Method for seam forming and pressure releasing in strata area of small coal pillar roadway

Abstract

This invention discloses a method for creating fractures and relieving pressure in the overlying strata of a small coal pillar roadway. The method includes: statistically analyzing the occurrence of the coal seam and roof; calculating the fracture zone height using formulas based on the known coal seam and roof conditions; initially estimating the location of the target fracturing layer; designing fracturing borehole parameters within the target fracturing layer; and using UDEC discrete element numerical simulation software to simulate and predict the stress-strain of the surrounding rock and the roof collapse morphology before and after weakening. A comparative experiment is conducted to determine the fracturing scheme. Regional fracture creation and pressure relief construction is carried out according to the fracturing scheme. During mining operations at the working face, a mine pressure monitoring system is used to dynamically monitor the surrounding rock environment within the roadway and evaluate the fracturing effect. The pressure relief method of this invention is highly operable, targeted, reliable, and effective. The use of discrete element numerical calculation allows for quantitative comparison of the weakening effects of different fracturing parameters and assessment of the interrelationships between various indicators.

Description

Technical Field

[0001] This invention relates to the field of small coal pillar roadway technology, and in particular to a method for creating fractures and relieving pressure in the overburden strata of small coal pillar roadways. Background Technology

[0002] Small coal pillar roadways are a widely used coal pillar size optimization technology in the coal mining industry, which can effectively improve coal recovery rate and reduce the overall tunneling workload. However, due to the high mining intensity and hard roof of some mines, severe mine pressure manifestations are prone to occur during the working face mining. In the main coal mining areas of my country, more than 50% of the mines have roofs composed of hard sandstone, limestone, etc., with about 30% of the coal reserves beneath these roofs. The compressive strength of the rock mass usually exceeds 60 MPa. Because the roof is not easy to collapse, the overhang length gradually increases during the working face advancement. When it collapses, it is often accompanied by a huge energy release, which can easily trigger severe mine pressure manifestation disasters. Therefore, regional fracture weakening of the roadway roof to maintain the stability of the surrounding rock is of great significance for ensuring the safe and efficient mining of the working face. Summary of the Invention

[0003] This invention is based on the inventor's discoveries and understanding of the following facts and problems:

[0004] Long-bore hydraulic fracturing technology in coal mines is a safe and environmentally friendly technique for weakening coal and rock masses, which can significantly improve the management of mine roof. Currently, when hydraulic fracturing is used for regional fracture creation and pressure relief in small coal pillar roadways, there are several shortcomings, including unclear key load layers in the roof of the small coal pillar roadway, insufficient design basis for the hydraulic fracturing regional fracture creation and pressure relief scheme, and a single method for evaluating the pressure relief effect.

[0005] This invention aims to at least partially solve one of the technical problems in related technologies. To this end, embodiments of this invention propose a method for creating fractures and relieving pressure in the overlying strata of small coal pillar roadways. This method is used to determine the underground construction process and key technical parameters, guide the on-site roof weakening construction, and provide technical support for maintaining the stability of the surrounding rock in the roadway.

[0006] The method for creating fractures and relieving pressure in the overburden strata of a small coal pillar roadway according to an embodiment of the present invention includes:

[0007] The occurrence of coal seams and roofs was statistically analyzed, and the physical and mechanical parameters of coal and rock mass were obtained by experimental methods to explore the distribution of supporting pressure of surrounding rock in roadways.

[0008] Based on the known information about the coal seam and roof, the following formula is used to calculate the fracture zone height and preliminarily estimate the location of the target fracturing layer:

[0009]

[0010] In the formula, H li The height of the fracture zone is taken as the larger calculated value from the two formulas, and the target fracturing layer is located above the fracture zone.

[0011] Design fracturing borehole parameters within the target fracturing layer, arrange fracturing drill sites within the roadway, and use UDEC discrete element numerical simulation software to simulate and predict the stress and strain of the surrounding rock and the roof collapse pattern before and after weakening. Through comparative experiments, determine the fracturing scheme.

[0012] According to the fracturing plan, regional fracture creation and pressure relief construction shall be carried out;

[0013] During the mining process, a mine pressure monitoring system is used to dynamically monitor the surrounding rock environment in the roadway and evaluate the fracturing effect.

[0014] This invention addresses the uncertainty in the design of small coal pillar roadway construction schemes by proposing a method for fracturing and decompression relief in the overburden strata of small coal pillar roadways. Based on the coal seam, roof conditions, and construction site conditions, this method utilizes hydraulic fracturing decompression mechanism, strong mine pressure manifestation mechanism, and key layer theory to identify target fracturing layers through theoretical calculations. It is highly operable, targeted, reliable, and effective, thus possessing certain advantages in practical applications.

[0015] To address the distribution characteristics of the supporting pressure in the surrounding rock of a roadway, a discrete element method (DEM) was employed to compare and analyze the stress-strain fields of the surrounding rock before and after fracturing, thereby determining the optimal fracturing scheme. This approach considers the key characteristics of the coal seam and the roof strata of the roadway, and allows for reasonable control of the mine pressure manifestation based on the fracturing mechanism and the mine pressure action mechanism. It also enables quantitative comparison of the weakening effects of different fracturing parameters and assessment of the interrelationships between various indicators.

[0016] The evaluation of on-site construction results allows for reasonable optimization of each process during on-site construction, determination of specific construction procedures, and ensures safe and efficient on-site construction. Real-time analysis of the weakening effect reduces construction risks and ultimately yields a complete jointing and pressure relief scheme for the overburden strata in the roadway.

[0017] In some embodiments, the step of statistically analyzing the occurrence of coal seams and roof includes at least the following: coal seam thickness, coal seam depth, mining method, roof lithology, layer thickness, and layer position; the physical and mechanical parameters of the coal and rock mass include at least the uniaxial compressive strength, tensile strength, Poisson's ratio, and elastic modulus; and the distribution of bearing pressure in the surrounding rock of the roadway includes at least the range of bearing pressure distribution, peak value, and location of the peak value.

[0018] In some embodiments, the target fracturing layer is initially estimated and then identified by combining this with borehole surveying.

[0019] The steps for borehole surveying are as follows:

[0020] Drilling operations are carried out on the top plate in front of the work area;

[0021] By visually inspecting the borehole wall, the integrity of the borehole wall and the spacing of the threads on the borehole wall are observed. The more intact the borehole wall and the larger the thread spacing, the higher the hardness of the rock layer.

[0022] Laboratory tests are conducted on borehole samples to determine the physical and mechanical parameters of the borehole, including at least the uniaxial compressive strength and tensile strength of the rock, thereby identifying the target fracturing layer.

[0023] In some embodiments, the specific details of designing the location of the fracturing drilling site within the target fracturing layer include:

[0024] The design includes borehole dimensions, borehole length, horizontal deviation of the final borehole from the roadway side, and height deviation of the final borehole from the coal seam roof. Based on these parameters, the borehole directional length and angle are calculated to determine the segmented fracturing length and the number of fracturing segments.

[0025] In some embodiments, the determined fracturing scheme includes at least the selection of fracturing fluid, injection pressure, flow rate, and fracturing sequence.

[0026] In some embodiments, the specific simulation process for simulating and predicting the stress-strain of the surrounding rock and the roof collapse morphology before and after weakening using UDEC discrete element numerical simulation software is as follows:

[0027] Based on the borehole columnar section and working face layout diagram, construct a scaled-down stratigraphic model;

[0028] The initial geostress of the equilibrium model was determined by segmenting the coal seam from the cut-out point and observing the roof collapse pattern, ground stress, and displacement.

[0029] Based on the fracturing target layer determined above, hydraulic fracturing is performed on the rock formation according to variables, including at least the injection fluid velocity, flow rate, fracturing time, fracturing fluid physical and mechanical parameters, and segmented fracturing length.

[0030] The model after fracturing is excavated in sections. The collapse mode of the roof, the magnitude and location of stress concentration, the range of the plastic zone, and the range of joint opening are compared between the two cases. By changing the variables mentioned in step 3, the fracturing scheme is finally determined.

[0031] In some embodiments, the regional jointing and pressure relief construction process specifically includes:

[0032] Preparations before fracturing include at least the layout of the fracturing site, the provision of electrical equipment for fracturing, the supply of water and electricity to the well, ventilation, the assembly of fracturing equipment upon arrival at the site, and the trial run of fracturing equipment.

[0033] Develop safety technical measures for hydraulic fracturing;

[0034] Hydraulic fracturing engineering construction includes at least the installation of packers, sliding sleeve tools, orifice equipment, multi-stage packer setting, segmented fracturing water injection or segmented jet fracturing, pressure and flow monitoring, video surveillance, fracturing zone inspection, packer release and tool string retrieval, and continuous orifice pumping.

[0035] In some embodiments, evaluating the fracturing effect specifically includes:

[0036] The weakening effect of segmented hydraulic fracturing on the roof was evaluated by comparing the deformation of the surrounding rock in the roadway before and after fracturing.

[0037] By comparing and analyzing the intensity of mine pressure manifestation before and after fracturing in the mining process, the overall fracturing effect can be evaluated.

[0038] In some embodiments, the evaluation indicators include at least the periodic pressure strength, periodic pressure step distance, dynamic load factor, support pressure, anchor bolt and anchor cable stress, and deformation of the roadway roof and walls.

[0039] In some embodiments, the method for creating fractures and relieving pressure in the overlying strata of a small coal pillar roadway further includes calculating the caving zone height using the following formula:

[0040]

[0041] In the formula, H k ∑M represents the height of the caving zone, and ∑M represents the cumulative thickness. Attached Figure Description

[0042] Figure 1 This is a flowchart of the method for creating fractures and relieving pressure in the overlying strata of a small coal pillar roadway according to an embodiment of the present invention.

[0043] Figure 2 This is a top view of the borehole layout in the method for creating fractures and relieving pressure in the overlying strata of a small coal pillar roadway according to an embodiment of the present invention.

[0044] Figure 3 This is a side view of the borehole layout in the method for creating fractures and relieving pressure in the overlying strata of a small coal pillar roadway according to an embodiment of the present invention (the working face has not been excavated).

[0045] Figure 4 This is a side view of the borehole layout in the method for creating cracks and relieving pressure in the overlying strata of a small coal pillar roadway according to an embodiment of the present invention (after the working face is excavated).

[0046] Figure label:

[0047] 1. Unmined working face; 2. Coal pillar; 3. Goaf; 4. Working face; 5. Working face support; 6. Roof borehole; 7. Roadway; 8. Target fracturing layer; 9. Collapsed roof. Detailed Implementation

[0048] Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0049] The following is based on Figures 1-4 The method for creating fractures and relieving pressure in the overburden strata of a small coal pillar roadway according to an embodiment of the present invention includes the following steps:

[0050] Step 1: Statistically analyze the occurrence of coal seams and roofs, obtain the physical and mechanical parameters of coal and rock mass using experimental methods, and investigate the distribution of supporting pressure of surrounding rock in roadways;

[0051] Step 2: Based on the known coal seam and roof conditions, the following formula is used to calculate the fracture zone height and preliminarily estimate the location of the target pressure fracture zone:

[0052]

[0053] In the formula, H li The height of the fracture zone is taken as the larger calculated value from the two formulas. The target fracturing layer is located above the fracture zone; in other words, the height of the target fracturing layer should be greater than the calculated fracture zone height H. li Based on the calculated fracture zone height H li This allows for the preliminary determination of the location of the target fracturing layer;

[0054] Step 3: Design fracturing borehole parameters within the target fracturing layer, set up fracturing drilling sites within the roadway, and use UDEC discrete element numerical simulation software to simulate and predict the stress and strain of the surrounding rock and the roof collapse pattern before and after weakening. Through comparative experiments, determine the fracturing scheme.

[0055] Step 4: Carry out regional fracture creation and pressure relief construction according to the fracturing scheme determined in Step 3;

[0056] In step 1, at least the cumulative mining thickness ∑M of the coal seam is obtained, which is used for calculation in step 2.

[0057] For example, the fracturing scheme in step 3 includes determining the fracturing drilling site and borehole layout scheme, including the selection of drilling site location, number and location of boreholes, borehole diameter and segmented fracturing length, borehole design length and specific construction process, etc.

[0058] It should be noted that steps 1-5 above are an example of the present invention and are not intended to limit the implementation sequence of the method for creating cracks and relieving pressure in the overburden strata of small coal pillar roadways of the present invention.

[0059] This invention addresses the uncertainty in the design of small coal pillar roadway construction schemes by proposing a method for fracturing and decompression relief in the overburden strata of small coal pillar roadways. Based on the coal seam, roof conditions, and construction site conditions, this method utilizes hydraulic fracturing decompression mechanism, strong mine pressure manifestation mechanism, and key layer theory to identify target fracturing layers through theoretical calculations. It is highly operable, targeted, reliable, and effective, thus possessing certain advantages in practical applications.

[0060] To address the distribution characteristics of the supporting pressure in the surrounding rock of a roadway, a discrete element method (DEM) was employed to compare and analyze the stress-strain fields of the surrounding rock before and after fracturing, thereby determining the optimal fracturing scheme. This approach considers the key characteristics of the coal seam and the roof strata of the roadway, and allows for reasonable control of the mine pressure manifestation based on the fracturing mechanism and the mine pressure action mechanism. It also enables quantitative comparison of the weakening effects of different fracturing parameters and assessment of the interrelationships between various indicators.

[0061] The evaluation of on-site construction results allows for reasonable optimization of each process during on-site construction, determination of specific construction procedures, and ensures safe and efficient on-site construction. Real-time analysis of the weakening effect reduces construction risks and ultimately yields a complete jointing and pressure relief scheme for the overburden strata in the roadway.

[0062] In some embodiments, step 1: Statistical analysis of the coal seam and roof occurrence includes at least basic parameters such as coal seam thickness, coal seam depth, mining method, roof lithology, layer thickness, and stratum position. Physical and mechanical parameters of the coal and rock mass obtained through laboratory testing include at least the uniaxial compressive strength, tensile strength, Poisson's ratio, and elastic modulus of the coal and rock mass, to understand the occurrence of the overburden strata in the roadway. The distribution of bearing pressure in the surrounding rock of the roadway includes at least the range of bearing pressure distribution, peak value, and location of the peak value.

[0063] In some embodiments, in step 2, after a preliminary estimation of the target fracturing layer, i.e., the hard top plate layer, the target fracturing layer is identified by combining borehole exploration. The steps of borehole exploration are as follows:

[0064] Step 201: Drill holes in the top plate in front of the workpiece;

[0065] Step 202: By visually inspecting the borehole wall, observe the integrity of the borehole wall and the thread pitch on the borehole wall. The more intact the borehole wall and the larger the thread pitch, the higher the hardness of the rock layer and the more pressure relief is needed.

[0066] Step 203: Conduct laboratory tests on the borehole samples to determine the physical and mechanical parameters of the borehole, including at least the uniaxial compressive strength and tensile strength of the rock, thereby determining the location of the target fracturing layer.

[0067] In step 2, by constructing weakening strips within the hard roof lateral to the overlying strata of the roadway, the spatial structure of the roof at the working face end and above the goaf is improved. This adjusts the spatial structure of the overlying strata on the goaf side of the small coal pillar working face, reduces the intensity of mine pressure manifestation in the goaf-adjacent small coal pillar roadway, improves the stress environment of the roadway surrounding rock, and reduces the degree of deformation of the surrounding rock in the goaf-adjacent small coal pillar roadway. Based on the known coal seam and roof conditions, the source strata of the overlying load and the target stress relief area are identified.

[0068] In some embodiments, step 2 further includes calculating the collapse zone height using the following formula:

[0069]

[0070] In the formula, H k Let M be the height of the caving zone and ∑M be the cumulative thickness.

[0071] The height of the caving zone is calculated to assess its approximate height at that mining thickness.

[0072] In some embodiments, in step 3, existing chambers within the mine can be used to arrange the drilling site, and the drilling site space should be large enough to accommodate drilling rigs and other equipment. The specific details of designing fracturing borehole parameters within the target fracturing layer and arranging the fracturing drilling site within the roadway include:

[0073] The borehole parameter design includes designing the borehole size, borehole length, horizontal deviation of the final borehole from the roadway side, and height deviation of the final borehole from the coal seam roof. Based on these parameters, the borehole directional length and angle are calculated to determine the segmented fracturing length and the number of fracturing segments.

[0074] In step 3, the specific simulation process for simulating and predicting the stress and strain of the surrounding rock and the roof collapse morphology before and after weakening using the UDEC discrete element numerical simulation software is as follows:

[0075] Step 301: Construct a scaled-down formation model based on the borehole columnar section and working face layout diagram;

[0076] Step 302: Equilibrium the initial ground stress of the model, excavate the coal seam in sections from the cut-out point, and observe the roof collapse pattern, ground stress and displacement.

[0077] Step 303: Based on the fracturing target layer determined above, hydraulic fracturing is performed on the rock formation according to variables, including at least the injection fluid velocity, flow rate, fracturing time, fracturing fluid physical and mechanical parameters, and segmented fracturing length.

[0078] Step 304: Perform segmented excavation on the fracturing model, compare the roof collapse morphology, stress concentration magnitude and location, plastic zone range, and joint opening range under the two conditions, and finally determine the fracturing scheme by changing the variables described in Step 3.

[0079] The final optimal fracturing scheme should include at least the selection of fracturing fluid, injection pressure, flow rate, and fracturing sequence.

[0080] In some embodiments, step 4, the regional jointing and pressure relief construction process specifically includes:

[0081] Preparations before fracturing include at least the layout of the fracturing site, the provision of electrical equipment for fracturing, the supply of water and electricity to the well, ventilation, the assembly of fracturing equipment upon arrival at the site, and the trial run of fracturing equipment.

[0082] Develop safety technical measures for hydraulic fracturing;

[0083] Hydraulic fracturing engineering construction includes at least the installation of packers, sliding sleeve tools, orifice equipment, multi-stage packer setting, segmented fracturing water injection or segmented jet fracturing, pressure and flow monitoring, video surveillance, fracturing zone inspection, packer release and tool string retrieval, and continuous orifice pumping.

[0084] The specific measures for developing safety technologies for hydraulic fracturing include:

[0085] Before starting the pump, check the circuit connection, gas concentration, pump set high-pressure pipeline connection, cooler pipeline connection, nitrogen pressure, water tank level, high-pressure pipe and orifice safety device.

[0086] During the fracturing process, real-time monitoring is conducted on pump injection pressure and flow rate, water leakage in fracturing pipelines and orifices, and roadway spalling and dripping.

[0087] After fracturing is completed, a comprehensive inspection of the surrounding rock conditions of the roadway is carried out. The water pressure in the borehole is reduced to zero, and the packer can only be removed after approval from the technical supervisor.

[0088] In some embodiments, step 5, evaluating the fracturing effect specifically includes:

[0089] During the mining process, a mine pressure monitoring system is used to dynamically monitor the surrounding rock environment in the roadway. By comparing the deformation of the surrounding rock before and after fracturing, the weakening effect of segmented hydraulic fracturing on the roof is evaluated.

[0090] By comparing and analyzing the intensity of mine pressure manifestation before and after fracturing in the mining process, the overall fracturing effect can be evaluated.

[0091] The evaluation indicators include at least the periodic pressure strength, periodic pressure step distance, dynamic load coefficient, support pressure, anchor bolt and anchor cable stress, and the deformation of the roadway roof and walls.

[0092] The following section details the implementation steps and results of the method for creating cracks and relieving pressure in the overburden layer area of ​​a small coal pillar roadway, using the parameters and construction process design for crack weakening in the hard roof of a mine roadway as an example.

[0093] like Figure 2 As shown, coal pillar 2 is located between unmined working face 1 and working face 4, roadway 7 is located between coal pillar 2 and working face 4, goaf 3 is located behind working face 4, working face support 5 is located near working face 4 and is used to support the roadway roof, and roof borehole 6 is set in the roof.

[0094] Step 1: As Figure 3 As shown, the occurrence of coal seams and roof is statistically analyzed, and it is understood that: the thickness of coal seam ① is h, and the overlying roof strata, from bottom to top, are medium-grained sandstone layer ②, medium-coarse-grained sandstone layer ③, mudstone layer ④, and medium-coarse-grained sandstone layer ⑤.

[0095] Step 2: Based on the known coal seam and roof conditions, the following formula is used to calculate the fracture zone height and preliminarily estimate the location of the target pressure fracture zone:

[0096]

[0097] In the formula, H li The height of the fracture zone is determined by taking the larger value from the two formulas. Based on the judgment mechanism that the target fractured layer is located above the fracture zone, and combined with the borehole survey method, the location of the target fractured layer 8 is determined to be the upper middle part of the medium-coarse sandstone layer ③, the mudstone layer ④, and the lower part of the medium-coarse sandstone layer ⑤.

[0098] Step 3: To ensure the structural stability of the roadway after the adjacent working face has been mined, it is necessary to take measures to weaken the target fracturing layer 8;

[0099] By utilizing the key layer ore pressure mechanism, the ore pressure effects of the immediate roof, basic roof 1, basic roof 2, and basic roof 3 were analyzed. It was found that basic roof 1 and basic roof 2 are the source rock layers of strong ore pressure and need to be weakened in order to ensure the structural stability of the roadway in the adjacent working face mining stage.

[0100] Based on the construction conditions within the mine, and taking into full account the space required for drilling equipment and drilling sites, the corresponding borehole design lengths are calculated according to the layer position and weakening length of the target fracturing layer 8 determined above, which are 550m, 690m, and 665m respectively. The horizontal deviations of the final borehole from the roadway side are 0m, 9m, and 15m respectively, and the height deviations of the final borehole from the coal seam roof are 12m, 36m, and 72m respectively.

[0101] Using UDEC discrete element numerical simulation software, a scaled-down coal mine formation model was constructed to simulate and predict the stress-strain of the surrounding rock and the roof collapse morphology before and after weakening. Through comparative experiments, the fracturing parameters were simulated and optimized, and the final fracturing scheme was determined as follows: borehole diameter 120mm, sealing length ≥35m, sealing method: cement grouting / one-stop-plugging-one-injection, fracturing time 23min, injection pressure 24~32MPa, and fracturing pump flow rate 0.8m / s².3 / min.

[0102] Step 4: Perform regional fracture creation and pressure relief construction according to the fracturing plan determined in Step 3, specifically including:

[0103] The on-site construction process and downhole construction safety measures were determined. The pre-fracturing construction preparation included: (1) fracturing site layout; (2) remote control site setup; (3) ventilation system and facility supervision and maintenance; (4) transportation; (5) communication; (6) fracturing equipment inspection; (7) fracturing equipment commissioning.

[0104] The fracturing operation includes: (1) monitoring pump injection pressure and flow rate; (2) completion of hydraulic fracturing; and (3) drainage and well flushing operations.

[0105] Safety measures for underground construction include: (1) Before starting the pump, check the circuit connection, gas concentration, high pressure pipeline connection of the pump group, cooler pipeline connection, nitrogen pressure, water tank level, high pressure pipe and wellhead safety device, etc.; (2) During the fracturing process, monitor the pump injection pressure and flow rate, water leakage of fracturing pipeline and wellhead, roadway spalling and dripping, etc. in real time; (3) After the fracturing is completed, conduct a comprehensive inspection of the surrounding rock of the roadway, reduce the water pressure in the borehole to zero pressure, and remove the packer only after approval by the technical person in charge.

[0106] Step 5: Weakening Effect Analysis: During the mining process, a mine pressure monitoring system is used to dynamically monitor the surrounding rock environment in the roadway. The weakening effect of segmented hydraulic fracturing on the roof is evaluated by comparing the deformation of the surrounding rock before and after fracturing. At the same time, the mine pressure manifestation intensity before and after the fracturing construction area during the mining process is compared and analyzed to evaluate the overall fracturing effect. The main indicators include the periodic pressure intensity, periodic pressure step distance, dynamic load coefficient, support pressure, anchor bolt and anchor cable stress, and the deformation of the roadway roof and walls.

[0107] After the working face was excavated, part of the roof collapsed, which led to Figure 4 The collapsed roof slab 9 is shown. (As shown) Figure 4 As shown, the peak value of the weakened stress curve is significantly lower than that of the unweakened stress curve, and the peak value is significantly shifted to the back, indicating a significant weakening effect.

[0108] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this invention and simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0109] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0110] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection, an electrical connection, or a connection that allows communication between them; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components, unless otherwise explicitly limited. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0111] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can mean that the first feature is in direct contact with the second feature, or that the first feature is in indirect contact with the second feature through an intermediate medium. Furthermore, "above," "over," and "on top" of the second feature can mean that the first feature is directly above or diagonally above the second feature, or simply that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply that the first feature is at a lower horizontal level than the second feature.

[0112] In this invention, the terms "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to a specific feature, structure, material, or characteristic described in connection with that embodiment or example, which is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0113] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A method for creating fractures and relieving pressure in the overlying strata of a small coal pillar roadway, characterized in that, include: The occurrence of coal seams and roofs was statistically analyzed, and the physical and mechanical parameters of coal and rock mass were obtained by experimental methods to explore the distribution of supporting pressure of surrounding rock in roadways. Based on the known information about the coal seam and roof, the following formula is used to calculate the fracture zone height and preliminarily estimate the location of the target fracturing layer: In the formula, The height of the fracture zone is taken as the larger calculated value from the two formulas, and the target fracturing layer is located above the fracture zone. This refers to the cumulative thickness of the coal seam. Design fracturing borehole parameters within the target fracturing layer, arrange fracturing drilling sites within the roadway, and use UDEC discrete element numerical simulation software to simulate and predict the stress and strain of the surrounding rock and the roof collapse pattern before and after weakening. Through comparative experiments, determine the fracturing scheme. According to the fracturing plan, regional fracture creation and pressure relief construction shall be carried out; During the mining process, a mine pressure monitoring system is used to dynamically monitor the surrounding rock environment in the roadway and evaluate the fracturing effect. The step of statistical analysis of coal seam and roof occurrence includes at least the statistical analysis of coal seam thickness, coal seam burial depth, mining method, roof lithology, layer thickness, and stratigraphic position. The physical and mechanical parameters of coal and rock mass include at least the uniaxial compressive strength, tensile strength, Poisson's ratio, and elastic modulus of the coal and rock mass; The distribution of bearing pressure in the surrounding rock of the roadway should include at least the range of bearing pressure distribution, the magnitude of the peak value, and the location of the peak value. After a preliminary estimation of the target fracturing layer, the target fracturing layer was identified by combining it with borehole surveying. The steps for borehole surveying are as follows: Drilling operations are carried out on the top plate in front of the work area; By visually inspecting the borehole wall, the integrity of the borehole wall and the spacing of the threads on the borehole wall are observed. The more intact the borehole wall and the larger the thread spacing, the higher the hardness of the rock layer. Laboratory tests were conducted on borehole samples to determine the physical and mechanical parameters of the borehole, including at least the uniaxial compressive strength and tensile strength of the rock, thereby identifying the target fracturing layer. The specific simulation process for using UDEC discrete element numerical simulation software to simulate and predict the stress-strain of the surrounding rock and the roof collapse pattern before and after weakening is as follows: Based on the borehole columnar section and working face layout diagram, construct a scaled-down stratigraphic model; The initial geostress of the equilibrium model was determined by segmenting the coal seam from the cut-out point and observing the roof collapse pattern, ground stress, and displacement. Based on the target fracturing layer determined above, hydraulic fracturing is performed on the rock formation according to variables, including at least the injection fluid velocity, flow rate, fracturing time, fracturing fluid physical and mechanical parameters, and segmented fracturing length. The model after fracturing is excavated in sections. The collapse mode of the roof, the magnitude and location of stress concentration, the range of the plastic zone, and the range of joint opening are compared between the two cases. By changing the variables mentioned in step 3, the fracturing scheme is finally determined.

2. The method for creating fractures and relieving pressure in the overlying strata of a small coal pillar roadway according to claim 1, characterized in that, The specific details of designing the location of fracturing drilling sites within the target fracturing zone include: The design includes borehole dimensions, borehole length, horizontal deviation of the final borehole from the roadway side, and height deviation of the final borehole from the coal seam roof. Based on these parameters, the borehole directional length and angle are calculated to determine the segmented fracturing length and the number of fracturing segments.

3. The method for creating fractures and relieving pressure in the overlying strata of a small coal pillar roadway according to claim 1, characterized in that, A well-defined fracturing scheme should include at least the selection of fracturing fluid, injection pressure, flow rate, and fracturing sequence.

4. The method for creating fractures and relieving pressure in the overlying strata of a small coal pillar roadway according to claim 1, characterized in that, The specific process of regional joint suturing and pressure relief construction includes: Preparations before fracturing include at least the layout of the fracturing site, the provision of electrical equipment for fracturing, the supply of water and electricity to the well, ventilation, the assembly of fracturing equipment upon arrival at the site, and the trial run of fracturing equipment. Develop safety technical measures for hydraulic fracturing; Hydraulic fracturing engineering construction includes at least the installation of packers, sliding sleeve tools, orifice equipment, multi-stage packer setting, segmented fracturing water injection or segmented jet fracturing, pressure and flow monitoring, video surveillance, fracturing zone inspection, packer release and tool string retrieval, and continuous orifice pumping.

5. The method for creating fractures and relieving pressure in the overlying strata of a small coal pillar roadway according to claim 1, characterized in that, The evaluation of fracturing effectiveness specifically includes: The weakening effect of segmented hydraulic fracturing on the roof was evaluated by comparing the deformation of the surrounding rock in the roadway before and after fracturing. By comparing and analyzing the intensity of mine pressure manifestation before and after fracturing in the mining process, the overall fracturing effect can be evaluated.

6. The method for creating fractures and relieving pressure in the overlying strata of a small coal pillar roadway according to claim 5, characterized in that, The evaluation indicators should include at least the periodic pressure strength, periodic pressure step distance, dynamic load factor, support pressure, anchor bolt and anchor cable stress, and the deformation of the roadway roof and walls.

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