Single coal seam permeability enhancement structure through alternating formation, compression, and blasting

Abstract

This utility model discloses a single coal seam permeability enhancement structure using alternating fracturing, hydraulic fracturing, and blasting methods. It includes cross-seam boreholes, hydraulic fracturing boreholes, mechanical cavity-creating boreholes, and blasting boreholes. Multiple rows of cross-seam boreholes are arranged, connecting the return air extraction roadway and the return air roadway. Multiple rows of hydraulic fracturing boreholes, mechanical cavity-creating boreholes, and blasting boreholes are also arranged, alternating between adjacent rows of cross-seam boreholes and connecting the return air extraction roadway and the return air roadway. This utility model can significantly improve the gas extraction efficiency of low-permeability coal seams and reduce the probability of coal and gas outbursts during tunneling.

Description

Technical Field

[0001] This utility model belongs to the field of single coal seam mining technology, and relates to a single coal seam alternating permeability enhancement structure of forming, pressing and blasting. Background Technology

[0002] Gas drainage is the primary means of coal mine gas control. Effective gas drainage can reduce or even prevent coal and gas outbursts. However, most coal seams in my country have poor permeability, and conventional methods of enhanced drainage through intensified drilling are not only labor-intensive and costly but also ineffective. Therefore, for single coal seams with low permeability and high gas content, methods such as hydraulic fracturing, hydraulic cavity creation, hydraulic hydraulic fracturing, deep-hole blasting, and gas-phase fracturing are often used to enhance drainage. In recent years, numerous researchers and field technicians in coal mines have conducted extensive research on different permeability enhancement methods, achieving a series of theoretical and practical results. However, research on the integrated permeability enhancement technology of deep-hole fracturing, pressure relief drainage, and mechanical cavity creation is limited, and individual schemes have limited permeability enhancement effects. The coal seam is located in the coal-bearing interlayer of the Emeishan basalt group, with 1-2 layers of 100-200mm coal interbedded with gangue in some areas. The roof is basalt, and the gas content of the coal seam is 12.28m³. 3 / t, gas pressure 2.84 MPa, coal seam permeability coefficient 0.07066 m 2 / Mpa 2 .d has problems such as high sealing index, high gas content, high gas pressure, low coal seam permeability coefficient, and strong adsorption. Utility Model Content

[0003] The technical problem to be solved by this utility model is to provide a single coal seam alternating permeability enhancement structure of forming, pressing and exploding, which improves the permeability of the coal body, increases the gas diffusion channel, increases the flow velocity in the borehole by depressurization and extraction, changes the gas from adsorbed to free state to increase the borehole extraction rate, reduces the gas adsorbed in the coal body to emerge during mining face recovery, and improves the gas control capacity and level.

[0004] The solution implemented by this utility model is: a single coal seam alternating permeability enhancement structure of fracturing, hydraulic fracturing, and blasting, including cross-layer drilling, hydraulic fracturing drilling, mechanical cavity-making drilling, and blasting drilling. The cross-layer drilling is arranged in multiple rows, connecting the return air extraction roadway and the return air roadway. The hydraulic fracturing drilling, mechanical cavity-making drilling, and blasting drilling are arranged in multiple rows, staggered between adjacent rows of cross-layer drilling and connecting the return air extraction roadway and the return air roadway.

[0005] Furthermore, the diameter of the aforementioned cross-layer boreholes is φ113mm, the extraction radius is 3.08m, and a row of cross-layer boreholes is constructed every 6m to control the outline of the tunneling roadway for 20m above and 15m below.

[0006] Furthermore, the above-mentioned hydraulic fracturing boreholes consist of three boreholes with inclination angles of +15°, +11° and +9°, and borehole depths of 42, 33 and 28 m, respectively.

[0007] Furthermore, the diameter of the aforementioned mechanical cavity drilling is 500cm, and three mechanical cavity drilling holes are used in a row. The inclination angles of the three mechanical cavity drilling holes are +15°, +11° and +9°, and the hole depths are 42, 33 and 28m, respectively.

[0008] Furthermore, the diameter of the above-mentioned row of deep-hole blasting boreholes is 75-150mm, the diameter of the charge is 50-100mm, and three blasting boreholes are used in the row. The inclination angles of the three blasting boreholes are +15°, +11° and +9°, and the hole depths are 42, 33 and 28m, respectively.

[0009] The effects of this utility model are as follows: This utility model can improve the permeability of coal, increase the gas diffusion channel, increase the flow velocity in the borehole through pressure relief extraction, change the gas from an adsorbed state to a free state, thereby increasing the borehole extraction rate, reducing the outburst of adsorbed gas during face mining, improving the gas control capacity and level, and effectively solving problems such as high sealing index, high gas content, high gas pressure, low coal seam permeability coefficient, and strong adsorption. Attached Figure Description

[0010] Figure 1 This is a schematic diagram of the lithological characteristics of the top and bottom plates of the coal-bearing interlayers in the basalt group;

[0011] 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 roadway.

[0012] Figure 3 This is the design cross-section of the hydraulic fracturing borehole in the 123202 return airway;

[0013] Figure 4 This is a cross-sectional view of the borehole design for the 123202 return airway.

[0014] Figure 5 This is a cross-sectional view of the deep-hole blasting drill design in the 123202 return airway. Detailed Implementation

[0015] The present invention will be further described below with reference to specific embodiments.

[0016] Example 1: As Figure 3As shown, the single coal seam permeability enhancement structure, which alternates between fracturing, hydraulic fracturing, and blasting, includes cross-seam boreholes 1, hydraulic fracturing boreholes 2, mechanical cavity-making boreholes 3, and blasting boreholes 4. The cross-seam boreholes 1 are arranged in multiple rows, connecting the return air extraction roadway 5 and the return air roadway 6. The hydraulic fracturing boreholes 2, mechanical cavity-making boreholes 3, and blasting boreholes 4 are arranged in multiple rows, staggered between adjacent rows of cross-seam boreholes 1, and connecting the return air extraction roadway 5 and the return air roadway 6.

[0017] Furthermore, the diameter of the above-mentioned cross-layer borehole 1 is φ113mm, the extraction radius is 3.08m, and a row of cross-layer boreholes 1 is constructed every 6m to control the outline of the tunneling roadway for 20m above and 15m below.

[0018] Furthermore, the aforementioned hydraulic fracturing borehole 2 consists of three boreholes with inclination angles of +15°, +11°, and +9°, and borehole depths of 42, 33, and 28 m, respectively.

[0019] Furthermore, the diameter of the aforementioned mechanical cavity drilling 3 is 500cm, and three mechanical cavity drilling holes are used in a row. The inclination angles of the three mechanical cavity drilling holes are +15°, +11° and +9°, and the hole depths are 42, 33 and 28m, respectively.

[0020] Furthermore, the diameter of the four deep-hole blasting boreholes in the row is 75-150mm, and the diameter of the charge is 50-100mm. There are three blasting boreholes in the row, with inclination angles of +15°, +11° and +9°, and hole depths of 42, 33 and 28m, respectively.

[0021] Example 2: A method for enhancing the permeability of a single coal seam with high capping index and low permeability through alternating processes of formation, compression, and blasting. This method includes the following steps:

[0022] Step 1: Drill through the layers in the return air extraction tunnel;

[0023] Step 2: Perform hydraulic fracturing, mechanical cavity creation, and blasting sequentially between adjacent rows of cross-layer boreholes.

[0024] The diameter of the cross-layer borehole is φ113mm, the extraction radius is 3.08m, and a set of cross-layer boreholes is constructed every 6m to control the outline of the tunnel for 20m above and 15m below.

[0025] The parameters for a set of hydraulic fracturing boreholes are implemented according to the table below.

[0026]

[0027] The diameter of the mechanical cavity is 500cm, and a set of mechanical cavity-making parameters are implemented according to the table below.

[0028]

[0029] Construct a set of deep-hole blasting boreholes with a borehole diameter of 75-150mm, a charge diameter of 50-100mm, and a charge amount of 0.5-5kg / m. Use segmented charging and control energy distribution through spacers. The parameters for a set of blasting boreholes are as follows.

[0030]

[0031] Specific example: The roof is basalt with a thickness of 35m and the floor is tuff with a thickness of 15m. The average coal thickness of coal seam #32 is 2.8m, with coal reserves of 36 million tons. It mainly consists of coking coal and lean coal, with a coking coal recovery rate of 85%. Coal seam #32 was selected as the main mining coal seam. Due to the complexity and special characteristics of this coal seam, single gas control measures are often insufficient to meet the current gas control needs. Continuous innovation and optimization are required in the current gas control process. Based on the actual situation of coal seam #32 and daily gas control experience, a high-capping-index, low-permeability single coal seam alternating permeability enhancement technology of building-pressure-explosion was proposed.

[0032] Working face overview: The 123202 return airway is located in the No. 2 mining area. It starts from the 123202 return air connecting roadway in the west and is excavated along the roof of the No. 32 coal seam at an azimuth of 118°. It passes under the No. 120 transport stone gate and the No. 120 dedicated return air stone gate in the east and ends at the designed exit position of the 123202 cut-off, with a designed length of 1271m. It mainly undertakes the return air task of the 123202 mining face. It is a full coal seam excavation. The overlying No. 29-3 coal seam has not been mined, and the distance between the No. 32 and No. 29-3 coal seams is 60-90m. There are no underlying coal seams and no mining works. There are no mining works in the upper and lower sections. The 123202 transport roadway is located in the No. 2 mining area. It starts from the 123201 transport inclined roadway in the west and is excavated along the roof of the No. 32 coal seam at an azimuth of 118°. It passes under the No. 121 transport stone gate and the No. 121 dedicated return air stone gate in the east and ends at the designed exit position of the No. 123202 cut-off face in the east. The designed length is 1313m. It mainly undertakes the transport task of the No. 123202 mining face. It is a full coal seam excavation. The No. 29-3 coal seam is overlying and has not been mined. The distance between the No. 32 and No. 29-3 coal seams is 60-90m. There are no underlying coal seams and no mining works. There are no mining works in the upper and lower sections. The coal and rock strata within the working face strike 122°, dip 212°, and have a dip angle of 26°–30°, generally 30°. The coal seam thickness is generally 2.6–3.0 m, with an average thickness of 2.8 m. The working face corresponds to a mountainous terrain with ridges and hills. The ground elevation is 1790–1825 m. The expected elevation of the return airway is 1580–1592 m, and the expected elevation of the transport airway is 1498–1512 m. The elevation difference between the working face and the ground surface is 645 m–454 m. There are no rivers, reservoirs, or other water bodies on the corresponding surface. The coal seam firmness coefficient is 0.25, the gas pressure is 2.25–2.84 MPa, the gas content is 8.84–12.28 m³ / t, and the coal seam permeability is 0.07066 m² / MPa²·d. The roadway is designed with a rectangular cross-section, using anchor wire mesh and steel strip support. The roadway's width (bottom width) × height (middle height) is 5.5m × 3.5m. Coal seam #32 is a single coal seam mined from the Emeishan Basalt Formation. The roof is basalt with a thickness of 35m, and the floor is tuff with a thickness of 15m. The average coal seam thickness of #32 is 2.8m. For detailed lithological characteristics of the roof and floor of the basalt formation coal-bearing interlayers, please refer to [link to relevant documentation]. Figure 1 See Table 1.

[0033] Table 1. Lithological characteristics of the top and bottom plates of coal-bearing interlayers in the basalt group.

[0034]

[0035] The key technology for gas control in single coal seam tunneling in the Emeishan basalt formation adopted in this utility model is as follows:

[0036] The key technologies for gas control in single coal seam tunneling of the Emeishan basalt formation are implemented in three steps: First, drilling through the 123202 return air extraction roadway as the main area anti-outburst measure during return air roadway tunneling; second, drilling hydraulic fracturing boreholes in the 123202 return air extraction roadway as an auxiliary measure to induce fracture expansion in the stress zone, weaken the roof, reduce the overhang area, and reduce coal seam stress concentration; third, drilling mechanical cavity drilling in the 123202 return air extraction roadway as a permeability enhancement measure to expand the coal body decompression range, increase coal seam permeability, release local stress, and increase gas extraction efficiency; and fourth, blasting. A detailed schematic diagram of the key technologies for gas control in single coal seam tunneling of the Emeishan basalt formation is available in [link to diagram]. Figure 2 .

[0037] 1) Pre-drainage of coal seam gas through cross-layer drilling: According to the "Investigation Report on Gas Drainage Radius of Coal Seams No. 3, No. 4, No. 12 and No. 32 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 drainage rate η of No. 32 coal seam of Songhe Company is 45%, and the effective drainage radii for drainage times of 20, 30, 60, 90 and 120 days are 2.49, 2.75, 3.04, 3.08 and 3.11 m respectively. Under the conditions of φ113mm borehole diameter and extraction negative pressure of 13.4~19.7kPa, the 123202 return air extraction roadway is designed with an extraction time of 90 days and an extraction radius of 3.08m. A set of cross-layer boreholes is constructed every 6m to control the roadway outline for 20m and 15m below as regional outburst prevention measures during the excavation of the 123202 return air roadway. Pre-extraction of coal seam gas is used to eliminate outbursts in advance within the roadway excavation range. The maximum borehole spacing is 5.9m, the minimum is 5.5m, and the average is 5.7m. A total of 96 sets of boreholes are designed for the return air extraction roadway, with each set having a length of 348m, for a total length of 33408m.

[0038] 2) Auxiliary measures for fracture propagation in the stress zone induced by hydraulic fracturing boreholes

[0039] In the 123202 return airway drainage roadway construction area, a set of anti-outburst boreholes was drilled intermittently with a set of hydraulic fracturing boreholes as an auxiliary measure. The fracturing grid was used to improve coal seam permeability. The 32# coal seam suffers from high capping index, high gas content, high gas pressure, low permeability coefficient, and strong adsorption. Hydraulic fracturing can create an artificial fracture grid, connecting natural fractures, significantly improving gas flow, reducing coal seam gas pressure, thereby enhancing gas desorption, migration, and recovery efficiency, solving the problem of coal mine rockburst, increasing gas extraction rate, improving gas extraction effect, enabling rapid release of coal seam gas, reducing the risk of gas outbursts or explosions during tunneling, and improving tunneling safety. See the detailed hydraulic fracturing borehole design profile diagram. Figure 3 The design parameters are detailed in Table 2.

[0040] Table 2 Design parameters for hydraulic fracturing borehole in return airway 123202

[0041]

[0042] 3) Mechanical cavity creation and permeability enhancement measures

[0043] 3.1. Gas Drainage and Control (Core Application) Coal mine gas is a major safety hazard, easily leading to explosions or outbursts. Cavity drilling can significantly improve gas drainage efficiency; firstly, it increases gas flow channels: ordinary boreholes are prone to collapse and blockage, while cavity drilling can create stable cavities, improving permeability and accelerating gas desorption and flow. Secondly, it relieves pressure and enhances permeability: after cavity drilling, coal seam stress is redistributed, reducing gas pressure and lowering the risk of outbursts. Thirdly, it improves drainage efficiency: applicable to drainage within the same coal seam, adjacent seams, and goaf areas, shortening drainage time and ensuring coal mining safety.

[0044] 3.2. Rockburst is a common disaster in deep coal mines. Cavity drilling can relieve pressure in several ways: First, stress transfer: creating cavities in high-pressure areas transfers stress in the coal and rock mass to deeper layers, reducing the risk of rockburst. Second, energy release: cavitation induces coal body fracturing, releasing accumulated elastic energy in advance. Third, monitoring and early warning: sensors are installed after cavitation to monitor stress changes.

[0045] 3.3. In coalbed methane development, cavity drilling can improve production capacity in several ways: First, it increases the desorption area by expanding the cavity volume and promoting gas desorption. Second, it improves permeability, making it suitable for low-permeability coal seams and reducing extraction resistance. Third, it aids in roadway support and roof management by drilling cavities in the roadway sides or roof to reduce surrounding rock stress and deformation. Fourth, it enhances anchoring by locally enlarging the boreholes in the anchor cables (rods) to improve grouting anchoring force.

[0046] 3.4. In the construction area of ​​the 123202 return airway drainage tunnel, anti-outburst measures include drilling one set of boreholes followed by one set of mechanical cavity drilling. Mechanical cavity drilling utilizes augers, reaming bits, and other mechanical methods to enlarge the borehole diameter from the original 113mm to 500cm to prevent outburst hazards caused by abnormal gas levels and stress concentration during the excavation of the 123202 return airway. Detailed design cross-sections of the cavity drilling are available in [reference needed]. Figure 4 The design parameters are detailed in Table 3.

[0047] Table 3 Design parameters for borehole construction in return airway 123202

[0048]

[0049] 4. Deep-hole blasting-assisted extraction measures

[0050] 4.1. Deep-hole blasting of coal seams is a technology that uses explosives inside boreholes to modify the coal seam structure and improve the efficiency of coalbed methane (or coal gas) extraction. It is mainly used for coal mine gas control and coalbed methane development. Deep-hole blasting can significantly improve gas extraction efficiency in several ways: First, it increases coal seam permeability: the shock wave and gas expansion force generated by the blast create a fracture network in the coal seam, breaking the closed nature of the original cleavage system and significantly increasing the gas flow channels, with permeability increasing several to tens of times. Second, it promotes gas desorption: the blasting vibration disrupts the adsorption balance of the coal body, accelerating the desorption process of adsorbed methane and shortening the extraction time (traditional extraction takes several months, but after blasting it can be shortened to several weeks). Third, it reduces coal body strength: the coal body is broken after blasting, which, combined with hydraulic fracturing and cavity drilling (especially in hard, low-permeability coal seams), reduces the risk of coal mine gas disasters: by releasing coal seam gas through pre-blasting, the risk of gas outbursts or explosions during coal mining is reduced.

[0051] 4.2. In the gas outburst prevention drilling area of ​​the 123202 return airway drainage roadway, deep-hole blasting boreholes are drilled at intervals between each set of boreholes. The deep-hole blasting borehole diameter is 75-150mm, the charge diameter is 50-100mm, and the charge rate is 0.5-5kg / m. A segmented charging method is used, and the energy distribution is controlled by spacers to form uniform fractures. This improves coal seam permeability and gas drainage efficiency. See the detailed deep-hole blasting design profile for details. Figure 5 The design parameters are detailed in Table 4.

[0052] Table 4 Design parameters for deep-hole blasting drilling in return airway 123202

[0053]

[0054] 5. Compressed air displacement positive pressure extraction

[0055] Positive pressure gas extraction is an active gas extraction method in coal mine gas control. It involves injecting high-pressure gas (such as air, nitrogen, or carbon dioxide) into the coal seam to create a positive pressure environment. This pressure displaces the gas in the coal seam, disrupting the original adsorption equilibrium, promoting gas desorption, and driving the gas (methane) to flow into the extraction borehole or pipeline, thereby improving gas extraction efficiency. Compared to traditional negative pressure gas extraction (relying solely on vacuum pumps), positive pressure gas extraction is more effective in promoting gas desorption and migration, and is particularly suitable for low-permeability coal seams.

[0056] High-pressure gas (such as air, nitrogen, or carbon dioxide) is injected into the coal seam to displace the methane gas, disrupting the original adsorption equilibrium and promoting methane desorption. Simultaneously, a drainage system (hydraulic fracturing borehole, deep-hole blasting borehole) is used to extract the free methane gas through negative pressure extraction via a large-diameter drill.

[0057] Key technologies for borehole construction and post-extraction effects: In the 567m return air extraction roadway 123202, a set of large-diameter boreholes was constructed every 6m, and a set of hydraulic fracturing boreholes, cavity-creating boreholes, and deep-hole blasting boreholes were constructed every 18m, with the hydraulic fracturing boreholes, cavity-creating boreholes, and deep-hole blasting boreholes being constructed concurrently. The total amount of large-diameter boreholes constructed in the return air extraction roadway was 33,060m, the amount of hydraulic fracturing boreholes was 4,982m, the amount of cavity-creating boreholes was 4,982m, and the amount of deep-hole blasting boreholes was 4,982m, with a total cavity volume of 1,474m³, producing 2,064.3t of coal. The average single-hole extraction concentration increased from 30% to 89%, a year-on-year increase of 296%; the main pipe concentration increased from 26% to 54%, a year-on-year increase of 208%.

[0058] The above description is merely a specific embodiment of this utility model, but the protection scope of this utility model is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in this utility model should be included within the protection scope of this utility model. Therefore, the protection scope of this utility model should be determined by the protection scope of the claims.

Claims

1. A single seam, build, compact and blast alternating permeability enhancing structure, characterized in that, The through-layer borehole, the hydraulic fracturing borehole, the mechanical cavity-making borehole and the blasting borehole are included, the through-layer boreholes are arranged in multiple rows, are connected between the air return drainage roadway and the air return roadway, the hydraulic fracturing boreholes, the mechanical cavity-making boreholes and the blasting boreholes are arranged in multiple rows, are staggered in turn between the two adjacent rows of through-layer boreholes and are connected between the air return drainage roadway and the air return roadway.

2. The single coal seam, compression and blasting alternating permeability structure according to claim 1, characterized in that, The through-layer borehole has a diameter of φ113mm and a drainage radius of 3.08m, and one row of through-layer boreholes is constructed every 6m to control the profile line of the tunneling roadway with a length of 20m and a depth of 15m.

3. The single coal seam, compression and blasting alternating permeability increasing structure according to claim 1, characterized in that, One row of hydraulic fracturing boreholes adopts three hydraulic fracturing boreholes, the inclinations of the three hydraulic fracturing boreholes are +15°, +11° and +9° respectively, and the depths of the three hydraulic fracturing boreholes are 42m, 33m and 28m respectively.

4. The single coal seam, compression and blasting alternating permeability increasing structure according to claim 1, characterized in that, The mechanical cavity-making borehole has a diameter of 500cm, one row of mechanical cavity-making boreholes adopts three mechanical cavity-making boreholes, the inclinations of the three mechanical cavity-making boreholes are +15°, +11° and +9° respectively, and the depths of the three mechanical cavity-making boreholes are 42m, 33m and 28m respectively.

5. The single coal seam, compression and blasting alternating permeability increasing structure according to claim 1, characterized in that, One row of deep-hole blasting boreholes has a diameter of 75-150mm and a charging diameter of 50-100mm, one row of blasting boreholes adopts three blasting boreholes, the inclinations of the three blasting boreholes are +15°, +11° and +9° respectively, and the depths of the three blasting boreholes are 42m, 33m and 28m respectively.

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