Composite pressure relief method of roof fracturing and frosted jet axial roof cutting

Abstract

The application relates to the technical field of deep mine coal mining, in particular to a roof fracturing and frosted jet axial roof cutting composite pressure relief method. The roof fracturing and frosted jet axial roof cutting composite pressure relief method comprises the following steps: dividing surrounding rocks on a target coal seam into low-position roof, middle-high-position roof and high-position roof, determining the positions of main rock strata controlling rock burst and mine shock above the target coal seam, relieving pressure on the main key strata above the target coal seam, monitoring the pressure relief effect of the pressure relief area to determine whether to supplement pressure relief on the roof. The roof fracturing and frosted jet axial roof cutting composite pressure relief method adopts regional hydraulic fracturing and local frosted jet axial roof cutting combination to relieve pressure on the main rock strata controlling rock burst and mine shock, so that the pressure relief effect is improved.

Description

Technical Field

[0001] This application relates to the field of deep coal mining technology, and in particular to a combined method for depressurization by roof fracturing and abrasive jet axial roof cutting. Background Technology

[0002] During coal mining, the integrity and stress state of the overlying roof strata, which are the primary controllers of rockbursts and seismic events, can potentially restrict safe mine production. This is especially true when multiple thick, hard roof layers exist above the coal seam, significantly increasing the risk of rockbursts or seismic events. The approach to treating thick, hard roof layers lies in modifying the overall rock structure by increasing fissures within the hard roof. Currently, commonly used methods for depressurizing thick, hard roofs include deep-hole blasting and hydraulic fracturing. While traditional deep-hole pre-fracture blasting is simple to operate and technically mature, it has limitations in terms of depressurization range and is not suitable for high-gas mines. Hydraulic fracturing technology was first used in the oil and gas field, employing volumetric fracturing to create artificial fractures within large areas of dense rock strata. It is a widely adopted fracturing and production enhancement technology. However, when facing multi-layered, thick, and hard roofs, single blasting or hydraulic fracturing techniques cannot simultaneously and accurately handle multiple target rock strata, resulting in unsatisfactory depressurization effects, leading to low efficiency and the need for multiple depressurization operations. Summary of the Invention

[0003] This application provides a combined decompression method of roof fracturing and abrasive jet axial cutting, which combines regional hydraulic fracturing and local abrasive jet axial cutting to decompress the rock strata controlled by rockburst and seismic events in the overlying roof, thereby improving the decompression effect.

[0004] This application provides a combined decompression method of top plate fracturing and abrasive jet axial top cutting, including:

[0005] The surrounding rock of the target coal seam is divided into low-level roof, middle-high-level roof and high-level roof; Determine the location of the rock strata that are the main control of rockburst and mine seismic events above the target coal seam in the overlying roof; Depressurize the rock strata above the target coal seam that are mainly controlled by rockburst and seismic activity; Monitor the depressurization effect in the depressurization area to determine whether additional depressurization of the roof is necessary.

[0006] The combined decompression method of top plate fracturing and abrasive jet axial cutting in this application combines hydraulic fracturing and abrasive jet axial cutting to decompress the rock strata controlled by rockburst and seismic events, thereby improving the decompression effect.

[0007] In some embodiments, when depressurizing the main control key layer above the target coal seam, a combination of one of the following methods—surface vertical well fracturing, surface horizontal well fracturing, and downhole long borehole segmented hydraulic fracturing—and abrasive jet axial top cutting is used for depressurization.

[0008] In some embodiments, it is determined whether there are rock strata controlled by rockburst and seismic events in the high-level roof. If so, the high-level roof is depressurized by fracturing with a vertical or horizontal well on the surface. If not, determine whether there are rock strata controlled by rockburst and mine seismic events in the middle and high-level roof. If so, carry out surface vertical well fracturing, surface horizontal well fracturing, or long borehole segmented hydraulic fracturing to relieve pressure in the middle and high-level roof. Determine whether there are rock strata controlled by rockburst and seismic events in the low-level roof. If so, perform axial cutting of the low-level roof using abrasive jet.

[0009] In some embodiments, axial cutting of the top of the abrasive jet includes the following steps: Drill holes of a predetermined diameter in the tunnel roof; connect the sealing device and the abrasive jet injector and send them to the predetermined drilling position to cut the drill hole; then perform fracturing on the drill hole.

[0010] In some embodiments, monitoring the depressurization effect of the depressurization area includes the following steps; Online monitoring of borehole stress, micro-vibration monitoring, and hydraulic support pressure monitoring are adopted for the working face; If any of the monitoring data for borehole stress, microvibration, or hydraulic support pressure exceeds the preset value, the alarm area will be subjected to axial cutting and pressure relief using a sandblasting jet to bring the monitoring indicators below the warning value.

[0011] In some embodiments, if any of the monitoring data of drilling stress, micro-vibration, or hydraulic support pressure exceeds a preset value, the alarm area is subjected to additional pressure relief using abrasive jet axial cutting technology. After the monitoring index is lower than the warning value, anchor bolts and cables and spraying support are applied within 10-15m of the adjacent alarm area.

[0012] In some embodiments, during borehole stress monitoring, boreholes are drilled on both sides of the working face and borehole stress is monitored, with the spacing between multiple boreholes in the mining direction of the working face not exceeding 30m.

[0013] In some embodiments, when the alarm area is subjected to axial cutting and pressure relief by abrasive jet, the spacing between the boreholes is 5 m to 10 m.

[0014] In some embodiments, 4 to 6 microseismic sensors are installed on the working face for microseismic monitoring.

[0015] In some embodiments, the goaf of the working face is filled. Attached Figure Description

[0016] To more clearly illustrate the embodiments of this application, the accompanying drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 This is one of the schematic diagrams illustrating the depressurization of the upper and lower roof slabs in an embodiment of this application; Figure 2 This is a schematic diagram illustrating the depressurization of the upper roof slab according to an embodiment of this application; Figure 3 This is a cross-sectional distribution diagram of the microseismic events at the working face in an embodiment of this application; Figure 4 This is a rock strata diagram showing the strike of the working face in an embodiment of this application; Figure 5 This is a schematic diagram illustrating the depressurization of the high-level roof plate, the mid-high-level roof plate, and the low-level roof plate according to an embodiment of this application.

[0018] Figure 6 This is a schematic diagram of the high-level roof slab and the mid-to-high-level roof slab according to an embodiment of this application; Figure 7 This is a schematic diagram illustrating the decompression of the upper and lower roof sections using surface vertical well fracturing, as described in an embodiment of this application.

[0019] Figure 8 This is a schematic diagram illustrating the depressurization process of using long downhole drilling for segmented hydraulic fracturing of the upper and middle sections of the roof and using abrasive jet axial cutting of the lower section of the roof, as described in this application.

[0020] The above figures include the following reference numerals: Target coal seam 1, Top cover 2, low-level top cover 21, mid-to-high-level top cover 22, high-level top cover 23. 3. Surface vertical well fracturing 4. Surface horizontal well fracturing 5. Downhole long borehole segmented hydraulic fracturing 6. Axial top cutting with abrasive jet 7. Detailed Implementation

[0021] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the protection scope of this application.

[0022] It should be noted that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential," etc., indicating orientation or positional relationships based on the orientation or positional relationships shown in the accompanying drawings, are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this application. The terms "installed," "connected," and "linked" should be interpreted broadly, for example, they can be fixed connections, detachable connections, or integral connections; they can be mechanical connections or electrical connections; they can be direct connections or indirect connections through an intermediate medium; they can be internal connections between two elements. The terms "parallel," "perpendicular," and "equal" include the described situation and situations similar to the described situation, the range of which is within an acceptable deviation range, wherein the acceptable deviation range is determined by those skilled in the art taking into account the measurement under discussion and the error associated with the measurement of a particular quantity (i.e., the limitations of the measurement system). For example, "parallel" includes absolute parallelism and approximate parallelism, where an acceptable deviation range for approximate parallelism can be, for example, within 5°; "perpendicular" includes absolute perpendicularity and approximate perpendicularity, where an acceptable deviation range for approximate perpendicularity can also be, for example, within 5°. "Equal" includes absolute equality and approximate equality, where an acceptable deviation range for approximate equality can be, for example, a difference between the two equal items being less than or equal to 5% of either one. Those skilled in the art will understand the specific meaning of the above terms in this application based on the specific circumstances.

[0023] To enable those skilled in the art to better understand the present application, the present application will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0024] This application provides a combined fracturing and abrasive jet axial top-cutting pressure relief method, including: The surrounding rock of the target coal seam 1 is divided into a low-level roof 21, a middle-high-level roof 22, and a high-level roof 23. The positions of the rock strata that are the main control of rockburst and seismic events in the surrounding rock above the target coal seam 1 are determined in the overlying roof above the target coal seam 1. The rock strata that are the main control of rockburst and seismic events above the target coal seam 1 are depressurized, and the depressurization effect in the depressurization area is monitored to determine whether additional depressurization of the roof is necessary.

[0025] The combined hydraulic fracturing and abrasive jet axial top cutting method of this application embodiment uses a combination of downhole long borehole segmented hydraulic fracturing 6 and abrasive jet axial top cutting 7 to depressurize the rock strata controlled by rockburst and seismic events in the overlying roof, so as to improve the depressurization effect.

[0026] Understandably, when multiple layers of rock exist within the overburden of a mining area, the layer that controls all or part of the rock mass movement is called the key layer. The activity of the key layer significantly affects the mine pressure, rock strata movement, and surface subsidence of the entire mining area. Furthermore, microseismic monitoring is used to identify the key layer that plays a dominant role in the occurrence of rockbursts or mine tremors; this is also known as the controlling key layer, the rockburst-controlling rock layer, or the mine tremor-controlling rock layer.

[0027] Rock strata that are the main controlling rock layers for rockbursts and mine tremors refer to the rock strata that play a leading role in the occurrence of rockbursts or mine tremors during coal seam mining.

[0028] Specifically, such as Figures 1 to 8 As shown, the target coal seam 1 is determined, and the surrounding rock above the target coal seam 1 is divided into a low roof 21, a middle-high roof 22, and a high roof 23. For example, the range of 0-50m above the target coal seam 1 is defined as the low roof 21, the range of 50-100m is defined as the middle-high roof 22, and the range above 100m is defined as the high roof 23.

[0029] Determining the location of multiple rock strata that are the main control of rockburst and seismic events above the target coal seam 1 can be understood as the height of the key strata in the vertical direction of the coal seam to be mined and their location in the surrounding rock, or as the location of multiple key strata in the low roof 21, the middle and high roof 22 and the high roof 23, i.e., the location of the key strata in the vertical direction.

[0030] Depressurize the key control layer and then monitor the depressurization effect. Different depressurization methods can be used for the roof. For example, for the low roof 21, use abrasive jet axial cutting 7 to depressurize. For the middle and high roof 22, use surface vertical well fracturing 4, surface horizontal well fracturing 5, or downhole long borehole segmented hydraulic fracturing 6. For the high roof 23, use surface vertical well fracturing 4 or surface horizontal well fracturing 5.

[0031] The combined fracturing and abrasive jet axial top cutting method of this application combines regional surface vertical well fracturing 4, surface horizontal well fracturing 5, or downhole long borehole segmented hydraulic fracturing 6 with local abrasive jet axial top cutting 7 to depressurize the rock strata mainly controlled by rockburst and mine tremor, thereby improving the depressurization effect, reducing stress concentration in the roof area, and preventing the occurrence of rockburst and mine tremor. The combination of regional fracturing and abrasive jet axial top cutting 7 for depressurization releases the stress in the roof, avoiding safety hazards caused by excessive stress differences. This process can not only effectively protect the safety of miners, but also improve the stability and efficiency of coal mining, reduce the impact of rockburst and mine tremor on production. Furthermore, according to the specific conditions of different coal mines, the parameters of fracturing and abrasive jet axial top cutting 7 can be flexibly adjusted, making this process applicable to coal mining under various geological conditions.

[0032] Furthermore, the determination of the main rock strata controlling rockbursts and mine seismic events can be achieved by combining borehole columnar section analysis, key layer theoretical calculations, and analysis of the spatial distribution patterns of microseismic events. Figure 4 As shown, Figure 4 This is a columnar section of the rock strata along the working face strike. The vertical axis represents the distance between boreholes and the target coal seam 1 in the vertical direction, while the horizontal axis represents the position of the boreholes and the cut-off point in the mining direction of the working face. Combined with physical and mechanical parameters of the roof strata, this reveals the lithology, strength, integrity, and continuity characteristics above the roof in this area, facilitating on-site personnel in determining which strata are likely to be critical layers. Alternatively, on-site personnel can directly calculate the critical layers using existing technology.

[0033] Determination of the main rock layers controlling rock bursts and mine tremors: First, borehole columnar sections and key layer calculations are used to calculate all the key layers above the coal seam. Then, microseismic monitoring is used to determine the key layers that play a dominant role in the occurrence of rock bursts or mine tremors, which are called the main controlling key layers, also known as the main rock layers controlling rock bursts and mine tremors.

[0034] When analyzing borehole columnar sections, geological boreholes along the strike direction of the mining face are counted and arranged according to their actual strike distance. Adjacent boreholes are classified and connected according to the same or similar lithology. A rock stratum profile along the strike direction of the working face is drawn. At the same time, combined with the physical and mechanical parameters of the roof strata, the characteristics of lithology, strength, integrity, and continuity within 100m above the roof of the area can also be revealed.

[0035] The critical layer theory calculation first identifies the critical layer. It assumes a certain rock layer is a critical layer, and that this rock layer controls a range reaching the [missing information - likely a specific area or region]. The first layer, then the second layer The conditions for a layer to become a second critical layer are:

[0036] In the formula: , Calculate up to the th Layer and First The load on the first critical layer, in MPa; The thickness of the rock strata is in meters (m). The unit weight of the rock strata is kN / m³. Let be the elastic modulus of the rock stratum, in MPa.

[0037] Therefore, the key layer can be determined according to the following procedure: First, using a comprehensive geological columnar section of specific rock strata, based on the thickness and lithology of the key strata, we can preliminarily identify the thick rock strata that may become key strata, which serves as the basis for determining the main key location.

[0038] Then, based on the stiffness conditions of the key layer, the objects requiring strength condition judgment are further determined:

[0039] If the above formula holds true, it indicates that the rock layer may be the key layer, and so on down to the last layer of hard rock. Therefore, the above formula can be used to identify each rock layer from top to bottom until the location of the uppermost hard rock layer that may be the key layer is determined.

[0040] Finally, in addition to meeting the requirements of the above formula, the key layer also needs to meet the strength conditions required for the key layer to determine whether the nth layer is a key layer. That is, the fault distance of the overlying hard rock layer must be greater than the fault distance of the underlying hard rock layer.

[0041] In the formula: For the first The fracture distance of the rock strata, in meters; This represents the number of hard rock layers; The thickness of the rock strata is in meters (m). The tensile strength of the rock stratum is given in MPa. The load borne by the rock strata is expressed in MPa.

[0042] If the first If the hard rock layer does not satisfy the above formula, then the first layer should be... All rock layer loads controlled by the hard rock layer act on the first On the next layer, recalculate the first... Further analysis will be conducted after determining the fracture distance of the hard rock layer.

[0043] Figure 3This is a microseismic event distribution profile. The vertical axis represents the distance between the borehole and the target coal seam 1 in the vertical direction, and the horizontal axis represents the position of the borehole and the cut-in point in the mining direction of the working face. The spatial distribution pattern of microseismic events is analyzed. Using existing microseismic monitoring systems for rockburst mines, the microseismic events monitored during the mining process of the rockburst-prone coal seam are statistically analyzed. First, the energy level distribution characteristics of the microseismic events are statistically analyzed to obtain the pattern of high-energy microseismic events during the mining process of this rockburst-prone coal seam. Then, the microseismic events are spatially projected to analyze the distribution pattern of microseismic events in different layers of the roof above the coal seam. Among them, the rock fracture energy of the layers where high-energy microseismic events accumulate pose a higher impact risk to the coal seam working face. For example, microseismic event analysis can also be used to monitor the position of the cut-in point when larger energy microseismic events occur, thus facilitating the determination of the distance between the cut-in point and the location of roof pressure or more intense activity in the mining direction of the working face. The spatial distribution pattern analysis of microseismic events, as well as borehole columnar section analysis and key layer calculation, are commonly used techniques in existing coal mining and will not be elaborated further here.

[0044] Determination of the main rock layers controlling rock bursts and mine tremors: First, borehole columnar sections and key layer calculations are used to calculate all the key layers above the coal seam. Then, microseismic monitoring is used to determine the key layers that play a dominant role in the occurrence of rock bursts or mine tremors, which are called the main controlling key layers, also known as the main rock layers controlling rock bursts and mine tremors.

[0045] In some embodiments, when depressurizing the rock strata controlled by rockburst and the rock strata controlled by seismic activity above the target coal seam 1, a combination of any one of the following methods is used for depressurization: regional surface vertical well fracturing 4, surface horizontal well fracturing 5, and downhole long borehole segmented hydraulic fracturing 6, and local abrasive jet axial top cutting 7.

[0046] Surface vertical well fracturing 4 involves drilling a vertical well (3) on the surface to reach the key control layer above the target coal seam (1), then injecting high-pressure fluid to create fractures in the key layer rock, thereby reducing stress in the key layer and achieving pressure relief. It is convenient to construct, can treat multiple target key layers simultaneously, has good pressure relief effect, effectively reduces stress in the key layer, and reduces gas emission. It is suitable for various geological conditions, especially areas with deep coal seams.

[0047] Surface horizontal well fracturing involves drilling three horizontal wells on the surface, with the horizontal well section penetrating the critical stratum before fracturing. Horizontal wells increase the contact area with the critical stratum, improving fracturing effectiveness. The larger contact area allows the horizontal well section to more effectively cover the critical stratum, enhancing fracturing efficiency. A wider pressure relief range enables pressure relief over a larger area of ​​the critical stratum, reducing gas outbursts. This method is suitable for areas with thick critical strata or high gas content.

[0048] Alternatively, when fracturing a horizontal well (5) or a vertical well (4), the following steps are taken: ① Drilling: Key technologies such as rotary steering and actual drilling trajectory control are used to sequentially complete the construction of wells of different diameters at specific target points. After drilling to a certain depth, casing is installed, and cement is poured into the annular space between the casing and the well wall to reinforce the exposed rock strata and borehole walls.

[0049] ②Perforation: The perforator is lowered into the fracturing zone using tubing or cable. The pressure difference causes the perforating projectile to explode, penetrating the casing and cement sheath, allowing the fracture to reach a certain depth in the formation and connecting the fracturing rock layer with the wellbore, providing a smooth channel for the fracturing fluid to enter the formation.

[0050] ③ Fracturing: After perforation, flush the wellbore. Connect the coiled tubing to the jetting tool and extend it to the bottom of the well. Seal the packer and inject fracturing fluid into the target formation through the coiled tubing at a certain flow rate and pressure. After this section of fracturing is completed, drag the tubing back to repeat the fracturing of the remaining sections of formation.

[0051] Downhole long-bore segmented hydraulic fracturing (6) uses high-pressure water to create fractures in the target rock formation, increasing its porosity, reducing its integrity, and releasing the elastic energy accumulated within the rock. Fracturing parameters, such as pressure and fluid composition, can be adjusted according to actual needs.

[0052] Alternatively, during the depressurization process of segmented hydraulic fracturing in long downhole boreholes, ① drilling: key technologies such as rotary steering and actual drilling trajectory control are used to complete the wellbore construction at specific target points. During drilling, visual methods are used to determine the strata position, lithology, and fracture state of the rock formations by observing the drilling speed, drilling pressure, and borehole cuttings.

[0053] ② Fracturing: The fracturing tool string is inserted deep into the bottom of the well through the fracturing drill pipe. The packer is sealed by the pressure difference, and the fracturing fluid is injected into the target rock formation at a certain flow rate and pressure. After this section of fracturing is completed, the drill pipe is dragged back to repeat the fracturing of the remaining rock formations, thus completing the downhole long borehole segmented hydraulic fracturing 6.

[0054] Abrasive jet axial cutting for stress relief utilizes abrasive jet technology to create axial cracks in critical layers, reducing stress in these layers by cutting off the top. Abrasive jets can create deep cracks in rock. They generate high energy, resulting in excellent cutting performance and deep cracks. Directional cutting is possible, allowing precise control over the direction and location of cracks. It is suitable for rocks of various hardnesses, especially for hard critical layers.

[0055] The combined fracturing and abrasive jet axial top-cutting depressurization method of this invention can comprehensively utilize surface vertical well fracturing 4, surface horizontal well fracturing 5, downhole long borehole segmented hydraulic fracturing 6, or abrasive jet axial top-cutting 7, depending on the specific circumstances, to achieve the best depressurization effect. For example, surface vertical well fracturing 4 can be performed on the high-level roof 23 or the mid-to-high-level roof 22 first, and then combined with abrasive jet axial top-cutting 7 to depressurize the low-level roof 21, improving the depressurization effect and reducing downhole gas emission, thereby improving construction safety.

[0056] In some embodiments, it is determined whether there are rock strata controlled by rockburst and mine seismic events in the high-level roof 23. If so, the high-level roof 23 is depressurized by surface vertical well fracturing 4 or surface horizontal well fracturing 5. If not, determine whether there are rock strata controlled by rockburst and mine seismic events in the middle and high-level roof 22. If so, perform surface vertical well fracturing 4, surface horizontal well fracturing 5, or downhole long borehole segmented hydraulic fracturing 6 on the middle and high-level roof 22. Determine whether there are rock strata controlled by rockburst and seismic events in the low-level roof 21. If so, perform axial cutting of the low-level roof 21 using a sandblasting jet.

[0057] Specifically, such as Figures 1 to 8 As shown, if the high-level roof 23 is located in rock strata controlled by rockburst and seismic events, the high-level roof 23 can be subjected to vertical well fracturing 4 or horizontal well fracturing 5 on the ground to relieve pressure. Construction can be carried out directly on the ground 3, which reduces the difficulty and cost of construction. It can also relieve pressure on the roof at a higher position, thus improving the stability of the underground working face.

[0058] If the upper and middle-high roof 22 contains rock strata controlled by rockburst and seismic activity, then any one of the following methods can be used: surface vertical well fracturing 4, surface horizontal well fracturing 5, or downhole long-bore segmented hydraulic fracturing 6. Surface vertical well fracturing 4 can directly act on the key layers of the upper and middle-high roof 22, forming fractures in the key layers through high-pressure fluid, effectively reducing stress and releasing gas. Surface construction 3 avoids the complex environment and safety risks downhole, reducing construction difficulty and cost. It can relieve pressure on the roof at higher positions, improving the stability of the downhole working face.

[0059] If the lower roof 21 contains rock strata primarily controlled by rockbursts and seismic events, axial roof cutting 7 using abrasive jets can be performed on the lower roof 21 separately. Abrasive jets have cutting capabilities, forming deep cracks in the critical layers of the lower roof 21, effectively reducing stress and releasing gas. The abrasive jet axial roof cutting 7 technique is suitable for the critical layers of the lower roof 21, especially in areas with harder rock. Precise treatment of the critical layers of the lower roof 21 reduces gas accumulation and improves the safety of the underground working face.

[0060] Furthermore, depending on the actual situation, the low-level roof 21 can be subjected to segmented hydraulic fracturing using long downhole drilling 6.

[0061] The combined pressure relief method of fracturing and abrasive jet axial top cutting in this invention, for key layers at different roof locations, takes into account cost and construction, and uses surface vertical well fracturing 4, surface horizontal well fracturing 5, downhole long borehole segmented hydraulic fracturing 6 or abrasive jet axial top cutting 7 to improve pressure relief effect and reduce pressure relief cost.

[0062] In some embodiments, when performing axial cutting of the top 7 using abrasive jets, the following steps are included: Drill holes of a predetermined diameter in the tunnel roof; connect the sealing device and the abrasive jet injector and send them to the predetermined drilling position to cut the drill hole; then perform fracturing on the drill hole.

[0063] Specifically, such as Figures 1 to 8 As shown, firstly, a drilling rig, matching drill bit, and drill rod are used to drill a hole of a certain diameter in the roof of the tunnel. After connecting the sealing device and the abrasive jet injector, they are sent to the preset position of the drilling hole. The water jet system is turned on and switched to jet mode. At this time, high-pressure water containing abrasive sand is sprayed from the nozzles on both sides of the injector. By operating the drilling rig to retract the drill rod at a uniform speed, an initial crack of a certain length and depth can be formed on both sides of the drilling hole.

[0064] Turn off the abrasive pump and switch the high-pressure pump to sealing mode. Inject high-pressure water into the sealing device to set the sealing devices at both ends of the fracture. Switch the high-pressure pump to fracturing mode. At this time, high-pressure water is continuously injected into the sealing section from the water outlet at the front end of the ejector. The initial fracture continues to expand along the fracture tip. When the pump pressure suddenly drops or the fracturing time reaches the design time, turn off the high-pressure pump and depressurize the sealing device to complete the fracturing work of this segment.

[0065] The combined pressure relief method of hydraulic fracturing and abrasive jet axial cutting of the top in this invention can effectively reduce roof stress, release gas, and improve the safety and stability of the downhole working face through three main steps: drilling, cutting, and hydraulic fracturing.

[0066] In some embodiments, monitoring the depressurization effect of the depressurization area includes the following steps; Online monitoring of borehole stress, micro-vibration monitoring, and hydraulic support pressure monitoring are adopted for the working face; If any of the monitoring data for borehole stress, micro-vibration, or hydraulic support pressure exceeds the preset value, the alarm area will be subjected to axial cutting of the top with a sandblasting jet to supplement the pressure relief, so that the monitoring indicators are lower than the warning value.

[0067] Specifically, such as Figures 1 to 8As shown, borehole stress monitoring involves drilling into the roadway sides and roof of the working face to monitor stress changes in the roof and coal seam in real time and evaluate the pressure relief effect. Borehole stress sensors are installed in pre-set locations in the boreholes, ensuring accurate sensor placement to effectively monitor stress changes in the target area. Stress data is collected in real time and transmitted to the monitoring center via a data transmission system. The collected stress data is analyzed and monitored in real time to determine whether the stress exceeds a preset value.

[0068] Microseismic monitoring is used to monitor microseismic activity in the roof and coal seam, and to assess crack propagation and stress release. Microseismic sensors are installed at predetermined locations on the working face. The sensors are deployed to ensure coverage of the monitored area. Microseismic data is acquired in real time and transmitted to the monitoring center via a data transmission system. The acquired microseismic data is analyzed in real time to determine if microseismic activity is abnormal.

[0069] Preset values ​​are set for online monitoring of borehole stress, microseismic monitoring, and hydraulic support pressure monitoring. When any monitoring data exceeds the preset value, the system will automatically issue an early warning signal. The monitoring system should have a real-time feedback function to promptly report abnormal data to the operator so that appropriate measures can be taken.

[0070] If any of the monitoring data for drilling stress, micro-vibration, or hydraulic support pressure exceeds the preset value, the alarm area will be subjected to axial cutting of the top with abrasive jet 7 to supplement the pressure relief and reduce stress.

[0071] After the pressure relief operation is completed, continue to monitor borehole stress, micro-vibration, and hydraulic support pressure to ensure that the monitored indicators are below the warning value within the preset time.

[0072] In some embodiments, if any of the monitored data such as borehole stress, microvibration, or hydraulic support pressure exceeds a preset value, the alarm area is supplemented with pressure relief using abrasive jet axial roof cutting technique. Once the monitored indicators fall below the warning value, anchor bolts and cables, along with spray coating, are applied to the area within 10m to 15m of the alarm area. Applying anchor bolts and cables, along with spray coating, is an effective roof management measure. This measure can further enhance roof stability, reduce gas accumulation, and improve the safety of the underground working face. Through reasonable design and strict construction, the support effect can be ensured, providing miners with a safer working environment.

[0073] Rock bolt support uses anchor bolts to anchor the roof rock together, preventing it from falling or deforming. Holes are drilled into the roof using a drilling rig; the hole diameter and depth are determined according to design requirements. Anchor bolts are inserted into the drilled holes and secured with anchoring compound. Tightening tools are used to secure the anchor bolts, ensuring a tight bond between them and the roof rock. A support plate is installed at the outer end of the anchor bolt; the support plate should fit tightly against the roof to ensure effective support. Cable anchor support uses anchor cables to anchor the roof rock together, preventing it from falling or deforming. This method is suitable for thicker roof rocks. Holes are drilled into the roof using a drilling rig; the hole diameter and depth are determined according to design requirements. Cable anchors typically have larger diameters and deeper holes. Anchor cables are inserted into the drilled holes and secured with anchoring compound. Tightening tools are used to secure the cable, ensuring a tight bond between it and the roof rock. A support plate is installed at the outer end of the cable; the support plate should fit tightly against the roof to ensure effective support. Spray coating support is a method of supporting the roof by spraying a layer of concrete or other materials onto the roof surface to form a protective shell, thereby improving the stability of the roof. Spraying materials include concrete, sprayed grout, etc., and appropriate materials are selected based on the properties of the roof rock and the support requirements. The material ratio is adjusted according to design requirements to ensure the strength and durability of the sprayed material. By spraying a protective shell, weathering and falling of the roof rock are prevented, improving the stability of the roof. Before spraying, loose coal, gravel, and other debris are cleaned from the roof surface to ensure cleanliness. A steel mesh is laid on the roof surface, ensuring it is tightly adhered to the roof to ensure adhesion of the sprayed material. The sprayed material is evenly sprayed onto the roof surface using spraying equipment, with the spray thickness determined according to design requirements. After spraying, appropriate curing is performed to ensure the strength and durability of the sprayed material.

[0074] The combined fracturing and abrasive jet axial roof cutting pressure relief method of this invention, using anchor bolts, anchor cables, and sprayed support, can effectively enhance the stability of the roof and prevent roof rock from falling and deforming. By enhancing roof stability, the formation of roof cracks is reduced, thereby reducing gas accumulation. These comprehensive support measures can effectively improve the safety of the downhole working face.

[0075] In some embodiments, during borehole stress monitoring, boreholes are drilled on both sides of the working face and borehole stress is monitored, with the spacing between multiple boreholes in the mining direction of the working face not exceeding 30m.

[0076] The spacing between multiple boreholes in the mining direction of the working face should not exceed 30m. The specific spacing should be determined according to the actual requirements.

[0077] Furthermore, in areas with complex geological conditions or large stress variations, the borehole spacing should be appropriately reduced; in areas with relatively stable geological conditions, the borehole spacing can be appropriately increased.

[0078] Furthermore, when supplementing pressure relief in the alarm area using abrasive jet axial cutting 7, the spacing between boreholes should be 5m to 10m. A spacing of 5m to 10m ensures effective stress release in the pressure relief area while avoiding resource waste caused by excessively dense drilling. Reasonable borehole spacing can improve construction efficiency, reduce the number of boreholes, and lower construction costs and time. The borehole spacing can be adjusted appropriately based on different geological conditions, such as rock hardness and joint and fracture development. In areas with harder rock and less developed joints and fractures, the spacing can be appropriately increased; in areas with softer rock and developed joints and fractures, the spacing can be appropriately decreased.

[0079] In some embodiments, 4 to 6 microseismic sensors are installed at the working face for microseismic monitoring. The specific number of microseismic sensors is determined based on the size of the working face and the monitoring requirements. Location: The microseismic sensors should be arranged at predetermined locations such as the sides of the working face, the roof, and the goaf to ensure comprehensive monitoring of microseismic activity. The spacing between the microseismic sensors should be determined according to the actual situation; the spacing between the microseismic sensors in the direction of the working face can be 200m to 500m.

[0080] Furthermore, in areas with large stress variations, the spacing can be appropriately reduced, while in areas with relatively stable stress variations, the spacing can be appropriately increased.

[0081] In some embodiments, the goaf of the working face is backfilled. Backfilling reduces roof subsidence and deformation, preventing roof collapse accidents, and reducing gas accumulation. The backfill material fills the voids in the goaf, reducing gas accumulation and lowering the risk of gas explosions. Backfilling the goaf can effectively control surface subsidence, reducing the impact on surface buildings and the ecological environment. It also improves resource recovery: by backfilling the goaf, the remaining coal pillars can be recovered, increasing the coal resource recovery rate.

[0082] The foregoing has provided a detailed description of the method provided in this application. Specific examples have been used to illustrate the principles and implementation methods of this application. The descriptions of the embodiments above are merely for the purpose of helping to understand the method and core ideas of this application. It should be noted that those skilled in the art can make various improvements and modifications to this application without departing from its principles, and these improvements and modifications also fall within the protection scope of the claims of this application.

Claims

1. A combined method for pressure relief using top plate fracturing and abrasive jet axial cutting, characterized in that, include: The surrounding rock of the target coal seam is divided into low-level roof, middle-high-level roof and high-level roof; Determine the location of the rock strata that are the main control of rockburst and seismic activity in the surrounding rock above the target coal seam in the overlying roof; Depressurize the rock strata above the target coal seam that are mainly controlled by rockburst and seismic activity; Monitor the depressurization effect in the depressurization area to determine whether additional depressurization of the roof is necessary; When depressurizing the rock strata controlled by rockburst and seismic activity above the target coal seam, one of the following methods is used in combination with axial roof cutting using a grinding jet: surface vertical well fracturing, surface horizontal well fracturing, or downhole long borehole segmented hydraulic fracturing. It is determined whether the rockburst and seismic activity-controlled rock strata are located on a high-level roof. If so, surface vertical well or horizontal well fracturing is used to depressurize the high-level roof. If not, determine whether the rock strata controlling the rockburst and the seismic events are located in the middle to high-level roof. If so, perform surface vertical well fracturing, surface horizontal well fracturing, or long-bore hydraulic fracturing in stages to relieve pressure on the middle to high-level roof. Determine whether the rock strata that are the main control of rockburst and the rock seismic strata are located in the low-level roof. If so, perform axial cutting of the low-level roof using abrasive jet. The following steps are included when performing axial cutting of the abrasive jet: Drill holes of a predetermined diameter in the tunnel roof; connect the sealing device and the abrasive jet injector and send them to the predetermined drilling position to cut the drill hole; perform fracturing on the drill hole; when monitoring the depressurization effect in the depressurization area, the following steps are included; Online monitoring of borehole stress, micro-vibration monitoring, and hydraulic support pressure monitoring are adopted for the working face; If any of the monitoring data for borehole stress, micro-vibration, or hydraulic support pressure exceeds the preset value, the alarm area will be subjected to axial cutting of the top using abrasive jet to supplement pressure relief, so that the monitoring index is lower than the warning value; if any of the monitoring data for borehole stress, micro-vibration, or hydraulic support pressure exceeds the preset value, the alarm area will be subjected to axial cutting of the top using abrasive jet to supplement pressure relief. After the monitoring index is lower than the warning value, anchor bolts and cables and spray coating support will be applied within 10-15m of the adjacent alarm area.

2. The combined depressurization method of top plate fracturing and abrasive jet axial cutting as described in claim 1, characterized in that, During borehole stress monitoring, boreholes are drilled on both sides of the working face and borehole stress is monitored. The spacing between multiple boreholes in the mining direction of the working face should not exceed 30m.

3. The combined depressurization method of top plate fracturing and abrasive jet axial cutting as described in claim 1, characterized in that, When performing axial cutting and pressure relief on the alarm area using abrasive jets, the spacing between boreholes should be 5-10m.

4. The combined depressurization method of top plate fracturing and abrasive jet axial cutting as described in claim 1, characterized in that, Four to six microseismic sensors are installed on the working face for microseismic monitoring.

5. The combined depressurization method of top plate fracturing and abrasive jet axial cutting according to any one of claims 1-4, characterized in that, The goaf in the working face is filled.

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