A method for perforating and staged fracturing of a long directional borehole in a coal mine roof

Abstract

The application discloses a coal mine underground roof directional long borehole perforation staged fracturing method and belongs to the technical field of coal mine underground fracturing and permeability improvement. The method comprises the following steps: target area geological condition exploration is carried out to obtain coal seam roof basic parameters; according to the obtained coal seam roof basic parameters, a target fracturing layer is preselected, and the compressibility of the roof stratum is evaluated; according to the determined target fracturing layer and the compressibility evaluation result of the roof stratum, the horizontal position and vertical interval of the directional borehole staged fracturing are determined; perforation parameter design and directional sandblasting perforation construction are carried out; staged hydraulic sand fracturing construction is carried out; after the fracturing construction, the fracturing effect is comprehensively evaluated; according to the effect evaluation result, selective supplementary fracturing or optimized fracturing construction parameters of the next round are implemented. The application can effectively guarantee the efficiency and safety of the gas control of the broken soft and strong outburst coal seam.

Description

Technical Field

[0001] This invention relates to the field of underground coal mine fracturing and permeability enhancement technology, and in particular to a method for segmented fracturing of the roof of an underground coal mine using directional long-hole perforation. Background Technology

[0002] In my country, fractured, soft, and highly prone to gas outbursts, coal seams generally suffer from prominent problems such as high gas content, high pressure, and poor permeability. In coal seams where the original gas pressure exceeds 3 MPa, without appropriate over-limit control measures, severe blowouts occur during underground drilling operations using cross-layer boreholes for outburst mitigation. This not only results in extremely low drilling efficiency but also frequent blowouts leading to gas over-limit accidents, posing serious safety hazards to underground drilling operations. Traditional regional pre-drainage drilling methods suffer from high blowout intensity and low drilling efficiency, making them unsuitable for the high-efficiency gas control requirements of deep mining conditions.

[0003] In existing technologies, the compressibility evaluation of coalbed methane reservoirs is mainly based on well logging data, core sampling tests, and mechanical parameter analysis. CNPC has proposed a method for evaluating the compressibility of deep coalbed methane reservoirs based on well logging data. This method obtains P-wave and S-wave transit times from acoustic data, calculates clay content using gamma values, and then calculates dynamic Young's modulus, tensile strength, and brittleness index for compressibility evaluation. Yanchang Petroleum has proposed a method for evaluating the compressibility of deep coalbed methane reservoirs containing interbedded rock. This method uses multiple indicators, including normalized coal brittleness index, coal structure index, and fracture toughness index, and employs triangular fuzzy hierarchical analysis to assign weights and form a compressibility index. China Coal Technology & Engineering Group Mining Research Institute has proposed a method for determining the fracturing horizon of the roof strata based on multi-scale rock mechanics characterization. This method involves preparing nano-indentation specimens from drill cuttings, conducting gridded point testing and mineral scanning, calculating microscopic mechanical parameters, constructing a macroscopic mechanical model, and normalizing and weighting the macroscopic and microscopic parameters to construct a comprehensive compressibility index and a comprehensive brittleness index.

[0004] In terms of engineering applications, Huaibei Mining's Luling Coal Mine has innovatively developed an integrated fracturing and permeability enhancement technology that integrates directional drilling of the roof of long-distance, near-outburst coal seams under complex geological conditions, full-hole casing cementing, directional sandblasting perforation, and segmented hydraulic sand fracturing.

[0005] Currently, existing technologies mainly suffer from the following technical problems: (1) Lack of a targeted roof compressibility evaluation system: Existing compressibility evaluations are mostly aimed at the coal reservoir itself, lacking an evaluation index system and evaluation method for the compressibility of target fracturing layers such as mudstone and sandstone in soft coal seams. Fracturing of hard roofs in coal mines does not require consideration of physical properties, but only the main factors such as whether cracks will form, whether cracks are easy to initiate and propagate. Existing evaluation methods fail to fully distinguish the essential differences between roof fracturing and coal seam fracturing.

[0006] (2) The correlation between evaluation indicators and engineering parameters is not strong: There is a lack of quantitative correlation between the existing compressibility evaluation results and the design of fracturing construction parameters. The compressibility evaluation is difficult to directly guide the optimization of key construction parameters such as fracturing section spacing, injection volume, pumping pressure, and sand addition ratio, resulting in insufficient engineering practicality of compressibility evaluation.

[0007] (3) Lack of integrated technical methods for the whole process: In the existing technology, the compressibility evaluation, drilling trajectory design, perforation parameter optimization, segmented fracturing construction and effect evaluation are relatively independent, and there is a lack of integrated technical methods that start from compressibility evaluation and run through the entire process of technical design-construction execution-effect verification. Summary of the Invention

[0008] To address the aforementioned technical problems, this invention proposes a method for segmented fracturing of the roof of underground coal mines using directional long-hole perforation.

[0009] The technical solution adopted in this invention is: A method for segmented fracturing of the roof of an underground coal mine using directional long-hole perforation includes the following steps: Step 1: Conduct geological condition surveys of the target area to obtain basic parameters of the coal seam roof; Step 2: Based on the basic parameters of the coal seam roof obtained in Step 1, pre-select the target fracturing layer and evaluate the compressibility of the roof strata; Step 3: Based on the target fracturing layer determined in Step 2 and the compressibility evaluation results of the top strata, determine the horizontal position and vertical range of the directional drilling segmented fracturing. Step 4: Based on Step 3, design the perforation parameters and carry out directional sandblasting perforation construction; Step 5: Based on the perforation parameter design in Step 4, carry out segmented hydraulic fracturing with sand injection. Step Six: Conduct a comprehensive evaluation of the fracturing effect after the fracturing operation; Step 7: Based on the effect evaluation results, selectively implement supplementary fracturing or optimize the fracturing construction parameters for the next round.

[0010] The principles upon which this invention is based and its beneficial technical effects are as follows: This invention establishes a specialized compressibility evaluation system for the roof strata of fractured and soft coal seams. The evaluation indicators cover the mechanical parameters of the roof strata (elastic modulus, Poisson's ratio, tensile strength, fracture toughness), brittleness index, mechanical matching parameters of the roof-coal seam interface (elastic modulus ratio, minimum horizontal principal stress difference), the degree of development of natural fractures, stress environment parameters (horizontal stress difference coefficient), and basic coal seam parameters (coal body structure index). This forms a specialized compressibility evaluation method that distinguishes between roof fracturing and coal seam fracturing. By constructing a specialized compressibility evaluation system for roof strata, this invention can scientifically and quantitatively select target fracturing layers, avoiding the uncertainty of fracturing effects caused by selecting fracturing layers based on experience, and improving the success rate of fracturing projects.

[0011] This invention establishes a compressibility index I F The quantitative mapping relationship between fracturing parameters (perforation spacing, single-stage injection volume, pump pressure, and proppant ratio) enables the compressibility evaluation results to directly guide the refined design of fracturing operation parameters, improving the targeting and effectiveness of fracturing schemes. This invention achieves differentiated and refined design of fracturing operation schemes, effectively avoiding the problems of insufficient or excessive fracturing caused by mismatch between fracturing parameters and geological conditions, and improving the economy and effectiveness of fracturing projects.

[0012] The mechanical parameters and geostress parameters of the roof strata in this invention can be obtained by field coring tests, well logging data interpretation, numerical simulation inversion or a combination of multiple methods. The degree of development of natural fractures can be obtained by core observation, imaging logging or sonic logging. The coal body structure index can be obtained by borehole coring observation or well logging response characteristics.

[0013] This invention, through an effect evaluation and feedback optimization mechanism, enables continuous correction of the compressibility evaluation model (i.e., the calculation formula of the compressibility comprehensive evaluation index) and continuous optimization of fracturing construction parameters, thereby improving the adaptability and engineering practicality of the technical method.

[0014] This invention forms an integrated technical process covering compressibility evaluation, borehole trajectory design, perforation parameter optimization, segmented fracturing construction, effect evaluation and feedback optimization, realizing a closed-loop control of the entire chain from target layer selection to construction parameter design and effect verification.

[0015] The method of this invention is applicable to the directional long-drilling perforation segmented fracturing project of the roof of fractured, soft and strong coal seams. It can be extended to the advanced management of gas disasters in mines with similar geological conditions, and has a wide range of applications and good prospects for promotion and application. Attached Figure Description

[0016] Figure 1 This is a schematic flowchart of the method for segmented fracturing of the underground roof of a coal mine using directional long drilling and perforation, according to the present invention. Figure 2This is a schematic diagram of the evaluation index system for the compressibility of the roof strata in this invention; Figure 3 This is a schematic diagram of the comprehensive evaluation and feedback optimization process for fracturing effect in this invention. Detailed Implementation

[0017] This invention proposes a method for segmented fracturing of the roof of underground coal mines using directional long-bore perforation. By constructing a compressibility evaluation system for the roof strata of soft and fractured coal seams, it achieves quantitative optimization of target fracturing layers and establishes a quantitative mapping relationship between compressibility index and key fracturing parameters, enabling refined design of construction schemes. This results in an integrated technical solution encompassing compressibility evaluation, borehole trajectory design, segmented perforation fracturing construction, effect evaluation, and feedback optimization, ensuring the high efficiency and safety of gas control in soft and fractured coal seams prone to outbursts.

[0018] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0019] like Figure 1 As shown, a method for segmented fracturing of the roof of a coal mine using directional long-hole perforation includes the following steps: Step 1: Geological condition survey and basic parameter acquisition of the target area; Collect geological data for the target area, including basic geological information such as stratigraphic columnar sections, gas geological maps, and structural development characteristics; obtain the lithology, thickness, occurrence, and spatial distribution characteristics of each stratum in the coal seam roof.

[0020] Step 2: Pre-selection of target fracturing sites and evaluation of the compressibility of the top strata; A graded compressibility evaluation method was adopted to evaluate and quantitatively rank the compressibility of different rock strata in the roof of the coal seam.

[0021] Specifically, the following steps are included: (1) Select multiple candidate fracturing layers from the top strata, with each candidate fracturing layer corresponding to a lithological segment.

[0022] (2) For each candidate fracturing layer, the following evaluation parameters are obtained: ① Mechanical parameters of the roof strata: including elastic modulus E, Poisson's ratio ν, and tensile strength σ t σ compressive strength c Fracture toughness K IC ; ② Brittleness index B: Calculated based on elastic modulus and Poisson's ratio, the formula is as follows: B = (E - E min ) / (E max - E min ) + (ν max - ν) / (ν max - νmin ) ; Among them, E max E min For the maximum and minimum elastic modulus of the regional rock strata, ν max ν min These represent the maximum and minimum values ​​of Poisson's ratio.

[0023] ③ Mechanical matching parameters of the roof strata and coal seam interface: roof-coal seam elastic modulus ratio: R E = E roof / E coal Minimum horizontal principal stress difference between roof and coal seam: Δσ h = σ h,roof - σ h,coal In the formula: E roof E represents the elastic modulus of the roof strata, reflecting the roof strata's ability to resist elastic deformation under external forces. A higher value indicates a denser, harder roof strata, making deformation more difficult. It is obtained through laboratory rock mechanics tests or interpretation of well logging data. coal σ is the elastic modulus of a coal seam, characterizing the coal's ability to resist elastic deformation. A smaller value indicates a softer and more fractured coal seam. It is obtained through laboratory tests or well logging interpretation. h,roof σ represents the minimum horizontal principal stress of the roof strata, which is the minimum of the three principal stresses in the roof strata. It reflects the horizontal stress environment of the roof strata and is obtained through geostress testing methods such as hydraulic fracturing or acoustic emission. h,coal The minimum horizontal principal stress of the coal seam is the minimum horizontal principal stress in the coal body, reflecting the minimum horizontal confining pressure state of the coal seam, and is also obtained through in-situ stress testing.

[0024] ④ Degree of development of natural cracks C f : Statistical analysis of fracture linear density or surface density through core observation or imaging logging.

[0025] ⑤ Combined stress environment parameters of coal seam and roof: horizontal stress difference coefficient K h = (σ H - σ h ) / σ h , where σ H For the maximum horizontal principal stress, σ h This represents the minimum horizontal principal stress.

[0026] ⑥ Basic parameters of coal seam compressibility: Coal body structure index S coal This reflects the degree of coal body fragmentation.

[0027] (3) Normalize the above parameters and unify the values ​​of each index to the range of [0,1].

[0028] (4) The weight coefficients of each evaluation index are determined by the analytic hierarchy process (AHP), and a formula for calculating the comprehensive evaluation index of the compressibility of the roof strata is established: I F = w1·B norm + w2·σ t,norm + w3·K IC,norm + w4·C f,norm + w5·R E,norm + w6·Δσ h,norm + w7·(1-K h,norm ) + w8·S coal,norm ; Among them, w i , i=1~8 are weight coefficients, satisfying ∑w i =1; the subscript norm represents the normalized parameter value.

[0029] like Figure 2 As shown, the roof compressibility evaluation index system is constructed through the steps of this invention. This system includes: rock mechanics parameters, fracture conditions, interface matching parameters, stress environment parameters, and coal seam basic parameters. Examples include: brittleness index, tensile strength, fracture toughness; natural fracture density; roof / coal seam elastic modulus ratio, minimum principal stress difference between roof and coal seam; horizontal stress difference coefficient; and coal body structure index.

[0030] Step 3: Design of directional long drilling trajectory and optimization of borehole structure; Based on the target fracturing layer determined in step two, and combined with the key layer theory analysis, the key bearing layer in the lower part of the overlying strata is determined, and the horizontal position and vertical range of the directional borehole segmented fracturing are comprehensively determined. The vertical range is determined based on the thickness and mechanical properties of the roof strata. The horizontal section of the borehole is located in the lower part of the target fracturing layer to ensure that the fracturing fractures can effectively extend towards the coal seam.

[0031] The borehole structure adopts a two-stage casing structure: the first-stage casing is lowered into the stable rock stratum with a diameter of not less than 219 mm; the second-stage casing is lowered into the target fracturing stratum with a diameter of not less than 114.3 mm, and the entire borehole is cemented with grout.

[0032] Step 4: Design of perforation parameters and directional sandblasting perforation construction; (1) Determine the perforation interval L based on the lithology, thickness, natural fracture development degree, and compressibility evaluation results of the target fracturing layer. p And the number of perforations and the number of holes in each segment.

[0033] The method for determining the perforation spacing Lp is: Lp = k1·H layer + k2·(1 / I F ) + k3·Δσh H layer The target fracturing layer thickness is given by k1, k2, and k3, which are empirical coefficients. F The compressibility index is Δσ. h This represents the horizontal stress difference.

[0034] Each perforation segment shall be perforated at least twice, with two holes formed each time, and the total number of holes in a single segment shall be at least four.

[0035] (2) Using directional sandblasting perforation technology, perforation operations are carried out at a predetermined depth in the target fracturing layer to form a perforation channel connecting the borehole cavity with the surrounding rock layer.

[0036] Step 5: Segmented hydraulic fracturing with sand addition; (1) Based on the perforation section division in step four, segmented hydraulic fracturing with sand is carried out sequentially for each perforation section.

[0037] (2) Method for determining fracturing fluid and proppant parameters: single-stage injection volume Q L The injection volume is determined based on the target fracturing layer thickness, compressibility index, and preset fracture length, with a range of 200–500 m³. 3 / Section design. Pumping pressure P pump The pumping pressure range is designed to be 15–35 MPa, determined based on the ground stress state and crack propagation pressure. The sand addition ratio R... sand The sand addition ratio is designed to be between 2.0% and 4.5%, depending on the requirements of proppant delivery capacity and fracture conductivity.

[0038] Compressibility Index I F A quantitative mapping relationship between I and the above fracturing parameters is established in advance. F When the level is high, the injection volume and pump pressure can be appropriately reduced; when I F When the pressure is low, the injection volume and pump pressure need to be increased to improve the fracturing effect.

[0039] Compressibility Index I F The engineering meanings are shown in Table 1 below.

[0040] Table 1

[0041] (3) The pumping bridge plug perforation process is adopted. The bridge plug is used to isolate the section that has been fracturing and advances section by section until the fracturing construction of all sections of the whole hole is completed.

[0042] Step Six: Comprehensive Evaluation of Fracturing Effect; (1) During the construction process, monitor the pumping pressure, discharge rate, sand concentration and other construction parameters in real time, and record the construction curves of each section.

[0043] (2) After the fracturing operation is completed, monitor the changes in gas extraction concentration and extraction volume of the fracturing borehole, and at the same time monitor the changes in the perforation rate and perforation intensity of the pre-extraction borehole in the fracturing area.

[0044] (3) Comprehensive evaluation of fracturing effect: If the cumulative extraction volume of fracturing boreholes reaches the design target and the blowout rate of pre-extraction boreholes in the area decreases by more than 50%, the fracturing effect is judged to be excellent; if the decrease is between 30% and 50%, the effect is judged to be good; if the decrease is less than 30%, the effect is judged to be average, and supplementary fracturing or parameter optimization is required.

[0045] (4) Establish an effect feedback mechanism, compare the evaluation results with the compressibility comprehensive evaluation index in step two, and correct the weight parameters and evaluation threshold of the compressibility evaluation model.

[0046] Step 7: Based on the effect evaluation results, selectively implement supplementary fracturing or optimize the fracturing construction parameters for the next round. That is, if the effect meets the standard, it is completed and archived; if the effect does not meet the standard, feedback is provided for optimization, the compressibility evaluation weight and parameters are corrected, and the above steps are repeated to complete the directional long-hole perforation segmented fracturing of the coal mine roof.

[0047] Specifically, such as Figure 3 As shown, after the fracturing operation is completed, the operation effect is evaluated in real time, and the fracturing pressure, extension pressure, discharge rate, and sand concentration are recorded. The extraction effect is evaluated, and the extraction concentration / pure quantity per hole and the perforation rate / hole formation rate of the pre-extraction boreholes in the monitoring area are monitored to establish a comprehensive evaluation standard. If it is judged as excellent (i.e., the perforation rate reduction is greater than or equal to 50%), a final report is output and archived. If it is judged as good / fair (i.e., the perforation rate reduction is less than 50%), a feedback correction mechanism is activated: the fracturing parameter mapping relationship is corrected, the empirical coefficient of perforation section spacing is corrected, and the compressibility evaluation weight coefficient is corrected for use in the next round of fracturing projects or similar geological conditions in the same mining area.

[0048] This invention forms an integrated technical process covering compressibility evaluation, borehole trajectory design, perforation parameter optimization, segmented fracturing construction, effect evaluation and feedback optimization, realizing a closed-loop control of the entire chain from target layer selection to construction parameter design and effect verification.

[0049] Engineering practice has verified that the roof directional long-hole perforation staged fracturing project implemented using the method of this invention can achieve a cumulative gas extraction volume exceeding 8 × 10⁻⁶ methane on the 257th day of fracturing borehole extraction. 5 m 3The pre-extraction rate in the region can reach 15.5%; the gas volume fraction reduction within 0-15 m on both sides of the horizontal section of the fracturing borehole can reach 27.05%, and the gas pressure at 0 m from the fracturing borehole plane can be reduced from 2.78 MPa to 1.14 MPa, a pressure reduction of over 37%; the perforation rate of 100 pre-extraction boreholes in the pre-extraction and depressurization area can be reduced by 57.89%, and the perforation intensity can be reduced by 67.11%; the one-time hole formation rate of pre-extraction boreholes increases by 19%, the hole repair rate decreases by 74.87%, and the average shift efficiency of drilling rigs increases by 34% year-on-year. The regional pre-extraction and depressurization effect of gas is significant, and the technical feasibility and effectiveness have been verified.

[0050] For any parts not mentioned above, existing technologies can be adopted or referenced.

[0051] Of course, the above description is only a preferred embodiment of the present invention. The present invention is not limited to the above-described embodiments. It should be noted that any equivalent substitutions or obvious modifications made by those skilled in the art under the guidance of this specification fall within the scope of this specification and should be protected by the present invention.

Claims

1. A method for segmented fracturing of the roof of a coal mine using directional long-hole perforation, characterized in that... Includes the following steps: Step 1: Conduct geological condition surveys of the target area to obtain basic parameters of the coal seam roof; Step 2: Based on the basic parameters of the coal seam roof obtained in Step 1, pre-select the target fracturing layer and evaluate the compressibility of the roof strata; Step 3: Based on the target fracturing layer determined in Step 2 and the compressibility evaluation results of the top strata, determine the horizontal position and vertical range of the directional drilling segmented fracturing. Step 4: Based on Step 3, design the perforation parameters and carry out directional sandblasting perforation construction; Step 5: Based on the perforation parameter design in Step 4, carry out segmented hydraulic fracturing with sand injection. Step Six: Conduct a comprehensive evaluation of the fracturing effect after the fracturing operation; Step 7: Based on the effect evaluation results, selectively implement supplementary fracturing or optimize the fracturing construction parameters for the next round.

2. The method for segmented fracturing of the roof of a coal mine by directional long drilling and perforation according to claim 1, characterized in that, In step one: during the geological condition exploration of the target area, geological data of the target area are collected, including stratigraphic columnar section, gas geological map and structural development characteristics; the basic parameters of the coal seam roof include the lithology, thickness, occurrence and spatial distribution characteristics of each rock layer in the coal seam roof.

3. The method for segmented fracturing of the roof of a coal mine by directional long drilling and perforation according to claim 2, characterized in that, Step two includes the following steps: (1) Select multiple candidate fracturing sites from the top strata, with each candidate fracturing site corresponding to a lithological segment; (2) For each candidate fracturing layer, the following evaluation parameters are obtained: ① Mechanical parameters of the roof strata: including elastic modulus E, Poisson's ratio ν, and tensile strength σ t σ compressive strength c Fracture toughness K IC ; ② Brittleness index B: Calculated based on elastic modulus and Poisson's ratio, the formula is as follows: B = (E - E min ) / (E max - E min ) + (n max - n) / (n) max - n min ); Among them, E max E represents the maximum elastic modulus of the regional rock strata. min The minimum elastic modulus of the regional rock strata; ν max This represents the maximum value of Poisson's ratio; ν min This represents the minimum value of Poisson's ratio. ③ Mechanical matching parameters of the roof strata and coal seam interface: roof-coal seam elastic modulus ratio: R E = E roof / E coal Minimum horizontal principal stress difference between roof and coal seam: Δσ h = σ h,roof - σ h,coal In the formula: E roof E represents the elastic modulus of the top strata. coal σ is the elastic modulus of the coal seam. h,roof For the minimum horizontal principal stress of the top strata, σ h,coal This represents the minimum horizontal principal stress in the coal seam. ④ Degree of development of natural cracks C f : Statistical analysis of fracture linear density or areal density through core observation or imaging logging; ⑤ Combined stress environment parameters of coal seam and roof: horizontal stress difference coefficient K h = (σ H - σ h ) / σ h , where σ H For the maximum horizontal principal stress, σ h The minimum horizontal principal stress; ⑥ Basic parameters of coal seam compressibility: Coal body structure index S coal This reflects the degree of coal body fragmentation; (3) Normalize the above parameters and unify the values ​​of each index to the range of [0,1]; (4) The weight coefficients of each evaluation index are determined by the analytic hierarchy process (AHP), and a formula for calculating the comprehensive evaluation index of the compressibility of the roof strata is established: I F = w1·B norm + w2·σ t,norm + w3·K IC,norm + w4·C f,norm + w5·R E,norm + w6·Δσ h,norm + w7·(1-K h,norm ) + w8·S coal,norm ; Among them, w i , i=1~8 are weight coefficients, satisfying ∑w i =1; the subscript norm indicates the normalized parameter value; The compressibility evaluation results were obtained based on the comprehensive evaluation index of the compressibility of the roof strata.

4. The method for segmented fracturing of the roof of a coal mine by directional long drilling and perforation according to claim 3, characterized in that, Step three includes the following steps: Based on the target fracturing layer determined in step two, and combined with the key layer theory analysis, the key bearing layer in the low-lying overburden is determined, and the horizontal position and vertical range of the directional borehole segmented fracturing are comprehensively determined. Among them, the vertical range is determined according to the thickness and mechanical properties of the top strata, and the horizontal section of the borehole is located in the lower part of the target fracturing layer.

5. A method for segmented fracturing of the roof of a coal mine by directional long drilling and perforation according to claim 4, characterized in that, In step three, the borehole structure adopts a two-stage casing structure: the first-stage casing is lowered into the stable rock stratum section with a diameter of not less than 219 mm; the second-stage casing is lowered into the target fracturing stratum section with a diameter of not less than 114.3 mm, and the entire borehole section is cemented with grout.

6. A method for segmented fracturing of the roof of a coal mine by directional long drilling and perforation according to claim 5, characterized in that, Step four includes the following steps: (1) Determine the perforation interval L based on the lithology, thickness, spatial distribution characteristics and compressibility evaluation results of the target fracturing layer. p And the number of perforations and the number of holes in each section; The method for determining the perforation spacing Lp is: Lp = k1·H layer + k2·(1 / I F ) + k3·Δσ h H layer The target fracturing layer thickness is given by k1, k2, and k3, which are empirical coefficients. F The compressibility index is Δσ. h The difference is horizontal stress. Each perforation segment shall be perforated at least twice, with two holes formed each time, and the total number of holes in a single segment shall be at least four. (2) Using directional sandblasting perforation technology, perforation operations are carried out at a predetermined depth in the target fracturing layer to form a perforation channel connecting the borehole cavity with the surrounding rock layer.

7. A method for segmented fracturing of the roof of a coal mine by directional long drilling and perforation according to claim 6, characterized in that, Step five includes the following steps: (1) Based on the perforation section division in step four, segmented hydraulic fracturing with sand is carried out sequentially for each perforation section; (2) Method for determining fracturing fluid and proppant parameters: injection volume Q L The range is 200–500 m 3 / section design; pump pressure P pump The design range is 15–35 MPa; sand addition ratio R sand The range is designed to be 2.0% to 4.5%; (3) The pumping bridge plug perforation process is adopted. The bridge plug is used to isolate the section that has been fracturing and advances section by section until the fracturing construction of all sections of the whole hole is completed.

8. A method for segmented fracturing of the roof of a coal mine by directional long drilling and perforation according to claim 7, characterized in that, Step 5: Establish the compressibility index I F A quantitative mapping relationship between injection volume, pump pressure, and sand addition ratio is established, and the injection volume and pump pressure are adjusted based on the compressibility index.

9. A method for segmented fracturing of the roof of a coal mine by directional long drilling and perforation according to claim 8, characterized in that, Step six includes the following steps: (1) During the construction process, the construction parameters are monitored in real time and the construction curves of each section are recorded; the construction parameters include pumping pressure, discharge rate and sand concentration; (2) After the fracturing operation is completed, monitor the changes in gas extraction concentration and extraction volume of the fracturing borehole, and at the same time monitor the changes in the perforation rate and perforation intensity of the pre-extraction borehole in the fracturing area. (3) Comprehensive evaluation of fracturing effect: If the cumulative extraction volume of fracturing boreholes reaches the design target and the blowout rate of pre-extraction boreholes in the area decreases by more than 50%, the fracturing effect is judged to be excellent; if the decrease is between 30% and 50%, the effect is judged to be good; if the decrease is less than 30%, the effect is judged to be average, and supplementary fracturing or parameter optimization is required.

10. A method for segmented fracturing of the roof of a coal mine by directional long drilling and perforation according to claim 9, characterized in that, Step six also includes the following steps: (4) Establish an effect feedback mechanism, compare the comprehensive evaluation fracturing results with the comprehensive evaluation index of the compressibility of the top strata in step two, and correct the weight coefficient of the comprehensive evaluation index of compressibility.

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