A method for accurately predicting the danger of deep coal seam outburst

Abstract

The present invention relates to a method for accurately predicting the risk of coal seam outburst in deep coal seams, and belongs to the field of coal and gas outburst prevention and control in coal mines. The method comprises: S1: determining the critical value of the coal seam outburst risk prediction index under general conditions, wherein the prediction index includes the original gas pressure and the original gas content; S2: determining the size of the characterization parameter of the factors affecting coal seam outburst; S3: calculating the difference coefficient of the coal seam outburst risk in the prediction area; S4: correcting the coal seam gas pressure and gas content in the prediction area; S5: predicting the outburst risk of the coal seam. The present invention solves the problem that the existing method for predicting the risk of coal seam outburst in deep coal seams does not fully consider factors such as ground stress, gas and coal rock physical and mechanical properties and their differences, and the prediction of outburst risk is not accurate enough. The present invention can not only make up for the shortcomings of the existing prediction method, but also improve the accuracy of the prediction of the risk of coal seam outburst in deep coal seams, which is of great significance for the accurate and efficient prevention of outburst in deep coal seams.

Description

Technical Field

[0001] The present invention belongs to the field of coal and gas outburst prevention and control in coal mines, and relates to a method for accurately predicting the danger of coal seam outburst in deep coal seams. Background Art

[0002] As coal mining depth increases, the in-situ stress in deep coal seams and the elastic potential energy of the roof rock strata further increase their impact on coal and gas outbursts. Coal and gas outburst disasters are gradually shifting from shallow gas-dominated to deep stress-dominated, making deep coal and gas outburst disasters one of the major issues hindering safe and efficient coal mine production. Secondly, the magnitude of deep coal seam outburst hazard is the result of the combined effects of in-situ stress, gas, and the physical and mechanical properties of coal and rock. Existing outburst hazard prediction methods rely solely on single indicators such as gas pressure or gas content, failing to fully consider the combined effects and contributions of in-situ stress, gas, and the physical and mechanical properties of coal and rock on outbursts. Furthermore, in-situ stress, gas, and the physical and mechanical properties of coal and rock vary across different prediction regions, making the use of the same indicator for prediction across different regions both unreasonable and inaccurate.

[0003] Based on the above problems, there is an urgent need for a coal seam outburst hazard prediction method that comprehensively considers parameters such as ground stress, gas, and physical and mechanical properties of coal and rock and their differences. Summary of the Invention

[0004] In view of this, the purpose of the present invention is to provide a method for accurately predicting the risk of coal outbursts in deep coal seams that comprehensively considers the parameters characterizing the in-situ stress, gas, and physical and mechanical properties of coal rocks, as well as their differences. This method addresses the technical difficulties that existing methods for predicting the risk of coal outbursts in deep coal seams fail to comprehensively consider factors such as in-situ stress, gas, and the physical and mechanical properties of coal rocks, as well as their differences, resulting in insufficiently reasonable and accurate predictions of the risk of coal outbursts. This method not only remedies the shortcomings of existing prediction methods but also improves the accuracy of deep coal seam coal outburst risk predictions, which is of great significance for the precise and efficient prevention of coal outbursts in coal seams.

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

[0006] A method for accurately predicting the danger of deep coal seam outburst, comprising the following steps:

[0007] S1: Determine the critical values ​​of coal seam outburst hazard prediction indicators under general conditions, where the prediction indicators include original gas pressure and original gas content;

[0008] S2: Determine the size of the characterization parameters of the factors affecting coal seam outburst;

[0009] S3: Calculate the difference coefficient of coal seam outburst hazard in the predicted area;

[0010] S4: Correct the gas pressure and gas content of coal seams in the predicted area;

[0011] S5: Predict the risk of coal seam outburst.

[0012] Furthermore, in step S2, the characterization parameters of the factors affecting coal seam outburst include the ground stress characterization parameters, gas characterization parameters and coal rock physical and mechanical property characterization parameters of the predicted area; the ground stress characterization parameters include self-weight stress, tectonic stress and structural stress; the gas characterization parameters include gas pressure and gas content; the coal rock physical and mechanical property characterization parameters include roof rock layer structural characteristic parameters, coal strength coefficient and coal gas release initial velocity.

[0013] Furthermore, in step S3, the calculation formula of the difference coefficient x of coal seam outburst hazard in the predicted area is:

[0014] x=a1×b1×b2×c1×c2×c3

[0015] Among them, a1, b1, b2, c1, c2, and c3 are the ground stress difference coefficient, gas pressure difference coefficient, gas content difference coefficient, roof rock structure characteristic parameter difference coefficient, coal strength coefficient difference coefficient, and coal gas release initial velocity difference coefficient, respectively.

[0016] Furthermore, in step S3, the calculation formula of the ground stress difference coefficient a1 is:

[0017] a1=σ t / σ d

[0018] Among them, a1 is the coefficient of regional stress difference, σ t To predict the regional coal seam ground stress, MPa; σ d is the ground stress of coal seam under general conditions, MPa.

[0019] Furthermore, in step S3, the calculation formula of the gas pressure difference coefficient b1 is:

[0020] b1=max(P c / P s , P c / P0)

[0021] Among them, b1 is the original gas pressure difference coefficient of the coal seam in the prediction area; P c To predict the original gas pressure of regional coal seams measured on site, MPa; P s is the gas pressure at the shallowest depth during coal seam outburst accident, MPa; P0 is the critical value of gas pressure of coal seam outburst prediction index determined by on-site investigation, MPa;

[0022] The calculation formula of gas content difference coefficient b2 is:

[0023] b2=max(W c / W s , W c / W0)

[0024] Wherein, b2 is the coefficient of difference of original gas content in coal seam in prediction area; W c To predict the original gas content of regional coal seams measured on site, m 3 / t;W s To highlight the gas content at the shallowest depth during an accident, m 3 / t; W0 is the critical value of the original gas content of the coal seam outburst prediction index determined by on-site investigation, m 3 / t.

[0025] Furthermore, in step S3, the calculation formula of the roof rock layer structural characteristic parameter difference coefficient c1 is:

[0026] c1=L c / L s

[0027] Where c1 is the difference coefficient of the structural characteristic parameters of the roof rock layer in the prediction area; L c is the structural characteristic parameter of the roof rock layer in the predicted area; L s It is the structural characteristic parameter of the roof rock layer under general conditions;

[0028] The calculation formula of the difference coefficient c2 of the coal solidity coefficient is:

[0029] c2=f c / f0

[0030] Among them, c2 is the coefficient of difference in the solidity coefficient of the coal in the prediction area; f c is the solidity coefficient of coal in the predicted area; f0 is the solidity coefficient of coal under general conditions;

[0031] The calculation formula of the difference coefficient c3 of coal gas emission initial velocity is:

[0032] c3=△P c / △P0

[0033] Where c3 is the coefficient of difference in initial gas emission velocity of coal in the prediction area; △P c is the initial gas emission velocity of coal in the predicted area; △P0 is the initial gas emission velocity of coal under general conditions.

[0034] Furthermore, in step S4, the calculation formulas for correcting the original gas pressure and original gas content of the coal seam in the prediction area are:

[0035] P1=x×Pc

[0036] W1=x×W c

[0037] Among them, P1 and W1 are the correction values ​​of the original gas pressure and original gas content of the prediction indicators, MPa; c To predict the original gas pressure of regional coal seams measured on site, MPa; W c To predict the original gas content of regional coal seams measured on site, m 3 / t.

[0038] Furthermore, in step S5, predicting the outburst hazard of the coal seam specifically includes: re-measuring the original gas pressure P2 and original gas content W2 of different predicted areas of the coal seam on site, and then comparing the maximum of the two measured values ​​and the predicted index correction value with the predicted index critical value to determine the outburst hazard of the predicted coal seam. The specific judgment criteria are:

[0039] When max(P c , P1, P2)≥min(P c 、P s ) or max(W c , W1, W2)≥min(W c 、W s ), the coal seam is predicted to have the danger of coal outburst; otherwise, the coal seam is predicted not to have the danger of coal outburst.

[0040] The beneficial effect of the present invention is that the present invention fully considers the various influencing factors and their differences of the ground stress, gas, and physical and mechanical properties of coal rocks in deep coal seams, which not only makes up for the shortcomings of existing prediction methods, but also improves the accuracy of prediction of deep coal seam outburst hazards, which is of great significance to the accurate and efficient prevention of deep coal seam outbursts.

[0041] Other advantages, objects, and features of the present invention will be described in part in the following description and, in part, will be apparent to those skilled in the art upon examination of the following or may be learned from practice of the present invention. The objects and other advantages of the present invention may be realized and obtained through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] 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 with reference to the accompanying drawings, in which:

[0043] Figure 1 This is a flow chart of the method for accurately predicting the danger of deep coal seam outburst according to the present invention. DETAILED DESCRIPTION

[0044] The following describes the embodiments of the present invention by means of 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 are only schematic illustrations of the basic concept of the present invention, and the following embodiments and features in the embodiments can be combined with each other without conflict.

[0045] See also Figure 1 The present invention provides a method for accurately predicting the danger of deep coal seam outburst, which specifically includes the following steps:

[0046] Step 1: Study and determine the critical values ​​of coal seam outburst hazard prediction indicators under general conditions.

[0047] According to current regulations, the main indicators for predicting coal seam outburst hazards are original gas pressure and original gas content. The method for determining the critical values ​​of these indicators is detailed as follows:

[0048] (1) Gas pressure

[0049] If there has been a coal and gas outburst accident in the mine history, the gas pressure P at the shallowest depth when the outburst accident occurred can be used. s As the critical value of the coal seam outburst hazard prediction index; if there has been no coal and gas outburst accident in the mine history, the coal seam outburst prediction index gas pressure critical value P0 is determined by on-site inspection; if both conditions are met at the same time, the minimum value min (P s , P0).

[0050] (2) Gas content

[0051] Similarly, if a coal and gas outburst accident has occurred in the mine history, the gas content W at the shallowest depth when the outburst accident occurred can be used. s As the critical value of the coal seam outburst hazard prediction index; if there has been no coal and gas outburst accident in the mine history, the critical value of the gas content of the coal seam outburst prediction index W0 is determined by on-site inspection; if both conditions are met at the same time, the minimum value min (W s , W0).

[0052] Step 2: Study and determine the size of the characterization parameters of the factors affecting coal seam outburst.

[0053] The main factors affecting coal seam outburst are ground stress, gas, and the physical and mechanical properties of coal and rock. The method for determining the size of the characterization parameters of each influencing factor is detailed as follows:

[0054] (1) Characterization parameters of geostress

[0055] Coal seam ground stress mainly consists of the superposition of three parts: self-weight stress, tectonic stress, and structural stress. The calculation formula is as follows:

[0056] σ d =γH+k1σ z +k2σ z (1)

[0057] Among them, σ d is the ground stress of the coal seam, MPa; γ is the bulk density of the overlying rock layer, N / m 3 ; H is the depth of coal seam, m; k1 is the stress concentration coefficient caused by geological structure; k2 is the stress concentration coefficient caused by the open space in the goaf; σ z is the self-weight stress of the coal seam, MPa.

[0058] (2) Gas characterization parameters

[0059] The main parameters characterizing coal seam gas are gas pressure and gas content. The gas pressure and gas content are generally tested on site. If the testing conditions are not available, the Langmuir calculation formula is used for calculation.

[0060]

[0061] Where W is the gas content, m 3 / t; a and b are adsorption constants; p is gas pressure, MPa; M ad is water content, %; A ad is ash content, %; F is porosity, %; ARD is apparent density, t / m 3 .

[0062] (3) Characterization parameters of coal rock physical and mechanical properties

[0063] The parameters characterizing the physical and mechanical properties of coal rock mainly include the structural characteristic parameters of the roof rock layer, the solidity coefficient of coal, the initial velocity of coal gas emission, etc. The determination methods are detailed as follows:

[0064] 1) Roof rock structure characteristic parameters

[0065] The roof rock of a coal seam has elastic potential energy, which contributes significantly to coal outbursts. The main rock layers that affect coal and gas outbursts are those within 100m of the roof from the coal seam upwards, with sandstone layers of high rock strength and thickness playing a major role. The formula for calculating the characteristic parameters of the roof rock layer thickness, using sandstone as a standard, is as follows:

[0066] L s =Σh i r i (3)

[0067] Among them, h i is the total thickness of the i-th rock layer within 100 m above the roof; r i is the weak plane decline coefficient of the given rock formation.

[0068] If the weak plane coefficient of sandstone is defined as 1.0, the weak plane reduction coefficients of mudstone, shale, and coal are 0.62, 0.29, and 0.31, respectively. Substituting the rock layers within 100 m of the coal seam roof into formula (3) in sequence, the structural characteristic parameters of the roof rock layers can be obtained.

[0069] 2) Coal solidity coefficient

[0070] The hardness of the coal seam is characterized by the coal's strength coefficient f and tested using the heavy hammer method. For details, please refer to Part 12: Determination of coal's strength coefficient in GBT23561.12-2010 Methods for determination of physical and mechanical properties of coal and rock.

[0071] 3) Initial velocity of coal gas emission

[0072] The index of gas release amount within a fixed time is characterized by the initial gas emission velocity ΔP of coal, and is tested by the variable volume and pressure method or the constant volume and pressure method. For details, please refer to the AQ 1080-2009 coal gas emission initial velocity index (ΔP) determination method.

[0073] Step 3: Calculate the difference coefficient of coal seam outburst hazard in the predicted area

[0074] When the coal seam prediction area changes, it is necessary to study and determine the difference coefficient of coal seam outburst hazard in the prediction area, that is, first calculate the difference coefficient of the characterization parameters of the influencing factors of the coal seams in different prediction areas, and then multiply the difference coefficients of the characterization parameters of the influencing factors of all determination methods. The determination method is detailed as follows:

[0075] (1) Geostress difference coefficient

[0076] It is known that the ground stress of coal seam under general conditions is σ d , calculate the ground stress of coal seams in different prediction areas as σ t , then, the calculation formula for the difference coefficient of coal seam stress characterization parameters in different prediction areas is as follows:

[0077] a1=σ t / σ d (4)

[0078] Where a1 is the coefficient of regional stress difference; σ t is the ground stress of coal seams in different prediction areas, MPa.

[0079] (2) Gas characterization parameter difference coefficient

[0080] 1) Gas pressure difference coefficient

[0081] When the coal seam prediction area changes, first test the coal seam gas pressure P in the prediction area on site. c , and then compare it with the gas pressure P at the shallowest depth during the outburst accident s Alternatively, the critical value P0 of the gas pressure for coal seam outburst prediction can be determined by examining and taking the ratio, and finally taking the maximum value of the two to obtain the gas pressure difference coefficient. The calculation formula is as follows:

[0082] b1=max(P c / P s , P c / P0) (5)

[0083] Among them, b1 is the original gas pressure difference coefficient of the coal seam in the prediction area; P c To predict the measured original gas pressure of regional coal seam, MPa; P s is the gas pressure at the shallowest burial depth during coal seam outburst accident, in MPa; P0 is the critical value of gas pressure of coal seam outburst prediction index determined by on-site investigation, in MPa.

[0084] 2) Gas content variability coefficient

[0085] Similarly, when the coal seam prediction area changes, the coal seam gas content W is tested on site. c and the gas content W at the shallowest depth during the outburst accident s Or, the critical value W0 of the gas content of the coal seam outburst prediction index can be determined by examining and taking the ratio, and taking the maximum value of the two to obtain the gas content difference coefficient, as shown in the following formula:

[0086] b2=max(W c / W s , W c / W0) (6)

[0087] Wherein, b2 is the coefficient of difference of original gas content in coal seam in prediction area; W c To predict the measured original gas content of regional coal seams, m 3 / t;W s To highlight the gas content at the shallowest depth during an accident, m 3 / t; W0 is the critical value of the original gas content of the coal seam outburst prediction index determined by on-site investigation, m 3 / t.

[0088] (3) Difference coefficient of parameters characterizing physical and mechanical properties of coal and rock

[0089] 1) Difference coefficient of structural characteristic parameters of roof rock layer

[0090] When the coal seam prediction area changes, calculate the roof rock structure characteristic parameter L c The roof rock structure characteristic parameter Ls under general conditions is then used to calculate the roof rock structure characteristic parameter difference coefficient, which is calculated as follows:

[0091] c1=L c / L s (7)

[0092] Where c1 is the difference coefficient of the structural characteristic parameters of the roof rock layer in the prediction area; L c is the structural characteristic parameter of the roof rock layer in the predicted area; L s It is the characteristic parameter of roof rock structure under general conditions.

[0093] 2) Coal solidity coefficient difference coefficient

[0094] Similarly, when the coal seam prediction area changes, take coal samples to test the coal strength coefficient f c and take the ratio with the solidity coefficient f0 of coal under general conditions, the calculation formula is as follows:

[0095] c2=f c / f0 (8)

[0096] Among them, c2 is the coefficient of difference in the solidity coefficient of the coal in the prediction area; f c is the strength coefficient of coal in the predicted area; f0 is the strength coefficient of coal under general conditions.

[0097] 3) Coefficient of initial velocity difference of coal gas emission

[0098] Similarly, when the coal seam prediction area changes, take coal samples to test the coal gas release initial velocity △P c The ratio of the initial gas emission velocity of coal under general conditions to △P0 is calculated as follows:

[0099] c3=△P c / △P0 (9)

[0100] Where c3 is the coefficient of difference in initial gas emission velocity of coal in the prediction area; △P c is the initial gas emission velocity of coal in the predicted area; △P0 is the initial gas emission velocity of coal under general conditions.

[0101] (4) Prediction of regional coal seam outburst hazard difference coefficient

[0102] By multiplying the difference coefficients of coal seam ground stress, gas, and coal rock physical and mechanical properties in the above-mentioned prediction area, the difference coefficient of coal seam outburst hazard in the prediction area can be obtained. The calculation formula is as follows:

[0103] x=a1×b1×b2×c1×c2×c3 (10)

[0104] Among them, x is the difference coefficient of coal seam outburst hazard in the predicted area.

[0105] Step 4: Correct the predicted regional coal seam gas pressure and gas content.

[0106] According to the prediction area coal seam outburst risk difference coefficient determined in step 3, it is x. The original gas pressure of the coal seam measured on site is known to be P. c , original gas content W c Then, in order to comprehensively reflect the coal seam outburst hazard under the combined effects of ground stress, gas, and the physical and mechanical properties of coal rock, the original gas pressure and original gas content, which are the prediction indicators of coal seam outburst hazard in the prediction area, are corrected. The calculation formula is as follows:

[0107] P1=x×P c (11)

[0108] W1=x×W c (12)

[0109] Among them, P1 and W1 are the correction values ​​of the prediction indicators original gas pressure and original gas content, respectively, in MPa.

[0110] Step 5: Predict the outburst hazard of the coal seam.

[0111] The original gas pressure P2 and original gas content W2 of different predicted areas of the coal seam are measured again on site. Then the maximum value of the two measured values ​​and the predicted index correction value is taken and compared with the predicted index critical value to determine the outburst hazard of the predicted coal seam. The judgment criteria are as follows:

[0112] When max(P c , P1, P2)≥min(P c 、P s ) or max(W c , W1, W2)≥min(W c 、W s ), the coal seam is predicted to have the danger of coal outburst; otherwise, the coal seam is predicted not to have the danger of coal outburst.

[0113] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not limiting. 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 solutions of the present invention can be modified or replaced by equivalents without departing from the purpose and scope of the technical solutions, which should all be included in the scope of the claims of the present invention.

Claims

1. A method for accurately predicting the danger of deep coal seam outburst, characterized in that: The method comprises the following steps: S1: Determine the critical values ​​of coal seam outburst hazard prediction indicators under general conditions, where the prediction indicators include original gas pressure and original gas content; S2: Determine the size of the characterization parameters of the factors affecting coal seam outburst; S3: Calculate the difference coefficient x of coal seam outburst hazard in the predicted area. The calculation formula is: x=a1×b1×b2×c1×c2×c3 Among them, a1, b1, b2, c1, c2, and c3 are the difference coefficient of ground stress, the difference coefficient of gas pressure, the difference coefficient of gas content, the difference coefficient of roof rock structure characteristic parameters, the difference coefficient of coal solidity coefficient, and the difference coefficient of coal gas release initial velocity respectively; S4: Correct the original gas pressure and original gas content of the coal seam in the predicted area. The calculation formulas are: P1=x×P c W1=x×W c Among them, P1 and W1 are the correction values ​​of the original gas pressure and original gas content of the prediction indicators respectively; P c To predict the original gas pressure of regional coal seams measured on site; W c To predict the original gas content of regional coal seams on site; S5: Predict the outburst hazard of coal seams, specifically including: re-measure the original gas pressure P2 and original gas content W2 of different predicted areas of coal seams on site, then compare the maximum of the two measured values ​​and the predicted index correction value with the predicted index critical value to determine the outburst hazard of the predicted coal seam. The specific judgment criteria are: when max(P c , P1, P2)≥min(P c 、P s ) or max(W c , W1, W2)≥min(W c 、W s ), the coal seam is predicted to have the risk of outburst; otherwise, the coal seam is predicted not to have the risk of outburst; where P s W is the gas pressure at the shallowest depth during an accident; s To highlight the gas content at the shallowest burial depth during an accident.

2. The method for accurately predicting the danger of deep coal seam outburst according to claim 1 is characterized in that: In step S2, the characterization parameters of the factors affecting coal seam outburst include the ground stress characterization parameters, gas characterization parameters and coal rock physical and mechanical property characterization parameters of the predicted area; the ground stress characterization parameters include self-weight stress, tectonic stress and structural stress; the gas characterization parameters include gas pressure and gas content; the coal rock physical and mechanical property characterization parameters include roof rock layer structural characteristic parameters, coal strength coefficient and coal gas release initial velocity.

3. The method for accurately predicting the danger of deep coal seam outburst according to claim 1 is characterized in that: In step S3, the calculation formula of the ground stress difference coefficient a1 is: a1=s t / s d Among them, a1 is the coefficient of regional stress difference, σ t To predict the magnitude of regional coal seam stress, σ d It is the ground stress of coal seam under general conditions.

4. The method for accurately predicting the danger of deep coal seam outburst according to claim 1 is characterized in that: In step S3, the calculation formula of the gas pressure difference coefficient b1 is: b1=max(P c / P s ,P c / P0) Among them, b1 is the original gas pressure difference coefficient of the coal seam in the prediction area; P c To predict the original gas pressure of regional coal seams measured on site; P s is the gas pressure at the shallowest depth during coal seam outburst accident; P0 is the critical value of gas pressure of coal seam outburst prediction index determined by on-site investigation; The calculation formula of gas content difference coefficient b2 is: b2=max(W c / W s ,W c / W0) Wherein, b2 is the coefficient of difference of original gas content in coal seam in prediction area; W c To predict the original gas content of regional coal seams measured on site; W s It is the gas content at the shallowest burial depth during coal seam outburst accident; W0 is the critical value of the original gas content of the coal seam outburst prediction indicator determined by on-site investigation.

5. The method for accurately predicting the danger of deep coal seam outburst according to claim 1 is characterized in that: In step S3, the calculation formula of the roof rock layer structural characteristic parameter difference coefficient c1 is: c1=L c / L s Where c1 is the difference coefficient of the structural characteristic parameters of the roof rock layer in the prediction area; L c is the structural characteristic parameter of the roof rock layer in the predicted area; L s It is the structural characteristic parameter of the roof rock layer under general conditions; The calculation formula of the difference coefficient c2 of the coal solidity coefficient is: c2= f c / f 0 Among them, c2 is the coefficient of difference in the solidity coefficient of coal in the prediction area; f c is the solidity coefficient of the coal in the predicted area; f 0 is the solidity coefficient of coal under general conditions; The calculation formula of the difference coefficient c3 of coal gas emission initial velocity is: c3=△P c / △P0 Where c3 is the coefficient of difference in initial gas emission velocity of coal in the prediction area; △P c is the initial gas emission velocity of coal in the predicted area; △P0 is the initial gas emission velocity of coal under general conditions.

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