Coal field fire area detection method based on charging method

Abstract

The invention provides a coal field fire area detection method based on a charging method, and relates to the technical field of geophysical exploration. The method specifically comprises the following steps: selecting a target coal field fire area containing at least one known fire source, setting a first-stage observation unit in the target coal field fire area by utilizing the definition of observation units, and measuring the potential of each measuring point in the first-stage observation unit by using a distributed resistivity method measuring instrument, determining the spreading direction of the hidden fire area in the first-stage observation unit, then arranging the next-stage observation unit, determining the spreading direction of the hidden fire area in the next-stage observation unit by measuring the potential of each measuring point in the next-stage observation unit, and continuing to arrange a plurality of stages of observation units; and determining the range of the hidden fire area in the target coal field fire area until the spreading trend of the hidden fire area does not exist in the current observation unit. According to the invention, the problem of space distribution for tracing the development and spreading of the hidden fire area in an extreme application environment is solved.

Description

Technical Field

[0001] The invention relates to the technical field of geophysical exploration, and in particular to a coalfield fire zone detection method based on a charging method. Background Art

[0002] Coalfield fires are a global disaster that poses a serious threat to the natural environment and human health, causing huge resource losses and environmental pollution. The main detection methods for hidden fire areas at home and abroad are: magnetic method, natural potential method, transient electromagnetic method and radon measurement method. However, due to the concealment of the fire location, the complexity of the geological structure and the limitations of geophysical exploration methods, there is still no very effective detection method at home and abroad to accurately determine the location of the fire area, and the detection of hidden fire sources has always been considered a global problem. Under the current technical background, actively increasing the detection signal strength of the target body and reducing the distance between the detection target body and the observation sensor are the key technical research directions for future fire zone detection. The current conventional detection methods cannot achieve an artificially active way to increase the signal strength of the abnormal body in the direction of fire zone detection.

[0003] The charging method is a method of charging a good conductor and observing the spatial distribution of its charging electric field to understand the size and spatial existence state of the target body. This method is widely used in metal mine exploration, environmental pollution investigation, and groundwater seepage channel exploration. The high temperature in the fire zone causes the organic matter in the coal to oxidize and decompose, and the carbon content increases. On the other hand, the microscopic particles in the coal break the energy barrier and become free-moving carriers due to the increase in temperature. The two act together, resulting in a decrease in the resistivity of the coal. Therefore, at a certain stage of the development of coal fire, the coal in the high-temperature fire zone can be considered as a sub-good conductor, which provides good application conditions for the charging method. The application of the charging method can not only reduce the distance between the target body and the sensor, but also increase the signal strength of the abnormal body.

[0004] However, the coalfield fire zone detection charging method has not yet been found in domestic and foreign applications. The main reasons are reflected in the following aspects:

[0005] 1. Traditional liquid non-polarizable electrodes and solid non-polarizable electrodes cannot withstand high temperature environments, and the coupling effect between metal electrodes and high-temperature coal rock is poor.

[0006] 2. The spatial distribution of hidden fire areas is complex and a single measurement cannot meet the requirements for detecting large-scale fire areas.

[0007] 3. The measurement efficiency of the traditional charging method is slow. In long-term on-site surveys, natural and human factors will affect the data.

[0008] 4. The data collected by the traditional charging method needs to be processed indoors for a certain period of time before the results can be obtained. When continuing to collect data based on the results, some of the original electrodes need to be re-arranged, which will cause errors. Summary of the invention

[0009] In view of the shortcomings of the above-mentioned prior art, the present invention utilizes the charging method to charge known fire source points and observes the generated natural potential signals, and proposes a coalfield fire area detection method based on the charging method to solve the problem of tracing the spatial distribution of the development and spread of hidden fire areas in extreme application environments.

[0010] The present invention proposes a coalfield fire zone detection method based on a charging method, the method comprising the following steps:

[0011] Step 1: Select a target coalfield fire area containing at least one known fire source, and respectively arrange a charging electrode point A, a charging electrode point B and a reference electrode point M in the target coalfield fire area;

[0012] Step 2: Define observation units;

[0013] Step 3: Based on the definition of the observation unit, the first-level observation unit is set with the charging electrode point A as the center point of the observation unit, a distributed resistivity measuring instrument is installed, and the charging electrode point A, the charging electrode point B and the reference electrode point M are respectively connected to the distributed resistivity measuring instrument;

[0014] Step 4: Set the observation parameters of the distributed resistivity measuring instrument, use the distributed resistivity measuring instrument to collect the position coordinates and potential data of different positions in the first-level observation unit, and draw the equipotential curve of the first-level observation unit in the form of contour lines;

[0015] Step 5: Determine whether there is a spreading trend of the hidden fire area in the first-level observation unit according to the equipotential curve of the first-level observation unit. If so, determine the spreading direction of the hidden fire area in the first-level observation unit according to the spreading trend of the hidden fire area, and execute step 6; if not, determine the scope of the hidden fire area in the target coalfield fire area;

[0016] Step 6: Based on the spreading direction of the hidden fire area in the first-level observation unit, set the next-level observation unit;

[0017] Step 7: Use a distributed resistivity measuring instrument to collect the position coordinates and potential data of different positions in the next-level observation unit, and draw the equipotential curve of the next-level observation unit in the form of contour lines;

[0018] Step 8: Take the next level observation unit as the current observation unit, and judge whether there is a new hidden fire zone spreading trend in the current observation unit according to the equipotential curve of the next level observation unit. If yes, execute step 9; if not, determine the scope of the hidden fire zone in the target coalfield fire zone based on the spreading direction of the hidden fire zone in the first level observation unit;

[0019] Step 9: Determine the spreading direction of the hidden fire area in the current observation unit according to the spreading trend of the new hidden fire area in the current observation unit, set the next level observation unit of the current observation unit, and return to step 7;

[0020] The step 1 further comprises:

[0021] Step 1.1: Select any known fire source in the target coalfield fire area and arrange charging electrode point A at the known fire source;

[0022] The arrangement method of the charging electrode point A is as follows: prepare a composite conductive slurry, and when the known fire source is an exposed fire source, fill the composite conductive slurry at the known fire source, and insert the electrode after the composite conductive slurry stops flowing; when the known fire source is a high-temperature fire source inside a borehole verified by drilling, pour the composite conductive slurry into the borehole through a grouting device, and insert the electrode after the composite conductive slurry stops flowing; in the process of pouring the composite conductive slurry into the borehole, the vertical thickness of the composite conductive slurry is not less than 2m, and the insertion depth of the electrode in the composite conductive slurry is not less than 1m;

[0023] Step 1.2: Measure the extension distance of the target coalfield fire zone, and set the charging electrode point B at a position at least 10 times the extension distance from the charging electrode point A and insert the electrode;

[0024] Step 1.3: Set the reference electrode point M at a position at least 10 times the extended distance from the charging electrode point A, and ensure that the reference electrode point M, the charging electrode point A and the charging electrode point B are on the same straight line, and the reference electrode point M and the charging electrode point B are in opposite directions relative to the charging electrode point A, and insert the electrode at the reference electrode point M;

[0025] The preparation method of the composite conductive slurry is as follows: prepare a composite conductive dry material composed of conductive particles, a matrix material and a chemical additive, wherein the components and proportions of the conductive particles include: 12% iron powder, 2.5% carbon fiber and 13% conductive graphite; the components and proportions of the matrix material include: 65% carbonaceous clay; the components and proportions of the chemical additive include: 4.5% sodium polyphosphate, 1.5% sodium molybdate, 1% polyaniline and 0.5% polyvinyl alcohol; wherein all percentages are weight percentages; add water to the composite conductive dry material and stir until it is semi-fluid to obtain the composite conductive slurry;

[0026] The observation unit in step 2 is: define a rectangular measurement network with a length of L and a width of W as the observation unit, take the center point of the observation unit as the coordinate origin, take the length direction of the observation unit as the x-axis direction, and take the width direction of the observation unit as the y-axis direction to establish a rectangular coordinate system; take the area of ​​the observation unit in each quadrant as an observation sub-unit, for any observation sub-unit, set a number of measurement lines parallel to the y-axis direction, and ensure that the distance between two adjacent measurement lines in the entire observation unit is d, wherein there are M measurement points on each measurement line, and the distance between every two measurement points is also d; for an observation unit, the design parameters of the observation unit include: length L, width W, point-line distance d and total number of measurement points Z, and the design parameters simultaneously meet the following conditions:

[0027] W=2d(M-1)+d (1)

[0028] W≤L≤1.2W (2)

[0029] d≤h (3)

[0030] Z=(W / d+1)(L / d+1) (4)

[0031] 0.4W≥W m (5)

[0032] Z≤T (6)

[0033] Where h is the average depth of the underground hidden fire area; W m is the maximum width perpendicular to the horizontal spreading direction of the underground hidden fire area; T represents the acquisition channel capacity of the distributed resistivity measuring instrument;

[0034] The distributed resistivity measuring instrument in step 3 comprises: a data acquisition host, a power supply, a plurality of measuring line cables, a plurality of observation electrodes and a plurality of conversion switches; wherein the data acquisition host and the power supply are connected by wires; and the data acquisition host and the measuring line cables are connected by wires;

[0035] The data acquisition host is used to send control instructions to the conversion switch, receive potential data detected by the observation electrode, and then display the received potential data in real time in the form of contour lines;

[0036] The power supply is used to supply power to the data acquisition host, the conversion switch and the observation electrode;

[0037] The measuring line cable is used to be laid on the measuring line in the observation unit, and a plurality of electrode fasteners are arranged in the measuring line cable, wherein the electrode fasteners are used to connect the observation electrodes;

[0038] The observation electrode is used to be inserted into each measuring point in the observation unit to measure the potential data at each measuring point;

[0039] The conversion switch is used to control the connection and switching of the observation electrodes according to the received control instructions;

[0040] The step 3 further comprises:

[0041] Step 3.1: Place the data acquisition host of the distributed resistivity measuring instrument at point A of the charging electrode;

[0042] Step 3.2: Set the charging electrode point A as the observation unit center point, and use the observation unit layout method to set an observation unit as the first-level observation unit;

[0043] The observation unit deployment method is as follows:

[0044] Step A1: Based on the definition of the observation unit, an observation unit is set according to the selected observation unit center point, and a survey line cable, observation electrode and conversion switch are laid in each observation sub-unit in the observation unit;

[0045] The method for laying the survey line cable, observation electrode and conversion switch is as follows: for any observation subunit, insert an observation electrode at each measurement point, lay a survey line cable on each survey line, and ensure that the position of each measurement point on the survey line corresponds to an electrode fastener, and use a wire to connect the electrode fastener and the observation electrode corresponding to each measurement point; select the observation electrode with the shortest straight-line distance between the observation subunit and the center point of the observation unit as the starting point, use the conversion switch to connect all the survey line cables in the observation subunit in series, and use the last observation electrode in series as the end point of the observation subunit;

[0046] Step A2: selecting two observation sub-units symmetrical about the center point of the observation unit in the observation unit, and connecting the starting points of the two selected observation sub-units to the data acquisition host by using wires;

[0047] Step A3: Use a conversion switch to connect the end points of the two observation sub-units symmetrical about the x-axis respectively, and ensure that all the measurement line cables in the two observation sub-units symmetrical about the x-axis form a series path;

[0048] Step 3.3: Use wires to connect the power supply A interface of the data acquisition host to the electrode inserted at the charging electrode A point, connect the power supply electrode B interface of the data acquisition host to the electrode inserted at the charging electrode B point, and connect the grounding C interface of the data acquisition host to the electrode inserted at the reference electrode M;

[0049] Step 3.4: Use the data acquisition host to test the connection status of all measuring cables in the first-level observation unit and the grounding effect of the observation electrode, and verify whether the test results meet the requirements. If they meet the requirements, proceed to step 4; if not, check the faulty measuring cables, observation electrodes or conversion switches according to the test results, and re-lay the measuring cables, observation electrodes or conversion switches;

[0050] The acquisition parameters in step 4 include: observation mode, potential acquisition time of a single observation electrode, and power supply current; wherein the observation mode includes: potential acquisition mode and gradient acquisition mode;

[0051] The step 5 further comprises:

[0052] Step 5.1: Extract features from the equipotential curve of the first-level observation unit to obtain the potential distribution features of the equipotential curve, and determine the potential abnormal area in the first-level observation unit according to the potential distribution features of the equipotential curve, and use the location of the potential abnormal area as the location of the hidden fire area in the first-level observation unit;

[0053] Step 5.2: Obtain and mark the boundaries of the hidden fire area in the first-level observation unit, and at the same time obtain and mark the boundaries of the first-level observation unit;

[0054] Step 5.3: Determine whether there is an intersection between the boundary of the hidden fire area in the first-level observation unit and the boundary of the first-level observation unit. If not, the hidden fire area in the first-level observation unit does not have a spreading trend, and execute step 5.4; if so, the hidden fire area in the first-level observation unit has a spreading trend, and execute step 5.5;

[0055] Step 5.4: Determine the range of the hidden fire area in the first-level observation unit according to the boundary of the hidden fire area in the first-level observation unit, and use it as the range of the hidden fire area in the target coalfield fire area;

[0056] Step 5.5: If there are two intersection points, it means that there is only one spreading direction of the hidden fire area in the first-level observation unit. The spreading direction of the hidden fire area in the first-level observation unit is determined according to the positions of the two intersection points, and step 6 is executed; if there are four intersection points, it means that there are two spreading directions of the hidden fire area in the first-level observation unit. The two intersection points between which there is no boundary of the hidden fire area are grouped into one group, and the two spreading directions of the hidden fire area in the first-level observation unit are determined according to the positions of the two intersection points in each group, and one spreading direction is arbitrarily selected, and step 6 is executed;

[0057] The method for determining the spreading direction of the hidden fire zone in the first-level observation unit according to the positions of the two intersection points is as follows: using the observation subunit containing the two intersection points as a fixed subunit in the first-level observation unit, and determining the spreading direction of the hidden fire zone in the first-level observation unit according to the positions of the fixed subunits;

[0058] The step 6 further comprises:

[0059] Step 6.1: Retract all the switches in the first-level observation unit, and remove the survey cables and observation electrodes in all observation subunits except the fixed subunit in the first-level observation unit;

[0060] Step 6.2: Select the observation unit center point of the next-level observation unit according to the position of the fixed sub-unit, and use the observation unit layout method to set the next-level observation unit, and ensure that the part of the next-level observation unit that overlaps with the first-level observation unit only includes the fixed sub-units in the first-level observation unit;

[0061] The method for selecting the observation unit center point of the next-level observation unit according to the position of the fixed sub-unit is as follows: if the fixed sub-unit in the first-level observation unit contains an observation sub-unit, the observation electrode with the farthest straight-line distance from the observation unit center point in the first-level observation unit is used as the observation electrode with the closest straight-line distance to the observation unit center point in the next-level observation unit, and the observation unit center point of the next-level observation unit is determined according to the position of the observation electrode; if the fixed sub-unit in the first-level observation unit contains two adjacent observation sub-units, and when the axis of symmetry of the two adjacent observation sub-units is the x-axis of the first-level observation unit, the observation unit center point of the first-level observation unit is translated along the x-axis direction of the first-level observation unit, and the translation distance is 0.5L; when the axis of symmetry of the two adjacent observation sub-units is the y-axis of the first-level observation unit, the observation unit center point of the first-level observation unit is translated along the y-axis direction of the first-level observation unit, and the translation distance is 0.5W;

[0062] The method described in step 8 for determining the scope of the hidden fire area in the target coalfield fire area according to the spreading direction of the hidden fire area in the first-level observation unit is: if the hidden fire area in the first-level observation unit has only one spreading direction, then the scope of the hidden fire area in the target coalfield fire area is determined according to the scope of the hidden fire area in all observation units; if the hidden fire area in the first-level observation unit has two spreading directions, then the scope of the hidden fire area in all observation units is used as the scope of the hidden fire area in the current spreading direction of the hidden fire area in the first-level observation unit, the first-level observation unit is re-laid, and another spreading direction of the hidden fire area in the first-level observation unit is selected, and return to step 6 until the scope of the hidden fire area in the two spreading directions in the hidden fire area in the first-level observation unit is determined, and the scope of the hidden fire area in the two spreading directions in the hidden fire area in the first-level observation unit is merged, and the merged hidden fire area scope is used as the scope of the hidden fire area in the target coalfield fire area.

[0063] The beneficial effects of adopting the above technical solution are:

[0064] The method of the present invention introduces the charging method into the problem of coalfield fire zone detection, directly connects the charging point with the known detected fire source point, and greatly increases the signal strength of the abnormal body.

[0065] The method of the present invention adopts a charging method to detect the spatial distribution position of hidden fire sources in a coalfield fire zone, thereby greatly improving the detection accuracy.

[0066] The method of the present invention is based on the average buried depth h of the underground hidden fire zone, the maximum width W perpendicular to the horizontal spreading direction of the underground hidden fire zone m , the acquisition channel capacity T of the distributed resistivity measuring instrument and the number of measuring points M on each measuring line are used to design a unified observation unit. At the same time, the method of the present invention proposes to divide the observation unit into four observation sub-units, and realizes the continuity of data acquisition through continuous measurement of multi-level observation units; and when arranging the next level of observation units, one or two sub-observation units do not need to be re-arranged as fixed sub-units. By comparing the measurement data of observation sub-units other than fixed sub-units in different observation units, the spread trend of hidden fire areas in coalfield fire areas can be accurately determined, meeting the detection requirements of large-area coalfield fire areas, and greatly improving the utilization efficiency of instruments and manpower.

[0067] The method of the present invention adopts the method of collecting data on site and performing data analysis in a graphical manner on site to judge the spreading trend of the hidden fire zone in each observation unit, and obtains the spreading trend of the hidden fire zone in the entire coalfield fire zone through multiple cycles. The operation is convenient and easy, and overcomes the influence of natural and human factors on the data caused by the long construction period.

[0068] The method of the present invention improves the contact coupling effect between the electrode and the ground measuring point in a high-temperature environment by preparing a composite conductive slurry, thereby avoiding the problem of poor coupling effect between the metal electrode and the high-temperature coal rock mass caused by the inability of traditional liquid non-polarized electrodes and solid non-polarized electrodes to withstand the high-temperature environment. BRIEF DESCRIPTION OF THE DRAWINGS

[0069] Figure 1 is a flow chart of a coalfield fire zone detection method based on the charging method in this embodiment;

[0070] Figure 2 is a schematic diagram of an observation unit in this embodiment;

[0071] Figure 3 is a schematic diagram of the arrangement of survey lines in each observation unit in this implementation mode;

[0072] Figure 4 This is a schematic diagram of the principle of detecting hidden fire sources in a coalfield fire zone in this embodiment;

[0073] In the figure: 1- observation unit; 2- measurement line; 3- measurement point; 4- data acquisition host; 5- conductor; 6- measurement line cable; 7- observation electrode; 8- conversion switch; 9- first-level observation unit; 10- boundary of target coalfield fire area; 11- scope of hidden fire area in target coalfield fire area. DETAILED DESCRIPTION

[0074] In order to facilitate the understanding of the present application, the specific embodiments of the present invention are further described in detail below in conjunction with the accompanying drawings and embodiments. The following embodiments are used to illustrate the present invention, but are not intended to limit the scope of the present invention. On the contrary, the purpose of providing these embodiments is to make the disclosure of the present application more thoroughly understood.

[0075] A coalfield fire zone detection method based on a charging method in this embodiment, such as Figure 1 As shown, the method includes:

[0076] Step 1: Select a target coalfield fire area containing at least one known fire source, and respectively arrange a charging electrode point A, a charging electrode point B and a reference electrode point M in the target coalfield fire area;

[0077] The known fire sources include: outcrop fire sources and high-temperature fire sources inside the borehole that have been verified by drilling.

[0078] In this embodiment, there are generally two types of known fire sources in the coalfield fire area, namely, shallow surface outcrop fire sources and high-temperature fire sources inside the boreholes that have been verified by drilling.

[0079] Step 1.1: Select any known fire source in the target coalfield fire area and arrange charging electrode point A at the known fire source.

[0080] The arrangement method of the charging electrode point A is as follows: prepare a composite conductive slurry, and when the known fire source is an exposed fire source, fill the known fire source with the composite conductive slurry, and insert the electrode after the composite conductive slurry stops flowing; when the known fire source is a high-temperature fire source inside a borehole verified by drilling, pour the composite conductive slurry into the borehole through a grouting device, and insert the electrode after the composite conductive slurry stops flowing; in the process of pouring the composite conductive slurry into the borehole, the vertical thickness of the composite conductive slurry is not less than 2m, and the insertion depth of the electrode in the composite conductive slurry is not less than 1m.

[0081] In this embodiment, the high temperature environment in the fire area will cause the soil to become dry and loose, and the rocks to break, so the ordinary electrodes cannot form a good electrical coupling with the ground, resulting in a weak or unstable measurement signal. Therefore, a special high temperature resistant conductive coupling material is required to enhance the coupling effect between the electrode and the ground. This composite conductive slurry material must comprehensively consider the conductivity, stability, adhesion and environmental applicability in the extreme environment of the coalfield fire area.

[0082] The preparation method of the composite conductive slurry is as follows: prepare a composite conductive dry material consisting of conductive particles, a matrix material and a chemical additive, wherein the components and proportions of the conductive particles include: 12% iron powder, 2.5% carbon fiber and 13% conductive graphite; the components and proportions of the matrix material include: 65% carbonaceous clay; the components and proportions of the chemical additive include: 4.5% sodium polyphosphate, 1.5% sodium molybdate, 1% polyaniline and 0.5% polyvinyl alcohol; wherein all percentages are weight percentages; add water to the composite conductive dry material and stir until it is semi-fluid to obtain the composite conductive slurry.

[0083] Step 1.2: Measure the extension distance of the target coalfield fire zone, and set the charging electrode point B at a position at least 10 times the extension distance from the charging electrode point A and insert the electrode.

[0084] In this embodiment, the distance between the two points with the longest relative distance on the target coalfield fire zone boundary 10 is used as the extension distance of the target coalfield fire zone. In order to meet the requirement that the charging electrode point B be installed far away from the fire source, this embodiment proposes to arrange the charging electrode point B at a position at least 10 times the extension distance from the charging electrode point A, and ensure that it is in a non-interference stable geoelectric field area.

[0085] Step 1.3: Set the reference electrode point M at a position at least 10 times the extended distance from the charging electrode point A, and ensure that the reference electrode point M, the charging electrode point A and the charging electrode point B are on the same straight line, and the reference electrode point M and the charging electrode point B are in opposite directions relative to the charging electrode point A, and insert the electrode at the reference electrode point M.

[0086] In this embodiment, the reference electrode point M is installed at a position opposite to the charging electrode point B, with a distance greater than 10 times the extension distance, and is ensured to be in an interference-free and stable geoelectric field area.

[0087] Step 2: Define observation units.

[0088] In this embodiment, a regular rectangular measurement network designed with a certain point spacing and line spacing is called a measurement network. In order to optimize the on-site exploration construction plan, it is necessary to define a single measurement measurement network based on the instrument acquisition channel capacity, observation period, target size and actual on-site conditions such as landmark working conditions and work difficulty, that is, to define observation unit 1.

[0089] The observation unit is as follows: a rectangular measurement network with a length of L and a width of W is defined as the observation unit 1, a rectangular coordinate system is established with the center point of the observation unit as the coordinate origin, the length direction of the observation unit as the x-axis direction, and the width direction of the observation unit as the y-axis direction; the area of ​​the observation unit in each quadrant is taken as an observation sub-unit, for any observation sub-unit, a number of measurement lines 2 are set along the direction parallel to the y-axis, and it is ensured that the distance between two adjacent measurement lines 2 in the entire observation unit 1 is d, wherein there are M measurement points 3 on each measurement line 2, and the distance between every two measurement points 3 is also d; for an observation unit 1, the design parameters of the observation unit 1 include: length L, width W, point-line distance d and total number of measurement points Z, and the design parameters simultaneously meet the following conditions:

[0090] W=2d(M-1)+d (1)

[0091] W≤L≤1.2W (2)

[0092] d≤h (3)

[0093] Z=(W / d+1)(L / d+1) (4)

[0094] 0.4W≥W m (5)

[0095] Z≤T (6)

[0096] Where h is the average depth of the underground hidden fire area; W m It is the maximum width perpendicular to the horizontal spread direction of the underground hidden fire area; T represents the acquisition channel capacity of the distributed resistivity measuring instrument.

[0097] In this embodiment, if Figure 2As shown in the figure, in order to use the charging method to explore the scope and direction of the underground hidden fire area according to the known fire source point, the underground hidden fire area is taken as the hidden fire area target body. In order to fully explore the scope of the hidden fire area target body, it is necessary to first estimate the h and W of the hidden fire area target body based on the previously collected mine mining data, surface temperature anomalies, surface burnout collapse and fissure signs, and the work experience of the staff. m , where h is the average depth of the underground hidden fire area, W m The maximum width perpendicular to the horizontal spreading direction of the underground hidden fire zone. The acquisition channel capacity T of the distributed resistivity measuring instrument is a fixed performance indicator of the instrument manufacturer when it leaves the factory. The number M of measuring points 3 on each measuring line 2 is also a fixed value determined by the manufacturer of the measuring line cable 6 subsequently laid on the measuring line 2 when it leaves the factory.

[0098] It should be noted that, in the present embodiment, when designing the observation unit 1, the measurement line 2 and the measurement point 3 are only used to represent a positional relationship to facilitate the subsequent laying of the measurement line cable 6 and the arrangement of the observation electrode 7, and are not actually existing components.

[0099] Step 3: Based on the definition of observation unit 1, an observation unit is set up with charging electrode point A as the center as the first-level observation unit 9, and a distributed resistivity measuring instrument is installed, and then the charging electrode point A, the charging electrode point B and the reference electrode point M are respectively connected to the distributed resistivity measuring instrument.

[0100] The distributed resistivity measuring instrument comprises: a data acquisition host 4, a power supply, a plurality of measuring line cables 6, a plurality of observation electrodes 7 and a plurality of conversion switches 8; wherein the data acquisition host 4 is connected to the power supply by a wire; and the data acquisition host 4 is connected to the measuring line cables 6 by a wire 5.

[0101] The data acquisition host 4 is used to send control instructions to the conversion switch 8, and receive the potential data detected by the observation electrode 7, and then display the received potential data in real time in the form of contour lines.

[0102] In this embodiment, the data acquisition host 4 can send a control instruction to the conversion switch 8 to control the on and off of the designated electrode and measure the potential data.

[0103] The power supply is used to supply power to the data acquisition host 4 , the conversion switch 8 and the observation electrode 7 .

[0104] The measuring line cable 6 is used to be laid on the measuring line 2 in the observation unit 1 , and a plurality of electrode fasteners are arranged in the measuring line cable 6 , wherein the electrode fasteners are used to connect the observation electrodes 7 .

[0105] The observation electrode 7 is used to be inserted into each measuring point 3 in the observation unit 1 to measure the potential data at each measuring point 3 .

[0106] The conversion switch 8 is used to control the connection and switching of the observation electrode 7 according to the received control instructions.

[0107] In this embodiment, the conversion switch 8 is a piece of hardware in the distributed resistivity measuring instrument, which plays the role of connecting the observation electrodes 7 on different measuring line cables 6 and controlling the switching on and off of the designated observation electrodes 7 .

[0108] Step 3.1: Place the data acquisition host 4 of the distributed resistivity measuring instrument at point A of the charging electrode.

[0109] Step 3.2: The charging electrode point A is used as the observation unit center point, and an observation unit is set up as the first-level observation unit 9 using the observation unit layout method.

[0110] The observation unit deployment method is as follows:

[0111] Step A1: Based on the definition of the observation unit, an observation unit 1 is set according to the selected observation unit center point, and a survey line cable 6, an observation electrode 7 and a conversion switch 8 are laid in each observation sub-unit in the observation unit.

[0112] In this embodiment, when the observation unit 1 is set with the charging electrode point A as the observation unit center point, the length direction and width direction of the observation unit are selected according to the actual situation on site, and a rectangular coordinate system is established.

[0113] The method for laying the survey line cable 6, the observation electrode 7 and the conversion switch 8 is as follows: for any observation subunit, an observation electrode 7 is inserted at each measuring point 3, a survey line cable 6 is laid on each survey line 2, and it is ensured that the position of each measuring point 3 on the survey line 2 corresponds to an electrode fastener, and the electrode fastener and the observation electrode 7 corresponding to each measuring point 3 are connected by a wire; the observation electrode 7 with the shortest straight-line distance between the observation subunit and the center point of the observation unit is selected as the starting point, and all the survey line cables 6 in the observation subunit are connected in series using the conversion switch 8, and the last observation electrode 7 in series is used as the end point of the observation subunit.

[0114] In this embodiment, if Figure 3As shown, in each observation subunit, the measuring line cables 6 are arranged vertically at a certain spacing, and the measuring line cables 6 cannot be arranged in an L shape. The measuring line spacing is the same as the spacing between adjacent electrode fasteners on each measuring line cable 6, that is, d; after the measuring line is arranged, the observation electrode 7 is inserted at each measuring line electrode fastener on the ground, and the observation electrode 7 is connected to its corresponding electrode fastener by a wire. A conversion switch 8 is used to connect all the measuring line cables 6 in the observation subunit in series. It should be noted that the series connection here only refers to connecting the measuring line cables 6 in each observation subunit, and does not constitute a closed loop.

[0115] Step A2: Select two observation sub-units symmetrical about the center point of the observation unit in the observation unit, and use the wire 5 to connect the starting points of the two selected observation sub-units to the data acquisition host 4 respectively.

[0116] Step A3: Use the conversion switch 8 to respectively connect the end points of the two observation sub-units symmetrical about the x-axis, and ensure that all the measuring line cables 6 in the two observation sub-units symmetrical about the x-axis form a series path.

[0117] Step 3.3: Use wire 5 to connect the power supply A interface of the data acquisition host 4 to the electrode inserted at the charging electrode A point, connect the power supply electrode B interface of the data acquisition host 4 to the electrode inserted at the charging electrode B point, and connect the grounding C interface of the data acquisition host 4 to the electrode inserted at the reference electrode M.

[0118] Step 3.4: Use the data acquisition host 4 to test the connection status of all measuring cables 6 in the first-level observation unit 9 and the grounding effect of the observation electrode 7, and verify whether the test effect meets the requirements. If so, execute step 4; if not, check the faulty measuring cables 6, observation electrodes 7 or conversion switches 8 according to the test results, and re-lay the measuring cables 6, observation electrodes 7 or conversion switches 8.

[0119] In this embodiment, after the first-level observation unit 9 is laid out, it is necessary to test the laid measurement line cables 6 and observation electrodes 7 to ensure that all measurement line cables 6 are successfully connected and all observation electrodes 7 can achieve good grounding effect.

[0120] Step 4: Set the observation parameters in the distributed resistivity measuring instrument, use the distributed resistivity measuring instrument to collect the position coordinates and potential data of each observation electrode 7 in the first-level observation unit 9, and draw the equipotential curve of the first-level observation unit in the form of contour lines.

[0121] The acquisition parameters include: observation mode, potential acquisition time of a single observation electrode and power supply current; wherein the observation mode includes: potential acquisition mode and gradient acquisition mode.

[0122] In this embodiment, a program is built into the data acquisition host 4 to record the position coordinates of each observation electrode 7, and the observation mode, the potential collection time of a single observation electrode, and the power supply current are set. After all the observation parameters are set, click to measure. The distributed resistivity measuring instrument will record the potential data collected by all the observation electrodes 7 one by one at a time. Based on the position coordinates and potential data of all the observation electrodes 7, the equipotential curve of the first-level observation unit is drawn in the form of contour lines and displayed in real time on the visual observation interface of the data acquisition host 4.

[0123] Step 5: Determine whether there is a spreading trend of the hidden fire area in the first-level observation unit 9 according to the equipotential curve of the first-level observation unit 9. If so, determine the spreading direction of the hidden fire area in the first-level observation unit 9 according to the spreading trend of the hidden fire area, and execute step 6; if not, determine the scope 11 of the hidden fire area in the target coalfield fire area.

[0124] Step 5.1: Extract features from the equipotential curve of the first-level observation unit 9 to obtain the potential distribution characteristics of the equipotential curve, and determine the potential abnormal area in the first-level observation unit 9 based on the potential distribution characteristics of the equipotential curve, and use the location of the potential abnormal area as the location of the hidden fire area in the first-level observation unit 9.

[0125] Step 5.2: Acquire and mark the boundary of the hidden fire area in the first-level observation unit 9, and at the same time acquire and mark the boundary of the first-level observation unit 9.

[0126] Step 5.3: Determine whether there is an intersection between the boundary of the hidden fire area in the first-level observation unit 9 and the boundary of the first-level observation unit 9. If not, the hidden fire area in the first-level observation unit 9 does not have a spreading trend, and execute step 5.4; if so, the hidden fire area in the first-level observation unit 9 has a spreading trend, and execute step 5.5.

[0127] Step 5.4: Determine the range of the hidden fire area in the first-level observation unit 9 according to the boundary of the hidden fire area in the first-level observation unit 9, and use it as the range 11 of the hidden fire area in the target coalfield fire area.

[0128] Step 5.5: If there are two intersection points, it means that there is only one spreading direction of the hidden fire area in the first-level observation unit 9. Determine the spreading direction of the hidden fire area in the first-level observation unit 9 according to the positions of the two intersection points, and execute step 6; if there are four intersection points, it means that there are two spreading directions of the hidden fire area in the first-level observation unit 9. The two intersection points between which there is no hidden fire area boundary are divided into a group, and the two spreading directions of the hidden fire area in the first-level observation unit 9 are determined according to the positions of the two intersection points in each group, and arbitrarily select one spreading direction and execute step 6.

[0129] The method for determining the spreading direction of the hidden fire zone in the first-level observation unit 9 according to the positions of the two intersection points is as follows: the observation subunit containing the two intersection points is used as a fixed subunit in the first-level observation unit 9, and the spreading direction of the hidden fire zone in the first-level observation unit 9 is determined according to the position of the fixed subunit.

[0130] In this embodiment, the direction of the position of the observation subunit containing the two intersections is used as the spreading direction of the hidden fire area in the first-level observation unit 9. If there are four intersections, the four intersections are grouped in pairs according to the position of the hidden fire area in the first-level observation unit 9, that is, two intersections without a boundary of the hidden fire area between the two points are grouped into one group.

[0131] Step 6: Based on the spreading direction of the hidden fire zone in the first-level observation unit 9, set the next-level observation unit.

[0132] Step 6.1: Retract all the conversion switches 8 in the first-level observation unit 9, and remove the survey line cables 6 and observation electrodes 7 in all observation sub-units in the first-level observation unit 9 except the fixed sub-unit.

[0133] Step 6.2: Select the observation unit center point of the next-level observation unit according to the position of the fixed sub-unit, and use the observation unit layout method to set the next-level observation unit, and ensure that the part of the next-level observation unit that overlaps with the first-level observation unit only includes the fixed sub-units in the first-level observation unit.

[0134] The method for selecting the observation unit center point of the next-level observation unit according to the position of the fixed sub-unit is as follows: if the fixed sub-unit in the first-level observation unit contains an observation sub-unit, the observation electrode with the farthest straight-line distance from the observation unit center point in the first-level observation unit is used as the observation electrode with the closest straight-line distance to the observation unit center point in the next-level observation unit, and the observation unit center point of the next-level observation unit is determined according to the position of the observation electrode; if the fixed sub-unit in the first-level observation unit contains two adjacent observation sub-units, and when the axis of symmetry of the two adjacent observation sub-units is the x-axis of the first-level observation unit, the observation unit center point of the first-level observation unit is translated along the x-axis direction of the first-level observation unit, and the translation distance is 0.5L; when the axis of symmetry of the two adjacent observation sub-units is the y-axis of the first-level observation unit, the observation unit center point of the first-level observation unit is translated along the y-axis direction of the first-level observation unit, and the translation distance is 0.5W.

[0135] Step 7: Use a distributed resistivity measuring instrument to collect the position coordinates and potential data of each observation electrode in the next-level observation unit, and draw the equipotential curve of the next-level observation unit in the form of contour lines;

[0136] Step 8: Take the next level observation unit as the current observation unit, and judge whether there is a new hidden fire zone spreading trend in the current observation unit according to the equipotential curve of the next level observation unit. If not, determine the scope of the hidden fire zone in the target coalfield fire zone according to the spreading direction of the hidden fire zone in the first level observation unit 11; if it exists, execute step 9;

[0137] The method for determining the scope of the hidden fire area in the target coalfield fire area according to the spreading direction of the hidden fire area in the first-level observation unit is as follows: if the hidden fire area in the first-level observation unit has only one spreading direction, then the scope 11 of the hidden fire area in the target coalfield fire area is determined according to the scope of the hidden fire area in all observation units; if the hidden fire area in the first-level observation unit has two spreading directions, then the scope of the hidden fire area in all observation units is used as the scope of the hidden fire area in the current spreading direction of the hidden fire area in the first-level observation unit, the first-level observation unit is re-laid, and another spreading direction of the hidden fire area in the first-level observation unit is selected, and the step 6 is returned until the scope of the hidden fire area in the two spreading directions in the hidden fire area in the first-level observation unit is determined, and the scope of the hidden fire area in the two spreading directions in the hidden fire area in the first-level observation unit is merged, and the merged hidden fire area scope is used as the scope 11 of the hidden fire area in the target coalfield fire area.

[0138] Step 9: Determine the spreading direction of the hidden fire area in the current observation unit according to the spreading trend of the new hidden fire area in the current observation unit, set the next level observation unit of the current observation unit, and return to step 7.

[0139] In this embodiment, if Figure 4 As shown, the first-level observation unit 9 has two spreading directions. One of the spreading directions is selected at random. That is, when the fire zone shows signs of extension, the position of the N+1-level observation unit is designed, and it is ensured that the N+1-level observation unit must have an observation sub-unit that overlaps with the N-level observation unit to ensure the continuity and comparability of the data. Then, the measuring line cables 6 that overlap with the N-level observation unit and the N+1-level observation unit are retained, and the measuring line cables 6 and observation electrodes 7 in the remaining positions are all retracted, and all the conversion switches 8 in the N-level observation unit are retracted, and the observation unit layout process and potential collection process are repeated; when no signs of extension of the fire zone are found, the potential collection work in the current spreading direction is stopped. According to the other spreading direction in the first-level observation unit 9, the above steps are re-executed until no new signs of fire zone extension are found in the two spreading directions, and the entire potential collection work is stopped.

[0140] In this embodiment, the boundaries of the hidden fire areas in all observation units during the detection process are integrated to obtain the boundaries of the hidden fire areas in the target coalfield fire area, and then the range 11 of the hidden fire areas in the target coalfield fire area is obtained.

[0141] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope defined by the claims of the present invention.

Claims

1. A coalfield fire zone detection method based on charging method, characterized in that: The method comprises the following steps: Step 1: Select a target coalfield fire area containing at least one known fire source, and respectively arrange a charging electrode point A, a charging electrode point B and a reference electrode point M in the target coalfield fire area; Step 2: Define observation units; Step 3: Based on the definition of the observation unit, the first-level observation unit is set with the charging electrode point A as the center point of the observation unit, a distributed resistivity measuring instrument is installed, and the charging electrode point A, the charging electrode point B and the reference electrode point M are respectively connected to the distributed resistivity measuring instrument; Step 4: Set the observation parameters of the distributed resistivity measuring instrument, use the distributed resistivity measuring instrument to collect the position coordinates and potential data of different positions in the first-level observation unit, and draw the equipotential curve of the first-level observation unit in the form of contour lines; Step 5: Determine whether there is a spreading trend of the hidden fire area in the first-level observation unit according to the equipotential curve of the first-level observation unit. If so, determine the spreading direction of the hidden fire area in the first-level observation unit according to the spreading trend of the hidden fire area, and execute step 6; if not, determine the scope of the hidden fire area in the target coalfield fire area; Step 6: Based on the spreading direction of the hidden fire area in the first-level observation unit, set the next-level observation unit; Step 7: Use a distributed resistivity measuring instrument to collect the position coordinates and potential data of different positions in the next-level observation unit, and draw the equipotential curve of the next-level observation unit in the form of contour lines; Step 8: Take the next level observation unit as the current observation unit, and judge whether there is a new hidden fire zone spreading trend in the current observation unit according to the equipotential curve of the next level observation unit. If yes, execute step 9; if not, determine the scope of the hidden fire zone in the target coalfield fire zone based on the spreading direction of the hidden fire zone in the first level observation unit; Step 9: Determine the spreading direction of the hidden fire area in the current observation unit according to the spreading trend of the new hidden fire area in the current observation unit, set the next level observation unit of the current observation unit, and return to step 7.

2. According to claim 1, a method for detecting coalfield fire areas based on charging method is characterized in that: The step 1 further comprises: Step 1.1: Select any known fire source in the target coalfield fire area and arrange charging electrode point A at the known fire source; The arrangement method of the charging electrode point A is as follows: prepare a composite conductive slurry, and when the known fire source is an exposed fire source, fill the composite conductive slurry at the known fire source, and insert the electrode after the composite conductive slurry stops flowing; when the known fire source is a high-temperature fire source inside a borehole verified by drilling, pour the composite conductive slurry into the borehole through a grouting device, and insert the electrode after the composite conductive slurry stops flowing; in the process of pouring the composite conductive slurry into the borehole, the vertical thickness of the composite conductive slurry is not less than 2m, and the insertion depth of the electrode in the composite conductive slurry is not less than 1m; Step 1.2: Measure the extension distance of the target coalfield fire zone, and set the charging electrode point B at a position at least 10 times the extension distance from the charging electrode point A and insert the electrode; Step 1.3: Set the reference electrode point M at a position at least 10 times the extended distance from the charging electrode point A, and ensure that the reference electrode point M, the charging electrode point A and the charging electrode point B are on the same straight line, and the reference electrode point M and the charging electrode point B are in opposite directions relative to the charging electrode point A, and insert the electrode at the reference electrode point M.

3. A coalfield fire zone detection method based on charging method according to claim 2, characterized in that: The preparation method of the composite conductive slurry is as follows: prepare a composite conductive dry material consisting of conductive particles, a matrix material and a chemical additive, wherein the components and proportions of the conductive particles include: 12% iron powder, 2.5% carbon fiber and 13% conductive graphite; the components and proportions of the matrix material include: 65% carbonaceous clay; the components and proportions of the chemical additive include: 4.5% sodium polyphosphate, 1.5% sodium molybdate, 1% polyaniline and 0.5% polyvinyl alcohol; wherein all percentages are weight percentages; add water to the composite conductive dry material and stir until it is semi-fluid to obtain the composite conductive slurry.

4. A method for detecting coalfield fire areas based on charging method according to claim 3, characterized in that: The observation unit in step 2 is: define a rectangular measurement network with a length of L and a width of W as the observation unit, take the center point of the observation unit as the coordinate origin, take the length direction of the observation unit as the x-axis direction, and take the width direction of the observation unit as the y-axis direction to establish a rectangular coordinate system; take the area of ​​the observation unit in each quadrant as an observation sub-unit, for any observation sub-unit, set a number of measurement lines parallel to the y-axis direction, and ensure that the distance between two adjacent measurement lines in the entire observation unit is d, wherein there are M measurement points on each measurement line, and the distance between every two measurement points is also d; For an observation unit, the design parameters of the observation unit include: length L, width W, point-line distance d and total number of measurement points Z, and the design parameters simultaneously meet the following conditions: W=2d(M-1)+d (1) W≤L≤1.2W (2) d≤h (3) Z=(W / d+1)(L / d+1) (4) 0.4W≥W m (5) Z≤T (6) Where h is the average depth of the underground hidden fire area; W m It is the maximum width perpendicular to the horizontal spread direction of the underground hidden fire area; T represents the acquisition channel capacity of the distributed resistivity measuring instrument.

5. A method for detecting coalfield fire areas based on charging method according to claim 4, characterized in that: The distributed resistivity measuring instrument in step 3 comprises: a data acquisition host, a power supply, a plurality of measuring line cables, a plurality of observation electrodes and a plurality of conversion switches; wherein the data acquisition host and the power supply are connected by wires; and the data acquisition host and the measuring line cables are connected by wires; The data acquisition host is used to send control instructions to the conversion switch, receive potential data detected by the observation electrode, and then display the received potential data in real time in the form of contour lines; The power supply is used to supply power to the data acquisition host, the conversion switch and the observation electrode; The measuring line cable is used to be laid on the measuring line in the observation unit, and a plurality of electrode fasteners are arranged in the measuring line cable, wherein the electrode fasteners are used to connect the observation electrodes; The observation electrode is used to be inserted into each measuring point in the observation unit to measure the potential data at each measuring point; The conversion switch is used to control the connection and switching of the observation electrodes according to the received control instructions.

6. A method for detecting coalfield fire areas based on charging method according to claim 5, characterized in that: The step 3 further comprises: Step 3.1: Place the data acquisition host of the distributed resistivity measuring instrument at point A of the charging electrode; Step 3.2: Set the charging electrode point A as the observation unit center point, and use the observation unit layout method to set an observation unit as the first-level observation unit; The observation unit deployment method is as follows: Step A1: Based on the definition of the observation unit, an observation unit is set according to the selected observation unit center point, and a survey line cable, observation electrode and conversion switch are laid in each observation sub-unit in the observation unit; The method for laying the survey line cable, observation electrode and conversion switch is as follows: for any observation subunit, insert an observation electrode at each measurement point, lay a survey line cable on each survey line, and ensure that the position of each measurement point on the survey line corresponds to an electrode fastener, and use a wire to connect the electrode fastener and the observation electrode corresponding to each measurement point; select the observation electrode with the shortest straight-line distance between the observation subunit and the center point of the observation unit as the starting point, use the conversion switch to connect all the survey line cables in the observation subunit in series, and use the last observation electrode in series as the end point of the observation subunit; Step A2: selecting two observation sub-units symmetrical about the center point of the observation unit in the observation unit, and connecting the starting points of the two selected observation sub-units to the data acquisition host by using wires; Step A3: Use a conversion switch to connect the end points of the two observation sub-units symmetrical about the x-axis respectively, and ensure that all the measurement line cables in the two observation sub-units symmetrical about the x-axis form a series path; Step 3.3: Use wires to connect the power supply A interface of the data acquisition host to the electrode inserted at the charging electrode A point, connect the power supply electrode B interface of the data acquisition host to the electrode inserted at the charging electrode B point, and connect the grounding C interface of the data acquisition host to the electrode inserted at the reference electrode M; Step 3.4: Use the data acquisition host to test the connection status of all measuring cables in the first-level observation unit and the grounding effect of the observation electrodes, and verify whether the test results meet the requirements. If so, execute step 4; if not, check the faulty measuring cables, observation electrodes or conversion switches according to the test results, and re-lay the measuring cables, observation electrodes or conversion switches.

7. A method for detecting coalfield fire areas based on charging method according to claim 6, characterized in that: The acquisition parameters in step 4 include: observation mode, potential acquisition time of a single observation electrode and power supply current; wherein the observation mode includes: potential acquisition mode and gradient acquisition mode.

8. A method for detecting coalfield fire areas based on charging method according to claim 7, characterized in that: The step 5 further comprises: Step 5.1: Extract features from the equipotential curve of the first-level observation unit to obtain the potential distribution features of the equipotential curve, and determine the potential abnormal area in the first-level observation unit according to the potential distribution features of the equipotential curve, and use the location of the potential abnormal area as the location of the hidden fire area in the first-level observation unit; Step 5.2: Obtain and mark the boundaries of the hidden fire area in the first-level observation unit, and at the same time obtain and mark the boundaries of the first-level observation unit; Step 5.3: Determine whether there is an intersection between the boundary of the hidden fire area in the first-level observation unit and the boundary of the first-level observation unit. If not, the hidden fire area in the first-level observation unit does not have a spreading trend, and execute step 5.4; if so, the hidden fire area in the first-level observation unit has a spreading trend, and execute step 5.5; Step 5.4: Determine the range of the hidden fire area in the first-level observation unit according to the boundary of the hidden fire area in the first-level observation unit, and use it as the range of the hidden fire area in the target coalfield fire area; Step 5.5: If there are two intersection points, it means that there is only one spreading direction of the hidden fire area in the first-level observation unit. The spreading direction of the hidden fire area in the first-level observation unit is determined according to the positions of the two intersection points, and step 6 is executed; if there are four intersection points, it means that there are two spreading directions of the hidden fire area in the first-level observation unit. The two intersection points between which there is no hidden fire area boundary are grouped into one group, and the two spreading directions of the hidden fire area in the first-level observation unit are determined according to the positions of the two intersection points in each group, and one spreading direction is arbitrarily selected, and step 6 is executed; The method for determining the spreading direction of the hidden fire zone in the first-level observation unit according to the positions of the two intersection points is as follows: the observation sub-unit containing the two intersection points is used as a fixed sub-unit in the first-level observation unit, and the spreading direction of the hidden fire zone in the first-level observation unit is determined according to the position of the fixed sub-unit.

9. A method for detecting coalfield fire areas based on charging method according to claim 8, characterized in that: The step 6 further comprises: Step 6.1: Retract all the switches in the first-level observation unit, and remove the survey cables and observation electrodes in all observation subunits except the fixed subunit in the first-level observation unit; Step 6.2: Select the observation unit center point of the next-level observation unit according to the position of the fixed sub-unit, and use the observation unit layout method to set the next-level observation unit, and ensure that the part of the next-level observation unit that overlaps with the first-level observation unit only includes the fixed sub-units in the first-level observation unit; The method for selecting the observation unit center point of the next-level observation unit according to the position of the fixed sub-unit is as follows: if the fixed sub-unit in the first-level observation unit contains an observation sub-unit, the observation electrode with the farthest straight-line distance from the observation unit center point in the first-level observation unit is used as the observation electrode with the closest straight-line distance to the observation unit center point in the next-level observation unit, and the observation unit center point of the next-level observation unit is determined according to the position of the observation electrode; if the fixed sub-unit in the first-level observation unit contains two adjacent observation sub-units, and when the axis of symmetry of the two adjacent observation sub-units is the x-axis of the first-level observation unit, the observation unit center point of the first-level observation unit is translated along the x-axis direction of the first-level observation unit, and the translation distance is 0.5L; when the axis of symmetry of the two adjacent observation sub-units is the y-axis of the first-level observation unit, the observation unit center point of the first-level observation unit is translated along the y-axis direction of the first-level observation unit, and the translation distance is 0.5W.

10. A method for detecting coalfield fire areas based on charging method according to claim 8, characterized in that: The method described in step 8 for determining the scope of the hidden fire area in the target coalfield fire area according to the spreading direction of the hidden fire area in the first-level observation unit is: if the hidden fire area in the first-level observation unit has only one spreading direction, then the scope of the hidden fire area in the target coalfield fire area is determined according to the scope of the hidden fire area in all observation units; if the hidden fire area in the first-level observation unit has two spreading directions, then the scope of the hidden fire area in all observation units is used as the scope of the hidden fire area in the current spreading direction of the hidden fire area in the first-level observation unit, the first-level observation unit is re-laid, and another spreading direction of the hidden fire area in the first-level observation unit is selected, and return to step 6 until the scope of the hidden fire area in the two spreading directions in the hidden fire area in the first-level observation unit is determined, and the scope of the hidden fire area in the two spreading directions in the hidden fire area in the first-level observation unit is merged, and the merged hidden fire area scope is used as the scope of the hidden fire area in the target coalfield fire area.

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