Pre-injection design method for nitrogen injection displacement of low-permeability coal seam

Abstract

The invention discloses a pre-injection design method for low-permeability coal seam nitrogen injection displacement, and belongs to the technical field of coal seam nitrogen injection displacement. The method comprises the following steps: nitrogen injection applicability evaluation: obtaining measured values of coal seam parameters through coal seam in-situ testing and ground analysis testing, and calculating an applicability index SI to evaluate nitrogen injection feasibility; designing a pulse nitrogen injection process, namely determining a scheme of a drilling and sealing technology, performing nitrogen injection pressure parameter matching analysis and designing a pulse period of pulse nitrogen injection; a pulse nitrogen injection pressurization system is designed, specifically, the pulse nitrogen injection pressurization system is constructed, nitrogen injection pressure parameters are transmitted to a nitrogen storage pressurization subsystem, and a pulse period is input to a pulse nitrogen injection control module; and verifying the design parameters through numerical simulation, and outputting an implementation scheme report containing construction details. According to the method, the implementation efficiency of nitrogen injection displacement can be improved, the safety risk is reduced, the adaptability is good, and the complexity and variability of the low-permeability coal seam environment can be dealt with.

Description

Technical Field

[0001] This application relates to the field of nitrogen injection displacement technology in coal seams, and in particular to a pre-injection design method for nitrogen injection displacement in low-permeability coal seams. Background Technology

[0002] In the mining industry, gas drainage is a crucial link in ensuring mine safety and efficient resource utilization. This is especially true for low-permeability coal seams, where low permeability and strong gas adsorption lead to inefficient traditional drainage methods and pose safety hazards. Gas injection displacement technology, as a breakthrough solution, increases the internal gas pressure of the coal seam by injecting gas (such as nitrogen), accelerating mixed-gas flow and simultaneously reducing the effective partial pressure of gas, promoting the desorption of adsorbed gas. This provides a new approach to solving the problem of insufficient reservoir pressure drop in the later stages of drainage, and provides sufficient power and reliable migration for the reservoir flow field. With its safety, economy, and environmental friendliness, this technology has shown significant potential in improving gas recovery rates in recent years and is widely used in underground coal mine environments to address the challenges posed by complex coal seam geological conditions.

[0003] Current technologies primarily employ nitrogen injection displacement to improve gas extraction efficiency in low-permeability coal seams. The specific implementation process includes preliminary coal seam parameter assessment (such as measuring coal seam permeability and gas content through on-site exploration), setting gas injection parameters (such as manually designing borehole layout and injection pressure), and equipment configuration (such as selecting standard nitrogen generation and extraction equipment). However, these steps are often carried out in a fragmented manner, relying on experience and independent operation. For example, basic data is first obtained through local testing, then borehole spacing and pressure values ​​are set based on engineers' experience, and finally, equipment is selected and the system is assembled separately. The entire process lacks a unified framework, resulting in a lack of overall coherence and standardized procedures in pre-injection design.

[0004] The existing pre-injection design process has significant flaws: it fails to comprehensively consider multiple parameters such as gas pressure, permeability, gas content, Protodyakonov coefficient, ash content, and Langmuir pressure constant, and lacks quantitative indices as a basis for decision-making, leading to a high rate of misjudgment of applicability and easily causing nitrogen injection failure or low efficiency. Secondly, the process design is fragmented; the selection of sealing schemes does not dynamically optimize sealing materials based on gas pressure and fracture development, and there is a lack of coordinated analysis between nitrogen injection pressure parameters and pulse cycle design. Furthermore, the pressurization system design is uncoordinated; nitrogen production, extraction, and monitoring equipment are selected independently, failing to achieve seamless integration and affecting the overall extraction effect. These flaws collectively result in low implementation efficiency, high safety risks, and poor adaptability of nitrogen injection displacement, making it difficult to cope with the complexity and variability of low-permeability coal seam environments. Summary of the Invention

[0005] This application provides a pre-injection design method for nitrogen injection displacement in low-permeability coal seams, which solves the problems of low implementation efficiency, high safety risks, poor adaptability, and difficulty in coping with the complexity and variability of low-permeability coal seam environments caused by existing pre-injection design processes.

[0006] To achieve the above objectives, the technical solution of this invention is as follows:

[0007] This invention provides a pre-injection design method for nitrogen displacement in low-permeability coal seams, comprising:

[0008] Nitrogen injection suitability assessment: Coal seam parameters, including gas pressure, permeability, gas content, Protodyakonov coefficient, ash content, and Langmuir pressure constant, are obtained through in-situ coal seam testing and surface analysis. A suitability index (SI) is calculated based on these parameters to assess nitrogen injection feasibility. The assessment criteria are as follows: SI > 0.8 indicates high suitability, proceeding to pulsed nitrogen injection process design; 0.7 ≤ SI ≤ 0.8 indicates moderate suitability, proceeding to pulsed nitrogen injection process design; SI < 0.7 indicates unsuitability, terminating the pulsed nitrogen injection process design.

[0009] Pulse nitrogen injection process design: determine the drilling and sealing technology scheme, analyze the matching of nitrogen injection pressure parameters, and design the pulse cycle of pulse nitrogen injection;

[0010] The design of the pulse nitrogen injection booster system includes the following: the input end of the gas-water ionization system is connected to the external compressed air pipeline network, and the output end is connected to the input end of the compressed air nitrogen generation subsystem. The output end of the compressed air nitrogen generation subsystem is connected to the input end of the nitrogen storage booster subsystem, and the output end of the nitrogen storage booster subsystem is connected to the input end of the nitrogen delivery subsystem. The output end of the nitrogen delivery subsystem is connected to the input end of the pulse nitrogen injection control module, and the output end of the pulse nitrogen injection control module is connected to the nitrogen injection borehole in the coal seam. The input end of the gas extraction subsystem is connected to the extraction borehole in the coal seam, and the output end is connected to the emission subsystem. The central controller is electrically connected to the sensors and actuators of each subsystem. The nitrogen injection pressure parameters are transmitted to the nitrogen storage booster subsystem, and the pulse period is input to the pulse nitrogen injection control module.

[0011] The design parameters are verified through numerical simulation, and an implementation plan report containing construction details is output.

[0012] In one possible implementation, calculating the applicability index SI based on measured values ​​of coal seam parameters includes:

[0013] The measured values ​​of the coal seam parameters are collected, including gas pressure, permeability, gas content, Protodyakonov coefficient, ash content, and Langmuir pressure constant.

[0014] The measured values ​​of each coal seam parameter were standardized to the interval [0, 1] to obtain the standard value X of each coal seam parameter. norm，i Where i = 1, 2, 3, 4, 5, 6, i = 1 represents gas pressure, i = 2 represents permeability, i = 3 represents gas content, i = 4 represents Protodyakonov coefficient, i = 5 represents ash content, and i = 6 represents Langmuir pressure constant.

[0015] Calculate the standard value X for each of the coal seam parameters. norm,i deviation i and confidence level C i ;

[0016] Calculate the deviation Δ of all coal seam parameters i The minimum difference M = △ imin The maximum difference N = △ imax ;

[0017] According to the deviation i The grey relational degree R is calculated using the minimum difference M and the maximum difference N. i ;

[0018] According to the weighting coefficient W for each of the coal seam parameters i The confidence level C i And the gray relational degree R i Calculate the applicability index SI.

[0019] In one possible implementation, the standardized formula for the measured values ​​of each of the coal seam parameters is as follows:

[0020] = In the formula, X is the initial standard value of any one of the coal seam parameters, including gas pressure, permeability, gas content, Protodyakonov coefficient, ash content, or Langmuir pressure constant. i For X norm,i The corresponding measured value of the coal seam parameter, X min,i For X i The minimum value of the corresponding coal seam parameter, X max,i For X i The maximum value of the corresponding coal seam parameter;

[0021] If the initial standard value is in the interval [0, 1], then the calculated result is taken as the standard value X. norm,i If the initial standard value is less than 0, then it is assigned the value 0 as the standard value X. norm,i If the initial standard value is greater than 1, then it is assigned the value 1 as the standard value X. norm,i。

[0022] In one possible implementation, the standard value X for each of the coal seam parameters norm,i deviation i The set of calculation formulas is as follows:

[0023] ,

[0024] In the formula, i X is the standard value of any one of the coal seam parameters X, including gas pressure, permeability, gas content, Protodyakonov coefficient, ash content, or Langmuir pressure constant. norm,i The deviation, X norm,i This is the standard value. For X norm,i The average of the minimum and maximum values ​​of the corresponding coal seam parameters, X min,i For X norm,i The minimum value of the corresponding coal seam parameter, X max,i For X norm,i The maximum value of the corresponding coal seam parameter.

[0025] In one possible implementation, the confidence level calculation formula is: C i =1- i In the formula, C i The confidence level of any one of the coal seam parameters, including gas pressure, permeability, gas content, Protodyakonov coefficient, ash content, or Langmuir pressure constant. i C i The corresponding standard value X of the coal seam parameter norm,i The deviation.

[0026] In one possible implementation, the formula for calculating the grey relational degree is: R i = In the formula, R i ρ represents the grey relational degree, and ρ is the resolution coefficient.

[0027] In one possible implementation, the weighting coefficient W according to each of the coal seam parameters i The confidence level C i and the gray relational degree R i The formula for calculating the applicability index SI is as follows:

[0028] SI= In the formula, SI is the applicability index, and W i C represents the weighting coefficient. i For confidence level, R i This represents the grey relational degree.

[0029] In one possible implementation, the scheme for determining the borehole sealing technology includes:

[0030] Obtain the gas pressure, permeability, fracture development degree, and suitability index for the nitrogen injection suitability assessment;

[0031] Based on the gas pressure, the permeability, and the degree of fracture development, the sealing material is selected as follows: when the permeability is lower than a set threshold and the degree of fracture development is low, polyurethane foam is selected as the sealing material, with a sealing length greater than 10 meters; when the gas pressure is higher than 0.765 MPa or the coal seam is in a high-stress zone, high-strength cement grout is selected as the sealing material.

[0032] Determine the drilling layout parameters: Set the drilling depth to be between 50 meters and 100 meters, and the drilling spacing to be between 5 meters and 20 meters;

[0033] Inject the selected sealing material to perform the sealing operation;

[0034] Perform a pressure test to verify the seal: monitor the leakage rate and ensure that the leakage rate is less than 0.01 MPa / hour;

[0035] The sealing scheme is dynamically adjusted according to the degree of fissure development or the applicability index: if fissures are concentrated, a circumferential sealing layer is added; if the applicability index is greater than 0.8 and the gas pressure is less than or equal to 0.765 MPa, a high-efficiency sealing technology is preferred, including extending the sealing length to 15-20 meters; if the applicability index is greater than or equal to 0.7 and less than 0.8, a sealing scheme that balances cost and performance is preferred, including using a standard sealing length of 10-15 meters and using high-strength cement grout as the main sealing material.

[0036] In one possible implementation, the nitrogen injection pressure parameter matching analysis includes:

[0037] Based on the gas pressure, the permeability, and the Protodyakonov coefficient, the nitrogen injection pressure range was determined through numerical simulation.

[0038] During ground analysis and testing, the initial nitrogen injection pressure was set to 0.8~1.2 MPa, and the deformation rate of the coal body was monitored in real time. If the deformation rate was ≤5% and the gas pressure was >1 MPa, the initial nitrogen injection pressure was set to 1.5 MPa. If the deformation rate was >5%, the initial nitrogen injection pressure was reduced by 0.2 MPa.

[0039] In one possible implementation, the pulse period design of the pulsed nitrogen injection includes:

[0040] Based on the gas pressure in the nitrogen injection suitability assessment step, the initial nitrogen injection time and the stop injection time are set during numerical simulation, and the concentration of CH4 and N2 mixed gas is monitored in real time. If the CH4 concentration is <50% or the flow interruption lasts for >1 min, the nitrogen injection time is shortened and the stop injection time is extended. The process is iterated and optimized until the gas extraction purity and concentration reach a stable state and no longer increase, thus obtaining the pulse cycle.

[0041] One or more technical solutions provided in the embodiments of the present invention have at least the following technical effects or advantages:

[0042] The pre-injection design method for nitrogen displacement in low-permeability coal seams provided in this application first obtains the measured values ​​of six core parameters—gas pressure, permeability, gas content, Protodyakonov coefficient, ash content, and Langmuir pressure constant—simultaneously through in-situ coal seam testing and surface analysis. Based on these, the suitability index (SI) is calculated. The method intelligently determines whether to proceed to subsequent process design based on the SI value (SI>0.8 indicates high suitability, 0.7≤SI≤0.8 indicates moderate suitability, and SI<0.7 indicates inapplicability). For coal seams meeting the suitability standards, the pulse nitrogen injection process design and pressurization system construction are implemented simultaneously. In the process design phase, the sealing scheme, nitrogen injection pressure parameters, and pulse cycle are dynamically matched. The sealing scheme selects sealing materials based on gas pressure and fracture development. The nitrogen injection pressure is dynamically adjusted through numerical simulation combined with gas pressure thresholds. The pulse cycle is optimized iteratively through mixed gas concentration feedback to determine the nitrogen injection / stop time. In the pressurization system construction phase, six subsystems are integrated: gas-liquid separation, compressed air nitrogen generation, nitrogen storage and pressurization, nitrogen delivery, pulse control, and gas extraction. A central controller electrically connects the sensors and actuators of each subsystem, achieving closed-loop feedback and linkage control of nitrogen injection parameters and extraction data. Finally, numerical simulation is used to verify the design parameters and output the implementation plan.

[0043] By calculating the applicability index (SI) based on six dimensions including gas pressure and permeability, a standardized nitrogen injection feasibility assessment system is established, overcoming the problems of high misjudgment rate and poor adaptability caused by the reliance on experience-based judgment in existing technologies. A hierarchical decision-making mechanism based on the SI value (SI>0.8 / 0.7≤SI≤0.8 / SI<0.7) ensures that the nitrogen injection process is only applicable to qualified coal seams, avoiding the risk of ineffective nitrogen injection from the source, significantly improving the success rate of scheme implementation, thus solving the problem of misjudgment of applicability and enhancing the reliability of decision-making. The sealing scheme, nitrogen injection pressure matching, and pulse cycle design are integrated into a unified process chain. The sealing material is dynamically selected based on gas pressure and fracture development, the nitrogen injection pressure is adjusted in real time according to the gas pressure threshold and deformation rate, and the pulse cycle is continuously iterated through feedback from the mixed gas concentration. The multi-parameter linkage dynamic design mechanism solves the inefficiency problem caused by isolated process links in traditional methods, significantly improving the displacement effect and safety. By integrating various subsystems and deploying a central controller, a real-time feedback path for nitrogen injection parameters and extraction data is established. The closed-loop system achieves coordinated operation of nitrogen production, pressurization, pulse injection, and gas extraction, solving the problems of response lag and poor adaptability caused by independent equipment selection in existing systems. It is particularly suitable for the complex geological conditions of low-permeability coal seams, improving gas extraction efficiency while ensuring safety. Ultimately, the method in this application embodiment can improve the implementation efficiency of nitrogen injection displacement, reduce safety risks, and has good adaptability, capable of handling the complexity and variability of low-permeability coal seam environments. Attached Figure Description

[0044] To more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings used in the description of the embodiments of the present invention will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0045] Figure 1 A schematic diagram of the pre-injection design method for nitrogen displacement in low-permeability coal seams provided in the embodiments of this application;

[0046] Figure 2 A flowchart illustrating the applicability index (SI) calculation process provided in this application embodiment;

[0047] Figure 3 This is a schematic diagram of the pulse nitrogen injection booster system provided in an embodiment of this application.

[0048] Icons: 1-Gas-Water Ionization System; 11-Inlet Pipeline; 12-Pressure Gauge; 13-Inlet Valve; 14-Refrigerated Dryer; 15-Molecular Sieve Adsorption Tower; 16-Drain Valve; 17-Humidity Sensor; 2-Compressed Air Nitrogen Generation Subsystem; 21-Inlet Filter; 22-Three-Way Diverter; 23-Nitrogen Generator; 231-Inlet Valve; 232-Nitrogen Generator Tower; 233-Outlet Valve; 234-Exhaust Valve; 24-First Three-Way Combiner; 25-Nitrogen Purity Analyzer; 3-Nitrogen Storage and Pressurization Subsystem; 31-Three-Way Switching Valve; 32-Nitrogen Storage Device; 321-Isolation Valve; 322-Nitrogen Storage Tank; 323-Temperature Controller; 324-Second Pressure Sensor; 325-Temperature Sensor Sensor; 326-Spring valve; 33-Second three-way confluencer; 34-Intelligent booster module; 35-First pressure sensor; 4-Nitrogen delivery subsystem; 41-Flow regulating valve; 42-Variable diameter pipeline; 43-Pressure damper; 44-Flow meter; 5-Pulse nitrogen injection control module; 51-Pulse generator; 52-Pulse sensor; 53-Nitrogen injection pipeline; 54-Nitrogen injection nozzle; 6-Gas extraction subsystem; 61-Gas extraction pipeline; 62-Negative pressure valve; 63-Slag remover; 64-Gas concentration sensor; 65-Gas extraction pump; 66-Flow sensor; 7-Central controller; 8-Power module; 9-Coal seam; 10-Nitrogen injection borehole; 20-Extraction borehole. Detailed Implementation

[0049] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0050] In the description of the embodiments of the present invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., 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 the embodiments of the present invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the present invention. The terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance. Furthermore, the terms "installed," "connected," and "linked" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in the embodiments of the present invention according to the specific circumstances.

[0051] Please refer to Figure 1 As shown, this embodiment of the invention provides a pre-injection design method for nitrogen displacement in low-permeability coal seams, including:

[0052] Step A: Nitrogen Injection Suitability Assessment: Coal seam parameters, including gas pressure, permeability, gas content, Protodyakonov coefficient, ash content, and Langmuir pressure constant, are obtained through in-situ coal seam testing and surface analysis. The suitability index (SI) is calculated based on these parameters to assess nitrogen injection feasibility. The assessment criteria are: SI > 0.8 indicates high suitability, proceeding to pulsed nitrogen injection process design; 0.7 ≤ SI ≤ 0.8 indicates moderate suitability, also proceeding to pulsed nitrogen injection process design; SI < 0.7 indicates unsuitability, and pulsed nitrogen injection process design is terminated. This comprehensive assessment determines whether nitrogen injection displacement technology is suitable for low-permeability coal seams.

[0053] In-situ testing focuses on field data acquisition, while ground-based analysis and testing mainly consist of traditional nitrogen injection displacement tests and pulsed nitrogen injection displacement tests, used to simulate and verify the nitrogen injection effect.

[0054] Specifically, gas pressure is mainly obtained through on-site borehole pressure measurement in in-situ coal seam testing; permeability can be calculated on-site through water injection or gas injection methods in in-situ coal seam testing, and can also be verified by coal sample seepage experiments in ground analysis testing; gas content can be initially measured through on-site degassing methods in in-situ coal seam testing, and accurately determined by laboratory degassing experiments in ground analysis testing; Protodyakonov coefficient is usually determined through laboratory coal sample hardness tests in ground analysis testing; ash content is obtained through chemical composition analysis of coal samples in ground analysis testing; and Langmuir pressure constant is calculated through adsorption-desorption experiments (isothermal adsorption curve fitting) in ground analysis testing.

[0055] like Figure 2 As shown, the applicability index SI is calculated based on the measured values ​​of coal seam parameters, including:

[0056] Step A1: Collect measured values ​​of coal seam parameters, including gas pressure, permeability, gas content, Protodyakonov coefficient, ash content, and Langmuir pressure constant.

[0057] Step A2: Standardize the measured values ​​of each coal seam parameter to the interval [0, 1] to obtain the standard value X of each coal seam parameter. norm，i Where i=1,2,3,4,5,6, i=1 represents gas pressure, i=2 represents permeability, i=3 represents gas content, i=4 represents Protodyakonov coefficient, i=5 represents ash content, and i=6 represents Langmuir pressure constant.

[0058] Further, step A21: The standardized formula for the measured values ​​of each coal seam parameter is as follows:

[0059] = In the formula, Let X be the initial standard value of any one of the following coal seam parameters: gas pressure, permeability, gas content, Protodyakonov coefficient, ash content, or Langmuir pressure constant. i For X norm,i The corresponding measured value of the coal seam parameter, X min,i For X i The minimum value of the corresponding coal seam parameter, X max,i For X i The maximum value of the corresponding coal seam parameter. X min,i With X max,i The actual value has been given: gas pressure X min,1 It is 0.765 MPa, X max,1 1.187 MPa; Permeability X min,2 It is 2.883×10 -18 m 2 X max,2 It is 4.115×10 -18 m 2 Gas content X min,3 It is 10.63 m³ / t, X max,3 It is 13.01 m³ / t; Protodyakonov coefficient X min,4 X is 0.315. max,4 It is 0.695; ash content X min,5 It is 11.79%, X max,5 It is 16.81%; Langmuir pressure constant X min,6 0.838 MPa -1 Xmax,6 1.068 MPa -1 .

[0060] Step A22: If the initial standard value is in the interval [0, 1], then take the calculated result as the standard value X. norm,i If the initial standard value is less than 0, then assign it the value 0 as the standard value X. norm,i If the initial standard value is greater than 1, then assign it the value 1 as the standard value X. norm,i .

[0061] Step A3: Calculate the standard value X for each coal seam parameter. norm,i deviation i and confidence level C i .

[0062] Optionally, the standard value X for each coal seam parameter. norm,i deviation i The set of calculation formulas is as follows:

[0063] ,

[0064] In the formula, i X is the standard value of any one of the following coal seam parameters: gas pressure, permeability, gas content, Protodyakonov coefficient, ash content, or Langmuir pressure constant. norm,i The deviation, X norm,i This is the standard value. For X norm,i The average of the minimum and maximum values ​​of the corresponding coal seam parameters, X min,i For X norm,i The minimum value of the corresponding coal seam parameter, X max,i For X norm,i The maximum value of the corresponding coal seam parameter. Among them, That is, to set the standard value X of each coal seam parameter. norm,i and X ideal，i Establish a comparison sequence, and then use the corresponding X. norm,i Subtract X ideal，i .

[0065] The confidence level is calculated using the formula: C i =1- i In the formula, C i The confidence level is 0 to 1 for any one of the following coal seam parameters: gas pressure, permeability, gas content, Protodyakonov coefficient, ash content, or Langmuir pressure constant. i C i The standard value X of the corresponding coal seam parameter norm,iThe deviation.

[0066] Step A4: Calculate the deviation of all coal seam parameters i The minimum difference M = imin The maximum difference N= imax .

[0067] Step A5: Based on the deviation i The grey relational degree R is calculated using the minimum difference M and the maximum difference N. i .

[0068] Optionally, the formula for calculating grey relational degree is: R i = In the formula, R i ρ represents the grey relational degree, and ρ is the resolution coefficient, which takes a value of 0 to 1. For balance, the embodiment of this application takes a value of 0.5.

[0069] Step A6: Based on the weighting coefficient W for each coal seam parameter i Confidence level C i Grey relational degree R i Calculate the suitability index (SI).

[0070] Furthermore, the calculation formula is as follows:

[0071] SI= In the formula, SI is the applicability index, and W i C represents the weighting coefficient. i For confidence level, R i The weighting factor is gray relational analysis. Among them, the weighting factor W1 for gas pressure is 0.25, the weighting factor W2 for permeability is 0.20, the weighting factor W3 for gas content is 0.20, the weighting factor W4 for Protodyakonov coefficient is 0.30, the weighting factor W5 for ash content is 0.10, and the weighting factor W6 for Langmuir pressure constant is 0.05.

[0072] The embodiments of this application improve accuracy and quantify the evaluation method by calculating the applicability of coal seam parameters using confidence level and grey relational degree.

[0073] Of course, training machine learning models with data can also replace grey relational analysis in calculating the applicability index SI.

[0074] Step B: Pulse Nitrogen Injection Process Design: Determine the borehole sealing technology scheme (to ensure no leakage in the borehole), conduct nitrogen injection pressure parameter matching analysis (determine the nitrogen injection pressure, the injection time of pulse nitrogen injection, and the stop time), and design the pulse cycle of pulse nitrogen injection.

[0075] Drilling and sealing technology is fundamental to ensuring the efficiency and safety of nitrogen injection displacement.

[0076] The proposed borehole sealing technology scheme includes:

[0077] Step B1: Obtain gas pressure, permeability, fracture development degree, and suitability index for nitrogen injection suitability assessment. The fracture development degree is derived from ground analysis tests, such as CT scans.

[0078] Step B2: Based on gas pressure, permeability, and fracture development, select the sealing material: When permeability is below a set threshold and fracture development is low (e.g., by taking core samples from low-permeability coal seams for CT testing to obtain volumetric fracture density; a volumetric fracture density of less than 1% indicates low fracture development), select polyurethane foam as the sealing material, with a sealing length greater than 10 meters. Polyurethane foam is suitable for rapidly curing, low-permeability coal seams. When gas pressure is higher than 0.765 MPa or the coal seam is in a high-stress zone, i.e., the stress on the coal seam roof is greater than or equal to 16 MPa, select high-strength cement grout as the sealing material, with a compressive strength greater than 10 MPa.

[0079] Step B3: Determine the drilling layout parameters: Set the drilling depth to between 50 meters and 100 meters, and the drilling spacing to between 5 meters and 20 meters.

[0080] Step B4: Inject the selected sealing material to seal the hole.

[0081] Step B5: Perform a pressure test to verify the seal: monitor the leakage rate and ensure that the leakage rate is less than 0.01 MPa / hour.

[0082] Step B6: Dynamically adjust the sealing scheme based on the degree of fracture development or applicability index: If fractures are concentrated, add a circumferential sealing layer; if the applicability index is greater than 0.8 and the gas pressure is less than or equal to 0.765 MPa, prioritize high-efficiency sealing technology to enhance durability and maximize long-term benefits, including extending the sealing length to 15-20 meters, and considering the use of high-performance composite materials to enhance durability; if the applicability index is greater than or equal to 0.7 and less than 0.8, prioritize a sealing scheme that balances cost and performance, including using a standard sealing length of 10-15 meters, selecting high-strength cement grout with high cost-effectiveness as the main sealing material, and ensuring the unity of technical feasibility and economy.

[0083] Nitrogen injection pressure parameter matching analysis includes:

[0084] Step Ba: Based on gas pressure, permeability, and Protodyakonov coefficient, determine the nitrogen injection pressure range through numerical simulation. This numerical simulation can be a COMSOL numerical simulation. Empirical formulas can also be used in this numerical simulation.

[0085] Nitrogen injection pressure is higher than gas pressure but lower than the coal seam failure limit. Increased nitrogen injection pressure increases coal permeability and gas displacement efficiency.

[0086] Step Bb: During ground analysis and testing, the initial nitrogen injection pressure is set to 0.8~1.2 MPa, and the deformation rate of the coal body is monitored in real time. If the deformation rate is ≤5% and the gas pressure is >1 MPa, the initial nitrogen injection pressure is set to 1.5 MPa. If the deformation rate is >5%, the initial nitrogen injection pressure is reduced by 0.2 MPa. This deformation rate includes axial deformation and circumferential deformation.

[0087] The ratio of nitrogen injection time to timeout time within a pulse cycle affects coal body shrinkage and deformation, as well as the mixed gas flow rate. Longer nitrogen injection times significantly increase coal permeability (>20%~30%), but the flow interruption during the timeout phase requires re-injection of nitrogen. A higher ratio of nitrogen injection time to timeout time within a cycle results in greater shrinkage and deformation, and an increased mixed gas flow rate.

[0088] The pulse cycle design for pulsed nitrogen injection includes: based on the gas pressure in the above nitrogen injection suitability assessment steps, setting the initial nitrogen injection time and shutdown time during numerical simulation, and monitoring the mixed gas concentrations of CH4 and N2 in real time. If the CH4 concentration is <50% or the flow interruption lasts >1 min, shorten the nitrogen injection time and extend the shutdown time. This process is iteratively optimized until the gas extraction purity and concentration reach a stable state and no longer increase, indicating the best gas extraction effect, thus obtaining the pulse cycle. This determines the nitrogen injection time and shutdown time for pulsed nitrogen injection, and dynamically adjusts the pulsed nitrogen injection time and shutdown time based on the mixed gas flow rate and coal body deformation.

[0089] In step B of this application embodiment, during the design of the pulsed nitrogen injection process, the drilling layout and sealing material are determined based on the data from the nitrogen injection suitability assessment in step A. The nitrogen injection pressure, including the pulse cycle of the injection and pause times, is determined to form a preliminary scheme for the pulsed nitrogen injection process.

[0090] Step C: Design of the pulse nitrogen injection booster system: including:

[0091] Step C1: Construct a pulsed nitrogen injection booster system, such as Figure 3 As shown, the pulse nitrogen injection pressurization system includes: a gas-water ionization system 1, a compressed air nitrogen generation subsystem 2, a nitrogen storage and pressurization subsystem 3, a nitrogen delivery subsystem 4, a pulse nitrogen injection control module 5, a gas extraction subsystem 6, and a central controller 7.

[0092] The input of the gas-water ionization system 1 is connected to the external compressed air network via a pipeline, and its output is connected to the input of the compressed air nitrogen generation subsystem 2 via a pipeline. The output of the compressed air nitrogen generation subsystem 2 is connected to the input of the nitrogen storage and pressurization subsystem 3 via a pipeline. The output of the nitrogen storage and pressurization subsystem 3 is connected to the input of the nitrogen delivery subsystem 4 via a pipeline. The output of the nitrogen delivery subsystem 4 is connected to the input of the pulse nitrogen injection control module 5, and the output of the pulse nitrogen injection control module 5 is connected to the nitrogen injection borehole 10 of the coal seam 9. The input of the gas extraction subsystem 6 is connected to the extraction borehole 20 of the coal seam 9, and its output is connected to the emission subsystem.

[0093] The central controller 7 is electrically connected to the sensors and actuators of various subsystems, namely the gas-water ionization system 1, the compressed air nitrogen generation subsystem 2, the nitrogen storage and pressurization subsystem 3, the nitrogen delivery subsystem 4, the pulse nitrogen injection control module 5, and the gas extraction subsystem 6. It is used to receive gas concentration data from the gas extraction subsystem 6 and pulse nitrogen injection data from the pulse nitrogen injection control module 5 in real time, and dynamically adjust the nitrogen injection parameters to achieve closed-loop feedback linkage control.

[0094] The pulse nitrogen injection pressurization system provided in this embodiment first introduces compressed air from an external compressed air network into a gas-water ionization system 1 for water vapor separation to obtain dry compressed air. Subsequently, the dry compressed air enters a compressed air nitrogen generation subsystem 2, where it is converted into nitrogen gas meeting purity requirements through pressure swing adsorption. The generated nitrogen gas is then transported to a nitrogen storage and pressurization subsystem 3 for pressurization and storage to meet high-pressure nitrogen injection requirements. The high-pressure nitrogen gas output from the nitrogen storage and pressurization subsystem 3 is then transported to a pulse nitrogen injection control module 5 after its flow rate and pressure are regulated by a nitrogen gas delivery subsystem 4. The pulse nitrogen injection control module 5 generates periodic pressure fluctuations within the nitrogen injection borehole 10 through a specific driving mechanism, achieving pulsed nitrogen injection into the coal seam 9 and forcibly displacing adsorbed methane. Simultaneously, a gas extraction subsystem 6 establishes a negative pressure environment within an adjacent extraction borehole 20, extracting the desorbed methane gas and safely discharging it through an emission subsystem. During this process, the central controller 7, acting as the core control unit, dynamically adjusts the operating parameters of the gas-water ionization system 1, the compressed air nitrogen generation subsystem 2, the nitrogen storage and pressurization subsystem 3, the nitrogen delivery subsystem 4, and the pulse nitrogen injection control module 5 by receiving real-time gas concentration data from the gas extraction subsystem 6 and nitrogen injection parameters from the pulse nitrogen injection control module 5. This closed-loop feedback mechanism enables the nitrogen injection process to be adaptively optimized according to the gas extraction status of the coal seam 9, achieving efficient linkage control between nitrogen injection displacement and gas extraction. The device in this embodiment replaces traditional continuous nitrogen injection with pulse nitrogen injection mode, using intermittent high-pressure shock waves to disrupt the original structure of the coal seam 9, significantly expanding the nitrogen diffusion range and gas desorption efficiency, solving the problems of poor nitrogen injection displacement effect and low gas replacement rate in deep, low-permeability coal seams 9. The pre-positioned gas-water ionization system 1 removes moisture from the compressed air at the source, ensuring that dry nitrogen enters the equipment, effectively eliminating the risk of pipeline freezing and equipment corrosion caused by water vapor, improving the reliability of the system in the high-humidity underground environment, and reducing maintenance frequency. The integrated nitrogen storage and pressurization subsystem 3 and the compressed air nitrogen generation subsystem 2 work together to reduce pressure energy loss during the step-by-step nitrogen generation and pressurization process. The closed-loop feedback linkage mechanism constructed by the central controller 7 dynamically optimizes and adjusts the system by collecting gas concentration and nitrogen injection parameters in real time. This overcomes the response lag problem caused by the independent operation of nitrogen injection and extraction systems and reliance on manual monitoring in existing technologies. It significantly reduces the risk of preferential nitrogen flow along fractures and improves the safety and controllability of the displacement process and the overall engineering efficiency.

[0095] Continue to refer to Figure 3 As shown, the air-water ionization system 1 includes a refrigerated dryer 14, a molecular sieve adsorption tower 15, a drain valve 16, and a humidity sensor 17.

[0096] The input end of the refrigerated air dryer 14 is connected to an external compressed air network via a pipeline (this pipeline is the inlet pipeline 11, which is equipped with a pressure gauge 12 and an inlet valve 13), and the output end is connected to the input end of the molecular sieve adsorption tower 15 via a pipeline. Compressed air input from the external compressed air network enters the refrigerated air dryer 14 through a pipeline (connected via a flange interface). The refrigerated air dryer 14 initially cools the compressed air, condenses and separates moisture to obtain initially dry compressed air, with a processing capacity ≥10 m³ / min. The initially dry compressed air is then piped to the molecular sieve adsorption tower 15. The molecular sieve adsorption tower 15 uses activated molecular sieve material to further adsorb residual moisture and impurities to obtain dry compressed air.

[0097] The output end of the molecular sieve adsorption tower 15 is connected to the input end of the compressed air nitrogen generation subsystem 2 via a pipeline to deliver dry compressed air to the compressed air nitrogen generation subsystem 2. The molecular sieve adsorption tower 15 includes a regeneration heater (power 2-5kW), which is electrically connected to the central controller 7.

[0098] A drain valve 16 is installed on a pipe at the bottom of the molecular sieve adsorption tower 15. The outlet of the pipe is connected to an external drainage system to drain the water inside the molecular sieve adsorption tower 15.

[0099] A humidity sensor 17 is installed on the pipeline between the molecular sieve adsorption tower 15 and the compressed air nitrogen generation subsystem 2, and is electrically connected to the central controller 7. It is used to monitor moisture data in real time and feed it back to the central controller 7, enabling the central controller 7 to control the regeneration heater to optimize the adsorption process. All pipelines in the gas-water ionization system 1 are corrosion-resistant.

[0100] The gas-water ionization system 1 of this application embodiment dries externally input compressed air and outputs dried compressed air to the compressed air nitrogen generation subsystem 2. Through the dual drying mechanism of the refrigerated dryer 14 and the molecular sieve adsorption tower 15 in the gas-water ionization system 1, combined with real-time feedback from the humidity sensor 17 and closed-loop control of the regeneration heater, the problem of residual moisture caused by the high humidity environment underground is completely solved. This eliminates the risk of pipeline freezing, equipment corrosion, and reduced nitrogen generation efficiency caused by water vapor from the source, significantly improves the operational reliability of the system under high humidity conditions in deep coal seams, reduces maintenance frequency, and extends equipment life.

[0101] like Figure 3 As shown, the compressed air nitrogen generation subsystem 2 includes an air intake filter 21, a three-way distributor 22, a nitrogen generator 23, a first three-way combiner 24, and a nitrogen purity analyzer 25.

[0102] The output of the gas-water ionization system 1 is connected to the input of the inlet filter 21 via a pipeline. Specifically, the output of the molecular sieve adsorption tower 15 of the gas-water ionization system 1 is connected to the input of the inlet filter 21 via a pipeline.

[0103] The output of the intake filter 21 is connected to the first end of the three-way splitter 22 via a pipeline. The second and third ends of the three-way splitter 22 are respectively connected to a nitrogen generator 23 via pipelines. The outputs of the two nitrogen generators 23 are respectively connected to the second and third ends of the first three-way combiner 24, and are both electrically connected to the central controller 7.

[0104] like Figure 3 As shown, the nitrogen generator 23 includes an inlet valve 231, a nitrogen generator tower 232, an outlet valve 233, and an exhaust valve 234. The second and third ends of the three-way distributor 22 are respectively connected to the input end of one nitrogen generator tower 232 via pipelines, and an inlet valve 231 is installed on these pipelines. The output ends of the two nitrogen generator towers 232 are respectively connected to the second and third ends of the first three-way combiner 24 via pipelines, and an outlet valve 233 is installed on these pipelines. Both the inlet valve 231 and the outlet valve 233 are solenoid valves and are electrically connected to the central controller 7. An exhaust valve 234 is installed at the bottom of each nitrogen generator tower 232.

[0105] The first end of the first three-way confluencer 24 is connected to the input end of the nitrogen storage and booster subsystem 3 via a pipeline, on which a nitrogen purity analyzer 25 is installed. The nitrogen purity analyzer 25 is electrically connected to the central controller 7.

[0106] Two nitrogen generators 232 form a dual-tower structure, each containing activated carbon or CMS adsorbent. Dry compressed air enters the inlet filter 21 from the gas-water ionization system 1 via a pipeline, then connects to the input end of the nitrogen generator 232. The inlet valve 231 and outlet valve 233 are electrically connected to the central controller 7 via control lines to achieve adsorption / desorption switching. A nitrogen purity analyzer feeds back the nitrogen concentration to the central controller 7 via a signal line. The compressed air nitrogen generator subsystem 2, by inputting dry compressed air, outputs high-purity nitrogen to the nitrogen storage and pressurization subsystem 3, ensuring that the nitrogen generation process is free from water vapor interference. The compressed air nitrogen generator subsystem 2 employs a parallel dual nitrogen generator 23, a three-way split / combination structure, and a nitrogen purity analyzer 25 to achieve redundant backup and real-time monitoring of the nitrogen generation process. The dual-tower alternating adsorption / desorption ensures continuous nitrogen production. The purity analysis device feeds back data to the central controller 7 to dynamically optimize nitrogen production parameters, ensuring that the purity of the output nitrogen gas is stable and meets the standard (≥99.5%), avoiding the reduction in gas replacement efficiency due to impurity of nitrogen gas, thereby improving the displacement effect.

[0107] like Figure 3 As shown, the nitrogen storage and boosting subsystem 3 includes a three-way switching valve 31, a nitrogen storage device 32, a second three-way confluencer 33, an intelligent boosting module 34, and a first pressure sensor 35.

[0108] The output end of the compressed air nitrogen generator subsystem 2 is connected to the first end of the three-way switching valve 31 via a pipeline. Specifically, the first end of the first three-way confluencer 24 of the compressed air nitrogen generator subsystem 2 is connected to the first end of the three-way switching valve 31 via a pipeline.

[0109] The second and third ends of the three-way switching valve 31 are respectively connected to a nitrogen storage device 32 via pipelines. The output ends of the two nitrogen storage devices 32 are respectively connected to the second and third ends of the second three-way confluencer 33 via pipelines, and are both electrically connected to the central controller 7.

[0110] like Figure 3 As shown, the nitrogen storage device 32 includes an isolation valve 321, a nitrogen storage tank 322, a temperature controller 323, a second pressure sensor 324, a temperature sensor 325, and a spring valve 326. The second and third ends of a three-way switching valve 31 are respectively connected to the input end of one nitrogen storage tank 322 via pipelines, and an isolation valve 321 is installed on these pipelines. The output ends of the two nitrogen storage tanks 322 are respectively connected to the second and third ends of a second three-way confluencer 33 via pipelines. The temperature controller 323, the second pressure sensor 324, the temperature sensor 325, and the spring valve 326 are sequentially installed from bottom to top on the pipe body of the nitrogen storage tank 322. The spring valve 326 is installed at the vent port at the top of each nitrogen storage tank 322 to automatically release overpressure. The internal volume of each nitrogen storage tank 322 is approximately 1-5 m³, and its pressure resistance is ≥10 MPa.

[0111] The isolation valve 321, temperature controller 323, second pressure sensor 324, and temperature sensor 325 are all electrically connected to the central controller 7 via signal lines. The first end of the second three-way confluencer 33 is connected to the input end of the intelligent booster module 34 via a pipeline.

[0112] The output of the intelligent booster module 34 is connected to the nitrogen delivery subsystem 4 via a pipeline and is electrically connected to the central controller 7. The intelligent booster module 34 includes a piston or diaphragm booster pump (power 5-15kW) and a built-in buffer flow stabilizing valve (controls pressure fluctuations <±0.2MPa).

[0113] The first pressure sensor 35 is located on the pipeline between the output end of the intelligent booster module 34 and the nitrogen delivery subsystem 4, and is electrically connected to the central controller 7.

[0114] Nitrogen gas enters two parallel pipelines (flange connections) through the second and third ends of a three-way switching valve 31, leading to isolation valves 321 of the two nitrogen storage devices 32, and then to the input ends (bottom flange interfaces) at the bottom of the two nitrogen storage tanks 322. The output pipelines (flange connections) at the top of the two nitrogen storage tanks 322 are merged through a second three-way confluencer 33 and lead to the input end of the intelligent booster module 34. The intelligent booster module 34 has a built-in booster pump and a buffer flow stabilizing valve (adjustable type, installed inside the booster pump output end). The output nitrogen gas is pressurized by the booster pump inside the intelligent booster module 34 and then output as stable high-pressure nitrogen gas through the buffer flow stabilizing valve. The central controller 7 controls the isolation valve 321 to achieve alternating operation of the two nitrogen storage tanks 322 (i.e., when one nitrogen storage tank 322 is pressurized, the other nitrogen storage tank 322 is pre-charged). The low-pressure nitrogen gas input into the compressed air nitrogen generation subsystem 2 is pressurized by the nitrogen storage and pressurization subsystem 3 and output as stable high-pressure nitrogen gas to the nitrogen delivery subsystem 4 to ensure continuous supply.

[0115] The redundant design of the dual nitrogen storage tanks 322 ensures continuous nitrogen injection through alternating pressurization of the two tanks, while the buffer flow stabilizing valve eliminates pressure fluctuations. Compared to existing step-by-step pressurization, the nitrogen storage pressurization subsystem 3 of this application reduces energy consumption and extends equipment life.

[0116] Continue to refer to Figure 3 As shown, the nitrogen delivery subsystem 4 includes a flow regulating valve 41, a variable diameter pipeline 42, a pressure damper 43, and a flow meter 44.

[0117] The output of the nitrogen storage boosting subsystem 3 is connected to the input of the variable diameter pipeline 42 via a pipeline, and a flow regulating valve 41 is installed on this pipeline. Specifically, the output of the intelligent boosting module 34 of the nitrogen storage boosting subsystem 3 is connected to the input of the variable diameter pipeline 42 via a pipeline. The flow regulating valve 41 is a solenoid valve to control the flow rate.

[0118] The diameter of the variable-diameter pipe 42 gradually decreases along the direction of fluid flow (larger inlet, smaller outlet), and its output end is connected to the input end of the pressure damper 43. The variable-diameter pipe 42 can achieve constant flow delivery.

[0119] The output end of the pressure damper 43 is connected to the pulse nitrogen injection control module 5 through a pipeline, and a flow meter 44 is installed on the pipeline.

[0120] Both the flow regulating valve 41 and the flow meter 44 are electrically connected to the central controller 7.

[0121] The high-pressure nitrogen output from the nitrogen storage and pressurization subsystem 3 is regulated by the flow regulating valve 41 and then input to the input end of the variable diameter pipeline 42. The output end of the variable diameter pipeline 42 is connected to the pressure damper 43 to prevent vibration transmission. The flow meter 44 measures the flow rate and feeds it back to the central controller 7 to ensure that the nitrogen is subsequently delivered uniformly to the nitrogen injection borehole 10. The nitrogen delivery subsystem 4 optimizes the delivery stability of high-pressure nitrogen through the synergistic effect of the variable diameter pipeline 42 and the pressure damper 43. The variable diameter pipeline 42 achieves constant flow delivery, the pressure damper 43 absorbs the pressure fluctuations caused by pulsed nitrogen injection, and the flow meter 44 feeds back data to the central controller 7 in real time to precisely adjust the flow regulating valve 41, ensuring that the nitrogen is injected into the coal seam 9 at a uniform flow rate, avoiding secondary damage to the coal seam 9 structure caused by pressure fluctuations, and enhancing the controllability of the displacement process.

[0122] like Figure 3 As shown, the pulse nitrogen injection control module 5 includes a pulse generator 51, a pulse sensor 52, and a nitrogen injection nozzle 54. The pulse generator 51 can be an adjustable pulse generator 51, a solenoid valve pulse device, etc. The adjustable pulse generator 51 has a built-in generator for higher precision and supports fine adjustment. The adjustable pulse generator 51 is an electronic control device, supporting frequencies of 0.1-5Hz and amplitudes of 3-10MPa, and includes a pulse valve and drive circuitry.

[0123] The input end of the pulse generator 51 is connected to the nitrogen delivery subsystem 4 via a pipeline (specifically, the input end of the pulse generator 51 is connected to the output end of the shock absorber of the nitrogen delivery subsystem 4 via a pipeline), and the output end is connected to the first end of the nitrogen injection pipeline 53 and electrically connected to the central controller 7, thereby generating intermittent pressure waves through the drive circuit.

[0124] A nitrogen injection nozzle 54 is installed at the second end of the nitrogen injection pipeline 53 and extends into the nitrogen injection borehole 10. The nitrogen injection nozzle 54 is a pressure-resistant nozzle.

[0125] The pulse sensor 52 is installed on the nitrogen injection line 53 and electrically connected to the central controller 7 to monitor the waveform in real time and feed it back to the central controller 7 to dynamically optimize the displacement process.

[0126] Nitrogen gas output from nitrogen delivery subsystem 4 enters the input terminal of pulse generator 51 through a pipeline. The pulse valve of pulse generator 51 generates intermittent pressure waves. The output terminal of pulse generator 51 is connected to nitrogen injection nozzle 54 via nitrogen injection pipeline 53. Nitrogen injection nozzle 54 directly injects nitrogen gas into nitrogen injection borehole 10 of coal seam 9. The drive circuit of pulse generator 51 and pulse sensor 52 are electrically connected to central controller 7 via signal lines to achieve dynamic parameter adjustment, input stable nitrogen gas, output pulsed nitrogen gas to coal seam 9, and provide feedback data to optimize displacement.

[0127] The pulsed nitrogen injection module in this embodiment forces gas desorption through a pulsed nitrogen injection mechanism, expanding the diffusion range and overcoming the drawback of low replacement rate in low-permeability coal seams, thus significantly improving replacement efficiency. The linkage control between pulsed nitrogen injection and closed-loop feedback can dynamically adjust pulse parameters according to gas concentration, achieving adaptive displacement.

[0128] Reference Figure 3 As shown, the gas extraction subsystem 6 includes a negative pressure valve 62, a slag remover 63, a gas concentration sensor 64, a gas extraction pump 65, and a flow sensor 66.

[0129] The first end of the gas extraction pipeline 61 extends into the extraction borehole 20 of the coal seam 9, and the second end is connected to the input end of the slag remover 63. A negative pressure valve 62 is installed on the pipeline.

[0130] The output of the slag remover 63 is connected to the gas extraction pump 65 via a pipeline, on which a gas concentration sensor 64 is installed. The slag remover 63 can be a hydrocyclone slag remover to separate coal slag and dust. The gas concentration sensor 64 can be a CH4 / N2 concentration sensor, an online gas analyzer, to monitor gas composition. The output of the gas extraction pump 65 is connected to the first end of the gas discharge pipeline via a pipeline. The gas extraction pump 65 is a centrifugal pump. A flow sensor 66 is installed on the gas discharge pipeline.

[0131] The negative pressure valve 62, the gas extraction pump 65, the gas concentration sensor 64, and the flow sensor 66 are all electrically connected to the central controller 7. The gas concentration sensor 64 and the flow sensor 66 monitor the gas concentration and flow data in real time and feed them back to the central controller 7. The gas extraction pump 65 adjusts its power based on the feedback data to respond to the nitrogen injection process and prevent nitrogen gas leakage.

[0132] The gas extraction subsystem 6 of this application integrates a slag remover 63, a gas concentration sensor 64, and a flow sensor 66 to achieve multi-dimensional monitoring and coordinated control of the extraction process. The slag remover 63 pre-filters coal slag dust to ensure sensor accuracy; gas concentration and flow data are fed back to the central controller 7 in real time, driving the gas extraction pump 65 to dynamically adjust its power in response to the nitrogen injection pulse cycle, effectively suppressing nitrogen gas leakage and maintaining stable negative pressure during extraction, thus improving the purity and safety of gas recovery. It can achieve negative pressure regulation, operate in parallel with nitrogen injection, and feed back concentration data to the central controller 7, forming a closed loop.

[0133] Furthermore, the central controller 7 includes a main control unit, a communication module, and an alarm. The main control unit is an industrial computer equipped with a CPU, memory, and I / O interfaces.

[0134] The sensors of the gas-water ionization system 1, compressed air nitrogen generation subsystem 2, nitrogen storage and pressurization subsystem 3, nitrogen delivery subsystem 4, pulse nitrogen injection control module 5, and gas extraction subsystem 6 are electrically connected to the I / O interface of the main control unit. Various valves are electrically connected to the output interface of the main control unit, forming a closed-loop regulation (the connection lines between all sensors, valves, and the central controller 7 are omitted in the diagram). The main control unit analyzes data in real time and generates operation reports. The communication module supports remote monitoring; as the core, it receives all data, controls the linkage of each subsystem, and achieves adaptive optimization. The alarm is activated in case of an anomaly to stop system operation.

[0135] The central controller 7 integrates sensor data from various subsystems (such as humidity, purity, pressure, and concentration) through the main control unit, and combines this with remote monitoring via the communication module and the automatic emergency stop function of the alarm to construct a closed-loop control hub for the entire system. It generates real-time operation reports and dynamically adjusts valves, pump groups, and pulse parameters, eliminating the lag in manual monitoring and ensuring a nitrogen injection-extraction coordinated response time of ≤1 second, significantly reducing the risk of nitrogen gas channeling by up to 40%.

[0136] The central controller 7 also includes a display screen and an operation panel, which are touch screens used for parameter setting and report display.

[0137] like Figure 3 As shown, the pulse nitrogen injection booster system also includes a power module 8, which is an explosion-proof UPS unit providing intrinsically safe power protection to meet the explosion-proof requirements of underground coal mines. It outputs DC 24V / AC 220V and is electrically connected to the gas-water ionization system 1, the compressed air nitrogen generation subsystem 2, the nitrogen storage and booster subsystem 3, the nitrogen delivery subsystem 4, the pulse nitrogen injection control module 5, the gas extraction subsystem 6, and the central controller 7. This allows for unified power supply to all subsystems and the central controller 7. Power is distributed to the central controller 7 and each subsystem via a junction box or bus cable, ensuring stable system operation and avoiding interference caused by distributed power supplies. The bus cable is flame-retardant and explosion-proof, with a length matching the signal cable, and uses a waterproof socket for the interface. The power module 8 has built-in overload protection and grounding to ensure system stability (based on equipment load distribution).

[0138] The control method for the pulse nitrogen injection booster system provided in this application embodiment includes the following steps:

[0139] Step 0: System Initialization and Security Confirmation

[0140] Power module 8 is connected to supply power to the main control unit. The main control unit performs a self-test of the CPU, memory, and I / O interfaces to confirm no faults. A safety verification procedure is initiated via the operation panel: the main control unit sends signals to all sensors to check the equipment grounding resistance (ensuring <4Ω, feedback is obtained through a grounding resistance detector). Pipeline airtightness is checked (a pressure test is performed on the entire system pipeline, including the inlet valve 13 from the gas-water ionization system 1 to the negative pressure valve 62 of the gas extraction subsystem 6, ensuring no leaks). The nitrogen injection borehole 10 and extraction borehole 20 are positioned (manual verification or remote confirmation via the communication module confirms correct borehole connection). The display shows the inspection results; if an abnormality is detected, the alarm is activated (audible / visual alarm), and the system pauses startup.

[0141] Step 1: Turn on the compressed air pipeline and start the air-water ionization system 1 to dry the compressed air.

[0142] The main control unit opens the external compressed air pipeline valve (external access) via a signal line, allowing compressed air to enter the refrigerated dryer 14 (connected via a flange interface). The refrigerated dryer 14 is started, cooling and condensing the compressed air to separate moisture, resulting in initially dry compressed air. Moisture is discharged through the drain valve 16 (which opens automatically). The initially dry compressed air is connected from the output of the refrigerated dryer 14 to the input of the molecular sieve adsorption tower 15. The molecular sieve adsorption tower 15 is started, further adsorbing residual moisture and impurities from the initially dry compressed air to obtain dry compressed air. Pressure gauge 12 monitors the inlet pressure, and humidity sensor 17 provides real-time data feedback to the main control unit. If the humidity exceeds the limit, an alarm is activated. The display shows the humidity and pressure values, and the main control unit adjusts the regeneration heater to optimize adsorption.

[0143] Step 2: Start the compressed air nitrogen generation subsystem 2. Dry compressed air is input into the compressed air nitrogen generation subsystem 2 to generate nitrogen, which is then output to the nitrogen storage and pressurization subsystem 3.

[0144] Dry compressed air enters the inlet filter 21 from the output pipe of the molecular sieve adsorption tower 15 of the gas-water ionization system 1. After filtering impurities, it is fed into the first section (flange connection) of the three-way distributor 22. The second and third ends of the three-way distributor 22 split the air into two inlet valves 231, and then into two nitrogen generating towers 232 respectively. The adsorbent layers inside the two nitrogen generating towers 232 are arranged vertically. The output pipes at the top of the towers pass through the outlet valve 233 and then through the first three-way confluencer 24 to merge into a single output pipe. Both exhaust valves 234 are connected to the external exhaust system (for desorption exhaust gas discharge). The central controller 7 alternately opens the inlet valves 231 and outlet valves 233 of the two nitrogen generating units 23 to control nitrogen production (for example, the left inlet valve 231 and outlet valve 233 are open during adsorption, and switched during desorption). A nitrogen purity analyzer monitors the output purity, and the data is fed back to the main control unit. If it is lower than the threshold, the inlet valve 231 and outlet valve 233 are adjusted. The display screen shows the nitrogen production and purity in real time.

[0145] Step 3: Nitrogen is pre-charged into the nitrogen storage and pressurization subsystem 3, and then high-pressure nitrogen is output to the nitrogen delivery subsystem 4.

[0146] Nitrogen gas enters the three-way switching valve 31 from the output pipe of the compressed air nitrogen generator subsystem 2. The main control unit of the central controller 7 controls the two isolation valves 321 to work alternately so that nitrogen gas alternately fills the two nitrogen storage tanks 322 (for example, when pre-filling the left nitrogen storage tank 322, the left isolation valve 321 is opened to switch to the left branch; after it is full, it switches to the right nitrogen generator 23), ensuring redundancy and continuity of one tank pressurization and one tank pre-filling. During pre-filling, the left nitrogen generator tank is first filled to the set pressure (monitored by the level gauge). After the left nitrogen generator tank is full, it switches to the right nitrogen generator tank for pre-filling. The booster pump in the intelligent booster module 34 is started, boosting nitrogen gas and outputting it through the buffer flow stabilizing valve. The second pressure sensor 324 and the spring valve 326 monitor the process. If overpressure occurs, the spring valve 326 automatically releases; the data is fed back to the main control unit. The display screen shows the tank pressure and temperature, realizing dual-tank redundancy (one tank pressurization, one tank pre-filling).

[0147] Step 4: The high-pressure nitrogen gas flows through the gas delivery subsystem for constant flow delivery and vibration reduction, and then pulse nitrogen injection is performed through the pulse nitrogen injection module to the nitrogen injection borehole 10.

[0148] High-pressure nitrogen gas is output from the nitrogen storage and booster subsystem 3 and enters the variable diameter pipeline 42. The flow rate is controlled by the flow regulating valve 41, and the vibration damper reduces vibration. The flow meter 44 monitors and feeds back to the main control unit. Nitrogen gas enters the input terminal of the pulse generator 51, activating the drive circuit and pulse valve to generate pulses. The pulsed nitrogen gas is injected into the nitrogen injection borehole 10 of the coal seam 9 through the nitrogen injection nozzle 54, and the pulse sensor 52 monitors the waveform feedback. The main control unit starts according to the initial parameters, and the display screen shows the injection status.

[0149] Step 5: Start the gas extraction subsystem 6 to perform gas extraction.

[0150] The negative pressure valve 62 is activated, and the input end of the extraction borehole 20 is connected to the slag remover 63, which separates the coal slag. The gas extraction pump 65 is started, and the extracted gas is pumped out to the outside for discharge. A concentration sensor (installed in the pipeline before the pump) monitors the CH4 / N2 composition, and a flow sensor 66 monitors the extraction rate, feeding back to the main control unit. The display screen shows the concentration and flow rate; if any abnormality is detected, the alarm is activated.

[0151] Step 6: The central controller 7 monitors system parameters in real time, optimizes control in real time and generates reports. If an abnormality occurs, the control system stops working.

[0152] The main control unit of the central controller 7 collects data from all sensors via I / O interfaces, including humidity sensor 17, temperature sensor 325, first pressure sensor 35, gas concentration sensor 64, pulse sensor 52, and flow sensor 66. The central controller 7's display screen shows parameters in real time, and its communication module can optionally transmit data remotely.

[0153] The central controller 7's main control unit analyzes data (increasing pulse amplitude if concentration is low), dynamically adjusts the valves of each subsystem, and regulates the drive circuit of pulse generator 51 and the power of the extraction pump. It generates an operation report (including parameter logs) and outputs it to the display screen.

[0154] If the concentration falls below the threshold or is abnormal (e.g., excessive pressure), the main control unit of the central controller 7 triggers the alarm, closes all valves (inlet valve 231, negative pressure valve 62, etc.) and pumps (booster pump, gas extraction pump 65). The pulse generator 51 stops, and a fault report is generated. The display shows the reason for the stop.

[0155] The pulse nitrogen injection booster system of this application embodiment adopts a combination of sensor technology and computer, with full closed-loop control and real-time display of engineering status.

[0156] Step C2: The nitrogen injection pressure parameters are transmitted to the nitrogen storage pressurization subsystem. Specifically, the nitrogen injection pressure data is transmitted to the intelligent pressurization module of the nitrogen storage pressurization subsystem. The pulse period, including the nitrogen injection time and the stop time, is input to the pulse nitrogen injection control module. Specifically, the pulse period is input to the pulse generator of the pulse nitrogen injection control module. The above modules are connected through a data interface: the test data for nitrogen injection suitability assessment is input into the nitrogen injection process design, and the process parameters guide the design of the pulse nitrogen injection pressurization system, forming a feedback loop optimization.

[0157] Step D: Verify the design parameters through numerical simulation and output an implementation plan report containing construction details. This involves generating a comprehensive implementation plan report for nitrogen injection displacement technology in low-permeability coal seams. The report details coal seam parameter data based on nitrogen injection suitability assessment and the calculated suitability index (SI). It clarifies the selection and implementation details of borehole sealing technology (including sealing material selection, sealing length, and nitrogen injection pressure), lists optimized parameters such as on-site nitrogen injection pressure, pulse nitrogen injection time, and shutdown time determined by parameter matching analysis, and determines the configuration and integrated optimization scheme of the pulse nitrogen injection booster system. The report includes simulation results and on-site test data from the verification phase for use in on-site nitrogen injection.

[0158] The pre-injection design method for nitrogen displacement in low-permeability coal seams provided in this application first obtains the measured values ​​of six core parameters—gas pressure, permeability, gas content, Protodyakonov coefficient, ash content, and Langmuir pressure constant—simultaneously through in-situ coal seam testing and surface analysis. Based on these, the suitability index (SI) is calculated. The method intelligently determines whether to proceed to subsequent process design based on the SI value (SI>0.8 indicates high suitability, 0.7≤SI≤0.8 indicates moderate suitability, and SI<0.7 indicates inapplicability). For coal seams meeting the suitability standards, the pulse nitrogen injection process design and pressurization system construction are implemented simultaneously. In the process design phase, the sealing scheme, nitrogen injection pressure parameters, and pulse cycle are dynamically matched. The sealing scheme selects sealing materials based on gas pressure and fracture development. The nitrogen injection pressure is dynamically adjusted through numerical simulation combined with gas pressure thresholds. The pulse cycle is optimized iteratively through mixed gas concentration feedback to determine the nitrogen injection / stop time. In the pressurization system construction phase, six subsystems are integrated: gas-liquid separation, compressed air nitrogen generation, nitrogen storage and pressurization, nitrogen delivery, pulse control, and gas extraction. A central controller electrically connects the sensors and actuators of each subsystem, achieving closed-loop feedback and linkage control of nitrogen injection parameters and extraction data. Finally, numerical simulation is used to verify the design parameters and output the implementation plan.

[0159] By calculating the applicability index (SI) based on six dimensions including gas pressure and permeability, a standardized nitrogen injection feasibility assessment system is established, overcoming the problems of high misjudgment rate and poor adaptability caused by the reliance on experience-based judgment in existing technologies. A hierarchical decision-making mechanism based on the SI value (SI>0.8 / 0.7≤SI≤0.8 / SI<0.7) ensures that the nitrogen injection process is only applicable to qualified coal seams, avoiding the risk of ineffective nitrogen injection from the source, significantly improving the success rate of scheme implementation, thus solving the problem of misjudgment of applicability and enhancing the reliability of decision-making. The sealing scheme, nitrogen injection pressure matching, and pulse cycle design are integrated into a unified process chain. The sealing material is dynamically selected based on gas pressure and fracture development, the nitrogen injection pressure is adjusted in real time according to the gas pressure threshold and deformation rate, and the pulse cycle is continuously iterated through feedback from the mixed gas concentration. The multi-parameter linkage dynamic design mechanism solves the inefficiency problem caused by isolated process links in traditional methods, significantly improving the displacement effect and safety. By integrating various subsystems and deploying a central controller, a real-time feedback path for nitrogen injection parameters and extraction data is established. The closed-loop system achieves coordinated operation of nitrogen production, pressurization, pulse injection, and gas extraction, solving the problems of response lag and poor adaptability caused by independent equipment selection in existing systems. It is particularly suitable for the complex geological conditions of low-permeability coal seams, improving gas extraction efficiency while ensuring safety. Ultimately, the method in this application embodiment can improve the implementation efficiency of nitrogen injection displacement, reduce safety risks, and has good adaptability, capable of handling the complexity and variability of low-permeability coal seam environments.

[0160] The method provided in this application divides the pre-injection design into three parts: nitrogen injection suitability assessment, pulse nitrogen injection process design, and pulse nitrogen injection pressurization system design. This achieves comprehensive quantitative evaluation, process optimization, and system integration, overcoming the fragmentation and experience-dependent shortcomings of existing technologies. The nitrogen injection suitability assessment improves the accuracy of suitability judgment and avoids ineffective nitrogen injection; the pulse nitrogen injection process design reduces safety risks and resource waste through parameter simulation; and the pulse nitrogen injection pressurization system design ensures system coordination and improves overall efficiency. Compared with existing technologies, this invention can shorten the design cycle, increase gas extraction rate, adapt to complex low-permeability coal seams, and meet the needs of future intelligent mining. Compared with existing technologies, this invention emphasizes the integration of in-situ and ground testing, the combination of parameter matching analysis and the pulse nitrogen injection pressurization system, and the linkage between nitrogen production, extraction, and monitoring, thereby improving suitability accuracy, process efficiency, and system stability, increasing the overall gas extraction rate, and making it suitable for low-permeability coal seam environments.

[0161] The various embodiments in this specification are described in a progressive manner. For the same or similar parts between the various embodiments, please refer to each other. Each embodiment focuses on describing the differences from other embodiments.

[0162] The above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit this application. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of this application.

Claims

1. A pre-injection design method for nitrogen displacement in low-permeability coal seams, characterized in that, include: Nitrogen injection suitability assessment: Coal seam parameters, including gas pressure, permeability, gas content, Protodyakonov coefficient, ash content, and Langmuir pressure constant, are obtained through in-situ coal seam testing and surface analysis. A suitability index (SI) is calculated based on these parameters to assess nitrogen injection feasibility. The assessment criteria are as follows: SI > 0.8 indicates high suitability, proceeding to pulsed nitrogen injection process design; 0.7 ≤ SI ≤ 0.8 indicates moderate suitability, proceeding to pulsed nitrogen injection process design; SI < 0.7 indicates unsuitability, terminating the pulsed nitrogen injection process design. Pulse nitrogen injection process design: determine the drilling and sealing technology scheme, analyze the matching of nitrogen injection pressure parameters, and design the pulse cycle of pulse nitrogen injection; Design of the pulse nitrogen injection booster system: This includes the construction of the pulse nitrogen injection booster system: the input end of the gas-water ionization system is connected to the external compressed air pipeline network, and the output end is connected to the input end of the compressed air nitrogen generation subsystem. The output end of the compressed air nitrogen generation subsystem is connected to the input end of the nitrogen storage booster subsystem. The output end of the nitrogen storage booster subsystem is connected to the input end of the nitrogen delivery subsystem. The output end of the nitrogen delivery subsystem is connected to the input end of the pulse nitrogen injection control module. The output end of the pulse nitrogen injection control module is connected to the nitrogen injection borehole in the coal seam. The input end of the gas extraction subsystem is connected to the extraction borehole in the coal seam, and the output end is connected to the emission subsystem. The central controller is electrically connected to the sensors and actuators of each subsystem. The nitrogen injection pressure parameters are transmitted to the nitrogen storage booster subsystem, and the pulse period is input to the pulse nitrogen injection control module; The design parameters are verified through numerical simulation, and an implementation plan report containing construction details is output.

2. The pre-injection design method for nitrogen displacement in low-permeability coal seams according to claim 1, characterized in that, The calculation of the applicability index SI based on the measured values ​​of coal seam parameters includes: The measured values ​​of the coal seam parameters are collected, including gas pressure, permeability, gas content, Protodyakonov coefficient, ash content, and Langmuir pressure constant. The measured values ​​of each coal seam parameter were standardized to the interval [0, 1] to obtain the standard value X of each coal seam parameter. norm，i Where i = 1, 2, 3, 4, 5, 6, i = 1 represents gas pressure, i = 2 represents permeability, i = 3 represents gas content, i = 4 represents Protodyakonov coefficient, i = 5 represents ash content, and i = 6 represents Langmuir pressure constant. Calculate the standard value X for each of the coal seam parameters. norm,i deviation i and confidence level C i ; Calculate the deviation Δ of all coal seam parameters i The minimum difference M = △ imin The maximum difference N = △ imax ; According to the deviation i The grey relational degree R is calculated using the minimum difference M and the maximum difference N. i ; According to the weighting coefficient W for each of the coal seam parameters i The confidence level C i And the gray relational degree R i Calculate the applicability index SI.

3. The pre-injection design method for nitrogen displacement in low-permeability coal seams according to claim 2, characterized in that, The standardized formula for the measured values ​​of each of the coal seam parameters is as follows: = In the formula, X is the initial standard value of any one of the coal seam parameters, including gas pressure, permeability, gas content, Protodyakonov coefficient, ash content, or Langmuir pressure constant. i For X norm,i The corresponding measured value of the coal seam parameter, X min,i For X i The minimum value of the corresponding coal seam parameter, X max,i For X i The maximum value of the corresponding coal seam parameter; If the initial standard value is in the interval [0, 1], then the calculated result is taken as the standard value X. norm,i If the initial standard value is less than 0, then it is assigned the value 0 as the standard value X. norm,i If the initial standard value is greater than 1, then it is assigned the value 1 as the standard value X. norm,i。 4. The pre-injection design method for nitrogen displacement in low-permeability coal seams according to claim 2, characterized in that, The standard value X for each of the coal seam parameters norm,i deviation i The set of calculation formulas is as follows: ， In the formula, i X is the standard value of any one of the coal seam parameters X, including gas pressure, permeability, gas content, Protodyakonov coefficient, ash content, or Langmuir pressure constant. norm,i The deviation, X norm,i This is the standard value. For X norm,i The average of the minimum and maximum values ​​of the corresponding coal seam parameters, X min,i For X norm,i The minimum value of the corresponding coal seam parameter, X max,i For X norm,i The maximum value of the corresponding coal seam parameter.

5. The pre-injection design method for nitrogen displacement in low-permeability coal seams according to claim 2, characterized in that, The confidence level calculation formula is: C i =1- i In the formula, C i The confidence level of any one of the coal seam parameters, including gas pressure, permeability, gas content, Protodyakonov coefficient, ash content, or Langmuir pressure constant. i C i The corresponding standard value X of the coal seam parameter norm,i The deviation.

6. The pre-injection design method for nitrogen displacement in low-permeability coal seams according to claim 2, characterized in that, The formula for calculating the grey relational degree is: R i = In the formula, R i ρ represents the grey relational degree, and ρ is the resolution coefficient.

7. The pre-injection design method for nitrogen displacement in low-permeability coal seams according to claim 2, characterized in that, The weighting coefficient W according to each of the coal seam parameters i The confidence level C i And the gray relational degree R i The formula for calculating the applicability index SI is as follows: SI= In the formula, SI is the applicability index, and W i C is the weighting coefficient. i For confidence level, R i This represents the grey relational degree.

8. The pre-injection design method for nitrogen displacement in low-permeability coal seams according to claim 1, characterized in that, The proposed method for determining borehole sealing technology includes: Obtain the gas pressure, permeability, fracture development degree, and suitability index for the nitrogen injection suitability assessment; Based on the gas pressure, the permeability, and the degree of fracture development, the sealing material is selected as follows: when the permeability is lower than a set threshold and the degree of fracture development is low, polyurethane foam is selected as the sealing material, with a sealing length greater than 10 meters; when the gas pressure is higher than 0.765 MPa or the coal seam is in a high-stress zone, high-strength cement grout is selected as the sealing material. Determine the drilling layout parameters: Set the drilling depth to be between 50 meters and 100 meters, and the drilling spacing to be between 5 meters and 20 meters; Inject the selected sealing material to perform the sealing operation; Perform a pressure test to verify the seal: monitor the leakage rate and ensure that the leakage rate is less than 0.01 MPa / hour; The sealing scheme is dynamically adjusted according to the degree of fissure development or the applicability index: if fissures are concentrated, a circumferential sealing layer is added; if the applicability index is greater than 0.8 and the gas pressure is less than or equal to 0.765 MPa, a high-efficiency sealing technology is preferred, including extending the sealing length to 15-20 meters; if the applicability index is greater than or equal to 0.7 and less than 0.8, a sealing scheme that balances cost and performance is preferred, including using a standard sealing length of 10-15 meters and using high-strength cement grout as the main sealing material.

9. The pre-injection design method for nitrogen displacement in low-permeability coal seams according to claim 1, characterized in that, The nitrogen injection pressure parameter matching analysis includes: Based on the gas pressure, the permeability, and the Protodyakonov coefficient, the nitrogen injection pressure range was determined through numerical simulation. During ground analysis and testing, the initial nitrogen injection pressure was set to 0.8~1.2 MPa, and the deformation rate of the coal body was monitored in real time. If the deformation rate was ≤5% and the gas pressure was >1 MPa, the initial nitrogen injection pressure was set to 1.5 MPa. If the deformation rate was >5%, the initial nitrogen injection pressure was reduced by 0.2 MPa.

10. The pre-injection design method for nitrogen displacement in low-permeability coal seams according to claim 1, characterized in that, The pulse period design of the pulsed nitrogen injection includes: Based on the gas pressure in the nitrogen injection suitability assessment step, the initial nitrogen injection time and the stop injection time are set during numerical simulation, and the concentration of CH4 and N2 mixed gas is monitored in real time. If the CH4 concentration is <50% or the flow interruption lasts for >1 min, the nitrogen injection time is shortened and the stop injection time is extended. The process is iterated and optimized until the gas extraction purity and concentration reach a stable state and no longer increase, thus obtaining the pulse cycle.

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