CN103411868A - Measuring method for coal seam gas permeability coefficient - Google Patents

Abstract

The invention discloses a method for testing the air permeability coefficient of a coal seam, which comprises the following steps: constructing two boreholes with the same depth at a certain distance and perpendicular to the coal seam, and recording the distance d between the boreholes; obtaining the absolute gas pressure P of the coal seam; Inject the tracer gas into the borehole and connect it with the air compressor to provide a certain pressure, and another borehole is sealed with the pipeline of the gas drainage system; detect the tracer gas and confirm that the borehole is self-connected The time t from the gas drainage system pipeline to the detection of the tracer gas; the test results are substituted into the calculation formula of the coal seam permeability coefficient to obtain the coal seam permeability coefficient; the calculation process is simple, and a certain gas injection pressure is provided by the compressor. And another borehole is connected with the pipeline of the gas drainage system to maintain negative pressure at the orifice, so that the tracer gas can be quickly measured, the test period is short, and the universal applicability is strong.

Description

A test method for coal seam permeability coefficient

technical field

The invention relates to the technical field of coal mine gas control, in particular to a method for testing the air permeability coefficient of coal seams.

Background technique

my country is not only the world's largest coal producer, but also the largest coal consumer. For a long time, coal has accounted for more than two-thirds of China's primary energy production and consumption structure. With the increase of mine mining depth and the increase of ground stress, the risk of coal seam outburst is increasing day by day. my country has become the country with the most serious coal and gas outburst accidents in the world, and the number and intensity of coal and gas outbursts have also reached best in the world. Gas drainage is a key technical means to effectively control gas accidents and solve the problem of safety production in coal mines in my country. The coal seam air permeability coefficient is a sign of the difficulty of coal seam gas flow, and is an important technical parameter for evaluating the difficulty of coal seam gas drainage and gas outburst prevention and control; coal seam air permeability coefficient is the basis and foundation of gas drainage design. Therefore, accurate testing of coal seam permeability coefficient plays a vital role in mine gas drainage.

At present, the borehole radial flow method is mainly used in my country to test the gas permeability coefficient of coal seams. However, this test method requires multiple trial calculations in a set of formulas to find a suitable calculation formula when calculating the air permeability coefficient, which brings inconvenience to the calculation. At the same time, the theoretical analysis also shows that the existing calculation methods still have problems such as the inability to find a suitable calculation formula or the existence of two contradictory calculation results. Moreover, the borehole radial flow method first needs to accurately measure the original gas pressure of the coal seam, and then test the borehole gas flow rate at each time; the test period is longer, and for coal seams with lower coal seam gas pressure, the coal seam gas pressure and borehole gas flow rate are often It is difficult to measure accurately, so its applicability is also limited.

Contents of the invention

The purpose of the invention is to overcome the defects of the prior art and provide a test method for coal seam air permeability coefficient which is simple in calculation, short in test period and capable of accurate measurement.

To achieve the above object, the present invention adopts the following technical solutions:

A method for testing the air permeability coefficient of a coal seam, comprising the steps of:

(1) In a place where the coal seam is relatively intact, without faults, and without broken zones, two boreholes of the same depth are constructed at a certain distance and perpendicular to the coal seam, and the borehole spacing d is recorded;

(2) Obtain the absolute gas pressure P of the coal seam;

(3) Inject tracer gas into one of the boreholes, and connect the air compressor to the borehole in a sealed manner. The pressure P _Y provided by the air compressor should be greater than the absolute gas pressure P of the coal seam obtained in step (2); The hole is sealed and connected with the pipeline of the gas drainage system, and the negative pressure P _C of the hole is measured;

(4) Test the tracer gas at the borehole connected to the gas drainage system every day until the tracer gas is detected; time t;

(5) Calculate the air permeability coefficient λ of the coal seam, which specifically includes the following steps:

1) To measure the seepage velocity of the tracer gas in the coal seam, the calculation formula is as follows:

$\mathrm{<span\; class="notranslate">\; v</span>}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; d</span>}}{\mathrm{<span\; class="notranslate">\; t</span>}}$

In the formula, v—the seepage velocity of the tracer gas in the coal seam, m/d;

d—drilling hole spacing, m;

t—the time taken to detect the tracer gas, d;

2) Calculate the coal seam permeability coefficient, the calculation process is as follows:

According to Darcy's law:

$\mathrm{<span\; class="notranslate">\; v</span>}<span\; class="notranslate">\; =</span><span\; class="notranslate">\; -</span>\frac{\mathrm{<span\; class="notranslate">\; k</span>}}{\mathrm{<span\; class="notranslate">\; \&mu;</span>}}\frac{<span\; class="notranslate">\; \&PartialD;</span>\mathrm{<span\; class="notranslate">\; p</span>}}{<span\; class="notranslate">\; \&PartialD;</span>\mathrm{<span\; class="notranslate">\; x</span>}}$

In the formula, k—permeability, m ² ;

μ—dynamic viscosity coefficient, Pa·s;

And the definition formula of coal seam permeability coefficient is:

$\mathrm{<span\; class="notranslate">\; \&lambda;</span>}<span\; class="notranslate">\; =</span><span\; class="notranslate">\; -</span>\frac{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="Bk"\; filenames="HDA00003567030300011.png"\; state="\{\{state\}\}">Bk</figure-callout></span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&mu;</span>}{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}}}$

In the formula, λ—coal seam permeability coefficient, m ² /(MPa ² ·d);

B—unit conversion factor;

P _n - standard atmospheric pressure, MPa;

Combining and integrating the above two formulas, the calculation formula of coal seam permeability coefficient can be obtained as follows:

$\mathrm{<span\; class="notranslate">\; \&lambda;</span>}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; Bvd</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; Y</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; C</span>}}<span\; class="notranslate">\; )</span>}$

In the formula, P _Y —the pressure provided by the air compressor, MPa;

P _C —Drainage negative pressure at the borehole orifice, MPa.

The specific steps for obtaining the absolute gas pressure P of the coal seam in the step 2) are:

1) After the drilling is in place, measure the gas content of the coal seam, and collect coal samples for industrial analysis of the coal to obtain the moisture content, ash content, porosity and bulk density of the coal, as well as the gas adsorption constants a and b of the coal;

2) Back-calculate the absolute gas pressure of the coal seam. The specific calculation method is: Substituting the measured gas content, industrial analysis results, and the gas adsorption constants a and b of coal into the following calculation model to calculate the absolute gas pressure P of the coal seam:

$\mathrm{<span\; class="notranslate">\; W</span>}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; abP</span>}}{\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; b</span>}}<span\; class="notranslate">\; \&CenterDot;</span>\frac{\mathrm{<span\; class="notranslate">\; 100</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; A</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; m</span>}}_{\mathrm{<span\; class="notranslate">\; ad</span>}}}{\mathrm{<span\; class="notranslate">\; 100</span>}}<span\; class="notranslate">\; \&CenterDot;</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 0.31</span>}{\mathrm{<span\; class="notranslate">\; m</span>}}_{\mathrm{<span\; class="notranslate">\; ad</span>}}}<span\; class="notranslate">\; +</span>\frac{\mathrm{<span\; class="notranslate">\; 10</span>}\mathrm{<span\; class="notranslate">\; \&pi;P</span>}}{\mathrm{<span\; class="notranslate">\; \&gamma;</span>}}$

In the formula, P—absolute gas pressure of coal seam, MPa;

W—coal seam gas content, m ³ /t;

a, b—coal gas adsorption constant;

A _d —ash content of coal, %;

M _ad —moisture content of coal, %;

π—porosity of coal, m ³ /m ³ :

γ—the bulk density of coal, t/m ³ .

The maximum value of the absolute gas content of the obtained coal seam is selected as the calculated value in the following steps.

For the borehole connected to the pipeline of the gas drainage system, the connecting pipe shall be provided with a tee and a valve at the orifice to measure the negative pressure at the orifice and perform tracer gas detection.

The tracer gas is SF ₆ tracer gas.

The invention provides a simple test method for the air permeability coefficient of a coal seam. Two boreholes of the same depth are constructed vertically in the coal seam to obtain the absolute gas pressure of the coal seam, inject tracer gas into one borehole, and detect the tracer gas from the other hole. Calculate the gas flow rate of the borehole by the time taken to detect the tracer gas and the borehole spacing, and combine the definition formula of the coal seam permeability coefficient to obtain the calculation formula of the coal seam permeability coefficient to obtain the coal seam permeability coefficient. The calculation process is simple; provided by the compressor A certain pressure, and another borehole is connected to the pipeline of the gas drainage system to maintain a negative pressure at the orifice, which can quickly measure the tracer gas, the test period is short, and the universal applicability is strong.

Further, the measured gas content, industrial analysis results, and coal gas adsorption constants a and b are substituted into the calculation model for calculation, and the absolute gas pressure of the coal seam is obtained by back calculation, which is obtained through the drilling distance and the time taken to detect the tracer gas The gas flow rate in the borehole is used to obtain the coal seam permeability coefficient; the problems of low gas pressure in the coal seam and the difficulty in accurately measuring the gas flow rate in the borehole are solved by the traditional test method of the gas permeability coefficient of the coal seam. The test process is simple and easy.

Description of drawings

Fig. 1 is the schematic diagram of testing system of the present invention;

In the figure: 1-air injection hole; 2-drainage detection hole; 3-coal seam; 4-air compressor; 5-pressure gauge; 6-connecting hose; 7-flange; 8-stop valve; 9-gas Drainage system piping; d- borehole spacing.

Detailed ways

The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments.

Referring to Fig. 1, in this embodiment, two boreholes are constructed on the coal seam 3 at a certain distance d, one is the gas injection hole 1, and the other is the extraction detection hole 2, and the gas injection hole 1 is connected to the air compressor 4 through the connecting hose 6 , the two are connected through the flange 7, the pressure provided by the air compressor 4 is observed through the pressure gauge 5; the drainage detection hole 2 is connected to the gas drainage system pipeline 9 through the connecting hose, and the The connection is made through the flange 7, and the pipelines of the gas drainage system are also connected through the flange, and the gas drainage system pipeline is under negative pressure, which can extract the gas in the detection hole 2; the drainage detection The connecting hose between the hole 2 and the gas extraction system pipeline 9 is provided with a gas detection port, and a shut-off valve 8 is installed. The shut-off valve 8 is usually closed. When gas detection is required, the shut-off valve 8 is opened for detection.

The coal seam permeability coefficient test method of the present embodiment comprises the steps:

(1) In a place where the coal seam is relatively intact, without faults, and without broken zones, two boreholes of the same depth are constructed at a certain distance and perpendicular to the coal seam, respectively, the gas injection hole 1 and the extraction detection hole 2, and the borehole spacing d is recorded .

(2) After the drilling is in place, test the gas content, collect coal samples for industrial analysis of coal and the values of the gas adsorption constants a and b of the coal; take the maximum value of the gas content measured in the two boreholes as the next step The calculated value in ; where the industrial analysis of coal mainly includes coal moisture, ash, volatile matter, and coal porosity and bulk density.

(3) Inverse calculation of coal seam gas pressure, the specific calculation method is: Substituting the measured gas content, industrial analysis results, and coal gas adsorption constants a and b values into the following calculation model to calculate the coal seam gas pressure P:

$\mathrm{<span\; class="notranslate">\; W</span>}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; abP</span>}}{\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; b</span>}}<span\; class="notranslate">\; \&CenterDot;</span>\frac{\mathrm{<span\; class="notranslate">\; 100</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; A</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; m</span>}}_{\mathrm{<span\; class="notranslate">\; ad</span>}}}{\mathrm{<span\; class="notranslate">\; 100</span>}}<span\; class="notranslate">\; \&CenterDot;</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 0.31</span>}{\mathrm{<span\; class="notranslate">\; m</span>}}_{\mathrm{<span\; class="notranslate">\; ad</span>}}}<span\; class="notranslate">\; +</span>\frac{\mathrm{<span\; class="notranslate">\; 10</span>}\mathrm{<span\; class="notranslate">\; \&pi;P</span>}}{\mathrm{<span\; class="notranslate">\; \&gamma;</span>}}$

In the formula, P—absolute gas pressure of coal seam, MPa;

W—coal seam gas content, m ³ /t;

a, b—gas adsorption constant of coal;

A _d —ash content of coal, %;

M _ad —moisture content of coal, %;

π—porosity of coal, m ³ /m ³ :

γ—the bulk density of coal, t/m ³ .

(4) Insert a certain length of sealing casing into the two completed boreholes, and seal between the borehole wall and the casing to prevent air leakage.

(5) Inject a certain amount of SF ₆ tracer gas into the gas injection hole 1, and connect the air compressor 4 to the gas injection hole 1. The pressure P _Y provided by the air compressor should be greater than the coal seam gas pressure calculated in step 3 The size of P, P _Y is observed by the pressure gauge 5; the drainage detection hole 2 is connected with the pipeline 9 of the gas drainage system, and the orifice negative pressure P _C is measured. All connecting sections are connected by connecting hoses 6 , and the pipes are connected by flanges 7 .

(6) Check the SF ₆ tracer gas at the stop valve 8 every day until the SF ₆ tracer gas is detected; and determine the time taken for the borehole to detect the SF ₆ tracer gas from the connection to the gas drainage system pipeline 9 t.

(7) Calculate the air permeability coefficient λ of the coal seam, which specifically includes the following steps:

1) To measure the seepage velocity of SF ₆ tracer gas in the coal seam, the calculation formula is as follows:

$\mathrm{<span\; class="notranslate">\; v</span>}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; d</span>}}{\mathrm{<span\; class="notranslate">\; t</span>}}$

In the formula, v—the seepage velocity of SF ₆ tracer gas in the coal seam, m/d;

d—drilling hole spacing, m;

t—the time taken to detect SF ₆ tracer gas, d.

2) Calculate the coal seam permeability coefficient, the calculation process is as follows:

According to Darcy's law:

$\mathrm{<span\; class="notranslate">\; v</span>}<span\; class="notranslate">\; =</span><span\; class="notranslate">\; -</span>\frac{\mathrm{<span\; class="notranslate">\; k</span>}}{\mathrm{<span\; class="notranslate">\; \&mu;</span>}}\frac{<span\; class="notranslate">\; \&PartialD;</span>\mathrm{<span\; class="notranslate">\; p</span>}}{<span\; class="notranslate">\; \&PartialD;</span>\mathrm{<span\; class="notranslate">\; x</span>}}$

In the formula, k—permeability, m ² ;

μ—dynamic viscosity coefficient, Pa·s;

And the definition formula of coal seam permeability coefficient is:

$\mathrm{<span\; class="notranslate">\; \&lambda;</span>}<span\; class="notranslate">\; =</span><span\; class="notranslate">\; -</span>\frac{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="Bk"\; filenames="HDA00003567030300011.png"\; state="\{\{state\}\}">Bk</figure-callout></span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&mu;</span>}{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}}}$

In the formula, λ—coal seam permeability coefficient, m ² /(MPa ² ·d);

B—unit conversion factor;

P _n - standard atmospheric pressure, MPa;

Combining and integrating the above two formulas, the calculation formula of coal seam permeability coefficient can be obtained as follows:

$\mathrm{<span\; class="notranslate">\; \&lambda;</span>}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; Bvd</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; Y</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; C</span>}}<span\; class="notranslate">\; )</span>}$

In the formula, P _Y —the pressure provided by the air compressor, MPa;

P _C —Drainage negative pressure at the borehole orifice, MPa.

The above descriptions are only preferred embodiments of the present invention, and are not intended to limit the present invention. Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalent technologies, the present invention also intends to include these modifications and variations.

Claims (5)

1. a test method of coal seam air permeability coefficient is characterized in that comprising the steps: (1) In a place where the coal seam is relatively intact, without faults, and without broken zones, two boreholes of the same depth are constructed at a certain distance and perpendicular to the coal seam, and the borehole spacing d is recorded; (2) Obtain the absolute gas pressure P of the coal seam; (3) Inject tracer gas into one of the boreholes, and connect the air compressor to the borehole in a sealed manner. The pressure P _Y provided by the air compressor should be greater than the absolute gas pressure P of the coal seam obtained in step (2); The hole is sealed and connected with the pipeline of the gas drainage system, and the negative pressure P _C of the hole is measured; (4) Test the tracer gas at the borehole connected to the gas drainage system every day until the tracer gas is detected; time t; (5) Calculate the air permeability coefficient λ of the coal seam, which specifically includes the following steps: 1) To measure the seepage velocity of the tracer gas in the coal seam, the calculation formula is as follows: $\mathrm{<span\; class="notranslate">\; v</span>}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; d</span>}}{\mathrm{<span\; class="notranslate">\; t</span>}}$ In the formula, v—the seepage velocity of the tracer gas in the coal seam, m/d; d—drilling hole spacing, m; t—the time taken to detect the tracer gas, d; 2) Calculate the coal seam permeability coefficient, the calculation process is as follows: According to Darcy's law: $\mathrm{<span\; class="notranslate">\; v</span>}<span\; class="notranslate">\; =</span><span\; class="notranslate">\; -</span>\frac{\mathrm{<span\; class="notranslate">\; k</span>}}{\mathrm{<span\; class="notranslate">\; \&mu;</span>}}\frac{<span\; class="notranslate">\; \&PartialD;</span>\mathrm{<span\; class="notranslate">\; p</span>}}{<span\; class="notranslate">\; \&PartialD;</span>\mathrm{<span\; class="notranslate">\; x</span>}}$ In the formula, k—permeability, m ² ; μ—dynamic viscosity coefficient, Pa·s; And the definition formula of coal seam permeability coefficient is: $\mathrm{<span\; class="notranslate">\; \&lambda;</span>}<span\; class="notranslate">\; =</span><span\; class="notranslate">\; -</span>\frac{\mathrm{<span\; class="notranslate">\; Bk</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&mu;</span>}{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}}}$ In the formula, λ—coal seam permeability coefficient, m ² /(MPa ² ·d); B—unit conversion factor; P _n - standard atmospheric pressure, MPa; Combining and integrating the above two formulas, the calculation formula of coal seam permeability coefficient can be obtained as follows: $\mathrm{<span\; class="notranslate">\; \&lambda;</span>}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; Bvd</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; Y</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; C</span>}}<span\; class="notranslate">\; )</span>}$ In the formula, P _Y —the pressure provided by the air compressor, MPa; P _C —Drainage negative pressure at the borehole orifice, MPa. 2. The method for testing the air permeability coefficient of coal seams according to claim 1, characterized in that: the specific steps for obtaining the absolute gas pressure P of coal seams in the step 2) are: 1) After the drilling construction is in place, measure the gas content of the coal seam, and collect coal samples for industrial analysis of the coal to obtain the moisture content, ash content, porosity and bulk density of the coal, as well as the gas adsorption constant a and b values of the coal; 2) Back-calculate the absolute gas pressure of the coal seam. The specific calculation method is: Substituting the measured gas content, industrial analysis results, and gas adsorption constants a and b of coal into the following calculation model to calculate the absolute gas pressure P of the coal seam: $\mathrm{<span\; class="notranslate">\; W</span>}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; abP</span>}}{\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; b</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span>\frac{\mathrm{<span\; class="notranslate">\; 100</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; A</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; m</span>}}_{\mathrm{<span\; class="notranslate">\; ad</span>}}}{\mathrm{<span\; class="notranslate">\; 100</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 0.31</span>}{\mathrm{<span\; class="notranslate">\; m</span>}}_{\mathrm{<span\; class="notranslate">\; ad</span>}}}<span\; class="notranslate">\; +</span>\frac{\mathrm{<span\; class="notranslate">\; 10</span>}\mathrm{<span\; class="notranslate">\; \&pi;P</span>}}{\mathrm{<span\; class="notranslate">\; \&gamma;</span>}}$ In the formula, P—absolute gas pressure of coal seam, MPa; W—coal seam gas content, m ³ /t; a, b—gas adsorption constant of coal; A _d —ash content of coal, %; M _ad —moisture content of coal, %; π—porosity of coal, m ³ /m ³ : γ—the bulk density of coal, t/m ³ . 3. The method for testing the air permeability coefficient of the coal seam according to claim 1 or 2, characterized in that: the maximum value of the absolute gas content of the coal seam obtained is selected as the calculated value in the following steps. 4. according to the test method of the coal seam air permeability coefficient described in claim 1 or 2, it is characterized in that: be connected to the borehole of gas drainage system pipeline, connecting pipe should be provided with tee and valve at the orifice, for Measure orifice negative pressure and tracer gas detection. 5. The method for testing coal seam permeability coefficient according to claim 1 or 2, characterized in that: the tracer gas is SF ₆ tracer gas.

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