Gas extraction optimization method based on goaf overlying strata fracture development and permeability distribution characteristics

Abstract

The invention discloses a gas extraction optimization method based on goaf overlying strata fracture development and permeability distribution characteristics, and relates to the technical field of mine gas extraction. The method comprises the specific steps that a data set F (A) of a fracture development comprehensive index F and a data set P (A) of a permeability comprehensive index P in the overlying rock drilling process are obtained through a built-in parameter measuring module of a drilling bit; by means of a built-in comprehensive index calculation module, index weight assignment is carried out on different fracture development and permeability characteristic response degrees according to parameter values, and accurate recognition and division of a fracture high-development area and a high-permeability area are achieved; gas extraction roadway horizon arrangement parameters are formulated by comprehensively considering goaf overlying strata fracture development partition and permeability distribution characteristics. According to the method, the drilling data is obtained in real time based on engineering drilling, inversion of the fracture development and permeability distribution characteristics of the goaf is achieved, an important parameter basis is provided for accurate horizon arrangement of the high drainage roadway, and the coal mine gas drainage effect is effectively improved.

Description

Technical Field

[0001] The patent of this invention relates to the field of mine gas extraction technology, specifically a gas extraction optimization method based on the development of overburden rock fissures and permeability distribution characteristics in the goaf area. Background Art

[0002] Coal seam gas has always been one of the important factors restricting the safe production of coal mines in my country. In particular, there are still a lot of gas resources in the coal left in the goaf and the adjacent coal seams. The gas in the mining area usually shows the characteristics of many gas outflow sources and large outflow volume, which seriously threatens the safe production of the working face. Therefore, strengthening the gas extraction in the goaf and fissure zone is a key measure to ensure the safe production of the mine and improve the energy utilization efficiency.

[0003] During the advancement of the working face, the overburden strata in the goaf are affected by mining and gradually form a complex fracture network, and the fracture development characteristics have an important control effect on the gas permeability law of the rock strata. For gas in goafs and fracture zones, high-extraction lanes, high-position drilling, directional long drilling and other methods are often used for extraction. The layout of lanes and boreholes directly affects the gas extraction effect, and the permeability characteristics of the overburden strata determine the layout height of the drilling holes and lanes. Therefore, studying the fracture development characteristics and permeability distribution laws of the overburden strata in the goaf is of great significance for the reasonable design of the layout of the extraction lanes and improving the gas extraction efficiency in goafs and fracture zones.

[0004] However, the current research on the development characteristics of cracks in the roof of goaf areas mainly uses formula estimation or numerical simulation methods, lacking accurate and quantitative analysis of the development characteristics of cracks in the overburden rock in goaf areas that fully considers the actual geological characteristics. At the same time, the most widely used drilling flushing fluid observation method in the field measurement method also has the disadvantages of poor timeliness, high technical requirements, long drilling cycle, and being greatly affected by the experience of technical personnel.

[0005] Therefore, there is an urgent need to provide a technical solution to the above-mentioned deficiencies in the prior art. Summary of the invention

[0006] The purpose of this application is to provide a gas extraction optimization method based on the development of overburden fractures and permeability distribution characteristics in the goaf area, so as to solve or alleviate the problems existing in the prior art.

[0007] To achieve the above objectives, this application provides the following technical solutions:

[0008] The present application provides a method for optimizing gas extraction based on the development of overburden rock fissures and permeability distribution characteristics in the goaf, which is characterized by comprising the following steps:

[0009] The cracks in the overlying rock strata of the S101 goaf are spatially distributed in three zones, namely, the curved subsidence zone, the crack zone, and the caving zone. In order to precisely detect the development and distribution of cracks in the coal and rock strata, the drill bit equipped with a vibration wave monitoring module, a flushing fluid leakage monitoring module, a borehole gas pressure measurement module, and a borehole gas flow monitoring module is first brought into contact with the coal and rock mass for drilling operations;

[0010] When the S102 drill bit is drilling into the coal and rock mass, the coal and rock mass is damaged and broken, accompanied by the generation of shock waves. When the sensor of the shock wave monitoring module detects the generation of shock waves and sends a start command to the built-in detector, the detector in the shock wave monitoring module monitors and records the shock wave velocity value I in real time. s At the same time, when the sensor of the flushing fluid loss monitoring module detects the loss of flushing fluid, the built-in liquid flow meter of the flushing fluid loss monitoring module starts working and records the flushing fluid loss per unit time in the drilling. l ;

[0011] S103 As the drilling operation proceeds, the drilling of the drill bit promotes the expansion of the original cracks in the coal rock mass and the development of new cracks. The gas inside the coal rock mass flows into the borehole under the action of the gas pressure gradient. At this time, the gas pressure sensor in the drilling gas pressure measurement module built into the drill bit dynamically monitors and records the gas pressure value I at the drill bit in real time. p At the same time, the gas flow meter of the borehole gas flow monitoring module records the borehole gas flow rate I flowing through the borehole per unit time c ;

[0012] S104 Then, the parameter values ​​(I s ,I l ,I p ,I c ) is transmitted to the comprehensive index calculation module by means of the data transmission system, and the calculation of the fracture development comprehensive index F and the permeability comprehensive index P is completed through the built-in algorithm, thereby obtaining the data set F(A) of the fracture development comprehensive index F and the data set P(A) of the permeability comprehensive index P;

[0013] Based on this, S105 transmits the data set F(A) of the comprehensive index F of fracture development and the data set P(A) of the comprehensive index P of permeability to the target area identification module respectively. According to the data value size characteristics of the comprehensive indexes F and P, the division threshold range is set respectively to realize the data grouping of the data set F(A) of the comprehensive index F of fracture development and the data set P(A) of the comprehensive index P of permeability, complete the identification of the areas with high fracture development and the areas with high permeability, and then propose the layer layout plan of the gas extraction tunnel of the overburden stratum which comprehensively considers the degree of overburden fracture development and the permeability distribution characteristics of the goaf area.

[0014] The gas extraction optimization method based on the development of overburden fractures and permeability distribution characteristics in the goaf area is mainly completed by relying on the gas extraction optimization device based on the development of overburden fractures and permeability distribution characteristics in the goaf area, and is characterized in that: the device is mainly composed of a shock wave monitoring module, a flushing fluid leakage monitoring module, a borehole gas pressure measurement module, a borehole gas flow monitoring module, a comprehensive index calculation module and a target area identification module.

[0015] Preferably, the comprehensive index calculation module obtains the fracture development comprehensive index F and the permeability comprehensive index P through a built-in calculation program, and then obtains a data set F(A) of the fracture development comprehensive index F and a data set P(A) of the permeability comprehensive index P; firstly, the built-in data processor of the comprehensive index calculation module determines the vibration wave velocity value I and I respectively through the hierarchical analysis method. s The weight value α1, the flushing fluid leakage per unit time I l The weight value β1 and the gas pressure value I p The weight value λ1 and the borehole gas flow I c The weight value μ1 is used to calculate the fracture development index F value, which represents the degree of fracture development of the coal and rock mass contacted by the drill bit per unit time and drilling distance. The expression of F is as follows: F=ξ1(αI s +βI l +λI p +μI c ) (1) Where, F is the comprehensive index of fissure development; I s ——vibration wave velocity, m / s; I l ——Flushing fluid leakage, mL / min; I p ——Gas pressure value, Pa; I c ——Drilling gas flow rate, mL / min; ξ1——comprehensive index coefficient of fissure development; α1, β1, λ1, μ1——weight coefficients of fracture development sub-indicators, where α+β+λ+μ=1; Similarly, the comprehensive physical parameter index P value reflecting the permeability characteristics of the coal and rock mass contacted by the drill bit per unit time can be obtained. The expression of P is as follows: P = ξ2(αI s +βI l +λI p +μI c ) (2) Where, P is the comprehensive index of permeability characteristics; ξ2——comprehensive index coefficient of permeability characteristics; α2, β2, λ2, μ2—weight coefficients of permeability characteristic sub-indicators, where α+β+λ+μ=1. Since the vibration wave velocity value I s and flushing fluid loss I l It mainly reflects the development of coal fissures when the borehole is drilled into the coal body, and the borehole gas pressure value I p and borehole gas flow I c It is mainly affected by the permeability distribution characteristics of the coal body. Therefore, when calculating the comprehensive index F of fracture development and the comprehensive index P of permeability, it is necessary to fully consider the influence of each sub-indicator on the comprehensive index and set the corresponding index weight coefficient value.

[0016] Preferably, the target area identification module has a built-in data processor, which divides the fissure development comprehensive index data set F(A) into: fissure high development comprehensive index data subset F(A) and fissure high development comprehensive index data subset F(A) according to the data value size characteristics of the comprehensive index F and P and by setting the data division threshold range. H ) and the subset of comprehensive indicators of fissure underdevelopment F(A L ), the permeability comprehensive index data set P(B) is divided into: high permeability comprehensive index data subset P(B H ) and low permeability comprehensive index data subset P(B L ), complete the identification of areas with high fissure development and high permeability, and then propose a stratum layout plan for gas extraction tunnels in the overlying strata that comprehensively considers the degree of fissure development and permeability distribution characteristics of the overburden rock in the goaf area.

[0017] Preferably, according to the distribution characteristics of the cracks in the overlying rock strata in the goaf, the space can be mainly divided into the curved sinking zone, the crack zone and the caving zone from top to bottom, referred to as the "three zones". The development of cracks in the coal rock mass at different spatial positions in the same crack zone is significantly different due to the influence of mining disturbance. Therefore, according to the data subset F(A) of the comprehensive index of high crack development, the H ) and the subset of comprehensive indicators of fissure underdevelopment F(A L ) value characteristics can further refine the “three zones” of the overburden in the goaf: vertical fracture fracture zone, delamination fracture zone, delamination compaction zone and caving fracture zone, thereby providing a basis for the formulation of accurate layout plan for the gas extraction tunnels in the overburden strata.

[0018] Preferably, the comprehensive index calculation module is based on the parameter value I measured per unit time of the drilling bit. s ,I l ,I p ,I c According to formula (1), the fracture development index F value representing the degree of fracture development of the coal rock mass contacted by the drill bit per unit time drilling distance can be calculated, and the fracture development index F of all fractures formed in the whole drilling cycle of the same borehole isi The fracture development index data subset F(a) can be constructed by using the fracture development index data subset F(a), namely F(a)(F1, F2, F3, F4…), where the fracture development index data subset F(a) records the index parameter values ​​of the fracture development degree of the coal rock mass contacted by the drill bit at different drilling spatial positions during the full drilling cycle of the same borehole, and the fracture development index data subsets F(a) of different boreholes can constitute the fracture development comprehensive index data set F(A), namely F(A)(F(a), F(b), F(c)…); further, the permeability distribution is obtained by formula (2): The data values ​​of the fracture development comprehensive index dataset F(A) and the permeability comprehensive index dataset P(B) fully consider the fracture development characteristics of the overburden in different spatial layers (different layers of drilling holes) and different drilling depths in the goaf area, forming a data index set that can reflect the three-dimensional spatial distribution characteristics of the overburden fractures in the goaf area, providing more detailed parameter basis for proposing an optimization plan for the layer layout of gas extraction tunnels in the overburden strata that comprehensively considers the degree of fracture development and permeability distribution characteristics of the overburden in the goaf area.

[0019] Due to the adoption of the above technical solution, the beneficial effects of the present invention at least include:

[0020] The present invention obtains drilling data in real time through the changes in parameter values ​​during the drilling process of the overburden rock strata in the goaf area, and forms a data set reflecting the development characteristics of the fissures in the overburden rock strata; through the built-in comprehensive index calculation module, the index weights are assigned according to the different response degrees of the fissure development and permeability characteristics of each parameter value, and the accurate identification and division of the high fissure development area and the high permeability area are realized; the degree of development of the overburden rock fissures and the permeability distribution characteristics of the goaf area are comprehensively considered, and then the optimization scheme of the stratum layout of the gas extraction roadway is proposed. The accurate acquisition of the advantageous stratum parameters of the high extraction roadway in the overburden rock strata in the goaf area is realized, the gas extraction efficiency of the high extraction roadway is improved, and the occurrence of gas over-limit accidents is effectively reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is a flow chart of the gas extraction optimization method of the present invention;

[0022] Figure 2 This is a schematic diagram of the comprehensive index data set of fissure development of the present invention;

[0023] Figure 3 The present invention is a flow chart of calculating the fissure development index based on hierarchical analysis;

[0024] Figure 4 This is a schematic diagram of the division of the overburden fracture zone in the goaf area of ​​the present invention;

[0025] Figure 5 This is a schematic diagram of the high permeability area of ​​the overburden rock in the goaf area of ​​the present invention;

[0026] Figure 6 This is a schematic diagram of the arrangement of the strata of the overburden high-drawn lane in the goaf area of ​​the present invention; DETAILED DESCRIPTION

[0027] In order to make the purpose, technical scheme and advantages of the embodiments of the present invention more clearly understood, the embodiments of the present invention are further described in detail below in conjunction with the embodiments and drawings. Here, the illustrative embodiments of the present invention and their descriptions are used to explain the present invention, but are not intended to limit the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0028] In the description of the present invention, it should be understood that terms such as “upper”, “lower”, “front”, “back”, “left”, “right”, “top”, “bottom”, “inside” and “outside” indicating directions or positional relationships are based on the directions or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the referred device, component or structure must have a specific direction, be constructed or operate in a specific direction, and should not be understood as a limitation on the present invention.

[0029] The specific implementation method of the present invention will be further described below in conjunction with the accompanying drawings.

[0030] like Figure 1-6 As shown, the gas extraction optimization method based on the development of overburden rock fractures and permeability distribution characteristics in the goaf is characterized by comprising the following steps:

[0031] The cracks in the overlying rock strata of the S101 goaf are spatially distributed in three zones, namely, the curved subsidence zone, the crack zone, and the caving zone. In order to precisely detect the development and distribution of cracks in the coal and rock strata, the drill bit equipped with a vibration wave monitoring module, a flushing fluid leakage monitoring module, a borehole gas pressure measurement module, and a borehole gas flow monitoring module is first brought into contact with the coal and rock mass for drilling operations;

[0032] When the S102 drill bit is drilling into the coal and rock mass, the coal and rock mass is damaged and broken, accompanied by the generation of shock waves. When the sensor of the shock wave monitoring module detects the generation of shock waves and sends a start command to the built-in detector, the detector in the shock wave monitoring module monitors and records the shock wave velocity value I in real time. s At the same time, when the sensor of the flushing fluid loss monitoring module detects the loss of flushing fluid, the built-in liquid flow meter of the flushing fluid loss monitoring module starts working and records the flushing fluid loss per unit time in the drilling. l ;

[0033] S103 As the drilling operation proceeds, the drilling of the drill bit promotes the expansion of the original cracks in the coal rock mass and the development of new cracks. The gas inside the coal rock mass flows into the borehole under the action of the gas pressure gradient. At this time, the gas pressure sensor in the drilling gas pressure measurement module built into the drill bit dynamically monitors and records the gas pressure value I at the drill bit in real time. p At the same time, the gas flow meter of the borehole gas flow monitoring module records the borehole gas flow rate I flowing through the borehole per unit time c ;

[0034] S104 Then, the parameter values ​​(I s ,I l ,I p ,I c ) is transmitted to the comprehensive index calculation module by means of the data transmission system, and the calculation of the fracture development comprehensive index F and the permeability comprehensive index P is completed through the built-in algorithm, thereby obtaining the data set F(A) of the fracture development comprehensive index F and the data set P(A) of the permeability comprehensive index P;

[0035] Based on this, S105 transmits the data set F(A) of the comprehensive index F of fracture development and the data set P(A) of the comprehensive index P of permeability to the target area identification module respectively. According to the data value size characteristics of the comprehensive indexes F and P, the division threshold range is set respectively to realize the data grouping of the data set F(A) of the comprehensive index F of fracture development and the data set P(A) of the comprehensive index P of permeability, complete the identification of the areas with high fracture development and the areas with high permeability, and then propose the layer layout plan of the gas extraction tunnel of the overburden stratum which comprehensively considers the degree of overburden fracture development and the permeability distribution characteristics of the goaf area.

[0036] The gas extraction optimization method based on the development of overburden fractures and permeability distribution characteristics in the goaf area is mainly completed by relying on a gas extraction optimization scheme design device based on the development of overburden fractures and permeability distribution characteristics in the goaf area, and is characterized in that: the device is mainly composed of a shock wave monitoring module, a flushing fluid leakage monitoring module, a borehole gas pressure measurement module, a borehole gas flow monitoring module, a comprehensive index calculation module and a target area identification module.

[0037] like Figure 2-3 As shown, the comprehensive index calculation module obtains the fracture development comprehensive index F and the permeability comprehensive index P through the built-in calculation program, and then obtains the data set F(A) of the fracture development comprehensive index F and the data set P(A) of the permeability comprehensive index P; firstly, the built-in data processor of the comprehensive index calculation module determines the vibration wave velocity value I respectively through the hierarchical analysis method s The weight value α1, the flushing fluid leakage per unit time I l The weight value β1 and the gas pressure value I p The weight value λ1 and the borehole gas flow Ic The weight value μ1 is used to calculate the fracture development index F value, which represents the degree of fracture development of the coal and rock mass contacted by the drill bit per unit time and drilling distance. The expression of F is as follows: F=ξ1(αI s +βI l +λI p +μI c ) (1) Where, F is the comprehensive index of fissure development; I s ——vibration wave velocity, m / s; I l ——Flushing fluid leakage, mL / min; I p ——Gas pressure value, Pa; I c ——Drilling gas flow rate, mL / min; ξ1——comprehensive index coefficient of fissure development; α1, β1, λ1, μ1——weight coefficients of fracture development sub-indicators, where α+β+λ+μ=1; Similarly, the comprehensive physical parameter index P value reflecting the permeability characteristics of the coal and rock mass contacted by the drill bit per unit time can be obtained. The expression of P is as follows: P = ξ2(αI s +βI l +λI p +μI c ) (2) Where, P is the comprehensive index of permeability characteristics; ξ2——comprehensive index coefficient of permeability characteristics; α2, β2, λ2, μ2—weight coefficients of permeability characteristic sub-indicators, where α+β+λ+μ=1. Since the vibration wave velocity value I s and flushing fluid loss I l It mainly reflects the development of coal fissures when the borehole is drilled into the coal body, and the borehole gas pressure value I p and borehole gas flow I c It is mainly affected by the permeability distribution characteristics of the coal body. Therefore, when calculating the comprehensive index F of fracture development and the comprehensive index P of permeability, it is necessary to fully consider the influence of each sub-indicator on the comprehensive index and set the corresponding index weight coefficient value.

[0038] like Figure 2-5 As shown, the target area identification module has a built-in data processor, which divides the fissure development comprehensive index data set F(A) into: fissure high development comprehensive index data subset F(A) according to the data value size characteristics of the comprehensive index F and P, by setting the data division threshold range.H ) and the subset of comprehensive indicators of fissure underdevelopment F(A L ), the permeability comprehensive index data set P(B) is divided into: high permeability comprehensive index data subset P(B H ) and low permeability comprehensive index data subset P(B L ), complete the identification of areas with high fissure development and high permeability, and then propose a stratum layout plan for gas extraction tunnels in the overlying strata that comprehensively considers the degree of fissure development and permeability distribution characteristics of the overburden rock in the goaf area.

[0039] like Figure 4 As shown in Figure 1, according to the distribution characteristics of fractures in the overlying rock strata in the goaf, the area can be mainly divided into the curved sinking zone, the fracture zone and the caving zone from top to bottom, referred to as the "three zones". The fracture development of coal rock mass at different spatial positions in the same fracture zone is significantly different due to the influence of mining disturbance. Therefore, according to the fracture high development comprehensive index data subset F(A H ) and the subset of comprehensive indicators of fissure underdevelopment F(A L ) value characteristics can further refine the “three zones” of the overburden in the goaf: vertical fracture fracture zone, delamination fracture zone, delamination compaction zone and caving fracture zone, thereby providing a basis for the formulation of accurate layout plan for the gas extraction tunnels in the overburden strata.

[0040] like Figure 1-6 As shown, the comprehensive index calculation module is based on the parameter value I measured by the drilling bit per unit time. s ,I l ,I p ,I c According to formula (1), the fracture development index F value representing the degree of fracture development of the coal rock mass contacted by the drill bit per unit time drilling distance can be calculated, and the fracture development index F of all fractures formed in the whole drilling cycle of the same borehole is iThe fracture development index data subset F(a) can be constructed by using the fracture development index data subset F(a), namely F(a)(F1, F2, F3, F4…), where the fracture development index data subset F(a) records the index parameter values ​​of the fracture development degree of the coal rock mass contacted by the drill bit at different drilling spatial positions during the full drilling cycle of the same borehole, and the fracture development index data subsets F(a) of different boreholes can constitute the fracture development comprehensive index data set F(A), namely F(A)(F(a), F(b), F(c)…); further, the permeability distribution is obtained by formula (2): The data values ​​of the fracture development comprehensive index dataset F(A) and the permeability comprehensive index dataset P(B) fully consider the fracture development characteristics of the overburden in different spatial layers (different layers of drilling holes) and different drilling depths in the goaf area, forming a data index set that can reflect the three-dimensional spatial distribution characteristics of the overburden fractures in the goaf area, providing more detailed parameter basis for proposing an optimization plan for the layer layout of gas extraction tunnels in the overburden strata that comprehensively considers the degree of fracture development and permeability distribution characteristics of the overburden in the goaf area.

[0041] At this point, those skilled in the art should recognize that, although the exemplary embodiments of the present invention have been shown and described in detail herein, many other variations or modifications that conform to the principles of the present invention can still be directly determined or derived based on the contents disclosed in the present invention without departing from the spirit and scope of the present invention. Therefore, the scope of the present invention should be understood and recognized as covering all such other variations or modifications.

Claims

1. A gas extraction optimization method based on the development of overburden fractures and permeability distribution characteristics in the goaf, characterized by: The method mainly includes the following steps: The cracks in the overlying rock strata of the S101 goaf are spatially distributed in three zones, namely, the curved subsidence zone, the crack zone, and the caving zone. In order to precisely detect the development and distribution of cracks in the coal and rock strata, the drill bit equipped with a vibration wave monitoring module, a flushing fluid leakage monitoring module, a borehole gas pressure measurement module, and a borehole gas flow monitoring module is first brought into contact with the coal and rock mass for drilling operations. When the S102 drill bit is drilling into the coal and rock mass, the coal and rock mass is damaged and broken, accompanied by the generation of shock waves. When the sensor of the shock wave monitoring module detects the generation of shock waves and sends a start command to the built-in detector, the detector in the shock wave monitoring module monitors and records the shock wave velocity value I in real time. s At the same time, when the sensor of the flushing fluid loss monitoring module detects the loss of flushing fluid, the built-in liquid flow meter of the flushing fluid loss monitoring module starts working and records the flushing fluid loss per unit time in the drilling. l ; S103 As the drilling operation proceeds, the drilling of the drill bit promotes the expansion of the original cracks in the coal rock mass and the development of new cracks. The gas inside the coal rock mass flows into the borehole under the action of the gas pressure gradient. At this time, the gas pressure sensor in the drilling gas pressure measurement module built into the drill bit dynamically monitors and records the gas pressure value I at the drill bit in real time. p At the same time, the gas flow meter of the borehole gas flow monitoring module records the borehole gas flow rate I flowing through the borehole per unit time c ; S104 Then, the parameter values ​​(I s ,I l ,I p ,I c ) is transmitted to the comprehensive index calculation module by means of the data transmission system, and the calculation of the fracture development comprehensive index F and the permeability comprehensive index P is completed through the built-in algorithm, thereby obtaining the data set F(A) of the fracture development comprehensive index F and the data set P(A) of the permeability comprehensive index P; Based on this, S105 transmits the data set F(A) of the comprehensive index F of fracture development and the data set P(A) of the comprehensive index P of permeability to the target area identification module respectively, and sets the division threshold range according to the data value size characteristics of the comprehensive indexes F and P respectively, so as to realize the data grouping of the data set F(A) of the comprehensive index F of fracture development and the data set P(A) of the comprehensive index P of permeability, complete the identification of the high fracture development area and the high permeability area, and then propose the overburden stratum gas extraction tunnel layer layout plan which comprehensively considers the comprehensive index F of the overburden fracture development degree and the comprehensive index P of the permeability distribution characteristics of the goaf area; The gas extraction optimization method based on the development of overburden fractures and permeability distribution characteristics in the goaf is mainly completed by relying on an analysis device based on the development of overburden fractures and permeability distribution characteristics in the goaf, and is characterized in that the device is mainly composed of a shock wave monitoring module, a flushing fluid leakage monitoring module, a borehole gas pressure measurement module, a borehole gas flow monitoring module, a comprehensive index calculation module and a target area identification module.

2. The method for optimizing gas extraction based on the development of overburden rock fissures and permeability distribution characteristics in goaf according to claim 1 is characterized in that: The drill bit is built with a shock wave monitoring module, a flushing fluid leakage monitoring module, a borehole gas pressure measurement module and a borehole gas flow monitoring module; wherein the shock wave monitoring module is provided with a detector, a data processor and a data storage device, the flushing fluid leakage monitoring module is provided with a liquid flow meter, a data processor and a data storage device, the borehole gas pressure measurement module is built with a gas pressure sensor, a data processor and a data storage device, and the borehole gas flow monitoring module is built with a gas flow meter, a data processor and a data storage device. The above four modules are mainly used to complete the parameter I during the drilling process s ,I l ,I p ,I c Determination of.

3. The method for optimizing gas extraction based on the development of overburden rock fissures and permeability distribution characteristics in goaf according to claim 1 is characterized in that: The comprehensive index calculation module obtains the fracture development comprehensive index F and the permeability comprehensive index P through the built-in calculation program, and then obtains the data set F(A) of the fracture development comprehensive index F and the data set P(A) of the permeability comprehensive index P; firstly, the built-in data processor of the comprehensive index calculation module determines the vibration wave velocity value I respectively through the hierarchical analysis method s The weight value α1, the flushing fluid leakage per unit time I l The weight value β1 and the gas pressure value I p The weight value λ1 and the borehole gas flow I c The weight value μ1 is used to calculate the fracture development index F value, which represents the degree of fracture development of the coal and rock mass contacted by the drill bit per unit time and drilling distance. The expression of F is as follows: F=ξ1(α1I s +β1I l +λ1I p +μ1I c ) (1) Where, F is the comprehensive index of fissure development; I s ——vibration wave velocity, m / s; I l ——Flushing fluid leakage, mL / min; I p ——Gas pressure value, Pa; I c ——Drilling gas flow rate, mL / min; ξ1——comprehensive index coefficient of fissure development; α1, β1, λ1, μ1——weight coefficients of fracture development sub-indicators, where α1+β1+λ1+μ1=1; Similarly, the comprehensive physical parameter index P value reflecting the permeability characteristics of the coal and rock mass contacted by the drill bit per unit time can be obtained. The expression of P is as follows: P=ξ2(α2I s +β2I l +λ2I p +μ2I c ) (2) Where, P is the comprehensive index of permeability characteristics; ξ2——comprehensive index coefficient of permeability characteristics; α2, β2, λ2, μ2—weight coefficients of permeability characteristic sub-indicators, where α2+β2+λ2+μ2=1. Since the vibration wave velocity value I s and flushing fluid loss I l It mainly reflects the development of coal cracks in the borehole, and the borehole gas pressure value I p and borehole gas flow I c It is mainly affected by the permeability distribution characteristics of the coal body. Therefore, when calculating the comprehensive index F of fracture development and the comprehensive index P of permeability, it is necessary to fully consider the influence of each sub-indicator on the comprehensive index and set the corresponding index weight coefficient value.

4. The method for optimizing gas extraction based on the development of overburden rock fissures and permeability distribution characteristics in goaf according to claim 1 is characterized in that: The target area identification module has a built-in data processor, which divides the fissure development comprehensive index data set F(A) into the following data subsets: the fissure high development comprehensive index data set F(A) and the fissure high development comprehensive index data set F(A) according to the data value characteristics of the comprehensive index F and P. H ) and the subset of comprehensive indicators of fissure underdevelopment F(A L ), the permeability comprehensive index data set P(B) is divided into: high permeability comprehensive index data subset P(B H ) and low permeability comprehensive index data subset P(B L ), complete the identification of areas with high fissure development and high permeability, and then propose a stratum layout plan for gas extraction tunnels in the overlying strata that comprehensively considers the degree of fissure development and permeability distribution characteristics of the overburden rock in the goaf area.

5. The method for optimizing gas extraction based on the development of overburden rock fissures and permeability distribution characteristics in goaf according to claim 4 is characterized in that: According to the distribution characteristics of the cracks in the overlying rock strata in the goaf, the space can be mainly divided into the curved sinking zone, the crack zone and the caving zone from top to bottom, referred to as the "three zones". The development of cracks in the coal rock mass at different spatial positions in the same crack zone is obviously different due to the influence of mining disturbance. Therefore, according to the data subset F(A) of the comprehensive index of high crack development, the H ) and the subset of comprehensive indicators of fissure underdevelopment F(A L ) value characteristics, the "three zones" of the overburden in the goaf can be further refined into: vertical fracture fracture zone, delamination fracture zone, delamination compaction zone and caving fracture zone, thus providing a basis for the formulation of accurate layout plan for gas extraction tunnels in the overburden strata.

6. The method for optimizing gas extraction based on the development of overburden fractures and permeability distribution characteristics in goaf according to claim 1, characterized in that: The comprehensive index calculation module is based on the parameter value I measured by the drilling bit per unit time. s ,I l ,I p ,I c According to formula (1), the comprehensive fracture development index F value representing the degree of fracture development of the coal rock mass contacted by the drill bit per unit time drilling distance can be calculated, and the total fracture development index F formed in the whole drilling cycle of the same borehole is i value, a fracture development index data subset F(a) can be constructed, namely F(a)(F1, F2, F3, F4…), wherein the fracture development index data subset F(a) records the index parameter values ​​of the fracture development degree of the coal rock mass contacted by the drill bit at different drilling space positions during the full drilling cycle of the same borehole, and the fracture development index data subsets F(a) of different boreholes can constitute a fracture development comprehensive index data set F(A), namely F(A)(F(a), F(b), F(c)…); wherein, the data values ​​of the fracture development comprehensive index data set F(A) fully consider The fracture development characteristics of the overburden in different spatial layers (different layers of drilling holes) and different drilling depths in the goaf area form a data indicator set that can reflect the three-dimensional spatial distribution characteristics of the overburden fractures in the goaf area. It is worth noting that the principle of obtaining the fracture development comprehensive indicator data set P(B) reflecting the permeability distribution characteristics is the same as that of the fracture development comprehensive indicator data set F(A), which will not be repeated here. Based on the above analysis results, a more detailed parameter basis is provided to propose an optimization plan for the layer layout of the overburden gas extraction tunnel that comprehensively considers the degree of fracture development and permeability distribution characteristics of the overburden in the goaf area.

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