Low-oxygen prevention and control device and method for blocking mining-induced fractures through advanced grouting of horizontal long drill hole of coal mine

Abstract

The invention relates to a low-oxygen prevention and control device and method for blocking mining-induced fractures through advanced grouting of a horizontal long drill hole of a coal mine, and belongs to the technical field of coal mining. The method comprises the following steps: determining a drilling target horizon by predicting development heights of a caving zone and a fissure zone of a goaf; a kilometer drilling machine is adopted for constructing horizontal long drill holes, the horizontal long drill holes comprise underground horizontal drill holes, ground vertical well drill holes and well-ground combined drill holes, and key areas of the fissure zone are covered; and yellow mud or water glass gel containing a sodium chloride inhibitor is injected into the drill hole in a pressed mode, cracks are filled through dynamic grouting, an air leakage channel is blocked, and the coal oxygen reaction is restrained. According to the method, by blocking mining-induced fractures in advance, air leakage and low-oxygen gas migration are blocked from the source, and the function of inhibiting spontaneous combustion of coal is achieved; multi-mode drilling is adopted to adapt to complex geological conditions, the coverage range is wide, and construction is flexible; the slurry material is environment-friendly and economical, the gel forming is controllable, and the slurry feeding risk is avoided; and dynamic grouting is matched with a crack expansion rule, so that the mining safety of the shallow buried coal seam group is remarkably improved, and the treatment cost is reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of coal mining, and relates to a hypoxia prevention and control device and method for sealing mining-induced fissures by advanced grouting of horizontal long boreholes in coal mines. Background Art

[0002] In the field of coal mining, high-yield and high-efficiency working faces in shallow coal seams are commonly faced with problems such as air leakage, coal spontaneous combustion, and hypoxic gas influx caused by mining-induced fissures. Existing prevention and control technologies often focus on post-process control. For example, they reduce air leakage by backfilling surface fissures, installing air guide curtains or wind screens, and implementing pressure-equalizing ventilation. Alternatively, they employ grouting, nitrogen injection, and spraying inhibitors to suppress coal spontaneous combustion. However, these methods have significant limitations: backfilling surface fissures requires repeated construction and has difficulty covering irregular fissures; grouting and nitrogen injection require significant resource investment, posing the risk of uncontrolled slurry fluidity or nitrogen leakage into the working face, leading to secondary hypoxia; and spraying inhibitors can only locally affect the coal behind the support and cannot cover the entire mining-induced fissure zone. Furthermore, existing technologies fail to effectively block the continuous air leakage channels between mining-induced fissures and the surface, allowing hypoxic gas to continue to influx into the working face through the fissures, resulting in passive and delayed control.

[0003] While existing research has attempted to improve sealing effectiveness through dynamic grouting or optimized drilling layouts to address these issues, a systematic approach to proactively controlling mining-induced fracture zones remains lacking. For example, conventional grouting techniques often employ a simultaneous grouting process, which limits the slurry's diffusion range and makes it difficult to adapt to the dynamic expansion of mining-induced fractures in high-mining working faces. Traditional drilling designs also struggle to precisely control the fracture zones under varying geological conditions, resulting in low sealing efficiency. Therefore, a comprehensive control technology is urgently needed that can fundamentally block air leakage channels, inhibit coal spontaneous combustion, and adapt to complex geological conditions. Summary of the Invention

[0004] In view of this, the purpose of the present invention is to provide a device and method for preventing and controlling hypoxia by using advance grouting to seal mining-induced fissures in horizontal long boreholes in coal mines. By innovatively introducing the horizontal long borehole advance grouting process and combining the composite functions of the inhibitor slurry, full-cycle dynamic sealing of the mining-induced fissure zone is achieved, while taking into account both economy and construction flexibility, providing a more efficient solution for the prevention and control of hypoxia in shallow buried coal seams.

[0005] In order to achieve the above object, the present invention provides the following technical solutions:

[0006] A hypoxia prevention and control device for sealing mining-induced fissures by advanced grouting in horizontal long boreholes in coal mines, comprising:

[0007] Drilling construction unit, including kilometer-long directional drilling rig, casing and sealing materials;

[0008] The end of the drill pipe of the kilometer-long directional drilling rig is connected to a casing, and the casing is fixed to the section of the borehole that has not entered the mining fracture zone;

[0009] The sealing material is connected to the orifice of the drilled hole through a grouting pipeline to seal the orifice;

[0010] Grouting unit, including grouting pump, mixer and slurry delivery pipeline;

[0011] The outlet of the grouting pump is connected to the casing of the borehole through a slurry delivery pipeline;

[0012] The input end of the mixer is connected to the yellow mud grouting station, the water glass solution tank and the coagulant solution tank of the fire prevention and extinguishing slurry preparation unit respectively, and the output end of the mixer is connected to the inlet of the grouting pump through the slurry delivery pipeline;

[0013] Fire prevention and extinguishing slurry preparation unit, including yellow mud grouting station, water glass solution tank and coagulant solution tank;

[0014] The yellow mud grouting station is connected to the first inlet of the mixer through a delivery pipeline;

[0015] The water glass solution tank and the coagulant solution tank are respectively connected to the second inlet and the third inlet of the mixer through independent liquid supply pipelines;

[0016] The drilling construction unit and the grouting unit are connected in series through a slurry delivery pipeline, and the output end of the fire prevention and extinguishing slurry preparation unit is connected to the mixer.

[0017] Optionally, the yellow mud grouting station is provided with an inhibitor adding device for adding sodium chloride or sodium salt to the yellow mud slurry.

[0018] Optionally, a monitoring and control unit is also included, including a pressure sensor and a flow controller;

[0019] The pressure sensor is installed on the grouting pipeline to monitor the drilling grouting pressure in real time;

[0020] The flow controller is electrically connected to the grouting pump and dynamically adjusts the grouting rate of the grouting pump according to the pressure data fed back by the pressure sensor; the monitoring and control unit forms a closed-loop control with the grouting pump.

[0021] Optionally, the drilling construction unit includes any one or more of the following implementation modes:

[0022] (a) Underground horizontal long borehole: The drilling site is arranged in the return air lane of the working face. Multiple boreholes are arranged in each drilling site, and the final hole layer is located within 10 to 20 meters above the caving zone of the goaf;

[0023] (b) Surface vertical well: Drill the well to the target layer in the mining fracture zone, run the surface casing and cement the well;

[0024] (c) Well-ground combined drilling: The vertical well on the ground is connected with the long horizontal borehole underground through directional drilling technology to form a continuous grouting channel.

[0025] Optionally, the fire extinguishing slurry is any one or a combination of the following:

[0026] (a) Yellow mud slurry, with sodium chloride or sodium salt inhibitor added;

[0027] (b) Water glass gel, which is prepared by mixing water glass solution and coagulant in a ratio of 7:1 or 5:1, and the gelling time is controlled within 3 to 60 minutes.

[0028] A method for preventing and controlling hypoxia by pre-grouting and plugging mining-induced fissures in a horizontal long borehole in a coal mine comprises the following steps:

[0029] S1 Determine the parameters of the mining fracture zone: Based on the mine geological data and the data of the adjacent working face, predict the height of the caving zone and fracture zone in the goaf, and define the drilling target layer as 10 to 20 meters above the caving zone;

[0030] S2 drilling construction: Use a kilometer-long directional drilling rig to construct a horizontal long borehole in the target layer. The drilling method is selected from one of the following: underground horizontal long drilling, surface vertical well, or well-surface combined drilling;

[0031] S3 prepares fire prevention and extinguishing slurry: select yellow mud slurry or water glass gel, add inhibitor to the yellow mud slurry, or mix water glass solution and coagulant in proportion to form gel;

[0032] S4 Grouting and plugging: Use the grouting pump to pressurize the fire extinguishing slurry into the borehole, control the grouting pressure to be stable, and replenish the slurry and increase the pressure when the slurry leaks until the slurry fills the mining fractures;

[0033] S5 Inhibition and Sealing: The inhibitor in the slurry adheres to the surface of the coal rock to inhibit spontaneous combustion, and at the same time the borehole opening is sealed with cement, with a sealing length of 5 to 10 meters.

[0034] Optional, in S2:

[0035] The drilling site spacing for underground horizontal long boreholes is 500m, with three boreholes arranged in each drilling site and a horizontal distance of 10m between the final holes.

[0036] The vertical well spacing on the ground is 300m, and the wells are cemented after drilling to 20-30m above the caving zone;

[0037] Well-ground combined drilling uses directional drilling technology to connect the ground vertical well with the horizontal section of the underground borehole.

[0038] Optionally, the grouting pressure in S4 is dynamically adjusted according to the crack expansion.

[0039] Optionally, the grouting rate is controlled by feeding back pressure data in real time through a monitoring and control unit.

[0040] Optionally, the inhibitor in S5 is sodium chloride or sodium salt, and the sealing material is cement slurry.

[0041] The beneficial effects of the present invention are:

[0042] This solution can block the through-flow air leakage channel between the mining fissures and the ground surface at the source by constructing long horizontal boreholes in advance and combining it with the dynamic injection of inhibitor slurry, thus significantly reducing the risk of low-oxygen gas migration to the working face. Compared with traditional passive control methods, this solution adopts an advanced prevention and control strategy, which realizes dynamic sealing by slurry filling in the early stage of the formation of mining fissures, effectively adapting to the expansion law of mining fissures in large mining height working faces, and avoiding the problem of continuous increase in air leakage with the mining process. The addition of inhibitors such as sodium chloride to the slurry not only enhances the ability to seal micro-cracks, but also forms an inert layer on the surface of the coal rock, inhibiting the coal-oxygen reaction, and simultaneously reducing the risk of spontaneous combustion in the goaf, thereby reducing the generation of low-oxygen gas.

[0043] In addition, by flexibly selecting underground horizontal drilling, surface vertical wells, or well-ground combined drilling construction methods, this solution can adapt to complex geological conditions and different mining layout requirements, taking into account both construction efficiency and economy. For example, underground horizontal long drilling can achieve precise layer control, surface vertical well grouting reduces interference with underground engineering, and well-ground combined drilling further expands the coverage of a single grouting and reduces the cost of repeated construction. The slurry material uses environmentally friendly and easily accessible raw materials such as yellow mud slurry and water glass gel, combined with a controllable gelation time design, which not only ensures the stable diffusion and consolidation of the slurry within the fracture zone, but also avoids the secondary risks caused by uncontrolled slurry fluidity or nitrogen leakage in traditional grouting processes.

[0044] Overall, this solution achieves a shift from passive response to active prevention and control of hypoxia through systematic advance sealing and dynamic resistance, providing a comprehensive solution that combines safety, economy and adaptability for high-yield and efficient mining of shallow coal seams.

[0045] Other advantages, objects, and features of the present invention will be described in part in the following description and, in part, will be apparent to those skilled in the art upon examination of the following description or may be learned from practice of the present invention. The objects and other advantages of the present invention may be realized and obtained through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention will be described in detail below with reference to the accompanying drawings, in which:

[0047] Figure 1This is a schematic diagram of the plan view of grouting to seal cracks in a horizontal long borehole underground;

[0048] Figure 2 This is a cross-sectional diagram of grouting to seal cracks in a horizontal long borehole underground;

[0049] Figure 3 This is a schematic diagram of grouting to seal cracks in a vertical well on the ground;

[0050] Figure 4 This is a schematic diagram of the well-ground combined drilling and grouting to seal the cracks;

[0051] Figure 5 This is a schematic diagram of downhole docking for well-ground combined drilling;

[0052] Figure 6 Diagram for the preparation of fire extinguishing slurry (water glass gel).

[0053] Figure numerals: 1. Collapse zone in the goaf, 2. Target layer for drilling, 3. Mining fissure, 4. Downhole drilling site, 5. Downhole horizontal long borehole fixed pipe section, 6. Surface vertical well drilling platform, 7. Surface vertical well casing section, 8. Surface vertical well bottom cave. DETAILED DESCRIPTION

[0054] The following describes the embodiments of the present invention by means of specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the illustrations provided in the following embodiments are only schematic illustrations of the basic concept of the present invention, and the following embodiments and features in the embodiments can be combined with each other without conflict.

[0055] Among them, the accompanying drawings are only for illustrative purposes and represent only schematic diagrams rather than actual pictures, and should not be understood as limiting the present invention. In order to better illustrate the embodiments of the present invention, some parts of the accompanying drawings may be omitted, enlarged or reduced, and do not represent the dimensions of actual products. For those skilled in the art, it is understandable that some well-known structures and their descriptions may be omitted in the accompanying drawings.

[0056] The same or similar numbers in the drawings of the embodiments of the present invention correspond to the same or similar parts; in the description of the present invention, it should be understood that if there are terms such as "upper", "lower", "left", "right", "front", "back", etc. indicating directions or positional relationships, they are based on the directions or positional relationships shown in the drawings. They are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific direction, be constructed and operate in a specific direction. Therefore, the terms describing the positional relationship in the drawings are only used for illustrative purposes and cannot be understood as limiting the present invention. For ordinary technicians in this field, the specific meanings of the above terms can be understood according to specific circumstances.

[0057] Coal is one of my country's primary energy sources, accounting for a significant portion of energy consumption. my country's coal seams have complex natural occurrence conditions, with well-developed folds and faults within coal mining areas. Coal seam structure and stability vary significantly, and the five major natural hazards of mine flooding, fire, gas, coal dust, and roof collapse are all present. The coal mine safety situation remains critical. With the increasing use of mechanized coal mining, fully mechanized caving (MLC) of large-scale coal seam clusters has gradually become the mainstream mining method. This is particularly true in mining areas with favorable geological conditions, such as the Shenfu-Dongsheng coalfield, where the geological structure is simple and most of the coal seams are shallow, and where fully mechanized caving (MLC) is often used. Mining shallow coal seams is subject to high mining intensity, significant surface fissures, and severe air leakage. This is particularly true during mining of lower coal seams, where mining-induced fissures can flow into old goafs in overlying coal seams. Under the influence of negative ventilation pressure and surface atmospheric pressure, low-oxygen gases can easily flow through these fissures into the mining face, leading to hypoxia in areas such as return air corners.

[0058] Currently, the problem of hypoxia in coal mining faces is mostly addressed through backfilling surface cracks, hanging air curtains at the corners of the working face intake and return airways, enhancing the sealing quality of the goaf, and implementing pressure-equalizing ventilation. This reduces pressure within the goaf, reduces air leakage, and mitigates the rate of hypoxia outburst. In addition, grouting and nitrogen injection are also performed in the goaf. For example, grouting and nitrogen injection pipelines are pre-laid in the two tunnels of the working face, allowing injection as mining progresses. There is also a method of spraying inhibitors on the rear of the working face support to retard the spontaneous combustion of the coal left in the goaf. Fire prevention and extinguishing technical measures are used to reduce the spontaneous combustion and oxidation of the coal left in the goaf, reducing the risk of gas outburst and hypoxia. During high-yield, high-efficiency working face mining in shallow coal seams, the large mining height and high mechanical mining intensity make the overlying coal rock extremely susceptible to mining, resulting in horizontal and vertical cracks. Surface air leakage affects these cracks, and through-going cracks also cause air leakage between the goaf and the overlying coal rock, exacerbating the risk of spontaneous combustion in the overlying coal rock. Low-oxygen gas, influenced by negative ventilation pressure and surface atmospheric pressure, easily migrates to the working face. Therefore, addressing the hypoxia issue in high-yield, high-efficiency working faces in shallow coal seams should primarily focus on sealing the coal rock cracks within the three mining-induced crack zones.

[0059] The mining of high-yield and high-efficiency working faces in shallow coal seams has led to the development of a large number of cracks in the overlying coal rocks. The penetration of cracks has led to surface air leakage, and the air leakage has caused spontaneous combustion in the goaf and the outburst of low-oxygen gas. This technology uses a thousand-meter-long horizontal drilling construction to drill a long hole in the mining crack 3 zone (or grouting in a vertical well on the ground), and injects fire-fighting slurry into the borehole to seal the mining crack 3 channel and isolate the surface air leakage. At the same time, the inhibitors such as ammonium salts and sodium salts in the slurry adhere to the surface of the coal rock to inhibit the spontaneous combustion of the coal body, so as to carry out proactive prevention and control of the spontaneous combustion and low-oxygen gas outburst caused by air leakage in the mining crack 3.

[0060] At present, the prevention and control of low oxygen problems in shallow coal seam mining working faces mainly focuses on controlling air leakage, reducing the outburst of low-oxygen gas, and reducing the risk of spontaneous combustion of coal in the goaf.

[0061] For example, wind guide curtains are installed at the return air corners of the working face to guide the wind flow to the return air corners, so that the wind volume near the return air corners increases and the fluidity of the gas here is increased; wind shield curtains are installed at the air inlet corners of the working face to prevent the air flow in the air inlet tunnel from flowing into the goaf by blocking the wind flow; pneumatic fans press the air into the low-oxygen area, thereby diluting the low-oxygen gas in the low-oxygen area and increasing the wind flow rate; surface cracks are filled in time, and after mining, secondary or multiple fillings may be required; the sealing strength of the goaf connecting tunnels is strengthened; the goaf is depressurized by drilling pressure relief; the working face is pressurized by pressure equalization ventilation technology to increase the working face pressure to reduce the pressure difference between the working face and the goaf.

[0062] Prevention of spontaneous combustion of coal in goafs primarily relies on conventional methods such as nitrogen injection, grouting, and spraying of inhibitors. Grouting and nitrogen injection pipelines are reserved in two tunnels, and nitrogen injection pipelines are installed at certain intervals at the nitrogen injection ports. Nitrogen injection begins after the pipelines are buried to a certain depth. Furthermore, spraying inhibitors on the coal residue behind the supports as the working face advances is also an effective measure to prevent spontaneous combustion of coal in goafs. Physical inhibitors, such as water-absorbing salts, polymers, and foam materials, can alter the physical environment surrounding the coal body to prevent spontaneous combustion. Chemical inhibitors, such as antioxidants, alkaline inhibitors, and acidic inhibitors, inert the activity of coal-oxygen reaction functional groups, weakening the chemical reactions of coal oxygen and suppressing spontaneous combustion.

[0063] The current common use of air curtains in mines can alleviate the accumulation of hypoxic gases in the short term, but when the amount of hypoxic gas gushing out is too large, it will actually slow the time it takes for the working face to return to normal oxygen concentration. Wind curtains are used to block the return air corners, but they need to be moved as the working face advances, which is cumbersome. Installing pneumatic fans can accelerate the flow of hypoxic gases out of the return airway, but they must be anticipated and activated in advance. Surface fissure backfilling is an important means of controlling surface air leakage in shallow coal seam working faces, which causes spontaneous combustion of coal in the goaf and the outburst of hypoxic gases. However, surface fissures develop irregularly and require timely secondary backfilling. Goafs require high nitrogen and grouting requirements, and are often injected on a shift-by-shift basis. Therefore, establishing a centralized surface grouting station requires laying a long pipeline to the working face, which is a large project with high economic costs. Furthermore, when the coal seam has a large inclination, the large amount of slurry injected into the goaf can easily flow to the lower part of the goaf, posing a certain risk of slurry feeding. Nitrogen injection in goafs primarily serves to dilute air leakage and inertify the goaf. However, high-volume nitrogen injection can cause nitrogen in the goaf to gush out from the working face supports or the air inlet and return corners, resulting in hypoxia in the working face. Retardant spraying is primarily targeted at the coal behind the supports, effectively inhibiting only the coal remaining in the goaf.

[0064] Therefore, in order to solve the problem of low oxygen in high-yield and high-efficiency mining working faces of shallow coal seams, the current focus is on controlling the low oxygen phenomenon after it occurs, and the root cause of the low oxygen phenomenon has not been addressed. In particular, problems such as air leakage, spontaneous combustion, and gas outbursts caused by crack channels within the mining crack zone 3 urgently need targeted prevention and control.

[0065] See also Figures 1 to 6 The present invention provides a hypoxia prevention and control device and method for pre-grouting and sealing mining-induced fissures (3) in coal mines using a kilometer-long horizontal borehole. The method primarily utilizes a kilometer-long drilling rig to construct a long horizontal borehole within the mining-induced fissure (3) zone within the coal face and inject a fire-fighting slurry. As the face is mined, the mining-induced fissure (3) gradually expands, and the slurry begins to fill the fissure channels, reducing air leakage from the face and suppressing the generation of hypoxic gases in the overlying coal rock and their migration to the face.

[0066] First, based on the mine geological data and the development of mining fissures 3 in the adjacent working face, combined with the occurrence conditions of the overlying coal rock of this coal seam, the physical and mechanical properties of the coal rock, and the mining layout conditions of the mining working face, the development height of the caving zone 1 and the fracture zone in the goaf of this working face are predicted.

[0067] Furthermore, according to the height of the caving zone 1 and the fracture zone in the goaf of the coal mining face, the range of 10 to 20 meters above the caving zone is divided into the main migration channel of low-oxygen gas, that is, the drilling target layer 2 (fracture height development interval), to ensure that the final drilling hole remains in this layer without collapse of the bare hole and has good slurry diffusion.

[0068] Furthermore, according to the mining layout conditions of the coal mining face and the performance of the kilometer drilling rig, combined with the overburden rock properties and the development boundary of the fracture zone, the reasonable drilling site construction location and hole layout method, as well as parameters such as the casing aperture are determined. There are three drilling construction methods: surface drilling, underground drilling, and well-ground combined drilling. They can be selected according to the mine geological conditions and coal mining face layout parameters.

[0069] Furthermore, grouting materials should be selected that are resistant to solidification and sedimentation, have the ability to seal microcracks, and inhibit coal spontaneous combustion, such as yellow mud slurry and water glass gel. Retardants such as sodium chloride should be added to the slurry to form a fire-fighting slurry. During the transportation of the fire-fighting slurry, the gelling time must be controlled to ensure continuous injection into the target stratum.

[0070] Furthermore, before the working face is mined, horizontal long boreholes are sequentially constructed according to the determined drilling parameters, and the boreholes are fixed with pipes. The size of the casing inserted into the boreholes is determined by the borehole diameter. After the working face is mined, a fire-fighting slurry is sequentially pressed into the horizontal long boreholes using grouting and pressure-maintaining equipment. As the working face is mined, mining-induced fissures 3 are formed in the overlying strata. The slurry seals these mining-induced pores and fissures. Based on the laws of fissure expansion, the inhibitors and other substances in the slurry penetrate into the coal rock fissures, enveloping the coal body and inhibiting the reaction between the overlying coal rock and oxygen, thereby reducing the risk of spontaneous combustion of the overlying coal rock and minimizing the generation of hypoxic gas.

[0071] Furthermore, as the working face advances, drilling and grouting continue to ensure that the grouting pressure of each hole remains relatively stable at all times. When the slurry leakage is large and the pressure drops, fluid must be added and pressure increased in time until it stabilizes again.

[0072] Figure 1 This is a schematic diagram of underground long horizontal borehole grouting to plug fissures. By drilling a long horizontal borehole at the target layer at the corresponding location in the mining face, fire-fighting slurry is then injected into the borehole to plug mining-induced fissures and prevent hypoxia. The target layer is set 10 to 20 meters above the caving zone in the goaf of the mining face, maintaining a certain distance from the caving zone to prevent slurry from leaking into the working face.

[0073] Figure 2 This is a schematic diagram of the cross-section of grouting to seal cracks in underground horizontal long boreholes. The drilling site spacing of the underground horizontal long boreholes is 500m, and 3 boreholes are arranged in each drill site. The horizontal distance between the end holes is 10m. The boreholes are numbered 1-1#, 1-2#, and 1-3# in sequence from the main wall of the return air tunnel. Each borehole is constructed towards the return air corner of the working face. The construction length of 1-1# borehole is 500m, the construction length of 1-2# borehole is 300m, and the construction length of 1-3# borehole is 100m. The boreholes in each drill site are arranged in this way to ensure full-cycle grouting and sealing during the mining of the working face.

[0074] Figure 3This is a schematic diagram of grouting cracks in surface vertical wells. According to the location of the underground working face, surface vertical wells corresponding to the surface are selected for grouting. Generally, surface grouting drilling is considered to be set up every 300m from the cutting position, and the drilling end hole position is within 20 to 30m above the caving zone of the coal mining working face. After the drilling is completed, the drill is lifted and the well is dredged, and the surface casing is lowered to start cementing and waiting for setting.

[0075] Figure 4 This is a schematic diagram of joint well-ground drilling and grouting for fissure plugging. A surface vertical well is constructed at the corresponding surface location to the mining-induced fissure range. The surface vertical well is then drilled to the target stratum. The drill is then pulled out of the wellbore, run through the well, and surface casing is lowered to form surface vertical well casing section 7. Cementing and setting are then initiated. Furthermore, a long horizontal borehole is drilled in the working face's return airway, 500 meters from the cut hole. The target stratum is within 10-20 meters above the caving zone 1 in the goaf. By drilling the long borehole and connecting it to the surface vertical well using the RMRS active ranging system, a single grouting operation can be performed within approximately 1000 meters of the mining-induced fissure zone 3, meeting the requirement for plugging mining-induced fissure 3 throughout the entire working face mining process.

[0076] Figure 5 This is a schematic diagram of the downhole docking process for combined well-surface drilling. After the surface vertical well reaches the target horizon, an RMRS probe is placed in the vertical wellbore to receive magnetic signals from the docking well drill bit. When the downhole docking hole (a long horizontal borehole) is drilled to within 80 meters of the vertical wellbore, a strong magnetic connector is installed at the end of the screw motor, rotating it along with the drill bit and emitting magnetic signals that are then uploaded to the surface computer for processing. Data analysis determines the relative position of the magnetic generator at the docking well drill bit and the receiving probe in the U-shaped vertical wellbore. The elevation of the strong magnetic sub and the target point are calculated. The vertical depth is then calculated to ensure that the required connection has been achieved. The inclination angle is stabilized and the azimuth is increased. When the return water suddenly increases at the downhole borehole mouth and the gas output from the surface well increases, the horizontal borehole is considered successfully connected to the surface vertical well.

[0077] Figure 6 The fire extinguishing slurry (water glass gel) used for drilling grouting generally consists of yellow mud slurry, water glass gel, and other materials. Water glass gel is prepared by mixing base material A (water glass) and coagulant B (baking soda) in a certain proportion. A (water glass) and B (baking soda) are each diluted in 85% to 95% water in a water tank, stirring them evenly. The concentration of liquid A (water glass solution) is 8% to 10%, and the concentration of liquid B (coagulant solution) is 5% to 6%. Then, two pumps are simultaneously turned on. Liquids A and B pumped out by the two pumps are mixed in a mixer and then pumped into the borehole via a high-pressure hose.

[0078] The key aspects of this plan are:

[0079] (1) Drilling construction method

[0080] The present invention designs three drilling construction methods: underground horizontal long drilling, ground drilling, and well-ground combined drilling.

[0081] 1. Underground horizontal long drilling grouting

[0082] The underground horizontal long borehole drilling site is arranged at the appropriate position of the return air tunnel of the working face (a drilling site is arranged every 500m from the start of the cutting eye), and 3 boreholes are arranged in each drilling site. The final hole layer is arranged within 10 to 20m above the caving zone 1 of the goaf. The boreholes are numbered 1-1#, 1-2#, and 1-3# in sequence from the distance from the main wall of the return air tunnel. Each borehole is constructed towards the return air corner of the working face, among which the construction length of 1-1# borehole is 500m, the construction length of 1-2# borehole is 300m, and the construction length of 1-3# borehole is 100m. The horizontal distance between each borehole is 10m, ensuring that there is drilling and grouting within 30m on one side of the return air tunnel of the working face.

[0083] 2. Ground vertical well grouting

[0084] A vertical surface well is constructed on the surface of the return airway on the working face. Appropriate equipment is selected based on the geological conditions and drilled on the surface drilling platform 6. After drilling to within 20-30 m above the caving zone of the coal mining face, the well is pulled out and run through. Surface casing is lowered, and cementing and setting are initiated. The number of surface wells can be determined based on the characteristics of the strata. Generally, grouting holes are drilled every 300 m from the cut-hole location.

[0085] 3. Well-ground combined drilling and grouting

[0086] By connecting the surface vertical well with the long underground borehole, grouting is achieved to fully cover the mining-induced fracture zone 3. Once the surface vertical well is drilled to the target layer, the drill is pulled out and the well is run through. Surface casing 7 is lowered to form a cavern 8 at the bottom of the surface vertical well, and cementing and waiting for setting begins.

[0087] The drilling point of the underground horizontal long borehole is arranged at a position 500m away from the cutting eye in the return air lane of the working face. The target layer is within 10 to 20m above the caving zone 1 of the goaf. Through long borehole drilling, the RMRS active ranging system is used to connect to the ground vertical well cave 8. After the connection is completed, a single grouting can be carried out in the area of ​​about 1000m within the mining fissure 3 zone, which can meet the requirement of sealing the mining fissure 3 throughout the entire cycle of the working face mining process.

[0088] (2) Fire extinguishing slurry

[0089] The main purpose of the fire-fighting slurry is to fill the mining fissures 3, reduce air leakage, and reduce the risk of spontaneous combustion in the stress concentration areas of the overburden and overlying coal pillars. Materials such as yellow mud slurry and water glass gel can be selected.

[0090] The yellow mud slurry for injection into the borehole this time can be the yellow mud grouting slurry commonly used in goaf areas of mines. It is generally mixed at the surface yellow mud grouting station. Inhibitors such as sodium chloride need to be added during the mixing to enhance the plugging and inhibitory effects of the yellow mud slurry. The slurry is then transported to the underground drilling site 4 through a pipeline and injected using grouting pumps and other equipment according to on-site conditions.

[0091] Waterglass gel is made by mixing base material A (waterglass) and coagulant B (baking soda) in a specific ratio. A (waterglass) and B (baking soda) are each diluted and stirred evenly in a water tank with 85% to 95% water. The concentration of liquid A (waterglass solution) is 8% to 10%, and the concentration of liquid B (coagulant solution) is 5% to 6%. (Generally, two water tanks are used for material A and material B, one for liquid supply and one for preparation, to achieve continuous injection.) Then, two pumps are simultaneously turned on. Liquids A and B pumped out by the two pumps are mixed in a mixer and then transported to the drill hole via a high-pressure hose. The gelling time of waterglass gel is closely related to the concentration of the coagulant: the higher the coagulant concentration, the shorter the gelling time. In field tests, the gelling time is generally 40 to 60 minutes when the main material A (water glass) and the coagulant B (baking soda) are mixed in a ratio of 7:1; the gelling time is 3 to 5 minutes when the ratio is 5:1. Based on the borehole length and the distance to the target layer, the ratio needs to be optimized through field tests, and then the gel grouting is started to ensure that the gel has sufficient consolidation capacity after reaching the target layer and does not precipitate in the pipeline.

[0092] (3) Drilling, fixing pipes and sealing holes

[0093] After drilling the underground horizontal long borehole and the ground vertical well, it is necessary to fix the pipe from the drilling point to the section that has not entered the mining fracture zone 3, forming the underground horizontal long borehole fixed pipe section 5. When the borehole enters the mining fracture zone 3, there is no need to fix the pipe, thereby keeping the slurry completely filling the fracture zone.

[0094] In order to prevent slurry from returning from long horizontal boreholes underground, the hole opening needs to be sealed. Depending on the inclination angle of the hole opening, the sealing length is maintained at 5 to 10 meters. Cement slurry is selected as the sealing material to ensure that the connection between the borehole and the slurry pipeline is firm and can withstand the maximum grouting pressure.

[0095] The present invention provides a technology for preventing and controlling hypoxia in a high-yield and high-efficiency mining working face of a shallow-buried coal seam group. In the early stage of working face mining, a long horizontal borehole is constructed toward the target layer of the mining fissure zone 3. As the working face is mined, a fire-fighting slurry is injected into the borehole to fill the fissures and inhibit spontaneous combustion of the coal body, thereby preventing the generation of hypoxic gas and its migration to the goaf of the face through the fissure channel.

[0096] The advantages of the present invention are:

[0097] (1) For high-yield and high-efficiency production mines in shallow coal seams such as the Shaanxi mining area, the mining fissures 3 are filled by drilling and grouting, which is efficient and simple. The generation and expansion of mining fissures 3 during the mining process of the working face are dynamically blocked, and the spontaneous combustion of coal in the goaf caused by surface leakage and the migration of low-oxygen gas to the goaf through the fissure channel are reduced from the source. There are various drilling arrangement methods, including underground, ground, and well-ground combined methods, which are suitable for coal mining working faces with different mining conditions. The method is scientific and the construction cost is low, which can effectively reduce the occurrence of low-oxygen problems in the working face.

[0098] (2) The fire-fighting slurry injected into the boreholes of the present invention has the characteristics of filling and sealing cracks and inhibiting spontaneous combustion of coal bodies. The slurry can be composed of yellow mud slurry, water glass gel, etc. By adding inhibitors such as sodium chloride to the slurry and adjusting the proportion of aggregates, the purpose of not being easy to consolidate and precipitate is achieved. The slurry is easy to obtain, the materials are environmentally friendly, economical and practical, and the cost is low.

[0099] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not limiting. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention can be modified or replaced by equivalents without departing from the purpose and scope of the technical solutions, which should all be included in the scope of the claims of the present invention.

Claims

1. A hypoxia prevention and control device for sealing mining-induced fissures by advanced grouting of horizontal long boreholes in coal mines, characterized in that: include: Drilling construction unit, including kilometer-long directional drilling rig, casing and sealing materials; The end of the drill pipe of the kilometer-long directional drilling rig is connected to a casing, and the casing is fixed to the section of the borehole that has not entered the mining fracture zone; The sealing material is connected to the orifice of the drilled hole through a grouting pipeline to seal the orifice; Grouting unit, including grouting pump, mixer and slurry delivery pipeline; The outlet of the grouting pump is connected to the casing of the borehole through a slurry delivery pipeline; The input end of the mixer is connected to the yellow mud grouting station, the water glass solution tank and the coagulant solution tank of the fire prevention and extinguishing slurry preparation unit respectively, and the output end of the mixer is connected to the inlet of the grouting pump through the slurry delivery pipeline; Fire prevention and extinguishing slurry preparation unit, including yellow mud grouting station, water glass solution tank and coagulant solution tank; The yellow mud grouting station is connected to the first inlet of the mixer through a delivery pipeline; The water glass solution tank and the coagulant solution tank are respectively connected to the second inlet and the third inlet of the mixer through independent liquid supply pipelines; The drilling construction unit and the grouting unit are connected in series through a slurry delivery pipeline, and the output end of the fire prevention and extinguishing slurry preparation unit is connected to the mixer.

2. The device according to claim 1, characterized in that The yellow mud grouting station is provided with an inhibitor adding device for adding sodium chloride or sodium salt to the yellow mud slurry.

3. The device according to claim 1, characterized in that It also includes a monitoring and control unit, including a pressure sensor and a flow controller; The pressure sensor is installed on the grouting pipeline to monitor the drilling grouting pressure in real time; The flow controller is electrically connected to the grouting pump and dynamically adjusts the grouting rate of the grouting pump according to the pressure data fed back by the pressure sensor; the monitoring and control unit forms a closed-loop control with the grouting pump.

4. The device according to claim 1, characterized in that The drilling construction unit includes any one or more of the following implementation modes: (a) Underground horizontal long borehole: The drilling site is arranged in the return air lane of the working face. Multiple boreholes are arranged in each drilling site, and the final hole layer is located within 10 to 20 meters above the caving zone of the goaf; (b) Surface vertical well: Drill the well to the target layer in the mining fracture zone, run the surface casing and cement the well; (c) Well-ground combined drilling: The vertical well on the ground is connected with the long horizontal borehole underground through directional drilling technology to form a continuous grouting channel.

5. The device according to claim 1, characterized in that The fire extinguishing slurry is any one or combination of the following: (a) Yellow mud slurry, with sodium chloride or sodium salt inhibitor added; (b) Water glass gel, which is prepared by mixing water glass solution and coagulant in a ratio of 7:1 or 5:1, and the gelling time is controlled within 3 to 60 minutes.

6. A method for preventing and controlling hypoxia by using advance grouting to seal mining-induced fissures in horizontal long boreholes in coal mines, characterized in that: The following steps are involved: S1 Determine the parameters of the mining fracture zone: Based on the mine geological data and the data of the adjacent working face, predict the height of the caving zone and fracture zone in the goaf, and define the drilling target layer as 10 to 20 meters above the caving zone; S2 drilling construction: Use a kilometer-long directional drilling rig to construct a horizontal long borehole in the target layer. The drilling method is selected from one of the following: underground horizontal long drilling, surface vertical well, or well-surface combined drilling; S3 prepares fire prevention and extinguishing slurry: select yellow mud slurry or water glass gel, add inhibitor to the yellow mud slurry, or mix water glass solution and coagulant in proportion to form gel; S4 Grouting and plugging: Use the grouting pump to pressurize the fire extinguishing slurry into the borehole, control the grouting pressure to be stable, and replenish the slurry and increase the pressure when the slurry leaks until the slurry fills the mining fractures; S5 Inhibition and Sealing: The inhibitor in the slurry adheres to the surface of the coal rock to inhibit spontaneous combustion, and at the same time the borehole opening is sealed with cement, with a sealing length of 5 to 10 meters.

7. The method according to claim 6, characterized in that In S2: The drilling site spacing for underground horizontal long boreholes is 500m, with three boreholes arranged in each drilling site and a horizontal distance of 10m between the final holes. The vertical well spacing on the ground is 300m, and the wells are cemented after drilling to 20-30m above the caving zone; Well-ground combined drilling uses directional drilling technology to connect the vertical well on the ground with the horizontal section of the long borehole underground.

8. The method according to claim 6, characterized in that In S4, the grouting pressure is dynamically adjusted according to the crack expansion.

9. The method according to claim 8, characterized in that The grouting rate is controlled by real-time feedback of pressure data through the monitoring and control unit.

10. The method according to claim 6, characterized in that The inhibitor in S5 is sodium chloride or sodium salt, and the sealing material is cement slurry.

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