Electrical source borehole transient electromagnetic perspective detection method

Abstract

The invention discloses an electrical source borehole transient electromagnetic perspective method detection method. The method comprises the following steps: S1, selecting two boreholes closest to a detection target body as transmitting and receiving boreholes; s2, arranging a grounding power supply lead in the emission drill hole, recording the grounding power supply lead as Tx, and exciting a secondary field; s3, a receiving measuring line is arranged in the receiving drill hole; s4, three-component probes are arranged on the receiving measuring line every 1-2 m for point-by-point measurement, and secondary field information after power failure is recorded; s5, positioning the boundary of the anomalous body through differential calculation, and determining the approximate horizontal position of the detection target according to the abrupt change point of the differential parameter; and S6, when a plurality of drill holes exist in front of the tunnel face, arranging a plurality of receiving measuring lines in other drill holes, obtaining position information in corresponding directions according to first-order difference results of the electric fields in different directions, and determining position coordinates of the detection target. According to the method, the detection precision and efficiency are improved, the construction risk and cost are effectively reduced, and powerful technical support is provided for safe construction of underground engineering.

Description

Technical Field

[0001] The present invention relates to the technical field of geological disaster detection, and particularly to a detection method for electrical source borehole transient electromagnetic penetration method. Background Art

[0002] During the construction of infrastructure such as railways and subways and the exploitation of coal mine resources, tunnel excavation often faces geological disaster risks such as water inrush and mud inrush. To ensure the smooth progress of the project, it is necessary to conduct early prediction of potential disasters. The transient electromagnetic method has been widely used in underground disaster warning due to its advantages such as high resolution for low-resistance abnormal bodies, convenient operation, and low cost. Currently, the commonly used transient electromagnetic devices include surface transient electromagnetic method, mine transient electromagnetic method, surface-tunnel transient electromagnetic method, and borehole transient electromagnetic method, etc. However, these methods have certain limitations in practical applications:

[0003] Surface transient electromagnetic method: The receiving and transmitting devices are far from the underground roadway, resulting in insufficient detection accuracy for deep parts; if there is a low-resistance covering layer, it is easy to shield the underground good conductor.

[0004] Mine transient electromagnetic method: Although the forward detection distance is relatively large and the directivity is good, there are blind areas, and it is seriously interfered by metals in the roadway, making it difficult to guarantee the data quality.

[0005] Surface-tunnel transient electromagnetic method: It requires real-time communication between the ground and the roadway, and the technology is still in its initial stage.

[0006] Drilling method: Although it can directly obtain information about the geological body in front, the cost is relatively high, and it cannot achieve full coverage.

[0007] Borehole transient electromagnetic method: Most of them use multi-turn small loops (magnetic sources) as the transmitting source, resulting in weak induction signals. Increasing the number of coil turns will enhance the self-inductance and mutual inductance phenomena.

[0008] Therefore, a single transient electromagnetic method or borehole coring is difficult to achieve an ideal detection effect, and the traditional magnetic source borehole transient electromagnetic method has low detection efficiency. Therefore, there is an urgent need for a detection method for electrical source borehole transient electromagnetic penetration method. Summary of the Invention

[0009] The present invention aims to solve the above-mentioned various problems and provides a detection method for electrical source borehole transient electromagnetic penetration method.

[0010] To solve the above technical problems, the technical solution provided by the present invention is: A detection method for electrical source borehole transient electromagnetic penetration method, including the following steps:

[0011] S1. Select two boreholes closest to the detection target body as the transmitting and receiving boreholes according to the existing boreholes on the tunnel face and the target detection area, and ensure that the boreholes are distributed on both sides of the detection target body;

[0012] S2. Lay a grounding power supply wire in the emission borehole, denoted as Tx, record the coordinates, hole depth, distance, and direction of the borehole, and supply a step current through the transmitter connected outside the borehole to excite the secondary field;

[0013] S3. Lay a receiving survey line in the receiving borehole. The length of the survey line depends on the position of the detection target and needs to cross the boundary of the target;

[0014] S4. Arrange three-component probes every 1 m to 2 m on the receiving survey line for point-by-point measurement. The point numbers are Rx11, Rx12, Rx13…, Rx1N, with a total of N measurement points. Record the secondary field information after power-off, i.e., the electric field parameters Ex, Ey, Ez, where Ez represents the electric field component along the borehole direction;

[0015] S5. Locate the boundary of the abnormal body through differential calculation. Specifically, discretize the electric field parameters of the measurement points in the form of first-order differences, and draw a broken line graph of the electric field difference - distance parameters to determine the approximate horizontal position of the detection target based on the mutation points of the difference parameters;

[0016] S6. When there are multiple boreholes in front of the tunnel face, lay multiple receiving survey lines in other boreholes to form a three-dimensional observation mode. Obtain the position information in the corresponding directions according to the first-order difference results of the electric fields in different azimuths, and finally determine the spatial position coordinates of the detection target.

[0017] As an improvement, the length of the grounding power supply wire Tx is adjusted according to the actual detection requirements, and the preferred range is 50 m to 200 m.

[0018] As an improvement, the layout length of the receiving survey line is preferably 50 m to 200 m, and the distance between the measurement points is 1 m to 2 m.

[0019] As an improvement, the locating of the boundary of the abnormal body through differential calculation is specifically as follows:

[0020]

[0021] The differential calculation is discretized in the form of first-order differences, specifically as follows:

[0022]

[0023] Among them, r represents the survey line direction vector, Δr represents the distance between the measurement points, and there are t moments and n measurement points in total. Perform differences on the electric field parameters of adjacent measurement points on the same line in sequence, and record all E′.

[0024] As an improvement, when there are multiple drill holes in front of the heading face, multiple receiving survey lines are arranged to form a three-dimensional observation mode. The number of survey lines is determined according to the actual number of drill holes, denoted as Line1, Line2, …, LineM.

[0025] The advantages of the present invention compared with the prior art are as follows:

[0026] 1. In the detection method of the electrical source borehole transient electromagnetic penetration method proposed by the present invention, by arranging the receiving probe in the drill hole close to the target geological body, the loss during the signal propagation process is effectively reduced, the signal-to-noise ratio and the lateral resolution of the data are improved, so that the distribution characteristics of the target geological body can be obtained more accurately. Using the grounded wire (electrical source) as the transmitter can use a high-power transmitter compared with the conventional multi-turn small loop (magnetic source), which can significantly increase the exploration depth and vertical resolution, and the signal attenuation is slower than that of the magnetic source. Therefore, the quality of the late-stage observation signal can be effectively guaranteed. At the same time, using the drill hole as the transmitting and receiving channel, the ferromagnetic interference sources in the roadway are avoided to the greatest extent, ensuring the quality and reliability of the collected data; the receiving probe receives the electromagnetic wave signal in front of the heading face, is close to the target geological body in position, and the secondary field has less loss and larger signal amplitude when propagating in the rock mass compared with the air, and the signal-to-noise ratio and the lateral resolution of the detection are correspondingly improved, so that the distribution characteristics of the geological body around the drill hole can be effectively obtained.

[0027] 2. The detection method of the electrical source borehole transient electromagnetic penetration method proposed by the present invention uses the electrical source as the transmitting device, which can not only achieve deeper and higher-precision detection, but also is conducive to the combination of multiple transmitters and receiving survey lines. According to the number of drill holes in front of the driving face, multiple receiving survey lines and transmitters are arranged, which can not only realize the transient electromagnetic exploration of multiple radiation sources, but also form a three-dimensional observation mode in space, laying a theoretical foundation for the three-dimensional inversion in the subsequent drill hole. In actual engineering construction, to ensure safety, even if geophysical forward prediction is carried out, the advanced drill hole will still be followed up. Therefore, using the existing roadway drill hole for geophysical exploration requires little investment and also avoids the one-sided view of the drill hole. Description of the Drawings

[0028] Figure 1 Schematic diagram of the electrical source borehole transient electromagnetic penetration method device;

[0029] Figure 2 Forward modeling model and grid of the water-containing collapse column;

[0030] Figure 3 Contour map of the electric field response obtained by detecting the water-containing collapse column using the electrical source borehole transient electromagnetic penetration method;

[0031] Figure 4It is a response differential contour map obtained by using the electrical source borehole transient electromagnetic penetration method to detect water-containing collapse columns. Specific embodiments

[0032] In the description of the present invention, it should be understood that the orientation or positional relationships indicated by the terms "upper", "lower", "front", "rear", "left", "right", "inner", "outer", "center", etc. are based on the orientation or positional relationships shown in the drawings. It is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation structure and operation. Therefore, it should not be construed as a limitation of the present invention.

[0033] In the description of the present invention, it should also be noted that unless otherwise clearly specified and limited, the terms "provided with", "installed", "connected", "coupled", etc. should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection. It can be a mechanical connection or an electrical connection. It can be directly connected or indirectly connected through an intermediate medium. It can be the communication inside two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0034] The present invention will be further described in detail below with reference to the accompanying drawings.

[0035] Combined with the attached Figure 1 , a detection method for the electrical source borehole transient electromagnetic penetration method, the specific implementation steps are as follows

[0036] S1: Borehole selection

[0037] According to the existing boreholes on the tunnel face and the target detection area, select the two boreholes closest to the detection target body as the transmitting and receiving boreholes, and ensure that these two boreholes are distributed on both sides of the detection target body. For example, in front of a coal mine roadway heading face, assuming there are multiple existing boreholes, by analyzing the geological data and the position of the target detection area, select two boreholes numbered A1 and A2, where A1 is used as the transmitting borehole and A2 is used as the receiving borehole.

[0038] S2: Layout of the transmitting device

[0039] Lay the grounding power supply wire (denoted as Tx) in the selected transmitting borehole (A1), and record parameters such as the coordinates, hole depth, distance, and direction of the borehole. Adjust the wire length according to the actual detection requirements, and the preferred range is 50m to 200m. For example, lay Tx to a length of 100m and supply a step current through the transmitter connected outside the borehole to excite the secondary field signal. During this process, it is necessary to ensure a stable current output to maximize the excitation of the abnormal response near the target geological body.

[0040] S3: Receiving survey line layout

[0041] Layout the receiving survey line in the selected receiving borehole (A2). The length of the survey line depends on the position of the detection target body and needs to cross the boundary of the target body. Preferably, the length of the survey line is 50m - 200m. For example, if the detection target body is expected to be within about 80m in front of the receiving borehole, the receiving survey line is laid out as 120m to ensure coverage of the target body and its surrounding area.

[0042] S4: Measurement and data acquisition

[0043] Arrange three-component probes every 1m - 2m on the receiving survey line for point-by-point measurement. The point numbers are sequentially recorded as Rx11, Rx12, Rx13…, Rx1N, with a total of N measurement points. Each probe records the secondary field information after power-off, including the electric field parameters Ex, Ey, and Ez, where Ez represents the electric field component along the borehole direction. For example, among the 60 measurement points on the receiving survey line, record the electric field parameter values of each measurement point to form a complete data set.

[0044] S5: Abnormal body positioning

[0045] Locate the boundary of the abnormal body through differential calculation. Specifically, discretize the electric field parameters of the measurement points in the form of first-order differences. The method of locating the boundary of the abnormal body through differential calculation is specifically as follows:

[0046]

[0047] The differential calculation is discretized in the form of first-order differences, specifically as follows:

[0048]

[0049] Among them, r represents the survey line direction vector, Δr represents the measurement point spacing, and there are t moments and n measurement points. Take the difference of the electric field parameters of adjacent measurement points on the same line in sequence, record all E′, take the difference of the electric field parameters of adjacent measurement points on the same line in sequence, record all the difference results, and draw a broken line graph of electric field difference - distance parameters. Determine the approximate horizontal position of the detection target by observing the position of the mutation point of the difference parameters. For example, if the difference parameter on a certain section of the survey line shows a significant mutation at a distance of 30m, it can be initially judged that this is the boundary of the target abnormal body.

[0050] S6: Three-dimensional observation mode

[0051] When there are multiple boreholes in front of the heading face, multiple receiving survey lines can be arranged in other boreholes to form a three-dimensional observation mode. The number of survey lines is determined according to the actual number of boreholes, denoted as Line1, Line2, …, LineM. For example, in a certain engineering case, in addition to boreholes A1 and A2, boreholes A3 and A4 were also used to arrange receiving survey lines, denoted as Line1 and Line2 respectively. By comprehensively analyzing the first-order difference results of the electric fields in different directions, the spatial position coordinates of the detection target are finally determined.

[0052] Verification and optimization

[0053] The forward response of the electrical source borehole transient electromagnetic sounding method is calculated by using the unstructured vector finite element method. As Figure 2 shown, there are a total of 5 survey lines, which are fan-shapedly distributed in the x-z plane, and the included angle between the survey lines is 15°. The spacing between the measurement points is 2m, and each survey line has 41 measurement points. The length of the emission source is 85m, and it forms an angle of 60° with the receiving survey line. There is a frustum-shaped collapse column between the emission source and the receiving survey line. The radii of the upper and lower bottom surfaces are 6m and 12m respectively, the height is 20m, and the resistivity is 1Ω·m.

[0054] In Figure 3 the contour maps of the electric field responses of the 5 survey lines at different times for the full-space model and the collapse column model are plotted. The color scales of the contour maps of the two models at the same time are the same, and the position of the collapse column is marked with a white dotted line. The survey line forms a certain angle with the emission source, and the distance between the two increases with the increase of the receiving point coordinates, while the electric field parameters of the full-space model decrease accordingly. Due to the existence of the water-containing collapse column, the electric field distribution of the receiving measurement points also changes, showing a low-value center at the position of the collapse column, and high-value anomalies are generated at the positions on both sides of the collapse column. This is particularly obvious in the late stage, making the range of the electric field response values of the entire model expand. Similarly, the first-order difference calculations are performed on the electric field parameters of the 5 survey lines respectively. The full-space model uses the color scale of the collapse column model, so the difference results of all time channels show uniformity. The electric field parameters of the collapse column model can better show the position of the collapse column anomaly, corresponding to a negative-value center. The two sides of the collapse column are positive-value centers, which is consistent with the Figure 3 electric field response law in

[0055] The above describes the present invention and its implementation manners. Such a description is not restrictive. What is shown in the drawings is only one of the implementation manners of the present invention, and the actual structure is not limited thereto. All in all, if those of ordinary skill in the art are inspired by it and design similar structural manners to cover the embodiments without creative work without departing from the gist of the present invention, they shall fall within the protection scope of the present invention.

Claims

1. A detection method for electrical source borehole transient electromagnetic perspective method, characterized in that, It includes the following steps: S1. Select two drill holes closest to the detection target body as the transmitting and receiving drill holes according to the existing drill holes at the tunnel face and the target detection area, and ensure that the drill holes are distributed on both sides of the detection target body; S2. Lay a grounded power supply wire, denoted as Tx, in the transmitting drill hole, record the coordinates, hole depth, distance and direction of the drill hole, and supply a step current through the transmitter connected outside the drill hole to excite the secondary field; S3. Lay a receiving survey line in the receiving drill hole, and the length of the survey line depends on the position of the detection target body and needs to cross the boundary of the target body; S4. Arrange three-component probes every 1 m to 2 m on the receiving survey line for point-by-point measurement. The point numbers are Rx11, Rx12, Rx13…, Rx1N, with a total of N measurement points. Record the secondary field information after power-off, that is, the electric field parameters Ex, Ey, Ez, where Ez represents the electric field component along the drill hole direction; S5. Locate the boundary of the abnormal body through differential calculation. Specifically, discretize the electric field parameters of the measurement points in the form of first-order difference, and draw a broken line graph of the electric field difference-distance parameters to determine the approximate horizontal position of the detection target according to the mutation point of the difference parameters; S6. When there are multiple drill holes in front of the tunnel face, lay multiple receiving survey lines to form a three-dimensional observation mode. Obtain the position information in the corresponding direction according to the first-order difference results of the electric field in different directions, and finally determine the spatial position coordinates of the detection target.

2. The detection method of electrical source borehole transient electromagnetic penetration method according to claim 1, characterized in that, The length of the grounded power supply wire Tx is adjusted according to the actual detection requirements, and the preferred range is 50 m to 200 m.

3. The detection method of electrical source borehole transient electromagnetic penetration method according to claim 1, characterized in that, The laid length of the receiving survey line is preferably 50 m to 200 m, and the distance between the measurement points is 1 m to 2 m.

4. The detection method of electrical source borehole transient electromagnetic penetration method according to claim 1, characterized in that The locating the boundary of the abnormal body through differential calculation is specifically as follows: The differential calculation is discretized in the form of first-order difference, specifically as follows: Among them, r represents the survey line direction vector, Δr represents the distance between measurement points, and there are t moments and n measurement points. Perform differences on the electric field parameters of adjacent measurement points on the same line in sequence, and record all E′.

5. The detection method of the electrical source borehole transient electromagnetic perspective method according to claim 1, characterized in that When there are multiple drill holes in front of the tunnel face, lay multiple receiving survey lines to form a three-dimensional observation mode. The number of survey lines is determined according to the actual number of drill holes, denoted as Line1, Line2, …, LineM.

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