A method for detecting electromagnetic transverse magnetic field from artificial sources on land

Abstract

The invention discloses a method for detecting a terrestrial artificial source electromagnetic transverse magnetic field, comprising the steps of: first, establishing a geoelectric model; second, laying out detection equipment; third, transmitting a step current for detection and receiving an electromagnetic response; and fourth, obtaining resistivity and determining a target body position according to the electromagnetic response inversion. The invention starts from a receiving mode and adopts a plurality of pairs of receiving electrodes to replace a traditional single electrode pair based on the reciprocity principle between source and receiver, thereby reducing the transverse electric field in the observed data, realizing transverse magnetic field observation from a receiving end, and enhancing the proportion of the transverse magnetic field, so that the observed data has a stronger resolution capability for high-resistance targets, thereby improving the resolution capability of the terrestrial electromagnetic method for high-resistance targets such as metal mineral ore-forming rock bodies, oil and gas, and adopting a traditional transmitting source for easy deployment and implementation.

Description

Technical Field

[0001] The present invention relates to the technical field of metal mineral and oil and gas resource exploration, and in particular to a method for detecting a terrestrial artificial source electromagnetic transverse magnetic field. Background Art

[0002] Artificial source electromagnetic exploration is a geophysical method for detecting mineral resources, oil and gas resources. Based on the electrical differences between underground metal ore bodies, oil and gas reservoirs and surrounding rocks, artificial source electromagnetic exploration is widely used in the fields of metal minerals, coal resources, geothermal energy, engineering surveys, etc.

[0003] Based on the principle of electromagnetic induction, the artificial source electromagnetic method has a stronger resolution for underground good-conducting targets. The horizontal electric field and the vertical magnetic field are the two most commonly used observation components. Compared with the vertical magnetic field which is only the transverse electric polarization field, the horizontal electric field contains the transverse electric field and the transverse magnetic field, and has a stronger resolution for high-resistance targets. However, the proportion of the transverse magnetic field in the horizontal electric field is limited. In order to realize the transverse magnetic field detection, vertical line sources (vertical electric dipole sources), multi-line sources (circular electric dipole sources), dual-line sources (differential electric dipole sources) and other devices have been proposed, and have achieved application results in marine electromagnetic exploration.

[0004] However, the observation methods currently used are not suitable for actual land exploration. The implementation of vertical electric dipole sources requires the use of boreholes that meet strict vertical extension requirements, which are easily affected by the actual terrain on land. The lateral offset of multi-line sources will bring huge response differences. A multi-line source standard device with a circular radius of about one kilometer is difficult to achieve. Therefore, the present invention proposes a land artificial source electromagnetic transverse magnetic field detection method to solve the problems existing in the prior art. Summary of the invention

[0005] In view of the above problems, the purpose of the present invention is to propose a method for detecting electromagnetic transverse magnetic fields of artificial terrestrial sources. The method starts from the receiving mode and is based on the reciprocity principle between source and receiver. It adopts multiple pairs of receiving electrodes to reduce the transverse electric field in the observation data, realizes transverse magnetic field observation from the receiving end, and improves the resolution ability of terrestrial electromagnetic method for high-resistance targets such as metal mineral mineralization rock bodies, oil and gas.

[0006] To achieve the purpose of the present invention, the present invention is implemented by the following technical scheme: a method for detecting electromagnetic transverse magnetic field of artificial source on land, comprising the following steps:

[0007] Step 1: Select the test mining area, build a geoelectric model using known geological data, forward simulate the electromagnetic response of the new method, and select appropriate observation parameters for actual detection;

[0008] Step 2: Arrange the detection equipment in the mining area, arrange the single-line source transmission source, bury the electrode pair connected to the transmitter, and bury multiple groups of electrode pairs equally with the common electrode N electrode as the center, and connect the multiple groups of electrode pairs to the terminal of the receiver;

[0009] Step 3: using the transmitter of the deployed detection equipment to transmit a step current, and using the receiver to receive the electromagnetic response;

[0010] Step 4: Process the received electromagnetic response, invert the distribution of underground resistivity in the test mining area, analyze the inversion results to determine the location of the target body, and complete the detection of the high-resistance target body.

[0011] A further improvement is that: in the step 1, electrodes A and B connected to the transmitter are buried, and electrodes A and B are connected to the positive electrode and negative electrode of the transmitter respectively.

[0012] A further improvement is that the geoelectric model parameters selected in step 1 include parameters of resistivity and depth.

[0013] Further improvement is that: when the resistivity and depth of the geoelectric model in step 1 are selected, the first layer has a resistivity of 300Ωm and a depth of 300m; the second layer has a high resistivity of 1500Ωm and a depth of 200m; and the third layer has a resistivity of 300Ωm.

[0014] A further improvement is that in step three, the transmitting current, offset distance and measuring point position of the transmitter are controlled to be consistent during calculation.

[0015] A further improvement is that: when burying multiple groups of electrode pairs in step 2, the electrode pairs use electrode N as a common electrode, and the other electrode of each electrode pair is evenly distributed around N as the center.

[0016] A further improvement is that in step 2, the buried N electrode is connected to a terminal of the receiving instrument, and the other electrode of the buried multiple electrode pairs is commonly connected to another terminal of the receiving instrument.

[0017] A further improvement is that in step three, a step current is used as a transmitting current, and a receiving device is used to receive a response during the current cut-off period.

[0018] A further improvement is that in step 4, the survey and resolution are performed specifically through the difference in electric field response when the high-resistance layer exists and when it does not exist.

[0019] The beneficial effects of the present invention are as follows: starting from the receiving method, based on the reciprocity principle between source and receiver, the present invention adopts multiple pairs of receiving electrodes to reduce the transverse electric field in the observation data, realizes transverse magnetic field observation from the receiving end, and enhances the proportion of transverse magnetic field, so that the detection capability of high resistance is enhanced, and the resolution capability of terrestrial electromagnetic method for high-resistance targets such as metal mineral mineralization rock bodies, oil and gas is improved. At the same time, the traditional transmitting source is adopted to facilitate the deployment and implementation. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is a survey flow chart of Example 1 of the present invention.

[0021] Figure 2 This is a diagram of the electrode layout structure of Example 1 of the present invention.

[0022] Figure 3 This is a flowchart of an improved method according to Embodiment 1 of the present invention.

[0023] Figure 4 This is a comparison diagram of the detection capabilities of the electric field components of the high-resistance layer in the conventional method and the method of the present application according to the second embodiment of the present invention.

[0024] Figure 5 This is a comparison chart of the inversion results of representative measuring points in Example 3 of the present invention.

[0025] Figure 6 This is a diagram of drilling and logging results according to the third embodiment of the present invention. DETAILED DESCRIPTION

[0026] In order to deepen the understanding of the present invention, the present invention will be further described in detail below in conjunction with examples. The examples are only used to explain the present invention and do not constitute a limitation on the protection scope of the present invention.

[0027] Embodiment 1

[0028] according to Figure 1 , Figure 2 and Figure 3 As shown, this embodiment provides a method for detecting a terrestrial artificial source electromagnetic transverse magnetic field, comprising the following steps:

[0029] Step 1: Arrange a single-line source transmitting source, bury electrodes A and B connected to the transmitter, and electrodes A and B are respectively connected to the positive and negative electrodes of the transmitter, bury an N electrode, and bury multiple groups of electrode pairs equally with the N electrode as the center, connect the buried N electrode to a terminal of the receiving instrument, and connect the buried multiple groups of electrode pairs to another terminal of the receiving instrument;

[0030] When multiple groups of electrode pairs are buried, the two electrodes of the same electrode pair are symmetrically arranged with the N electrode as the center, that is, the midpoint of the line between the two electrodes of the same electrode pair is the point where the N electrode is located;

[0031] Step 2: Construct a K-type geoelectric model and select the resistivity and depth of the geoelectric model. The first layer has a resistivity of 300Ωm and a depth of 300m. The second layer has a high resistivity of 1500Ωm and a depth of 200m. The third layer has a resistivity of 300Ωm. Then use the transmitter to control the emission of electromagnetic waves for detection.

[0032] Step 3: According to the transient electromagnetic method forward modeling theory, the electric field response of a single electrode pair when receiving is calculated in combination with the detection results of step 2, and the emission current, offset distance and measurement point position of the transmitter are controlled to be consistent during the calculation;

[0033] Step 4: Detect and identify the high-resistance target based on the difference in electric field response when the high-resistance layer exists and does not exist, and obtain the precise composition of the high-resistance target.

[0034] Embodiment 2

[0035] according to Figure 1-Figure 4 As shown, this embodiment provides a method for detecting electromagnetic transverse magnetic fields from artificial sources on land, as shown in the appendix of the specification. Figure 1 As shown, a single-line source transmitting source is arranged, electrodes A and B connected to the transmitter are buried, and electrodes A and B are respectively connected to the positive and negative electrodes of the transmitter, an N electrode is buried, and multiple groups of electrode pairs are equally buried with the N electrode as the center, the buried N electrode is connected to a terminal of the receiving instrument, and the buried multiple groups of electrode pairs are commonly connected to another terminal of the receiving instrument, wherein when multiple groups of electrode pairs are buried, the electrode pairs use electrode N as a common electrode, and the other electrode of each electrode pair is equally distributed with N as the center.

[0036] Taking the combination of four pairs of electrodes as an example, the receiving device consists of 9 electrodes, one of which is buried at point N and connected to a terminal of the receiving instrument, and the other 8 electrodes are symmetrically buried at point M. 1 、M 2 、M 3 、M 4 、M 5 、M 6 、M 7 、M 8 8 points, and connected together to another terminal of the receiving instrument. For a pair of electrodes such as M 1 NM 5 When the electrode distance is small, the electrode pair NM 1 and NM 5 The received horizontal electric fields are in opposite directions and are almost equal in magnitude, so the horizontal electric fields in that direction can be eliminated. The same is true for other electrode pairs. When 4 or more electrode pairs are arranged, the horizontal electric fields in each direction can be eliminated, so the observed response is only the transverse magnetic field response.

[0037] The transmitting source adopts the traditional single-line source device AB, which is easy to lay out and realize electromagnetic field excitation. The receiving end is composed of 4 pairs of electrodes, including M 1 NM 5 、M 2 NM 6 、M 3 NM 7 、M 4 NM 8 The electrode pairs at the receiving end have a small electrode distance, and a symmetrical distribution can be easily achieved. If conditions permit, the number of electrode pairs can still be increased. Any pair of electrode pairs obtains the electric field difference in the same direction, which can reduce the transverse electric field and enhance the transverse magnetic field. At the same time, since the directions of the electrode pairs are opposite, the received electric field differences are also opposite and almost equal in size. The two cancel each other out, eliminating the horizontal electric field, thereby effectively reducing the changes in shallow surface inhomogeneities in the horizontal direction and reducing information from underground layered electrical structures. When the method of the present application is used for observation, due to the symmetry of the electrodes to the ground, the electric fields in the horizontal directions cancel each other out, and electric field data with higher lateral resolution can be obtained.

[0038] A one-dimensional K-type geoelectric model was constructed, and the resistivity and depth of the geoelectric model were selected. The first layer had a resistivity of 300Ωm and a depth of 300m. The second layer had a high resistivity of 1500Ωm and a depth of 200m. The third layer had a resistivity of 300Ωm. The transmitter was then used to control the emission of electromagnetic waves for detection.

[0039] The horizontal electric field observed by a single electrode pair at the same measuring point and the electric field obtained by the method of the present application have the ability to resolve the high resistance layer as shown in the attached manual. Figure 4 shown.

[0040] The difference in response when the high-resistance layer exists and does not exist can be used to analyze the resolution of different methods for high-resistance targets. Figure 4 As shown, in 10 -3 After s, the response difference of the method of the present application represented by the solid line is much greater than that of the conventional method represented by the dotted line. The method of the present application shows a stronger resolution ability for high-resistance targets.

[0041] Embodiment 3

[0042] according to Figure 5 , Figure 6As shown, this embodiment provides a method for detecting a terrestrial artificial source electromagnetic transverse magnetic field. Taking the exploration of high-resistance mineralized rock mass in Xinjiang copper-nickel ore as an example, the Karatongke copper-nickel ore mining area is under the jurisdiction of Fuyun County, Xinjiang, 34 kilometers northwest of the county seat, and National Highway 216 passes 2.6 kilometers from the southwest side of the mining area, with convenient transportation. The geographical coordinates are: 89°36′55″~89°47′55″ east longitude, 46°41′01″~46°49′01″ north latitude. The geographical coordinates of the center point are: 89°41′00″ east longitude, 46°45′15″ north latitude, and an area of ​​89.93 square kilometers. The mining area is located in the northeastern edge of the Junggar Basin and the piedmont area at the southern foot of the Altai Mountains. The terrain is flat, with weak cutting, only small hills with small undulations, 1000 to 1048 meters above sea level, with a relative height difference of 20 to 50 meters, no perennial runoff on the surface, and only rare wells and springs. Quaternary residual slope deposits are well developed, covering more than 80% of the area. The area has a typical continental climate, with long and cold winters and hot and dry summers. The annual average temperature is 3.4℃, the highest in summer is 37.9℃, and the lowest in winter is -40℃. The annual average precipitation is 182mm and the evaporation is 2004.8mm. It is windy in late spring and early autumn, with wind force generally 4-5 and maximum 7-8.

[0043] Based on the known data and the latest physical property measurement results, a statistical table of physical properties of the mining area is obtained, as shown in Table 1.

[0044] Table 1 Statistics of physical properties of ore clusters

[0045] Lithology Resistivity ρ(Ωm) Lump ore 2.61-18.5(5.5) Disseminated ore 273-4450(675) Gabbro 685-6976(1469) Diorite 1034-11286(2567) Carbonaceous layer 46.3-649(107) tuff 443-3676(857)

[0046] The resistivity of massive and brecciated copper-nickel ores tends to zero, with the smallest resistivity; the resistivity of disseminated copper-nickel ores and mineralized diorite and gabbro is the largest; and the resistivity of carbonaceous sedimentary tuff is medium. The polarizability of ore bodies, mineralized rock bodies, and carbonaceous surrounding rocks is relatively high, among which the polarizability of massive rich ore bodies and surrounding rocks rich in graphite and pyrite is the highest, followed by intermediate-basic rock bodies and siliceous sedimentary tuff. The polarizability of near-surface strata, surrounding rocks and rock bodies without carbon and pyrite is very low.

[0047] Key sections were selected at the western and eastern ends of the Y3 rock body in the Kalatongke mining area, the southeast extension direction of the Y3 rock body and the peripheral G21 gravity anomaly area, and detection work was mainly carried out using the method of this application and traditional methods.

[0048] Instructions attached Figure 5 The inversion results of representative measurement points are shown in the figure. There are obvious differences in resistivity between the method of this application and the traditional method. Especially in the depth range of 400-800, the results of the method of this application are significantly higher than those of the traditional method. Figure 6As shown, the relatively high-resistance area is diorite, and the resistivity range is above 2000 ohm.m. The inversion result of the present application method is more in line with the actual situation, indicating that the present application method can more accurately detect underground high-resistance mineralized rock bodies.

[0049] The above shows and describes the basic principles, main features and advantages of the present invention. It should be understood by those skilled in the art that the present invention is not limited to the above embodiments. The above embodiments and descriptions are only for explaining the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention may have various changes and improvements, which fall within the scope of the present invention. The scope of protection of the present invention is defined by the attached claims and their equivalents.

Claims

1. A method for detecting electromagnetic transverse magnetic field of artificial sources on land, characterized in that: The following steps are involved: Step 1: Select the test mining area, use known geological data to build a geoelectric model, simulate the electromagnetic response, and select the observation parameters for actual detection; Step 2: Arrange the detection equipment in the mining area, arrange the single-line source transmission source, bury the electrode pair connected to the transmitter, and bury multiple groups of electrode pairs equally divided in the circumferential direction with the common electrode N electrode as the center, and connect the multiple groups of electrode pairs to the terminal of the receiving instrument; When multiple groups of electrode pairs are buried, the two electrodes of the same electrode pair are symmetrically arranged with the N electrode as the center, that is, the midpoint of the line between the two electrodes of the same electrode pair is the point where the N electrode is located; Step 3: Use the transmitter of the deployed detection equipment to transmit a step current for detection, and use a receiver to receive the electromagnetic response; Step 4: Process the received electromagnetic response, invert the distribution of underground resistivity in the test mining area, analyze the inversion results to determine the location of the target body, and complete the detection of the high-resistance target body.

2. A method for detecting terrestrial artificial electromagnetic transverse magnetic field according to claim 1, characterized in that: In the step 2, electrodes A and B connected to the transmitter are buried, and electrodes A and B are connected to the positive electrode and negative electrode of the transmitter respectively.

3. A method for detecting terrestrial artificial electromagnetic transverse magnetic field according to claim 1, characterized in that: The geoelectric model parameters selected in step 1 include parameters of resistivity and depth.

4. A method for detecting terrestrial artificial electromagnetic transverse magnetic field according to claim 1, characterized in that: When the resistivity and depth of the geoelectric model in step 1 are selected, the first layer has a resistivity of 300Ωm and a depth of 300m; the second layer has a high resistivity of 1500Ωm and a depth of 200m; and the third layer has a resistivity of 300Ωm.

5. The method for detecting terrestrial artificial electromagnetic transverse magnetic field according to claim 1, characterized in that: In the step 2, the buried N electrode is connected to a terminal of the receiving instrument, and the buried multiple groups of electrode pairs are connected to another terminal of the receiving instrument.

6. A method for detecting terrestrial artificial electromagnetic transverse magnetic field according to claim 1, characterized in that: In the step three, the step current is used as the transmitting current, and the receiving instrument is used to receive the response during the current off period.

7. A method for detecting terrestrial artificial electromagnetic transverse magnetic field according to claim 1, characterized in that: In the step 4, the detection and resolution are performed specifically through the difference in electric field response when the high-resistance layer exists and when it does not exist.

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