High-capping-index low-air-permeability single coal seam building, pressing and blasting alternate permeability increasing method

Abstract

The invention discloses a high-capping-index and low-permeability single coal seam construction, pressing and explosion alternate permeability increasing method, which comprises the following steps of: performing pressure relief and permeability increasing on a coal seam through large-drill-diameter extraction, hole formation through a seam penetrating machine, and changing rock stratum structures of a coal seam top and a bottom plate through hydraulic fracturing so as to increase a gas diffusion channel, during large-drill-diameter extraction, drill holes are controlled to incline upwards by 20 m and incline downwards by 15 m respectively, the trend of the left contour line and the trend of the right contour line are controlled to be 15 m respectively, one group of drill holes are constructed at the interval of 5 m, and the drill hole construction diameter is phi 133 mm; hydraulic fracturing is carried out through the large-drill-diameter layer-penetrating drill holes to respectively fracture a top plate and a bottom plate of the coal seam, damage the rock stratum structure of the top plate and the bottom plate of the coal seam, change stress distribution of the coal seam and increase gas diffusion channels; after the outburst prevention measure layer-crossing construction in the large-drill-diameter area is carried out, fixed-point hole forming is carried out on a coal seeing section according to the actual coal seeing condition of the layer-crossing drilling holes at intervals of one group of construction layer-crossing hole forming drilling holes, and hole forming phi is 500 mm. According to the method, the gas extraction effect of the low-permeability coal seam can be greatly improved, and the probability of coal and gas outburst during tunneling is reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of single coal seam mining in Emeishan basalt group, and relates to a permeability enhancement method of a single coal seam with high capping index and low permeability by alternating formation, compression and blasting. Background Art

[0002] Gas extraction is the main means of coal mine gas control. Effective gas extraction can reduce or even prevent the occurrence of coal and gas outbursts. The conventional method of intensified extraction through dense drilling is not only large in engineering volume and high in cost, but also has unsatisfactory results. Therefore, for single coal seams with low permeability and high gas content, hydraulic cutting, hydraulic cavitation, hydraulic fracturing, deep hole blasting, gas phase fracturing and other permeability enhancement methods are often used to enhance extraction. In recent years, a large number of scientific research and coal mine field technical workers have conducted extensive research on different permeability enhancement methods and achieved a series of theoretical and practical results. However, there are few studies on the three-in-one synergistic permeability enhancement technology of deep hole fracturing, pressure relief extraction and mechanical cavitation, and the permeability enhancement effect of a single scheme is limited. The coal seam is arranged in the coal-bearing interlayer of the Emeishan basalt group. There are 1-2 layers of 100-200mm coal interlayers in some areas, and the roof belongs to basalt. The gas content of the coal seam is 12.28m 3 / t, gas pressure 2.84Mpa, coal seam permeability coefficient 0.07066m 2 / Mpa 2 .d. There are problems such as high sealing index, high gas content, high gas pressure, low coal seam permeability coefficient, and strong adsorption. Summary of the Invention

[0003] The technical problem to be solved by the present invention is: to provide a method for increasing the permeability of a single coal seam with a high sealing index and low permeability by alternating pressure and blasting, thereby improving the permeability of the coal body, increasing the gas diffusion channel, and increasing the flow velocity in the hole by unloading pressure and extraction, thereby changing the gas from an adsorbed state to a free state to increase the drilling extraction rate, reduce the outburst of gas adsorbed by the coal body during face mining, and improve the gas control capacity and level.

[0004] The solution implemented by the present invention is:

[0005] A method for increasing the permeability of a single coal seam with a high capping index and low permeability by alternating formation, compression and blasting, the method comprising the following steps:

[0006] Step 1: Drill holes through the return air extraction tunnel;

[0007] Step 2: hydraulic fracturing, mechanical cavitation and blasting are carried out in sequence between two adjacent rows of through-layer drill holes.

[0008] Furthermore, the diameter of the through-layer drilling hole is The extraction radius is 3.08m, and a group of through-layer drilling holes is constructed every 6m to control the 20m above and 15m below the contour line of the excavation tunnel.

[0009] Furthermore, the above set of hydraulic fracturing drilling parameters are implemented according to the following table.

[0010]

[0011] Furthermore, the aperture of the mechanical cavitation is 500 cm, and a set of mechanical cavitation parameters are implemented as shown in the following table.

[0012]

[0013] Furthermore, the above construction involves a group of deep hole blasting drilling, with a deep hole blasting hole diameter of 75-150 mm, a charge diameter of 50-100 mm, a charge amount of 0.5-5 kg / m, a segmented charge method, and energy distribution controlled by a spacer. The parameters of a group of blasting drilling are implemented as shown in the table below.

[0014]

[0015] The effects of the present invention are as follows: the present invention can improve the permeability of the coal body, increase the gas diffusion channel, unload the pressure and extract to increase the flow rate in the hole, change the gas from an adsorbed state to a free state to increase the drilling extraction rate, reduce the coal body adsorbed gas outburst during face mining, improve the gas control capacity and level, and effectively solve the problems of high sealing index, high gas content, high gas pressure, low coal seam permeability coefficient, strong adsorption, etc. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 This is a schematic diagram of the lithologic characteristics of the top and bottom plates of the coal-bearing interlayers in the basalt group;

[0017] Figure 2 This is a schematic diagram of the "drilling, pressing, and blasting" alternating permeability enhancement technology used in the construction of the 123202 return air extraction tunnel;

[0018] Figure 3 This is the cross-sectional drawing of the hydraulic fracturing drilling design for the 123202 return airway;

[0019] Figure 4 This is the cross-sectional drawing of the hole drilling design for the return air channel 123202;

[0020] Figure 5 This is the cross-sectional drawing of the deep hole blasting drilling design for the 123202 return air channel. DETAILED DESCRIPTION

[0021] The present invention will be further described below with reference to specific embodiments.

[0022] Example 1: A method for increasing the permeability of a single coal seam with a high capping index and low permeability by alternating formation, compression, and blasting, the method comprising the following steps:

[0023] Step 1: Drill holes through the return air extraction tunnel;

[0024] Step 2: hydraulic fracturing, mechanical cavitation and blasting are carried out in sequence between two adjacent rows of through-layer drill holes.

[0025] The diameter of the through-layer drilling hole is The extraction radius is 3.08m, and a group of through-layer drilling holes is constructed every 6m to control the 20m above and 15m below the contour line of the excavation tunnel.

[0026] A set of hydraulic fracturing drilling parameters are implemented as shown in the table below.

[0027]

[0028] The aperture of the mechanical cavitation is 500 cm, and a set of mechanical cavitation parameters are implemented as shown in the table below.

[0029]

[0030] A group of deep hole blasting drilling was constructed, with a deep hole blasting hole diameter of 75-150mm, a charge diameter of 50-100mm, a charge amount of 0.5-5kg / m, a segmented charge method, and energy distribution controlled by a spacer. The parameters of a group of blasting drilling were implemented as shown in the table below.

[0031]

[0032] For example, the 32# coal seam within the mine field of Guizhou Songhe Coal Industry Development Co., Ltd. is a single coal seam mined from the Emeishan basalt formation. Its roof is 35 meters thick, and its floor is 15 meters thick, consisting of tuff. The average coal thickness of the 32# coal seam is 2.8 meters, and its coal reserves are 36 million tons, primarily clean coal and lean coal, with a clean coal recovery rate of 85%. Our company has selected the 32# coal seam as its primary mining seam. Due to the complex and unique characteristics of this seam, single gas control measures are often inadequate to meet current gas control needs. Continuous innovation and optimization are required in the current gas control process. Based on the actual conditions of the 32# coal seam and our daily gas control experience, we have proposed a high-capping index, low-permeability single coal seam alternating permeability enhancement technology based on pressure-pressurization and blasting.

[0033] Overview of the working face: The 123202 return air tunnel is located in the second mining area. It starts from the 123202 return air connecting tunnel in the west, excavates along the roof of the 32# coal seam at an angle of 118°, passes through the tunnel under the 120 transport stone gate and the 120 special return air stone gate to the east, and reaches the designed position of the upper exit of the 123202 cutting eye in the east. It is designed to be 1271m. It mainly undertakes the return air task of the 123202 mining face. It is a full coal seam excavation. The overlying 29-3# coal seam has not been mined, and the inter-layer distance between the 32# and 29-3# coal seams is 60-90m; there is no underlying coal seam and no mining project, and there is no mining project in the upper and lower sections. The 123202 transport tunnel is located in the second mining area. It starts from the 123201 transport inclined tunnel in the west, excavates along the roof of the 32# coal seam at an angle of 118°, passes through the tunnel under the 121 transport stone gate and the 121 special return air stone gate in the east, and reaches the designed position of the lower exit of the 123202 cutting eye in the east. It is designed to be 1313m long and mainly undertakes the transportation task of the 123202 mining face. It is a full coal seam excavation. The overlying 29-3# coal seam has not been mined, and the inter-layer distance between the 32# and 29-3# coal seams is 60-90m; there is no underlying coal seam and no mining project, and there is no mining project in the upper and lower sections. The coal seam in the working face strikes 122°, dips 212°, and has an inclination of 26° to 30°, generally 30°. The coal seam is generally 2.6-3.0m thick, with an average thickness of 2.8m. The working face corresponds to a ridge and mountainous terrain with a ground elevation of 1790 to 1825m. The return air lane is expected to have an elevation of 1580 to 1592m, and the transport lane is expected to have an elevation of 1498 to 1512m. The height difference between the working face and the ground is 645m to 454m. There are no rivers, reservoirs, or water bodies on the corresponding surface. Coal seam strength coefficient

[0034] 0.25, gas pressure: 2.25~2.84Mpa, gas content: 8.84~12.28m 3 / t, coal seam permeability 0.07066m2 / MPa2.d. The tunnel is designed with a rectangular cross section and uses anchor mesh + steel belt support. The tunnel width × middle height = 5.5m × 3.5m. The 32# coal seam belongs to the Emeishan basalt group single coal seam mining. The roof is basalt with a thickness of 35m and the floor is tuff with a thickness of 15m. The average coal thickness of the 32# coal seam is 2.8m. For detailed lithologic characteristics of the roof and floor of the basalt group coal-measure interlayer, see Figure 1 and Table 1.

[0035] Table 1 Lithologic characteristics of the top and bottom plates of the coal-bearing interlayers in the basalt group

[0036]

[0037] The key technologies for gas control during tunneling in a single coal seam of the Emeishan basalt formation adopted in this invention are:

[0038] The key technologies for gas control in single coal seam excavation of Emeishan Basalt Formation are divided into three steps: first, through-layer drilling is constructed in 123202 return air extraction tunnel as the main regional anti-blowout measure during the excavation of return air tunnel; second, hydraulic fracturing drilling is constructed in 123202 return air extraction tunnel as an auxiliary measure to induce stress zone crack expansion, weaken the roof, reduce the hanging roof area, and reduce coal seam stress concentration; third, mechanical hole drilling is constructed in 123202 return air extraction tunnel as a permeability enhancement measure to expand the coal body pressure relief range, increase coal seam permeability, release local stress and increase gas extraction efficiency, release local stress, relieve stress concentration, and increase gas extraction efficiency; fourth, blasting. Schematic diagram of key technologies for gas control in single coal seam excavation of Emeishan Basalt Formation can be found at Figure 2 .

[0039] 1) Pre-extraction of coal seam gas by drilling through the seam: According to the "Investigation Report on Gas Extraction Radius of 3#, 4#, 12# and 32# Coal Seams of Guizhou Songhe Coal Industry Development Co., Ltd." issued by the Southwest Gas Prevention and Control Engineering Research Center of Guizhou Anhe Mining Technology Engineering Co., Ltd., the extraction rate of 32# coal seam of Songhe Company is η=45%, and the effective extraction radius of the extraction time of 20, 30, 60, 90 and 120 days is 2.49, 2.75, 3.04, 3.08 and 3.11m respectively. The borehole diameter is Under a negative extraction pressure of 13.4 to 19.7 kPa, the 123202 return air extraction lane was designed with a 90-day extraction period and a 3.08m extraction radius. A set of through-layer boreholes was constructed every 6m to control the 20m above and 15m below the lane outline. This served as a regional anti-blowout measure during the excavation of the 123202 return air lane. Pre-extraction of coal seam gas eliminated sudden outbursts within the lane excavation area. The maximum spacing between the final boreholes was 5.9m, the minimum spacing was 5.5m, and the average spacing was 5.7m. A total of 96 return air extraction lanes were designed, each with a construction volume of 348m, for a total construction volume of 33,408m.

[0040] 2) Auxiliary measures for crack expansion in hydraulic fracturing drilling-induced stress zones

[0041] In the construction area of 123202 return air channel and extraction channel, a group of hydraulic fracturing holes are constructed at intervals among the anti-burst measures drilling holes. As an auxiliary measure, the permeability of the coal seam is improved by the fracturing grid. The 32# coal seam has problems such as high capping index, high gas content, high gas pressure, low coal seam permeability coefficient, and strong adsorption. Hydraulic fracturing can be used to form an artificial fracture grid to connect natural fractures, greatly improve gas mobility, reduce coal seam gas pressure, thereby enhancing gas desorption, migration and recovery efficiency, solving the problem of coal mine rock burst, increasing gas extraction rate, improving gas extraction effect, quickly releasing coal seam gas, reducing the risk of gas outburst or explosion during excavation, and improving excavation safety. For details of the hydraulic fracturing drilling design profile, please see Figure 3 ,The design parameters are detailed in Table 2.

[0042] Table 2 Design parameters of hydraulic fracturing drilling holes in the 123202 return air lane

[0043]

[0044] 3) Mechanical cavitation and permeability enhancement measures

[0045] 3.1. Gas Extraction and Management (Core Application) Coal mine gas is a major safety hazard, easily causing explosions or outbursts. Hole drilling can significantly improve gas extraction efficiency. First, it increases the gas flow channel: conventional boreholes are prone to collapse and blockage, while hole drilling can form a stable cavity, improving permeability and accelerating gas desorption and flow. Second, it relieves pressure and increases permeability: after hole drilling, stress in the coal seam is redistributed, reducing gas pressure and minimizing outburst risks. Third, it improves extraction efficiency: applicable to extraction from the coal seam, adjacent layers, and goafs, it shortens extraction time and ensures coal mining safety.

[0046] 3.2. Rock burst is a common hazard in deep coal mines. Drilling holes can relieve pressure. First, stress transfer: Drilling holes in high-pressure areas transfers stress in the coal and rock mass deeper, reducing rock burst risk. Second, energy release: Drilling holes induces coal fracture, prematurely releasing accumulated elastic energy. Third, monitoring and early warning: Sensors are installed after hole creation to monitor stress changes.

[0047] 3.3. In coalbed methane development, cavitation drilling can increase production capacity. First, it increases the desorption area: expanding the cavity volume promotes gas desorption. Second, it improves permeability: applicable to low-permeability coal seams, it reduces extraction resistance. Third, it supports tunnel support and roof management: drilling cavitation holes in the tunnel side or roof reduces surrounding rock stress and deformation. Fourth, it strengthens anchoring: locally enlarging the anchor cable (rod) drill hole improves grouting anchoring strength.

[0048] 3.4. In the construction area of the 123202 return airway and exhaust tunnel, a mechanical hole drilling group is constructed every other drill hole. The mechanical hole drilling uses mechanical means such as spiral drills and reaming drill bits to expand the borehole diameter from the original 113mm to 500cm to prevent abnormal gas and stress concentration during the excavation of the 123202 return airway and the risk of bursting. For details of the hole drilling design cross-section, see Figure 4 ,The design parameters are detailed in Table 3.

[0049] Table 3 123202 return air channel hole drilling design parameters

[0050]

[0051] 4. Deep hole blasting assisted extraction measures

[0052] 4.1. Deephole blasting in coal seams is a technique that uses explosive blasting inside drill holes to transform the coal seam structure and improve coalbed methane (or gas) extraction efficiency. It is primarily used for coal mine gas control and development, and can significantly improve gas extraction efficiency. First, it increases coal seam permeability: the shock wave and gas expansion generated by blasting create a network of fractures in the coal seam, breaking the closed structure of the original cleat system and significantly increasing gas flow channels, potentially increasing permeability by several to dozens of times. Second, it promotes gas desorption: the vibrations from blasting disrupt the adsorption equilibrium in the coal mass, accelerating the desorption of adsorbed methane and shortening extraction time (traditional extraction takes months, but blasting can reduce this to weeks). Third, it reduces coal strength: blasting shatters the coal mass, enabling hydraulic fracturing and cavitation drilling (particularly in hard, low-permeability coal seams). Fourth, it prevents coal mine gas disasters: pre-blasting releases coal seam gas, reducing the risk of gas outbursts or explosions during mining.

[0053] 4.2. In the construction area of the 123202 return airway and exhaust tunnel, a group of deep hole blasting holes will be drilled at intervals. The deep hole blasting hole diameter is 75-150mm, the charge diameter is 50-100mm, and the charge amount is 0.5-5kg / m. The segmented charging method is used, and the energy distribution is controlled by spacers to form uniform cracks. This will improve the permeability of the coal seam and enhance the gas extraction efficiency. For details of the deep hole blasting design profile, please see Figure 5 ,The design parameters are detailed in Table 4.

[0054] Table 4 Design parameters of deep hole blasting drilling in 123202 return air lane

[0055]

[0056] 5. Pressure wind displacement and positive pressure extraction

[0057] Positive pressure extraction is an active extraction method used in coal mine gas management. By injecting high-pressure gas (such as air, nitrogen, or carbon dioxide) into the coal seam, a positive pressure environment is created. This pressure displaces gas from the coal seam, disrupting the existing adsorption equilibrium and promoting gas desorption. This drives gas (methane) toward the extraction borehole or pipeline, thereby improving gas extraction efficiency. Compared to traditional negative pressure extraction (which relies solely on vacuum pump suction), positive pressure extraction more effectively promotes gas desorption and migration, making it particularly suitable for low-permeability coal seams.

[0058] High-pressure gas (such as air, nitrogen, or carbon dioxide) is injected into the coal seam, using the gas pressure to displace the gas in the coal seam, breaking the original adsorption equilibrium and promoting gas desorption. While the high-pressure gas is being injected, the free gas is centrally extracted through negative pressure extraction using a large-diameter drill (hydraulic fracturing drilling, deep hole blasting drilling) through a large-diameter drill.

[0059] Key technical drilling construction and post-extraction effects: 123202 return air extraction tunnel is 567m long, with a large-diameter borehole constructed every 6m, and a hydraulic fracturing borehole, cavitation borehole, and deep hole blasting borehole constructed every 18m. Hydraulic fracturing boreholes, cavitation boreholes, and deep hole blasting boreholes are constructed in an interlaced manner. The return air extraction tunnel construction project volume is 33,060m of large-diameter boreholes, 4,982m of hydraulic fracturing boreholes, 4,982m of cavitation boreholes, and 4,982m of deep hole blasting boreholes, with a total cavitation volume of 1,474m. 3 The coal mining volume was 2064.3t, and the single-hole extraction concentration increased from the original 30% to 89% on average, a year-on-year increase of 296%; the main pipe concentration increased from the original 26% to 54%, a year-on-year increase of 208%.

[0060] The above description is only a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any technician familiar with the technical field can easily think of changes or replacements within the technical scope disclosed by the present invention, which should be included in the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be based on the scope of protection of the claims.

Claims

1. A method for increasing the permeability of a single coal seam with a high capping index and low permeability by alternating formation, compression and blasting, characterized in that: The method comprises the following steps: Step 1: Drill holes through the return air extraction tunnel; Step 2: hydraulic fracturing, mechanical cavitation and blasting are carried out in sequence between two adjacent rows of through-layer drill holes.

2. The method for increasing the permeability of a single coal seam with high capping index and low permeability by alternating formation, compression and blasting according to claim 1 is characterized in that: The diameter of the through-layer drilling hole is The extraction radius is 3.08m, and a group of through-layer drilling holes is constructed every 6m to control the 20m above and 15m below the contour line of the excavation tunnel.

3. The method for increasing the permeability of a single coal seam with high capping index and low permeability by alternating coal mining, pressure and blasting according to claim 1 is characterized in that: A set of hydraulic fracturing drilling parameters are implemented as shown in the table below.

4. The method for increasing the permeability of a single coal seam with a high capping index and low permeability according to claim 1, characterized in that: The aperture of the mechanical cavitation is 500 cm, and a set of mechanical cavitation parameters are implemented as shown in the table below.

5. The method for increasing the permeability of a single coal seam with high capping index and low permeability by alternating formation, compression and blasting according to claim 1 is characterized in that: A group of deep hole blasting drilling was constructed, with a deep hole blasting hole diameter of 75-150mm, a charge diameter of 50-100mm, a charge amount of 0.5-5kg / m, a segmented charge method, and energy distribution controlled by a spacer. The parameters of a group of blasting drilling were implemented as shown in the table below.

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