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Article

Analysis of the Difference of Gas Extraction Quantity from Coal Seam under the Influence of Permeability, Gas Pressure, and Buried Depth of Coal Seam: A Case Study

by
Hao Wang
1,
Enyuan Wang
2,3,*,
Zhonghui Li
2,3,
Xiaofei Liu
2,3,
Xiaolei Liu
1 and
Kan Wang
1
1
College of Ocean Science and Engineering, Shanghai Maritime University, Shanghai 201308, China
2
Key Laboratory of Gas and Fire Control for Coal Mines (China University of Mining and Technology), Ministry of Education, Xuzhou 221008, China
3
School of Safety Engineering, China University of Mining and Technology, Xuzhou 221008, China
*
Author to whom correspondence should be addressed.
Processes 2023, 11(11), 3086; https://doi.org/10.3390/pr11113086
Submission received: 10 October 2023 / Revised: 25 October 2023 / Accepted: 26 October 2023 / Published: 27 October 2023
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Abstract

:
Gas extraction quantity from coal seam is the key index to evaluating the effect of eliminating coal and gas outbursts. The prerequisite for increasing the gas extraction quantity and improving the effect of gas control is to make clear the influencing factors of gas extraction. The main factors affecting gas extraction are permeability, gas pressure, and buried depth of coal seam in this paper. The qualitative and quantitative analyses of gas extraction quantity by three factors are carried out according to the test data. The research results show that: (1) In the areas with high permeability and gas pressure, the gas extraction volume shows random characteristics, indicating clear regional differences. (2) The increase of buried depth of coal seam will reduce the fluctuation of gas extraction quantity, resulting in a lower extreme value of gas extraction quantity. The possibility of gas extraction at a lower level will be significantly increased. (3) The correlation analysis shows the change law of the positive correlation coefficient between gas extraction quantity, gas pressure, and permeability, and shows the opposite trend with the increase of the buried depth of coal seam. The results show an important guiding significance for improving the efficiency of gas control.

1. Introduction

China is the largest producer and consumer of coal resources in the world. In 2022, the world produced 8.3 billion tons of coal, more than half of which came from China. Coal resources account for more than half of primary energy production in China [1,2]. For a long time, coal will be the country’s main source of energy. China is also the country with the worst coal and gas outburst accidents. The mining of deep coal resources has gradually become the norm with the depletion of shallow coal resources, which leads to the increased risk of coal and gas outburst accidents [3,4,5]. Over the past decade, a total of 115 coal and gas outburst accidents have occurred in China, resulting in 578 deaths [6]. It can be seen in Figure 1 that mining working face and driving working face are areas where accidents occur frequently. Traditional measures to prevent coal and gas outburst accidents are faced with severe challenges. At the same time, the advantages of gas have also begun to attract attention with the shortage of energy in the world, and it is considered to be a very clean energy that can be used for clean power generation [7,8]. Therefore, it is of great importance to strengthen gas control and improve gas utilization efficiency from the perspectives of safety and environment.
Coal is a porous medium with a large number of pore and fracture systems that can be used to store and transport gas. When drilling into the coal seam to form a gas extraction hole, there will be a pressure gradient between the coal seam and the hole, resulting in gas constantly entering the hole. Inside the coal seam, the dynamic balance between cracks and pores is broken, which further promotes gas resolution and migration to the borehole [9,10,11,12]. Gas extracted from the coal seam and transferred to the ground through the borehole can effectively reduce the coal seam gas content and eliminate the risk of coal and gas outbursts. Therefore, the gas extraction quantity from coal seam is the key index to evaluate the effect of eliminating coal and gas outbursts. The gas extraction quantity is directly related to the storage and gas migration characteristics of coal seam [13,14]. The permeability, gas pressure, and buried depth of coal seam control the storage characteristics and gas flow characteristics of coal seam.
The permeability of coal seam is very important for gas extraction. Many scholars have conducted in-depth studies on the initial permeability of coal seam and the dynamic change law of coal seam permeability during the extraction process [15]. Mckee et al. [16] experimentally investigated the relationship between permeability and effective stress. Robertson et al. [17] analyzed the variation of permeability under different gas pressures under a fixed confining pressure. Palmer et al. [18] constructed a new mathematical model to analyze the effect of coal seam permeability change on gas extraction under different conditions. Liu et al. [19] studied the change law of permeability in the process of steam injection in coal seam in order to improve gas extraction and recovery. Sadegh et al. [20] used the method of experimental and numerical modeling of digital coalbed methane to predict the permeability, which can be used to analyze the gas extraction quantity.
The changes mainly caused by the decrease of gas pressure led to the increase of permeability change when flue gas was injected into the coal seam. Compared to injecting carbon dioxide into the coal seam, this method had a better gas control effect. Yang et al. [21] used carbon dioxide gas fracturing technology to increase the number and quality of fractures around the drilling hole, improve the permeability of coal seam, and effectively increase the gas extraction amount of the borehole.
Gas pressure provides the power source for gas flow. There is a clear correlation between gas migration law and gas pressure. Zhao et al. [22] analyzed the distribution law of gas pressure in coal body in the process of gas extraction through the gas seepage model established, which had a certain guiding significance for improving gas extraction. Liu et al. [23] found that gas pressure can promote gas flow through experimental research. High gas pressure can achieve rapid gas migration. Chen et al. [24] believed that the gas diffusivity would show an increasing trend when the gas pressure decreases. The negative correlation between gas pressure and gas diffusivity is not universal, mainly because the differences in diffusion coefficients calculated under equal volume and pressure conditions were ignored [25]. A growing number of studies have shown that the diffusion coefficient increases with the gas equilibrium pressure [26].
The closure of cracks in the coal seam blocks the gas transmission channel under the condition of high ground stress, resulting in long extraction time and poor effect [27]. It is of great practical importance to study the relationship between coal seam ground stress and gas extraction. Guo et al. [28] proposed a gas transport model considering stress and strain, which enriched the theory of the interrelation between in situ stress and gas flow. Cheng et al. [29] studied the effect of ground stress release on gas extraction under the mining condition of a protective layer. Liu et al. [30] showed that the change of ground stress had a significant impact on the diffusion of gas in cracks by comparing the diffusion behavior of gas under unconstrained conditions. The increase of ground stress would lead to the gradual decrease of effective diffusivity. Xu et al. [31] studied the change law of seep characteristics of coal body in the process of coal seam mining under the condition of high ground stress with different mining methods and mining intensity. The results showed that the increase of ground stress would delay the response time of coal damage and reduce the effect of gas extraction.
The above studies analyzed gas extraction from different angles. However, most of them stayed in the theoretical stage, and the data used came from numerical simulation, which could not restore the real gas extraction process. The gas extraction quantity is affected by gas pressure, permeability, and coal seam buried depth in the actual process of gas extraction, which is variable and complex. There is an interaction influence between each factor, which provides us with valuable guidance for analyzing the coupling change law of gas extraction quantity. The gas pressure, permeability, and gas extraction volume in Xuehu Coal Mine under different burial depths were measured by means of a field test in this study. Then, the influence of permeability, gas pressure and buried depth of coal seam on gas extraction was determined through single-factor analysis, and the main controlling factors affecting gas extraction were obtained. Finally, the correlation analysis between the three factors and gas extraction volume was carried out using statistical methods to reveal the reasons for the differences in gas extraction effects under different influencing factors based on the results of multi-factor coupling analysis. The results can be used for pre-analysis of gas extraction effect during the transition from shallow coal seam mining to deep coal seam mining.

2. Materials and Methods

2.1. Field Application

Xuehu Coal Mine is located in the northwest of Yongcheng City, Henan Province. The field is 16 km long from east to west, 2.8–6.5 km wide from north to south, and covers an area of 74 km2. The location of the mine and the buried depth of the coal seam are shown in Figure 2. At present, the mining depth of coal seam is 492~1035 m. The gas pressure of coal seam is 0.7–2.4 MPa. The permeability of coal seam is 89 × 10−16~514 × 10−16 m2. The parameters show that the mine is a typical mine with low permeability and high outburst risk. In May 2017, a coal and gas outburst occurred at the Xuehu Coal Mine, killing three people. The main reason for the accident was that the gas extracted quantity from coal seam did not reach the standard of outburst elimination completely, resulting in the wrong prediction of safety.

2.2. Data Testing Method

The effective gas extraction measures should be implemented to prevent coal and gas outburst accidents in the production process before the new coal seam is excavated. According to the previous gas extraction experience, the time needed to reach the standard for outburst elimination in Xuehu Coal Mine is generally three months. The time of gas extraction will be further shortened if the measures to strengthen gas extraction are implemented in coal seams. It is not possible to implement enhanced measures for gas extraction in all coal seams due to cost considerations. Therefore, most of the coal seams are used by ordinary gas extraction methods. It is well known that the main factors affecting gas extraction are permeability, gas pressure, and buried depth of coal seam. The gas extracted quantity will also change when the occurrence condition of coal seam changes, especially for coal seam with anisotropy. Even in different positions of the same coal seam, the amount of gas extraction will fluctuate randomly, showing clear regional differences. Three main coal seams with buried depths of 492–507 m, 736–762 m, and 994–1035 m were selected for gas extraction drilling construction in this study. The construction methods of all boreholes were unified standards to ensure the same forming conditions of drilling holes and ensure the reliability and accuracy of the research. The size of the borehole was as consistent as possible. At the same time, the placement of boreholes needed to avoid geological faults, which would have affected the gas extraction data. The gas extraction time of all boreholes was 100 days. Gas pressure and permeability were measured and calculated before and after gas extraction. In the determination of permeability and gas pressure, the determination conditions aimed to be consistent. Gas extraction quantity, permeability, gas pressure, and coal seam depth of all boreholes were collected and analyzed.

3. Results and Discussion

3.1. Results of Univariate Analysis

3.1.1. The Relationship between Gas Extraction Quantity and Permeability

The permeability determines the difficulty of gas migration in coal seam. The test data from coal seams with three buried depths are collected in order to facilitate the analysis of the relationship between gas extraction quantity and permeability of coal seam, which is drawn for the kernel density map. Most of the data are concentrated in the permeability of 100 × 10−16–200 × 10−16 m2, as shown in Figure 3. The corresponding gas extraction quantity is between 20 m3 and 30 m3, which indicates low permeability and poor gas extraction effect in most areas of coal seam. The conclusion also proves that it is the difficult extraction coal seam in Xuehu Coal Mine. There are two dense areas in which the average gas extraction quantity is 150 m3 and 90 m3, which may be related to the gas pressure or the buried depth of coal seam when the permeability is 500 × 10−16 m2. As can be seen in Figure 3, the permeability of the three coal seams is basically 100 × 10−16–400 × 10−16 m2, and the area exceeding 500 × 10−16 m2 is basically difficult to exist, which also shows the characteristics of low permeability in coal seams. Gas extraction still presents a relatively clear increasing trend with the increase of permeability. However, the gradually deteriorating data concentration indicates that the regional difference is clearer in the high-penetration region. The conclusion shows that the permeability is very important in determining the migration channel inside the coal seam when the permeability of coal seam is low. While the gas migration in the high permeability area is more affected by other factors, it shows a more obvious difference.

3.1.2. The Relationship between Gas Extraction Quantity and Gas Pressure

Gas pressure is the dynamic source of gas migration. The pressure gradient will be generated between the coal seam and the free space inside the borehole after the formation of the borehole. Higher gas pressure will lead to a larger pressure gradient, promoting gas flow and increasing gas extraction quantity. Therefore, it is necessary to study the relationship between gas pressure and extraction quantity. Figure 4 shows the variation trend of data density of gas extraction under different gas pressure conditions. On the whole, the distribution area of gas extraction data is very loose, and the discretization is very clear. There are two regions with high data density values. The corresponding gas pressure in the area is high gas pressure and low gas pressure, respectively, and the corresponding gas extraction volume ranges are 7–30 m3 and 16–40 m3, respectively, which means low gas extraction volume. Similarly, there is also a large amount of gas extraction in high gas pressure area and low gas pressure area. When the gas pressure is 1.0 MPa, the corresponding maximum and minimum gas extraction amounts are 119.6 m3 and 9 m3, respectively. The corresponding gas extraction quantity is between 175.05 m3 and 21.45 m3 when the gas pressure is 2.0 MPa. The uncertainty indicates that the influence of gas pressure on gas extraction is weaker than that of permeability. At the same time, it can be seen in Figure 4 that the data density of gas extraction corresponding to high gas pressure is low. The above analysis results show that gas pressure as a single factor could not completely determine the gas extraction quantity. The fluctuation range of gas extraction quantity is high under the known gas pressure condition. However, low gas pressure leads to a greater probability of low gas extraction. The conclusion explains why most high-gas outburst mines tend to have low extraction efficiency.

3.1.3. The Relationship between Gas Extraction Quantity and Buried Depth of Coal Seam

Coal mining gradually developed deep underground with the gradual depletion of shallow resources. More and more evidence shows that the main problem of deep mining is the poor gas extraction efficiency and the low gas extraction quantity. It is impossible to fundamentally solve the risk of coal and gas outburst accidents, which is more serious than shallow mining. Therefore, it is of great practical significance to study the relationship between gas extraction and buried depth of coal seam. Figure 5 shows the gas extraction quantity from coal seams with different burial depths. It can be seen in Figure 5 that the maximum value of gas extraction is 195.05 m3, the minimum value is 21.62 m3, and the maximum difference is 173.43 m3 when the buried depth of coal seam is from 492 m to 507 m, indicating that the fluctuation range of gas extraction corresponding to shallow buried coal seam is larger. The corresponding value range of gas extraction is from 18.65 m3 to 170.45 m3, and the maximum difference is 151.8 m3 when the buried depth of coal seam is 736–762 m. When the buried depth of coal seam is 994–1035 m, the corresponding gas extraction quantity ranges from 6.12 m3 to 90 m3, and the maximum difference is 83.88 m3. The coal seam with large deep means low gas extraction and small fluctuation range. Clearly, the difficulty of gas extraction will be greater and the difficulty will increase faster in deep coal mining, which means that the prevention and control requirements for coal and gas outburst accidents are also higher. Therefore, gas extraction in deep coal fields often needs to increase strong and prominent elimination measures to solve the serious gas problems.
In summary, the increase of permeability and gas pressure will lead to the increase of gas extraction quantity. However, it will also increase the uncertainty of gas extraction to a certain extent. Lower permeability and gas pressure result in a lower gas extraction quantity in most cases. The reason is because the higher the parameter, the greater the degree of influence by other factors, which means that a single factor could not maintain the influence weight of gas extraction at a higher level. It is easier to extract gas from shallow coal seams. The coal seam with large buried depth has a side effect on gas extraction, which can be used to determine the lower gas extraction volume. Permeability, gas pressure, and buried depth of coal seam have a clear influence on gas extraction amount, and a single factor could not completely determine the change trend of gas extraction quantity.

3.2. Results of Multivariate Analysis

Figure 6 reflects the combined effects of permeability, gas pressure, and buried depth of coal seam on gas extraction. In Figure 6, red, green, and blue represent the coal seam buried depth of 492–507 m, 736–762 m, and 994–1035 m, respectively. It can be clearly seen that high gas pressure and high permeability cannot necessarily obtain a large gas extraction quantity under the condition of the same burial depth. It is possible to obtain the large gas extraction quantity when the permeability and gas pressure are at a high level at the same time. For example, the gas extraction quantity is 44.7 m3 when the gas pressure is 2.19 MPa and the permeability is 95 × 10−16 m2. The gas extraction amount is 43.19 m3 when the gas pressure is 0.96 MPa and the permeability is 478 × 10−16 m2. When the gas pressure is 1.94 MPa and the permeability is 480 × 10−16 m2, the gas extraction quantity can reach 175 m3. From the overall trend, gas extraction has gradually increased the change law with the increase of gas pressure and permeability. However, the gas extraction volume will decrease significantly when one of the parameters of gas pressure and permeability is at a low level. Ignoring the influence of gas pressure, the increase trend of gas extraction will be clear with the increase of permeability when the buried depth of coal seam is low. The trend will be clearly suppressed when the coal seam is buried deep. The maximum gas extraction quantity corresponding to the maximum permeability is 68.3 m3 when the buried depth of coal seam is from 994 m to 1035 m. When the buried depth of coal seam is from 492 m to 507 m, the maximum gas extraction volume corresponding to the maximum permeability is 140.07 m3. The former is half of the latter. More gas extraction quantity can be obtained from the coal seam with shallow buried depth than that of the coal seam with deep buried depth under the same condition of gas pressure and permeability. At the same time, Figure 6 also shows that the permeability corresponding to most of the data is small under the condition of large burial depth, which is in line with the current geological exploration results of coal mines. The influence of gas pressure and buried depth of coal seam on gas extraction volume is also clear. Shallow coal seam and high gas pressure make it easier to obtain larger gas extraction quantity. Under the same permeability condition, the maximum gas pressure corresponding to the maximum extraction quantity is 117.67 m3 when the buried depth of coal seam is from 492 m to 507 m. When the buried depth of coal seam is from 994 m to 1035 m, the maximum gas extraction amount corresponding to the maximum gas pressure is 45.2 m3. The former is 2.5 times the latter. Figure 6 also reflects the influence of three factors on the amount of gas extraction to some extent. The geological conditions corresponding to the maximum gas extraction volume are coal seam with the buried depth of 499 m, the gas pressure of 1.94 MPa, and the permeability of 480 × 10−16 m2. The minimum value of gas extraction volume corresponding to the geological conditions is buried depth of 1030 m, gas pressure of 0.84 MPa, and permeability of 244 × 10−16 m2. The data results show that the extreme value of gas extraction quantity could not be determined by any one factor or two factors. The comprehensive effect of the three factors on the gas extraction is clear.

3.3. Correlation Analysis

Ge et al. [32] found that the size of the gas flow area in the coal seam is affected by the permeability and gas pressure, showing a power function relationship. Kong et al. [33] explained that the gas extraction quantity would be affected by ground stress, permeability, and gas pressure. Then, the quadratic polynomial relationship between gas extraction, gas pressure, and permeability is established based on the response surface method. Clearly, permeability, gas pressure, and buried depth of coal seam jointly determine gas extraction quantity. From the macroscopic point of view, permeability can evaluate the difficulty of gas flow, gas pressure determines the dynamic strength of gas flow, and the buried depth of coal seam determines the continuity of gas extraction. From the microscopic point of view, the pore structure and adsorption analytic characteristics of coal seam, characterized by three factors, can determine gas extraction quantity of coal seam. However, it is necessary to quantitatively analyze whether permeability, gas pressure, and buried depth of coal seam have the same influence on gas extraction. Then, the correlation analysis of three factors is carried out. The general formula for calculating Pearson’s correlation coefficient is:
ρ ( x , y ) = cov ( x , y ) σ x σ y
where cov ( x , y ) is the covariance; σ x , σ y is the standard deviation. The following expansion can be obtained from the formula for the calculation of variance and standard deviation:
ρ ( x , y ) = E ( x , y ) − E ( x ) E ( y ) E ( x 2 ) − E 2 ( x ) E ( y 2 ) − E 2 ( y )
The following expansion can be obtained from the formula for the calculation of variance and standard deviation:
r = ∑ i = 1 n ( x i − x ¯ ) ( y i − y ¯ ) ∑ i = 1 n ( x i − x ¯ ) 2 ∑ i = 1 n ( y i − y ¯ ) 2
where r is the covariance.
Since the test data comes from three different buried depths of coal seams, there is no continuity between coal seams. Therefore, the correlation analysis between the three factors and gas extraction quantity in three coal seams with different buried depths is carried out. As shown in Figure 7, the maximum correlation coefficient between gas extraction quantity and permeability is 0.83 for shallow coal seams, indicating a high positive correlation between the two. The correlation between extraction quantity and gas pressure is 0.15, and that between extraction and buried depth is 0.22. The correlation between extraction quantity, gas pressure, and buried depth of coal seam is 0.15 and 0.22, respectively; this indicates that the influence of gas pressure and buried depth on gas extraction quantity is random for the shallow coal seam, and the influence degree of the two is not consistent with the permeability. A large number of cracks are formed in the coal seam for shallow coal seams because of geological weathering; this makes it easier for gas to escape from the coal seam, explaining that the correlation between gas pressure and permeability is negative. Therefore, the increase in buried depth of coal seam is more conducive to gas storage to improve gas pressure to a certain extent, which can provide a larger pressure gradient for gas extraction. It provides a theoretical basis for the positive correlation between buried depth, gas pressure, and gas extraction volume.
The correlation coefficient between gas extraction quantity and permeability is 0.83 when the buried depth of coal seam is 736–762 m (Figure 8). It can be seen that the skeleton structure and pore characteristics inside the coal seam begin to change under the action of ground stress with the increase of buried depth, which increases the difficulty of gas extraction. The weathering of the surface could not provide a good environment for the development of coal seam cracks under the buried depth condition, resulting that the gas no longer escapes from the surface. The increase of burial depth promotes the increase of gas pressure to make the correlation coefficient of the two become larger. The increase of gas pressure also provides a larger pressure gradient for gas migration. Clearly, the correlation between gas extraction quantity and gas pressure is enhanced.
The correlation coefficient between gas extraction and permeability decreases to 0.75 when the buried depth of coal seam is from 994 m to 1035 m, indicating that the low permeability of coal seam will significantly reduce gas extraction. The correlation between gas extraction quantity and gas pressure continues to rise, which indicates that the influence of gas pressure on increasing gas extraction quantity is gradually increasing when gas extraction is carried out in deep coal seams. At the same time, the negative correlation coefficient between gas extraction volume and buried depth of coal seam is also increasing, which indicates that the increase of ground stress will significantly reduce gas extraction volume during deep mining. Figure 9 shows that the permeability and gas pressure present opposite trends under the condition of high burial depth. The reason is that higher ground stress will improve the gas storage characteristics of coal seams, which can reduce the channel of gas flow and increase the difficulty of gas migration [34].
To sum up, there are great differences in the influence of gas pressure and permeability on gas extraction under different buried depths of coal seams. There is a strong positive correlation between permeability and gas extraction, which will be weak with the increase of buried depth of coal seam. There is a weak positive correlation between gas pressure and gas extraction that will be strengthened with the increase of buried depth of coal seam. The increase of coal seam buried depth will reduce the amount of gas extraction, and the negative correlation will increase. At the same time, the increase of burial depth of coal seam may lead to the decrease of permeability and the increase of gas pressure.

4. Conclusions

Gas extraction is mainly affected by permeability, gas pressure, and buried depth of coal seam. The influence of a single factor and multiple factors on gas extraction were analyzed in this paper based on the measured data at first. Then, the influence of three factors on gas extraction was qualitatively analyzed according to the correlation analysis, and the conclusions are as follows:
  • Single factor analysis shows that the increase of permeability and gas pressure will increase the extreme value of gas extraction and the fluctuation range of data, showing the obvious regional difference. The increase of ground stress will clearly lead to the decrease of gas extraction and weaken the volatility of data.
  • The strong positive correlation between permeability and gas extraction will decrease with the increase of burial depth. The weak positive correlation between gas pressure and gas extraction will increase with the increase of burial depth. The buried depth of coal seam is negatively correlated with the gas extracted quantity, which will increase with the increase of the buried depth of coal seam.

Author Contributions

Conceptualization, E.W. and H.W.; methodology, H.W. and X.L. (Xiaolei Liu); software, H.W.; validation, Z.L. and X.L. (Xiaofei Liu); formal analysis, E.W. and Z.L.; investigation, H.W.; resources, E.W. and Z.L.; data curation, H.W.; writing—original draft preparation, H.W.; writing—review and editing, H.W. and K.W.; visualization, H.W.; supervision, E.W. and Z.L.; project administration, Z.L. and X.L. (Xiaofei Liu); funding acquisition, E.W. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by the Fundamental Research Funds for the Central University, grant number 2020CXNL10.

Data Availability Statement

This research data has been presented in the current paper.

Acknowledgments

All authors would like to express their sincere thanks to the editor and reviewers for valuable comments.

Conflicts of Interest

The authors declare no conflict of interest.

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Figure 1. Location distribution of coal and gas outburst accidents.
Figure 1. Location distribution of coal and gas outburst accidents.
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Figure 2. The diagram of the location of the mine and the buried depth of the coal seam.
Figure 2. The diagram of the location of the mine and the buried depth of the coal seam.
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Figure 3. Data density distribution of gas extraction quantity under the conditions of different permeability.
Figure 3. Data density distribution of gas extraction quantity under the conditions of different permeability.
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Figure 4. Data density distribution of gas extraction quantity under the conditions of different gas pressure.
Figure 4. Data density distribution of gas extraction quantity under the conditions of different gas pressure.
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Figure 5. Comparison of gas extraction quantity under different buried depths of coal seams.
Figure 5. Comparison of gas extraction quantity under different buried depths of coal seams.
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Figure 6. Variation law of gas extraction under different permeability, gas pressure, and buried depth of coal seam.
Figure 6. Variation law of gas extraction under different permeability, gas pressure, and buried depth of coal seam.
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Figure 7. Correlation analysis between gas extraction quantity and three factors when buried depth of coal seam is from 492 m to 507 m.
Figure 7. Correlation analysis between gas extraction quantity and three factors when buried depth of coal seam is from 492 m to 507 m.
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Figure 8. Correlation analysis between gas extraction quantity and three factors when buried depth of coal seam is from 736 m to 762 m.
Figure 8. Correlation analysis between gas extraction quantity and three factors when buried depth of coal seam is from 736 m to 762 m.
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Figure 9. Correlation analysis between gas extraction quantity and three factors when buried depth of coal seam is from 994 m to 1035 m.
Figure 9. Correlation analysis between gas extraction quantity and three factors when buried depth of coal seam is from 994 m to 1035 m.
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MDPI and ACS Style

Wang, H.; Wang, E.; Li, Z.; Liu, X.; Liu, X.; Wang, K. Analysis of the Difference of Gas Extraction Quantity from Coal Seam under the Influence of Permeability, Gas Pressure, and Buried Depth of Coal Seam: A Case Study. Processes 2023, 11, 3086. https://doi.org/10.3390/pr11113086

AMA Style

Wang H, Wang E, Li Z, Liu X, Liu X, Wang K. Analysis of the Difference of Gas Extraction Quantity from Coal Seam under the Influence of Permeability, Gas Pressure, and Buried Depth of Coal Seam: A Case Study. Processes. 2023; 11(11):3086. https://doi.org/10.3390/pr11113086

Chicago/Turabian Style

Wang, Hao, Enyuan Wang, Zhonghui Li, Xiaofei Liu, Xiaolei Liu, and Kan Wang. 2023. "Analysis of the Difference of Gas Extraction Quantity from Coal Seam under the Influence of Permeability, Gas Pressure, and Buried Depth of Coal Seam: A Case Study" Processes 11, no. 11: 3086. https://doi.org/10.3390/pr11113086

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