A method for precise directional jet fracturing cutting and pressure relief and channel protection of deep thick hard roof

Abstract

This invention discloses a method for precise directional jet fracturing and pressure relief in deep, thick, hard roofs, belonging to the field of coal mine gob-side roadway retention technology. The method first determines the target fracture surface for roof cutting and pressure relief based on the characteristics of the thick, hard roof, and then constructs directional fracturing boreholes along its dip direction. Next, an ultra-high pressure sand-laden jet is used within the borehole to impact and form multiple fish-ridge-shaped precise directional fracturing perforations along the target fracture surface. Finally, adjacent fracturing perforations are grouped and simultaneously hydraulically fractured. Utilizing the mutual attraction and expansion characteristics of multi-point fracturing hydraulic fractures, the fracture surface coincides with the target fracture surface, achieving precise roof cutting and pressure relief in thick, hard roofs. This invention effectively guides hydraulic fractures to expand long distances along a predetermined direction, improving roof cutting accuracy, eliminating the risk of uncontrolled fracture damage to roadway support, improving the stress environment of gob-side roadway retention, and reducing maintenance costs.

Description

Technical Field

[0001] This invention relates to a method for precise directional jet fracturing, roof cutting, and pressure relief in deep, thick, hard-roofed coal seams, belonging to the technical field of deep hard-roofed coal seam roadway retention, roof cutting, and roadway protection. Background Technology

[0002] Goaf retention technology, by preserving a portion of the roadway from the previous working face to serve the next working face, can significantly reduce the amount of tunneling work in coal mines, alleviate the pressure of mining succession, and simultaneously eliminate coal pillars in sections, thereby increasing coal resource recovery rates. It has become a widely used cutting-edge technology in the coal mining industry. However, when a thick, high-strength, and high-load-bearing roof exists above the coal seam, the extremely high lateral support stress generated within the roof after coal seam mining will be transmitted to the goaf retention roadway, leading to a surge in surrounding rock stress, intensified deformation, and a significant increase in maintenance costs. To address this problem, if fissures can be artificially created along the roadway's direction to cut off the cantilevered load-bearing structure of the thick roof above the goaf retention roadway, eliminating the transmission path of the extremely high support stress and achieving roof cutting and pressure relief, the stress environment of the surrounding rock can be significantly improved, and maintenance costs reduced.

[0003] Hydraulic fracturing technology utilizes high-pressure water to overcome the tensile strength of rock mass, causing it to fracture and generate hydraulic fractures, thereby optimizing the rock mass structure and weakening its strength. This technology is low-cost, simple to operate, and carries minimal safety risks, making it an ideal means of achieving roof cutting and pressure relief for massive, hard roofs. However, due to the uncontrollable propagation of hydraulic fractures during hydraulic fracturing, the fracture surfaces formed by conventional fracturing methods often differ significantly from the target fracture surface for roof cutting and pressure relief. When the hydraulic fractures are completely horizontal or oblique to the roadway direction, not only is effective roof cutting and pressure relief impossible, but it may also severely damage the surrounding rock and its support structure in the goaf-side retention, posing a significant safety hazard. Therefore, there is an urgent need to develop a method that can precisely control the propagation direction of hydraulic fractures in massive, hard roofs, ensuring that the fracture surface essentially coincides with the target fracture surface for roof cutting and pressure relief, thereby achieving safe and efficient roof cutting and pressure relief in goaf-side retention.

[0004] To address the aforementioned issues, some technologies have attempted improvements. For example, patent CN119712206B discloses a method for coal roadway gas extraction and roof cutting based on directional fracturing. This method induces direct roof fracture and pressure relief by pre-cutting directional grooves within the borehole and performing hydraulic fracturing. The drawback of this method is that while directional cutting can cause stress concentration in the surrounding rock mass in a predetermined direction, reducing the initiation stress and guiding the initial hydraulic fractures along that direction, the limited groove length restricts its guiding effect to a small area (typically 2-3 times the groove length). It cannot achieve artificial control over the long-distance directional propagation of hydraulic fractures in large-area rock masses.

[0005] Another patent, CN112855155B, discloses a method for segmented directional hydraulic fracturing of a thick, hard roof along a goaf. It uses a lateral jet cutting device to create annular radial weak surfaces and continuous axial weak surfaces in the fracturing borehole, causing hydraulic fractures to initiate along the weak surfaces. The range of fracture expansion is observed through a guide borehole to achieve directional fracturing. The method has the following shortcomings: (1) When the high-pressure jet washes the rock wall, most of the energy is released in the fracture cracks, the energy is dispersed, the cutting effect on the intact rock wall is limited, and the length of the weak surface formed is small (usually 3 to 5 times the borehole diameter); (2) When radial fracturing is carried out in the continuous axial weak surface area, since a long axial weak surface has been formed in the borehole, and the length of the sealing device is limited, it is difficult to completely seal the axial weak surface, resulting in a large amount of high-pressure water leakage, and the length of the hydraulic fracture formed by fracturing is small; (3) The guide hole has a small diameter, and the range of stress field change is limited (usually 3 to 6 times the borehole diameter), the guiding control ability of hydraulic fracture expansion is weak, and it is difficult to achieve long-distance and large-scale directional guidance.

[0006] In summary, existing technologies still have significant limitations in the controllable directional propagation of hydraulic fractures, and there is an urgent need to propose a new method that can achieve precise directional cutting and pressure relief of massive, thick hard roofs. Summary of the Invention

[0007] To address the problems of the existing technologies, this invention discloses a method for precise directional jet fracturing and pressure relief in deep, thick, hard roofs. This method involves constructing directional fracturing boreholes in the advanced area of ​​the goaf-retaining roadway within a deep, thick, hard roof, and using ultra-high pressure sand-bearing jets to form fish-ridge-shaped fracturing perforations. Combined with grouped induced hydraulic fracturing, this ensures that the fracture surface formed by hydraulic fracturing of the thick, hard roof essentially coincides with the target fracture surface for pressure relief along the goaf-retaining roadway. This solves the problem that conventional fracturing methods often result in significant differences between the fracture surface and the target cutting surface, failing to achieve pressure relief in thick, hard roofs and damaging the surrounding rock and support structure of the goaf-retaining roadway. This method achieves precise directional fracturing and pressure relief in goaf-retaining roadways with thick, hard roofs.

[0008] To achieve the above objectives, the present invention adopts the following technical solution:

[0009] A method for precise jet fracturing, roof cutting, pressure relief, and roadway protection in deep, thick, and hard roof structures includes the following steps:

[0010] (1) Based on the occurrence conditions and physical and mechanical characteristics of the deep thick hard roof, and combined with the bearing strength of the filling body, the length and inclination of the borehole for cutting the roof along the goaf in the deep thick hard roof are obtained, and the key parameters of the target fracture surface for cutting the roof and relieving pressure are determined.

[0011] (2) In accordance with the target fracture surface for cutting the top and relieving pressure, directional fracturing boreholes are constructed in the advanced area of ​​the deep, thick, hard roof along the goaf and the inclined direction of the target fracture surface for cutting the top and relieving pressure.

[0012] (3) At different depths of the directional fracturing borehole, ultra-high pressure jets are applied along the direction of the top-cutting and pressure-relieving target fracture surface to form a fishback-shaped precise fracturing perforation.

[0013] (4) The fish spine-shaped precision-directed fracturing perforations are grouped and induced by hydraulic pressure to form grouped induced fracturing hydraulic fractures, and finally the target fracture surface of deep, thick, hard-top precision-directed jet fracturing to cut the top and relieve pressure is obtained.

[0014] Furthermore, the determined borehole length in step S1 and drilling inclination angle Based on the steady-state equilibrium theory of thin plates, and taking the ultimate bearing capacity of the filler in the goaf as the criterion for non-failure, the theoretical calculation formula is as follows:

[0015] In the formula: The strength of the filling body for the goaf retention; The density of the extremely thick, hard-topped rock layer; This represents the thickness of a very thick hard caprock layer; To determine the width of the alleyway along the clearance; The length of the borehole that caused the fracture; The angle of inclination of the borehole to cause cracking.

[0016] Furthermore, the parameters of the target fracture surface for cutting the roof along the goaf in step S1 include the maximum elevation of the fracture surface. Minimum elevation , fracture surface dip angle and the angle of fracture surface orientation The maximum elevation of the fracture surface Based on the length of the borehole and drilling inclination angle According to the formula The minimum elevation of the fracture surface was calculated. Based on safe top cutting distance and drilling inclination angle According to the formula The calculated fracture surface dip angle With drilling inclination angle The same, the orientation angle of the fracture surface Angle with the direction of the alley same.

[0017] Furthermore, the spacing of the directional fracturing boreholes is twice the length of the fracturing perforation.

[0018] Furthermore, in step S3, the specific steps for forming the fishback-shaped precisely oriented fracturing perforation include:

[0019] At a predetermined depth at the bottom of the directional fracturing borehole, an ultra-high pressure sand-bearing jet is used to form a directional fracturing perforation that aligns with the direction of the target fracture surface. Once the current fracturing perforation reaches a predetermined length, it is stepped back towards the borehole opening along the borehole axis, and the sand-bearing jet operation is repeated, thereby forming multiple spaced, fish-ridge-shaped, precisely directional fracturing perforations within the borehole along the direction of the target fracture surface.

[0020] Furthermore, the ultra-high pressure sand-containing jet is a jet that is simultaneously delivered from both sides of the directional fracturing borehole.

[0021] Furthermore, within the directional fracturing borehole, the borehole sections between adjacent fracturing perforations are sealed off; high-pressure water is injected to simultaneously induce hydraulic fracturing in two adjacent fracturing perforations, utilizing the mutual attraction and expansion characteristics of hydraulic fractures to form a continuous group of induced hydraulic fractures; after the fractures between this group of fracturing perforations are connected, the borehole is stepped back along the borehole axis towards the borehole opening, and the above sealing and hydraulic fracturing operations are repeated for the next group of adjacent fracturing perforations until hydraulic fracturing of all preset fracturing perforation groups is completed.

[0022] Furthermore, the distance between two adjacent precisely oriented fracturing perforations within the directional fracturing borehole is twice the maximum length of the fracture during hydraulic fracturing.

[0023] Furthermore, in step S2, the orientation angle of the fracturing borehole and the orientation angle of the target fracture surface for top cutting and pressure relief... The relationship is Drilling angle Angle of inclination of the fracture surface relative to the top pressure relief target same.

[0024] Furthermore, an apparatus for the above method includes:

[0025] Directional drilling rigs are used to construct directional fracturing boreholes that are aligned with the inclination direction of the target fracture surface for top cutting and pressure relief.

[0026] The ultra-high pressure sand-containing jet system includes a high-pressure sealing drill rod, a sand-containing jet guide head, a sand-containing jet nozzle, an ultra-high power water pump, and an aggregate fine sand additive, which are used to form a fishback-shaped precise fracturing perforation along the direction of the target fracture surface in the directional fracturing borehole.

[0027] A grouped hydraulic fracturing system includes a high-pressure sealed drill rod, a hydraulic fracturing guide head, at least two sets of cross-type hydraulic fracturing devices and connecting mechanisms, used to perform grouped and simultaneous hydraulic fracturing of at least two adjacent precision-directed fracturing perforations within the directional fracturing borehole.

[0028] Furthermore, the water outlet direction of the sand-containing jet inlet of the ultra-high pressure sand-containing jet system is configured to always coincide with the intersection line of the fracture surface and the horizontal plane of the top-cutting and pressure-relieving target during the construction process.

[0029] Furthermore, each group of cross-sectional hydraulic fracturing devices in the grouped induced hydraulic fracturing system includes a front-end sealer and a rear-end sealer, used to form independent sealed fracturing spaces in the borehole sections where two adjacent fracturing perforations are located. Compared with the prior art, the beneficial effects of the present invention are:

[0030] 1. Directional drilling rigs are used to construct directional fracturing boreholes along the inclined direction of the target fracture surface for top cutting and pressure relief. This greatly improves the matching rate between the fracturing boreholes and the target fracture surface for top cutting and pressure relief, providing a prerequisite guarantee for the precise direction of top cutting and pressure relief in deep, thick, hard roof roadway retention.

[0031] 2. Using ultra-high pressure sand-containing jets, fracturing perforations are artificially created along the fracture surface of the top-cutting and pressure-relieving target. By adding fine sand aggregate to the ultra-high pressure medium water, the maximum energy transferred by the jet is greatly increased, significantly improving the straightness and drilling efficiency of the fracturing perforation. At the same time, the position and direction of the sand-containing jet on the borehole wall are fixed, which concentrates the energy of the sand-containing jet and significantly increases the maximum distance of the fracturing perforation, thereby reducing the number of directional fracturing boreholes by a factor of two.

[0032] 3. Utilizing the characteristic of the hydraulic fractures in the rock mass being simultaneously fractured at multiple points and attracting each other for propagation, the fish-ridge-shaped hydraulic fracturing perforations are grouped and simultaneously subjected to hydraulic fracturing. This induces the hydraulic fractures between the fish-ridge-shaped hydraulic fracturing perforations to propagate in a directional manner, thereby ensuring that the hydraulic fracture surface of the roof is basically coincident with the target fracture surface for roof cutting and pressure relief. This ensures that the deep, thick, hard roof roadway is accurately positioned towards roof cutting and pressure relief for roadway protection. Attached Figure Description

[0033] Figure 1 This is a calculation diagram of the length and inclination angle of the borehole for cutting the roof in deep, thick, hard roof along the goaf in an embodiment of the present invention;

[0034] Figure 2 This is a three-dimensional diagram of fracturing borehole construction according to an embodiment of the present invention;

[0035] Figure 3 This is a front view of the fracturing borehole construction according to an embodiment of the present invention;

[0036] Figure 4 This is a side view of the fracturing borehole construction according to an embodiment of the present invention;

[0037] Figure 5 This is a three-dimensional diagram of ultra-high pressure sand-bearing jet construction in fracturing boreholes according to an embodiment of the present invention;

[0038] Figure 6 This is a front view of the ultra-high pressure sand-bearing jet construction in a fracturing borehole according to an embodiment of the present invention;

[0039] Figure 7 This is a side view of the ultra-high pressure sand-bearing jet construction in a fracturing borehole according to an embodiment of the present invention;

[0040] Figure 8 This is a three-dimensional diagram of the hydraulic fracturing operation induced by grouping fracturing boreholes according to an embodiment of the present invention;

[0041] Figure 9 This is a front view of the hydraulic fracturing operation induced by grouping fracturing boreholes according to an embodiment of the present invention;

[0042] Figure 10 This is a side view of the hydraulic fracturing operation induced by grouping fracturing boreholes according to an embodiment of the present invention;

[0043] In the diagram: 1. Deep coal seam; 2. Thick, hard roof overlying the deep coal seam; 3. Goaf; 4. Roadway left along the goaf under the thick, hard roof; 5. Backfill body for the roadway; 6. Longwall face; 7. Advance roadway; 8. Roof-cutting and pressure-relieving fracturing borehole; 9. Precision-oriented fracturing perforation; 10. Grouped induced hydraulic fractures; 11. Target fracture surface for roof-cutting and pressure-relieving; 12. Directional drill bit; 13. High-strength drill rod; 14. Directional drilling rig; 15. Side wing roadway for the roadway left along the goaf under the thick, hard roof; 16. Ultra-high pressure sand-bearing jet guide head; 17. Ultra-high pressure sand-bearing jet nozzle; 18. High pressure-bearing density... 19. Hollow water guide channel; 20. High-pressure sealed drill rod pushing device; 21. High-pressure sealed drill rod tailing device; 22. High-pressure sealed steel pipe; 23. Aggregate and fine sand additive; 24. Ultra-high power hydraulic pump; 25. Large-diameter water pipe; 26. Ton-class water tank; 27. Hydraulic fracturing guide head; 28. Front-end sealing device of the first group of cross-sectional hydraulic fracturing devices; 29. ​​Hydraulic fracturing outlet of the first group of cross-sectional hydraulic fracturing devices; 30. Rear-end sealing device of the first group of cross-sectional hydraulic fracturing devices; 31. Connection mechanism between the first and second groups of cross-sectional hydraulic fracturing devices; 32. Front-end sealing device of the second group of cross-sectional hydraulic fracturing devices; 33. Hydraulic fracturing outlet of the second group of cross-sectional hydraulic fracturing devices; 34. Rear-end sealing device of the second group of cross-sectional hydraulic fracturing devices. Detailed Implementation

[0044] To make the objectives, technical solutions, and advantages of this invention clearer, the following description is provided in conjunction with... Figures 1 to 9 The present invention will be further described in detail below. However, it should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the scope of the invention. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains, and the terminology used herein in the specification of the invention is for the purpose of describing particular embodiments only and is not intended to limit the invention.

[0045] In the embodiment of the present invention, the project is located in a coal mine. The average burial depth of the coal seam in the mine is 843.65m, which is a deep coal seam. The average dip angle of the coal seam is 6.4°. Above it is a hard coarse sandstone layer with a thickness of 14.47m. Through on-site sampling and testing, the uniaxial compressive strength and uniaxial tensile strength of the rock layer are 38.48MPa and 11.45MPa, respectively, which are typical of a huge and thick hard roof. The mine is currently mining the 1441 working face from south to north. The working face has a strike length of 2205.45m and a dip length of 210.54m. The 1441 transport roadway on the west side of the working face is used as a goaf retainer for the return airway of the next mining working face, 1443. This transport roadway has a rectangular cross section of 4.3m × 3.2m (width × height). After the working face is mined, a 1.5m × 3.2m (width × height) concrete goaf retainer will be built along the goaf side to isolate the 1443 return airway from the goaf.

[0046] During the application of the conventional gob-side entry water-pressure fracturing and roof-cutting decompression method, a large amount of water flowed through multiple roof anchors (cables) in the reserved roadway of 1441 transport roadway. Drilling revealed that most of the fractures within the boreholes were horizontal. In this case, the conventional gob-side entry water-pressure fracturing and roof-cutting decompression method not only failed to create the target fracture surface for roof-cutting decompression along the roadway direction, but also damaged the strength of the surrounding rock and the support structure. Subsequent monitoring showed that the surrounding rock stress in the gob-side entry of the 1443 return airway was consistently at a high stress environment of 23.87 MPa, with roadway deformation maintained at 2.31 cm / day. The roadway required repair on average every 15 days. Simultaneously, the stress within the concrete filling reached as high as 15.48 MPa, with 9 surface cracks exceeding 20 cm in length per meter. 2 .

[0047] Therefore, this invention provides a method for precise directional jet fracturing, roof cutting, and pressure relief in deep, thick, hard roofs to protect the roadway. The specific implementation steps in the embodiment are as follows:

[0048] (1) such as Figure 1 and Figure 2 As shown, based on the occurrence characteristics of coal seam 1 and the overlying thick hard roof 2 in the mine, and according to the thin plate steady-state equilibrium theory, the borehole length is calculated based on the criterion that the ultimate bearing capacity of the filling body in the goaf-side entry should not fail. The theoretical calculation formula for the priority review request for borehole inclination angle is as follows:

[0049]

[0050] In the formula: The strength of the filling body for the goaf retention; The density of the extremely thick, hard-topped rock layer; This represents the thickness of a very thick hard caprock layer; To determine the width of the alleyway along the clearance; The length of the borehole that caused the fracture; The angle of inclination of the borehole to cause cracking.

[0051] The calculated length of the borehole for cutting and decompression along the goaf in the 1441 transport roadway is 13.72m, with a dip angle of 60°. The strike direction of the target fracture surface 11 for cutting and decompression in the pre-reserved roadway 7 along the goaf in the 1441 working face is then determined. Angle with the direction of lane 7 Parallel, fracture surface dip angle Same as borehole inclination angle The inclination angle is 60° upward from the horizontal, and the maximum height of the target fracture surface 11 is... Minimum height is 11m above the coal seam roof. The elevation is 5m above the coal seam roof, where the maximum elevation of the fracture surface is determined by the borehole length. and drilling inclination angle According to the formula The minimum elevation of the fracture surface was calculated. Based on safe top cutting distance and drilling inclination angle According to the formula Calculated.

[0052] (2) such as Figure 2 , Figure 3 and Figure 4 As shown, a directional drilling rig 14 is arranged perpendicular to the direction of the pre-reserved roadway 7 along the goaf in the 1441 working face transport roadway. Guided by a 60mm diameter directional drill bit 12 and a 55mm diameter, 75cm long high-strength drill rod 13, fracturing boreholes 8 with a diameter of 65mm are drilled from bottom to top along the roadway towards the working face, with a borehole strike angle of 90° and an inclination angle of 60° (the same as the inclination angle of the target fracture surface 11). The depth of the fracturing boreholes 8 is 13.72m, and the spacing between the fracturing boreholes 8 is 8m. The strike angle ϕ of the fracturing boreholes is the same as the strike angle of the target fracture surface for top cutting and pressure relief. The relationship is Drilling angle Angle of inclination of the fracture surface relative to the top pressure relief target same.

[0053] (3) such as Figure 5 , Figure 6 and Figure 7As shown, after the first fracturing borehole is completed, a high-pressure sealing borehole pushing device 20 is arranged perpendicular to the direction of the pre-reserved roadway 7 along the goaf in the transport roadway of the 1441 working face. Using a 60mm diameter, 1.5m long high-pressure sealing drill rod 18, the sand-containing jet guide head 16 and the sand-containing jet nozzle 17 are sent to a depth of 12.72m in the fracturing borehole 8, while ensuring that the water outlet direction of the sand-containing jet nozzle 17 is the same as the direction of the target fracture surface 11. Then, the ultra-high power generator with a maximum power of 110KW is started. A high-pressure water pump 24 pumps medium water through a large-diameter water pipe 25 (16cm diameter) from a 2-ton capacity water tank 26 into a high-pressure sealed steel pipe 22 with a maximum pressure of 110MPa. Aggregate and fine sand are added via an aggregate and fine sand additive 23, and the sand-containing medium water is then forced into the hollow water guide channel 19 of the high-pressure sealed drill rod 18 through a water tail device 21. Finally, the water is ejected from the sand-containing jet outlet 17, achieving ultra-high pressure sand-containing jet impact on the rock mass with strong kinetic energy, forming a fishback-shaped, precisely oriented fracturing perforation. The ultra-high pressure sand-containing jet is injected simultaneously from both sides of the directional fracturing borehole, forming a fracturing perforation symmetrical along the axial direction of the directional fracturing borehole. When the length of the fracturing perforation 9 reaches 4m, the ultra-high power water pump 24 is stopped. Then, the high pressure sealing drill rod 18 is retrieved using the high pressure sealing drill pushing device 20, so that the sand-bearing jet outlet 17 moves back 2.3m from the bottom of the hole to the opening. During this process, it must be ensured that the water outlet direction of the sand-bearing jet outlet 17 is the same as the direction of the target fracture surface (i.e., the trajectory line of the ultra-high pressure sand-bearing jet always coincides with the intersection line of the top-cutting and pressure-relieving target fracture surface and the horizontal plane). Then, the rock mass is subjected to strong kinetic energy impact of ultra-high pressure sand-bearing jet again to form a precisely oriented fracturing perforation 9. The first fracturing borehole ultra-high pressure sand-bearing jet construction can be completed by performing the above steps 4 times.

[0054] The spacing between the fracturing boreholes 8 is twice the length of the fracturing perforation 9.

[0055] (4) such as Figure 8 , Figure 9 and Figure 10As shown, after the first fracturing borehole completes the ultra-high pressure sand-bearing jet construction, the high pressure-bearing sealed drill rod 18 and the sand-bearing jet guide head 16 are retrieved using the high pressure-bearing sealed drill rod pushing device 20. The hydraulic fracturing guide head 27, the first set of cross-sectional hydraulic fracturing front-end sealing device 28 and the rear-end sealing device 30 are installed in sequence. Then, the first and second sets of cross-sectional hydraulic fracturing device connection mechanism 31 are connected. Next, the second set of cross-sectional hydraulic fracturing front-end sealing device 28 and the rear-end sealing device 30 are installed. Finally, the high pressure-bearing sealed drill rod 18 is connected. After completing the above device connection, the high-pressure sealing drill rod pushing device 20 is used to send the outlet 29 of the first set of cross-sectional water pressure fracturing sealing device into the fracturing borehole 8 at a depth of 12.72m (i.e., the first precisely oriented fracturing perforation). At this time, the outlet of the second set of cross-sectional water pressure fracturing sealing device will be located at a depth of 10.42m (i.e., the second precisely oriented fracturing perforation) in the fracturing borehole 8. Then, the ultra-high power water pump 24 with a maximum power of 110KW is started to pressurize the medium water through the large-diameter water pipe 25 with a diameter of 16cm from the ton-class water tank 26 with a maximum capacity of 2t into the high-pressure sealing steel pipe 22 with a maximum pressure of 110MPa, and then through... The high-pressure sealing drill pipe water tail device 21 pressurizes the medium water into the hollow water guiding channel 19 of the high-pressure sealing drill pipe 18, and expands the front sealing device of the cross-section water pressure fracturing device (the front sealing device of the first cross-section water pressure fracturing device and the front sealing device of the second cross-section water pressure fracturing device 32) and the rear sealing device (the rear sealing device of the first cross-section water pressure fracturing device 30 and the rear sealing device of the second cross-section water pressure fracturing device 34) to seal the fracturing borehole 8. Finally, the high-pressure water is forced out from the water pressure fracturing outlet (the water pressure fracturing outlet of the first cross-section water pressure fracturing device 29 and the water pressure fracturing outlet of the second cross-section water pressure fracturing device 33). By grouping the first and second precisely oriented fracturing perforations 9 into groups and simultaneously inducing hydraulic fracturing, and taking advantage of the mutual attraction and expansion characteristics of the hydraulic fractures 10 caused by simultaneous fracturing at multiple points in the rock mass, the directional induced expansion of the hydraulic fractures 10 between the first and second fracturing perforations is achieved. The spacing of the fracturing perforations 9 in the drilled hole is twice the maximum expansion length of the hydraulically induced fracture. After the hydraulic fracture 10 between the first and second fracturing perforations 9 is interconnected, the ultra-high power hydraulic pump 24 is stopped. Then, the high pressure sealing drill rod 18 is retrieved using the high pressure sealing drill pusher 20, so that the outlets of the first and second sets of cross-sectional hydraulic fracturing sealing devices are both moved back 2.3m from the bottom of the hole to the opening. At this time, the outlets of the first and second sets of cross-sectional hydraulic fracturing sealing devices are located at the second and third precisely pointing fracturing perforations, respectively. Then, the second and third fracturing perforations are subjected to group-induced hydraulic fracturing to form group-induced hydraulic fracture 10 between the fracturing perforations. The group-induced hydraulic fracturing construction of the first fracturing drill hole can be completed by performing the above steps 3 times.

[0056] It is worth noting that in the embodiment of the present invention, the deep, thick, hard roof rock mass of a coal mine's 1441 working face is protected by precise directional jet fracturing and roof cutting / pressure relief using a directional drilling rig. First, precise fracturing boreholes are drilled according to the target fracture surface for the rock mass of the gob-side entry and roof cutting / pressure relief. Then, ultra-high pressure sand-bearing jets are used to apply strong kinetic energy to the deep, thick, hard roof rock mass, forming a series of fish-ridge-shaped precise directional fracturing perforations within the rock mass. Secondly, based on the characteristic of the hydraulic fractures in the rock mass simultaneously fracturing at multiple points and mutually attracting and expanding, the precise directional fracturing perforations are grouped and simultaneously subjected to hydraulic fracturing. Grouped induced hydraulic fractures are generated between the precise directional fracturing perforations, ultimately achieving the goal of artificially controlling the roof cutting / pressure relief fracture surface to always follow the direction of the gob-side entry, thus realizing precise directional jet fracturing and roof cutting / pressure relief protection for the deep, thick, hard roof rock mass.

[0057] In this embodiment, after adopting the method of precise directional jet fracturing and roof cutting / pressure relief in the deep, thick, hard roof of the 1441 working face of a coal mine, precise fracturing boreholes were drilled along the goaf using a directional drilling rig according to the target fracture surface for roof cutting / pressure relief in the goaf-keeping roadway. This increased the matching rate between the fracturing boreholes and the target fracture surface from 23% to 86%, significantly improving the accuracy of the fracturing boreholes. The use of an ultra-high power hydraulic pump combined with fine aggregate sand increased the jet kinetic energy by 74%, achieving a strong kinetic energy impact of ultra-high pressure sand-bearing jet on the deep, thick, hard roof rock mass. This increased the maximum fracturing perforation length from 2.4m to 4.3m, and the spacing between fracturing boreholes from... The original 4m was expanded to 8m, and the amount of hydraulic fracturing drilling was reduced from 7659.43m to 3829.72m, a reduction of 50%. The use of group-induced hydraulic fracturing not only reduced the hydraulic fracture initiation pressure from 22.45MPa to 16.48MPa, but also kept the hydraulic fracture within the target fracture surface for roof cutting and pressure relief, achieving a 79% match rate. This enabled precise artificial targeting of the deep, thick, hard roof for roof cutting and pressure relief, eliminating the safety hazards of hydraulic fracturing and roof cutting / pressure relief fractures damaging the surrounding rock and support structure of the roadway. Furthermore, the precise targeting of the deep, thick, hard roof in the goaf-side roadway of the 1441 working face... During the implementation of the jet fracturing method for roof cutting and pressure relief in the 1441 transport roadway, the water seepage from the roof in the reserved roadway was significantly reduced, indicating that the hydraulic fractures had not extended to the roadway roof and had not damaged the roadway support structure. Drilling inspection results showed that the fractures in the boreholes along the goaf in the 1441 working face extended along the borehole axis, indicating that the hydraulic fractures were parallel to the roadway direction, achieving a match between the hydraulic fractures and the target fracture surface for roof cutting and pressure relief. Subsequent monitoring showed that the surrounding rock stress in the 1443 return airway along the goaf decreased from 23.87 MPa to 12.49 MPa, a reduction of 47.67%. The deformation decreased from 2.31 cm / d to 1.57 cm / d, a reduction of 32.03%. The roadway repair interval increased from 15 days to 23 days, an increase of 53.34%. Roadway maintenance costs decreased from 731 yuan / m to 247 yuan / m, a reduction of 66.21%, resulting in a total saving of 10.6744 million yuan in roadway maintenance funds. In addition, the internal stress of the concrete filling in the goaf-retention roadway decreased from 15.48 MPa to 8.47 MPa, a reduction of 43.28%, and the number of surface cracks exceeding 20 cm in length decreased from 9 per m. 2 Reduced to 2 strips / m 2 The reduction reached 77.78%, saving a total of 2.6741 million yuan in construction and maintenance costs for concrete filling bodies along the goaf.

[0058] This invention addresses the problems of conventional hydraulic fracturing and roof-cutting decompression methods along goaf entry, which not only fail to create target fracture surfaces along the goaf entry direction but also cause damage to the surrounding rock strength and support structure. It proposes a method for deep, thick, hard-roofed rock mass using precise directional jet fracturing and roof-cutting decompression. First, directional drilling is used to precisely drill fracturing holes according to the target fracture surface along the goaf entry direction. Then, ultra-high pressure sand-bearing jets are used to strongly impact the deep, thick, hard-roofed rock mass, forming a series of fish-ridge-shaped precise directional fracturing perforations within the rock mass. Next, based on the mutual attraction and expansion characteristics of hydraulic fractures caused by simultaneous fracturing at multiple points in the rock mass, the precise directional fracturing perforations are grouped and simultaneously subjected to hydraulic fracturing. This generates groups of induced hydraulic fractures between the precise directional fracturing perforations, ultimately achieving the goal of artificially controlling the roof-cutting decompression fracture surface to always follow the goaf entry direction, thus realizing precise directional jet fracturing and roof-cutting decompression protection for deep, thick, hard-roofed rock masses.

[0059] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0060] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions or improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for precise jet fracturing, roof cutting, pressure relief, and tunnel protection in deep, thick, hard roof structures, characterized in that... Includes the following steps: (1) Based on the occurrence conditions and physical and mechanical characteristics of the deep thick hard roof, and combined with the bearing strength of the filling body, the length and inclination of the borehole for cutting the roof along the goaf in the deep thick hard roof are obtained, and the key parameters of the target fracture surface for cutting the roof and relieving pressure are determined. (2) In accordance with the target fracture surface for cutting the top and relieving pressure, directional fracturing boreholes are constructed in the advanced area of ​​the deep, thick, hard roof along the goaf and the inclined direction of the target fracture surface for cutting the top and relieving pressure. (3) At different depths of the directional fracturing borehole, ultra-high pressure jets are applied along the direction of the top-cutting and pressure-relieving target fracture surface to form a fishback-shaped precise fracturing perforation. (4) The fish spine-shaped precision-directed fracturing perforations are grouped and induced by hydraulic pressure to form grouped induced fracturing hydraulic fractures, and finally the target fracture surface of deep, thick, hard-top precision-directed jet fracturing to cut the top and relieve pressure is obtained.

2. The method for precise directional jet fracturing, roof cutting, and pressure relief in deep, thick, hard-roofed tunnels according to claim 1, characterized in that, The determined borehole length in step (1) and drilling inclination angle Based on the steady-state equilibrium theory of thin plates, and taking the ultimate bearing capacity of the filler in the goaf as the criterion for non-failure, the theoretical calculation formula is as follows: In the formula: The strength of the filling body for the goaf retention; The density of the extremely thick, hard-topped rock layer; This represents the thickness of a very thick hard caprock layer; To determine the width of the alleyway along the clearance; The length of the borehole that caused the fracture; The angle of inclination of the borehole to cause cracking.

3. The method for precise directional jet fracturing, roof cutting, and pressure relief in deep, thick, hard-roofed tunnels according to claim 1, characterized in that... The parameters of the target fracture surface in the deep, thick, hard roof goaf-keeping and roof-cutting in step (1) include the maximum elevation of the fracture surface. Minimum elevation , fracture surface dip angle and the angle of fracture surface orientation The maximum elevation of the fracture surface Based on the length of the borehole and drilling inclination angle According to the formula The minimum elevation of the fracture surface was calculated. Based on safe top cutting distance and drilling inclination angle According to the formula The calculated fracture surface dip angle With drilling inclination angle The same, the orientation angle of the fracture surface Angle with the direction of the alley same.

4. The method for precise directional jet fracturing, roof cutting, and pressure relief in deep, thick, hard-roofed tunnels according to claim 1, characterized in that... The spacing between the directional fracturing boreholes is twice the length of the fracturing perforation.

5. The method for precise directional jet fracturing, roof cutting, and pressure relief in deep, thick, hard-roofed tunnels according to claim 1, characterized in that... In step (3), the specific steps for forming the fishback-shaped, precisely oriented fracturing perforation include: At a predetermined depth at the bottom of the directional fracturing borehole, an ultra-high pressure sand-bearing jet is used to form a directional fracturing perforation that aligns with the direction of the target fracture surface. Once the current fracturing perforation reaches a predetermined length, it is stepped back towards the borehole opening along the borehole axis, and the sand-bearing jet operation is repeated, thereby forming multiple spaced, fish-ridge-shaped, precisely directional fracturing perforations within the borehole along the direction of the target fracture surface.

6. The method for precise directional jet fracturing, roof cutting, and pressure relief in deep, thick, hard-roofed tunnels according to claim 5, characterized in that... The ultra-high pressure sand-bearing jet is a jet that is simultaneously delivered from both sides of the directional fracturing borehole.

7. The method for precise directional jet fracturing, roof cutting, and pressure relief in deep, thick, hard-roofed tunnels according to claim 1, characterized in that... In step (4), the specific steps of the group-induced hydraulic fracturing include: Within the directional fracturing borehole, the borehole sections between adjacent fracturing perforations are sealed off; high-pressure water is injected to simultaneously induce hydraulic fracturing in two adjacent fracturing perforations, utilizing the mutual attraction and expansion characteristics of hydraulic fractures to form a continuous group of induced hydraulic fractures; after the fractures between this group of fracturing perforations are connected, the borehole is stepped back along the borehole axis towards the borehole opening, and the above sealing and hydraulic fracturing operations are repeated for the next group of adjacent fracturing perforations until hydraulic fracturing of all preset fracturing perforation groups is completed.

8. The method for precise jet fracturing, roof cutting, and pressure relief in deep, thick, hard-roofed tunnels according to claim 7, characterized in that... The distance between two adjacent precisely oriented fracturing perforations within the directional fracturing borehole is twice the maximum length of the fracture during hydraulic fracturing.

9. The method for precise directional jet fracturing, roof cutting, and pressure relief in deep, thick, hard-roofed tunnels according to claim 1, characterized in that, The orientation angle of the fracturing borehole and the orientation angle of the target fracture surface for top cutting and pressure relief in step (2) The relationship is Drilling angle Angle of inclination of the fracture surface relative to the top pressure relief target same.

10. An apparatus for the deep, thick, hard roof precision-directed jet fracturing, roof cutting, pressure relief, and roadway protection method according to any one of claims 1 to 9, characterized in that, include: Directional drilling rigs are used to construct directional fracturing boreholes that are aligned with the inclination direction of the target fracture surface for top cutting and pressure relief. The ultra-high pressure sand-containing jet system includes a high-pressure sealing drill rod, a sand-containing jet guide head, a sand-containing jet nozzle, an ultra-high power water pump, and an aggregate fine sand additive, which are used to form a fishback-shaped precise fracturing perforation along the direction of the target fracture surface in the directional fracturing borehole. A grouped hydraulic fracturing system includes a high-pressure sealed drill rod, a hydraulic fracturing guide head, at least two sets of cross-type hydraulic fracturing devices and connecting mechanisms, used to perform grouped and simultaneous hydraulic fracturing of at least two adjacent precision-directed fracturing perforations within the directional fracturing borehole.

11. The apparatus according to claim 10, characterized in that, The water outlet direction of the sand-containing jet inlet of the ultra-high pressure sand-containing jet system is configured to always coincide with the intersection line of the fracture surface and the horizontal plane of the top-cutting and pressure-relieving target during construction.

12. The apparatus according to claim 10, characterized in that, Each group of cross-sectional hydraulic fracturing devices in the grouped induced hydraulic fracturing system includes a front-end sealing device and a rear-end sealing device, which are used to form an independent sealed fracturing space in the borehole sections where two adjacent fracturing perforations are located.

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