Water-containing rock stratum targeted cavitation impact fracturing pressure relief regulation and control method

Abstract

The invention discloses a water-containing rock stratum targeted cavitation impact fracturing pressure relief regulation and control method, which comprises the following steps of: firstly, performing one-way slotting according to the characteristics of high temperature and energy concentration of laser, so that water in argillization rock mass around a prefabricated crack is evaporated and escaped, argillization and residual water effects of the rock mass around the prefabricated crack are eliminated, and a firm formed crack is cut; then, high-pressure and high-speed shock waves generated during neglecting of the cavitation bubbles are used for conducting impact cracking on rock mass around the prefabricated cracks, the integrity of a dynamic load impact key layer of a top plate is destroyed, the dynamic load strength generated by rotation sinking of the top plate is effectively reduced, the surrounding rock stress environment is improved, and roadway surrounding rock deformation is controlled. By means of the method, the dynamic load generated by rotary sinking of the overlying rock stratum can be effectively weakened, and a guarantee is provided for safe and efficient production of a water-containing rock stratum mine.

Description

Technical Field

[0001] The invention relates to a method for regulating and controlling water-containing rock formation targeted cavitation impact fracturing pressure relief, and belongs to the technical field of mine production safety. Background Art

[0002] At present, the mining of coal resources in the west has gradually become the new normal of coal resource mining in my country. The strata in the western mining area are Jurassic and Cretaceous strata. Due to their late diagenesis time and special sedimentary process, there are many water-containing weakly cemented rock layers above the coal seams. In order to ensure the safe and efficient production of the working face, the roof drainage project needs to be used to treat the water-containing rock layer before the working face is mined. However, the roof drainage project can only discharge most of the water, so there is still residual water in the rock layer. The residual water and the weakly cemented rock layer have a water-rock coupling effect, and the rock layer is seriously muddied. As the western mining area enters deep mining, the mining tunnel is affected by the dynamic load generated by the rotation and sinking of the overlying rock layer. The stress environment of the surrounding rock is complex, and the deformation continues to increase, which has seriously restricted the safe and efficient production of deep buried mines in the western mining area. To this end, in order to weaken the strength of the dynamic load generated by the rotation and sinking of the overlying rock layer, the roof directional fracturing technology is often used.

[0003] At present, the commonly used roof directional fracturing technologies can be roughly divided into two categories. One is to use special tools or slot drill bits to cut annular grooves, and then inject high-pressure water into the slotted section for roof directional hydraulic fracturing. For example, Chinese patent application No. CN200910034388.6 discloses a hydraulic slot directional fracturing method. This method inputs high-pressure water into the slot drill bit, and at the same time, the drill rod drives the slot drill bit to rotate, thereby prefabricating annular cracks in the coal rock mass, solving the problem of uncontrollable expansion direction of hydraulic fracturing cracks and realizing directional hydraulic fracturing of the roof. The other type is to install an energy-gathering device in the borehole so that the detonation shock wave generates concentrated tension in the set direction, realizes tensile fracture in the predetermined direction, and then forms an initial guided crack, and then blasts the roof directional blasting pressure relief. For example, Chinese patent application number CN202411282590.1 discloses a method for pre-directional pre-splitting blasting pressure relief and parameter determination for cutting the top and leaving the lane. This method uses the energy-gathering effect caused by the energy-gathering device to make the surrounding rock of the blasthole subject to uniform pressure in a non-set direction and concentrated tension in a set direction, so that the rock undergoes tensile fracture in the set direction, thus realizing the directional pre-splitting blasting pressure relief of the roof. These technologies have good application effects under water-free or weakly water-containing roof conditions, but with the application under water-containing rock conditions, due to the serious mudification of the rock mass around the borehole and the weakening of residual water, there are problems such as soft and unformed prefabricated cracks and failure of blasting to effectively fracture the rock mass. At the same time, the grooves cut by special tools or slot drill bits are annular, and there are problems such as inaccurate orientation. This means that the commonly used roof directional fracturing technology fails to effectively weaken the dynamic loads generated by the rotation and sinking of the overlying rock strata, seriously restricting the safe and efficient production of water-bearing rock strata mines. Summary of the invention

[0004] In view of the shortcomings of the prior art roof directional fracturing technology, the present invention provides a method for regulating and controlling targeted cavitation impact fracturing pressure relief of water-containing rock formations, which eliminates the mud and residual water effects of the rock mass around the prefabricated fractures, realizes targeted and precise cutting of the prefabricated fractures, and effectively impacts and fractures the key layer impacted by dynamic loads through the high-pressure and high-speed shock waves generated when the cavitation bubbles are extinct, destroys the integrity of the rock formation, reduces the dynamic load intensity generated by its rotation and sinking, and controls the deformation of the tunnel surrounding rock.

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

[0006] A method for regulating and controlling the pressure relief of targeted cavitation impact fracturing of water-bearing rock formations, characterized in that it comprises the following steps:

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

[0008] Construct the overburden engineering structure model based on the geological drilling information, mining technical conditions and roof rock mechanical response characteristics of the pressure relief control implementation site;

[0009] Step 2: Identify the key layer of roof dynamic load impact

[0010] Based on the constructed overburden engineering structure model, the dynamic load generated by the rotation and sinking of each rock layer of the roof is calculated, and the rock layer with the largest dynamic load generated by the rotation and sinking is selected as the key layer for dynamic load impact of the roof;

[0011] Step 3: Determine the location of prefabricated cracks in the roof rock

[0012] Determine the location of prefabricated cracks in the roof rock layer according to the "retaining lane" or "driving lane" situation of the mining lane plan and the stress distribution characteristics of the surrounding rock;

[0013] Step 4: Design key parameters of targeted cavitation impact fracturing pressure relief control technology

[0014] Design cavitation crack hole parameters, laser targeted precise prefabricated crack parameters and cavitation impact crack parameters within the key layer of roof dynamic load impact;

[0015] Step 5: Laser targeted precise prefabrication of cracks

[0016] The implementation site is constructed in sections. First, cavitation cracking holes are constructed at the first implementation site. After the construction is completed, laser targeted precise unidirectional cutting is performed in the cavitation cracking holes along the direction of the tunnel to control the impact cracking direction of the cavitation water jet, thereby forming a precise and continuous fracture surface along the direction of the tunnel; the laser has the characteristics of high temperature and concentrated energy, so that the water in the muddy rock mass around the prefabricated cracks evaporates and escapes, eliminating the muddy and residual water effects of the rock mass around the prefabricated cracks, thereby cutting out solid and formed cracks, and achieving targeted and precise cutting of prefabricated cracks;

[0017] Step 6: Cavitation impact cracking of roof rock

[0018] The cavitation water jet is ejected in the prefabricated crack, and the cavitation bubbles react with the rock surface and extinguish. When the cavitation bubbles extinguish, a high-pressure and high-speed shock wave is generated, which impacts and cracks the rock around the prefabricated crack;

[0019] Step 7: Check the cavitation impact cracking effect

[0020] Establish a cavitation impact fracturing effect test index that can directly reflect the peak stress of the surrounding rock, the deformation of the surrounding rock and the microseismic energy value of the roof, test the cavitation impact fracturing effect of the roof rock 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] The above steps 4 to 7 are repeated to complete the impact fracturing pressure relief of each section at the construction site in sequence.

[0022] Furthermore, the method for determining the key layer of dynamic load impact in step 2 is:

[0023] According to the constructed overburden engineering structure model, the dynamic load generated by the rotation and sinking of each rock layer above the coal seam is quantitatively calculated, namely:

[0024]

[0025] Where D i is the dynamic load caused by the rotation and sinking of the i-th rock layer, m i is the thickness of the i-th rock layer, γi is the bulk density of the i-th rock layer, l i is the fracture length of the i-th rock layer, Δh i , Δh i-1 is the rotational subsidence of the i-th and i-1-th rock layers;

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

[0027] D i >D i+1

[0028] Where D i+1 It is the dynamic load generated by the rotation and sinking of the i+1th rock layer.

[0029] Further, the specific method of step three is:

[0030] According to the plan of "retaining lane" or "digging lane" in the mining tunnel, the surrounding rock stress distribution characteristics are analyzed under three conditions: the prefabricated cracks in the roof strata are located above the solid coal, above the mining tunnel and above the goaf. The prefabricated crack position corresponding to the minimum surrounding rock stress peak is the optimal prefabricated crack position in the roof strata.

[0031] Furthermore, the cavitation crack hole parameters in step 4 mainly include the inclination angle, spacing and depth of the cavitation crack holes, wherein:

[0032] The cavitation-induced fracture hole inclination angle α is determined by the location of the prefabricated fractures in the roof rock layer, the equipment layout in the tunnel 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 the construction of the geological drilling rig, and α < 90°;

[0033] The spacing R of cavitation cracks is determined by the thickness of the solid coal, the burial depth and the rock formation properties, namely:

[0034]

[0035] Where, δ is the correction coefficient of cavitation impact cracking, δ is between 0 and 1.5, d is the diameter of the cavitation crack hole, m is the thickness of the solid coal, f is the strength coefficient of the roof rock layer, and M is the depth of the working face;

[0036] The depth H of the cavitation crack hole is determined by the vertical distance L between the initial position of the slit and the working surface and the inclination angle α of the cavitation crack hole, that is:

[0037]

[0038] The laser targeted precise prefabricated crack parameters mainly include the initial position of the slit, the number of slits, the laser power, the spot diameter and the irradiation time, wherein the initial position of the slit is the lower part of the first rock layer above the dynamic load impact key layer, the number of slits is determined in combination with the initial position of the slit 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 slitting device with coal safety certification is used to implement targeted precise unidirectional slitting.

[0041] Furthermore, in step six, cavitation impact fracturing is carried out using a cavitation impact fracturing platform with coal safety certification.

[0042] Further, the cavitation impact cracking effect test index K described in step 7 is determined by the following formula:

[0043]

[0044] Where P0, S0, and E0 are the peak value of surrounding rock stress, surrounding rock deformation, and located microseismic energy value before implementation, respectively; P1, S1, and E1 are the peak value of surrounding rock stress, surrounding rock deformation, and located microseismic energy value after implementation, respectively;

[0045] The method for testing the cavitation impact fracturing effect of the roof rock strata is: when K≥0.6, it means 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 means 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 slitting device mainly includes 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 the components is: the laser control system 16 controls the laser generator to generate a laser with set parameters, and the laser is transmitted to the laser lens through the optical fiber cable to perform targeted and precise prefabrication of cracks; at the same time, the laser control system controls the laser monitoring system to monitor the characteristics of the laser output by the laser generator in real time, and the laser control system controls the water cooling system to perform heat dissipation and cooling of the laser generator in real time. Before the laser targeted slitting device of the present invention works, it is first necessary to use a geological drill to send the laser lens to the set position in the cavitation-induced crack hole.

[0047] Furthermore, the cavitation impact fracturing platform in step six mainly includes 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, a jet device and an annular nozzle; the working relationship between the components is: the cavitation jet control system controls the high-pressure pump to convert the normal-pressure water in the well into stable high-pressure water, the high-pressure water is transported to the cavitation jet generating device through the high-pressure water pipe, the cavitation jet control system controls the cavitation jet generating device to convert the high-pressure water into a cavitation water jet and then transport it to the jet device, and then the annular nozzle sprays it into the prefabricated crack, and at the same time, the cavitation jet control system controls the cavitation jet monitoring system to monitor the characteristics of the high-pressure water output by the high-pressure pump and the cavitation jet output by the cavitation jet generating device in real time. Before the cavitation impact fracturing platform of the present invention works, the geological drilling rig needs to first send the jet device to the prefabricated crack position.

[0048] The effective effects of the present invention are:

[0049] 1. The present invention uses the characteristics of high temperature and concentrated energy of laser to perform unidirectional cutting, so that the water in the muddy rock mass around the prefabricated cracks evaporates and escapes, eliminating the muddy and residual water effects of the rock mass around the prefabricated cracks, cutting out solid and formed cracks, and realizing targeted and precise cutting of prefabricated cracks.

[0050] 2. The high-pressure and high-speed shock wave generated by the cavitation bubble extinction in the present invention will impact and crack the rock mass around the prefabricated cracks, destroy the integrity of the key layer of dynamic load impact, effectively reduce the dynamic load intensity generated by its rotation and sinking, improve the stress environment of the surrounding rock, and control the deformation of the tunnel surrounding rock.

[0051] 3. The present invention establishes key indicators for testing the cavitation impact fracturing effect, which can directly reflect the peak value of surrounding rock stress, surrounding rock deformation and roof microseismic energy value, and conducts a comprehensive and comprehensive test on the implementation effect of the targeted cavitation impact fracturing method, which can provide scientific guidance for the on-site implementation of the targeted cavitation impact fracturing method. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings required for use 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 ordinary technicians in this field, other accompanying drawings can be obtained based on these accompanying drawings without paying creative work.

[0053] Figure 1 A schematic flow chart of a method for regulating and controlling targeted cavitation impact fracturing and pressure relief of water-bearing rock formations provided by an embodiment of the present invention;

[0054] Figure 2 A schematic diagram of stress distribution characteristics of surrounding rock in a tunnel with prefabricated cracks located above solid coal provided by an embodiment of the present invention;

[0055] Figure 3 A schematic diagram of stress distribution characteristics of surrounding rocks of a roadway where prefabricated fractures are located above a mining roadway provided in an embodiment of the present invention;

[0056] Figure 4 A schematic diagram of stress distribution characteristics of surrounding rock in a tunnel with prefabricated cracks located above a goaf provided by an embodiment of the present invention;

[0057] Figure 5 A schematic diagram of cavitation crack hole parameter design provided by an embodiment of the present invention;

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

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

[0060] Figure 8 A schematic diagram of a dip section of a water-bearing rock formation targeted cavitation impact fracturing pressure relief control method provided by an embodiment of the present invention;

[0061] Fig. 9 A schematic cross-sectional view of a method for regulating and controlling targeted cavitation impact fracturing and pressure relief in water-bearing rock formations provided in an embodiment of the present invention.

[0062] In the figure: 1. mining tunnel, 2. direct bottom, 3. basic bottom, 4. solid coal, 5. coal pillar, 6. goaf, 7. direct top, 8. basic top, 9. surrounding rock stress, 10. overburden load, 11. prefabricated cracks in the roof rock layer, 12. coal seam, 13. dynamic load impact key layer, 14. cavitation cracking hole, 15. laser targeted cutting device, 16. laser control system, 17. laser monitoring system, 18. water cooling system, 19. laser generator, 20. optical fiber cable, 21. laser lens, 22. cavitation impact fracturing platform, 23. cavitation jet control system, 24. cavitation jet monitoring system, 25. high-pressure pump, 26. high-pressure water pipe, 27. cavitation jet generating device, 28. injection device, 29. annular nozzle. DETAILED DESCRIPTION

[0063] In order to make the purpose, technical scheme and beneficial effects of the present invention more clearly understood, the present invention is further described in detail below in combination with the current situation of a mine in Ningdong mining area and with reference to the accompanying drawings.

[0064] A mine in Ningdong Mining Area mainly mines No. 2 coal. Since the formation period of the mine was the Jurassic Cretaceous System of the Mesozoic Era, there is a water-bearing weakly cemented rock layer above the No. 2 coal. Although the roof drainage project has been adopted, there is still residual water in the roof rock layer. The direct roof 7 of the No. 2 coal is a composite rock layer composed of mudstone and siltstone, the basic roof 8 is fine-grained to coarse-grained sandstone, the direct bottom 2 is mudstone, and the basic bottom 3 is siltstone. With the mining of No. 2 coal, the working face recovery tunnel is affected by the overburden load 10, and the surrounding rock is severely deformed, which seriously restricts the safe and efficient production of the mine. To this end, the mine has successively adopted directional hydraulic fracturing and directional pre-splitting blasting technology to reduce the dynamic load strength generated by the roof rock layer. However, the application results show that due to the water-bearing weakly cemented rock layer conditions of the mine, the rock mass around the borehole is severely muddy and the residual water is weakened. There are problems such as soft and unformed prefabricated cracks and ineffective cracking of the rock mass by blasting. The dynamic load strength generated by the roof rock layer has not been effectively reduced, and the deformation of the tunnel surrounding rock is still relatively serious. Therefore, in view of the shortcomings of the roof directional pressure relief technology under water-containing rock formation conditions, the water-containing rock formation targeted cavitation impact fracturing pressure relief control method of the present invention is proposed.

[0065] Reference Figure 1-Figure 9 The present invention provides a method for regulating and controlling water-bearing rock formation targeted cavitation impact fracturing pressure relief, comprising the following steps:

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

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

[0068] Step 2: Identify the key layer of roof dynamic load impact

[0069] According to the constructed overburden engineering structure model, the dynamic load generated by the rotation and sinking of each rock layer above the coal seam 12 is quantitatively calculated, namely:

[0070]

[0071] Where D i is the dynamic load caused by the rotation and sinking of the i-th rock layer, m i is the thickness of the i-th rock layer, γi is the bulk density of the i-th rock layer, l i is the fracture length of the i-th rock layer, Δh i , Δh i-1 is the rotational subsidence of the i-th and i-1-th rock layers, and the rock layer with the largest dynamic load due to rotational subsidence is selected as the key layer for dynamic load impact, that is:

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

[0073] D i >D i+1

[0074] Where D i+1 It is the dynamic load generated by the rotation and sinking of the i+1th rock layer.

[0075] Step 3: Determine the location of the prefabricated cracks 11 in the roof rock formation

[0076] like Figures 2 to 4 As shown, since the mining tunnel 1 is a "dig", the distribution characteristics of the surrounding rock stress 9 under the conditions that the prefabricated cracks 11 in the roof rock strata are located above the solid coal 4, above the mining tunnel 1 and above the goaf 6 respectively are analyzed, and it is found that when the prefabricated cracks 11 in the roof rock strata are located above the goaf 6, the peak values ​​of the surrounding rock stress 9 of the solid coal 4 and the coal pillar 5 are both the smallest, then it is determined that the position of the prefabricated cracks 11 in the roof rock strata is located above the goaf 6.

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

[0078] The key parameters include cavitation crack hole parameters, laser targeted precision prefabricated crack parameters and cavitation impact crack parameters; among which:

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

[0080] The inclination angle of the cavitation-induced fracture hole 14 is generally determined by factors such as the position of the prefabricated fracture 11 of the roof rock layer, the equipment layout in the mining tunnel 1, and the performance of the drilling rig. The determined inclination angle α of the cavitation-induced fracture hole should be the maximum angle under the premise of facilitating the construction of the geological drilling rig, and α<90°;

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

[0082]

[0083] Wherein, δ is the correction coefficient of cavitation impact cracking, d is the diameter of the cavitation cracking hole 14, m is the thickness of the solid coal 4, f is the strength coefficient of the roof rock layer, and M is the depth of the working face.

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

[0085]

[0086] (2) The laser targeted precise prefabricated crack parameters mainly include the initial position of the slit, the number of slits, the laser power, the spot diameter, and the irradiation time. The initial position of the slit is the lower part of the first rock layer above the dynamic load impact key layer 13. The number of slits is determined in combination with the initial position of the slit and the thickness of the dynamic load impact key layer 13. 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.

[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 targeting to accurately preform cracks

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

[0090] First, the geological drill rig performs drilling construction according to the designed cavitation-induced crack hole 14. After the construction is completed, a laser targeted slitting device 15 with coal safety certification is used to set the direction of the prefabricated crack 11 in the drill hole for unidirectional slitting;

[0091] Said laser targeting slit device 15 refers to Figure 6The whole system includes 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 respectively, and the water cooling system 18 is connected to the laser generator 19. The laser generator 19 is connected to the laser monitoring system 17 and the water cooling system respectively, and then connected to the laser lens 21 through the optical fiber cable 20. The working method is: first, the geological drill is used to send the laser lens 21 to the set position in the cavitation-induced fracture hole 14, and then the laser control system 16 controls the laser generator 19 to generate a laser with set parameters. The laser is transmitted to the laser lens 21 through the optical fiber cable 20 to realize unidirectional cutting. The laser has the characteristics of high temperature and concentrated energy, so that the water in the muddy rock mass around the prefabricated fracture 11 evaporates and escapes, eliminating the mud and residual water effects of the rock mass around the prefabricated fracture 11, thereby cutting a solid and formed crack, and realizing targeted and precise cutting of the prefabricated fracture 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 fracture of roof rock

[0093] Use the cavitation impact fracturing platform 22 with coal safety certification to carry out cavitation impact fracturing of the roof rock layer, see 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 an annular 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 respectively. The cavitation jet monitoring system 24 is connected to the high-pressure pump 25 and the cavitation jet generating device 27 respectively. The high-pressure pump 25 is also connected to the cavitation jet generating device 27 through a high-pressure water pipe 26. The cavitation jet generating device 27 is connected to the injection device 28 through a high-pressure water pipe 26. The injection device 28 is provided with an annular nozzle 29. The working principle is: first, the injection device 28 is sent to the prefabricated fracture position by the geological drilling rig, and then the cavitation jet control system 23 controls the high-pressure pump 25 to convert the normal-pressure water in the well into stable high-pressure water, and 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 a cavitation water jet and then transport it to the injection device 28, and then it is sprayed out in the prefabricated fracture by the annular nozzle 29. The cavitation bubbles sprayed by the annular nozzle 29 react with the surface of the rock mass and extinguish. The high-pressure and high-speed shock wave generated when the cavitation bubble extinguishes will impact and fracture the rock mass around the prefabricated fracture 11, destroy the integrity of the key layer of dynamic load impact, effectively reduce the dynamic load strength generated by its rotation and sinking, improve the stress environment of the surrounding rock, and control the deformation of the surrounding rock of 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: Check the cavitation impact cracking effect

[0095] The key index K for testing the cavitation impact fracturing effect is established by selecting the surrounding rock stress peak value, surrounding rock deformation and roof microseismic energy value before and after the implementation of the targeted cavitation impact fracturing pressure relief control technology, namely:

[0096]

[0097] Where P0, S0, and E0 are the peak value of surrounding rock stress, surrounding rock deformation, and located microseismic energy values ​​before implementation; P1, S1, and E1 are the peak value of surrounding rock stress, surrounding rock deformation, and located microseismic energy values ​​after implementation.

[0098] When K≥0.6, it is determined that the cavitation impact fracturing effect meets the on-site needs, and the current targeted cavitation impact fracturing pressure relief control technical parameters are the optimal parameters under this condition, and the next implementation site continues to use the current technical parameters; when K<0.6, it is determined that the current cavitation impact fracturing effect does not meet the on-site needs, and the key parameters of the current targeted cavitation impact fracturing pressure relief control technology need to be optimized before construction of the next implementation site can be carried out.

[0099] The specific embodiments described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific embodiment of the present invention and is used to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for regulating and controlling the pressure relief of targeted cavitation impact fracturing of water-bearing rock formations, characterized in that: The steps include: Step 1: Construct a structural model of the overburden engineering at the implementation site The overburden engineering structure model is constructed based on the geological drilling information, mining technical conditions and mechanical response characteristics of the roof rock at the implementation site of the pressure relief control. Step 2: Identify the key layer of roof dynamic load impact Based on the constructed overburden engineering structure model, the dynamic load generated by the rotation and sinking of each rock layer of the roof is calculated, and the rock layer with the largest dynamic load generated by the rotation and sinking is selected as the key layer for dynamic load impact of the roof; Step 3: Determine the location of prefabricated cracks in the roof rock Determine the location of prefabricated cracks in the roof rock layer according to the planned reserved or excavated roadway and the surrounding rock stress distribution characteristics; Step 4: Design key parameters of targeted cavitation impact fracturing pressure relief control technology Design cavitation crack hole parameters, laser targeted precise prefabricated crack parameters and cavitation impact crack parameters within the key layer of roof dynamic load impact; Step 5: Laser targeted precise prefabrication of cracks The implementation site is constructed in sections. First, cavitation cracking holes are constructed at the first implementation site. After the construction is completed, laser-targeted, precise unidirectional slits are cut in the cavitation cracking holes along the direction of the roadway to control the impact cracking direction of the cavitation water jet, thereby forming a precise and continuous fracture surface along the direction of the roadway. Step 6: Cavitation impact cracking of roof rock The cavitation water jet is ejected in the prefabricated crack, and the cavitation bubbles react with the rock surface and extinguish. When the cavitation bubbles extinguish, a high-pressure and high-speed shock wave is generated, which impacts and cracks the rock around the prefabricated crack; Step 7: Check the cavitation impact cracking effect Establish a cavitation impact fracturing effect test index that can directly reflect the peak stress of the surrounding rock, the deformation of the surrounding rock and the microseismic energy value of the roof, test the cavitation impact fracturing effect of the roof rock 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; The above steps 4 to 7 are repeated to complete the impact fracturing pressure relief of each section at the construction site in sequence.

2. The method for controlling pressure relief of targeted cavitation impact fracturing of water-bearing rock formations according to claim 1, characterized in that: The method for determining the key layer of the top plate dynamic load impact in step 2 is: According to the constructed overburden engineering structure model, the dynamic load generated by the rotation and sinking of each rock layer above the coal seam is quantitatively calculated, namely: Where D i is the dynamic load caused by the rotation and sinking of the i-th rock layer, m i is the thickness of the i-th rock layer, γi is the bulk density of the i-th rock layer, l i is the fracture length of the i-th rock layer, Δh i , Δh i-1 are the rotational subsidence of the i-th and i-1-th rock layers, respectively; If the i-th layer is the key layer for dynamic load impact, the dynamic load relationship satisfied by the i+1-th layer is: D i >D i+1 Where D i+1 It is the dynamic load generated by the rotation and sinking of the i+1th rock layer.

3. The method for controlling pressure relief of targeted cavitation impact fracturing of water-bearing rock formations according to claim 1, characterized in that: The specific method of step three is: According to the planned retaining or excavation of the mining roadway, the surrounding rock stress distribution characteristics are analyzed under three conditions: the prefabricated cracks in the roof strata are located above the solid coal, above the mining roadway, and above the goaf. The prefabricated crack position corresponding to the minimum surrounding rock stress peak is the optimal prefabricated crack position in the roof strata.

4. The method for controlling pressure relief of targeted cavitation impact fracturing of water-bearing rock formations according to claim 1, characterized in that: The cavitation crack hole parameters in step 4 mainly include the inclination angle, spacing and depth of the cavitation crack holes, wherein: The cavitation-induced fracture hole inclination angle α is determined by the location of the prefabricated fractures in the roof rock layer, the equipment layout in the tunnel 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 the construction of the geological drilling rig, and α < 90°; The spacing R of cavitation cracks is determined by the thickness of the solid coal, the burial depth and the rock formation properties, namely: Where, δ is the correction coefficient of cavitation impact cracking, δ is between 0 and 1.5, d is the diameter of the cavitation crack hole, m is the thickness of the solid coal, f is the strength coefficient of the roof rock layer, and M is the depth of the working face; The depth H of the cavitation crack hole is determined by the vertical distance L between the initial position of the slit and the working surface and the inclination angle α of the cavitation crack hole, that is: The laser targeted precise prefabricated crack parameters mainly include the initial position of the slit, the number of slits, the laser power, the spot diameter and the irradiation time, wherein the initial position of the slit is the lower part of the first rock layer above the dynamic load impact key layer, the number of slits is determined in combination with the initial position of the slit 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 controlling pressure relief of targeted cavitation impact fracturing of water-bearing rock formations according to claim 1, characterized in that: In step five, a laser targeted slitting device with coal safety certification is used to implement targeted, precise unidirectional slitting.

6. The method for controlling pressure relief of targeted cavitation impact fracturing of water-bearing rock formations according to claim 5, characterized in that: In step six, cavitation impact fracturing is carried out using a cavitation impact fracturing platform with coal safety certification.

7. The method for controlling pressure relief of targeted cavitation impact fracturing of water-bearing rock formations according to claim 1, characterized in that: The cavitation impact cracking effect test index K described in step 7 is determined by the following formula Where P0, S0, and E0 are the peak value of surrounding rock stress, surrounding rock deformation, and located microseismic energy value before implementation, respectively; P1, S1, and E1 are the peak value of surrounding rock stress, surrounding rock deformation, and located microseismic energy value after implementation, respectively; The method for testing the cavitation impact fracturing effect of the roof rock strata is: when K≥0.6, it means 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 means 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 controlling pressure relief of targeted cavitation impact fracturing of water-bearing rock formations according to claim 6, characterized in that: The laser targeted slitting device mainly includes 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 the components is: the laser control system controls the laser generator to generate a laser with set parameters, and the laser is transmitted to the laser lens through the optical fiber cable to perform targeted and precise prefabrication of cracks; at the same time, the laser control system controls the laser monitoring system to monitor the characteristics of the laser 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 controlling pressure relief of targeted cavitation impact fracturing of water-bearing rock formations according to claim 8, characterized in that: The cavitation impact fracturing platform mainly includes 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 an annular nozzle; the working relationship between the components is: the cavitation jet control system controls the high-pressure pump to convert the normal-pressure water in the well into stable high-pressure water, and the high-pressure water is transported to the cavitation jet generating device through the high-pressure water pipe; the cavitation jet control system controls the cavitation jet generating device to convert the high-pressure water into a cavitation water jet and then transport it to the injection device, and then it is sprayed into the prefabricated crack by the annular nozzle; at the same time, the cavitation jet control system controls the cavitation jet monitoring system to monitor the characteristics of the high-pressure water output by the high-pressure pump and the cavitation jet output by the cavitation jet generating device in real time.

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