A method for targeted cavitation impact fracturing and pressure relief control in water-bearing strata

Abstract

This invention discloses a targeted cavitation impact fracturing and pressure relief control method for water-bearing strata. The method first utilizes the high temperature and concentrated energy of a laser to perform unidirectional fracturing, causing water in the surrounding muddy rock mass to evaporate and escape, eliminating the muddy rock mass and residual water effects, and cutting out a solid, well-formed crack. This achieves targeted and precise cutting of the pre-fabricated crack. Then, the high-pressure, high-speed shock wave generated during cavitation bubble annihilation impacts and fracturing the surrounding rock mass, disrupting the integrity of the critical layer under dynamic load on the roof, effectively reducing the dynamic load intensity generated by its rotation and subsidence, improving the stress environment of the surrounding rock, and controlling the deformation of the surrounding rock in the roadway. Using this method, the dynamic load generated by the rotation and subsidence of the overlying strata can be effectively weakened, providing a guarantee for the safe and efficient production of water-bearing strata mines.

Description

Technical Field

[0001] This invention relates to a method for controlling the pressure relief of targeted cavitation impact fracturing in water-bearing rock formations, belonging to the field of mine safety production technology. Background Technology

[0002] Currently, coal mining in western my country is gradually becoming the new normal. The strata in western mining areas are Jurassic and Cretaceous. Due to their late formation time and unique sedimentary processes, many water-bearing, weakly cemented rock layers exist above the coal seams. To ensure safe and efficient production at the working face, roof drainage projects are necessary to treat the water-bearing rock layers before mining. However, these projects can only drain most of the water, leaving residual water in the rock layers. This residual water interacts with the weakly cemented rock layers, leading to severe mudification. As mining in western areas progresses to deeper levels, the mining roadways are affected by the dynamic loads generated by the rotation and subsidence of the overlying strata. The surrounding rock stress environment is complex, and deformation continues to worsen, severely restricting the safe and efficient production of deep-buried mines in western areas. Therefore, to weaken the intensity of the dynamic loads generated by the rotation and subsidence of the overlying strata, directional roof fracturing technology is widely used.

[0003] Currently, commonly used roof directional fracturing technologies can be broadly classified into two categories. One category involves using specialized tools or slotting drill bits to cut annular grooves, and then injecting high-pressure water into the cut section for fracturing. For example, Chinese patent application number CN200910034388.6 discloses a hydraulic slotting directional fracturing method. This method injects high-pressure water into the slotting drill bit, while simultaneously causing the drill rod to drive the slotting drill bit to rotate, thereby pre-fabricating annular cracks in the coal and rock mass. This solves the problem of uncontrollable crack propagation direction in hydraulic fracturing and realizes directional hydraulic fracturing of the roof. Another type involves installing a shaped charge device inside the borehole to generate concentrated tension in a predetermined direction from the detonation shock wave, achieving tensile fracture in the intended direction and forming an initial directional crack. This is followed by directional blasting to relieve pressure on the roof. For example, Chinese patent application CN202411282590.1 discloses a method for pre-directed directional fracturing blasting to relieve pressure and determine parameters for roof cutting and roadway retention. This method utilizes the shaped charge effect induced by the shaped charge device to subject the surrounding rock of the borehole to uniform pressure in a non-defined direction and concentrated tension in the defined direction, causing the rock to tensile fracture in the defined direction, thus achieving directional pre-fracturing blasting to relieve pressure on the roof. These technologies perform well in water-free or weakly water-bearing roof conditions. However, with application in water-bearing strata, problems arise due to severe mudification of the surrounding rock mass and weakening of residual water, leading to issues such as incomplete formation of pre-fabricated cracks and ineffective fracturing of the rock mass during blasting. Furthermore, the grooves cut by special tools or slotted drill bits are annular, resulting in inaccurate orientation. This means that the commonly used roof directional fracturing technology has not effectively weakened the dynamic load generated by the rotation and subsidence of the overlying strata, which seriously restricts the safe and efficient production of water-bearing strata mines. Summary of the Invention

[0004] To address the shortcomings of existing roof-directed fracturing technologies, this invention provides a targeted cavitation impact fracturing and pressure relief control method for water-bearing strata. This method eliminates the mudification and residual water effects of the rock mass surrounding the pre-fabricated cracks, enabling precise targeted cutting of the pre-fabricated cracks. The high-pressure, high-speed shock wave generated during the cavitation bubble annihilation effectively impacts and fractures the key dynamic load impact layer, disrupting the integrity of the rock strata, reducing the dynamic load intensity generated by its rotation and subsidence, and controlling the deformation of the surrounding rock in the roadway.

[0005] To achieve the above objectives, the technical solution of the present invention is as follows:

[0006] A method for targeted cavitation impact fracturing and pressure relief control in water-bearing strata, characterized by comprising the following steps:

[0007] Step 1: Construct a structural model of the overburden engineering site.

[0008] A structural model of the overburden engineering was constructed based on geological borehole information, mining technology conditions, and the mechanical response characteristics of the roof rock at the location where pressure relief and control were implemented.

[0009] Step 2: Identify the critical layer for dynamic load impact on the roof.

[0010] Based on the constructed overburden engineering structure model, the dynamic load generated by the rotational subsidence of each rock layer in the top plate is calculated, and the rock layer with the largest dynamic load generated by the rotational subsidence is selected as the key layer for dynamic load impact of the top plate.

[0011] Step 3: Determine the location of pre-fabricated cracks in the roof slab.

[0012] The location of prefabricated cracks in the roof strata is determined based on the "leaving" or "excavating" of the mining roadway plan and the stress distribution characteristics of the surrounding rock.

[0013] Step 4: Design key parameters for targeted cavitation impact-induced fracturing and pressure relief control technology

[0014] Within the critical layer of dynamic load impact on the top plate, design cavitation-induced crack parameters, laser-targeted precise pre-fabrication crack parameters, and cavitation impact-induced crack parameters.

[0015] Step 5: Laser-targeted precision pre-creation of cracks

[0016] The implementation site is divided into sections. First, cavitation-induced fracture holes are constructed at the first implementation site. After the construction is completed, laser-targeted precise unidirectional cutting is performed within the cavitation-induced fracture holes along the roadway direction. The direction of the cavitation water jet impacting the fracture is controlled, thereby forming a precise and continuous fracture surface along the roadway direction. Utilizing the characteristics of high temperature and concentrated energy of the laser, the water in the muddy rock mass around the pre-fabricated fracture evaporates and escapes, eliminating the muddy rock mass and residual water effect around the pre-fabricated fracture, thereby cutting out a solid and well-formed fracture and achieving targeted and precise cutting of the pre-fabricated fracture.

[0017] Step Six: Cavitation Impact Fracturing of Top Rock Layers

[0018] Cavitation water jets are sprayed into the precast cracks. The cavitation bubbles interact with the rock surface and are extinguished. When the cavitation bubbles are extinguished, high-pressure and high-speed shock waves are generated, which impact and crack the rock mass around the precast cracks.

[0019] Step 7: Verify the effect of cavitation impact fracturing

[0020] Establish cavitation impact fracturing effect test index that can directly reflect the peak stress of surrounding rock, the amount of surrounding rock deformation and the microseismic energy value of the roof, test the cavitation impact fracturing effect of the roof strata at the first implementation site, and provide a basis for adjusting the key parameters of the targeted cavitation impact fracturing pressure relief control technology at the next implementation site;

[0021] Repeat steps four through seven above to sequentially complete the impact-induced fracturing and pressure relief at each section of the construction site.

[0022] Furthermore, the method for determining the critical layer of dynamic load impact in step two is as follows:

[0023] Based on the constructed overburden engineering structure model, the dynamic load generated by the rotational subsidence of each stratum above the coal seam is quantitatively calculated, namely:

[0024]

[0025] In the formula, D i m is the dynamic load generated by the rotational subsidence of the i-th rock layer. i Let γi be the thickness of the i-th rock layer, γi be the unit weight of the i-th rock layer, and l i Let Δh be the fracture length of the i-th rock layer. i Δh i-1 Let be the rotational subsidence of the i-th and i-1th rock layers;

[0026] If the i-th layer is the critical layer for dynamic load impact, then the dynamic load relationship satisfied by the (i+1)-th layer is:

[0027] D i >D i+1

[0028] In the formula, D i+1 This refers to the dynamic load generated by the rotation and subsidence of the (i+1)th rock layer.

[0029] Furthermore, the specific method for step three is as follows:

[0030] Based on the "retention" or "excavation" of the mining roadway plan, the stress distribution characteristics of the surrounding rock under three conditions—above the solid coal, above the mining roadway, and above the goaf—are analyzed. The optimal location for precast cracks in the roof strata is the location where the peak stress of the surrounding rock is at its minimum.

[0031] Furthermore, the cavitation-induced fracture parameters in step four mainly include the inclination angle, spacing, and depth of the cavitation-induced fractures, wherein:

[0032] The cavitation-induced fracture hole inclination angle α is determined by the location of pre-fabricated fractures in the roof strata, the equipment layout in the roadway, and the performance of the drilling rig. The determined cavitation-induced fracture hole inclination angle α should be the maximum angle under the premise of facilitating geological drilling rig construction, and α < 90°.

[0033] The spacing R of cavitation-induced fracture pores is determined by the thickness of the solid coal, its burial depth, and the properties of the rock strata, i.e.:

[0034]

[0035] In the formula, δ is the cavitation impact fracturing correction coefficient, which takes a value between 0 and 1.5, d is the diameter of the cavitation fracturing pore, m is the thickness of the solid coal, f is the roof rock firmness coefficient, and M is the working face burial depth.

[0036] The depth H of the cavitation-induced fracture is determined by the vertical distance L between the initial position of the cut and the working surface and the inclination angle α of the cavitation-induced fracture, that is:

[0037]

[0038] The laser-targeted precision prefabrication parameters mainly include the initial position of the cut, the number of cuts, the laser power, the spot diameter, and the irradiation time. The initial position of the cut is the lower part of the first rock layer above the dynamic load impact key layer. The number of cuts is determined in combination with the initial position of the cut and the thickness of the dynamic load impact key layer. The laser power is set to 5kW to 10kW, the spot diameter is set to 8mm to 10mm, and the irradiation time is set to 120s to 300s.

[0039] The cavitation impact fracturing parameters mainly include water pump pressure, nozzle pressure drop and impact time. The water pump pressure is set to 45MPa~75MPa, the nozzle pressure drop is set to 35MPa~60MPa, and the impact time is set to 15min~30min.

[0040] Furthermore, in step five, a laser-targeted slit-cutting device with coal mine safety certification is used to perform targeted, precise, unidirectional slit-cutting.

[0041] Furthermore, in step six, a cavitation impact fracturing platform with coal mine safety certification is used to carry out cavitation impact fracturing.

[0042] Furthermore, the cavitation impact fracturing effect test index K mentioned in step seven is determined by the following formula.

[0043]

[0044] In the formula, P0, S0, and E0 are the peak value of surrounding rock stress, the amount of surrounding rock deformation, and the energy value of the positioning microseismic event before implementation, respectively; and P1, S1, and E1 are the peak value of surrounding rock stress, the amount of surrounding rock deformation, and the energy value of the positioning microseismic event after implementation, respectively.

[0045] The method for verifying the effect of cavitation impact fracturing in the roof strata is as follows: when K≥0.6, it indicates that the current cavitation impact fracturing effect meets the on-site requirements, and the current control technical parameters are the control technical parameters for the next implementation site; when K<0.6, it indicates that the current cavitation impact fracturing effect does not meet the on-site requirements, and the key parameters of the current targeted cavitation impact fracturing pressure relief control technology need to be optimized before construction can be carried out at the next implementation site.

[0046] Furthermore, the laser-targeted fracturing device mainly comprises six components: a laser control system, a laser monitoring system, a water cooling system, a laser generator, an optical fiber cable, and a laser lens. The working relationship between these components is as follows: the laser control system controls the laser generator to produce laser light with set parameters; the laser light is transmitted to the laser lens via the optical fiber cable for targeted and precise pre-fabrication of the fracture; simultaneously, the laser control system controls the laser monitoring system to monitor the characteristics of the laser light output from the laser generator in real time, and the laser control system controls the water cooling system to dissipate heat and cool the laser generator in real time. Before the laser-targeted fracturing device of this invention operates, a geological drilling rig is first used to send the laser lens to the set position within the cavitation-induced fracture hole.

[0047] Furthermore, the cavitation impact fracturing platform in step six mainly comprises seven components: a cavitation jet control system, a cavitation jet monitoring system, a high-pressure pump, a high-pressure water pipe, a cavitation jet generating device, an injection device, and a circumferential nozzle. The working relationship between these components is as follows: the cavitation jet control system controls the high-pressure pump to convert downhole atmospheric pressure water into stable high-pressure water. This high-pressure water is then transported through the high-pressure water pipe to the cavitation jet generating device. The cavitation jet control system controls the cavitation jet generating device to convert the high-pressure water into a cavitation water jet, which is then transported to the injection device and ejected through the circumferential nozzle into the pre-fabricated fracture. Simultaneously, the cavitation jet control system controls the cavitation jet monitoring system to monitor the characteristics of the high-pressure water output from the high-pressure pump and the cavitation jet output from the cavitation jet generating device in real time. Before operation, the cavitation impact fracturing platform of this invention requires the geological drilling rig to first deliver the injection device to the pre-fabricated fracture location.

[0048] The effective effects of this invention are as follows:

[0049] 1. This invention utilizes the high temperature and concentrated energy of lasers to perform unidirectional cutting, causing the water in the muddy rock mass surrounding the precast crack to evaporate and escape, eliminating the muddy rock mass and residual water effect around the precast crack, cutting out a solid and well-formed crack, and achieving targeted and precise cutting of the precast crack.

[0050] 2. The present invention utilizes the high-pressure, high-speed shock wave generated during the cavitation bubble extinguishing to impact and fracture the rock mass surrounding the pre-fabricated crack, thereby destroying the integrity of the key dynamic load impact layer, effectively reducing the dynamic load intensity generated by its rotation and subsidence, improving the stress environment of the surrounding rock, and controlling the deformation of the surrounding rock in the roadway.

[0051] 3. This invention establishes key indicators for verifying the cavitation impact fracturing effect, which can directly reflect the peak stress, deformation, and microseismic energy of the surrounding rock. It provides a comprehensive and thorough verification of the implementation effect of the targeted cavitation impact fracturing method and can provide scientific guidance for the field implementation of the targeted cavitation impact fracturing method. Attached Figure Description

[0052] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. The accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0053] Figure 1 A schematic flowchart of a targeted cavitation impact fracturing and pressure relief control method for water-bearing rock formations provided in an embodiment of the present invention;

[0054] Figure 2 A schematic diagram illustrating the stress distribution characteristics of the surrounding rock in a roadway where pre-fabricated cracks are located above solid coal, provided in an embodiment of the present invention.

[0055] Figure 3 A schematic diagram illustrating the stress distribution characteristics of the surrounding rock in a roadway where the pre-fabricated crack is located above the mining roadway, as provided in an embodiment of the present invention.

[0056] Figure 4 A schematic diagram illustrating the stress distribution characteristics of the surrounding rock in a roadway with prefabricated cracks located above a goaf, provided for an embodiment of the present invention.

[0057] Figure 5 This is a schematic diagram of the cavitation-induced cracking hole parameter design provided in an embodiment of the present invention;

[0058] Figure 6 A schematic diagram of a laser-targeted slit-cutting device provided in an embodiment of the present invention;

[0059] Figure 7 This is a schematic diagram of a cavitation impact fracturing platform provided in an embodiment of the present invention;

[0060] Figure 8 A schematic diagram of the dip section of a targeted cavitation impact fracturing and decompression control method for water-bearing strata provided in an embodiment of the present invention;

[0061] Figure 9 This is a schematic diagram of the strike cross section of a targeted cavitation impact-induced fracturing and pressure relief control method for aquifers provided in an embodiment of the present invention.

[0062] In the diagram: 1. Mining roadway, 2. Immediate floor, 3. Subsurface floor, 4. Solid coal, 5. Coal pillar, 6. Goaf, 7. Immediate roof, 8. Subsurface roof, 9. Surrounding rock stress, 10. Overburden load, 11. Pre-fabricated cracks in roof strata, 12. Coal seam, 13. Dynamic impact critical stratum, 14. Cavitation-induced fracture hole, 15. Laser-targeted fracture cutting device, 16. Laser control system, 17. Laser monitoring system, 18. Water cooling system, 19. Laser generator, 20. Fiber optic cable, 21. Laser lens, 22. Cavitation impact fracture platform, 23. Cavitation jet control system, 24. Cavitation jet monitoring system, 25. High-pressure pump, 26. High-pressure water pipe, 27. Cavitation jet generator, 28. Injection device, 29. Annular nozzle. Detailed Implementation

[0063] To make the objectives, technical solutions, and beneficial effects of this invention clearer, the invention will be further described in detail below with reference to the current situation of a mine in the Ningdong mining area and the accompanying drawings.

[0064] A mine in the Ningdong mining area mainly mines No. 2 coal seam. Due to the formation of the mine's strata dating back to the Mesozoic Jurassic-Cretaceous period, a water-bearing, weakly cemented rock layer exists above No. 2 coal seam. Despite the implementation of roof drainage systems, residual water remains in the roof strata. The immediate roof (7) of No. 2 coal seam is a composite rock layer composed of mudstone and siltstone, the basic roof (8) is fine- to coarse-grained sandstone, the immediate floor (2) is mudstone, and the basic floor (3) is siltstone. With the mining of No. 2 coal seam, the working face and roadways are subjected to severe deformation of the surrounding rock due to the overlying load (10), seriously hindering the mine's safe and efficient production. To address this, the mine has successively adopted directional hydraulic fracturing and directional pre-splitting blasting techniques to reduce the dynamic load intensity generated by the roof strata. However, the application results show that due to the water-bearing, weakly cemented rock conditions in the mine, the surrounding rock mass around the boreholes is severely muddy, and the residual water is weakened. This has resulted in problems such as pre-fabricated cracks failing to form properly and blasting not effectively fracturing the rock mass. Consequently, the dynamic load intensity generated by the roof strata has not been effectively reduced, and the deformation of the roadway surrounding rock remains severe. Therefore, in view of the shortcomings of the top plate directional decompression technology under water-bearing strata conditions, the present invention proposes a targeted cavitation impact-induced fracturing decompression control method for water-bearing strata.

[0065] Reference Figures 1-9 The present invention provides a method for controlling the pressure relief of targeted cavitation impact fracturing in water-bearing strata, comprising the following steps:

[0066] Step 1: Construct a structural model of the overburden engineering site.

[0067] Determine the implementation location of the targeted cavitation impact-induced fracturing and pressure relief control method, and construct an overburden engineering structure model based on the geological drilling information, mining technology conditions, and roof rock mechanical response characteristics of the implementation location;

[0068] Step 2: Identify the critical layer for dynamic load impact on the roof.

[0069] Based on the constructed overburden engineering structure model, the dynamic load generated by the rotational subsidence of each rock stratum above coal seam 12 is quantitatively calculated, namely:

[0070]

[0071] In the formula, D i m is the dynamic load generated by the rotational subsidence of the i-th rock layer. i Let γi be the thickness of the i-th rock layer, γi be the unit weight of the i-th rock layer, and l i Let Δh be the fracture length of the i-th rock layer. i Δh i-1 Given the rotational subsidence of the i-th and i-1th rock layers, the rock layer with the largest dynamic load generated by the rotational subsidence is selected as the key layer for dynamic load impact, i.e.:

[0072] If the i-th layer is the critical layer 13 for dynamic load impact, then the dynamic load relationship satisfied by the (i+1)-th layer is:

[0073] D i >D i+1

[0074] In the formula, D i+1 This refers to the dynamic load generated by the rotation and subsidence of the (i+1)th rock layer.

[0075] Step 3: Determine the location of pre-fabricated crack 11 in the roof slab.

[0076] like Figures 2 to 4 As shown, since the mining roadway 1 is a "dug-out roadway", the distribution characteristics of the surrounding rock stress 9 under the conditions that the pre-fabricated crack 11 in the roof stratum is located above the solid coal 4, above the mining roadway 1, and above the goaf 6 are analyzed. It is found that when the pre-fabricated crack 11 in the roof stratum is located above the goaf 6, the peak value of the surrounding rock stress 9 of the solid coal 4 and the coal pillar 5 is the smallest. Therefore, it is determined that the location of the pre-fabricated crack 11 in the roof stratum is above the goaf 6.

[0077] Step 4: Design key parameters for targeted cavitation impact fracturing and pressure relief control technology

[0078] Key parameters include cavitation-induced crack parameters, laser-targeted precision-pre-induced crack parameters, and cavitation impact-induced crack parameters; among which:

[0079] (1) The parameters of the cavitation-induced fracture holes 14 mainly include the inclination angle, spacing and depth of the cavitation-induced fracture holes 14;

[0080] The inclination angle of the cavitation fracture hole 14 is generally determined by factors such as the location of the pre-fabricated crack 11 in the roof strata, the equipment layout in the mining roadway 1, and the performance of the drilling rig. The determined inclination angle α of the cavitation fracture hole should be the maximum angle under the premise of facilitating geological drilling rig construction, and α < 90°.

[0081] The spacing R of the cavitation-induced fracture holes 14 can be determined by the thickness of the solid coal 4, the burial depth, the properties of the rock strata, etc., that is:

[0082]

[0083] In the formula, δ is the cavitation impact fracture correction coefficient, d is the diameter of cavitation fracture hole 14, m is the thickness of solid coal 4, f is the roof rock firmness coefficient, and M is the working face burial depth.

[0084] The depth H of the cavitation-induced fracture hole 14 can be determined by the vertical distance L between the initial position of the cut and the working surface and the inclination angle α, that is:

[0085]

[0086] (2) The laser-targeted precision prefabrication crack parameters mainly include the initial position of the cut, the number of cuts, the laser power, the spot diameter, and the irradiation time. The initial position of the cut is the lower part of the first rock layer above the dynamic load impact key layer 13. The number of cuts is determined in combination with the initial position of the cut and the thickness of the dynamic load impact key layer 13. The laser power is set to 5kW~10kW, the spot diameter is set to 8mm~10mm, and the irradiation time is set to 120s~300s.

[0087] (3) The cavitation impact fracturing parameters mainly include water pump pressure, nozzle pressure drop and impact time. The water pump pressure is set to 45MPa~75MPa, the nozzle pressure drop is set to 35MPa~60MPa, and the impact time is set to 15min~30min.

[0088] Step 5: Laser-targeted precise pre-creation of cracks

[0089] It should be noted that the construction method of this invention at the implementation site is segmented construction.

[0090] First, the geological drilling rig drills the cavitation fracture hole 14 as designed. After the drilling is completed, a laser-targeted cutting device 15 with coal mine safety certification is used to cut the pre-made crack 11 in the borehole in a unidirectional direction.

[0091] The laser-targeted kerfing device mentioned above is referred to in section 15. Figure 6The system comprises a laser control system 16, a laser monitoring system 17, a water cooling system 18, a laser generator 19, an optical fiber cable 20, and a laser lens 21. The laser control system 16 is connected to the laser monitoring system 17, the water cooling system 18, and the laser generator 19. The water cooling system 18 is connected to the laser generator 19, and the laser generator 19 is then connected to the laser monitoring system 17 and the water cooling system, and finally connected to the laser lens 21 via the optical fiber cable 20. The working method is as follows: First, the laser lens 21 is sent to the set position in the cavitation fracture hole 14 using a geological drilling rig. Then, the laser control system 16 controls the laser generator 19 to generate laser with set parameters. The laser is transmitted to the laser lens 21 through the optical fiber cable 20 to achieve unidirectional cutting. Taking advantage of the high temperature and concentrated energy of the laser, the water in the muddy rock mass around the pre-fabricated crack 11 evaporates and escapes, eliminating the muddy rock mass and residual water effect around the pre-fabricated crack 11, thereby cutting out a solid and well-formed crack and achieving targeted and precise cutting of the pre-fabricated crack 11. At the same time, the laser control system 16 controls the laser monitoring system 17 to monitor the characteristics of the laser output by the laser generator 19 in real time, and the laser control system 16 controls the water cooling system 18 to dissipate heat and cool the laser generator in real time.

[0092] Step 6: Cavitation impact fracturing of the top strata

[0093] Cavitation impact fracturing of the roof strata was carried out using a cavitation impact fracturing platform 22 with coal mine safety certification. (See also...) Figure 7The cavitation impact fracturing platform 22 mainly includes a cavitation jet control system 23, a cavitation jet monitoring system 24, a high-pressure pump 25, a high-pressure water pipe 26, a cavitation jet generating device 27, an injection device 28, and a circumferential nozzle 29. The cavitation jet control system 23 is connected to the cavitation jet monitoring system 24, the high-pressure pump 25, and the cavitation jet generating device 27. The cavitation jet monitoring system 24 is then connected to the high-pressure pump 25 and the cavitation jet generating device 27. The high-pressure pump 25 is also connected to the cavitation jet generating device 27 through the high-pressure water pipe 26. The cavitation jet generating device 27 is connected to the injection device 28 through the high-pressure water pipe 26. The injection device 28 is equipped with a circumferential nozzle 29. The working principle is as follows: First, the jetting device 28 is delivered to the pre-fabricated fracture location by the geological drilling rig. Then, the cavitation jet control system 23 controls the high-pressure pump 25 to convert the underground atmospheric water into stable high-pressure water. The high-pressure water is transported to the cavitation jet generating device 27 through the high-pressure water pipe 26. The cavitation jet control system 23 controls the cavitation jet generating device 27 to convert the high-pressure water into cavitation water jets and then transport them to the jetting device 28. The jets are then ejected from the pre-fabricated fracture by the circumferential nozzle 29. The cavitation bubbles ejected from the circumferential nozzle 29 interact with the rock surface and are extinguished. The high-pressure, high-speed shock wave generated when the cavitation bubbles are extinguished will impact and fracture the rock mass surrounding the pre-fabricated fracture 11, destroying the integrity of the key layer of dynamic load impact, effectively reducing the dynamic load intensity generated by its rotation and subsidence, improving the stress environment of the surrounding rock, and controlling the deformation of the surrounding rock in the tunnel. At the same time, the cavitation jet control system 23 controls the cavitation jet monitoring system 24 to monitor the characteristics of the high-pressure water output by the high-pressure pump 25 and the cavitation jet output by the cavitation jet generating device 27 in real time.

[0094] Step 7: Verify the effect of cavitation impact fracturing

[0095] The peak stress, deformation, and microseismic energy of the roof were used to establish K as a key indicator for verifying the effectiveness of cavitation impact fracturing, based on the values ​​of the surrounding rock stress, deformation, and microseismic energy of the roof before and after the implementation of the targeted cavitation impact fracturing control technology.

[0096]

[0097] In the formula, P0, S0, and E0 are the peak value of surrounding rock stress, the amount of surrounding rock deformation, and the energy value of the positioning microseismic event before implementation, and P1, S1, and E1 are the peak value of surrounding rock stress, the amount of surrounding rock deformation, and the energy value of the positioning microseismic event after implementation.

[0098] When K ≥ 0.6, the cavitation impact fracturing effect is deemed to meet the on-site requirements, and the current targeted cavitation impact fracturing pressure relief control technology parameters are the optimal parameters under this condition. The next implementation site will continue to use the current technology parameters. When K < 0.6, the current cavitation impact fracturing effect is deemed to not meet the on-site requirements, and the key parameters of the current targeted cavitation impact fracturing pressure relief control technology need to be optimized before construction can proceed to the next implementation site.

[0099] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., 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 controlling the pressure relief of water-bearing rock strata through targeted cavitation impact fracturing, characterized in that, Includes the following steps: Step 1: Construct a structural model of the overburden engineering site. A structural model of the overburden engineering was constructed based on the geological borehole information, mining technology conditions, and the mechanical response characteristics of the roof rock at the location where the pressure relief and control measures were implemented. Step 2: Identify the critical layer for dynamic load impact on the roof. Based on the constructed overburden engineering structure model, the dynamic load generated by the rotational subsidence of each rock layer in the top plate is calculated, and the rock layer with the largest dynamic load generated by the rotational subsidence is selected as the key layer for dynamic load impact of the top plate. Step 3: Determine the location of pre-fabricated cracks in the roof slab. The location of prefabricated cracks in the roof strata is determined based on the planned roadway retention or excavation and the stress distribution characteristics of the surrounding rock. Step 4: Design key parameters for targeted cavitation impact-induced fracturing and pressure relief control technology Within the critical layer of dynamic load impact on the top plate, design cavitation-induced crack parameters, laser-targeted precise pre-fabrication crack parameters, and cavitation impact-induced crack parameters. Step 5: Laser-targeted precision pre-creation of cracks The implementation site will be constructed in sections. First, cavitation fracturing holes will be constructed at the first implementation site. After the construction is completed, laser-targeted precise unidirectional cutting will be carried out in the cavitation fracturing holes along the direction of the roadway to control the direction of the cavitation water jet impact and fracturing, thereby forming a precise and continuous fracture surface along the direction of the roadway. Step Six: Cavitation Impact Fracturing of Top Rock Layers Cavitation water jets are sprayed into the precast cracks. The cavitation bubbles interact with the rock surface and are extinguished. When the cavitation bubbles are extinguished, high-pressure and high-speed shock waves are generated, which impact and crack the rock mass around the precast cracks. Step 7: Verify the effect of cavitation impact fracturing Establish cavitation impact fracturing effect test index that can directly reflect the peak stress of surrounding rock, the amount of surrounding rock deformation and the microseismic energy value of the roof, test the cavitation impact fracturing effect of the roof strata at the first implementation site, and provide a basis for adjusting the key parameters of the targeted cavitation impact fracturing pressure relief control technology at the next implementation site; Repeat steps four through seven above to sequentially complete the impact-induced fracturing and pressure relief at each section of the construction site.

2. The method for targeted cavitation impact fracturing and pressure relief control of water-bearing strata as described in claim 1, characterized in that, The method for determining the critical layer for dynamic load impact on the top plate in step two is as follows: Based on the constructed overburden engineering structure model, the dynamic load generated by the rotational subsidence of each stratum above the coal seam is quantitatively calculated, namely: In the formula, D i m is the dynamic load generated by the rotational subsidence of the i-th rock layer. i Let γi be the thickness of the i-th rock layer, γi be the unit weight of the i-th rock layer, and l i Let Δh be the fracture length of the i-th rock layer. i Δh i-1 These are the rotational subsidence amounts of the i-th and i-1th rock layers, respectively; If the i-th layer is the critical layer for dynamic load impact, then the dynamic load relationship satisfied by the (i+1)-th layer is: D i >D i+1 In the formula, D i+1 This refers to the dynamic load generated by the rotation and subsidence of the (i+1)th rock layer.

3. The method for targeted cavitation impact fracturing and pressure relief control of water-bearing strata as described in claim 1, characterized in that, The specific method for step three is as follows: Based on the planned roadway retention or excavation in the mining roadway, the stress distribution characteristics of the surrounding rock under three conditions—where the precast cracks in the roof strata are located above the solid coal, above the mining roadway, and above the goaf—are analyzed. The optimal location for the precast cracks in the roof strata is the location where the peak stress of the surrounding rock is at its minimum.

4. The method for targeted cavitation impact fracturing and pressure relief control of water-bearing strata as described in claim 1, characterized in that, The cavitation-induced fracture parameters in step four mainly include the inclination angle, spacing, and depth of the cavitation-induced fractures, wherein: The cavitation-induced fracture hole inclination angle α is determined by the location of pre-fabricated fractures in the roof strata, the equipment layout in the roadway, and the performance of the drilling rig. The determined cavitation-induced fracture hole inclination angle α should be the maximum angle under the premise of facilitating geological drilling rig construction, and α < 90°. The spacing R of cavitation-induced fracture pores is determined by the thickness of the solid coal, its burial depth, and the properties of the rock strata, i.e.: In the formula, δ is the cavitation impact fracturing correction coefficient, which takes a value between 0 and 1.5, d is the diameter of the cavitation fracturing pore, m is the thickness of the solid coal, f is the roof rock firmness coefficient, and M is the working face burial depth. The depth H of the cavitation-induced fracture is determined by the vertical distance L between the initial position of the cut and the working surface and the inclination angle α of the cavitation-induced fracture, that is: The laser-targeted precision prefabrication parameters mainly include the initial position of the cut, the number of cuts, the laser power, the spot diameter, and the irradiation time. The initial position of the cut is the lower part of the first rock layer above the dynamic load impact key layer. The number of cuts is determined in combination with the initial position of the cut and the thickness of the dynamic load impact key layer. The laser power is set to 5kW to 10kW, the spot diameter is set to 8mm to 10mm, and the irradiation time is set to 120s to 300s. The cavitation impact fracturing parameters mainly include water pump pressure, nozzle pressure drop and impact time. The water pump pressure is set to 45MPa~75MPa, the nozzle pressure drop is set to 35MPa~60MPa, and the impact time is set to 15min~30min.

5. The method for targeted cavitation impact fracturing and pressure relief control of water-bearing strata as described in claim 1, characterized in that, In step five, a laser-targeted slit cutting device with coal mine safety certification is used to perform targeted, precise, unidirectional slit cutting.

6. The method for targeted cavitation impact fracturing and pressure relief control of water-bearing strata as described in claim 5, characterized in that, In step six, cavitation impact fracturing is carried out using a cavitation impact fracturing platform with coal mine safety certification.

7. The method for targeted cavitation impact fracturing and pressure relief control of water-bearing strata as described in claim 1, characterized in that, The cavitation impact fracturing effect test index K mentioned in step seven is determined by the following formula. In the formula, P0, S0, and E0 are the peak value of surrounding rock stress, the amount of surrounding rock deformation, and the energy value of the positioning microseismic event before implementation, respectively; and P1, S1, and E1 are the peak value of surrounding rock stress, the amount of surrounding rock deformation, and the energy value of the positioning microseismic event after implementation, respectively. The method for verifying the effect of cavitation impact fracturing in the roof strata is as follows: when K≥0.6, it indicates that the current cavitation impact fracturing effect meets the on-site requirements, and the current control technical parameters are the control technical parameters for the next implementation site; when K<0.6, it indicates that the current cavitation impact fracturing effect does not meet the on-site requirements, and the key parameters of the current targeted cavitation impact fracturing pressure relief control technology need to be optimized before construction can be carried out at the next implementation site.

8. The method for targeted cavitation impact fracturing and pressure relief control of water-bearing strata as described in claim 6, characterized in that, The laser-targeted kerf cutting device mainly comprises six components: a laser control system, a laser monitoring system, a water cooling system, a laser generator, an optical fiber cable, and a laser lens. The working relationship between these components is as follows: the laser control system controls the laser generator to produce laser light with set parameters, and the laser light is transmitted to the laser lens through the optical fiber cable for targeted and precise pre-cutting of cracks; at the same time, the laser control system controls the laser monitoring system to monitor the characteristics of the laser light output by the laser generator in real time, and the laser control system controls the water cooling system to dissipate heat and cool the laser generator in real time.

9. The method for targeted cavitation impact fracturing and pressure relief control of water-bearing strata as described in claim 8, characterized in that, The cavitation impact fracturing platform mainly comprises seven components: a cavitation jet control system, a cavitation jet monitoring system, a high-pressure pump, a high-pressure water pipe, a cavitation jet generating device, an injection device, and a circumferential nozzle. The working relationship between these components is as follows: the cavitation jet control system controls the high-pressure pump to convert downhole atmospheric water into stable high-pressure water. The high-pressure water is then transported through the high-pressure water pipe to the cavitation jet generating device. The cavitation jet control system controls the cavitation jet generating device to convert the high-pressure water into a cavitation water jet, which is then transported to the injection device and ejected through the circumferential nozzle into the pre-fabricated fracture. Simultaneously, the cavitation jet control system controls the cavitation jet monitoring system to monitor the characteristics of the high-pressure water output from the high-pressure pump and the cavitation jet output from the cavitation jet generating device in real time.

Images