Space-time monitoring method for fracture of mine earthquake key layer of overlying strata of coal mine

Abstract

The invention discloses a time-space monitoring method for fracture of an overlying strata mine earthquake key layer in a coal mine, which is characterized in that the DAS technology can realize accurate sensing of underground tiny vibration by measuring the change of sound wave signals in optical fibers, and preliminarily determines the position range of the key layer by analyzing the characteristics of vibration data at the key layer; and meanwhile, high-precision strain data can be provided by utilizing a DSS technology, the position range of the key layer is determined by analyzing the characteristics of the strain data at the key layer, and finally the key layer and the key layer are mutually verified to take an overlapped part and finally accurately position the key layer. After the key layer is positioned, follow-up monitoring is continuously carried out, if new fracture occurs in the key layer, whether the fracture occurs can be judged through vibration data obtained by the DAS host and strain data obtained by the DSS host, the vibration data and the strain data are synchronously subjected to data analysis and judgment and combined analysis, the monitoring precision of the fracture of the key layer is further improved, and the monitoring accuracy of the fracture of the key layer is improved. Therefore, the safety of coal mining is effectively ensured.

Description

Technical Field

[0001] The present invention belongs to the field of underground engineering monitoring, and specifically relates to a method for spatio-temporal monitoring of the breaking of key strata of mine tremors in coal mines. Background Art

[0002] The key strata in coal mines refer to the strata that have an important impact on the stability of coal seams, the safety of coal mining, and the resource recovery rate during the coal mining process. These strata usually have specific lithology, thickness, and mechanical properties, and can control or affect the movement and deformation of overlying strata. The key strata play a supporting and protective role in coal mining. Once damaged or unstable, during the coal face mining process, with the increase of the hanging span L of the key strata, large-energy mine tremors will be induced, further leading to dynamic disasters such as rock bursts and outbursts in the coal face or roadway, and then resulting in safety hazards such as roof caving, roadway deformation, and gas outburst; during this process, acoustic waves, stress, and energy changes often occur. According to the change characteristics of the inversion images of these parameters, the key strata can be located, and then disasters such as roadway deformation and gas outburst can be prevented. Therefore, accurately identifying and locating the key strata in coal mines is of great significance for ensuring the safety of coal mine production and improving the mining efficiency. Through geological exploration and monitoring technologies, the accurate identification and location of the key strata can be achieved, providing a scientific basis for coal mining.

[0003] Traditional coal key stratum location technologies mainly rely on methods such as geological exploration and geophysical exploration. However, these methods have certain limitations in practical applications, such as limited exploration accuracy, high cost, and complex operation. Traditional coal key stratum location, such as drilling: using drilling machinery and technology to obtain cores below the ground surface to obtain geological and mineral resource parameters. For some strata (such as marl and carbonate rocks), problems such as borehole collapse may occur, and the mechanical efficiency is low and the labor intensity of workers is high.

[0004] In recent years, with the rapid development of fiber optic sensing technology, DAS (Distributed Acoustic Sensing) technology has gradually been applied to the location of seismic sources in coal and rock masses. DAS technology is a distributed acoustic sensing technology based on the principle of fiber optic sensing, which can achieve high-sensitivity and long-distance distributed measurement of seismic wave signals. And it can realize the perception of acoustic wave signals along the fiber optic line, that is, distributed perception, and can capture the acoustic wave signals at all positions along the line. By selecting a smaller sampling interval, high-spatial-resolution monitoring data can be obtained, reducing the impact of spatial aliasing on exploration data. However, due to the complexity of the coal mine geology, the existing methods cannot accurately locate the key strata in coal mines, nor can they continuously monitor the subsequent key strata.

[0005] Therefore, how to provide a new monitoring method that can identify and locate the key strata of coal mines and continuously monitor the changes of the key strata during the subsequent coal face mining process to ensure the safe mining of coal mines is the research direction required by the present invention. Summary of the Invention

[0006] In view of the problems existing in the above-mentioned prior art, the present invention provides a method for monitoring the breakage time and space of the key strata of overlying strata seismicity in coal mines, which can identify and locate the key strata of coal mines and continuously monitor the changes of the key strata during the subsequent coal face mining process to ensure the safe mining of coal mines.

[0007] To achieve the above object, the technical solution adopted by the present invention is: a method for monitoring the breakage time and space of the key strata of overlying strata seismicity in coal mines, comprising the following steps:

[0008] Step 1: Install a monitoring system: Construct a group of boreholes from the roadway on one side of the coal face upward into the rock mass above the coal face. The group of boreholes consists of four boreholes, and the four boreholes are distributed in a square on the same cross-section; an optical fiber is arranged along the axial direction of each borehole. After completion, select the optical fibers in two boreholes on the diagonal of the cross-section to be connected to the DAS host (distributed optical fiber acoustic wave monitoring host), and the optical fibers in the other two boreholes are connected to the DSS host (distributed optical fiber strain monitoring host);

[0009] Step 2: Locate the key strata: The DAS host collects the vibration data of rock strata at different horizons through the phase change of Rayleigh scattered light in the optical fiber; the DSS host uses the optical fiber as a continuous strain sensor and collects the strain data of rock strata at different horizons by detecting the intensity and frequency changes of the backscattered Rayleigh scattering or Brillouin scattering of the optical signal in the optical fiber; strong seismic signals will be generated during the breakage and migration of the key strata. Among them, the DAS host judges the position range of the key strata according to the vibration data of different horizons, and at the same time, the DSS host judges the position range of the key strata according to the strain data of different horizons. Finally, the overlapping part of the two is used as the final position range of the key strata;

[0010] Step 3: Monitor the key strata: The DAS host and the DSS host continuously receive the vibration data and strain data fed back by the optical fiber at the position of the key strata. Strong seismic signals will be generated during the breakage and migration of the key strata. Among them, the DAS host determines whether the key strata are broken by determining the acoustic wave intensity through the vibration data, and at the same time, the DSS host determines whether the key strata are broken by determining the strain change situation through the strain data; the combination of the two realizes the continuous monitoring of the breakage of the key strata of overlying strata seismicity in coal mines.

[0011] Further, in Step 1, a plurality of groups of boreholes are arranged along the roadway according to needs.

[0012] Further, each borehole in the borehole group in Step 1 is constructed from the roadway roof at an angle of 15° to 45° with the vertical direction towards the rock mass above the working face; the distance between two adjacent boreholes in the borehole group is 20 m.

[0013] Further, the optical fiber is in coupled contact with the borehole, and the optical fiber is armored optical fiber.

[0014] Further, in Step 2, the DAS host judges the position range of the key stratum according to the vibration data of different horizons:

[0015] ① Signal characteristics: The breaking of the key stratum will generate strong mine tremor signals, and the vibration data will be reflected, refracted or scattered at the key stratum, resulting in amplitude mutation, frequency component change or phase shift of the received vibration data at this position; ② Characteristics of the vibration data inversion diagram: It has strong amplitude pulses. In the frequency domain analysis, the high-frequency energy decays significantly, forming a low-frequency enhancement feature; the time-domain waveform of the vibration data is smooth, the frequency-domain energy is concentrated in the high-frequency band, and there is no abnormal reflection signal;

[0016] When the above characteristics are met, the following processing is carried out on the vibration data: Invert the vibration data received by the DAS host, continuously monitor the change of acoustic wave intensity and velocity. If the acoustic wave intensity detected by a certain section of the optical fiber suddenly changes to 10 4 J or above, it is inferred that a strong mine tremor occurs in this section, and the horizon corresponding to this section is determined as the position and range of the key stratum;

[0017] The DSS host judges the position range of the key stratum according to the strain data of different horizons:

[0018] ① Signal characteristics: When the key stratum begins to break, the deformation amount of the rock stratum will suddenly increase, and the strain gradient of the strain data at the key stratum will increase or fluctuate abnormally; ② Characteristics of the strain data inversion diagram: A strain mutation zone will appear at the key stratum in the strain distribution diagram, corresponding to the deformation amount and deformation position of the key stratum breaking and migrating;

[0019] When the above characteristics are met, the following processing is carried out on the strain data: Continuously monitor the strain data received by the DSS host. Before the key stratum breaks, the strain is often small. When it breaks and migrates, the deformation amount suddenly increases. If the strain detected by a certain section of the optical fiber suddenly changes to more than 500 με, the horizon corresponding to this section is determined as the position and range of the key stratum.

[0020] Further, if the position of the key stratum is not obtained in Step 2, it means that the depth of the optical fiber does not reach the key stratum. At this time, it is necessary to repeat Step 1 to increase the borehole depth and then perform the key stratum positioning again.

[0021] Further, in Step 3, the DAS host determines whether the key stratum breaks by determining the acoustic wave intensity through the vibration data, specifically:

[0022] Invert the vibration data received by the DAS host, continuously monitor the changes in acoustic wave intensity and velocity. The acoustic wave intensity of normal rock formations is generally within 10 4 J. If the acoustic wave intensity detected by the optical fiber in a certain section suddenly changes to more than 10 4 J, it is inferred that a strong mine earthquake has occurred in that section and the corresponding key stratum has broken;

[0023] The DSS host determines the strain change situation through strain data to judge whether the key stratum has broken. Specifically:

[0024] Invert the vibration data received by the DAS host, continuously monitor the changes in acoustic wave intensity and velocity. If the acoustic wave intensity detected by the optical fiber within the key stratum suddenly changes to more than 10 4 J, it is determined that a new breakage has occurred in the key stratum;

[0025] The DSS host determines the strain change situation through strain data to judge whether the key stratum has broken. Specifically:

[0026] Continuously monitor the strain data received by the DSS host. The strain of the key stratum is often small before breaking. When the deformation suddenly increases after the breaking and migration, if the strain monitored by the optical fiber within the key stratum suddenly changes to more than 500 με, it is determined that a new breakage has occurred in the key stratum;

[0027] If both the DAS host and the DSS host judge that a new breakage has occurred in the key stratum, it is finally determined that a new breakage migration has occurred in the key stratum.

[0028] Compared with the prior art, the present invention combines the method of using the DSS host to obtain strain data and the DAS host to obtain vibration data, and has the following advantages:

[0029] 1. The DAS technology of the present invention can accurately sense underground micro-vibrations by measuring the changes in acoustic wave signals in the optical fiber. By analyzing the characteristics of the vibration data at the key stratum, the position range of the key stratum can be initially determined. At the same time, the DSS technology can provide high-precision strain data. By analyzing the characteristics of the strain data at the key stratum, it is used to determine the position range of the key stratum. Finally, the two confirm each other and take the overlapping part to accurately locate the key stratum.

[0030] 2. After the optical fiber is laid for key stratum positioning in the present invention, subsequent monitoring can be continuously carried out. If the key stratum breaks, it can judge whether the breakage has occurred respectively through the vibration data obtained by the DAS host and the strain data obtained by the DSS host. If one of the judgments indicates breakage, an early warning is given; this method of synchronously analyzing and judging data through two technologies can effectively ensure the safety of coal mine mining.

[0031] 3. The present invention uses optical fiber as the sensing medium, enabling monitoring over a relatively long distance. This allows the technology to cover a wider area when locating the key coal seams, providing more comprehensive geological information. At the same time, the present invention adopts a non-invasive design, which will not cause damage or pollution to the geological environment. This makes the technology more advantageous in scenarios such as coal mining where the geological environment needs to be protected. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 is a schematic diagram of the optical fiber layout of the present invention;

[0033] Figure 2 is Figure 1 the left view of

[0034] Figure 3 is a three-dimensional perspective view of the optical fiber layout of the present invention;

[0035] Figure 4 is a schematic diagram of the distribution of each borehole in the borehole group of the present invention;

[0036] Figure 5 is a two-dimensional inversion imaging diagram of the vibration data obtained by the DAS host in the present invention;

[0037] Figure 6 is a change diagram of the strain data obtained by the DSS host in the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0038] The present invention will be further described below.

[0039] As Figures 1 to 3 shown, the present invention includes the following steps:

[0040] Step 1. Install the monitoring system: Construct a borehole group from the roadway on one side of the working face to the rock mass above the working face. The borehole group consists of four boreholes, and the four boreholes are distributed in a square on the same cross-section; each borehole is constructed from the roadway roof at an angle of 15° - 45° to the vertical direction towards the rock mass above the working face; as Figure 4 shown, the distance between two adjacent boreholes in the borehole group is 20m. An optical fiber is laid along the axial direction of each borehole. After completion, the optical fibers in the two boreholes on the diagonal of the cross-section are connected to the DAS host, and the optical fibers in the other two boreholes are connected to the DSS host;

[0041] Step 2. Key layer positioning: The DAS host collects the vibration data of rock formations at different horizons through the phase change of Rayleigh scattered light in the optical fiber; the DSS host uses the optical fiber as a continuous strain sensor and collects the strain data of rock formations at different horizons by detecting the intensity and frequency changes of the backward Rayleigh scattering or Brillouin scattering of the optical signal in the optical fiber; the breaking and migration of the key layer will generate strong mine tremor signals. Among them, the DAS host judges the position range of the key layer according to the vibration data of different horizons, and at the same time the DSS host judges the position range of the key layer according to the strain data of different horizons. Finally, the overlapping part of the two is used as the final key layer position range. Among them, the DAS host judges the position range of the key layer according to the vibration data of different horizons:

[0042] ① Signal characteristics: The breaking of the key layer will generate strong mine tremor signals. The vibration data will be reflected, refracted or scattered at the key layer, resulting in an abrupt change in amplitude, a change in frequency components or a phase shift in the received vibration data at this position; ② Characteristics of the vibration data inversion diagram: It has strong amplitude pulses. In the frequency domain analysis, the high-frequency energy decays significantly, forming a low-frequency enhancement feature; the time-domain waveform of the vibration data is smooth, the frequency-domain energy is concentrated in the high-frequency band, and there is no abnormal reflection signal;

[0043] When the above characteristics are met, the vibration data is processed as follows: Invert the vibration data received by the DAS host, and continuously monitor the changes in the acoustic wave intensity and velocity. If the acoustic wave intensity detected by a certain section of the optical fiber suddenly changes to 10 4 J or more, it is inferred that a strong mine tremor has occurred in this section, and the horizon corresponding to this section is determined as the key layer position and range;

[0044] The DSS host judges the position range of the key layer according to the strain data of different horizons:

[0045] ① Signal characteristics: The initial breaking of the key layer will cause a sudden increase in the deformation of the rock formation, and the strain gradient of the strain data at the key layer will increase or fluctuate abnormally; ② Characteristics of the strain data inversion diagram: There will be a strain mutation zone at the key layer in the strain distribution diagram, corresponding to the deformation amount and deformation position of the key layer breaking and migration;

[0046] When the above characteristics are met, the strain data is processed as follows: Continuously monitor the strain data received by the DSS host. The strain of the key layer is usually small before breaking. When the deformation amount suddenly increases after breaking and migration, if the strain monitored by a certain section of the optical fiber suddenly changes to more than 500 με, the horizon corresponding to this section is determined as the key layer position and range.

[0047] If the key layer position is not obtained, it means that the optical fiber depth has not reached the key layer. At this time, it is necessary to repeat Step 1 to increase the borehole depth and then perform key layer positioning again.

[0048] Step 3. Key layer monitoring: Continuously receive the vibration data and strain data fed back by the optical fiber at the key layer position through the DAS host and the DSS host. The breaking and migration of the key layer will generate strong mine tremor signals. Among them, the DAS host determines the acoustic wave intensity through the vibration data to judge whether the key layer breaks. Specifically:

[0049] Invert the vibration data received by the DAS host, and continuously monitor the changes in acoustic wave intensity and velocity. If the acoustic wave intensity detected by the optical fiber within the key layer suddenly changes to 10 4 J or more, it is determined that a new break occurs in the key layer;

[0050] The DSS host determines the strain change situation through the strain data to judge whether the key layer breaks. Specifically:

[0051] Continuously monitor the strain data received by the DSS host. The strain of the key layer is usually small before breaking. When the deformation suddenly increases after breaking and migration, if the strain monitored by the optical fiber within the key layer suddenly changes to more than 500 με, it is determined that a new break occurs in the key layer;

[0052] If both the DAS host and the DSS host judge that a new break occurs in the key layer, it is finally determined that a new breaking and migration of the key layer occurs. The continuous monitoring of the breaking of the key layer of the overlying strata in the coal mine is realized through the combination of the two. If either the DAS host or the DSS host judges that a new break occurs in the key layer, continuously monitor the data of the other host until both judge that the key layer breaks, and give an early warning.

[0053] As an improvement of the present invention, in Step 1, a plurality of drilling groups are arranged along the roadway according to needs. The coupling contact between the optical fiber and the drilling hole is realized through plugging and grouting, and the optical fiber is an armored optical fiber.

[0054] The above is only the preferred embodiment of the present invention. It should be pointed out that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A method for spatio-temporal monitoring of the breaking of key strata in overlying strata of coal mines, characterized in that, It includes the following steps: Step 1, arranging a monitoring system: constructing a set of boreholes from a roadway on one side of the working face to the rock mass above the working face. There are four boreholes in this set of boreholes, and the four boreholes are distributed in a square on the same cross-section; an optical fiber is arranged along the axial direction of each borehole. After completion, the optical fibers in two diagonal boreholes on the cross-section are connected to the DAS host, and the optical fibers in the other two boreholes are connected to the DSS host; Step 2, key stratum positioning: The DAS host collects the vibration data of rock strata at different horizons through the phase change of Rayleigh scattered light in the optical fiber; the DSS host uses the optical fiber as a continuous strain sensor and collects the strain data of rock strata at different horizons by detecting the intensity and frequency changes of backscattered Rayleigh scattering or Brillouin scattering of the optical signal in the optical fiber; The breaking and migration of the key stratum will generate strong mine tremor signals. Among them, the DAS host judges the position and range of the key stratum through the vibration data. At the same time, the DSS host judges the position and range of the key stratum according to the strain data at different horizons. Finally, the overlapping part of the two is used as the final position range of the key stratum; Step 3, key stratum monitoring: The DAS host and the DSS host continuously receive the vibration data and strain data fed back by the optical fiber at the key stratum position. The new breaking and migration of the key stratum will generate strong mine tremor signals. Among them, the DAS host determines whether a new break occurs in the key stratum by determining the acoustic wave intensity through the vibration data. At the same time, the DSS host determines whether a new break occurs in the key stratum by determining the strain change situation through the strain data; The combination of the two realizes the continuous monitoring of the breaking of the key stratum of the overlying rock mine tremor in the coal mine.

2. The key stratum breaking time and space monitoring method for mine rock bursts in overlying strata of coal mines according to claim 1, characterized in that In Step 1, multiple sets of boreholes are arranged along the roadway according to needs.

3. The key stratum breaking time and space monitoring method for mine rock bursts in overlying strata of coal mines according to claim 1, wherein In each borehole of the set of boreholes in Step 1, the borehole is constructed from the roadway roof at an angle of 15° to 45° with the vertical direction to the rock mass above the working face; the distance between two adjacent boreholes in the set of boreholes is 20m.

4. The key stratum breaking time and space monitoring method for mine rock bursts in overlying strata of coal mines according to claim 1, characterized in that, The optical fiber is in coupled contact with the borehole, and the optical fiber is an armored optical fiber.

5. The key stratum breaking time and space monitoring method for mine rock bursts in overlying strata of coal mines according to claim 1, characterized in that, In Step 2, the DAS host judges the position range of the key stratum according to the vibration data at different horizons: ① Signal characteristics: The breaking of the key stratum will generate strong mine tremor signals. The vibration data will be reflected, refracted or scattered at the key stratum, resulting in amplitude mutation, frequency component change or phase shift in the received vibration data at this position; ② Characteristics of the vibration data inversion diagram: It has strong amplitude pulses. In the frequency domain analysis, the high-frequency energy decays significantly, forming a low-frequency enhancement feature; The time-domain waveform of the vibration data is smooth, the frequency-domain energy is concentrated in the high-frequency band, and there is no abnormal reflection signal; When the above characteristics are met, the vibration data is processed as follows: The vibration data received by the DAS host is inverted, and the changes in the acoustic wave intensity and velocity are continuously monitored. If the acoustic wave intensity detected by a certain section of the optical fiber suddenly changes to 10 4 J or more, it is inferred that a strong mine earthquake has occurred in that section, and the corresponding horizon of that section is determined as the position and range of the key stratum; The DSS host judges the position range of the key stratum according to the strain data at different horizons: ① Signal characteristics: When the key stratum begins to break, the deformation amount of the rock stratum will suddenly increase, and the strain gradient of the strain data at the key stratum will increase or fluctuate abnormally; ② Characteristics of the strain data inversion diagram: A strain mutation zone will appear at the key stratum on the strain distribution diagram, corresponding to the deformation amount and deformation position of the breaking and migration of the key stratum; When the above characteristics are met, the strain data is processed as follows: Continuously monitor the strain data received by the DSS host. The strain of the key stratum is usually small before fracture. When fracture migration occurs, the deformation suddenly increases. If the monitored strain of a certain section of optical fiber mutates to more than 500 με, the corresponding stratum of this section is determined as the position and range of the key stratum.

6. The method for spatio-temporal monitoring of the breaking of the key strata of the overlying strata of a coal mine according to claim 5, wherein If the position of the key stratum is not obtained in the second step, it means that the depth of the optical fiber does not reach the key stratum. At this time, it is necessary to repeat the first step to increase the drilling depth and then perform key stratum positioning again.

7. The key stratum breaking time and space monitoring method for mine rock bursts in overlying strata of coal mines according to claim 1, characterized in that, In the third step, the DAS host determines the acoustic wave intensity through vibration data to judge whether the key stratum has fractured. Specifically: Invert the vibration data received by the DAS host, continuously monitor the changes in the acoustic wave intensity and velocity. If the acoustic wave intensity suddenly changes to 10 4 J or more in the optical fiber within the critical layer, it is determined that a new break has occurred in the critical layer; The DSS host determines the strain change situation through strain data to judge whether the key stratum has fractured. Specifically: Continuously monitor the strain data received by the DSS host. The strain of the key stratum is usually small before fracture. When fracture migration occurs, the deformation suddenly increases. If the monitored strain of the optical fiber within the key stratum mutates to more than 500 με, it is determined that a new fracture has occurred in the key stratum; If both the DAS host and the DSS host judge that a new fracture has occurred in the key stratum, it is finally determined that a new fracture migration has occurred in the key stratum.

Images