] Step S15: Select an appropriate order to perform polynomial fitting on the time-domain electromagnetic data to obtain transient electromagnetic response data.

[0039] After preprocessing, the transient electromagnetic response is monotonically decaying, and the late-stage data will not be greater than the early-stage data.

[0040] In one embodiment, the above-mentioned step S2: Decompose the transient electromagnetic response data into an upward field and a downward field, and retain the transient electromagnetic response data of the upward field, specifically including:

[0041] Separate the transient electromagnetic response data, and retain the transient electromagnetic response data of the upward field in formula (1);

[0042]

[0043] wherein, F u is the transient electromagnetic response data of the upward field, H is the magnetic field, ω is a preset frequency, which can be selected according to the attenuation characteristics of the transient electromagnetic spectrum, μ is the magnetic permeability, σ is the conductivity, z0 is the depth where the receiving coil is located; z is the origin of the coordinate system;

[0044] The vertical gradient of the magnetic field H in formula (1) can be expressed as formula (2):

[0045]

[0046] wherein, E is the electric field, and σ is the conductivity.

[0047] In this step, select the frequency corresponding to the sampling moment, and use the above-mentioned field separation method to separate each frequency point, and only retain the transient electromagnetic response data of the upward field.

[0048] In one embodiment, the above-mentioned step S3: Determine the start time and time step of interpolation, and perform interpolation on the transient electromagnetic response data of the upward field in the spatial and time dimensions, specifically including:

[0049] Step S31: Select the moment after the current is completely turned off as the start time of interpolation, or select the moment when the induced potential of each measuring point is closest as the start time, and set the time step of interpolation to 1 / 50 of the total observation duration;

[0050] Step S32: Perform cubic spline interpolation on the horizontal electromagnetic field components of the transient electromagnetic response data of the upward field.

[0051] Perform cubic spline interpolation on the horizontal electromagnetic field components to ensure the calculation of the horizontal gradient in step S2. The basis for selecting the starting time of the valid data is as follows: Select the data after the current is completely turned off as the starting time data, or select the time when the induced potential of each measuring point is closest as the starting time, or select the time step as 1 / 50 of the total observation duration. If the number of observation data channels is less than 50, return to step S15 for polynomial fitting interpolation.

[0052] In the embodiment of the present invention, the turn-off time is 1 μs, and the data decays stably after turn-off. The minimum simulation step is 10 -7 μs, so 1.1 μs is selected as the starting time. Since the embodiment of the present invention is theoretical simulation data, the simulation step is relatively small, the total observation duration is 10 ms, and there are 488 time points in total. Therefore, a sampling window of 5 pairs of simulation times is selected for sampling as the time step.

[0053] In one embodiment, the above step S4: Calculate the time gradient and space gradient of the transient electromagnetic data. The gradient includes: The gradient includes two-dimensional gradient and three-dimensional gradient. Among them, the two-dimensional gradient calculates the gradient with respect to the measuring point spacing and time of the sensor respectively, and the three-dimensional gradient calculates the gradient with respect to time and calculates the two-dimensional gradient for the spatial dimension, specifically including:

[0054] When calculating the gradient, different grid sampling numbers are selected according to the different dimensions of the data. When the data is two-dimensional data, the two-dimensional gradient is calculated along the measuring point spacing and time. When the data is three-dimensional data, the two-dimensional gradient is calculated for the data in the x and y directions in space, and the gradient is calculated with respect to time in the time direction.

[0055] In the example of the present invention, there is only 1 measuring line, so the data is two-dimensional data, and the two-dimensional gradient is calculated with respect to time - measuring point spacing respectively.

[0056] In one embodiment, the above step S5: Perform time-depth conversion on the measuring point with the smallest gradient change range to obtain the visual depth, and after normalizing the time gradient and space gradient, synthesize data imaging, specifically including:

[0057] Step S51: Along the data of the measuring point with the smallest gradient change in the time direction, use the electromagnetic wave diffusion velocity formulas (3) - (4) to perform time-depth conversion to obtain the apparent depth H r :

[0058]

[0059]

[0060] Among them, d r1 and d r2are the radii of current diffusion at two adjacent moments, t is the time, σ is the conductivity; μ0 is the magnetic permeability;

[0061] Step S52: Select a suitable background field, perform a normalization operation on the time gradient and the spatial gradient to obtain a normalized resistivity gradient distribution, and combine it with H r , and finally synthesize data imaging.

[0062] Taking Figure 4 and Figure 5 as examples, show how to select a suitable background field. Figure 4 is the imaging result of selecting a reference point as the background field, Figure 5 is the imaging result of selecting a homogeneous half-space as the background field. In the embodiments of the present invention, Figure 4 's reference point background field can relatively reliably restore the position and size of the plate-like body. While Figure 5 's background field only shows the lateral position of the plate-like body and does not have a good restoration of its shape.

[0063] The present invention discloses a real-time imaging method for electromagnetic data while drilling, which can be applied to electromagnetic data while drilling to perform structural imaging on transient electromagnetic data. The method provided by the present invention does not require iteration and can quickly obtain the structural information of the underground structure to achieve real-time imaging. In addition, the imaging method proposed by the present invention can be applied to two-dimensional and three-dimensional data.

[0064] Embodiment Two

[0065] As Figure 6 shown, the embodiments of the present invention provide a real-time imaging system for electromagnetic data while drilling, including the following modules:

[0066] A preprocessing module 61, configured to collect time-domain electromagnetic data by using a sensor, perform preprocessing on it to obtain transient electromagnetic response data;

[0067] An obtaining module 62 for the transient electromagnetic response data of the upward field, configured to decompose the transient electromagnetic response data into an upward field and a downward field, and retain the transient electromagnetic response data of the upward field;

[0068] An interpolation module 63, configured to determine the start time and time step of interpolation, and perform interpolation on the transient electromagnetic response data of the upward field in the spatial and time dimensions;

[0069] A module 64 for calculating the time gradient and the spatial gradient, configured to calculate the time gradient and the spatial gradient of the transient electromagnetic data. The gradient includes: the gradient includes a two-dimensional gradient and a three-dimensional gradient. Among them, the two-dimensional gradient respectively takes the gradient of the measuring point spacing of the sensor and time, and the three-dimensional gradient takes the gradient of time and calculates the two-dimensional gradient in the spatial dimension;

[0070] The synthetic data imaging module 65 is used to perform time-depth conversion on the measurement points with the smallest gradient change range to obtain the visual depth, and after normalizing the time gradient and the spatial gradient, perform synthetic data imaging.

[0071] The above embodiments are provided only for the purpose of describing the present invention and are not intended to limit the scope of the present invention. The scope of the present invention is defined by the appended claims. All equivalent substitutions and modifications made without departing from the spirit and principle of the present invention shall be covered within the scope of the present invention.

Claims

1. A real-time imaging method for transient electromagnetic data while drilling, characterized in that, Including: Step S1: Collect time-domain electromagnetic data using a sensor, preprocess it, and obtain transient electromagnetic response data. Step S2: Decompose the transient electromagnetic response data into an upward field and a downward field, and retain the transient electromagnetic response data of the upward field. Step S3: Determine the start time and time step of interpolation, and perform interpolation on the transient electromagnetic response data of the upward field in both spatial and temporal dimensions. Step S4: Calculate the temporal gradient and spatial gradient of the transient electromagnetic data. The gradients include two-dimensional gradients and three-dimensional gradients. Among them, the two-dimensional gradients are obtained by taking the gradients with respect to the measuring point spacing and time of the sensor respectively, and the three-dimensional gradients are obtained by taking the gradient with respect to time and calculating the two-dimensional gradient in the spatial dimension. Step S5: Perform time-depth conversion on the measuring point with the smallest gradient change range to obtain the visual depth, and after normalizing the temporal gradient and spatial gradient, synthesize data for imaging.

2. The real-time imaging method for transient electromagnetic data while drilling according to claim 1, wherein The above-mentioned Step S1: Collect time-domain electromagnetic data using a sensor, preprocess it, and obtain transient electromagnetic response data, specifically including: Step S11: Manually remove bad points and abnormal data from the time-domain electromagnetic data. Step S12: Use wavelet denoising method to remove random noise. Step S13: Use a five-point or seven-point filtering method to smooth the time-domain electromagnetic data. Step S14: Then use the trace smoothing method to smooth the jump-point data between traces. Step S15: Select an appropriate order to perform polynomial fitting on the time-domain electromagnetic data to obtain transient electromagnetic response data.

3. The real-time imaging method for transient electromagnetic data while drilling according to claim 1, characterized in that, The above-mentioned Step S2: Decompose the transient electromagnetic response data into an upward field and a downward field, and retain the transient electromagnetic response data of the upward field, specifically including: Separate the transient electromagnetic response data, and retain the transient electromagnetic response data of the upward field in formula (1). Among them, F u is the transient electromagnetic response data of the up-going field, H is the magnetic field, ω is the preset frequency, which can be selected according to the attenuation characteristics of the transient electromagnetic spectrum, μ is the magnetic permeability, σ is the conductivity, z0 is the depth where the receiving coil is located; z is the origin of the coordinate system; The vertical gradient of the magnetic field H in formula (1) can be expressed as formula (2): Where E is the electric field and σ is the conductivity.

4. The real-time imaging method for transient electromagnetic data while drilling according to claim 1, characterized in that, The above-mentioned Step S3: Determine the start time and time step of interpolation, and perform interpolation on the transient electromagnetic response data of the upward field in both spatial and temporal dimensions, specifically including: Step S31: Select the moment after the current is completely turned off as the start time of interpolation, or select the moment when the induced potential of each measuring point is closest as the start time, and set the time step of interpolation to 1 / 50 of the total observation duration. Step S32: Perform cubic spline interpolation on the horizontal electromagnetic field components of the transient electromagnetic response data of the upward field.

5. The real-time imaging method for transient electromagnetic data while drilling according to claim 1, wherein The above-mentioned Step S5: Perform time-depth conversion on the measuring point with the smallest gradient change range to obtain the visual depth, and after normalizing the temporal gradient and spatial gradient, synthesize data for imaging, specifically including: Step S51: For the measurement point data with the smallest gradient change along the time direction, perform time-depth conversion using the electromagnetic wave diffusion velocity formulas (3) to (4) to obtain the apparent depth H r : where d r1 and d r2 are the radii of current diffusion at two adjacent moments respectively, t is the time, σ is the conductivity; μ0 is the permeability; Step S52: Select a suitable background field, perform a normalization operation on the time gradient and the spatial gradient to obtain a normalized resistivity gradient distribution, and combine it with H r , and finally synthesize data imaging.

6. A real-time imaging system for transient electromagnetic data while drilling, characterized in that, Including the following modules: A preprocessing module, which is used to collect time-domain electromagnetic data using a sensor, preprocess it, and obtain transient electromagnetic response data. A module for obtaining transient electromagnetic response data of the upward field, which is used to decompose the transient electromagnetic response data into an upward field and a downward field, and retain the transient electromagnetic response data of the upward field. An interpolation module, which is used to determine the start time and time step of interpolation, and perform interpolation on the transient electromagnetic response data of the upward field in both spatial and temporal dimensions. A module for calculating time gradient and spatial gradient, which is used to calculate the time gradient and spatial gradient of transient electromagnetic data. The gradients include two-dimensional gradients and three-dimensional gradients. Among them, the two-dimensional gradients calculate gradients with respect to the measurement point spacing and time of the sensor respectively, and the three-dimensional gradients calculate gradients with respect to time and calculate two-dimensional gradients for the spatial dimension; A synthetic data imaging module, which is used to perform time-depth conversion on the measurement points with the smallest gradient change range to obtain the visual depth, and after performing standardization operations on the time gradient and spatial gradient, perform synthetic data imaging.

Images