阅读说明：本技术 地面高效抽采多层位老空区煤层气的防灭火抽采方法 (Fire prevention and extinguishing extraction method for efficiently extracting coal bed gas in multi-layer old goaf on ground ) 是由 李振 杨鹏 杨晓军 冯国瑞 刘继勇 康天慧 张慧芳 余奕睿 刘一鸣 杨洁 张纯旺 于 2021-09-22 设计创作，主要内容包括：本发明公开了一种地面高效抽采多层位老空区煤层气的防灭火抽采方法,通过向最上部同一水平层位多个老空区卸压解吸带的上部边界处注入大量浆体材料及聚氨酯材料,形成覆盖整个老空区的隔氧层,同时在老空区相邻的生产矿井靠近老空区边界煤柱一侧施工密闭墙隔绝相邻生产矿井的空气涌入老空区,施工完毕后,用SF-(6)示踪气体、氧气传感器验证老空区的密闭性。然后从地面向中央老空区内部施工垂直井,抽采多层位老空区煤层气；抽采过程中,针对老空区不同位置处的温度传感器和CO传感器的示数变化,及时采取相应的灭火措施,消除了煤层气抽采过程中的火灾隐患。该方法解决了老空区煤层气地面抽采时遗煤自燃及爆炸事故,保证了煤层气抽采的安全进行。(The invention discloses a fire prevention and extinguishing extraction method for efficiently extracting coal bed gas of a multi-layer old goaf on the groundSF 6 And the tracer gas and oxygen sensors verify the airtightness of the old goaf. Then constructing a vertical well from the ground to the inside of the central goaf, and extracting coal bed gas of the multi-layer goaf; in the extraction process, corresponding fire extinguishing measures are taken in time according to the indication changes of the temperature sensors and the CO sensors at different positions of the goaf, and the fire hazard in the extraction process of the coal bed gas is eliminated. The method solves the problems of spontaneous combustion and explosion accidents of residual coal during the ground extraction of the coal bed gas in the old goaf, and ensures the safe operation of the extraction of the coal bed gas.)

1. A fire prevention and extinguishing extraction method for efficiently extracting coal bed gas of a multi-layer old goaf on the ground is characterized by comprising the following steps: injecting water into the upper boundary of a plurality of old empty areas on the same horizontal layer at the uppermost part for pressure relief desorptionA large amount of slurry-polyurethane material is added to form an oxygen isolation layer covering the whole goaf, meanwhile, a coal pillar sealing wall and an overlying strata sealing wall are constructed on one side of the production mine adjacent to the goaf, which is close to the boundary coal pillar of the goaf, to isolate the air of the adjacent production mine from flowing into the goaf, and after the construction is finished, SF is used₆The tracer gas verifies the tightness of the old dead zone; then, constructing a vertical well from the ground to the inside of the central goaf, and extracting coal bed gas of the multi-layer goaf; in the extraction process, the position of a possible fire source in the goaf is judged according to the indication changes of the CO sensors and the temperature sensors at different positions of the goaf, nitrogen is injected or a stopping agent is sprayed to extinguish the possible local fire, and the safe extraction of the coal bed gas is ensured.

2. The fire prevention and extinguishing extraction method for the ground high-efficiency extraction of the coal bed gas of the multi-layer old goaf according to claim 1, which is characterized by comprising the following steps:

(1) determining parameters of an excavation range, coal pillar distribution, an air guide fracture zone and a pressure relief desorption zone height of a multi-layer old goaf formed by an underground excavated coal seam and a wind leakage channel between the uppermost old goaf and the ground by combining a physical exploration means according to mine excavation data and a coal seam geological histogram;

(2) taking the area of the transverse plastic destruction development area of the uppermost old goaf orthographically projected to the ground as a grouting area A₁At A₁Respectively extending 10-20m towards the peripheral boundary to be used as a final grouting area A; arranging a ground grouting drill hole in the grouting area A; the aperture of the drill hole is 90-110mm, the transverse and longitudinal row spacing of the drill hole is 20-30m, and the drill hole is constructed to the upper part of the pressure relief desorption belt;

arranging a ground end grouting pipeline in the grouting area A, namely: the grouting station is provided with a slurry pump and connected with a grouting main pipe, the grouting main pipe is provided with a slurry discharge gate valve, and the grouting main pipe is connected with a grouting branch pipe extending into a grouting drill hole through a tee joint;

(3) starting a ground grouting pump station, injecting grout into the upper boundary of the pressure-relief desorption zone through a drill hole to form a grout layer of 0.5-1 m, wherein the grouting pressure is 1-3 MPa; after grouting, cleaning a grouting pipeline, and injecting polyurethane to the upper part of a slurry layer on the upper boundary of the pressure relief desorption belt through the grouting pipeline again, wherein the thickness of the polyurethane is 0.1-0.2 m, so as to form an oxygen isolation layer structure constructed by slurry-polyurethane;

(4) in a production roadway of an adjacent mine in an old goaf, carrying out undercutting treatment on a top bottom plate and two roadway walls at the position close to a coal pillar at the boundary of the old goaf, wherein the undercutting depth is 0.2-0.5 m, the width is 1-2m, float coal in a groove is cleaned, and then a coal pillar oxygen-separation sealing wall is constructed at the position; the coal pillar oxygen-isolating sealed wall is formed by sequentially constructing cement mortar, sealing rubber and polyurethane in a manner of extending from the coal wall side to the direction of the adjacent mine production roadway; wherein the thickness of cement mortar is 0.8m-1.5m, the thickness of sealing rubber is 0.1m-0.3m, the thickness of polyurethane is 0.1m-0.3m, and reinforcing mesh is used for reinforcing after the three-layer structure is constructed; meanwhile, after the oxygen-isolating closed wall is constructed, constructing a drill site from the position of the closed wall to the roadway wall, constructing an inclined hole in the drill site to the rock stratum on the constructed closed wall, injecting slurry and polyurethane to form an overlying rock stratum oxygen-isolating closed wall, and preventing air of a production mine from flowing into an old goaf under the action of ground extraction negative pressure of the old goaf together with a coal pillar oxygen-isolating closed wall in the constructed roadway;

(5) in a production mine adjacent to the old dead zone, a drill hole is constructed at one side close to a boundary coal pillar of the old dead zone, the drill hole penetrates through the coal pillar of the old dead zone and an oxygen-isolating closed wall of the coal pillar, and a final hole is positioned in a gas-guiding crack zone of the old dead zone and is 5-10m away from the boundary coal pillar;

temperature sensor, CO sensor and O₂The concentration sensor is arranged in the old goaf through a drill hole, and the sensor is connected to a monitoring device on the ground through a line;

(6) constructing a vertical well from the ground to the goaf, stopping construction until the vertical well is constructed to a position 1-3m away from the bottom plate of the upper layer of the goaf, then laying a casing pipe to the vertical well for well cementation, and putting a temperature sensor and a CO sensor into a gas guide fracture zone of the goaf from the ground through a vertical well mouth; continuing to extend the vertical well to a distance of 1-3m from the bottom plate of the lower-layer gob, laying a casing for well cementation, and then placing the temperature sensor and the CO sensor into the gas guide fracture zone of the gob from the ground through the vertical well mouth; the temperature sensor and the CO sensor are connected to a monitoring device on the ground through a line; conveying a casing gun to a position 1-3 meters away from the upper-layer old goaf bottom plate by using a cable, launching the energy-gathered perforating bullets to the casing wall by the casing gun, and forming a plurality of holes on the casing with the upward height of 5-10m from the upper-layer old goaf bottom plate;

(7) the vertical well is sealed at the end close to the ground, and a sealing device is arranged on the ground; the pipeline at the ground end of the vertical well is divided into two parts by a tee joint, wherein one part is a nitrogen injection pipe which is provided with a valve III and is connected with a nitrogen storage tank; one part is an air extraction pipeline, is provided with a valve II and is connected with a coal bed gas storage tank;

(8) release of SF at surface fractures₆Gas, using SF₆The air leakage channel has good diffusivity, can be rapidly and uniformly distributed in a disturbed flow field, and can be used as a tracer gas to verify the air leakage channel of an old dead zone;

(9) opening a valve II, and extracting the coal bed gas through an extraction pipe;

firstly, if the extracted coal bed gas contains SF₆Closing the valve II and stopping the extraction of the coal bed gas; injecting polyurethane into the upper boundary of the pressure-relief desorption zone of the upper-layer old goaf through the ground drilling; after injection is complete, SF is released cyclically₆Gas sampling and SF measuring₆Gas concentration and stopping pumping and grouting until the pumped coal bed gas does not contain SF any more₆A gas;

secondly, if the coal bed gas is extracted, displaying O in the monitoring device₂If the concentration is continuously increased, closing the valve II, spraying polyurethane to the closed wall in the adjacent production mine for reinforcement, opening the valve II again after the oxygen concentration is reduced, and continuing to extract the coal bed gas;

thirdly, if the extracted coal bed gas is measured not to contain SF₆Gas and O₂If the concentration does not change obviously, continuously extracting the coal bed gas;

(10) paying attention to the indication change of CO concentration and temperature in the ground monitoring device in real time in the process of extracting coal bed gas; if a CO sensor vertically placed in an underground old dead zone on the ground shows that the volume fraction of CO reaches a certain determined value between 24 ppm and 150ppm and has a trend of stable increase or a temperature sensor shows that the temperature reaches 60-80 ℃, closing a valve II, opening a valve III and continuously injecting nitrogen into the old dead zone; when the concentration and the temperature of CO are reduced to be below critical values, continuously injecting nitrogen into the old goaf for 12 hours; then, closing the valve III, opening the valve II again, and continuing extracting the coal bed gas;

if the CO sensor placed in the old goaf through the drill hole on the boundary coal pillar shows that the CO volume fraction reaches a certain determined value between 24 and 150ppm and has a trend of stable increase or the temperature sensor shows that the temperature reaches 60 to 80 ℃, closing the valve II, and then spraying a stopping agent to the old goaf through the drill hole, wherein the stopping agent adopts 10 to 20 percent of CaCl₂The flow rate of the solution is 35-50L/min, and when the concentration and the temperature of CO are reduced to be lower than critical values, the valve II is opened again to extract the coal bed gas; and thirdly, if the CO sensors placed in the old goaf through the ground vertical well and the drill holes on the boundary coal pillars simultaneously display a certain determined value of which the CO volume fraction reaches 24-150ppm and have a trend of stable increase or the temperature sensors simultaneously display that the temperature reaches 60-80 ℃, closing a valve II, simultaneously injecting nitrogen and spraying a stopping agent into the old goaf through the ground vertical well and the drill holes on the boundary coal pillars respectively, and opening the valve II to extract the coal bed gas after the CO concentration and the temperature are reduced to be below critical values.

3. The fire prevention and extinguishing extraction method for the ground high-efficiency extraction of the coal bed gas of the multi-layer old goaf according to claim 2, characterized by comprising the following steps: the solid-phase material of the slurry is fly ash or pulverized and ground coal gangue and is matched with cement, the liquid-phase material is water, the water-solid ratio of the slurry is 2:1-5:1, and the mass ratio of the fly ash or pulverized coal gangue to the cement in the solid-phase material is 1:1-4: 1.

4. The fire prevention and extinguishing extraction method for the ground high-efficiency extraction of the coal bed gas of the multi-layer old goaf according to claim 2, characterized by comprising the following steps: and (7) forming a sealing device by a metal sealing ring and a pressing ring, wherein when the pressing ring is locked by the locking device, the metal sealing ring is plastically deformed to form sealing.

5. The fire prevention and extinguishing extraction method for efficiently extracting coal bed gas of the multi-layer old goaf on the ground according to claim 2The method is characterized in that: release of SF in step (8)₆The gas adopts a constant release mode, the release amount is 20-40mL/min, and the release duration is 3-5 h.

6. The fire prevention and extinguishing extraction method for the ground high-efficiency extraction of the coal bed gas of the multi-layer old goaf according to claim 2, characterized by comprising the following steps: in the step (9), collecting extracted coal bed gas samples every 10-20min, sending the samples to a laboratory for analysis, and measuring SF₆And (4) concentration.

7. The fire prevention and extinguishing extraction method for the ground high-efficiency extraction of the coal bed gas of the multi-layer old goaf according to claim 2, characterized by comprising the following steps: the grouting drill holes are arranged in a grid mode, the grouting amount is determined according to the area of a crack and a cavity formed by collapse of an overlying rock stratum, and the length of each drill hole extends into the height position of the pressure relief desorption zone of the uppermost old empty area; for the goaf with the area of 12 hectare and shallow burial depth, the grouting amount is 100-.

Technical Field

The invention relates to a fire prevention and extinguishing extraction method for efficiently extracting coal bed gas in a multi-layer old goaf on the ground, and belongs to the technical field of coal bed gas extraction fire prevention and extinguishing.

Background

With the continuous elimination of backward capacity in the coal industry, a large number of small coal kilns with backward mining technologies and coal mines with exhausted coal resources are closed successively, and a large amount of gas resources still remain in the closed mines. Since 2010, nearly 3 thousands of coal mines have been closed nationally, and 2030 is expected to reach 15000. 5000 billion cubic meters of coal bed gas remained in coal mines are estimated to be closed nationwide, and 2000 billion cubic meters exist in Shanxi alone. The coal bed gas is taken as a high-quality clean energy and chemical raw material, and reasonable extraction of the coal bed gas is of great significance for adjusting the energy structure and relieving the natural gas supply pressure in China.

However, the coal bed gas extraction of the old goaf of the coal mine in China is still in a starting stage, and the existing old goaf coal bed gas extraction mainly adopts ground extraction. For most of the caving type goafs formed after coal mining in China, cracks are easily formed on the ground along with the caving of overlying strata, and an air leakage channel communicated with the goafs is formed. And moreover, the mining process is limited by technical conditions, the mining rate of the coal mine is low, and more residual coal is left in old goafs. Therefore, the old goaf is easily affected by spontaneous combustion of the residual coal in the ground extraction process, and safe and efficient mining of the coal bed gas in the old goaf is severely restricted.

At present, fire prevention research in the process of extracting and exploiting the coal bed gas in the old goaf is few. Chinese patent CN105971563A discloses a coal bed gas extraction method of a composite goaf with the upper part and the lower part both mined by a cutter column method; chinese patent CN106014345A discloses a method for extracting coal bed gas in a composite goaf formed by a lower caving method. However, the extraction technology is only suitable for simple working conditions that natural ignition tendency is small and the ground surface and the old goaf are not communicated. The method can not be used for solving the complex working conditions that the old goaf has a ground air leakage channel and the spontaneous ignition of the left coal is strong. Chinese patent CN110486079B discloses a gas extraction method for layered mining of an extra-thick coal seam, which applies a gob-side entry retaining technology to construct drill holes in a return airway of a working face of a downward section of a gob-side entry retaining roadway, and injects nitrogen into a mined-out area where gas is extracted for fire prevention and extinguishment after the gas extraction of the mined-out area is completed through the drill holes after the working face passes through each group of drill holes. Although the method explores fire prevention and extinguishment in the gas extraction process of the goaf to a certain extent, the method is the fire prevention and extinguishment technology exploration which is carried out under the premise that the production mine performs mining and extraction at the same time and under the condition that the goaf is carefully known and mastered. The gas extraction fire prevention and extinguishing in the goaf belongs to fire prevention and extinguishing in a fully-closed space after the pit is closed in a mine, the internal condition of the goaf cannot be known on the ground, and the inside of the goaf does not have the condition that personnel and equipment can reach the goaf from an underground roadway. Due to the fact, fire prevention and extinguishing in the old goaf and fire prevention and extinguishing in the mining goaf of the production mine are essentially different. Therefore, the method is not completely suitable for the gas extraction of the goaf. In summary, at present, no targeted method for preventing and extinguishing fire in the process of extracting gas from the ground of the goaf exists.

In fact, after the coal seam is mined, the overlying strata collapse, and after the coal seam is fully developed for a long time, cracks are easily formed on the ground, so that the surface air enters the old goaf under the action of the ground drilling extraction negative pressure. Particularly, for a coal seam which is buried relatively shallowly, ground cracks are easy to form after the coal seam is mined. The condition of natural ignition of the left coal is met to a great extent, serious fire accidents (explosion) are caused, and further the ground drilling fails. For fire disasters in the old goaf, different from fire ignition in a mining goaf, various fire extinguishing devices and personnel can not be transported into the old goaf from original roadways and chambers of a mine. Therefore, the existing goaf fire extinguishing technology cannot be applied to goaf fire prevention and extinguishing, and the existing goaf fire prevention and extinguishing measures are still in a blank state. Therefore, how to prevent fire in the old dead zone in the gas extraction process is urgently researched.

Disclosure of Invention

In order to solve the problems, the invention provides a fire prevention and extinguishing extraction technology for extracting the high-efficiency multi-layer old goaf coalbed methane on the ground from the perspective of preventing and controlling the fire of the old goaf and safely and efficiently extracting the old goaf coalbed methane, and on the premise of ensuring safety, the economic cost is considered, and the waste coalbed methane resources are utilized to the maximum extent.

The invention provides a fire prevention and extinguishing extraction method for efficiently extracting coal bed gas of a multi-layer old goaf on the ground, which comprises the following steps:

1) according to mine excavation data and a coal seam geological histogram, determining parameters such as an excavation range, coal pillar distribution, an air guide fracture zone, a pressure relief desorption zone height and the like of a multi-layer old goaf formed by an underground excavated coal seam and an air leakage channel between the uppermost old goaf and the ground by combining a physical exploration means;

2) taking the area of the transverse plastic destruction development area of the uppermost old goaf orthographically projected to the ground as a grouting area A₁At A₁And respectively extending 10-20m towards the peripheral boundary to be used as a final grouting area A.A borehole is provided inside the grouting area a. The aperture of the drill hole is 90-110mm, the transverse and longitudinal row spacing of the drill hole is 20-30m, and the drill hole is constructed to the upper part of the pressure relief desorption belt.

Arranging a ground end grouting pipeline in the grouting area A, namely: the grouting station is provided with a slurry pump and connected with a grouting main pipe, the grouting main pipe is provided with a slurry discharge gate valve, and the grouting main pipe is connected with a grouting branch pipe extending into a grouting drill hole through a tee joint;

3) starting a ground grouting pump station, injecting grout into the upper boundary of the pressure-relief desorption zone through a drill hole to form a grout layer of 0.5-1 m, wherein the grouting pressure is 1-3 MPa; after grouting, cleaning a grouting pipeline, and injecting polyurethane to the upper part of a slurry layer on the upper boundary of the pressure relief desorption belt through the grouting pipeline again, wherein the thickness of the polyurethane is 0.1-0.2 m, so as to form an oxygen isolation layer structure constructed by slurry-polyurethane;

4) in the production roadway of the adjacent mine in the old goaf, a top bottom plate and two roadway walls close to the coal pillar on the boundary of the old goaf are subjected to undercutting treatment, the undercutting depth is 0.2-0.5 m, the width is 1-2m, float coal in the groove is cleaned, and then a coal pillar oxygen-insulating sealing wall is constructed at the position. The coal pillar oxygen-isolating sealed wall is formed by sequentially constructing cement mortar, sealing rubber and polyurethane from the coal wall side to the direction of the adjacent mine production roadway. Wherein the thickness of cement mortar is 0.8m-1.5m, the thickness of sealing rubber is 0.1m-0.3m, the thickness of polyurethane is 0.1m-0.3m, and reinforcing mesh is used for reinforcing after the three-layer structure is constructed; meanwhile, after the oxygen-isolating closed wall is constructed, constructing a drill site from the position of the closed wall to the roadway wall, constructing an inclined hole in the drill site to the rock stratum on the constructed closed wall, injecting slurry and polyurethane to form an overlying rock stratum oxygen-isolating closed wall, and preventing air of a production mine from flowing into an old goaf under the action of ground extraction negative pressure of the old goaf together with a coal pillar oxygen-isolating closed wall in the constructed roadway;

5) in a production mine adjacent to the old dead zone, a drill hole is constructed at one side close to a boundary coal pillar of the old dead zone, the drill hole penetrates through the coal pillar of the old dead zone and an oxygen-isolating closed wall of the coal pillar, and a final hole is positioned in a gas-guiding crack zone of the old dead zone and is 5-10m away from the boundary coal pillar;

temperature sensor, CO sensor and O₂The concentration sensor is arranged in the old goaf through drilling, and the sensor warpThe road is connected to the monitoring device of the ground;

6) constructing a vertical well from the ground to the goaf, stopping construction until the vertical well is constructed to a position 1-3m away from the bottom plate of the upper layer of the goaf, then laying a casing pipe to the vertical well for well cementation, and putting a temperature sensor and a CO sensor into a gas guide fracture zone of the goaf from the ground through a vertical well mouth; continuing to extend the vertical well to a distance of 1-3m from the bottom plate of the lower-layer gob, laying a casing for well cementation, and then placing the temperature sensor and the CO sensor into the gas guide fracture zone of the gob from the ground through the vertical well mouth; the temperature sensor and the CO sensor are connected to a monitoring device on the ground through a line; conveying a casing gun to a position 1-3 meters away from the upper-layer old goaf bottom plate by using a cable, launching the energy-gathered perforating bullets to the casing wall by the casing gun, and forming a plurality of holes on the casing with the upward height of 5-10m from the upper-layer old goaf bottom plate;

7) the vertical well is sealed at the end close to the ground, and a sealing device is arranged on the ground; the pipeline at the ground end of the vertical well is divided into two parts by a tee joint, wherein one part is a nitrogen injection pipe which is provided with a valve III and is connected with a nitrogen storage tank; one part is an air extraction pipeline, is provided with a valve II and is connected with a coal bed gas storage tank;

8) release of SF at surface fractures₆Gas, using SF₆The air leakage channel has good diffusivity, can be rapidly and uniformly distributed in a disturbed flow field, and can be used as a tracer gas to verify the air leakage channel of an old dead zone;

9) opening a valve II, and extracting the coal bed gas through an extraction pipe;

firstly, if the extracted coal bed gas contains SF₆Closing the valve II and stopping the extraction of the coal bed gas; injecting polyurethane into the upper boundary of the pressure-relief desorption zone of the upper-layer old goaf through the ground drilling; after injection is complete, SF is released cyclically₆Gas sampling and SF measuring₆Gas concentration and stopping pumping and grouting until the pumped coal bed gas does not contain SF any more₆A gas;

secondly, if the coal bed gas is extracted, displaying O in the monitoring device₂And (4) after the concentration is continuously increased, closing the valve II, spraying polyurethane to the closed wall for reinforcement in the adjacent production mine, opening the valve II again after the oxygen concentration is reduced, and continuing to extract the coal bed gas.

Thirdly, if the extracted coal bed gas is measured not to contain SF₆Gas and O₂If the concentration does not change obviously, continuously extracting the coal bed gas;

10) paying attention to the indication change of CO concentration and temperature in the ground monitoring device in real time in the process of extracting coal bed gas; if a CO sensor vertically placed in an underground old dead zone on the ground shows that the volume fraction of CO reaches a certain determined value between 24 ppm and 150ppm and has a trend of stable increase or a temperature sensor shows that the temperature reaches 60-80 ℃, closing a valve II, opening a valve III and continuously injecting nitrogen into the old dead zone; when the concentration and the temperature of CO are reduced to be below critical values, continuously injecting nitrogen into the old goaf for 12 hours; and then, closing the valve III, opening the valve II again, and continuing extracting the coal bed gas. Secondly, if the CO sensor placed in the old goaf shows that the CO volume fraction reaches a certain determined value between 24 and 150ppm and has a trend of stable increase or the temperature sensor shows that the temperature reaches 60 to 80 ℃ through the drill holes on the boundary coal pillars (the old goaf is constructed by adjacent production mines to the old goaf), closing the valve II, and then spraying a stopping agent (the stopping agent adopts CaCl with the concentration of 10 to 20 percent) to the old goaf through the drill holes₂The flow rate of the solution is 35-50L/min), and when the CO concentration and the temperature are reduced to be lower than critical values, the valve II is opened again to extract the coal bed gas; if the CO sensors placed in the old goaf through the ground vertical well and the drill holes on the boundary coal pillars simultaneously display a certain determined value of which the CO volume fraction reaches 24-150ppm and have a trend of stable increase or the temperature sensors simultaneously display that the temperature reaches 60-80 ℃, closing a valve II, simultaneously injecting nitrogen and spraying a stopping agent into the old goaf through the ground vertical well and the drill holes on the boundary coal pillars respectively, and opening the valve II to extract the coal bed gas after the CO concentration and the temperature sensors are reduced to be below critical values;

in the method, the pipeline at the ground end is divided into two parts, wherein one part is a grouting pipeline: the grouting station is provided with a slurry pump which is connected with a grouting main pipe, a slurry discharge gate valve is arranged on the grouting pipe, and the grouting pipe is connected with a grouting branch pipe extending into a grouting drill hole through a tee joint. One part is an extraction pipeline: the ground end is divided into two branches by a tee joint, an extraction pipe and a nitrogen injection pipe, the extraction pipe is connected with the coal bed gas storage tank through a valve II, and the nitrogen injection pipe is connected with a nitrogen gas storage tank through a valve III.

In the method, the ground grouting drill holes are arranged in a grid mode, the grouting amount is determined according to the fracture area formed by collapse of the overlying rock stratum, and the drill hole length is determined according to the thickness of the surface rock stratum and the heights of the air guide fracture zone and the pressure relief desorption zone of the old vacant zone. For the goaf with the area of 12 hectare and shallow burial depth, the grouting amount is about 100-.

The invention has the beneficial effects that:

according to the invention, from the perspective of preventing and controlling fire in the goaf in the extraction process of the coal bed gas resources, the coal bed gas in the multi-layer goaf is safely extracted on the premise of ensuring no fire. The method firstly solves the problems that when the coal bed gas in the old goaf is extracted by the ground well drilling, air is easy to flow into the old goaf through ground cracks, and the remaining coal is spontaneous combustion under the condition of sufficient oxygen participation, so that the well drilling scrapping and the extraction work termination are caused; meanwhile, the problems that the surface air sequentially enters the old dead zone through a ventilation system of an adjacent production mine, a boundary coal pillar of the old dead zone and an overlying rock layer above the coal pillar of the old dead zone and the production mine, and the remaining coal is spontaneously combusted under the participation of sufficient oxygen, so that the ground drilling is scrapped and the extraction work is stopped are solved. Secondly, the construction of the oxygen isolation layer and the sealing wall aiming at the overlying rock stratum of the old goaf, the boundary coal pillar of the old goaf and the rock stratum above the boundary coal pillar adopts a multi-layer composite structure for sealing, and low-permeability and high-molecular gas barrier materials such as polyurethane, sealing rubber and the like are effectively matched with cement mortar, so that the air leakage plugging effect is greatly improved, the sealing performance is ensured, and air is efficiently blocked from entering; finally, the invention effectively distinguishes the positions of the fire sources by monitoring the parameters of the sensors at different positions in real time, and effectively and differentially takes fire extinguishing measures aiming at different fire positions, thereby effectively ensuring the safe extraction of the coal bed gas.

Drawings

FIG. 1 is a layout diagram of extraction of coal bed gas;

FIG. 2 is a diagram of a surface borehole layout;

FIG. 3 is a drawing of a cut structure of a coal pillar sealing wall;

FIG. 4 is a structural view of a reinforcing mesh of a coal pillar sealing wall;

FIG. 5 is a diagram of a coal pillar closing wall;

FIG. 6 is a view showing the structure of an oxygen barrier layer.

In the figure, 1, ground drilling holes are firstly, 2, a grouting station is arranged, 3, a slurry pump is arranged, 4, a slurry discharge gate valve is arranged, 5, a grouting main pipe is arranged, 6, a grouting branch pipe is arranged, 7, a slurry-polyurethane oxygen isolation layer is arranged, 8, a coal pillar sealing wall is arranged, 9, a drilling field is arranged, 10, an oblique drilling hole is arranged, 11, an overlying rock stratum sealing wall is arranged, 12, a boundary coal pillar drilling hole is arranged, 13, a temperature sensor is arranged, 14, a CO sensor is arranged, 15, O₂The system comprises a concentration sensor, 16 vertical wells, 17 perforations, 18, a sealing device, 19 extraction pipes, 20, valves II and 21, coal bed gas storage tanks, 22, nitrogen injection pipes, 23, valves III and 24, nitrogen storage tanks, 25, tee joints, 26, earth surface rock strata, 27, boundary coal pillars, 28, production roadways of adjacent mines, 29 and coal pillar cracks.

Detailed Description

The present invention is further illustrated by, but is not limited to, the following examples.

Example 1:

as shown in fig. 1 to 6, two layers of caving-type goafs, a single goaf has a run length of 800m, a longitudinal length of 150m, a shallow burial depth, a plurality of goafs in the same horizontal layer, and obvious crack channels in the ground are taken as examples to illustrate the implementation steps of the invention:

1. according to mine excavation data and a coal seam geological histogram, parameters such as an excavation range, coal pillar distribution, an air guide fracture zone, a pressure relief desorption zone height and the like of a multi-layer old goaf formed by an underground excavated coal seam and an air leakage channel between the uppermost old goaf and the ground are determined by a physical exploration means;

2. taking the area of the transverse plastic destruction development area of the uppermost old goaf orthographically projected to the ground as a grouting area A₁At A₁And then respectively extending 15m towards the peripheral boundary to form a final grouting area A. Inside the grouting area a ground borehole 1 is provided. The hole diameter of a drilled hole is 100mm, the hole depth is 120m, the hole sealing length is 4m, the transverse and longitudinal row spacing is 25m, and the drilling direction is vertical to the ground surface; drilling to the upper part of the pressure-relief desorption belt;

arranging a ground end grouting pipeline in the grouting area A, namely: the grouting station 2 is provided with a slurry pump 3 and connected with a grouting main pipe 5, a slurry discharge gate valve 4 is arranged on the grouting main pipe, and the grouting main pipe is connected with a grouting branch pipe 6 extending into a grouting drill hole through a tee joint 25;

3. starting a ground grouting pump station, injecting grout into the upper boundary of the pressure-relief desorption zone through a drill hole to form a grout layer of 0.7m, wherein the grouting pressure is 2 MPa; after grouting, cleaning a grouting pipeline, and injecting polyurethane to the upper part of the slurry layer on the upper boundary of the pressure relief desorption belt through the grouting pipeline again, wherein the thickness of the polyurethane is 0.2m, so as to form an oxygen isolation layer structure 7 (shown in figure 6) constructed by slurry-polyurethane;

the water-solid ratio of the slurry is 3: 1, the mass ratio of the fly ash or the crushed coal gangue to the cement in the solid material is (2.5): 1;

4. in a production roadway 28 of an adjacent mine in an old goaf, a top bottom plate and two roadway walls close to a coal pillar on the boundary of the old goaf are subjected to undercutting treatment, the undercut depth is 0.2m, the undercut width is 1.5m, float coal in the undercutting is cleaned, and then a coal pillar oxygen-insulating sealing wall 8 is constructed at the position. The coal pillar oxygen-isolating closed wall is formed by sequentially constructing cement mortar, sealing rubber and polyurethane in a manner of extending from the coal wall side to the direction of the adjacent mine production roadway (as shown in figure 5). Wherein the thickness of cement mortar is 0.8m, the thickness of sealing rubber is 0.2m, the thickness of polyurethane is 0.2m, and reinforcing mesh is used for reinforcement after the three-layer structure is constructed; meanwhile, after the oxygen-isolating sealed wall is constructed, constructing a drill site 9 from the position of the sealed wall to the roadway wall, constructing an inclined drill hole 10 from the drill site to a rock layer above the constructed sealed wall, injecting slurry and polyurethane to form an overlying rock layer oxygen-isolating sealed wall 11, and preventing air of a production mine from flowing into an old goaf under the action of ground extraction negative pressure of the old goaf together with a coal pillar oxygen-isolating sealed wall in the constructed roadway;

drilling in an inclined manner: the aperture is 260mm, the hole depth is 60-200m, the hole sealing length is 2m, and the grouting pressure is 4-6 MPa;

5. in a production mine adjacent to the old goaf, a drill hole 12 is constructed on one side close to a boundary coal pillar 27 of the old goaf, the drill hole penetrates through the coal pillar of the old goaf and a coal pillar oxygen-isolating sealing wall, and the final hole is positioned in a gas guide crack zone of the old goaf and is 8m away from the boundary coal pillar;

the temperature sensor 13, the CO sensor 14 and O₂The concentration sensor 15 is arranged in the old goaf through a drill hole, and the sensor is connected to a monitoring device on the ground through a line;

6. constructing a vertical well 16 from the ground to the old dead zone, stopping construction until the vertical well is constructed to a position 1-3m away from the bottom plate of the upper old dead zone, then laying a casing pipe to the vertical well for well cementation, and putting a temperature sensor and a CO sensor into the air guide crack zone of the old dead zone from the ground through a vertical well mouth; continuing to extend the vertical well to a distance of 2m from the bottom plate of the lower-layer goaf, laying a casing pipe for well cementation, and then placing the temperature sensor and the CO sensor into the gas guide fracture zone of the goaf from the ground through the vertical well mouth; the temperature sensor and the CO sensor are connected to a monitoring device on the ground through a line; conveying a casing gun to a position 2 meters away from the upper-layer gob base plate by using a cable, launching the energy-gathered perforating bullets to the casing wall by using the casing gun, and forming a plurality of holes 17 on the casing with the upward height of 7m from the upper-layer gob base plate;

7. the vertical well is sealed at the end close to the ground, and the ground is provided with a sealing device 18; the pipeline at the ground end of the vertical well is divided into two parts by a tee joint, wherein one part is an air extraction pipeline 19 which is provided with a valve II 20 and is connected with a coal bed gas storage tank 21; one part is a nitrogen injection pipe 22 which is provided with a valve III 23 and is connected with a nitrogen storage tank 24;

8. release of SF at surface fractures₆Gas, using SF₆The air leakage channel has good diffusivity, can be rapidly and uniformly distributed in a disturbed flow field, and can be used as a tracer gas to verify the air leakage channel of an old dead zone;

9. opening a valve II, and extracting the coal bed gas through an extraction pipe;

firstly, if the extracted coal bed gas contains SF₆Closing the valve II and stopping the extraction of the coal bed gas; injecting polyurethane into the upper boundary of the pressure-relief desorption zone of the upper-layer old goaf through the ground drilling; after injection is complete, SF is released cyclically₆Gas sampling and SF measuring₆Gas concentration and stopping pumping and grouting until the pumped coal bed gas does not contain SF any more₆A gas;

secondly, if the coal bed gas is extracted, displaying O in the monitoring device₂When the concentration is continuously increased, the valve II is closedAnd spraying polyurethane to the closed wall for reinforcement in the adjacent production mine, opening the valve II again after the oxygen concentration is reduced, and continuing extracting the coal bed gas.

Thirdly, if the extracted coal bed gas is measured not to contain SF₆Gas and O₂If the concentration does not change obviously, continuously extracting the coal bed gas;

10. paying attention to the indication change of CO concentration and temperature in the ground monitoring device in real time in the process of extracting coal bed gas; if the CO volume fraction reaches a certain determined value between 50ppm and has a trend of stable increase or the temperature sensor displays that the temperature reaches 65 ℃ after the CO sensor is placed down through a ground vertical well and in the old dead zone, closing a valve II, opening a valve III and continuously injecting nitrogen into the old dead zone; when the concentration and the temperature of CO are reduced to be below critical values, continuously injecting nitrogen into the old goaf for 12 hours; and then, closing the valve III, opening the valve II again, and continuing extracting the coal bed gas. Secondly, if the CO sensor placed in the old goaf shows that the CO volume fraction reaches a certain determined value between 50ppm and has a trend of stably increasing or the temperature sensor shows that the temperature reaches 65 ℃ through the drill holes in the boundary coal pillars (the adjacent production mines in the old goaf construct towards the old goaf), closing the valve II, and then spraying a stopping agent (the stopping agent adopts 16% CaCl) to the old goaf through the drill holes₂The flow rate of the solution is 45L/min), and when the CO concentration and the temperature are reduced to be lower than critical values, the valve II is opened again to extract the coal bed gas; and thirdly, if the CO sensors placed in the old goaf through the drill holes in the ground vertical well and the boundary coal pillar simultaneously display a certain determined value of which the CO volume fraction reaches 50ppm and have a trend of stable increase or the temperature sensors simultaneously display that the temperature reaches 65 ℃, closing a valve II, simultaneously injecting nitrogen and spraying a stopping agent into the old goaf through the drill holes in the ground vertical well and the boundary coal pillar respectively, and opening the valve II to extract the coal bed gas after the CO concentration and the temperature are both reduced to be lower than critical values.