A method for designing pressure relief parameters of directional hydraulic fracturing for roof of underground coal mine working face

Abstract

The present invention belongs to the technical field of coal mining. It relates to a method for designing parameters of directional hydraulic fracturing pressure relief for the roof of an underground working face in a coal mine, which takes into account parameters such as coal seam burial depth, coal seam thickness, tunnel height, working face strike length, roof solidity coefficient, and borehole diameter, and designs a method for calculating parameters such as the spacing of boreholes, borehole length, borehole inclination, number of boreholes, pilot seam depth, and sealing hole length for directional hydraulic fracturing pressure relief for the roof. The calculation process is simple and fast, and comprehensive considerations are taken into account, which helps to improve the implementation effect of directional hydraulic fracturing pressure relief for the roof.

Description

Technical Field

[0001] The invention belongs to the technical field of coal mining, and relates to a method for designing pressure relief parameters of directional hydraulic fracturing of a roof of an underground working face in a coal mine. Background Art

[0002] In recent years, the number of coal mine rock burst or rock burst-dominated roof accidents and the number of deaths per accident have been on the rise. Especially in western mining areas and deep mines, the elastic energy of thick and hard roof layers is suddenly released under the condition of stress concentration, which can easily cause rock burst without warning.

[0003] Rock burst is the most serious form of pressure in mines. It is essentially the release of elastic energy of coal rock mass caused by concentrated ground stress. To solve the fundamental problem from the source, it is necessary to take measures to relieve pressure by cutting the top of the thick and hard roof layer, reduce the length and area of ​​the suspended top in the goaf of the working face, so as to weaken the high stress stored in the overlying rock strata on the working face and avoid rock burst disasters. At present, the most commonly used methods of top cutting and pressure relief are blasting and hydraulic fracturing. Due to the increasingly strict control of pyrotechnics, the safety of top cutting and pressure relief by blasting is low and it is increasingly restricted, while the advantages of hydraulic fracturing are becoming more and more prominent.

[0004] In the mining process, the hydraulic fracturing method is used to pre-crack the thick hard roof above the two lanes, which can reduce the hanging roof area on both sides of the working face during the mining process, realize stress transfer, reduce the deformation degree of the lane due to dynamic pressure, reduce the peak value of concentrated stress of the coal pillar, and reduce the maintenance cost of the lane. However, the current directional hydraulic fracturing pressure relief method has only been improved in terms of process flow and equipment, and lacks corresponding parameter design methods. Summary of the invention

[0005] In view of this, the purpose of the present invention is to solve the above-mentioned problem and to propose a method for designing pressure relief parameters of directional hydraulic fracturing of the roof of an underground working face in a coal mine.

[0006] In order to achieve the above object, the present invention provides the following technical solutions:

[0007] A method for designing pressure relief parameters for directional hydraulic fracturing of a roof of an underground coal mine working face, characterized in that it comprises the following steps:

[0008] Step 1: Obtain the coal seam depth M of the underground working face of the coal mine a , coal seam thickness h, tunnel height H, working face strike length L c , roof strength coefficient f, drilling diameter d z , height c of double nozzle slotter;

[0009] Step 2, calculate the top plate directional hydraulic fracturing pressure relief drilling hole spacing b, top plate directional hydraulic fracturing pressure relief drilling hole length L, top plate directional hydraulic fracturing pressure relief drilling hole inclination θ:

[0010] b is calculated as follows:

[0011]

[0012] Where h is the thickness of the coal seam, d z is the borehole diameter, f is the roof strength coefficient, M a is the depth of coal seam;

[0013] L is calculated as follows:

[0014]

[0015] Where M a is the buried depth of coal seam, f is the roof solidity coefficient, h is the thickness of coal seam, and H is the height of tunnel;

[0016] θ is calculated as follows:

[0017]

[0018] Where, f is the roof solidity coefficient;

[0019] Step 3, calculate the number of roof directional hydraulic fracturing pressure relief holes P:

[0020]

[0021] Where, L c is the strike length of the working face, b is the spacing of the top plate directional hydraulic fracturing pressure relief drilling holes;

[0022] Step 4: Calculate the required pilot seam depth d g :

[0023]

[0024] Where b is the spacing between the top plate directional hydraulic fracturing pressure relief holes, d z is the drilling diameter;

[0025] Step 5, calculate the sealing depth S of the roof directional hydraulic fracturing pressure relief drilling hole, S is calculated as follows:

[0026] S=0.3L

[0027] Where, L is the length of the roof directional hydraulic fracturing pressure relief borehole;

[0028] Step 6, calculate the top plate directional hydraulic fracturing pressure relief drilling slot height K, K is calculated as follows:

[0029] K=0.7Lc

[0030] Where L is the length of the roof directional hydraulic fracturing pressure relief borehole, and c is the height of the double-nozzle slotter.

[0031] The beneficial effects of the present invention are as follows: the method for designing parameters of directional hydraulic fracturing pressure relief for the roof of an underground working face in a coal mine in the present invention takes into account parameters such as coal seam burial depth, coal seam thickness, tunnel height, working face strike length, roof solidity coefficient, and borehole diameter, and provides on-site implementation personnel with a method for designing parameters such as roof directional hydraulic fracturing pressure relief drilling spacing, drilling length, drilling inclination, number of drilling holes, pilot seam depth, and sealing hole length. The calculation is simple and fast, and comprehensive considerations are taken into account, which helps to improve the implementation effect of roof directional hydraulic fracturing pressure relief.

[0032] Other advantages, objectives and features of the present invention will be described in the following description to some extent, and to some extent, will be obvious to those skilled in the art based on the following examination and study, or can be taught from the practice of the present invention. The objectives and other advantages of the present invention can be realized and obtained through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention will be described in detail below in conjunction with the accompanying drawings, wherein:

[0034] Figure 1 It is a schematic plan view of the arrangement of directional hydraulic fracturing pressure relief drilling holes for the top plate of the working face in the present invention;

[0035] Figure 2 for Figure 1 Middle II section diagram;

[0036] Figure 3 , 4 It is a schematic diagram of the directional hydraulic fracturing pressure relief process for the working face roof in the present invention.

[0037] Figure numerals: 1. Drilling rig; 2. High-pressure sealed drill pipe; 3. Pilot seam; 4. Double-nozzle slotter; 5. Hydraulic fracturing pressure relief borehole; 6. Top plate; 7. Fracturing pump set; 8. Abrasive tank; 9. High-pressure pipeline; 10. High-pressure four-way; 11. Fracturing steel pipe; 12. Cement mortar; 13. High-pressure water. DETAILED DESCRIPTION

[0038] The following describes the embodiments of the present invention by specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the illustrations provided in the following embodiments only illustrate the basic concept of the present invention in a schematic manner, and the following embodiments and features in the embodiments can be combined with each other without conflict.

[0039] Among them, the drawings are only used for illustrative explanations, and they only represent schematic diagrams rather than actual pictures, and should not be understood as limitations on the present invention. In order to better illustrate the embodiments of the present invention, some parts of the drawings may be omitted, enlarged or reduced, and do not represent the size of actual products. For those skilled in the art, it is understandable that some well-known structures and their descriptions in the drawings may be omitted.

[0040] The same or similar numbers in the drawings of the embodiments of the present invention correspond to the same or similar parts; in the description of the present invention, it should be understood that if the terms "upper", "lower", "left", "right", "front", "rear", etc. indicate the orientation or position relationship, they are based on the orientation or position relationship shown in the drawings, which is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operate in a specific orientation. Therefore, the terms describing the position relationship in the drawings are only used for illustrative purposes and cannot be understood as limiting the present invention. For ordinary technicians in this field, the specific meanings of the above terms can be understood according to specific circumstances.

[0041] See also Figures 1 to 4 The directional hydraulic fracturing pressure relief process of the roof of the underground coal mine working face includes two processes: pilot seam cutting and directional hydraulic fracturing. Figure 3 As shown, the drilling rig 1 is equipped with a high-pressure sealed drill pipe 2 and connected to an abrasive tank 8 through a high-pressure pipeline 9. The abrasive tank 8 is connected to a fracturing pump group 7. A double-nozzle slotter 4 is installed on the high-pressure sealed drill pipe 2. A directional abrasive water jet is used to cut a pilot seam 3 of a certain depth along both sides of the hole wall of a hydraulic fracturing pressure relief borehole 5 in a fracturing target rock formation selected by a top plate 6; then directional hydraulic fracturing is performed. The directional hydraulic fracturing process is shown in FIG. Figure 4As shown, the drilling rig 1 is exited, a fracturing steel pipe 11 is installed in the hydraulic fracturing pressure relief borehole 5, and the orifice is blocked with cement mortar 12, the fracturing steel pipe 11 is connected to the fracturing pump group 7 through the high-pressure pipeline 9, and the high-pressure pipeline 9 is simultaneously connected to multiple fracturing steel pipes 11 through the high-pressure four-way 10; high-pressure water 13 is introduced into the hydraulic fracturing pressure relief borehole 5 through the fracturing pump group 7, and under the pressure of the high-pressure water 13, the fracturing crack is directionally extended within a certain range along the pilot seam 3, and the length of the directional extension is called the extension radius. By arranging multiple hydraulic fracturing pressure relief boreholes 5 within the extension radius to make them penetrate or nearly penetrate, finally a cutting top line within the fracturing range is formed.

[0042] The method for designing pressure relief parameters of directional hydraulic fracturing for roof of underground coal mine working face includes the following steps:

[0043] Step 1: Assume that the coal seam depth M of the underground working face of the coal mine is obtained. a =500m, coal seam thickness h=3m, tunnel height H=2.8m, working face strike length L c =1200m, roof strength coefficient f=2.4, borehole diameter d z =0.096m, height c of double nozzle slotter 4 =0.2m;

[0044] Step 2, calculate the top plate directional hydraulic fracturing pressure relief drilling hole spacing b, top plate directional hydraulic fracturing pressure relief drilling hole length L, top plate directional hydraulic fracturing pressure relief drilling hole inclination θ:

[0045] b is calculated as follows:

[0046]

[0047] Where h is the thickness of the coal seam, d z is the borehole diameter, f is the roof strength coefficient, M a is the buried depth of coal seam, the calculated result is rounded to one decimal place, and after calculation, b=13.8m;

[0048] L is calculated as follows:

[0049]

[0050] Where M a is the buried depth of coal seam, f is the roof solidity coefficient, h is the coal seam thickness, H is the roadway height, the calculation result is rounded to 1 decimal place, and it is calculated that L = 21m;

[0051] θ is calculated as follows:

[0052]

[0053] In the formula, f is the roof strength coefficient, and the calculation result is rounded to one decimal place. After calculation, θ=65.4°m;

[0054] Step 3, calculate the number of roof directional hydraulic fracturing pressure relief holes P:

[0055]

[0056] Where, L c is the strike length of the working face, b is the spacing of the top plate directional hydraulic fracturing pressure relief holes, the calculation result is taken as the integer part, and after calculation, P=86;

[0057] Step 4, calculate the required depth d of the pilot seam 3 g :

[0058]

[0059] Where b is the spacing between the top plate directional hydraulic fracturing pressure relief holes, d z The calculation result is rounded to 2 decimal places. g =0.14m;

[0060] Step 5, calculate the sealing depth S of the roof directional hydraulic fracturing pressure relief drilling hole, S is calculated as follows:

[0061] S=0.3L

[0062] Where, L is the length of the roof directional hydraulic fracturing pressure relief borehole, the calculation result is rounded to one decimal place, and after calculation, S = 6.3m;

[0063] Step 6, calculate the top plate directional hydraulic fracturing pressure relief drilling slot height K, K is calculated as follows:

[0064] K=0.7Lc

[0065] Where, L is the length of the roof directional hydraulic fracturing pressure relief borehole, c is the height of the double-nozzle slotter, and the calculation result is rounded to one decimal place. After calculation, K=14.5m.

[0066] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the purpose and scope of the technical solution, which should be included in the scope of the claims of the present invention.

Claims

1. A method for designing pressure relief parameters for directional hydraulic fracturing of the roof of an underground coal mine working face, characterized in that: The steps include: Step 1: Obtain the coal seam depth M of the underground working face of the coal mine a , coal seam thickness h, tunnel height H, working face strike length L c , roof strength coefficient f, drilling diameter d z , height of double nozzle slotter c; Step 2, calculate the top plate directional hydraulic fracturing pressure relief drilling hole spacing b, top plate directional hydraulic fracturing pressure relief drilling hole length L, top plate directional hydraulic fracturing pressure relief drilling hole inclination θ: b is calculated as follows: Where h is the thickness of the coal seam, d is z is the borehole diameter, f is the roof strength coefficient, M a is the depth of coal seam; L is calculated as follows: Where M a is the buried depth of coal seam, f is the roof solidity coefficient, h is the thickness of coal seam, and H is the height of tunnel; θ is calculated as follows: Where, f is the roof solidity coefficient; Step 3, calculate the number of roof directional hydraulic fracturing pressure relief holes P: Where, L c is the strike length of the working face, b is the spacing of the top plate directional hydraulic fracturing pressure relief drilling holes; Step 4: Calculate the required pilot seam depth d g : Where b is the spacing between the top plate directional hydraulic fracturing pressure relief holes, d z is the drilling diameter; Step 5, calculate the sealing depth S of the roof directional hydraulic fracturing pressure relief drilling hole, S is calculated as follows: S=0.3L Where, L is the length of the roof directional hydraulic fracturing pressure relief borehole; Step 6, calculate the top plate directional hydraulic fracturing pressure relief drilling slot height K, K is calculated as follows: K=0.7Lc Where L is the length of the roof directional hydraulic fracturing pressure relief borehole, and c is the height of the double-nozzle slotter.

Images