Rock burst prevention method in overlying residual coal pillar influence area

Abstract

The present application relates to the technical field of impact low pressure prevention and treatment, and particularly relates to a method for preventing and treating impact ground pressure in an overlying residual coal pillar influence area, which comprises the following steps: determining a key layer of surrounding rock above a working face to be mined and a residual coal pillar in an overlying layer as a preset fracturing layer; determining a fracturing area to be fractured of the preset fracturing layer through the working face to be mined and the residual coal pillar, and the projection of the fracturing area to be fractured in a gravity direction covers the working face to be mined and the residual coal pillar; drilling a horizontal well in the preset fracturing layer after setting a vertical shaft on the ground, and then fracturing the preset fracturing layer; and adjusting the fracturing operation through a crack extension rate in the fracturing process. The method for preventing and treating impact ground pressure in the overlying residual coal pillar influence area adjusts the fracturing operation according to the crack extension rate to pre-fracture the surrounding rock above the residual coal pillar, and improves the safety of coal mining.

Description

Technical Field

[0001] This invention relates to the field of rockburst prevention and control technology, specifically to a method for preventing rockburst in the area affected by overlying residual coal pillars. Background Technology

[0002] In the history of coal mining, due to limitations in early mining technology, adjustments to mining area planning, and the interleaved mining of multiple ore layers, a large number of residual coal pillars have been formed within the mining area. These residual coal pillars bear the load of the overlying strata for a long time, forming stable and high-intensity stress concentration cores. In most mining areas, thick, hard sandstone, conglomerate, and other hard rock strata are generally located above these residual coal pillars. Because of their good rock mass integrity, high strength, and resistance to collapse, these thick, hard rock strata form a "coal pillar-thick, hard rock strata" stress coupling system with the underlying residual coal pillars. The two superimpose and synergistically act on each other, transferring high static and strong dynamic loads directly to the coal seam to be mined below the coal pillar through overlying stress transmission. The downward force transmitted by the overlying residual coal pillars and thick, hard rock strata leads to localized stress concentration during the working face mining process, increasing the risk of rockburst. For rockburst prevention, existing methods such as underground pressure relief drilling, coal seam water injection, and blasting pressure relief have formed a mature technical system. However, when facing the combined impact zone of "overlying coal pillars + thick and hard rock layers", traditional prevention methods have obvious limitations: First, underground construction is mostly carried out in high-stress coal seam areas, and the working environment itself has a high impact risk, which can easily cause dynamic disasters during construction. Second, underground methods can only relieve pressure on the coal seam locally and cannot cut off the stress coupling transmission path between the thick and hard rock layers and the overlying coal pillars, making it difficult to fundamentally eliminate the high static load and strong dynamic load transmitted by the overlying rock. Summary of the Invention

[0003] The present invention aims to at least partially solve one of the technical problems in the related art.

[0004] Therefore, embodiments of the present invention propose a method for preventing rockburst in the affected area of ​​overlying residual coal pillars. The method adjusts the fracturing operation according to the fracture extension rate to pre-fracture the surrounding rock above the residual coal pillars, thereby improving the safety of coal mining.

[0005] The method for preventing rockbursts in the affected area of ​​overlying residual coal pillars according to embodiments of the present invention includes:

[0006] The key layers of the surrounding rock above the working face to be mined and the coal pillars left in the overlying strata are identified as the pre-designated fracturing layers; The fracturing area of ​​the pre-set fracturing layer is determined by the working face to be mined and the remaining coal pillars, and the projection surface of the fracturing area in the gravity direction covers the working face to be mined and the remaining coal pillars. After setting up a vertical shaft on the ground, horizontal wells are drilled into the pre-set fracturing layer, and then horizontal well fracturing is performed on the pre-set fracturing layer. The fracturing operation can be adjusted by measuring the fracture propagation rate during the fracturing process.

[0007] The method for preventing rockburst in the overlying residual coal pillar area according to the embodiment of the present invention adjusts the fracturing operation according to the fracture extension rate to pre-fracture the surrounding rock above the residual coal pillar, thereby improving the safety of coal mining.

[0008] The surface is drilled vertically to the center of the T-shaped long cantilever structure. Then, the well axis is adjusted to be aligned with the horizontal well axis of the T-shaped long cantilever structure rock formation and drilled to the range specified in ①. After the well axis arrangement is completed, fracturing fluid is injected from the surface to weaken the T-shaped long cantilever structure. In some embodiments, the projection plane of the working face to be mined along the gravity direction is located within the pressure zone, and the edge of the projection plane of the working face to be mined along the gravity direction is 10m to 30m away from the edge of the fracturing zone. Furthermore, the projection surface of the overlying coal pillar along the gravity direction is located within the pressure area, and the edge distance of the projection surface of the overlying coal pillar along the gravity direction is greater than 15m.

[0009] In some embodiments, adjusting the fracturing operation by the fracture propagation rate during the fracturing process includes: When the fracture propagation rate is <0.5m / h, it indicates that the fracturing energy is insufficient. The fracturing pressure should be increased by 5MPa~8MPa, and the flow rate should be increased by 2~3m³ / min. The amount of fracturing fluid should be increased by 20-30% of the initial value. No adjustments are made to the fracturing operation if the fracture propagation rate is ≤2m / h and ≥0.5m / h.

[0010] In some embodiments, when the fracture extension rate is >2m / h, it indicates that the fracturing intensity is too high, which may lead to excessive fracture development and cause rock collapse. The fracturing pressure is reduced by 3MPa~5MPa, and the fracturing fluid discharge rate is reduced by 1-2m³ / min from the initial discharge rate. At the same time, the single-stage fracturing time is shortened from the original 30~40min / stage to 20~25min / stage.

[0011] In some embodiments, stress sensors are arranged in the coal seam and roof of the working face to be mined to monitor stress changes before and after fracturing, and the fracturing effect is determined by the stress changes before and after fracturing.

[0012] In some embodiments, monitoring the depressurization effect at the working face is also 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, 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.

[0013] In some embodiments, if any of the monitoring data of borehole stress, micro-vibration, or support pressure exceeds a preset value, the alarm area is subjected to additional pressure relief using abrasive jet axial cutting technique. Once the monitoring index is lower than the warning value, anchor bolts and cables are installed within a 20m radius of the alarm area.

[0014] In some embodiments, if any of the monitored data such as borehole stress, microvibration, or support pressure exceeds a preset value, spray support shall be applied within a 20m radius of the alarm zone in the return airway and transport roadway corresponding to the working face to be mined, before mining begins.

[0015] In some embodiments, the goaf of adjacent working faces is filled.

[0016] In some embodiments, a micro-vibration sensor is installed on the working face for micro-vibration monitoring. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the overlying coal pillar in an embodiment of the present invention.

[0018] Figure 2 This is a cross-sectional view of the working surface after fracturing according to an embodiment of the present invention.

[0019] Figure 3 This is a cross-sectional view of the working face before fracturing according to an embodiment of the present invention.

[0020] Figure 4 This is a schematic flowchart of the method for preventing rockbursts in the affected area of ​​overlying residual coal pillars according to an embodiment of the present invention.

[0021] Figure label: 1. Working face to be mined, 2. Remaining coal pillar, 3. Surface vertical shaft, 4. Horizontal shaft, 5. Goaf, 6. T-shaped long cantilever structure, 7. Return airway, 8. Transport roadway, 9. Surface, 10. Thick hard rock strata. Detailed Implementation

[0022] Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0023] The method for preventing rockburst in the affected area of ​​the overlying residual coal pillar 2 according to an embodiment of the present invention includes: S100: The key layers of the surrounding rock above the working face 1 to be mined and the coal pillar 2 left in the overlying layer are identified as the pre-set fracturing layers; S200: The fracturing area of ​​the preset fracturing layer is determined by the working face to be mined 1 and the remaining coal pillar 2, and the projection surface of the fracturing area in the gravity direction covers the working face to be mined 1 and the remaining coal pillar 2. S300: After setting up a vertical shaft at ground level 9, drill a horizontal well 4 into the preset fracturing layer, and then perform horizontal well 4 fracturing on the area to be fractured in the preset fracturing layer. S400: Adjust the fracturing operation by measuring the fracture propagation rate during the fracturing process.

[0024] Specifically, such as Figures 1 to 4 As shown, in the direction of gravity, due to the limitations of early mining technology, there will be a residual coal pillar 2 above the unmined coal seam. In most mining areas, the residual coal pillar 2 is generally accompanied by thick and hard rock layers such as sandstone and conglomerate. The thick and hard rock layer 10 has good rock mass integrity, high strength and is not easy to collapse. It forms a T-shaped long cantilever structure 6 with the residual coal pillar 2 below, which causes the roof of the working face to be mined to bear pressure and is prone to rockburst during mining.

[0025] 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.

[0026] For example, a rock stratum in the key layer above the abandoned coal pillar 2, whose thickness and hardness are within a certain preset range, can be set as a preset fracturing layer. The preset fracturing layer, corresponding to the area of ​​the abandoned coal pillar 2 and the working face 1 to be mined in the vertical direction, is set as the fracturing area. This can be understood as the projection of the fracturing area in the vertical direction, or the direction of gravity, covering the abandoned coal pillar 2 and the working face 1 to be mined. In other words, the projection of the abandoned coal pillar 2 along the vertical direction onto the preset fracturing layer is included in the fracturing area, and the projection of the working face 1 along the vertical direction onto the preset fracturing layer is also included in the fracturing area. This ensures that the horizontal transmission path of coal pillar stress to both sides of the working face is blocked after fracturing of the horizontal well 4.

[0027] Vertical drilling is performed at the surface (9) to the center of the T-shaped long cantilever structure (6). The well axis is then aligned with the direction of the T-shaped long cantilever structure (6) rock formation, and the horizontal well axis (4) is drilled into the area to be fracturing. After the horizontal well axis (4) is positioned, fracturing fluid is injected from the surface (9) to weaken the T-shaped long cantilever structure (6). The fracture propagation rate during fracturing is then monitored, and adjustments are made based on this rate. For example, if the fracture propagation rate is within a preset range, no adjustments are made. If the fracture propagation rate is lower or higher than the preset range, adjustments can be made by increasing the pressure or volume of the injected fracturing fluid to ensure the fracturing effect is within the desired range.

[0028] in, Figure 2 and Figure 3 The horizontal axis represents the width of the working face to be mined, or can be understood as a cross-sectional view of the working face in a direction orthogonal to the mining direction and not in the vertical direction. The vertical axis represents the stress on the medium.

[0029] The method for preventing rockburst in the affected area of ​​the overlying residual coal pillar 2 according to an embodiment of the present invention involves fracturing the key controlling layer in the thick and hard rock strata 10 using surface horizontal well 4 fracturing technology. Unlike traditional localized and passive treatment measures such as underground roof breaking and pressure relief or large-diameter borehole pressure relief in the coal body, this invention simultaneously covers the projection surface of the area to be fracturing with the residual coal pillar 2 and the working face 1 to be mined. This proactively disrupts the integrity of the roof before the working face is mined, cutting off the path of concentrated stress from the residual coal pillar 2 to be horizontally transmitted to both sides of the working face, thus disintegrating the load-bearing structure for rockburst. The fracturing parameters are dynamically adjusted by the fracture extension rate to ensure the coverage and fracture width of the fracturing effect. This allows the high-level hard roof to fracture under pressure, reducing the probability of rockburst. In other words, adjusting the fracturing operation according to the fracture extension rate pre-fracturing the surrounding rock above the residual coal pillar 2 improves the safety of coal mining. Compared to deep-hole pre-fracturing blasting of the roof in underground roadways, this invention employs a surface-based 9-well drilling + 4-well horizontal fracturing operation mode. This moves most of the fracturing process to the surface, avoiding the risk of underground workers being directly exposed to mining disturbance zones. The surface-based 9-well fracturing operation is not limited by the cross-section of the underground roadways, allowing for large-volume, large-scale, multi-stage fracturing with a wider treatment range and more uniform weakening effect. It can also directly act on the hard rock strata, cutting off the stress coupling transmission path between the thick hard rock strata and the remaining coal pillars. Furthermore, by reducing the amount of underground blasting operations and roadway maintenance, it can lower the overall anti-rock erosion cost and improve the economic efficiency of the mine in the long run.

[0030] In some embodiments, the projection plane of the working face 1 to be mined along the gravity direction is located within the pressure zone, and the edge of the projection plane of the working face 1 to be mined along the gravity direction is 10m to 30m away from the edge of the fracturing zone. Furthermore, the projection surface of the overlying coal pillar 2 along the gravity direction is located within the pressure area, and the edge distance of the projection surface of the overlying coal pillar 2 along the gravity direction is greater than 15m.

[0031] Specifically, such as Figures 1 to 4As shown, the direction of gravity is vertical. The projection of the working face 1 to be mined along the vertical direction onto the preset fracturing layer is located within the area to be fracturing, meaning the area to be fracturing covers or includes the projection of the working face 1 along the vertical direction onto the preset fracturing layer. Similarly, the projection of the overlying coal pillar 2 along the vertical direction onto the preset fracturing layer is located within the area to be fracturing, meaning the area to be fracturing covers or includes the projection of the overlying coal pillar 2 along the vertical direction onto the preset fracturing layer. Furthermore, the area to be fracturing extends beyond the overlying coal pillar 2 and the projection of the working face 1 along the vertical direction onto the preset fracturing layer in both the front-back and left-right directions, ensuring the cutting off of the extended bearing structure of the thick, hard rock layer 10 on the front and back sides of the coal pillar, preventing stress diffusion and superposition to both ends of the working face. This ensures the horizontal transmission path of coal pillar stress to both sides of the working face is blocked. The target rock layer for fracturing is the full thickness of the thick, hard rock layer 10, completely covering it from the top to the bottom plate, avoiding residual stress transmission channels due to incomplete vertical fracturing.

[0032] In other words, if the fracturing zone is only flush with the edge of the coal pillar, high stress may bypass the rock strata below the coal pillar edge (the unfracturing zone) and continue to propagate towards the working face. It is required that the projected edge of the coal pillar be more than 15 meters away from the fracturing boundary to ensure that even if stress spreads laterally above the coal pillar, it cannot bypass the weakened fracturing zone. A margin of 10-30 meters is reserved to account for the influence range of the advance support pressure during working face mining. This margin ensures that the edge of the fracturing zone has sufficient integrity to block the intrusion of external stress before the mining pressure arrives, preventing the working face from being directly exposed to the high stress gradient zone at the boundary of the fracturing zone.

[0033] This embodiment achieves the blocking of rockbursts by horizontally fracturing the fracturing area with a margin of >15m on the coal pillar side and 10~30m on the working face side, and vertically "fully covering" (full-thickness fracturing of the thick hard rock layer 10), thus creating a three-dimensional spatial limitation. First, an over-covered fracturing area is set up on the horizontal plane to ensure that the stress transmission path is completely physically isolated. Second, in the vertical direction, the integrity of the thick hard rock layer 10 is completely destroyed by a fracture network that penetrates the roof and floor, dismantling its mechanical basis as a "cantilever beam" for stress transmission and eliminating any residual vertical stress channels due to incomplete fracturing. Finally, the boundary values ​​are defined in the optimal range of 10~30m, ensuring that the pressure relief effect is not destroyed by mining, while avoiding engineering waste caused by excessive fracturing, thereby reducing fracturing costs.

[0034] In some embodiments, adjusting the fracturing operation by the fracture propagation rate during the fracturing process includes: When the fracture propagation rate is <0.5m / h, it indicates that the fracturing energy is insufficient. Increase the fracturing pressure by 5MPa~8MPa and increase the flow rate by 2~3m³ / min. Increase the fracturing fluid volume by 20-30% of the initial value.

[0035] No adjustments are made to the fracturing operation if the fracture propagation rate is ≤2m / h and ≥0.5m / h.

[0036] Specifically, such as Figures 1 to 4 As shown, the existing microseismic monitoring system was used throughout the process to monitor the development direction, extension range, and continuity of the hydraulic fracturing fractures in real time, in order to reduce costs.

[0037] When the fracture extension rate in the surrounding rock is less than 0.5 m / h, it indicates that the current fracturing energy is insufficient to effectively overcome the geostress of the target rock layer or the closing force of natural weak surfaces. In this case, the pressure is increased by 5 MPa to 8 MPa to forcibly open the closed surrounding rock or the closed fracture, and drive the fracture tip to overcome rock resistance and extend forward, ensuring that the fracturing operation will not be halted due to insufficient energy.

[0038] Increasing the flow rate by 2-3 m³ / min increases the flow velocity of the fracturing fluid within the fracture, enhances the impact load on the fracture tip, and facilitates the continued extension of the fracture. Sufficient flow rate ensures that the formed fracture has effective conductivity, preventing the formation of ineffective fractures.

[0039] In addition to increasing pressure and displacement, an additional 20% to 30% of fracturing fluid is used, providing a sufficient material basis for the continued extension of fractures. This ensures that the fracture network can extend to the predetermined boundary of the fracturing area, ensuring that the fracturing stimulation volume meets design requirements and achieves the designed pressure relief range.

[0040] This embodiment combines increasing pressure, displacement, and additional fluid volume to form a complete solution for dealing with "insufficient energy" conditions. Its core effect is to force the fracturing operation back from an "under-fracturing" state to the designed trajectory, ensuring that a sufficiently large fracture network can still be formed in areas with complex geological conditions and high energy loss, thereby guaranteeing the reliability and effectiveness of the anti-scour project.

[0041] In some embodiments, when the fracture extension rate is >2m / h, it indicates that the fracturing intensity is too high, which may lead to excessive fracture development and cause rock collapse. The fracturing pressure is reduced by 3MPa~5MPa, and the fracturing fluid discharge rate is reduced by 1-2m³ / min from the initial discharge rate. At the same time, the single-stage fracturing time is shortened from the original 30~40min / stage to 20~25min / stage.

[0042] Specifically, such as Figures 1 to 4As shown, when the fracture extension rate exceeds 2 m / h, it indicates that the current fracturing energy far exceeds the rock mass fracturing requirements, and the fracture is in a state of high-speed uncontrolled expansion. Reducing the pressure by 3-5 MPa at this point directly weakens the main driving force for fracture expansion, bringing the fracture extension rate back to a reasonable range. This avoids excessive fracture extension into non-target areas and prevents uneven effective stress release due to excessively long fractures. Reducing the discharge rate by 1-2 m³ / min from the initial level reduces the impact load of the fracturing fluid on the fracture tip, slowing the fracture expansion rate. Excessive discharge rate can easily create instantaneous high pressure within the fracture, potentially inducing unexpected rock mass fracturing or even local collapse. Reducing the discharge rate makes the pressure distribution within the fracture more balanced, preventing rock mass instability caused by excessive energy density. Shortening the single-stage fracturing time from 30-40 min / stage to 20-25 min / stage is a further strengthening of control based on "pressure reduction and discharge reduction." Shortening the time means reducing the total energy injection per unit area, preventing excessive development of fractures under continuous high pressure. This "small amount, multiple times" rapid switching strategy ensures that the target strata are effectively modified, while avoiding secondary problems such as collapse or proppant embedding in local rock strata due to prolonged pressure.

[0043] This invention, through a three-pronged approach of reducing pressure (lowering the input pressure of fracturing fluid), reducing emissions (reducing impact), and controlling time (limiting the total amount), pulls fracturing operations back from the brink of being out of control to a controllable range. While ensuring that the fracture network effectively expands to the design range, it also prevents engineering disasters such as rock collapse and fracture cross-layering caused by excessive fracturing intensity, thus achieving a dynamic balance between safety and effectiveness.

[0044] In some embodiments, stress sensors are arranged in the coal seam and roof of the working face 1 to monitor stress changes before and after fracturing, and the fracturing effect is determined by the stress changes before and after fracturing.

[0045] Specifically, such as Figures 1 to 4 As shown, the maximum principal stress of the coal body should be reduced to 0.4-0.6 times the original stress, and the stress distribution should be uniform with no obvious stress concentration areas, ensuring that the stress transmission channel of the T-shaped long cantilever structure 6 is cut off.

[0046] The maximum principal stress of the coal seam should be reduced to 0.4 to 0.6 times the original stress. If the stress reduction is too small (greater than 0.6 times the original stress), it indicates that the fracturing has not sufficiently cut off the stress transmission path. If the stress reduction is too large (less than 0.4 times the original stress), it may mean that the roof is excessively weakened, posing a risk of instability. This range ensures that the pressure relief effect is just right.

[0047] Furthermore, when the stress decreases excessively, i.e. less than 0.4 times the original stress, it is necessary to strengthen the roof support, such as through grouting support, anchoring support, or increasing the number of hydraulic single-unit columns in the roadway, in order to support the roof as much as possible.

[0048] In some embodiments, monitoring of the depressurization effect at the working face is also 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, 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.

[0049] A borehole stress sensor is installed in a pre-defined borehole location, ensuring accurate sensor placement to effectively monitor stress changes in the target area. Stress data is collected in real-time and transmitted to a monitoring center via a data transmission system. The collected stress data is then analyzed and monitored in real-time to determine if the stress exceeds a preset value.

[0050] 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.

[0051] Preset values ​​are set for online monitoring of borehole stress, micro-vibration 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.

[0052] 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 and pressure relief using a sandblasting jet to reduce stress.

[0053] 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.

[0054] Furthermore, if any of the monitoring data such as borehole stress, micro-vibration, or support pressure exceeds the preset value, the alarm area will be subjected to additional pressure relief using abrasive jet axial cutting technology. Once the monitoring indicators are below the warning value, anchor bolts and cables will be installed within 20m of the alarm area to improve the safety and stability of coal mining.

[0055] In some embodiments, if any of the monitoring data of borehole stress, micro-vibration, or support pressure exceeds a preset value, spray support shall be applied within 20m of the adjacent alarm area of ​​the return airway 7 and transport roadway 8 corresponding to the working face to be mined before mining, in order to prevent flying rock.

[0056] In some embodiments, the goaf 5 of adjacent working faces is filled to support the collapsed or deformed thick, hard rock strata 10, thereby reducing the probability and severity of rockbursts.

[0057] Furthermore, micro-vibration sensors are installed on the working face for micro-vibration monitoring. By locating the spatial distribution of micro-vibration events on the working face, the fracture location and extent of the thick, rigid roof slab can be dynamically determined. In the description of this invention, it should be understood that terms such as "center," "longitudinal," "transverse," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential," indicating orientation or positional relationships, are based on the orientation or positional relationships shown in the accompanying drawings and are only for the convenience of describing the invention and simplifying the description. They 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 the invention.

[0058] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0059] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection, an electrical connection, or a connection that allows communication between them; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components, unless otherwise explicitly limited. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0060] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can mean that the first feature is in direct contact with the second feature, or that the first feature is in indirect contact with the second feature through an intermediate medium. Furthermore, "above," "over," and "on top" of the second feature can mean that the first feature is directly above or diagonally above the second feature, or simply that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply that the first feature is at a lower horizontal level than the second feature.

[0061] In this invention, the terms "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to a specific feature, structure, material, or characteristic described in connection with that embodiment or example, which is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0062] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A method for preventing rockburst in the affected area of ​​an overlying residual coal pillar, characterized in that, include: The key layers of the surrounding rock above the working face to be mined and the coal pillars left in the overlying strata are identified as the pre-designated fracturing layers; The fracturing area of ​​the pre-set fracturing layer is determined by the working face to be mined and the remaining coal pillars, and the projection surface of the fracturing area in the gravity direction covers the working face to be mined and the remaining coal pillars. After setting up a vertical shaft on the ground, horizontal wells are drilled into the pre-set fracturing layer, and then horizontal well fracturing is performed on the pre-set fracturing layer. The fracturing operation can be adjusted by measuring the fracture propagation rate during the fracturing process.

2. The method for preventing rockburst in the affected area of ​​overlying residual coal pillars according to claim 1, characterized in that, The projection of the working face to be mined along the direction of gravity is located within the pressure zone, and the edge of the projection of the working face to be mined along the direction of gravity is 10m to 30m away from the edge of the fracturing zone. Furthermore, the projection surface of the overlying coal pillar along the gravity direction is located within the pressure area, and the edge distance of the projection surface of the overlying coal pillar along the gravity direction is greater than 15m.

3. The method for preventing rockburst in the affected area of ​​overlying residual coal pillars according to claim 1, characterized in that, Adjusting fracturing operations by controlling the fracture propagation rate during the fracturing process includes: When the fracture propagation rate is <0.5m / h, it indicates that the fracturing energy is insufficient. The fracturing pressure should be increased by 5MPa~8MPa, and the flow rate should be increased by 2~3m³ / min. The amount of fracturing fluid should be increased by 20-30% of the initial value. No adjustments are made to the fracturing operation if the fracture propagation rate is ≤2m / h and ≥0.5m / h.

4. The method for preventing rockburst in the affected area of ​​overlying residual coal pillars according to claim 3, characterized in that, When the fracture extension rate is greater than 2 m / h, it indicates that the fracturing intensity is too high, which can easily lead to excessive fracture development and cause rock collapse. Reduce the fracturing pressure by 3 MPa to 5 MPa, and reduce the fracturing fluid discharge rate by 1 to 2 m³ / min from the initial discharge rate. At the same time, shorten the single-stage fracturing time from the original 30 to 40 min / stage to 20 to 25 min / stage.

5. The method for preventing rockburst in the affected area of ​​overlying residual coal pillars according to claim 1, characterized in that, Stress sensors are placed in the coal seam and roof of the working face to be mined to monitor stress changes before and after fracturing, and the fracturing effect is determined by the stress changes before and after fracturing.

6. The method for preventing rockburst in the affected area of ​​overlying residual coal pillars according to claim 5, characterized in that, This also includes monitoring the pressure relief effect at the working face: 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.

7. The method for preventing rockburst in the affected area of ​​overlying residual coal pillars according to claim 6, characterized in that, If any of the monitoring data for borehole stress, microvibration, or support pressure exceeds the preset value, the alarm area will be subjected to additional pressure relief using abrasive jet axial cutting technique. Once the monitoring indicators fall below the warning value, anchor bolts and cables will be installed within a 20m radius of the alarm area.

8. The method for preventing rockburst in the affected area of ​​overlying residual coal pillars according to claim 1, characterized in that, If any of the monitoring data for borehole stress, micro-vibration, or support pressure exceeds the preset value, spray support shall be applied within 20m of the alarm area in the return airway and transport roadway corresponding to the working face to be mined before mining.

9. The method for preventing rockbursts in the affected area of ​​overlying residual coal pillars according to claim 1, characterized in that, The goaf of adjacent working faces is filled.

10. The method for preventing rockburst in the affected area of ​​overlying residual coal pillars according to claim 1, characterized in that, Micro-vibration sensors are installed at the working face for micro-vibration monitoring.

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