Method for preventing and treating overlying strata separation layer water disasters during mining of Jurassic coal seam

Abstract

The invention relates to the technical field of coal mining, and provides a Jurassic coal mining overlying strata separation layer water disaster prevention and control method which comprises the following steps: S1) acquiring and analyzing geological and hydrological conditions of a stoping mining area, and determining whether a separation layer exists on a top plate of overlying strata or not; s2) if it is determined that there is a separation layer, obtaining separation layer parameters, and determining a separation layer type and a separation layer water disaster type according to the separation layer parameters; s3) if the separation layer type is determined to be a disaster type, cutting off the aquifer of the top plate or cutting off a water channel flowing to the separation layer through the surrounding rock strong runoff fault zone; s4) guiding and discharging accumulated water in the separation layer through the upper flow guide hole and / or the lower flow guide hole; according to the prevention and control method, the hidden danger of separation water storage can be found as soon as possible, then the measures of cutting off a water source and guiding and draining water storage are adopted to reduce the separation water disaster in the germination stage, and the problem that in the prior art, a separation water disaster prevention and control system is lacked is solved.

Description

Technical Field

[0001] This invention relates to the field of coal mining technology, specifically to a method for preventing water hazards caused by overburden separation in Jurassic coal seam mining. Background Technology

[0002] Jurassic coalfields have unique geological conditions, with coal seam roofs consisting mostly of thick sandstone or alternating layers of sandstone and mudstone, overlain by abundant aquifers. Coal mining causes segregation of the overlying strata, easily forming segregation cavities (also known as segregation or segregation spaces) between key roof layers and aquitards. When water from the upper aquifer enters these segregation spaces, it can evolve into a new form of roof water hazard—segregation water hazard. Segregation water hazard is highly sudden, complex, or insidious, often causing a sudden surge of water without obvious warning, leading to flooding of the working face and damage to equipment, and in severe cases, casualties and significant economic losses. For example, in a segregation water inrush accident, the thick, hard igneous roof collapses suddenly after a large span, and a large amount of water sealed in the underlying thick sandstone segregation breaks through the aquitard under high water pressure, rushing into the working face along the mining-induced water-conducting fracture zone, causing a major disaster. Therefore, roof delamination water hazards have become one of the major challenges in coal mine water control. Research has found that the formation of roof delamination water accumulation hazards requires several conditions: First, the delamination space must be located above the mining-induced water-conducting fracture zone, possessing structural conditions suitable for water accumulation; second, there must be a stable water source supply around the delamination (such as overlying water-bearing sandstone layers or fracture water); third, the delamination must remain open for a sufficient period to allow water to fill and accumulate within it; and finally, the surrounding rock medium should possess a certain degree of permeability and water conductivity. Once these conditions are met and effective drainage intervention is lacking, the water accumulation within the delamination space will gradually increase and maintain a high head; when the key roof strata further collapse or external disturbances create a "dynamic breakthrough zone" that connects with the lower goaf, the sealed delamination water will rupture and overflow instantly, causing a water inrush accident. Therefore, the prevention and control of extrusion water hazards must revolve around the core concept of "blocking water sources and releasing water pressure," proactively eliminating potential hazards before disasters occur. Current mine water hazard prevention and control measures mainly target confined water in the floor and conventional water inflow in the roof, lacking specific assessment and treatment methods for extrusion water hazards in overburden. Traditional methods often involve passive emergency response after a water inrush, or rely solely on advance water release at the working face to mitigate general roof water seepage, making it difficult to promptly detect and address "extrusion water storage bags" buried within thick overburden. Existing research has explored the formation mechanism, classification, and evaluation methods of extrusion water hazards. For example, it has categorized extrusion water hazards into different types based on the location relationship between the stope and the extrusion water body and established a hazard index model; it has also proposed the main controlling factors for extrusion water storage, such as the thickness of the mudstone aquitard layer, which is a key parameter determining the extrusion water storage capacity, and the existence of a critical thickness based on the vertical seepage velocity distribution. However, an effective technological system for prevention and control is still lacking, resulting in insufficient early warning and untimely prevention when mines face such hidden water hazards, which can easily lead to serious water inrush accidents. Therefore, it is urgent to develop a method for preventing and controlling overburden water hazards that combines the hydrological characteristics of Jurassic strata, and to proactively control and eliminate the disaster-causing factors of overburden water hazards from a proactive management perspective.

[0003] Therefore, there is an urgent need for a screening device to solve at least one of the above problems. Summary of the Invention

[0004] The purpose of this invention is to provide a method for preventing and controlling water hazards caused by overburden separation in Jurassic coal seam mining, in order to solve the problem of the lack of a system for preventing and controlling water hazards caused by overburden separation in the prior art.

[0005] To achieve the above objectives, the present invention provides a method for preventing water hazards caused by overburden separation during Jurassic coal seam mining, the method comprising: S1) Before coal seam mining operations, obtain and analyze the geological and hydrological conditions of the mining area to determine whether there is delamination in the roof of the overlying strata; S2) If it is determined that a delamination layer exists, obtain the delamination layer parameters and determine whether the delamination layer type is harmless or hazardous based on the delamination layer parameters; S3) If the delamination type is determined to be disaster type, a water interception zone is set in the top plate to cut off the aquifer of the top plate or cut off the water channel flowing to the delamination through the strong runoff fracture zone of the surrounding rock. S4) Construct an upper diversion hole on the surface to connect with the detachment layer, and / or construct a lower diversion hole on the top plate to connect with the detachment layer, and drain the water accumulated in the detachment layer through the upper diversion hole and / or the lower diversion hole; S5) Use blasting or hydraulic fracturing to pre-fracturing and cutting the key layers of the roof to reconstruct the fracture structure of the overlying rock; S6) Perform coal seam mining operations.

[0006] Specifically, the geological and hydrological conditions of the mining area are obtained through geophysical exploration, advanced drilling, or borehole imaging.

[0007] Specifically, the delamination parameters include: the location of the delamination, the height of the delamination, the span of the delamination, the relative position of the delamination and the water-conducting fracture zone, and the water storage volume within the delamination.

[0008] Specifically, after step S3) and before step S4), the prevention and control method further includes: determining the timing for draining water accumulated in the absorptive layer, including: S60) Obtain the water storage volume within the abscission layer and monitor whether the water storage volume within the abscission layer increases within a set time period; S61) If the water storage in the abscess does not increase, proceed to step S4) to drain the water stored in the abscess. S62) If the water storage in the separation layer increases, proceed to step S3). S63) Repeat steps S60)-S62) until all the accumulated water in the separation layer is drained.

[0009] Specifically, step S3) includes: Multiple grouting holes are set in the top plate, and high-pressure grout is injected into the aquifer or the strong runoff fracture zone of the surrounding rock through the multiple grouting holes to form a water-cutting zone in the key layer of the top plate.

[0010] Specifically, in step S4), a lower guide hole is made in the top plate, including: A process hole is formed by drilling a borehole into the roof through an auxiliary roadway excavated during coal seam mining. During the drilling operation, a first casing and a second casing are used to protect the wall of the process hole. The first casing is used for wall protection before the process hole is connected to the roof, and the second casing is used for wall protection after the process hole is connected to the roof. Drainage holes are opened on the wall of the second casing. Water accumulated in the roof enters the second casing through the drainage holes and then flows through the first casing to be discharged.

[0011] Specifically, the method further includes: while performing step S4), forming branch guide holes in multiple branch horizontal wells toward the separation borehole to communicate with the separation, and draining the water accumulated in the separation through the branch guide holes; wherein, the multiple branch horizontal wells radiate from the wellbore of the coal mining well used for coal seam mining.

[0012] Specifically, step S5) involves pre-fracture and cutting of the critical layers of the roof using hydraulic fracturing, including: Drill holes toward the critical layer in the top plate or on the surface to create fracturing holes; Fracturing is performed by injecting fracturing fluid into the critical layers of the top plate through fracturing holes, in order to pre-fracture and cut the critical layers of the top plate.

[0013] Specifically, step S5) involves pre-splitting and cutting the critical layers of the roof using explosives, including: Holes are drilled along the top plate to form blasting holes, and multiple blasting sections are designated within the blasting holes. Each blasting section uses micro-delay blasting to pre-crack and cut the key layers of the top plate.

[0014] Specifically, the method further includes: Before carrying out coal seam mining operations, an abscess water monitoring system is installed on the roof to obtain the changes in roof condition and the changes in water storage within the abscess.

[0015] Specifically, the installation of the delamination water monitoring system on the top slab includes: S01) Install a roof separation meter in the working face roadway to monitor the displacement data of the roof strata; wherein, the working face roadway is a roadway used for coal transportation, ventilation and equipment layout in coal seam mining operations; install a mine electrical resistivity detection system on the roof of the working face roadway to monitor the water storage in the separation layer; monitor the water level data around the mining face. S02) Analyze the displacement data of the roof strata, the water storage and water level data in the abscess, and obtain the laws of roof state change and water storage change in the abscess.

[0016] The method for preventing and controlling overburden delamination water hazards in Jurassic coal seam mining provided by this invention first determines whether delamination exists in the roof of the overburden based on the geological and hydrological conditions of the mining area. After confirming the existence of delamination, delamination parameters are obtained, and the type of delamination is determined to be harmless or hazardous based on these parameters. If the delamination is determined to be hazardous, a water interception zone is set up in the roof to cut off the aquifer or the water flowing towards the delamination through the strong runoff zone of the surrounding rock, ensuring that the amount of water accumulated in the delamination does not increase. After cutting off the water channel to the delamination, the accumulated water in the delamination is drained, reducing the amount of water accumulated in the delamination and alleviating the pressure on the rock strata. Subsequently, the key layer of the roof is cut, dividing the delamination into multiple small units, which is equivalent to reconstructing the fracture structure of the overburden. By reconstructing the fracture structure of the overburden, the hidden danger of sudden collapse of the overburden is eliminated, ensuring the safe execution of subsequent coal seam mining. After the delamination water hazard treatment is completed, coal seam mining operations are carried out.

[0017] The present invention provides a method for preventing and controlling water hazards caused by overburden separation in Jurassic coal seam mining. By conducting advanced geological surveys and risk assessments, it identifies potential water storage hazards in the overburden separation early on. It then employs measures such as cutting off water sources and diverting water storage to mitigate the water hazards at the nascent stage. Subsequently, it reduces the risk of overburden collapse by reconstructing the fracture structure of the overburden to separate the separation layer. The entire prevention and control method greatly improves the initiative and targeting of water hazard prevention and control, and solves the problem of the lack of a comprehensive system for preventing and controlling water hazards in existing technologies.

[0018] Other features and advantages of the embodiments of the present invention will be described in detail in the following detailed description section. Attached Figure Description

[0019] The accompanying drawings are provided to further illustrate embodiments of the present invention and form part of the specification. They are used together with the following detailed description to explain the embodiments of the present invention, but do not constitute a limitation thereof. In the drawings: Figure 1 This is a flowchart illustrating the method for preventing water hazards caused by overlying rock delamination in Jurassic coal seam mining provided by the present invention. Figure 2 This is a design drawing of the drilling hole for water hazard exploration in the roof of the working face in the method for preventing and controlling water hazards caused by overlying rock separation in Jurassic coal seam mining provided by the present invention. Figure 3 This is a schematic diagram of multi-branch horizontal well drilling in the method for preventing water hazards caused by overlying strata separation in Jurassic coal seam mining provided by the present invention; Figure 4 This is a schematic diagram of surface directional drilling in the method for preventing water hazards caused by overlying rock separation in Jurassic coal seam mining provided by the present invention. Detailed Implementation

[0020] The specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are for illustration and explanation only and are not intended to limit the scope of the present invention.

[0021] Figure 1 This is a flowchart illustrating the method for preventing water hazards caused by overlying rock delamination in Jurassic coal seam mining. Figure 2 This is a design drawing for boreholes for detecting water hazards on the roof of the working face in the method of preventing water hazards caused by overlying delamination in Jurassic coal seam mining; Figure 3 This is a schematic diagram of a multi-branch horizontal well drilling method for preventing water hazards caused by overburden separation in Jurassic coal seam mining; Figure 4 This is a schematic diagram of surface directional drilling for preventing water hazards caused by overlying rock separation in Jurassic coal seam mining.

[0022] like Figures 1-4 As shown, this invention provides a method for preventing water hazards caused by overlying strata separation in Jurassic coal seam mining, the method comprising: S1) Before coal seam mining operations, obtain and analyze the geological and hydrological conditions of the mining area to determine whether there is delamination in the roof of the overlying strata; S2) If it is determined that a delamination layer exists, obtain the delamination layer parameters and determine whether the delamination layer type is harmless or hazardous based on the delamination layer parameters; S3) If the delamination type is determined to be disaster type, a water interception zone is set in the top plate to cut off the aquifer of the top plate or cut off the water channel flowing to the delamination through the strong runoff fracture zone of the surrounding rock. S4) Construct an upper diversion hole on the surface to connect with the detachment layer, and / or construct a lower diversion hole on the top plate to connect with the detachment layer, and drain the water accumulated in the detachment layer through the upper diversion hole and / or the lower diversion hole; S5) Use blasting or hydraulic fracturing to pre-fracturing and cutting the key layers of the roof to reconstruct the fracture structure of the overlying rock; S6) Perform coal seam mining operations.

[0023] The method for preventing water hazards caused by overlying strata separation in Jurassic coal seam mining provided by this invention involves collecting geological and hydrological conditions of the coal seam mining area before coal seam mining operations. These conditions include geological and hydrological factors. Geological conditions further include coal seam structure, roof and floor rock properties, geological structures, and surrounding rock stability. The coal seam thickness, continuity, and occurrence state directly affect the difficulty and safety of coal seam mining. The rock strength and joint development of the roof and floor rocks affect the stability of the roadways formed during mining and the design of roadway support. Geological structures such as faults and folds disrupt coal seam continuity, increasing the complexity of mining. The physical properties of the surrounding rock (such as hardness and brittleness) directly influence the support scheme implemented during coal seam mining. Hydrological conditions include aquifer characteristics, recharge conditions, inflow volume, and the difficulty of water control. The water-bearing capacity (water storage capacity) and heterogeneous water flow channels of an aquifer directly affect its inflow and risk of sudden water inrush. Recharge conditions, i.e., the source of recharge (such as atmospheric precipitation or surface water seepage), determine the sustainability of the water source. A deposit is considered strongly water-bearing when the inflow exceeds 10 L / sm. The difficulty of water control requires comprehensive consideration of the aquifer's water-bearing capacity, heterogeneous water flow, geological structural complexity, and control costs. Therefore, after collecting geological and hydrological conditions of the mining area, staff analyze the collected geological and hydrological conditions to determine whether delamination exists in the overlying strata, and to obtain delamination parameters and determine the type of delamination.

[0024] This application analyzes the geological and hydrological conditions of the mining area to determine whether there is a delamination (delamination refers to a delamination space or delamination overburden) in the roof. After confirming the existence of a delamination in the roof, in order to determine whether the delamination will cause harm to coal seam mining, delamination parameters are obtained and the delamination type is determined based on the delamination parameters (delamination types are divided into harmless and hazardous types).

[0025] If the abscission type is determined to be hazardous, to avoid excessive water accumulation in the abscission space potentially causing a water inrush accident, this application proposes setting up a water-cutting strip in the roof to cut off the roof aquifer, or to cut off the water channel flowing into the abscission space through the strong runoff zone of the surrounding rock, thereby preventing excessive water accumulation in the abscission space. Subsequently, by constructing upper diversion holes on the surface connected to the abscission, and / or constructing lower diversion holes in the roof connected to the abscission, the water accumulated in the abscission space is drained, significantly reducing the pressure of the accumulated water within the abscission and preventing a water inrush accident caused by water accumulation in the abscission space. In specific implementation, the use of upper and / or lower diversion holes to drain the accumulated water in the abscission is selected based on the actual construction conditions. For abscission water hazard treatment of most coal seam thicknesses, lower diversion holes are constructed in the roof to drain the accumulated water; for abscission water hazard treatment of extra-thick coal seams, upper diversion holes are constructed on the surface to drain the accumulated water. In actual coal seam mining, the geological conditions of the coal seam are complex and the thickness of the coal seam varies. Therefore, upper diversion holes can be made on the surface and lower diversion holes can be made on the roof at the same time to drain the accumulated water.

[0026] After obtaining the delamination parameters (such as delamination height and delamination span), the size of the formed delamination space is known. Based on the location of the delamination and its relative position to the water-conducting fracture zone, it can be determined whether water supply enters the delamination. If water supply enters the delamination and forms water accumulation, the delamination can be determined to be a disaster type. If there is no water supply in the delamination, it can be determined to be a harmless type.

[0027] To prevent sudden collapse of the overburden due to large, suspended sections in the delamination space, pre-fracture by blasting or hydraulic fracturing is employed to cut the critical layers of the overburden. This divides the delamination space into multiple smaller units, reducing the scale and impact of a single collapse and accelerating the drainage of residual water within the delamination space. The specific pre-fracture procedure is determined based on the overburden condition. In areas with intact overburden, hydraulic fracturing is preferred due to its precise control over fracture orientation. In areas with fractured overburden, blasting is chosen, as blasting effectively breaks the rock mass and blocks stress transmission paths. When cutting key layers of the roof, a combination of blasting and hydraulic fracturing can be used for pre-fracking. Hydraulic fracturing can be used first to pre-fracture and cut the overburden into large rock blocks. Then, blasting can be used to blast the large rock blocks separately to pre-fracture and divide them into smaller rock blocks, thereby reconstructing the fracture structure of the roof overburden. This combination not only facilitates the slow release and diversion of water accumulated in the separation space, but also eliminates the hidden danger of roof overburden collapse, providing a safety guarantee for coal seam mining.

[0028] After completing the treatment of water hazard caused by the separation of the coal seam, coal seam mining operations will continue.

[0029] The present invention relates to a method for preventing and controlling water hazards caused by overburden separation in Jurassic coal seam mining. By conducting advanced geological surveys and risk assessments, it identifies potential water storage hazards in the overburden separation early on. By adopting measures such as cutting off water sources and diverting water storage, the water hazards are reduced at the nascent stage. Subsequently, the fracture structure of the overburden is reconstructed, which separates the abscesses located in the overburden, thereby reducing the risk of overburden collapse. The entire prevention and control method greatly improves the initiative and pertinence of water hazard prevention and control, and solves the problem of the lack of a system for preventing and controlling water hazards in the existing technology.

[0030] In one embodiment, before deploying mining operations, the geological and hydrological conditions of the mining area are obtained through geophysical exploration, advanced drilling, or borehole imaging. The obtained geological and hydrological conditions are analyzed to determine whether a delamination exists in the roof. Once the existence of a delamination is confirmed, the structure of the roof and the distribution of aquifers within it are investigated using advanced drilling or geophysical methods. Taking a Jurassic coal mine as an example, before deploying mining operations, after exploring and analyzing the geological and hydrological conditions of the mining area, a delamination was found in the mudstone layer approximately 15 meters above the roof after 150 meters of mining. The roof is the coal seam roof. The delamination height was found to be approximately 0.5 meters, and the mudstone layer, acting as an aquitard, was approximately 20 meters thick. No water-conducting fractures were observed. Based on this, it was determined that the delamination formed in this mudstone layer is a closed space with water-bearing capacity. The location and water content of the abscess space are determined by methods such as core drilling and borehole imaging. Based on the coal seam mining method and the relative position of the abscess space to the water-conducting fracture zone, the types of abscess water hazards are classified. If there is no water accumulation within the abscess, it is considered harmless and can be mined normally. If signs of water accumulation are found within the abscess and it may pose a threat, it is classified as a disaster-type abscess. Disaster-type abscesses require subsequent prevention and control measures; otherwise, a water inrush accident may occur during coal seam mining. Geophysical exploration analyzes the physical differences between coal seams and surrounding rocks, such as density, magnetism, and electrical properties, to study the geological structure and strata characteristics of the coalfield area. For example, well logging tools are used for coal mine geological exploration to detect aquifer thickness and fault zone locations; tunnel imaging instruments using electromagnetic equipment detect geological anomalies underground in coal mining, utilizing the principles of electromagnetic wave transmission, scattering, and reflection to detect anomalies such as faults and collapse columns; transient electromagnetic instruments use time-domain electromagnetic methods to detect coal seams and surrounding water-bearing structures; and seismic exploration instruments are used for geological exploration. Seismic exploration instruments artificially generate seismic waves into the strata and receive their reflected or refracted signals, analyzing the propagation characteristics of the seismic waves to infer underground geological structures. Advanced drilling involves horizontal drilling at the working face using drilling rigs to obtain geological information ahead, helping to predict geological structures, assess hydrological conditions, and assist in optimizing construction plans. Borehole imaging technology uses equipment such as borehole imaging instruments to create high-definition images of the borehole interior, providing a visual representation of geological information such as lithology, fractures, and faults. Analysis of the imaging data allows for the quantitative assessment of delamination length, width, and strike, providing technical support for safe mining operations. In practical construction applications, the method of obtaining delamination parameters is not limited to a single approach; geophysical exploration, advanced drilling, or borehole imaging can be used in combination to acquire these parameters.

[0031] The delamination parameters include: the location, height, span, relative position of the delamination to the water-conducting fracture zone, and water storage capacity of the delamination. Once these parameters are known, the location of the delamination within the roof can be determined. Based on the position of the delamination relative to the water-conducting fracture zone, it can be determined whether there is water supply within the delamination. Workers can then determine whether the delamination is harmless or hazardous based on these parameters and take timely action. For example, using borehole imaging technology, not only can the water storage within the delamination be observed directly, but the length, width, and orientation of the delamination can also be determined by analyzing the imaging data. Furthermore, the relative position of the delamination to the water-conducting fracture zone can be determined, and the location of the delamination, its relative position to the water-conducting fracture zone, and the water storage capacity within the delamination can be confirmed by analyzing the core samples obtained from the borehole imaging.

[0032] After determining that the aquifer is a disaster-type aquifer, in order to avoid water inrush accidents, the water flowing from the aquifer or through the strong runoff zone of the surrounding rock to the aquifer is first cut off to control the water level in the aquifer. Specifically, step S3) includes: Multiple grouting holes are set in the top plate, and high-pressure grout is injected into the aquifer or the strong runoff fracture zone of the surrounding rock through the multiple grouting holes to form a water-cutting zone in the key layer of the top plate.

[0033] To address external water sources causing aquifer water damage, grouting is first employed to seal off the channel between the external water source and the aquifer, thus forming a water-stopping zone. This water-stopping zone acts as a water-stopping curtain or cemented zone. Grouting is preferentially implemented above or around the mining face in aquifers and areas with strong runoff fractures in the surrounding rock. Specifically, multiple grouting holes can be arranged in the roof along the direction of water replenishment within the aquifer, either on the surface or in auxiliary mining roadways. A fast-setting, high-strength grout (such as cement-water glass grout) is used for high-pressure grouting through these holes. The grout injected into the roof diffuses and solidifies in the aquifer and surrounding rock fissures, forming an impermeable barrier or reinforcement ring—essentially a water-stopping curtain or cemented zone. This significantly reduces the intensity of seepage from the aquifer into the aquifer space. For example, in the treatment of water hazard caused by aquifer separation, surface drilling was used to grout the Zhiluo Formation sandstone aquifer in the overlying rock. The grouting cut off the water channel between the aquifer and the aquifer, thus successfully blocking the water source that continuously flowed into the aquifer through the Zhiluo Formation sandstone aquifer, preventing the water volume in the aquifer from increasing, and creating safe conditions for the next step of aquifer drainage.

[0034] After cutting off the channel between the water source and the abscess space, in order to avoid the water already accumulated in the abscess posing a safety hazard to subsequent coal seam mining, advanced drilling is used to remove the water accumulated in the abscess. In step S4), a lower guide hole is constructed in the roof, including: A process hole is formed by drilling a borehole into the roof through an auxiliary roadway excavated during coal seam mining. During the drilling operation, a first casing and a second casing are used to protect the wall of the process hole. The first casing is used for wall protection before the process hole is connected to the roof, and the second casing is used for wall protection after the process hole is connected to the roof. Drainage holes are opened on the wall of the second casing. Water accumulated in the roof enters the second casing through the drainage holes and then flows through the first casing to be discharged.

[0035] Specifically, the method further includes: while performing step S4), forming branch guide holes in multiple branch horizontal wells toward the separation borehole to communicate with the separation, and draining the water accumulated in the separation through the branch guide holes; wherein, the multiple branch horizontal wells radiate from the wellbore of the coal mining well used for coal seam mining.

[0036] While sealing off external water sources, advanced drilling is used to safely drain the water accumulated in the abscission space. This water is also known as abscission water or accumulated water. The specific method for draining the accumulated water is to drill several lower guide holes at the predicted abscission location in the roof before coking operations begin. The depth of these lower guide holes is sufficient to penetrate the abscission space. Controlled water release and pressure relief are then implemented through these lower guide holes, guiding the accumulated water in the roof abscission to a safe location or pumping it to the surface. This significantly reduces the pressure of the abscission water and minimizes the threat of water ingress to the working face during coal seam mining.

[0037] The lower guide hole is mainly formed through pre-embedded drilling. Specifically, it starts from the pre-embedded drilling in the auxiliary roadway of the coal mining shaft and extends to the vicinity of the pre-analyzed separation location. The drilling forms a process hole. During the drilling process, a first casing and a second casing are used to form a full casing wall. When the borehole reaches the estimated separation location, the casing is changed, and the second casing is used for wall protection. That is, the first casing is used for wall protection before the borehole reaches the separation location, and the second casing is used after reaching the separation location. The second casing is a self-made perforated pipe. The perforated pipe wall forms drainage holes, which can effectively prevent the borehole from being blocked and also serve to guide water. The first and second casings are connected to form the lower guide hole. According to the step distance of the separation location, boreholes can be laid in sections in the overlying strata of the working face to facilitate subsequent pre-embedded drilling.

[0038] For safety reasons, multiple branch horizontal wells of the coal mining shaft can be used to jointly drain water accumulated in the delamination layer. Specifically, branch guide holes are made in multiple branch horizontal wells facing the delamination layer and connected to it. The water accumulated in the delamination layer is drained through the branch guide holes. The branch guide holes supplement the lower guide holes. If the initial estimation error of the delamination layer location is large, making the lower guide holes constructed from the coal mining auxiliary roadway ineffective, the roof can be laterally explored and drained through underground directional multi-branch horizontal wells. That is, branch guide holes are made laterally in the branch horizontal wells facing the delamination layer and connected to it. The water accumulated in the delamination layer can also be drained through the branch guide holes, further ensuring safe mining. Coal mining shafts are usually horizontal wells, with multiple branch horizontal wells radiating from the wellbore of the coal mining shaft used for coal seam mining.

[0039] After step S3) and before step S4), the prevention and control method further includes: determining the timing for draining water accumulated in the separation layer, including: S60) Obtain the water storage volume within the abscission layer and monitor whether the water storage volume within the abscission layer increases within a set time period; S61) If the water storage in the abscess does not increase, proceed to step S4) to drain the water stored in the abscess. S62) If the water storage in the separation layer increases, proceed to step S3). S63) Repeat steps S60)-S62) until all the accumulated water in the separation layer is drained.

[0040] When draining water accumulated in the aquifer, a combination of underground drilling and surface drilling can be used. For example, in a working face of the Laohutai Coal Mine, both surface and underground directional boreholes were deployed to jointly drain water accumulated in the aquifer, effectively reducing the water head of the roof aquifer. It should be emphasized that the exploration and drainage of aquifer water should be carried out at the optimal time, preferably after the water body has formed in the aquifer but before the mudstone aquitard has broken through. At this point, the aquifer water has largely accumulated, while the roof structure has not yet completely destabilized; thus, the drainage efficiency and safety are highest. To determine the optimal time for drainage, the water volume within the aquifer is monitored. Within a set time period, the water volume is monitored for any increase. If the water volume does not increase within this period, it indicates that the water level is stable, the mudstone aquifer has not yet broken through, and the aquifer water remains outside the aquifer. The roof structure is temporarily stable, and drainage is safest at this time. If the water volume increases within the set time period, it indicates that the mudstone aquifer has broken through, and water from the aquifer can now enter the aquifer through the breakthrough channel. The larger the water volume within the aquifer, the greater the pressure on the roof. In this case, a water-cutting strip is immediately installed to block the breakthrough channel, thus cutting off the water supply from the aquifer to the aquifer and preventing further water accumulation. The water is then drained. Through this pre-drainage method, most of the accumulated water in the aquifer can be removed beforehand, greatly reducing the risk of sudden water inrush during mining.

[0041] After draining the water accumulated in the abscess, in order to avoid the danger of sudden fracture of the abscess, blasting or hydraulic fracturing is used to pre-fracture the key layers of the top plate to reconstruct the fracture structure of the overburden.

[0042] Step S5) Pre-fracking and cutting of the critical layers of the roof using hydraulic fracturing, including: Drill holes toward the critical layer in the top plate or on the surface to create fracturing holes; Fracturing is performed by injecting fracturing fluid into the critical layers of the top plate through fracturing holes, in order to pre-fracture and cut the critical layers of the top plate.

[0043] Step S5) Pre-splitting and cutting the critical layers of the roof using explosives, including: Holes are drilled along the top plate to form blasting holes, and multiple blasting sections are designated within the blasting holes. Each blasting section uses micro-delay blasting to pre-crack and cut the key layers of the top plate.

[0044] In one embodiment, for working faces with particularly hard and thick roofs, such as those containing igneous intrusions or massive sandstone layers, this invention further introduces measures for artificial weakening and fracture reconstruction of the roof strata. Because such roofs are not prone to collapse, they often create large-span suspended delamination spaces. If the roof suddenly fractures later, it will generate enormous dynamic effects and water inrush hazards. To avoid this, controlled blasting or hydraulic fracturing can be used to pre-fracture and cut the key layers of the roof when the working face has been mined to a certain distance. For example, blasting holes are drilled along the strike of the thick sandstone roof to form blasting holes. Micro-delay blasting is then performed within these holes. Specifically, multiple micro-delay directional blasting sections are set at predetermined intervals within the blasting holes. Explosives are buried within each micro-delay directional blasting section. During micro-delay blasting, the blasting time interval between two adjacent micro-delay directional blasting sections is set to a range of several milliseconds to tens of milliseconds. The extremely short time interval between adjacent micro-delay directional blasting sections, blasted sequentially, allows the energy fields generated by each micro-delay directional blasting section to influence each other, improving the blasting effect while reducing the blasting seismic effect and shock wave, thus preventing coal mine roadway collapse. After blasting, the originally monolithic delamination space is divided into multiple small units, significantly reducing the scale and impact effect of a single collapse. Simultaneously, the new fractures generated by pre-splitting connect part of the delamination space with the lower or branch diversion holes constructed for drainage, thereby accelerating the discharge of residual water within the delamination. This is equivalent to "reconstructing" the fracture field of the roof, making it conducive to the slow release and diversion of water stored within the delamination. Through the above pre-splitting treatment, the hidden danger of sudden collapse of the thick and hard roof can be eliminated, providing a guarantee for safe mining.

[0045] When using hydraulic fracturing to pre-fracturing and cutting the critical layer of the roof, a fracturing hole can be formed by drilling a hole in the roof or on the surface towards the critical layer of the roof. Then, a fracturing fluid inlet pipe is inserted into the fracturing hole, which is connected to a high-pressure pump. The high-pressure pump delivers fracturing fluid through the fracturing fluid inlet pipe into the fracturing hole to fracture the critical layer of the roof, thereby creating fractures in the critical layer of the roof. The fractures connect part of the separation space with the drainage holes or branch drainage holes, which is equivalent to reconstructing the fracture structure of the overlying rock.

[0046] To ensure the safe mining of the coal seam after the treatment of water hazard, the method further includes: Before carrying out coal seam mining operations, an abscess water monitoring system is installed on the roof to obtain the changes in roof condition and the changes in water storage within the abscess.

[0047] The installation of a delamination water monitoring system on the top slab includes: S01) Install a roof separation meter in the working face roadway to monitor the displacement data of the roof strata; wherein, the working face roadway is a roadway used for coal transportation, ventilation and equipment layout in coal seam mining operations; install a mine electrical resistivity detection system on the roof of the working face roadway to monitor the water storage in the separation layer; monitor the water level data around the mining face. S02) Analyze the displacement data of the roof strata, the water storage in the abscess, and the water level data to obtain the laws governing the changes in the roof state and the changes in the water storage in the abscess.

[0048] After implementing the above water hazard control measures, to address the remaining potential for small amounts of accumulated water in the abscess and uncertainties in the roof, the risk of water inrush can be further reduced by optimizing coal seam mining parameters and strengthening monitoring of the mining process. On one hand, the mining process parameters for coal seam recovery can be adjusted based on the abscess location and residual water volume. For example, the face advance speed can be slowed to accommodate the gradual pressure from the roof abscess, and phased recovery can be implemented if necessary to reduce pressure. The recovery sequence of the face and the establishment of isolation coal pillars can also be rationally planned to avoid large-scale roof overhangs at once. On the other hand, before coal seam mining operations, a delamination water monitoring system is deployed on the roof. First, a roof delamination meter is installed in the working face roadway to monitor the displacement data of the roof strata. The working face roadway is a key roadway used for coal transportation, ventilation, and equipment layout during coal mining operations. Second, a long-distance mine electrical resistivity tomography (EPT) system is installed on the roof of the working face roadway. The EPT system is a geological monitoring technology that detects groundwater distribution, water abundance, and seepage status by monitoring changes in the electrical properties of the strata. In this application, the EPT system can monitor the water storage within the delamination layer. The EPT system mainly consists of an electrode system, acquisition base stations, sensors, and a data transmission system, and is typically installed in key underground areas for real-time monitoring. Multiple acquisition substations of the acquisition base stations are deployed underground, and the electrode system is suspended or fixed to the surface of the strata via cables to sense changes in the electric field and convert them into electrical signals. When installing sensors, avoid hazardous areas such as equipment operating areas and flammable and explosive areas. Drill holes at selected locations in the rock strata, clean the holes, and then install double-ended bolts to secure the sensors. The sensors mainly include microseismic sensors and electromagnetic sensors. Microseismic sensors are used to detect vibration signals inside the rock mass, and the changes in the mine's geological structure are analyzed by monitoring the microseismic activity of the rock mass. Electromagnetic sensors infer geological structure or mine environmental parameters by measuring changes in the electromagnetic field. Next, water level monitoring instruments are used to monitor water level data around the coal face and underground in the coal mine. Finally, the displacement data of the roof strata, the storage area of ​​water accumulated in the roof delamination, the water volume and water level data in the roof delamination are analyzed to obtain the patterns of roof condition changes and water volume changes in the delamination. Roof condition changes refer to phenomena such as roof subsidence, step subsidence, and pressure buildup. These changes are closely related to rock strata stress imbalance and surrounding rock movement. Therefore, monitoring the displacement data of the roof strata through a roof delamination instrument helps workers understand roof condition changes. The delamination water monitoring system also enables borehole water pressure observation and microseismic monitoring, allowing for timely monitoring of roof condition changes and variations in water storage within the delamination zone. If any roof anomalies are detected, such as abnormal water pressure fluctuations or increased roof pressure intervals, proactive measures can be taken to address the issues promptly, such as suspending mining, supplementing water supply, or increasing support density, ensuring safe coal seam mining. By optimizing coal seam mining parameters and implementing the delamination water monitoring system, the risk of roof delamination water hazards can be minimized, ensuring the coal face operates under constant control.

[0049] The method for preventing and controlling overburden delamination water hazards in Jurassic coal seam mining provided by this invention first determines whether delamination exists in the roof of the overburden based on the geological and hydrological conditions of the mining area. After confirming the existence of delamination, delamination parameters are obtained, and the type of delamination is determined to be harmless or hazardous based on these parameters. If the delamination is determined to be hazardous, a water interception zone is set up in the roof to cut off the aquifer or the water flowing towards the delamination through the strong runoff zone of the surrounding rock, ensuring that the amount of water accumulated in the delamination does not increase. After cutting off the water channel to the delamination, the accumulated water in the delamination is drained, reducing the amount of water accumulated in the delamination and alleviating the pressure on the rock strata. Subsequently, the key layer of the roof is cut, dividing the delamination into multiple small units, which is equivalent to reconstructing the fracture structure of the overburden. By reconstructing the fracture structure of the overburden, the hidden danger of sudden collapse of the overburden is eliminated, ensuring the safe execution of subsequent coal seam mining. After the delamination water hazard treatment is completed, coal seam mining operations are carried out.

[0050] The present invention provides a method for preventing and controlling water hazards caused by overburden separation in Jurassic coal seam mining. By conducting advanced geological surveys and risk assessments, it identifies potential water storage hazards in the overburden separation early on. It then employs measures such as cutting off water sources and diverting water storage to mitigate the water hazards at the nascent stage. Subsequently, it reduces the risk of overburden collapse by reconstructing the fracture structure of the overburden to separate the separation layer. The entire prevention and control method greatly improves the initiative and targeting of water hazard prevention and control, and solves the problem of the lack of a comprehensive system for preventing and controlling water hazards in existing technologies.

[0051] The optional embodiments of the present invention have been described in detail above with reference to the accompanying drawings. However, the embodiments of the present invention are not limited to the specific details in the above embodiments. Within the scope of the technical concept of the embodiments of the present invention, various simple modifications can be made to the technical solutions of the embodiments of the present invention, and these simple modifications all fall within the protection scope of the embodiments of the present invention.

[0052] It should also be noted that the various specific technical features described in the above embodiments can be combined in any suitable manner without contradiction. To avoid unnecessary repetition, the embodiments of the present invention will not describe the various possible combinations separately.

[0053] Furthermore, various different implementations of the present invention can be combined arbitrarily, as long as they do not violate the spirit of the present invention, they should also be regarded as the content disclosed in the present invention.

Claims

1. A method for preventing water hazards caused by overlying rock separation during Jurassic coal seam mining, characterized in that, The method includes: S1) Before coal seam mining operations, obtain and analyze the geological and hydrological conditions of the mining area to determine whether there is delamination in the roof of the overlying strata; S2) If it is determined that a delamination layer exists, obtain the delamination layer parameters and determine whether the delamination layer type is harmless or hazardous based on the delamination layer parameters; S3) If the delamination type is determined to be disaster type, a water interception zone is set in the top plate to cut off the aquifer of the top plate or cut off the water channel flowing to the delamination through the strong runoff fracture zone of the surrounding rock. S4) Construct an upper diversion hole on the surface to connect with the detachment layer, and / or construct a lower diversion hole on the top plate to connect with the detachment layer, and drain the water accumulated in the detachment layer through the upper diversion hole and / or the lower diversion hole; S5) Use blasting or hydraulic fracturing to pre-fracturing and cutting the key layers of the roof to reconstruct the fracture structure of the overlying rock; S6) Perform coal seam mining operations.

2. The method for preventing water hazards caused by overlying strata separation in Jurassic coal seam mining according to claim 1, characterized in that, Geological and hydrological conditions of the mining area are obtained through geophysical exploration, advanced drilling, or borehole imaging.

3. The method for preventing water hazards caused by overlying strata separation in Jurassic coal seam mining according to claim 1, characterized in that, The delamination parameters include: the location of the delamination, the height of the delamination, the span of the delamination, the relative position of the delamination and the water-conducting fracture zone, and the water storage capacity of the delamination.

4. The method for preventing water hazards caused by overlying strata separation in Jurassic coal seam mining according to claim 3, characterized in that, After step S3) and before step S4), the prevention and control method further includes: determining the timing for draining water accumulated in the separation layer, including: S60) Obtain the water storage volume within the abscission layer and monitor whether the water storage volume within the abscission layer increases within a set time period; S61) If the water storage in the abscess does not increase, proceed to step S4) to drain the water stored in the abscess. S62) If the water storage in the separation layer increases, proceed to step S3). S63) Repeat steps S60)-S62) until all the accumulated water in the separation layer is drained.

5. The method for preventing water hazards caused by overlying strata separation in Jurassic coal seam mining according to claim 1, characterized in that, Step S3) specifically includes: Multiple grouting holes are set in the top plate, and high-pressure grout is injected into the aquifer or the strong runoff fracture zone of the surrounding rock through the multiple grouting holes to form a water-cutting zone in the key layer of the top plate.

6. The method for preventing water hazards caused by overlying strata separation in Jurassic coal seam mining according to claim 1, characterized in that, In step S4), a lower guide hole is made in the top plate, including: A process hole is formed by drilling a borehole into the roof through an auxiliary roadway excavated during coal seam mining. During the drilling operation, a first casing and a second casing are used to protect the wall of the process hole. The first casing is used for wall protection before the process hole is connected to the roof, and the second casing is used for wall protection after the process hole is connected to the roof. Drainage holes are opened on the wall of the second casing. Water accumulated in the roof enters the second casing through the drainage holes and then flows through the first casing to be discharged.

7. The method for preventing water hazards caused by overlying strata separation in Jurassic coal seam mining according to claim 6, characterized in that, The method further includes: while performing step S4), forming branch guide holes in multiple branch horizontal wells toward the separation borehole to communicate with the separation, and draining the water accumulated in the separation through the branch guide holes; wherein, the multiple branch horizontal wells radiate from the wellbore of the coal mining well used for coal seam mining.

8. The method for preventing water hazards caused by overlying strata separation in Jurassic coal seam mining according to claim 1, characterized in that, Step S5) Pre-fracking and cutting of the critical layers of the roof using hydraulic fracturing, including: Drill holes toward the critical layer in the top plate or on the surface to create fracturing holes; Fracturing is performed by injecting fracturing fluid into the critical layers of the top plate through fracturing holes, in order to pre-fracture and cut the critical layers of the top plate.

9. The method for preventing water hazards caused by overlying strata separation in Jurassic coal seam mining according to claim 8, characterized in that, Step S5) Pre-splitting and cutting the critical layers of the roof using explosives, including: Holes are drilled along the top plate to form blasting holes, and multiple blasting sections are designated within the blasting holes. Each blasting section uses micro-delay blasting to pre-crack and cut the key layers of the top plate.

10. The method for preventing water hazards caused by overlying strata separation in Jurassic coal seam mining according to claim 1, characterized in that, The method further includes: Before carrying out coal seam mining operations, an abscess water monitoring system is installed on the roof to obtain the changes in roof condition and the changes in water storage within the abscess.

11. The method for preventing water hazards caused by overlying strata separation in Jurassic coal seam mining according to claim 10, characterized in that, The installation of a delamination water monitoring system on the top slab includes: S01) Install a roof separation meter in the working face roadway to monitor the displacement data of the roof strata; wherein, the working face roadway is a roadway used for coal transportation, ventilation and equipment layout in coal seam mining operations; install a mine electrical resistivity detection system on the roof of the working face roadway to monitor the water storage in the separation layer; monitor the water level data around the mining face. S02) Analyze the displacement data of the roof strata, the water storage in the abscess, and the water level data to obtain the laws governing the changes in the roof state and the changes in the water storage in the abscess.

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