A Method for Selecting Hydraulic Pressure Relief Technology in Boreholes of Mine Coal and Rock Masses

Abstract

A method for selecting hydraulic pressure relief technology in boreholes of mine coal and rock masses includes: for the mine coal and rock masses to be pressure-relieved, taking out the coal and rock mass cores within the pressure-relief range through a mine coring tube; grading the taken coal and rock mass cores according to the degree of fragmentation: I, II, III, IV, and V; determining the hydraulic pressure relief technology type of the mine coal and rock masses according to the grading of the coal and rock mass cores. For type I, the hydraulic fracturing technology is adopted; for type V, the hydraulic punching technology is adopted; for type II, III, or IV, uniaxial compressive strength testing is carried out, and when the uniaxial compressive strength is greater than the preset threshold, the hydraulic slotting technology is adopted, otherwise the hydraulic punching technology is adopted. The present invention takes cores of the coal and rock masses within the pressure-relief range and grades them according to the state of the obtained coal and rock mass cores, so as to determine the best hydraulic pressure relief type for different coal and rock masses; and through comprehensive judgment based on the core-taking state and the uniaxial compressive strength of the coal and rock cores, the best hydraulic pressure relief type is determined.

Description

Technical Field

[0001] The present invention relates to the technical field of mine coal and rock pressure relief, and particularly relates to a method for selecting a hydraulic pressure relief technology in boreholes of mine coal and rock masses. Background Art

[0002] In recent years, with the increase of coal seam burial depth, non-outburst dangerous mines have been transformed into outburst mines, and non-impact dangerous mines have been transformed into impact mines. Special mines have double disasters of impact and outburst, which greatly threatens the safety of mine production and personnel. In the past, general mines usually adopted explosive blasting technology to achieve pressure relief in boreholes of coal and rock masses, but various problems would occur during the blasting process, such as relatively high risk, difficult approval; serious noise and dust pollution; generation of harmful gases, damaging human health; small fragmentation range, etc.

[0003] The hydraulic pressure relief technology in boreholes of coal and rock masses has a high safety factor, significant effects on increasing coal seam permeability and relieving rock pressure, does not generate harmful gases, and the underground water source is convenient. Hydraulic pressure relief has become a key technology for mine coal and rock pressure relief. The current hydraulic pressure relief technologies in boreholes of coal and rock masses include hydraulic fracturing, hydraulic slotting, and hydraulic punching. Their equipment is large in volume and mass, not easy to carry, and different mine disaster types are suitable for different hydraulic pressure relief technologies. If the equipment cannot be successfully tested underground, withdrawing it from the mine will waste manpower and material resources.

[0004] In addition, currently, mines select the hydraulic pressure relief technology in boreholes of coal and rock masses according to the mine disaster type, generally using the uniaxial compressive strength or the Proctor coefficient f of coal and rock masses as the selection reference. Impact mines mostly select hydraulic fracturing in boreholes, and coal and gas outburst mines mostly select hydraulic punching in boreholes. However, the rock mass has a large uniaxial compressive strength and well-developed joints, which is not suitable for the hydraulic fracturing technology in boreholes. On the contrary, the rock mass has a small uniaxial compressive strength and the uniaxial compressive strength ≥ 15 MPa, and the joints are not well-developed. The scope of the hydraulic slotting technology in boreholes is small, and the permeability increasing effect is not obvious compared with that of hydraulic fracturing in boreholes.

[0005] Therefore, how to select a suitable hydraulic pressure relief technology according to the mine disaster type to eliminate potential mine disaster hazards is a technical problem that needs to be solved urgently at present. Summary of the Invention

[0006] Based on this, the present invention provides a method for selecting a hydraulic pressure relief technology in boreholes of mine coal and rock masses to solve the technical problems that the selection of the existing hydraulic pressure relief technology in boreholes simply relies on the uniaxial compressive strength for selection, without considering the degree of joint development, resulting in inaccurate selection, and the handling and on-site tests of hydraulic pressure relief equipment cause waste of manpower and material resources and cannot effectively eliminate on-site potential hazards.

[0007] To achieve the above object, the present invention provides a method for selecting a hydraulic pressure relief technology in boreholes of mine coal and rock masses, which includes the following steps:

[0008] S1. For the mine coal and rock mass to be depressurized, take out the core of the coal and rock mass within the depressurized range through a mine coring tube. The coring diameter is D and the coring length is L.

[0009] S2. Classify the taken coal and rock mass cores according to their fragmentation degree, which are respectively:

[0010] Type I: The length of the rod in the taken coal and rock mass core is greater than 80% of the coring length L, and it has no fracture when picked up.

[0011] Type II: The length of the rod in the taken coal and rock mass core accounts for 20% - 80% of the coring length L, and it has no fracture when picked up.

[0012] Type III: The length of the rod in the taken coal and rock mass core is less than 20% of the coring length L, and the mass of the blocks in the taken coal and rock mass core accounts for more than 80% of the total mass of the coal and rock mass core.

[0013] Type IV: The length of the rod in the taken coal and rock mass core is less than 20% of the coring length L, and the mass of the powder in the taken coal and rock mass core accounts for more than 80% of the total mass of the coal and rock mass core.

[0014] Type V: All of the taken coal and rock mass core is powder.

[0015] S3. Determine the hydraulic depressurization technology type of the mine coal and rock mass according to the classification of the coal and rock mass core, where:

[0016] When the classification of the coal and rock mass core is Type I, use the water pressure fracturing technology; when the classification of the coal and rock mass core is Type V, use the hydraulic punching technology; when the classification of the coal and rock mass core is Type II, III or IV, conduct uniaxial compressive strength testing, and when the uniaxial compressive strength is greater than the preset threshold, use the hydraulic slotting technology, otherwise use the hydraulic punching technology.

[0017] As a further preferred technical solution of the present invention, in step S1, the coring diameter and coring length satisfy: D≥75mm, 1000mm≤L≤1500mm.

[0018] As a further preferred technical solution of the present invention, in step S3, the preset threshold of the uniaxial compressive strength is 15Mpa.

[0019] The method for selecting the in - hole hydraulic depressurization technology of the mine coal and rock mass of the present invention, by adopting the above - mentioned technical solutions, has the following beneficial technical effects:

[0020] (1) The present invention cores the coal and rock mass within the pressure relief range and classifies it according to the state of the coal and rock mass cores obtained by coring, so as to determine the optimal type of hydraulic pressure relief for different types of coal and rock masses; for the coal and rock masses with a cored state of semi-rod-shaped, massive and powdery massive, a comprehensive determination is made in combination with the uniaxial compressive strength of the coal and rock cores to determine the optimal type of hydraulic pressure relief;

[0021] (2) The method of the present invention is simple. By classifying the coal and rock mass cores through borehole coring and combining with the uniaxial compressive strength, the type of in-hole hydraulic pressure relief technology for underground coal and rock masses can be judged, thus being able to eliminate disasters to the greatest extent;

[0022] (3) The method of the present invention can select a suitable hydraulic pressure relief technology according to the type of mine disasters to eliminate potential mine disaster hazards. It has low construction costs, saves manpower and material resources, and is efficient, providing a good guiding role for eliminating potential mine disaster hazards. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The present invention will be further described in detail below in conjunction with the drawings and specific embodiments.

[0024] Figure 1 It is a schematic diagram of the main process of an embodiment provided for the method of selecting the in-hole hydraulic pressure relief technology for mine coal and rock masses of the present invention;

[0025] Figure 2 It is a flowchart of the method of an embodiment provided for the method of selecting the in-hole hydraulic pressure relief technology for mine coal and rock masses of the present invention.

[0026] The implementation, functional characteristics and advantages of the present invention will be further described in conjunction with the embodiments with reference to the drawings. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0027] The present invention will be further described below in conjunction with the drawings and specific embodiments. Terms such as "upper", "lower", "left", "right", "middle" and "one" cited in the preferred embodiments are only for the convenience of description and are not used to limit the scope of implementation of the present invention. The change or adjustment of their relative relationships shall also be regarded as the scope of implementation of the present invention without substantial change in the technical content.

[0028] As Figure 1 and Figure 2 shown, the present invention provides a method for selecting the in-hole hydraulic pressure relief technology for mine coal and rock masses, including the following steps:

[0029] S1. For the mine coal and rock mass to be pressure-relieved, the coal and rock mass cores within the pressure relief range are taken out through a mine coring pipe. The coring diameter D and the coring length L satisfy D≥75mm (usually there is no limit to the maximum value of D, and a mine coring pipe with a coring diameter greater than 75mm can meet the requirements), and 1000mm≤L≤1500mm;

[0030] S2. Classify the taken coal and rock core according to its degree of fragmentation, which are respectively:

[0031] Class I, the taken coal and rock core is mainly rod-shaped, the length of the rod body is greater than 80% of the core-taking length L, and there is no fracture when picked up;

[0032] Class II, the taken coal and rock core is mainly semi-rod-shaped, the length of the rod body accounts for 20% - 80% of the core-taking length L, and there is no fracture when picked up;

[0033] Class III, the taken coal and rock core is mainly block-shaped, the length of the rod body is less than 20% of the core-taking length L, and the mass of the block accounts for more than 80% of the total mass of the coal and rock core;

[0034] Class IV, the taken coal and rock core is mainly powder-block-shaped, the length of the rod body is less than 20% of the core-taking length L, and the mass of the powder accounts for more than 80% of the total mass of the coal and rock core;

[0035] Class V, the taken coal and rock core is all powder;

[0036] S3. Determine the hydraulic pressure relief technology type of the coal and rock mass in this mine according to the classification of the coal and rock core, where:

[0037] For Class I coal and rock core (in this classification, the integrity of the rod body is relatively good), use the water pressure fracturing technology; for Class V coal and rock core (in this classification, all are powder), use the hydraulic punching technology; for Class II, Class III, and Class IV coal and rock cores, uniaxial compressive strength testing is also required, and when the uniaxial compressive strength ≥ 15 MPa, use the hydraulic cutting technology, otherwise use the hydraulic punching technology.

[0038] It should be noted here that according to the types and textures of the coal and rock masses in different mines, the softness degrees are also different. Then, for the coal and rock masses with hard and dense textures, the coal and rock cores obtained by core-taking are not easy to disintegrate and show a rod shape; for the coal and rock masses with general hardness and density, the taken coal and rock cores will partially disintegrate, showing part rod-shaped, part block-shaped, or part powder-shaped; for the coal and rock masses with very soft textures, the taken coal and rock cores will all disintegrate and all show a powder shape. Therefore, according to the types and textures of the coal and rock masses, combined with the classification of the taken coal and rock cores, a suitable hydraulic pressure relief technology scheme can be selected.

[0039] Example 1

[0040] Apply the above-mentioned method for selecting the in-hole hydraulic pressure relief technology of the coal and rock mass in the mine to the Haishiwan Coal Mine of the Yaojie Coal and Power Group for selecting the hydraulic pressure relief technology.

[0041] Haishiwan Coal Mine of Yaojie Coal and Power Group belongs to a coal and carbon dioxide outburst and weak impact mine. The uniaxial compressive strength of siltstone, gravel-bearing siltstone, and fine sandstone in the coal seam roof of the 6125-1 working face is 30.8 - 46.9 MPa. After hydraulic coring, the length of the rod-shaped body of the obtained coal and rock core is greater than 80% of the coring length, and it does not break when picked up, belonging to Class I core.

[0042] Therefore, in-situ water pressure fracturing of rock mass was carried out on the roof of the return air crossheading of the coal seam in the 6125-1 working face. After on-site peeping with a borehole peeping instrument in the hole, through observing the crack development in the hole and the water outlet range of adjacent holes on-site, the water outlet radius is 30 m, which is 12 times the radius of hydraulic slotting (the theoretical range of hydraulic slotting is 1 - 2.5 m). Therefore, it shows that the effect of in-situ water pressure fracturing in coal and rock mass with Class I core is the best.

[0043] Example Two

[0044] The above-mentioned method for selecting the type of in-situ hydraulic pressure relief technology for mine coal and rock mass was applied to select the in-situ hydraulic pressure relief technology in Jinhe Coal Mine of Yaojie Coal and Power Group.

[0045] Jinhe Coal Mine of Yaojie Coal and Power Group belongs to a coal and carbon dioxide outburst and impact mine. The uniaxial compressive strength of the second coal group in the 16215 working face is 30 - 40 MPa. After hydraulic coring, the coal and rock core is mainly block-shaped, the length of the rod-shaped body is less than 20% of the coring length L, and the mass of the block accounts for more than 80% of the total mass of the coal and rock core, with a grade of Class III. First, hydraulic fracturing of the second coal group was carried out between the supports in the 16215 working face. During the hydraulic fracturing process, the maximum pressure of the pressure pump is 8 MPa, and after 10 s, the pressure drops to 2 MPa and remains unchanged, indicating that the water of the fracturing pump seeps along the primary cracks of the coal and does not play a role in relieving the pressure of the coal seam. Then, a hydraulic slotting test of coal was carried out in the return air crossheading of the 16215 working face, and the average extraction concentration of single-hole coal seam gas increased by 20 - 30%. Although the range of in-situ hydraulic fracturing in the coal body is large, due to the developed joints in the coal seam, no effect of in-situ pressure relief in the coal body hole was achieved. The range of in-situ pressure relief in the hydraulic slotting hole is less than that of hydraulic fracturing, but it overcomes the influence of joints and significantly improves the gas extraction rate of the coal body. Therefore, the effect of in-situ water pressure slotting in coal and rock mass with developed joints and uniaxial compressive strength of coal and rock mass ≥ 15 MPa is the best. The pressure of hydraulic punching is limited and can only act on soft coal and rock. And the effect of creating cavities in soft coal and rock is good and fast. The effect of in-situ hydraulic punching in coal and rock mass with uniaxial compressive strength < 15 MPa is the best.

[0046] Although the specific implementation manners of the present invention have been described above, those skilled in the art should understand that these are only examples. Various changes or modifications can be made to this implementation manner without departing from the principle and essence of the present invention. The protection scope of the present invention is only defined by the appended claims.

Claims

1. A method for selecting hydraulic pressure relief technology in boreholes of mine coal and rock mass, characterized in that, it includes the following steps: S1. For the mine coal and rock mass to be pressure relieved, take out the coal and rock mass core within the pressure relief range through a mine coring tube. The coring diameter is D and the coring length is L; S2. According to the fragmentation degree of the taken coal and rock mass core, classify the taken coal and rock mass core, which are respectively: Type I, the length of the rod in the taken coal and rock mass core is greater than 80% of the coring length L, and there is no fracture when picked up; Type II, the length of the rod in the taken coal and rock mass core accounts for 20% - 80% of the coring length L, and there is no fracture when picked up; Type III, the length of the rod in the taken coal and rock mass core is less than 20% of the coring length L, and the mass of the blocks in the taken coal and rock mass core accounts for more than 80% of the total mass of the coal and rock mass core; Type IV, the length of the rod in the taken coal and rock mass core is less than 20% of the coring length L, and the mass of the powder in the taken coal and rock mass core accounts for more than 80% of the total mass of the coal and rock mass core; Type V, all in the taken coal and rock mass core are powder; S3. According to the classification of the coal and rock mass core, determine the hydraulic pressure relief technology type of the mine coal and rock mass, where: When the classification of the coal and rock mass core is Type I, use the water pressure fracturing technology; when the classification of the coal and rock mass core is Type V, use the hydraulic punching technology; when the classification of the coal and rock mass core is Type II, Type III or Type IV, conduct uniaxial compressive strength detection, and when the uniaxial compressive strength is greater than the preset threshold, use the hydraulic slotting technology, otherwise use the hydraulic punching technology.

2. The method for selecting hydraulic pressure relief technology in boreholes of mine coal and rock mass according to claim 1, characterized in that, in step S1, the coring diameter and coring length satisfy: D≥75mm, 1000mm≤L≤1500mm.

3. The method for selecting hydraulic pressure relief technology in boreholes of mine coal and rock mass according to claim 1, characterized in that, in step S3, the preset threshold of the uniaxial compressive strength is 15Mpa.

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