Gas disaster early warning method based on borehole optical fiber sensing monitoring

Abstract

The invention relates to the technical field of gas disaster prediction, in particular to a gas disaster early warning method based on borehole optical fiber sensing monitoring, which comprises the following steps: screening and numbering crossing extraction boreholes penetrating through a to-be-excavated coal roadway area as monitoring boreholes; a composite optical fiber sensing cable integrated with temperature and pressure sensing functions is installed in the monitoring drill hole; the gas desorption and outburst risk is early warned by recognizing the abrupt change modes such as continuous temperature drop and first temperature rise and then temperature drop, and the drill hole collapse is early warned by recognizing the modes such as pressure fluctuation and sudden drop. And in the tunneling process, the composite optical fiber sensing cable crossed in the rear tunneling process rolls and moves forwards to a new drilled hole in the front, and continuous monitoring of gas extraction information is achieved. According to the method, the physical process in the coal seam is directly perceived, early warning is remarkably advanced compared with traditional roadway gas monitoring, accuracy is improved through mode recognition, meanwhile, dual early warning of gas disasters and drilling stability is achieved, cost is low, and reliability is high.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of gas disaster prediction, and particularly relates to a gas disaster early warning method based on borehole optical fiber sensing monitoring. BACKGROUND

[0002] Coal and gas outburst is a major disaster in underground coal production, which throws a large amount of coal and gas into the production space in a short time, causing mass casualties. Early warning of coal and gas outburst is of great significance to coal safety production. The existing coal and gas outburst early warning means can be divided into two categories: ① Signals generated during the coal and rock mass rupture process are monitored, such as microseismic, electromagnetic radiation, etc. The disadvantage is the lack of gas information. Although coal and rock damage induces gas desorption, coal and rock damage will not occur without gas.

[0003] ② The gas information in the airflow of the roadway is monitored. Accident experience shows that before the coal and gas outburst occurs, the airflow gas will appear to be large or small, but the law has not been clearly defined. The false positive rate of the airflow gas early warning is high, and the long-term false positives reduce the credibility of the index, which cannot be applied in the field.

[0004] Based on the problems in the prior art, the present application provides a gas disaster early warning method based on borehole optical fiber sensing monitoring. SUMMARY

[0005] The purpose of the present application is to provide a gas disaster early warning method based on borehole optical fiber sensing monitoring to solve the technical problems of late coal and gas outburst early warning and high false positive rate in the prior art.

[0006] The technical scheme of the present application is a gas disaster early warning method based on borehole optical fiber sensing monitoring, comprising: Layered extraction boreholes are constructed in the roadway, and all layered extraction boreholes passing through the coal roadway area to be excavated are set as monitoring boreholes. A composite optical fiber sensing cable is installed in the monitoring borehole to continuously monitor the gas extraction information. Whether temperature anomaly and borehole pressure anomaly appear in the gas extraction information is analyzed and judged. According to the characteristics of the anomaly phenomenon, the corresponding early warning level is matched, and the post-processing of the corresponding early warning level is performed.

[0007] Preferably, the layered extraction boreholes are constructed in groups, each group of layered boreholes has the same drilling site, the same horizontal azimuth angle and different inclination angles, so that each group of layered extraction boreholes has a monitoring borehole passing through the roadway area to be excavated.

[0008] Preferably, the composite optical fiber sensing cable is conveyed into the monitoring borehole through the gas extraction flower pipe and is fixed in the monitoring borehole by the bag seal. The composite optical fiber sensing cable comprises a temperature sensor optical fiber and a pressure sensor optical fiber; and the gas extraction information collected by the composite optical fiber sensing cable is demodulated by an optical fiber demodulator to obtain the temperature and pressure information in the monitoring borehole.

[0009] Preferably, the spacing of the through-layer extraction boreholes is not more than the range of the roadway pressure relief zone and is not less than 2 meters per drill field.

[0010] Preferably, the number of the composite optical fiber sensing cables in one roadway is not less than 10.

[0011] Preferably, in the installation layout of the composite optical fiber sensing cables in one roadway, when the excavation passes through X composite optical fiber sensing cables, M composite optical fiber sensing cables are moved, N composite optical fiber sensing cables are retained, and the installation is rolled forward. The time for moving and assembling the M composite optical fiber sensing cables is not more than the time for assembling N composite optical fiber sensing cables in the roadway excavation, so as to avoid a gap period in the early warning, and M≤X.

[0012] Preferably, the data recording form of the composite optical fiber sensing cable is that, in a normal working state, one data is saved every 1 minute; and in the case that the monitoring data appears abnormal, 30 seconds of data before and after the abnormal point are retained, and one data is saved every second.

[0013] Preferably, based on the temperature abnormality phenomenon, the corresponding early warning information and early warning levels include: The early warning information corresponding to the first-level temperature early warning is coal rock rupture; the early warning information corresponding to the second-level temperature early warning is gas desorption; and the early warning information corresponding to the third-level temperature early warning is high risk of gas outburst. Based on the pressure abnormality phenomenon, the corresponding early warning information and early warning levels include: The early warning information corresponding to the first-level pressure early warning is borehole instability, the early warning information corresponding to the second-level pressure early warning is borehole fracture penetration, and the early warning information corresponding to the third-level pressure early warning is borehole collapse emergency.

[0014] Preferably, based on the abnormality phenomenon, the characteristic phenomena for determining the early warning level respectively include: If the temperature of the borehole section shows a sustained rising trend, the temperature rising amplitude is 1℃-3℃, and the duration is ≥15min, then the first-level temperature early warning is determined. If the monitored borehole section shows a temperature reduction phenomenon, the temperature reduction amplitude is 2℃-4℃, and the duration is ≥10min, then the second-level temperature early warning is determined. The monitoring characteristic is that the monitored borehole section first shows a temperature rising phenomenon, the amplitude is 2℃-4℃, and the duration is 5-10min, then the temperature rapidly reduces, the amplitude is 3℃-5℃, and the duration is ≥8min, then the third-level temperature early warning is determined.

[0015] Preferably, based on the emerging abnormal phenomenon, the three-level pressure early warning includes: The pressure persistence fluctuates greatly, the drilling pressure of the easy-to-collapse hole appears ≥3 times of fluctuation within 1 hour, the single fluctuation amplitude is 0.03MPa-0.08MPa, and the fluctuation has no obvious rule, and the first-level pressure early warning is determined; The pressure mutation reduces, the drilling pressure of the easy-to-collapse hole mutation reduces 0.08MPa-0.15MPa within 5-10min, and the pressure is stable at the low value lower limit level after the reduction, and the second-level pressure early warning is determined; The pressure mutation reduces and continuously keeps the low value lower limit level, the drilling pressure of the easy-to-collapse hole mutation reduces 0.15MPa or more within 1-3min, and continuously keeps no rising trend for 1 hour, and the third-level pressure early warning is determined.

[0016] Compared with the prior art, the advantages of the present application are: The present application can monitor the gas extraction information in the through-hole drilling by arranging the composite optical fiber sensing cable in the through-hole drilling, analyze the internal changes of the coal seam in front of the working face and after the excavation based on the obtained temperature and pressure information in the through-hole drilling, directly reflect the energy conversion and gas state change in the coal seam by monitoring the temperature anomaly in the extraction drilling, evaluate the drilling stability and surrounding rock stress state by monitoring the pressure change, realize the double early warning of the coal and gas outburst and the drilling collapse. Since the temperature information and pressure information in the internal through-hole drilling in the coal seam are monitored, the present application is ahead of the existing roadway airflow gas prediction mode, and is more comprehensive than simply monitoring the coal and rock rupture signal, thereby improving the monitoring and early warning reliability.

[0017] The present application can monitor the temperature and pressure in the through-hole drilling based on the composite optical fiber sensing cable, effectively utilize the original through-hole gas extraction drilling, realize the one-hole multi-use of "extraction and early warning", low cost, promote the drilling informatization development, and the optical fiber sensing has the advantages of anti-electromagnetic interference, corrosion resistance and long service life, and is suitable for the harsh environment in the mine. BRIEF DESCRIPTION OF DRAWINGS

[0018] The present application will be further described below in combination with the drawings and embodiments: Figure 1 The tunneling working face gas disaster early warning technical route map of the present application; Figure 2 The single through-hole drilling field profile and sensor arrangement drilling schematic diagram of the present application; Figure 3 The installation schematic diagram of the composite optical fiber sensing cable in the drilling of the present application; Figure 4 The composite optical fiber sensing cable layout schematic diagram provided by the present application at the monitoring drilling hole of the roadway not yet excavated; Figure 5The composite optical fiber sensing cable layout schematic diagram provided by the present application is provided to the roadway excavation to the monitoring drill hole.

[0019] Wherein: 1, floor rock roadway; 2, coal roadway; 3, coal seam; 4, cross-layer extraction drill hole; 5, monitoring drill hole; 6, bag sealer; 7, rock layer; 8, gas extraction flower pipe; 9, optical fiber demodulator; 10, composite optical fiber sensing cable. DETAILED DESCRIPTION

[0020] The content of the present application will be further described in detail below in combination with specific embodiments: The coal roadway excavation working face is a high-incidence area of coal and gas outburst disasters, and according to statistics, 90% of outburst accidents occur in the excavation working face. Before the excavation operation in the coal roadway with outburst danger, it is necessary to first carry out strip outburst elimination, that is, a new roadway is arranged in the rock layer near the coal seam to be excavated, cross-layer drill holes are drilled from the new roadway to the strip area of the coal roadway to be excavated, and gas pre-extraction is carried out. Based on this, the present application proposes a gas disaster early warning method of drill hole optical fiber sensing monitoring, analyzes the abnormal law according to the monitoring information such as temperature and pressure of the original cross-layer drill hole in the coal mine underground, so as to achieve the purpose of early warning of gas overrun / outburst and drill hole collapse in the coal roadway excavation working face.

[0021] The present application provides a gas disaster early warning method of drill hole optical fiber sensing monitoring, and the overall process includes drill hole screening, system installation, real-time monitoring and mode recognition, system dynamic forward movement and iterative optimization cycle. The principle route is shown in the accompanying Figure 1 , and the specific implementation steps are as follows: Step one, cross-layer drill hole layout installation.

[0022] Before the coal roadway 2 is excavated, the cross-layer extraction drill hole 4 is constructed in the floor rock roadway 1 to the coal roadway 2 to be excavated area in the coal seam 3, and the drill hole is constructed in groups, the drill hole opening location of each group is the same, the horizontal azimuth angle is the same, and the inclination angle is different, so as to ensure that each group of drill holes has a cross-layer extraction drill hole 4 passing through the roadway to be excavated area, see the cross-sectional view of a single group of drill holes in the accompanying Figure 2 .

[0023] From all the cross-layer extraction drill holes 4 in the strip area of the excavated roadway, the monitoring drill holes 5 passing through the coal roadway 2 to be excavated area are selected, and the numbering is carried out according to the distance from the initial point of the excavated coal roadway 2, and the numbering sequence from near to far is 1-n. The single cross-layer drill field cross-sectional view and the sensor arrangement drill hole schematic diagram are shown in the accompanying Figure 2 .

[0024] The spacing of the cross-layer extraction drill hole 4 does not exceed the range of the roadway pressure relief area, and too large spacing of the cross-layer extraction drill hole 4 may lead to loss of early warning information, and the spacing of the cross-layer extraction drill hole 4 is not less than 2 meters per drill field, for example, numbering is carried out every one or two drill fields.

[0025] Step two, assemble the composite optical fiber sensing cable for monitoring gas extraction information.

[0026] In the floor rock roadway 1, there are optical fiber demodulator 9 and several composite optical fiber sensing cables 10, which include temperature sensing optical fiber and pressure sensing optical fiber, can detect the temperature and pressure of the monitoring borehole 5 in real time, the number is A. The borehole which does not pass through the coal roadway 2 to be excavated area does not need to install the composite optical fiber sensing cable 10.

[0027] Appendix Figure 3 The specific installation schematic of the composite optical fiber sensing cable 10 in the borehole is shown.

[0028] The monitoring borehole 5 extends through the rock layer 7 to the coal seam 3, when installing, the composite optical fiber sensing cable 10 is bound outside the prefabricated gas extraction flower pipe 8, and is transported into the monitoring borehole 5 at the preset depth, and the bag seal 6 is used for hole sealing, the bag seal 6 presses the composite optical fiber sensing cable 10 on the hole wall of the monitoring borehole 5, ensures that the composite optical fiber sensing cable 10 is in good contact with the stratum, and can reflect the real stratum condition. The tail end of the composite optical fiber sensing cable 10 is led out to the borehole, connected to the explosion-proof junction box, and finally connected to the optical fiber demodulator 9 through the main cable.

[0029] Before the coal roadway 2 starts to excavate, the optical fiber sensing equipment is inspected and calibrated.

[0030] Step three, during the step coal roadway 2 excavation process, the gas extraction information is continuously monitored.

[0031] After the coal roadway 2 starts to excavate, whether there is temperature change phenomenon and whether there is borehole pressure change phenomenon in the extraction information of the 1-A monitoring borehole 5 is observed.

[0032] The data recording form of the composite optical fiber sensing cable 10 is that when the monitoring data appears abnormal, 30 seconds of data before and after the abnormal point (one data is saved every second) is reserved, and one data is saved every 1 minute in the remaining time period. The data is uploaded to the ground server through the underground ring network for fine mode recognition by the ground system.

[0033] Among them, the adsorbed gas in the coal seam changes into free gas in a large amount and quickly, the heat absorption leads to temperature reduction, or the stress concentration of the coal and rock mass leads to deformation heat, which produces temperature change phenomenon. The sudden rise of pressure may indicate that the surrounding rock stress is concentrated, which has the risk of falling, or the sudden drop of pressure may indicate that cracks appear around the borehole, which leads to gas leakage and pressure drop, but it may also be a precursor of collapse, which produces pressure change phenomenon.

[0034] Step four, based on the abnormal phenomenon, the warning information is issued.

[0035] When abnormal phenomena occur, timely warning information is sent to the underground coal roadway excavation construction; the warning information is corresponding to the warning level.

[0036] In detail, the mine manager determines the warning level corresponding to the abnormal degree of change of different extraction information according to the relationship between the warning information and the gas dynamic phenomenon and the drilling stability based on the characteristics of the coal mine.

[0037] The warning level of the temperature mode includes: first-level temperature warning, second-level temperature warning and third-level temperature warning.

[0038] The abnormal characteristic phenomenon corresponding to the first-level temperature warning is that the monitored drilling section has a sustained temperature rise, the temperature rise amplitude is 1-3℃, and the duration is ≥15min. The phenomenon corresponding to the first-level temperature warning indicates that the coal and rock mass is broken due to the excavation disturbance, but the coal seam in the region has low gas occurrence, and the gas desorption is not triggered. Although there is no gas outburst risk at present, the coal seam region corresponding to the drilling should be marked as a “low gas but high breaking risk area”. If the same temperature rise phenomenon occurs in other regions with high gas occurrence, gas desorption may occur, and early warning is needed.

[0039] The abnormal characteristic phenomenon corresponding to the second-level temperature warning is that the monitored drilling section has a temperature drop, the temperature drop amplitude is 2-4℃, and the duration is ≥10min. The phenomenon corresponding to the second-level temperature warning is caused by the excavation pressure relief, which leads to the conversion of adsorbed gas in the coal seam to free state. The heat absorption in the desorption process causes the temperature to drop. Although the coal and rock structure is complete, a large amount of gas desorption may lead to local gas concentration exceeding the limit. If the desorption amount continues to increase, it is easy to cause subsequent air flow gas anomaly.

[0040] The abnormal characteristic phenomenon corresponding to the third-level temperature warning is that the monitored drilling section first has a temperature rise, the amplitude is 2-4℃, and the duration is 5-10min, and then the temperature rapidly drops, the amplitude is 3-5℃, and the duration is ≥8min. The phenomenon corresponding to the third-level temperature warning is a direct manifestation of the synergistic effect of coal and rock rupture and gas desorption. The heat generated by the early coal and rock rupture leads to temperature rise, the cracks produced by the rupture provide a channel for gas desorption, and then a large amount of gas desorption absorbs heat, causing the temperature to drop sharply. It is the core precursor of coal and gas outburst, and the risk level is the highest.

[0041] For drilling pressure warning, first, drilling collapse / closure identification is performed, including: The corresponding identification feature phenomenon is that the drilling pressure slowly rises continuously for 7 days before excavation to the initial stage of excavation, with a pressure rise amplitude of 0.05 MPa-0.2 MPa and a duration of ≥24 h. This feature phenomenon indicates that the coal seam where the drill hole is located is soft and high-stress, and under the action of high ground stress, the soft coal body is easily extruded into the drill hole, causing the drill hole to gradually close and continuously press the optical fiber. The easy-caving drill hole needs to be screened out and distinguished from stable drill holes for subsequent monitoring.

[0042] For easy-caving drill hole pressure anomaly early warning, the early warning levels include: first-level pressure early warning, second-level pressure early warning, and third-level pressure early warning.

[0043] The first-level pressure early warning corresponds to the abnormal feature phenomenon that the pressure fluctuates continuously with a large amplitude, the easy-caving drill hole pressure fluctuates ≥3 times within 1 h, the single fluctuation amplitude is 0.03 MPa-0.08 MPa, and the fluctuation has no obvious regularity. The pressure fluctuation of this feature phenomenon is caused by the plastic deformation of the soft coal body, and the coal body slowly flows under stress, causing the drill hole space to repeatedly shrink and slightly expand. Although it does not immediately cave in, the coal structure is already in an unstable state, which can easily lead to subsequent sudden caving.

[0044] The second-level pressure early warning corresponds to the abnormal feature phenomenon that the pressure suddenly decreases, the easy-caving drill hole pressure suddenly decreases by 0.08 MPa-0.15 MPa within 5-10 min, and the pressure stabilizes at a lower level after the decrease. The sudden decrease in pressure indicates that the coal body around the drill hole has lost local structure stability, which may be caused by plastic deformation of the coal body leading to crack penetration, or the drill hole locally caving in to form a new gas / stress release channel. If not promptly addressed, it is easy to develop into a full-hole caving.

[0045] The third-level pressure early warning corresponds to the abnormal feature phenomenon that the pressure suddenly drops and continues to be low, the easy-caving drill hole pressure drops by more than 0.15 MPa within 1-3 min and continues to be low without a rising trend for 1 h. This feature phenomenon is an emergency signal that the drill hole is about to cave in, and the coal structure has lost stability in a large area, causing serious collapse inside the drill hole, resulting in complete pressure release. If the operation continues, it may cause the roadway side to collapse or gas to abnormally gush out.

[0046] According to the early warning data and verification results during the excavation process, the early warning threshold is continuously adjusted and updated.

[0047] Ground personnel analyze the early warning reasons and develop corresponding underground early warning construction schemes according to the early warning levels based on the early warning information sent from underground. The early warning information includes: The first-level temperature early warning is a coal rock rupture early warning, and the first-level pressure early warning is a drill hole instability early warning. The early warning measures are to mark the corresponding coal rock rupture area and prompt "stress concentration, pay attention to observation".

[0048] The secondary temperature warning is a gas desorption warning, and the secondary pressure warning is a drill hole fracture breakthrough warning. The warning measure is to prompt "coal seam gas is active, and there is an over-limit risk".

[0049] The tertiary temperature warning is a high risk warning, and the tertiary pressure warning is a drill hole collapse emergency warning. The warning measure is to issue a tertiary emergency warning information, and to link to a sound and light alarm to prompt "suspected outburst precursor, immediately evacuate".

[0050] Step five, dynamic forward movement of the composite optical fiber sensing cable.

[0051] During the roadway excavation process, when the excavation exceeds X composite optical fiber sensing cables 10, the composite optical fiber sensing cables 10 are dynamically moved in the mode of moving M and leaving N (M+N=A). The increase of the number of M can reduce the moving frequency of the equipment, but it should be ensured that the number of N is not too low to avoid the problem that the time used for moving M composite optical fiber sensing cables 10 is greater than the time used for excavating N composite optical fiber sensing cables 10, resulting in discontinuous warning. Therefore, M≤X should be met.

[0052] For ease of illustration, the excavation process diagrams provided in the accompanying Figure 4 and the accompanying Figure 5 are taken as examples, wherein A=3.

[0053] Figure 4 A diagram showing that the coal roadway 2 has not been excavated to the monitoring drill hole 5 is shown; Figure 5 A diagram showing that the coal roadway 2 has been excavated to the monitoring drill hole 5 is shown. When the roadway excavation reaches (and has exceeded) A / 2 composite optical fiber sensing cables 10, 1-A / 2 composite optical fiber sensing cables 10 are disassembled and moved and installed at (A+1)-(A+A / 2), and the observation drill hole is changed from 1-A to (A / 2+1)-(A+A / 2). Continuous monitoring and warning of the coal roadway excavation area is achieved, and the full-length monitoring of the long-distance roadway is achieved with limited equipment quantity, taking into account the cost and effect.

[0054] In theory, the more the number of composite optical fiber sensing cables 10 A is, the better it is, but the increase in the number will significantly increase the equipment cost, and the decrease in the number will increase the moving frequency, and increase the labor and time cost. Therefore, considering the cost, labor and time budget, the number of composite optical fiber sensing cables 10 is set. In this embodiment, the number of composite optical fiber sensing cables 10 A is not less than 10 to ensure continuous monitoring.

[0055] Steps three and four are repeatedly executed. Whenever the roadway excavation exceeds half of the number of the laid composite optical fiber sensing cables, the half of the composite optical fiber sensing cables that have been excavated and exceeded are moved in sequence in the excavation direction, and step five is referred to.

[0056] Step six, roadway updating and threshold optimization.

[0057] After the tunnel excavation is completed, the early warning data and verification results in the excavation process are analyzed, the early warning threshold in step five is improved, all composite optical fiber sensing cables are removed, and are installed in the next tunnel to be excavated.

[0058] An embodiment of the gas disaster early warning method in the coal roadway 2 excavation process is provided below.

[0059] An industrial test was conducted on a high-gas and outburst-prone excavation face in a certain mine. The basic environmental parameters included a coal seam 3 thickness of 4.0 m and an original gas content of 14 m³ / t. The implementation process was as follows: Sixty layer-penetrating boreholes (i.e., monitoring boreholes 5) that met the conditions were selected.

[0060] Ten sets (A=10) of composite optical fiber sensing cables 10 were installed in monitoring boreholes 5 numbered 1-10. On the 12th day of excavation, monitoring borehole 7 located 18 m in front of the working face detected abnormal characteristic phenomena corresponding to a third-level temperature early warning: the temperature rose from 31.5°C to 34.0°C within 7 minutes, and then sharply dropped to 29.8°C within 9 minutes. The ground early warning analysis software immediately triggered a "third-level temperature early warning" and automatically cut off the power supply of the excavation face and urgently evacuated the site construction personnel. Subsequent investigation found that the drill cuttings gas desorption indicators Δh2 and K1 values in this area were severely exceeded, verifying the accuracy of the early warning. No dynamic phenomenon occurred due to timely disposal.

[0061] During the entire 500 m tunnel excavation, the system issued 4 effective second-level temperature early warnings and third-level temperature early warnings, which were 65 minutes ahead of the average tunnel gas sensor alarm. During the same period, the traditional gas concentration monitoring system produced more than 20 false alarms due to blasting, process changes, etc., while the system only had 2 false alarms (eliminated after the early warning threshold was optimized). At the same time, 2 borehole collapse risks were early warned (second-level pressure early warning), and supplementary hole measures were taken in time to ensure gas extraction safety.

[0062] Compared with the current commonly used coal roadway excavation gas disaster early warning method, the early warning method in the present application is aimed at gas temperature signals and coal and rock fracture signals, and is more sensitive to disasters.

[0063] Gas abnormal outburst in the roadway is an external manifestation characteristic of the disaster, and external characteristics usually lag behind internal changes in the coal seam. Since the monitoring of abnormal changes in the internal gas of the coal seam is ahead of the abnormal changes in the roadway airflow, the present application is more advanced in prediction.

[0064] Each coal lane tunneling working face strip area is arranged with a large number of through layer boreholes, thousands to tens of thousands of which are different. At present, the purpose of these through layer boreholes is only for gas extraction. The through layer boreholes of the embodiment are not only used for gas extraction, but also for monitoring gas extraction information, without the need to construct new pressure measuring boreholes, and the cost is low.

[0065] The present application is suitable for coal and gas outburst mine, high gas mine, and coal lane tunneling working face gas disaster early warning, which is a new method for ensuring coal mine safety production and promoting intelligent mine construction.

[0066] The above embodiments are only for illustrating the technical concept and characteristics of the present application, and the purpose is to enable those skilled in the art to understand the content of the present application and implement it, and cannot limit the protection scope of the present application. For those skilled in the art, it is obvious that the present application is not limited to the details of the above exemplary embodiments, and can be implemented in other specific forms without departing from the spirit or basic characteristics of the present application, therefore, from any point of view, the embodiments should be regarded as exemplary and non-limiting, the scope of the present application is defined by the appended claims rather than the above description, therefore, all changes falling within the meaning and scope of the equivalent elements of the claims are intended to be included in the present application.

Claims

1. A method for early warning of gas disasters using borehole fiber optic sensing, characterized in that, include: In the roadway, drilling holes for gas extraction through layers are constructed. All drilling holes that pass through the coal roadway to be excavated are selected as monitoring holes. Composite fiber optic sensing cables are installed in the monitoring holes to continuously monitor gas extraction information. Analyze and determine whether there are abnormal temperature and borehole pressure phenomena in the gas extraction information; Based on the characteristics of the observed anomalies, the corresponding warning level is matched, and the corresponding post-processing is executed.

2. The method for early warning of gas disasters using borehole fiber optic sensing monitoring according to claim 1, characterized in that, The cross-layer extraction boreholes are constructed in groups. Each group of cross-layer extraction boreholes has the same drilling location, the same horizontal azimuth, and different dip angles, ensuring that each group of cross-layer extraction boreholes has a monitoring borehole that passes through the area to be excavated in the roadway.

3. The method for early warning of gas disasters using borehole fiber optic sensing monitoring according to claim 2, characterized in that, The composite optical fiber sensing cable is delivered to the monitoring borehole through the gas extraction pipe and fixed inside the monitoring borehole by a bag sealer. The composite optical fiber sensing cable includes a temperature sensor fiber and a pressure sensor fiber; the gas extraction information collected by the composite optical fiber sensing cable is demodulated by an optical fiber demodulator to obtain the temperature and pressure information inside the monitoring borehole.

4. The method for early warning of gas disasters using borehole fiber optic sensing monitoring according to claim 2, characterized in that, The spacing between the cross-layer extraction boreholes shall not exceed the pressure relief zone of the roadway, and shall be no less than 2 meters between each drilling site.

5. The method for early warning of gas disasters using borehole fiber optic sensing monitoring according to claim 1, characterized in that, The number of composite optical fiber sensing cables in a single tunnel shall not be less than 10.

6. The method for early warning of gas disasters using borehole fiber optic sensing monitoring according to claim 1, characterized in that, In the installation layout of the composite optical fiber sensing cable in a tunnel, when the tunnel passes X composite optical fiber sensing cables, M composite optical fiber sensing cables are moved, N composite optical fiber sensing cables are retained, and the installation is rolled forward. The time required for the mobile assembly of M composite fiber optic sensor cables shall not exceed the time required for the tunnel excavation of N composite fiber optic sensor cables, thus avoiding gaps in early warning. M≤X.

7. The method for early warning of gas disasters using borehole fiber optic sensing monitoring according to claim 1, characterized in that, The data recording format of the composite optical fiber sensing cable is as follows: under normal working conditions, one data point is saved every minute; when abnormal data is detected, data for 30 seconds before and after the abnormal point is retained, and one data point is saved every second.

8. The method for early warning of gas disasters using borehole fiber optic sensing monitoring according to claim 1, characterized in that, Based on temperature anomalies, the corresponding early warning information and warning levels include: A Level 1 temperature warning corresponds to the warning information of coal and rock fracturing; a Level 2 temperature warning corresponds to the warning information of gas desorption; and a Level 3 temperature warning corresponds to the warning information of high risk of gas outburst. Based on the phenomenon of pressure anomalies, the corresponding early warning information and early warning levels include: The warning information corresponding to the first-level pressure warning is borehole instability, the warning information corresponding to the second-level pressure warning is borehole fracture penetration, and the warning information corresponding to the third-level pressure warning is borehole collapse emergency.

9. A method for early warning of gas disasters using borehole fiber optic sensing monitoring according to claim 8, characterized in that, Based on the observed anomalies, the characteristic phenomena for determining the warning level include: If the temperature in the borehole section shows a continuous upward trend, with a temperature rise of 1℃-3℃ and a duration of ≥15min, it is determined to be a Level 1 temperature warning. If the monitored borehole section shows a temperature decrease, with a temperature drop of 2℃-4℃ and a duration of ≥10min, it is judged as a level two temperature warning; The monitoring characteristics are as follows: if the temperature rises first in the monitored borehole section, with an amplitude of 2℃-4℃ and a duration of 5-10 minutes, and then the temperature drops rapidly, with an amplitude of 3℃-5℃ and a duration of ≥8 minutes, it is judged as a level three temperature warning.

10. A method for early warning of gas disasters using borehole fiber optic sensing monitoring according to claim 8, characterized in that, Based on the observed anomalies, the Level 3 pressure warning includes: If the pressure fluctuates significantly and continuously, and the pressure of the easily collapsed borehole fluctuates ≥3 times within 1 hour, with a single fluctuation range of 0.03MPa-0.08MPa and no obvious pattern, it is judged as a level one pressure warning. A sudden decrease in pressure, where the pressure in a hole prone to collapse decreases abruptly by 0.08 MPa to 0.15 MPa within 5 to 10 minutes, and then stabilizes at the lower limit of the low value, is identified as a level two pressure warning. A sudden drop in pressure that remains at a low lower limit, with the pressure in a prone-to-collapse borehole decreasing abruptly by more than 0.15 MPa within 1-3 minutes and showing no upward trend for 1 hour, is classified as a Level III pressure warning.

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