A method for preventing coal outbursts in deep coal seams by graded method

Abstract

The present invention relates to a method for preventing coal outbursts in deep coal seams by classification, and belongs to the field of coal and gas outburst prevention and control in coal mines. The method comprises: S1: classifying the ground stress hazard level of coal seams that are outbursts; S2: classifying the gas hazard level of coal seams that are outbursts; S3: classifying the extraction performance level of coal seams that are outbursts; S4: determining the coal seam outburst prevention level; S5: classifying outburst prevention according to the coal seam outburst prevention level. The present invention solves the technical problem that the existing outburst prevention methods do not fully consider factors such as ground stress, gas and coal seam extraction performance and their differences, and are not reasonable and accurate enough. The present invention not only makes up for the shortcomings of the existing outburst prevention methods, but also improves the rationality and accuracy of coal seam outburst prevention, which is of great significance to the reasonable, accurate and efficient outburst prevention of deep coal seams that are outbursts.

Description

Technical Field

[0001] The invention belongs to the field of coal and gas outburst prevention and control in coal mines, and relates to a deep outburst coal seam graded outburst prevention method. Background Art

[0002] With the increase in the depth of coal mining, the effect of deep ground stress on coal and gas outbursts is further increased, while the existing anti-outburst methods are mainly carried out around gas factors, without considering ground stress factors. On the contrary, deep ground stress factors are important factors that cannot be ignored in preventing outbursts. Secondly, coal and gas outbursts are the result of the combined effects of ground stress, gas, and the physical and mechanical properties of coal rocks, while the existing anti-outburst methods only use gas extraction to reduce gas pressure and gas content, and do not fully consider factors such as ground stress, gas, and coal seam extraction performance. Furthermore, the ground stress, gas, and coal seam extraction performance in different coal seam areas are all different, and the existing anti-outburst methods use the same anti-outburst method for coal seams in different regions, and its rationality and accuracy need to be discussed.

[0003] Therefore, there is an urgent need for a graded method for preventing sudden coal outbursts that comprehensively considers parameters such as ground stress, gas, and coal seam extraction performance and their differences, to make up for the shortcomings of existing methods for preventing sudden coal outbursts that do not comprehensively consider factors such as ground stress, gas, and coal seam extraction performance and their differences, and to solve the technical problems that existing methods for preventing sudden coal outbursts are not reasonable and accurate enough. Summary of the invention

[0004] In view of this, the purpose of the present invention is to provide a hierarchical outburst prevention method that comprehensively considers parameters such as ground stress, gas, and coal seam extraction performance and their differences, and solves the technical problem that the existing outburst prevention method does not comprehensively consider factors such as ground stress, gas, and coal seam extraction performance and their differences, and is not reasonable and accurate enough. This method can not only make up for the deficiency that the existing outburst prevention method does not comprehensively consider factors such as ground stress, gas, and coal seam extraction performance and their differences, but also improves the rationality and accuracy of coal seam outburst prevention, which is of great significance for the precise and efficient outburst prevention of deep outburst coal seams.

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

[0006] A method for preventing coal outbursts in deep coal seams by graded method comprises the following steps:

[0007] S1: Classification of the dangerous level of ground stress of the protruding coal seam;

[0008] S2: Classification of gas hazard levels in outburst coal seams;

[0009] S3: Classify the performance level of extraction of outburst coal seams;

[0010] S4: Determine the coal seam outburst prevention level;

[0011] S5: Carry out graded coal seam outburst prevention measures according to the coal seam outburst prevention level.

[0012] Further, step S1 specifically includes: dividing the coal seam ground stress hazard level into three levels: general, medium and severe according to the size of the stress increment coefficient, and the division intervals are: k<1 / 3, 1 / 3≤k≤2 / 3, k>2 / 3, where k is the stress increment coefficient (concentration coefficient).

[0013] Further, in step S1, the calculation formula of the stress increment coefficient k is:

[0014] k=k0+k1+k2

[0015] Among them, k0 = (H1-H) / H, H is the burial depth of the coal seam, the burial depth of the coal seam in a certain area is H1; k1 is the stress concentration coefficient caused by geological structure; k2 is the stress concentration coefficient caused by the air in the goaf.

[0016] Further, step S2 specifically includes: dividing the coal seam gas hazard level into three levels: general, medium, and severe according to the original gas pressure and original gas content of the coal seam, and the division intervals are: P < 1MPa, 1MPa ≤ P ≤ 2MPa, P > 2MPa, W < 10m 3 / t、10m 3 / t≤W≤15m 3 / t、W>15m 3 / t; where P is the original gas pressure of the coal seam and W is the original gas content, both of which can be obtained through on-site testing.

[0017] Further, step S3 specifically includes: dividing the coal seam extraction performance level into three levels: difficult to extract coal seams, extractable coal seams and easy to extract coal seams according to the coal seam permeability coefficient λ, and the division intervals are: λ<0.1(m 2 / MPa 2 .d)、0.1(m 2 / MPa 2 .d)≤λ≤10(m 2 / MPa 2 .d) λ>10(m 2 / MPa 2 .d); According to the solidity coefficient f of coal, the coal seam extraction performance level is divided into three levels: soft coal seam, medium hard coal seam and hard coal seam, and the division intervals are: f<0.3, 0.3≤f≤0.5, f>0.5. Among them, the coal seam permeability coefficient λ and the coal solidity coefficient f can be obtained through field testing.

[0018] Further, step S5 specifically includes: performing ground stress classification prevention, gas classification prevention and coal seam extraction performance classification prevention according to the determined coal seam ground stress hazard level, gas hazard level and extraction performance level, and performing comprehensive prevention of ground stress classification prevention and coal seam extraction performance classification prevention according to the coupling of the three.

[0019] Further, in step S5, the ground stress graded outburst prevention is to use large-diameter pressure relief drilling, hydraulic hole expansion or hydraulic slotting technology to discharge part of the coal body in the coal seam to prevent outburst;

[0020] Coal discharge volume V from large-diameter pressure relief boreholes in areas with general geostress hazard levels yb The calculation formula is:

[0021] V yb =π×r p 2 ×L×X

[0022] Among them, r p is the radius of the pressure relief drilling hole, m; L is the depth of the pressure relief drilling hole, m; X is the number of pressure relief drilling holes, pieces;

[0023] Similarly, the coal discharge volume V of hydraulic expansion or hydraulic slot drilling is ybs The calculation formula is:

[0024] V ybs =π×r p 2 ×L×X+V1×Y

[0025] Where V1 is the volume of coal discharged from a hydraulically expanded hole or a hydraulically cut seam, m 3 ; Y is the number of hydraulically expanded holes or the number of hydraulically cut slots, pieces;

[0026] In the medium and severe risk levels of geostress, the coal discharge volume using the same technology is the ratio of the stress increment coefficient to the stress increment coefficient of the general risk level of geostress multiplied by V yb or V ybs ; Eliminate the danger of ground stress by adjusting parameters such as X or Y.

[0027] Further, in step S5, gas graded outburst prevention is to reduce the gas pressure and gas content in the coal seam by extracting gas through extraction drilling;

[0028] The amount of gas that needs to be extracted from a gas hazardous area is Q yb The calculation formula is:

[0029] Q yb =Q r ×X

[0030] Among them, Qr is the gas volume after extraction time t of a drainage borehole when the extraction radius is r, m 3 ; X is the number of holes drilled, pieces;

[0031] Since the amount of gas extracted is proportional to the gas content, the amount of gas that needs to be extracted in the medium-risk and severe-risk areas of gas is adjusted to meet the requirements of burst prevention by adjusting one or more parameters such as extraction radius r, extraction time t and number of boreholes X;

[0032] Similarly, the method for reducing gas pressure is implemented with reference to the gas content.

[0033] Further, in step S5, the coal seam extraction performance classification and outburst prevention improve the extraction effect of the borehole by increasing the coal seam permeability coefficient, increasing the drilling porosity and protecting the borehole;

[0034] The amount of gas that needs to be extracted from the coal seam area that is easy to extract is Q ry The calculation formula is:

[0035] Q ry =Q λ1 ×X

[0036] Among them, Q λ1 is the gas volume of a drainage borehole in the easily drainable coal seam after drainage time t, m 3 ; X is the number of holes drilled, pieces;

[0037] Since the amount of extracted gas is proportional to the gas content, the amount of gas that needs to be extracted from coal seams that are difficult to extract and those that can be extracted is mainly achieved by increasing the permeability coefficient of the coal seams using permeability enhancement technology. The requirements for gas outburst prevention can also be met by adjusting one or more parameters such as the extraction radius r, extraction time t, and number of drill holes X. The same applies to coal seams that are difficult to extract and those that can be extracted, thereby achieving graded gas outburst prevention for coal seam gas extraction performance.

[0038] Furthermore, in step S5, special drilling rigs and drilling tools are used in soft coal seams to increase the drilling rate or to adopt hole protection measures such as casing throughout the process to improve the extraction effect and achieve the effect of preventing sudden coal outbursts.

[0039] The beneficial effect of the present invention is that the present invention not only makes up for the deficiency of existing coal seam outburst prevention methods that do not fully consider factors such as ground stress, gas and coal seam extraction performance and their differences, but also improves the rationality and accuracy of coal seam outburst prevention, which is of great significance for accurate and efficient coal seam outburst prevention.

[0040] Other advantages, objectives and features of the present invention will be described in the following description to some extent, and to some extent, will be obvious to those skilled in the art based on the following examination and study, or can be taught from the practice of the present invention. The objectives and other advantages of the present invention can be realized and obtained through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention will be described in detail below in conjunction with the accompanying drawings, wherein:

[0042] Figure 1 The present invention is a flow chart of the method for preventing coal outbursts in deep coal seams by graded method. DETAILED DESCRIPTION

[0043] The following describes the embodiments of the present invention by specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the illustrations provided in the following embodiments only illustrate the basic concept of the present invention in a schematic manner, and the following embodiments and features in the embodiments can be combined with each other without conflict.

[0044] See also Figure 1 The present invention provides a method for preventing coal outbursts in deep coal seams by graded method, which specifically comprises the following steps:

[0045] Step 1: Classify the ground stress hazard level of the protruding coal seam.

[0046] The ground stress of coal seams is mainly composed of the superposition of three parts: self-weight stress, tectonic stress and structural stress. The calculation formula is as follows:

[0047] σ d =γH+k1σ z +k2σ z (1)

[0048] Among them, σ d is the ground stress of coal seam, MPa; γ is the bulk density of overlying rock layer, N / m 3 ; H is the buried depth of coal seam, m; k1 is the stress concentration coefficient caused by geological structure; k2 is the stress concentration coefficient caused by the empty space in the goaf; σ z is the self-weight stress of the coal seam, MPa.

[0049] The buried depth of coal seams in different regions is different. As the buried depth increases, the self-weight stress of the coal seams also increases. Assuming that the buried depth of coal seams in a certain area is H1, the self-weight stress increase coefficient k0 of the coal seams can be calculated using the following formula:

[0050] k0=(H1-H) / H (2)

[0051] Then, the coal seam here considers the self-weight stress, geological structure stress concentration, and goaf stress concentration at the same time, and the stress increment coefficient (concentration coefficient) k here is expressed as:

[0052] k=k0+k1+k2 (3)

[0053] According to regulatory standards and domestic field practical experience, the coal seam geostress hazard level can be divided into three levels: general, moderate and severe, and the division intervals are: k < 1 / 3, 1 / 3 ≤ k ≤ 2 / 3, k > 2 / 3.

[0054] Step 2: Classify the gas hazard level of the protruding coal seam.

[0055] The main parameters characterizing the coal seam gas hazard level are gas pressure and gas content. According to regulatory standards and domestic field practice experience, the coal seam gas hazard level can be divided into three levels: general, medium and severe. The division intervals are: P < 1MPa, 1MPa ≤ P ≤ 2MPa, P > 2MPa, W < 10m 3 / t、10m 3 / t≤W≤15m 3 / t、W>15m 3 / t. Among them, the original gas pressure P and original gas content W of the coal seam can be obtained through on-site testing.

[0056] Step 3: Classify the extraction performance level of the prominent coal seam.

[0057] The main parameters characterizing the coal seam extraction performance level are the coal seam permeability coefficient λ and the coal solidity coefficient f. According to the regulations and standards and domestic field practice experience, the coal seams can be divided into three levels: difficult to extract coal seams, extractable coal seams, and easy to extract coal seams according to the measured coal seam permeability coefficient λ. The division intervals are: λ<0.1(m 2 / MPa 2 .d)、0.1(m 2 / MPa 2 .d)≤λ≤10(m 2 / MPa 2 .d) λ>10(m 2 / MPa 2.d). According to regulatory standards and domestic field practice experience, coal seams can be divided into three levels: soft coal seams, medium-hard coal seams, and relatively hard coal seams according to the measured coal seam solidity coefficient f, and the division intervals are: f<0.3, 0.3≤f≤0.5, f>0.5. Among them, the coal seam permeability coefficient λ and the coal solidity coefficient f can be obtained through field testing.

[0058] Step 4: Determine the coal seam burst prevention level.

[0059] According to the classification method of deep coal seam ground stress hazard level, gas hazard level and extraction performance level in steps 1 to 3, calculate or measure the stress increment coefficient (concentration coefficient) k, the original gas pressure P and original gas content W of the coal seam, the coal seam permeability coefficient λ and the coal solidity coefficient f in turn, and determine the coal seam ground stress hazard level, gas hazard level and extraction performance level respectively, and then determine the coal seam ground stress, gas and extraction performance prevention level.

[0060] Step 5: Carry out graded coal seam outburst prevention measures according to the coal seam outburst prevention grade.

[0061] According to the coal seam ground stress hazard level, gas hazard level, and extraction performance level determined in step 4, graded prevention of outbursts is carried out respectively, and the coupling of the three is comprehensively prevented, as detailed as follows:

[0062] (1) Ground stress classification and prevention of outbursts

[0063] The ground stress grading method for preventing coal and gas outbursts mainly uses large-diameter pressure-relief drilling or hydraulic hole expansion and hydraulic cutting technology to discharge part of the coal in the coal seam, which increases the deformation of the coal seam and has the effect of reducing ground stress. The specific amount of coal discharged can be determined by referring to the "Detailed Rules for Preventing and Controlling Coal and Gas Outbursts" or on-site actual measurements.

[0064] Assume that the coal discharge volume of the large-diameter pressure relief borehole in the general grade area of ​​geostress hazard is V yb When the ground stress hazard is reduced, the coal body discharge volume V yb The calculation expression is:

[0065] V yb =π×r p 2 ×L×X (4)

[0066] Among them, r p is the radius of the pressure relief drilling hole, m; L is the depth of the pressure relief drilling hole, m; X is the number of pressure relief drilling holes, pieces.

[0067] Similarly, the coal discharge volume of hydraulic expansion or hydraulic slot drilling is V ybs The calculation expression is:

[0068] V ybs=π×r p 2 ×L×X+V1×Y (5)

[0069] Among them, V ybs The coal discharge volume of hydraulic expansion or hydraulic slot drilling in the general dangerous area of ​​ground stress, m 3 ; V1 is the volume of coal discharged from a hydraulically expanded hole or a hydraulically cut seam, m 3 ; Y is the number of hydraulically expanded holes or the number of hydraulically cut slots, pieces.

[0070] Theoretical analysis shows that the amount of coal discharged is proportional to the ground stress, that is, the volume of coal that needs to be discharged in the area with medium or severe ground stress is V. zd 、V yz = The ratio of their respective stress increment coefficients to the stress increment coefficients of the general grade of geostress hazard areas multiplied by V yb or V ybs Taking the area with medium-risk level of ground stress as an example, when using large-diameter pressure relief drilling or hydraulic expansion and hydraulic slotting technology, V zd 、V zds The calculation formulas are shown in formula (6) and (7) respectively:

[0071] V zd =(k zd / k yb )×π×r p 2 ×L×X (6)

[0072] Among them, k zd (1 / 3≤k zd ≤2 / 3) is the stress increment coefficient in the area with medium-risk level of ground stress; k yb (k yb <1 / 3) is the stress increment coefficient of the general dangerous area of ​​ground stress; V zd is the coal discharge volume after decompression in large-diameter decompression boreholes in medium-risk areas of geostress, m 3 .

[0073] V zds =(k zd / k yb )×(π×r p 2 ×L×X+V1×Y) (7)

[0074] Among them, V zds The coal discharge volume of hydraulic expansion or hydraulic slot drilling in medium-risk areas of ground stress, m 3 .

[0075] Therefore, in order to make the medium-risk level area of ​​ground stress meet the requirements of burst prevention, the ground stress danger can be eliminated by adjusting the parameters such as X or Y in equations (6) and (7);

[0076] The same applies to areas with severe grades, thus achieving graded prevention of ground stress hazards.

[0077] (2) Gas burst prevention by graded method

[0078] The main method for preventing gas outbursts by graded extraction is to extract gas through extraction drilling to reduce the gas pressure and gas content in the coal seam. The specific amount of gas to be extracted can be determined by referring to the "Detailed Rules for Preventing and Controlling Coal and Gas Outbursts" or by on-site actual measurement and investigation.

[0079] Assume that the amount of gas to be extracted from a general gas hazardous area is Q yb The gas hazard can be reduced and the gas volume Q yb The calculation expression is:

[0080] Q yb =Q r ×X (8)

[0081] Among them, Q r is the gas volume after extraction time t of a drainage borehole when the extraction radius is r, m 3 ; X is the number of holes drilled, pcs.

[0082] The general gas danger zone can meet the requirements of burst prevention by adjusting one or more parameters such as extraction radius r, extraction time t, number of drilling holes X, etc. Since the amount of extracted gas is proportional to the gas content, the amount of gas to be extracted in the medium and severe gas danger zone is Q zd , Q yz , then the same method can be used to achieve graded prevention of gas danger in areas with medium and severe gas dangers. Similarly, the method of reducing gas pressure shall be implemented with reference to gas content.

[0083] (3) Coal seam extraction performance classification and outburst prevention

[0084] Coal seam extraction performance classification and outburst prevention mainly improve the extraction effect of drilling holes by increasing the coal seam permeability coefficient, increasing the drilling porosity, protecting the holes and other methods.

[0085] 1) Coal seam permeability coefficient

[0086] Assume that the amount of gas that needs to be extracted from the easily drained coal seam area is Q ry The gas outflow prevention requirement can be met in 1 hour. ry The calculation expression is:

[0087] Q ry =Q λ1 ×X (9)

[0088] Among them, Q λ1 is the gas volume of a drainage borehole in the easily drainable coal seam after drainage time t, m 3 ; X is the number of holes drilled, pcs.

[0089] The method of increasing the permeability coefficient of coal seams by permeability enhancement technology can also be used to achieve the requirements of preventing gas outbursts by adjusting one or more parameters such as the extraction radius r, the extraction time t, and the number of drill holes X. Since the amount of gas extracted is proportional to the gas content, the amount of gas that needs to be extracted in the area of ​​the coal seams that are difficult to extract and can be extracted is Q jn , Q ky , then the same method can be used to achieve graded prevention of coal seam gas extraction performance in areas where coal seams are difficult or can be extracted.

[0090] 2) Coal solidity coefficient

[0091] Practice shows that the drilling construction of extraction holes in medium-hard coal seams and relatively hard coal seams has a high borehole completion rate, and generally does not require measures to prevent the hole from collapsing, and the gas extraction effect can be achieved; however, it is different in soft coal seams. The drilling of extraction holes in soft coal seams not only has a low borehole completion rate and is difficult to reach the designed length, but also the hole is very easy to collapse after drilling, causing the hole to collapse. Therefore, special drilling rigs and drilling tools are used in soft coal seams to increase the drilling completion rate or to adopt measures to protect the hole with casing throughout the process, so as to improve the extraction effect and achieve the effect of preventing sudden outbursts.

[0092] (4) Comprehensive classification of coal seam ground stress, gas, and extraction performance to prevent coal outbursts

[0093] It should be noted that the above (1) to (3) only describe the single factor graded prevention of coal seam ground stress, gas, and drainage performance. In the actual prevention process, the three factors are coupled, and it is necessary to consider the coupling of the three to carry out comprehensive graded prevention of coal seam ground stress, gas, and drainage performance. That is, first, the single factor graded prevention of coal seam ground stress, gas, and drainage performance is met respectively, and the three factors meet the graded prevention requirements at the same time and are taken into account in a comprehensive manner.

[0094] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the purpose and scope of the technical solution, which should be included in the scope of the claims of the present invention.

Claims

1. A method for preventing coal outbursts in deep coal seams by graded method, characterized in that: The method comprises the following steps: S1: Classify the dangerous level of geostress of the protruding coal seam, specifically: divide the dangerous level of geostress of the coal seam into three levels: general, medium and severe according to the size of the stress increment coefficient; Stress increment factor k The calculation formula is: k = k 0 + k 1 + k 2 in, k 0=(H1-H) / H, H is the depth of coal seam, the depth of coal seam in a certain area is H1; k 1 is the stress concentration factor caused by geological structure; k 2 is the stress concentration coefficient caused by the goaf; S2: Classification of gas hazard levels in outburst coal seams; S3: Classify the performance level of extraction of outburst coal seams; S4: Determine the coal seam outburst prevention level; S5: Carry out graded prevention of coal seam outbursts according to the coal seam outburst prevention grade. Specifically, carry out graded prevention of coal seam outbursts according to the determined coal seam in-situ stress hazard grade, gas hazard grade and extraction performance grade, and carry out comprehensive prevention of coal seam outbursts according to the coupling of the three. Ground stress graded outburst prevention is to use large diameter pressure relief drilling, hydraulic hole expansion or hydraulic slotting technology to discharge part of the coal body in the coal seam to prevent outburst; Coal discharge volume V from large-diameter pressure relief boreholes in areas with general geostress hazard levels yb The calculation formula is: In yb = π ×r p 2 ×L×X Among them, r p is the radius of the pressure relief drilling hole; L is the depth of the pressure relief drilling hole; X is the number of pressure relief drilling holes; Similarly, the coal discharge volume V of hydraulic expansion or hydraulic slot drilling is ybs The calculation formula is: In ybs = π ×r p 2 ×L×X + V1×Y Wherein, V1 is the volume of coal discharged from a hydraulically expanded cavity or a hydraulically cut slot; Y The number of hydraulically expanded holes or hydraulically cut seams; In the medium and severe risk levels of geostress, the coal discharge volume using the same technology is the ratio of the stress increment coefficient to the stress increment coefficient of the general risk level of geostress multiplied by V yb or V ybs ; Eliminate the danger of ground stress by adjusting X or Y.

2. The method for preventing coal outbursts in deep coal seams by graded method according to claim 1 is characterized in that: Step S2 specifically includes: classifying the coal seam gas hazard level into three levels: general, medium and severe according to the original gas pressure and original gas content of the coal seam.

3. The method for preventing coal outbursts in deep coal seams by graded method according to claim 1, characterized in that: Step S3 specifically includes: according to the coal seam permeability coefficient λ The coal seam extraction performance level is divided into three levels: difficult to extract coal seams, extractable coal seams and easy to extract coal seams; according to the solidity coefficient of coal f The coal seam extraction performance level is divided into three levels: soft coal seam, medium hard coal seam and relatively hard coal seam.

4. The method for preventing coal outbursts in deep coal seams by graded method according to claim 1, characterized in that: In step S5, gas graded outburst prevention is to reduce the gas pressure and gas content in the coal seam by extracting gas through extraction drilling holes; The amount of gas that needs to be extracted from a gas hazardous area is Q yb The calculation formula is: Q yb =Q r ×X Among them, Q r is the gas volume of a drainage borehole after drainage time t when the drainage radius is r; X is the number of boreholes; The amount of gas that needs to be extracted from the medium-risk and severe-risk areas of gas is adjusted to meet the requirements of burst prevention by adjusting one or more parameters among the extraction radius r, extraction time t and number of boreholes X; Similarly, the method for reducing gas pressure is implemented with reference to the gas content.

5. The method for preventing coal outbursts in deep coal seams by graded method according to claim 1, characterized in that: In step S5, the coal seam extraction performance classification and outburst prevention improve the extraction effect of the borehole by increasing the coal seam permeability coefficient, increasing the drilling porosity and the hole protection method; The amount of gas that needs to be extracted from the coal seam area that is easy to extract is Q ry The calculation formula is: Q ry =Q λ1 ×X Among them, Q λ1 is the gas volume of a drainage borehole in the easily drainable coal seam after drainage time t; X is the number of boreholes; The amount of gas that needs to be extracted from the coal seams that are difficult to extract and the coal seams that can be extracted is achieved by increasing the permeability coefficient of the coal seams through permeability enhancement technology, or by adjusting one or more parameters among the extraction radius r, extraction time t and number of drill holes X to meet the requirements of gas outburst prevention, thereby achieving graded gas outburst prevention of coal seam gas extraction performance.

6. The method for preventing coal outbursts in deep coal seams by graded method according to claim 1, characterized in that: In step S5, the soft coal seam adopts measures such as increasing the drilling rate or using casing throughout the process to protect the borehole, so as to improve the extraction effect and achieve the effect of preventing sudden coal outbursts.

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