A coalfield fire area detection method based on charging method

Abstract

The application provides a coalfield fire area detection method based on a charging method, and relates to the technical field of geophysical prospecting. The method specifically comprises the following steps: selecting a target coalfield fire area containing at least one known fire source, setting a first-level observation unit in the target coalfield fire area by using the definition of an observation unit, measuring the potential of each measuring point in the first-level observation unit by using a distributed resistivity method measuring instrument, judging the spreading direction of a hidden fire area in the first-level observation unit, then setting a next-level observation unit, judging the spreading direction of a hidden fire area in the next-level observation unit by measuring the potential of each measuring point in the next-level observation unit, continuously setting several levels of observation units, and stopping until there is no hidden fire area spreading trend in the current observation unit, so as to determine the range of the hidden fire area in the target coalfield fire area. The application solves the problem of tracing the spatial distribution of the development and spread of a hidden fire area in an extreme application environment.

Description

Technical Field

[0001] This invention relates to the field of geophysical exploration technology, and in particular to a method for detecting coalfield fire zones based on the charging method. Background Technology

[0002] Coalfield fires are a global disaster, severely threatening the natural environment and human health, causing enormous resource losses and environmental pollution. Domestic and international methods for detecting concealed fire zones mainly include magnetic methods, spontaneous potential methods, transient electromagnetic methods, and radon measurement methods. However, due to the concealment of the ignition location, the complexity of geological structures, and the limitations of geophysical methods, no highly effective detection method has yet been found to accurately determine the location of the ignition area, and the detection of concealed fire sources has long been considered a global challenge. Under current technological conditions, actively increasing the detection signal intensity of the target and reducing the distance between the target and the observation sensor are key technological directions for future fire zone detection. Current conventional detection methods cannot achieve the ability to actively increase the signal intensity of anomalies in fire zone detection.

[0003] The charging method is a technique that involves charging a good conductor and observing the spatial distribution of its charging electric field to understand the size and spatial state of a target object. This method has wide applications in metal ore exploration, environmental pollution investigation, and groundwater seepage channel detection. The high temperature of a fire zone causes the organic matter in coal to oxidize and decompose, increasing its carbon content. Simultaneously, the microscopic particles in the coal break down energy barriers due to the increased temperature, becoming freely moving charge carriers. These two factors combined lead to a decrease in the resistivity of the coal. Therefore, at a certain stage of coal fire development, coal in a high-temperature fire zone can be considered a sub-good conductor, providing favorable conditions for the application of the charging method. Applying the charging method can both reduce the distance between the target object and the sensor and increase the signal strength of anomalies.

[0004] However, no application cases of the coalfield fire detection charging method have been found at home and abroad. The main reasons are as follows:

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

[0006] 2. The spatial distribution of concealed fire zones is complex and intricate, and a single measurement cannot meet the requirements for detecting large-area fire zones.

[0007] 3. Traditional charging methods are slow in measurement efficiency, and natural and human factors can affect the data during long-term field investigations.

[0008] 4. Data collected by the traditional charging method needs to be processed indoors for a certain period of time before results can be obtained. When data collection continues based on the results, some of the original electrodes need to be re-laid out, which will cause errors. Summary of the Invention

[0009] To address the shortcomings of the existing technologies, this invention proposes a coalfield fire zone detection method based on the charging method, which utilizes a charging method to charge known fire sources and observe the resulting natural potential signals. This method aims to solve the problem of tracing the spatial distribution of the development and spread of hidden fire zones under extreme application environments.

[0010] This invention proposes a coalfield fire zone detection method based on the charging method, which includes the following steps:

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

[0012] Step 2: Define the observation unit;

[0013] Step 3: Based on the definition of the observation unit, set up the first-level observation unit with the charging electrode A point as the center point of the observation unit, install the distributed resistivity measuring instrument, and connect the charging electrode A point, the charging electrode B point and the reference electrode M point to the distributed resistivity measuring instrument respectively.

[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 locations within 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 hidden fire zone spreading trend within the first-level observation unit based on the equipotential curve of the first-level observation unit. If so, determine the spreading direction of the hidden fire zone within the first-level observation unit based on the spreading trend of the hidden fire zone, and proceed to Step 6; if not, determine the range of the hidden fire zone within the target coalfield fire area.

[0016] Step 6: Based on the spread direction of the concealed fire zone within the first-level observation unit, set up the next-level observation unit;

[0017] Step 7: Use a distributed resistivity measuring instrument to collect the position coordinates and potential data at different locations within the next-level observation unit, and plot 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 determine whether there is a new hidden fire zone spread trend in the current observation unit based on the equipotential curve of the next level observation unit. If there is, proceed to step 9; if not, determine the range of the hidden fire zone in the target coalfield fire area based on the spread direction of the hidden fire zone in the first level observation unit.

[0019] Step 9: Determine the spread direction of the hidden fire zone in the current observation unit based on the spread trend of the new hidden fire zone in the current observation unit, set the next level observation unit for the current observation unit, and return to Step 7;

[0020] Step 1 further includes:

[0021] Step 1.1: Select any known fire source within the target coalfield fire zone and set up charging electrode point A at that known fire source;

[0022] The method for arranging the charging electrode at point A is as follows: Prepare a composite conductive grout. When the known fire source is an exposed fire source, fill the known fire source with the composite conductive grout. Insert the electrode after the composite conductive grout stops flowing. When the known fire source is a high-temperature fire source inside a borehole that has been verified by drilling, inject the composite conductive grout into the borehole using a grouting device. Insert the electrode after the composite conductive grout stops flowing. During the process of injecting the composite conductive grout into the borehole, the vertical thickness of the composite conductive grout injection shall not be less than 2m, and the insertion depth of the electrode in the composite conductive grout shall not be less than 1m.

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

[0024] Step 1.3: Set up a reference electrode M at a distance of at least 10 times the extension distance from the charging electrode A, and ensure that the reference electrode M, the charging electrode A, and the charging electrode B are on the same straight line, and that the reference electrode M and the charging electrode B are in opposite directions relative to the charging electrode A. Insert an electrode at the reference electrode M.

[0025] The method for preparing the composite conductive paste is as follows: A composite conductive dry material consisting of conductive particles, a matrix material, and chemical additives is prepared. The conductive particles comprise 12% iron powder, 2.5% carbon fiber, and 13% conductive graphite. The matrix material comprises 65% carbonaceous clay. The chemical additives comprise 4.5% sodium polyphosphate, 1.5% sodium molybdate, 1% polyaniline, and 0.5% polyvinyl alcohol. All percentages are by weight. Water is added to the composite conductive dry material and stirred until it reaches a semi-fluid state to obtain the composite conductive paste.

[0026] The observation unit in step 2 is defined as follows: a rectangular measurement network with length L and width W is defined as the observation unit. A rectangular coordinate system is established with the center point of the observation unit as the 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 considered as an observation sub-unit. For any observation sub-unit, several measurement lines are set along the direction parallel to the y-axis, ensuring that the distance between any two adjacent measurement lines in the entire observation unit is d. Each measurement line has M measurement points, and the distance between any two measurement points is also d. For an observation unit, the design parameters include: length L, width W, point-to-line distance d, and total number of measurement points Z. The design parameters simultaneously satisfy 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 burial depth of the underground concealed fire zone; W m The maximum width perpendicular to the horizontal spread direction of the underground concealed fire zone; T represents the acquisition channel capacity of the distributed resistivity meter.

[0034] The distributed resistivity measuring instrument described in step 3 includes: a data acquisition host, a power supply, several measuring cables, several observation electrodes, and several selector switches; wherein the data acquisition host and the power supply are connected by wires; and the data acquisition host and the measuring cables are connected by wires.

[0035] The data acquisition host is used to send control commands 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 power the data acquisition host, the transfer switch and the observation electrodes;

[0037] The measuring cable is used to lay on the measuring line within the observation unit, and the measuring cable contains several electrode fasteners, wherein the electrode fasteners are used to connect the observation electrodes.

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

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

[0040] Step 3 further includes:

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

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

[0043] The method for deploying the observation units is as follows:

[0044] Step A1: Based on the definition of the observation unit, set up an observation unit according to the selected center point of the observation unit, and lay the measuring line cable, observation electrode and changeover switch in each observation sub-unit of the observation unit respectively;

[0045] The method for laying the measuring cable, observation electrode, and changeover switch is as follows: For any observation sub-unit, an observation electrode is inserted at each measuring point, a measuring cable is laid on each measuring line, and it is ensured that each measuring point on the measuring line corresponds to an electrode fastener. The electrode fastener and observation electrode corresponding to each measuring point are connected by a wire. The observation electrode with the shortest straight-line distance to the center point of the observation sub-unit is selected as the starting point. All measuring cables in the observation sub-unit are connected in series using a changeover switch, and the last observation electrode in the series connection is taken as the ending point of the observation sub-unit.

[0046] Step A2: Select two observation sub-units that are symmetrical about the center point of the observation unit within the observation unit, and use wires to connect the starting points of the two selected observation sub-units to the data acquisition host respectively;

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

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

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

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

[0051] Step 5 further includes:

[0052] Step 5.1: Extract features from the isoelectric curve of the first-level observation unit to obtain the potential distribution characteristics of the isoelectric curve, and determine the potential anomaly area in the first-level observation unit based on the potential distribution characteristics of the isoelectric curve. The location of the potential anomaly area is taken as the location of the hidden fire zone in the first-level observation unit.

[0053] Step 5.2: Obtain and mark the boundary of the concealed fire zone within the first-level observation unit, and simultaneously obtain and mark the boundary of the first-level observation unit;

[0054] Step 5.3: Determine whether there is an intersection between the boundary of the concealed fire zone within the first-level observation unit and the boundary of the first-level observation unit. If there is no intersection, the concealed fire zone within the first-level observation unit does not have a spreading trend, and proceed to step 5.4; if there is an intersection, the concealed fire zone within the first-level observation unit has a spreading trend, and proceed to step 5.5.

[0055] Step 5.4: Determine the extent of the concealed fire zone within the first-level observation unit based on the boundary of the concealed fire zone within the first-level observation unit, and use this extent as the extent of the concealed fire zone within the target coalfield fire zone;

[0056] Step 5.5: If there are two intersection points, it means that the concealed fire zone in the first-level observation unit has only one spread direction. Determine the spread direction of the concealed fire zone in the first-level observation unit based on the position of the two intersection points, and proceed to step 6; If there are four intersection points, it means that the concealed fire zone in the first-level observation unit has two spread directions. Divide the two intersection points between the two points into two groups, determine the two spread directions of the concealed fire zone in the first-level observation unit based on the position of the two intersection points in each group, and arbitrarily select one spread direction, and proceed to step 6;

[0057] The method for determining the spread direction of the concealed fire zone within the first-level observation unit based on the position of the two intersection points is as follows: the observation sub-unit containing the two intersection points is taken as the fixed sub-unit within the first-level observation unit, and the spread direction of the concealed fire zone within the first-level observation unit is determined based on the position of the fixed sub-unit.

[0058] Step 6 further includes:

[0059] Step 6.1: Collapse all the switching switches in the first-level observation unit, and remove the measuring cables and observation electrodes from all observation sub-units in the first-level observation unit except for the fixed sub-unit;

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

[0061] The method for selecting the observation unit center point of the next-level observation unit based on the position of the fixed sub-unit is as follows: If the fixed sub-unit in the first-level observation unit contains one observation sub-unit, then the observation electrode with the longest straight-line distance between that observation sub-unit and the observation unit center point in the first-level observation unit is taken as the observation electrode with the shortest straight-line distance between that observation sub-unit and 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 that 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, then 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, then 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 for determining the extent of the concealed fire zone within the target coalfield fire area based on the spread direction of the concealed fire zone within the first-level observation unit, as described in step 8, is as follows: If the concealed fire zone within the first-level observation unit has only one spread direction, then the extent of the concealed fire zone within the target coalfield fire area is determined based on the extent of the concealed fire zones within all observation units; if the concealed fire zone within the first-level observation unit has two spread directions, then the extent of the concealed fire zone within all observation units is taken as the extent of the concealed fire zone in the current spread direction within the first-level observation unit, the first-level observation unit is re-laid, another spread direction of the concealed fire zone within the first-level observation unit is selected, and the process returns to step 6 until the extent of the concealed fire zone in the two spread directions within the concealed fire zone within the first-level observation unit is determined. The extent of the concealed fire zone in the two spread directions within the concealed fire zone within the first-level observation unit is then merged, and the merged extent of the concealed fire zone is taken as the extent of the concealed fire zone within the target coalfield fire area.

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

[0064] The method of this invention introduces the charging method into the problem of coalfield fire detection, and directly connects the charging point to the known fire source point, which greatly increases the signal strength of the anomaly.

[0065] The method of this invention uses the charging method to detect the spatial distribution of hidden fire sources in coalfield fire zones, which greatly improves the detection accuracy.

[0066] The method of this invention is based on the average burial depth h of the underground concealed fire zone and the maximum width W perpendicular to the horizontal spread direction of the underground concealed fire zone. m The distributed resistivity measuring instrument's acquisition channel capacity T and the number of measuring points M on each measuring line are designed with a unified observation unit. Furthermore, this invention proposes dividing the observation unit into four observation sub-units and achieving continuous data acquisition through continuous measurement of multi-level observation units. When setting up the next level of observation units, one or two sub-observation units do not need to be re-deployed and can serve as fixed sub-units. By comparing the measurement data of observation sub-units other than the fixed sub-units in different observation units, the spread trend of hidden fire zones in coalfield fire areas can be accurately determined, meeting the detection requirements of large-area coalfield fire areas and significantly improving the utilization efficiency of instruments and personnel.

[0067] The method of this invention uses on-site data collection and on-site graphical analysis to determine the spread trend of hidden fire zones in each observation unit. By repeatedly iterating, the spread trend of hidden fire zones in the entire coalfield fire area can be obtained. The method is convenient and easy to operate, and overcomes the influence of natural and human factors on the data caused by the long construction period.

[0068] The method of this invention improves the contact coupling effect between the electrode and the ground measuring point in a high-temperature environment by formulating a composite conductive slurry, and avoids the problem of poor coupling effect between metal electrodes and high-temperature coal and rock masses caused by the inability of traditional liquid non-polarized electrodes and solid non-polarized electrodes to withstand high-temperature environments. Attached Figure Description

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

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

[0071] Figure 3 This is a schematic diagram of the survey line arrangement in each observation unit in this embodiment;

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

[0073] In the diagram: 1-Observation unit; 2-Survey line; 3-Survey point; 4-Data acquisition host; 5-Traverse line; 6-Survey line cable; 7-Observation electrode; 8-Changeover switch; 9-First-level observation unit; 10-Boundary of target coalfield fire zone; 11-Range of concealed fire zone within the target coalfield fire zone. Detailed Implementation

[0074] To facilitate understanding of this application, specific embodiments of the present invention will be described in further detail below with reference to the accompanying drawings and embodiments. The following embodiments are illustrative of the invention but are not intended to limit its scope. Rather, these embodiments are provided to provide a more thorough and complete understanding of the disclosure of this application.

[0075] This embodiment provides a coalfield fire zone detection method based on the charging method, such as... Figure 1 As shown, the method includes:

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

[0077] The known ignition sources include: exposed ignition sources and high-temperature ignition sources inside boreholes that have been verified through drilling.

[0078] In this embodiment, the known fire sources in coalfield fire areas generally fall into two categories: shallow surface outcrop fire sources and high-temperature fire sources inside boreholes that have been verified through drilling.

[0079] Step 1.1: Select any known fire source within the target coalfield fire zone and set up charging electrode point A at that known fire source.

[0080] The method for arranging the charging electrode at point A is as follows: Prepare a composite conductive grout. When the known fire source is an exposed fire source, fill the known fire source with the composite conductive grout. Insert the electrode after the composite conductive grout stops flowing. When the known fire source is a high-temperature fire source inside a borehole that has been verified by drilling, inject the composite conductive grout into the borehole using a grouting device. Insert the electrode after the composite conductive grout stops flowing. During the process of injecting the composite conductive grout into the borehole, the vertical thickness of the injected composite conductive grout shall not be less than 2m, and the insertion depth of the electrode in the composite conductive grout shall not be less than 1m.

[0081] In this embodiment, the high-temperature environment of the fire zone causes the soil to become dry and loose, and the rocks to break, making it impossible for ordinary electrodes to form good electrical coupling with the ground, resulting in weak or unstable measurement signals. Therefore, special high-temperature resistant conductive coupling materials are needed to enhance the coupling effect between the electrodes and the ground. This composite conductive adhesive material must comprehensively consider its conductivity, stability, adhesion, and environmental suitability under the extreme environment of the coalfield fire zone.

[0082] The method for preparing the composite conductive paste is as follows: A composite conductive dry material consisting of conductive particles, a matrix material, and chemical additives is prepared. The conductive particles comprise 12% iron powder, 2.5% carbon fiber, and 13% conductive graphite. The matrix material comprises 65% carbonaceous clay. The chemical additives comprise 4.5% sodium polyphosphate, 1.5% sodium molybdate, 1% polyaniline, and 0.5% polyvinyl alcohol. All percentages are by weight. Water is added to the composite conductive dry material and stirred until it reaches a semi-fluid state to obtain the composite conductive paste.

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

[0084] In this embodiment, the distance between the two points furthest apart on the boundary 10 of the target coalfield fire zone is taken as the extension distance of the target coalfield fire zone. In order to meet the requirement that the charging electrode B point needs to be located far away from the fire source, this embodiment proposes to place the charging electrode B point at a position at least 10 times the extension distance away from the charging electrode A point, and ensure that it is in an interference-free and stable geoelectric field region.

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

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

[0087] Step 2: Define the observation unit.

[0088] In this embodiment, a rectangular measurement network designed according to certain point and line spacing is called a measurement network. In order to optimize the on-site exploration and construction plan, a measurement network for a single measurement needs to be defined based on the instrument acquisition channel capacity, observation period, target size, and actual on-site conditions such as landmark working conditions and difficulty of work, i.e., defining observation unit 1.

[0089] The observation unit is defined as follows: a rectangular measurement network with length L and width W is defined as observation unit 1. A rectangular coordinate system is established with the center point of the observation unit as the 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 considered as an observation sub-unit. For any observation sub-unit, several measurement lines 2 are set along the direction parallel to the y-axis, ensuring that the distance between any two adjacent measurement lines 2 in the entire observation unit 1 is d. Each measurement line 2 has M measurement points 3, and the distance between any 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-to-line distance d, and total number of measurement points Z. The design parameters simultaneously satisfy 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 burial depth of the underground concealed fire zone; W m The maximum width is perpendicular to the horizontal spread direction of the underground concealed fire zone; T represents the acquisition channel capacity of the distributed resistivity measuring instrument.

[0097] In this embodiment, such as Figure 2As shown, in order to subsequently use the charging method to explore the range and direction of the underground hidden fire zone based on the known fire source, the underground hidden fire zone is taken as the target body of the hidden fire zone. In order to fully explore the range of the target body of the hidden fire zone, it is necessary to first estimate the h and W of the target body of the hidden fire zone based on the previously collected mine mining data, surface temperature anomalies, signs of surface burn-out collapse and fissures, and the work experience of the staff. m Where h is the average burial depth of the underground concealed fire zone, and W m This refers to the maximum width perpendicular to the horizontal spread direction of the concealed underground fire zone. The acquisition channel capacity T of the distributed resistivity measuring instrument is a fixed performance specification determined by the instrument manufacturer at the time of manufacture. The number M of measuring points 3 on each measuring line 2 is also a fixed value determined by the manufacturer of the measuring cable 6 subsequently laid on the measuring line 2 at the time of manufacture.

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

[0099] Step 3: Based on the definition of observation unit 1, set up an observation unit 9 with charging electrode point A as the center, and install a distributed resistivity measuring instrument. Then connect charging electrode point A, charging electrode point B and reference electrode point M to the distributed resistivity measuring instrument respectively.

[0100] The distributed resistivity measuring instrument includes: a data acquisition host 4, a power supply, several measuring cables 6, several observation electrodes 7, and several changeover switches 8; wherein the data acquisition host 4 and the power supply are connected by wires; and the data acquisition host 4 and the measuring cables 6 are connected by wires 5.

[0101] The data acquisition host 4 is used to send control commands to the changeover switch 8, receive 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 control commands to the changeover switch 8 to control the on / off state of the designated electrode and measure the potential data.

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

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

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

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

[0107] In this embodiment, the changeover switch 8 is a piece of hardware in the distributed resistivity measuring instrument, which serves to connect the observation electrodes 7 on different measuring cables 6 and control the on / off state of the designated observation electrode 7.

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

[0109] Step 3.2: Take the charging electrode A point as the center point of the observation unit, and use the observation unit layout method to set up an observation unit as the first-level observation unit 9.

[0110] The method for deploying the observation units is as follows:

[0111] Step A1: Based on the definition of the observation unit, set up an observation unit 1 according to the selected observation unit center point, and lay the measuring cable 6, observation electrode 7 and changeover switch 8 in each observation sub-unit of the observation unit.

[0112] In this embodiment, when setting up observation unit 1 with charging electrode A as the center point of the observation unit, the length and width directions 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 measuring cable 6, observation electrode 7, and changeover switch 8 is as follows: For any observation sub-unit, an observation electrode 7 is inserted at each measuring point 3, a measuring cable 6 is laid on each measuring line 2, and each measuring point 3 on the measuring line 2 corresponds to an electrode fastener. The electrode fastener and observation electrode 7 corresponding to each measuring point 3 are connected by a wire. The observation electrode 7 with the shortest straight-line distance to the center point of the observation sub-unit is selected as the starting point. All measuring cables 6 in the observation sub-unit are connected in series using the changeover switch 8, and the last observation electrode 7 connected in series is taken as the end point of the observation sub-unit.

[0114] In this embodiment, such as Figure 3As shown, within each observation unit, measuring cables 6 are laid vertically at certain intervals, and the measuring cables 6 cannot be laid in an L-shape. The spacing between the measuring cables is the same as the spacing between adjacent electrode fasteners on each measuring cable 6, i.e., d. After the measuring cables are laid out, observation electrodes 7 are inserted at each measuring cable electrode fastener on the ground, and the observation electrodes 7 are connected to their corresponding electrode fasteners using wires. A changeover switch 8 is used to connect all the measuring cables 6 in series within the observation unit. It should be noted that this series connection only refers to connecting the measuring cables 6 in each observation unit, not forming a closed loop.

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

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

[0117] Step 3.3: Using wire 5, 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 it does, proceed to step 4; if it does not, check the faulty measuring cable 6, observation electrode 7 or changeover switch 8 according to the test results, and re-lay the measuring cable 6, observation electrode 7 or changeover switch 8.

[0119] In this embodiment, after the first-level observation unit 9 is set up, the laid measuring cables 6 and observation electrodes 7 need to be tested to ensure that all measuring 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, the position coordinates of each observation electrode 7 are recorded by the built-in program of the data acquisition host 4, and the observation mode, the potential acquisition time of a single observation electrode and the power supply current are set. After all the observation parameters are set, the measurement is clicked. The distributed resistivity method measuring instrument will record the potential data collected by all observation electrodes 7 one by one. Based on the position coordinates and potential data of all 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 visualization observation interface of the data acquisition host 4.

[0123] Step 5: Determine whether there is a hidden fire zone spreading trend within the first-level observation unit 9 based on the equipotential curve of the first-level observation unit 9. If so, determine the spreading direction of the hidden fire zone within the first-level observation unit 9 based on the spreading trend of the hidden fire zone, and proceed to step 6. If not, determine the range 11 of the hidden fire zone within 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 anomaly area in the first-level observation unit 9 based on the potential distribution characteristics of the equipotential curve. The location of the potential anomaly area is taken as the location of the concealed fire zone in the first-level observation unit 9.

[0125] Step 5.2: Obtain and mark the boundary of the concealed fire zone within the first-level observation unit 9, and at the same time obtain 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 concealed fire zone within the first-level observation unit 9 and the boundary of the first-level observation unit 9. If there is no intersection, the concealed fire zone within the first-level observation unit 9 does not have a spreading trend, and proceed to step 5.4; if there is an intersection, the concealed fire zone within the first-level observation unit 9 has a spreading trend, and proceed to step 5.5.

[0127] Step 5.4: Determine the extent of the concealed fire zone within the first-level observation unit 9 based on the boundary of the concealed fire zone within the first-level observation unit 9, and use this extent as the extent 11 of the concealed fire zone within the target coalfield fire zone.

[0128] Step 5.5: If there are two intersection points, it means that the concealed fire zone in the first-level observation unit 9 has only one spread direction. Determine the spread direction of the concealed fire zone in the first-level observation unit 9 based on the position of the two intersection points, and proceed to step 6. If there are four intersection points, it means that the concealed fire zone in the first-level observation unit 9 has two spread directions. Divide the two intersection points that do not have a concealed fire zone boundary into a group. Determine the two spread directions of the concealed fire zone in the first-level observation unit 9 based on the position of the two intersection points in each group, and arbitrarily select one spread direction, and proceed to step 6.

[0129] The method for determining the spread direction of the concealed fire zone within the first-level observation unit 9 based on the position of the two intersection points is as follows: the observation sub-unit containing the two intersection points is taken as the fixed sub-unit within the first-level observation unit 9, and the spread direction of the concealed fire zone within the first-level observation unit 9 is determined based on the position of the fixed sub-unit.

[0130] In this embodiment, the direction of the location of the observation sub-unit containing two intersection points is taken as the spread direction of the concealed fire zone within the first-level observation unit 9. If there are four intersection points, the four intersection points are grouped into pairs according to the location of the concealed fire zone within the first-level observation unit 9, that is, the two intersection points that do not have a boundary between them are grouped together.

[0131] Step 6: Based on the spread direction of the concealed fire zone within the first-level observation unit 9, set up the next-level observation unit.

[0132] Step 6.1: Collapse all the changeover switches 8 in the first-level observation unit 9, and remove the measuring cables 6 and observation electrodes 7 from all observation sub-units in the first-level observation unit 9 except for the fixed sub-unit.

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

[0134] The method for selecting the observation unit center point of the next-level observation unit based on the position of the fixed sub-unit is as follows: If the fixed sub-unit in the first-level observation unit contains one observation sub-unit, then the observation electrode with the longest straight-line distance between that observation sub-unit and the observation unit center point in the first-level observation unit is taken as the observation electrode with the shortest straight-line distance between that observation sub-unit and 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 that 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, then 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, then 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 isopotential 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 determine whether there is a new hidden fire zone spread trend in the current observation unit based on the equipotential curve of the next level observation unit. If not, determine the range of the hidden fire zone in the target coalfield fire area according to the spread direction of the hidden fire zone in the first level observation unit; if it exists, proceed to step 9.

[0137] The method for determining the extent of the concealed fire zone within the target coalfield fire area based on the spread direction of the concealed fire zone within the first-level observation unit is as follows: If the concealed fire zone within the first-level observation unit has only one spread direction, then the extent 11 of the concealed fire zone within the target coalfield fire area is determined based on the extent of the concealed fire zones within all observation units; if the concealed fire zone within the first-level observation unit has two spread directions, then the extent of the concealed fire zone within all observation units is taken as the extent of the concealed fire zone in the current spread direction of the concealed fire zone within the first-level observation unit, the first-level observation unit is re-laid, another spread direction of the concealed fire zone within the first-level observation unit is selected, and the process returns to step 6 until the extent of the concealed fire zone in the two spread directions within the concealed fire zone within the first-level observation unit is determined, the extent of the concealed fire zone in the two spread directions within the concealed fire zone within the first-level observation unit is merged, and the merged extent of the concealed fire zone is taken as the extent 11 of the concealed fire zone within the target coalfield fire area.

[0138] Step 9: Determine the spread direction of the hidden fire zone in the current observation unit based on the spread trend of the new hidden fire zone 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, such as Figure 4 As shown, the first-level observation unit 9 has two spread directions. One of these directions is chosen; that is, when signs of fire zone expansion are detected, the position of the (N+1)th level observation unit is designed, ensuring that the (N+1)th level observation unit has an observation sub-unit overlapping with the Nth level observation unit to guarantee data continuity and comparability. Then, the overlapping measuring cables 6 in the Nth and (N+1)th level observation units are retained, while all other measuring cables 6 and observation electrodes 7 are retracted. All changeover switches 8 within the Nth level observation unit are retracted, and the observation unit setup and potential acquisition process is repeated. When no signs of fire zone expansion are detected, potential acquisition in the current spread direction is stopped. The above steps are repeated according to the other spread direction in the first-level observation unit 9 until no new signs of fire zone expansion are detected in either spread direction, at which point the entire potential acquisition process stops.

[0140] In this embodiment, based on the boundaries of the concealed fire zones within all observation units during the detection process, the boundaries of the concealed fire zones within the target coalfield fire zone are integrated, thereby obtaining the range 11 of the concealed fire zones within the target coalfield fire zone.

[0141] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions 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 method for detecting coalfield fire zones based on the charging method, characterized in that, The method includes the following steps: Step 1: Select a target coalfield fire zone containing at least one known fire source, and set up charging electrode point A, charging electrode point B and reference electrode point M respectively in the target coalfield fire zone; Step 2: Define the observation unit; The observation unit is defined as follows: a rectangular measurement network with length L and width W is defined as the observation unit. A rectangular coordinate system is established with the center point of the observation unit as the 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 defined as an observation sub-unit. For any observation sub-unit, several measurement lines are set along the direction parallel to the y-axis, and it is ensured that the distance between any two adjacent measurement lines in the entire observation unit is d. There are M measurement points on each measurement line, and the distance between any two measurement points is also d. Step 3: Based on the definition of the observation unit, set up the first-level observation unit with the charging electrode A point as the center point of the observation unit, install the distributed resistivity measuring instrument, and connect the charging electrode A point, the charging electrode B point and the reference electrode M point to the distributed resistivity measuring instrument respectively. 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 locations within 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 hidden fire zone spreading trend within the first-level observation unit based on the equipotential curve of the first-level observation unit. If so, determine the spreading direction of the hidden fire zone within the first-level observation unit based on the spreading trend of the hidden fire zone, and proceed to Step 6; if not, determine the range of the hidden fire zone within the target coalfield fire area. Step 6: Based on the spread direction of the concealed fire zone within the first-level observation unit, set up the next-level observation unit; Step 7: Use a distributed resistivity measuring instrument to collect the position coordinates and potential data at different locations within the next-level observation unit, and plot 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 determine whether there is a new hidden fire zone spread trend in the current observation unit based on the equipotential curve of the next level observation unit. If there is, proceed to step 9; if not, determine the range of the hidden fire zone in the target coalfield fire area based on the spread direction of the hidden fire zone in the first level observation unit. Step 9: Determine the spread direction of the hidden fire zone in the current observation unit based on the spread trend of the new hidden fire zone in the current observation unit, set the next level observation unit of the current observation unit, and return to step 7.

2. The method for detecting coalfield fire zones based on the charging method according to claim 1, characterized in that, Step 1 further includes: Step 1.1: Select any known fire source within the target coalfield fire zone and set up charging electrode point A at that known fire source; The method for arranging the charging electrode at point A is as follows: Prepare a composite conductive grout. When the known fire source is an exposed fire source, fill the known fire source with the composite conductive grout. Insert the electrode after the composite conductive grout stops flowing. When the known fire source is a high-temperature fire source inside a borehole that has been verified by drilling, inject the composite conductive grout into the borehole using a grouting device. Insert the electrode after the composite conductive grout stops flowing. During the process of injecting the composite conductive grout into the borehole, the vertical thickness of the composite conductive grout injection shall not be less than 2m, and the insertion depth of the electrode in the composite conductive grout shall not be less than 1m. Step 1.2: Measure the extension distance of the target coalfield fire zone, and set up charging electrode point B at a position at least 10 times the extension distance away from charging electrode point A and insert the electrode; Step 1.3: Set up a reference electrode M at a distance of at least 10 times the extension distance from the charging electrode A, and ensure that the reference electrode M, the charging electrode A, and the charging electrode B are on the same straight line, and that the reference electrode M and the charging electrode B are in opposite directions relative to the charging electrode A. Insert an electrode at the reference electrode M.

3. The method for detecting coalfield fire zones based on the charging method according to claim 2, characterized in that, The method for preparing the composite conductive paste is as follows: A composite conductive dry material consisting of conductive particles, a matrix material, and chemical additives is prepared. The conductive particles comprise 12% iron powder, 2.5% carbon fiber, and 13% conductive graphite. The matrix material comprises 65% carbonaceous clay. The chemical additives comprise 4.5% sodium polyphosphate, 1.5% sodium molybdate, 1% polyaniline, and 0.5% polyvinyl alcohol. All percentages are by weight. The composite conductive dry material is then mixed with water until it reaches a semi-fluid state to obtain the composite conductive paste.

4. The method for detecting coalfield fire zones based on the charging method according to claim 3, characterized in that, In step 2, for an observation unit, the design parameters of the observation unit include: length L, width W, point-to-line distance d, and total number of measuring points Z. The design parameters simultaneously satisfy 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 burial depth of the underground concealed fire zone; W m The maximum width is perpendicular to the horizontal spread direction of the underground concealed fire zone; T represents the acquisition channel capacity of the distributed resistivity measuring instrument.

5. The method for detecting coalfield fire zones based on the charging method according to claim 4, characterized in that, The distributed resistivity measuring instrument described in step 3 includes: a data acquisition host, a power supply, several measuring cables, several observation electrodes, and several selector switches; wherein the data acquisition host and the power supply are connected by wires; and the data acquisition host and the measuring cables are connected by wires. The data acquisition host is used to send control commands 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 power the data acquisition host, the transfer switch and the observation electrodes; The measuring cable is used to lay on the measuring line within the observation unit, and the measuring cable contains several electrode fasteners, wherein the electrode fasteners are used to connect the observation electrodes. The observation electrode is used to be inserted at each measuring point within the observation unit to measure the potential data at each measuring point. The switching switch is used to control the connection and switching of the observation electrodes according to the received control commands.

6. The method for detecting coalfield fire zones based on the charging method according to claim 5, characterized in that, Step 3 further includes: Step 3.1: Place the data acquisition host of the distributed resistivity method measuring instrument at point A of the charging electrode; Step 3.2: Take the charging electrode A point as the center point of the observation unit, and use the observation unit layout method to set up an observation unit as the first-level observation unit; The method for deploying the observation units is as follows: Step A1: Based on the definition of the observation unit, set up an observation unit according to the selected center point of the observation unit, and lay the measuring line cable, observation electrode and changeover switch in each observation sub-unit of the observation unit respectively; The method for laying the measuring cable, observation electrode, and changeover switch is as follows: For any observation sub-unit, an observation electrode is inserted at each measuring point, a measuring cable is laid on each measuring line, and it is ensured that each measuring point on the measuring line corresponds to an electrode fastener. The electrode fastener and observation electrode corresponding to each measuring point are connected by a wire. The observation electrode with the shortest straight-line distance to the center point of the observation sub-unit is selected as the starting point. All measuring cables in the observation sub-unit are connected in series using a changeover switch, and the last observation electrode in the series connection is taken as the ending point of the observation sub-unit. Step A2: Select two observation sub-units that are symmetrical about the center point of the observation unit within the observation unit, and use wires to connect the starting points of the two selected observation sub-units to the data acquisition host respectively; Step A3: Use the switch to connect the termination points of the two observation sub-units that are symmetrical about the x-axis, and ensure that all the measuring cables in the two observation sub-units that are symmetrical about the x-axis form a series path; Step 3.3: Connect the power supply A interface of the data acquisition host to the electrode inserted at charging electrode point A using wires, connect the power supply B interface of the data acquisition host to the electrode inserted at charging electrode point B, and connect the grounding C interface of the data acquisition host to the electrode inserted at reference electrode M. Step 3.4: Use the data acquisition host to test the connection status of all measuring cables and the grounding effect of the observation electrodes in the first-level observation unit, and verify whether the test results meet the requirements. If they do, proceed to step 4; if they do not, check the faulty measuring cables, observation electrodes or changeover switches according to the test results, and re-lay the measuring cables, observation electrodes or changeover switches.

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

8. The method for detecting coalfield fire zones based on the charging method according to claim 7, characterized in that, Step 5 further includes: Step 5.1: Extract features from the isoelectric curve of the first-level observation unit to obtain the potential distribution characteristics of the isoelectric curve, and determine the potential anomaly area in the first-level observation unit based on the potential distribution characteristics of the isoelectric curve. The location of the potential anomaly area is taken as the location of the hidden fire zone in the first-level observation unit. Step 5.2: Obtain and mark the boundary of the concealed fire zone within the first-level observation unit, and simultaneously obtain and mark the boundary of the first-level observation unit; Step 5.3: Determine whether there is an intersection between the boundary of the concealed fire zone within the first-level observation unit and the boundary of the first-level observation unit. If there is no intersection, the concealed fire zone within the first-level observation unit does not have a spreading trend, and proceed to step 5.4; if there is an intersection, the concealed fire zone within the first-level observation unit has a spreading trend, and proceed to step 5.

5. Step 5.4: Determine the extent of the concealed fire zone within the first-level observation unit based on the boundary of the concealed fire zone within the first-level observation unit, and use this extent as the extent of the concealed fire zone within the target coalfield fire zone; Step 5.5: If there are two intersection points, it means that the concealed fire zone in the first-level observation unit has only one spread direction. Determine the spread direction of the concealed fire zone in the first-level observation unit based on the position of the two intersection points, and proceed to step 6; If there are four intersection points, it means that the concealed fire zone in the first-level observation unit has two spread directions. Divide the two intersection points that do not have a concealed fire zone boundary into a group. Determine the two spread directions of the concealed fire zone in the first-level observation unit based on the position of the two intersection points in each group, and arbitrarily select one spread direction, and proceed to step 6; The method for determining the spread direction of the concealed fire zone within the first-level observation unit based on the position of the two intersection points is as follows: the observation sub-unit containing the two intersection points is taken as the fixed sub-unit within the first-level observation unit, and the spread direction of the concealed fire zone within the first-level observation unit is determined based on the position of the fixed sub-unit.

9. The method for detecting coalfield fire zones based on the charging method according to claim 8, characterized in that, Step 6 further includes: Step 6.1: Collapse all the switching switches in the first-level observation unit, and remove the measuring cables and observation electrodes from all observation sub-units in the first-level observation unit except for the fixed sub-unit; Step 6.2: Select the center point of the observation unit of the next level observation unit according to the position of the fixed sub-unit, and set up the next level observation unit using the observation unit layout method, and ensure that the part of the next level observation unit that overlaps with the first level observation unit only includes the fixed sub-unit within the first level observation unit. The method for selecting the observation unit center point of the next-level observation unit based on the position of the fixed sub-unit is as follows: If the fixed sub-unit in the first-level observation unit contains one observation sub-unit, then the observation electrode with the longest straight-line distance between that observation sub-unit and the observation unit center point in the first-level observation unit is taken as the observation electrode with the shortest straight-line distance between that observation sub-unit and 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 that 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, then 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, then 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. The method for detecting coalfield fire zones based on the charging method according to claim 8, characterized in that, The method for determining the extent of the concealed fire zone within the target coalfield fire area based on the spread direction of the concealed fire zone within the first-level observation unit, as described in step 8, is as follows: If the concealed fire zone within the first-level observation unit has only one spread direction, then the extent of the concealed fire zone within the target coalfield fire area is determined based on the extent of the concealed fire zones within all observation units; if the concealed fire zone within the first-level observation unit has two spread directions, then the extent of the concealed fire zone within all observation units is taken as the extent of the concealed fire zone in the current spread direction of the concealed fire zone within the first-level observation unit, the first-level observation unit is re-laid, another spread direction of the concealed fire zone within the first-level observation unit is selected, and the process returns to step 6 until the extent of the concealed fire zone in the two spread directions within the concealed fire zone within the first-level observation unit is determined. The extent of the concealed fire zone in the two spread directions within the concealed fire zone within the first-level observation unit is then merged, and the merged extent of the concealed fire zone is taken as the extent of the concealed fire zone within the target coalfield fire area.

Images