Cooperative permeability increasing method for drilling, pressing and building of single coal seam of Emei mountain basalt group

Abstract

The invention discloses an Emei mountain basalt group single coal seam drilling, pressing and manufacturing cooperative permeability increasing method which comprises the steps that pressure relief permeability increasing is conducted on a coal seam through large-drilling-diameter extraction, layer penetrating mechanical hole forming, and hydraulic fracturing is conducted to change a coal seam top and bottom plate rock stratum structure to increase a gas diffusion channel, drilling holes in large-drilling-diameter extraction are controlled to be 20 m above the coal seam and 15 m below the coal seam respectively, and the gas diffusion channel is increased; a left contour line and a right contour line are controlled to be 15 m respectively, one group is constructed at the interval of 5 m, and the drilling 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 mining of Emeishan basalt group, and relates to a coordinated permeability enhancement method of drilling, pressing and manufacturing a single coal seam of Emeishan basalt group. Background Art

[0002] The coal seam within a certain mining area belongs to the Emeishan Basalt Formation, a single coal seam. Its roof is 35 meters thick, its floor is 15 meters thick, and its coal seam has an average thickness of 2.8 meters. Coal reserves are 36 million tons, primarily clean coal and lean coal, with a clean coal recovery rate of 85%. In line with the strategic development strategy of "rich mines and fine mining," this seam was selected as the primary mining seam. However, due to the complex and unique characteristics of this seam, single gas control measures are often inadequate, necessitating continuous innovation and optimization. Consequently, numerous scholars, both domestically and internationally, have proposed various gas control measures for low-permeability coal seams, including mechanical cavitation, through-layer hydraulic punching, CO2 pre-fracture permeability enhancement, and hydraulic fracturing. Mechanical cavitation is widely used across coal mining sectors. Conventional standalone technologies for low-permeability coal seams suffer from poor gas extraction efficiency and a high probability of coal and gas outbursts during tunneling. Summary of the Invention

[0003] The technical problem to be solved by the present invention is to provide a collaborative permeability enhancement method for drilling, pressing and creating a single coal seam in the Emeishan basalt group, greatly improving the gas extraction effect of low-permeability coal seams and reducing the probability of coal and gas outbursts during excavation.

[0004] The solution implemented by the present invention is: A coordinated permeability enhancement method of drilling, pressing and fracturing for a single coal seam in the Emeishan basalt group is as follows: large-diameter extraction + through-layer mechanical cavitation to relieve pressure and enhance permeability of the coal seam + hydraulic fracturing to change the rock structure of the coal seam roof and floor to increase the gas diffusion channel. Among them, the drilling holes in the large-diameter extraction control the coal seam dip 20m above and 15m below the dip, control the left and right contour lines 15m each, construct a group at an interval of 5m, and the drilling diameter is φ133mm; large-diameter through-layer drilling is used for hydraulic fracturing to fracture the roof and floor of the coal seam respectively, destroy the rock structure of the roof and floor of the coal seam, change the stress distribution of the coal seam, and increase the gas diffusion channel; after the large-diameter regional anti-blowout measures are constructed through the through-layer, one group of through-layer cavitation drilling is constructed at intervals to carry out targeted cavitation of the coal section according to the actual coal rock conditions seen in the through-layer drilling, and the cavitation hole is φ500mm.

[0005] Furthermore, in the above hydraulic fracturing, a packer is used to seal the fracturing borehole, and a high-pressure pump is connected to perform hydraulic fracturing. Single-hole multiple fracturing or single-hole single fracturing is adopted, and the single fracturing time is 10 minutes from fracturing to initiation.

[0006] Furthermore, the order of the above-mentioned large-diameter extraction, through-layer mechanical cavitation to relieve pressure and increase permeability of the coal seam, and hydraulic fracturing to change the rock structure of the top and bottom of the coal seam is: one row of large-diameter extraction, one row of through-layer mechanical cavitation, one row of large-diameter extraction and one row of hydraulic fracturing constitute a group of permeability-enhancing structures, and multiple groups of permeability-enhancing structures are arranged in sequence at set intervals between the transport tunnel and the transport and extraction tunnel.

[0007] The present invention achieves the following results: It maximizes the combined application of pressure-relief and permeability-enhancing gas control technologies, significantly improving gas extraction efficiency in low-permeability coal seams and reducing the probability of coal and gas outbursts during tunneling. Compared with traditional gas control technologies, the extracted gas concentration is effectively increased by 27%, shortening the extraction time by approximately 158 days, and the return airflow gas content during tunneling does not exceed 0.24%. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Figure 1 This is a schematic diagram of the drilling arrangement for outburst prevention measures in large drill diameter areas; Figure 2 It is a comparison diagram before and after hydraulic fracturing, where (a) before hydraulic fracturing, (b) after hydraulic fracturing; Figure 3 This is a schematic diagram of the arrangement structure of the drilling-pressing-making trinity coordinated pressure relief and permeability enhancement drilling hole; Figure 4 This is a comparison chart of main gas extraction concentration. DETAILED DESCRIPTION

[0009] The present invention will be further described below with reference to specific embodiments.

[0010] Example 1: A synergistic permeability enhancement method for drilling, pressing and fracturing a single coal seam in the Emeishan basalt group, the method comprising: unloading the coal seam and enhancing its permeability through large-diameter extraction + mechanical cavitation through the layer + hydraulic fracturing to change the rock structure of the coal seam roof and floor to increase the gas diffusion channel, wherein, in large-diameter extraction, the drilling holes are respectively controlled 20m above the dip and 15m below the dip, and the left and right contour lines are controlled 15m each, with a group constructed at intervals of 5m, and the drilling diameter is φ133mm; hydraulic fracturing is performed using large-diameter through-layer drilling holes to respectively fracture the roof and floor of the coal seam to destroy the rock structure of the roof and floor of the coal seam, change the stress distribution of the coal seam, and increase the gas diffusion channel; after the large-diameter regional anti-blowout measures are constructed through the layer, a group of through-layer cavitation drilling holes are constructed at intervals to carry out targeted cavitation of the coal section according to the actual coal rock conditions seen in the through-layer drilling holes, and the cavitation holes are φ500mm.

[0011] Furthermore, the order of the large-diameter extraction, mechanical hole-making through the layer to relieve the pressure and increase the permeability of the coal seam, and hydraulic fracturing to change the rock structure of the top and bottom of the coal seam is as follows: one row of large-diameter extraction, one row of mechanical hole-making through the layer, one row of large-diameter extraction and one row of hydraulic fracturing constitute a group of permeability-enhancing structures, and multiple groups of permeability-enhancing structures are arranged in sequence at set intervals between the transport tunnel and the transport and extraction tunnel, such as Figure 3 shown.

[0012] In hydraulic fracturing, a packer is used to seal the fracturing borehole, and a high-pressure pump is connected for hydraulic fracturing. Single-hole multiple fracturing or single-hole single fracturing is used. The single fracturing time is 10 minutes after fracturing to initiation. Figure 2 .

[0013] Mechanical cavitation through the coal seams can, firstly, release adsorbed gas by destroying the coal mass; secondly, it can change the stress distribution in the coal seam and promote gas flow. This solves the problems of traditional drilling, such as "inability to extract gas or slow extraction."

[0014] The three-in-one coordinated pressure-relief and permeability-increasing technology is used to improve the efficiency of single-hole extraction through large-diameter extraction, unload the coal seam and increase its permeability through mechanical hole-making through the layer, and change the rock structure of the coal seam roof and floor through hydraulic fracturing to increase the gas diffusion channel. The coal seam is coordinated for gas control. While ensuring the effective arrangement of regional anti-burst measures, the coal seam can be unloaded and increased in permeability to the greatest extent to achieve "one hole for multiple uses".

[0015] A specific example: The 32# coal seam within the mining area 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, with coal reserves of 36 million tons, primarily clean coal and lean coal, and a clean coal recovery rate of 85%. In line with the strategic development strategy of "rich ore and fine mining," our company selected the 32# coal seam as its primary mining seam. Due to the complex and unique characteristics of this coal 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 proposed the application of a three-in-one, coordinated permeability enhancement technology, "drilling-pressing-creation," for this single coal seam in the Emeishan Basalt Formation.

[0016] Coal seam working face overview: 123202 working face is located in the east wing of mining area 2. The average thickness of 32# coal seam is 2.8m, the average dip angle is 28°, the average strike length is 650m, the designed coal production is 402,000 tons, and the roof is basalt with a thickness of 35m. The overlying 29# coal seam has an interlayer spacing of 85m and no underlying coal seam. It belongs to the original stress area mining of a single coal seam. Its capping index is 92% and the original gas content is 12.28m 3 / t, original gas pressure 2.84Mpa, coal seam permeability coefficient 0.07066m 2 / MPa 2 .d.

[0017] Adopting the "drilling-pressing-making" three-in-one coordinated pressure relief and permeability enhancement technology 1Large diameter drilling Through the research and practice of gas scholars, increasing the effective extraction length of the borehole and the exposed area in the hole can improve the permeability of the coal seam and enhance the gas extraction capacity. Compared with small-diameter boreholes, large-diameter boreholes can significantly increase the flow rate in the hole, increase the total and pure amount of gas extraction, and extend the service time. According to the "Detailed Rules for Preventing and Controlling Coal and Gas Outbursts" and "Guizhou Songhe Coal Industry Development Co., Ltd. 3#, 4#, 12#, 32# Coal Seam Gas Extraction Radius Measurement Report", the gas extraction boreholes are reasonably arranged, with an extraction rate of η45%, extraction for 120d, and an effective extraction radius of 3.11m. The boreholes control the inclination of the 32# coal seam 20m up and 15m down, and control the left and right contour lines of 15m each, with a construction interval of 5m. The drilling diameter is changed from the traditional φ94mm to φ133mm. Regional anti-outburst measures drilling design as follows Figure 1 shown.

[0018] 2Hydraulic fracturing The use of large-diameter through-layer drilling to perform hydraulic fracturing to fracture the top and bottom of the coal seam separately destroys the rock structure of the top and bottom of the coal seam, changes the stress distribution of the coal seam, and increases the gas diffusion channel. This technology uses a packer to seal the fracturing borehole, connects a high-pressure pump for hydraulic fracturing, and adopts single-hole multiple fracturing or single-hole single fracturing. The single fracturing time is 10 minutes after fracturing to fracture initiation. Figure 2 .

[0019] 3-layer mechanical puncture In large-diameter areas, after drilling through the interlayer to prevent sudden outbursts, a group of drill holes is drilled every other time. Based on the actual coal and rock exposure during the drilling, holes are drilled at specific locations within the exposed coal section. Each hole is 500 mm in diameter. This method features mechanical hole creation, which can release adsorbed gas by breaking up the coal mass and altering the stress distribution in the coal seam to promote gas flow. This solves the problems of traditional drilling, such as difficulty or slow extraction.

[0020] 4 large drilling diameter extraction + mechanical cavitation through layers + hydraulic fracturing The three-in-one coordinated pressure relief and permeability enhancement technology of large-diameter drilling to improve the efficiency of single-hole extraction + mechanical hole drilling to relieve coal seam pressure and increase permeability + hydraulic fracturing to change the rock structure of the coal seam roof and floor to increase gas diffusion channels is used to carry out coordinated gas control on the 32# coal seam. While ensuring the effective arrangement of regional anti-burst measures, it can also maximize the pressure relief and permeability enhancement of the coal seam to achieve "one hole for multiple uses". The design of the "drilling-pressure-making" three-in-one coordinated permeability enhancement technology is as follows: Figure 3 shown.

[0021] Technical effectiveness analysis 1) Analysis of measured gas extraction effects In the past, in the traditional gas control measures of 123201 working face, 8 boreholes were constructed in each group. After 70 groups of construction, the gas concentration in the main pipe was measured to be maintained at 5% to 8% for a long time, and the pure amount of gas extracted was 1m 3 / min~1.6m 3 / min. In the 123202 working face, the concentration of the main pipe under the same number of drilling holes and extraction was maintained at 30% to 35%, and the extraction volume was maintained at 8m 3 After adopting this technology, the concentration of gas extraction main pipe increased by 27% year-on-year, and the extraction volume increased by 7 to 8 times, effectively solving the problems of low permeability and difficult extraction of 32# coal seam. Figure 4 shown.

[0022] 2) Analysis of the effect of extraction time Comparing the drilling and extraction time and extraction effect of 123201 transport lane and 123202 transport lane, a total of 78 groups of through-layer drilling holes were constructed in 123201 transport lane for pre-extraction of 32# coal seam for 228 days, and the measured residual gas content was 5.8826m 3 / t, the measured residual gas pressure is 0.652Mpa, and the 123202 transportation adopts the "drilling-pressing-making" three-in-one collaborative permeability enhancement technology. A total of 75 groups of through-layer drilling holes were constructed to pre-drain the 32# coal seam for 70 days. The measured residual gas content is 2.7664m 3 / t, the measured residual gas pressure is 0.226Mpa.

[0023] 3) Analysis of prediction indicators for outburst hazards in 100-meter excavation working faces According to the "Detailed Rules for Preventing and Controlling Coal and Gas Outbursts", coal mines with outbursts should determine the sensitive indicators and critical values for working face prediction for each coal seam. Our company's 32# coal seam is based on the K1 value of 0.44mL / (g.min 1 / 2 ), the drilling cuttings volume was 5kg / m, and the K1 value of the K0-K0+100m section of the 123201 transport tunnel exceeded the critical index 5 times, with the maximum K1 value reaching 1.2mL / (g.min1 / 2), and the maximum increase in return air flow gas was 0.5%. After the key technology was adopted in the 123202 transport tunnel, 185m has been constructed at this stage, and the K1 value did not exceed the critical index during the period, with the maximum K1 value of 0.25mL / (g.min 1 / 2 ), the maximum gas concentration in the return air flow does not exceed 0.24%.

[0024] in conclusion: 1) This technology maximizes the combined application of pressure relief and permeability-enhancing gas control technologies, significantly improving gas extraction efficiency in low-permeability coal seams and reducing the probability of coal and gas outbursts during tunneling. Compared with traditional gas control technologies, extraction concentration increased by 27%, shortening extraction time by approximately 158 days, and ensuring that return airflow gas concentrations did not exceed 0.24% during tunneling.

[0025] 2) The application of the three-in-one synergistic permeability enhancement technology of “drilling-pressing-making” in a single coal seam of the Emeishan basalt formation has a technical and practical guiding significance for coal seams with characteristics such as high gas content, high pressure, poor permeability, strong adsorption, high sealing index, and high ground stress.

[0026] 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 synergistic permeability enhancement method for a single coal seam of the Emeishan basalt formation by drilling, pressing and creating, characterized in that: The method is as follows: through large-diameter extraction + through-layer mechanical cavitation to relieve pressure and increase permeability of coal seams + hydraulic fracturing to change the rock structure of the coal seam roof and floor to increase gas diffusion channels, among which, in large-diameter extraction, the drilling holes control the coal seam dip 20m above and 15m below the dip, control the left and right contour lines 15m each, construct a group at intervals of 5m, and the drilling diameter is φ133mm; use large-diameter through-layer drilling holes for hydraulic fracturing to fracture the roof and floor of the coal seam respectively, destroy the rock structure of the roof and floor of the coal seam, change the stress distribution of the coal seam, and increase the gas diffusion channel; after the large-diameter regional anti-burst measures are constructed through the layer, one group of through-layer cavitation drilling holes is constructed at intervals to carry out fixed-point cavitation in the coal section according to the actual coal and rock conditions seen in the through-layer drilling holes, and the cavitation holes are φ500mm.

2. The collaborative permeability enhancement method of drilling, pressing and producing a single coal seam of the Emeishan basalt formation according to claim 1, characterized in that: During hydraulic fracturing, a packer is used to seal the fracturing borehole, and a high-pressure pump is connected for hydraulic fracturing. Single-hole multiple fracturing or single-hole single fracturing is adopted, and the single fracturing time is 10 minutes from fracturing to initiation.

3. The synergistic permeability enhancement method of drilling, pressing and producing a single coal seam of the Emeishan basalt formation according to claim 1, characterized in that: The order of large-diameter extraction, mechanical cavitation through layers to relieve pressure and increase permeability of coal seams, and hydraulic fracturing to change the rock structure of the top and bottom plates of coal seams is: one row of large-diameter extraction, one row of mechanical cavitation through layers, one row of large-diameter extraction and one row of hydraulic fracturing constitute a group of permeability-enhancing structures, and multiple groups of permeability-enhancing structures are arranged in sequence at set intervals between the transport tunnel and the transport and extraction tunnel.

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