Analysis of Methods for Determining Expected Gas Emission in Coal Mines
Abstract Generated abstract
This article examines the problem of forecasting methane emission for ventilation design in coal mines of the Kuznetsk Basin, where reliance on gas abundance or neighboring mine data is shown to be unreliable. It critically reviews practical methods for determining seam gas content, including face sampling, borehole sampling, pressure-based indirect determination, and Pechuk’s tabular geological method, and compares forecast results with observations at Mine No. 135. The author argues that gas maps by seam and horizon are necessary for rational ventilation planning, because gas content varies with geology, depth, structure, and local zones of increased emission. A combined method is proposed that integrates borehole sampling during exploration with Pechuk’s geological tables, aiming to improve estimates of initial gas content and provide more scientifically grounded data for mine design.
Full Text
Analysis of Methods for Determining Expected Gas Emission in Coal Mines
A. F. Karataev
Introduction
In designing new mines under the conditions of the Kuznetsk Basin, the question of ventilating mine workings, especially in the upper horizons, is being resolved unsatisfactorily, since designers do not have data on expected gas emission at their disposal. Nevertheless, investigations in this direction make it possible to eliminate these shortcomings.
In the present article we provide a critical review of existing methods for determining gas content that are of practical significance, and present the results of observations made to verify the forecast of gas content by the method of Prof. Dr. I. M. Pechuk at Mine No. 135. This question has not been reflected in print.
The Inadequacy of Gas Abundance for Calculating the Required Quantity of Air
The chief and fundamental factor determining the quantity of air to be supplied to projected coal mines is gas emission. Correct, technically and economically advantageous ventilation of a mine can be designed and implemented only with a clear and precise conception of the gas emission of the mine being projected.
Until now, design organizations have determined the gas emission of a projected mine only very approximately, on the basis of the gas emission of neighboring mines. Consequently, the development of the question of determining the expected gas emission of a projected mine is quite relevant and timely.
Determining the expected gas emission of a projected mine presents great difficulty, because it depends:
1) on the nature of the coal, i.e., the conditions of its origin, occurrence, and the form in which gas is retained in it;
2) on geological factors: the character of the occurrence of coal seams, whether it is calm or disturbed and accompanied by faults or not, on the number and thickness of gas-bearing seams, their dip angle, and the degree of convergence;
3) on mining-engineering factors, i.e., the productivity of the mine, the mining systems applied, the rate of advance of the faces, etc. [1, 64].
The gas content of seams—the quantity of mine gas (methane), in m³, contained in 1 t of unmined coal—depends mainly on the nature of the coal and on geological factors [2, 13].
Gas emission, i.e., the quantity of mine gas (methane) released at a given point per unit time (in m³/min), and gas abundance—the quantity of it, in m³, released in the mine per day, referred to 1 t of daily [[unclear: text continues on next page]]
...of daily output, are determined by the gas content of the seams, but to a considerable extent depend on mining-engineering factors: the productivity of the mine, the development systems used, the rate of advance of the faces, etc. Consequently, the method for determining the expected gas emission, used in the comprehensive design of ventilation for a newly planned mine, must take into account the entire diversity of factors affecting gas emission.
It follows from the foregoing that one of the most important factors determining the gas emission of a mine is the gas content of the seams; therefore, correct determination of the gas content of seams considerably facilitates establishing the influence of mining-engineering factors.
The modern method of designing ventilation for a projected mine must be based on a forecast of expected gas emission that would take into account the nature of the coal, the geological features of the deposit, and mining-engineering factors.
Under the conditions of the Kuznetsk Basin, a considerable quantity of gas is released during development workings, especially when thick seams are being worked. This gas emission presents the greatest danger with respect to the possibility of explosions, and also causes stoppages of mining operations as a result of gassing of the faces. In one district of mine No. 125, during development work, six times more gas was released than during stoping operations. Similar phenomena are observed at mine No. 120 of the Kemerovougol trust, at mine No. 100 of the Anzherougol trust, and at other mines of the Kuznetsk Basin.
Gas emission in development workings depends mainly on the thickness of the seam and the rate of advance of the face, and not on daily output. This explains why, at mine No. 135, in the first half of 1947 the gas abundance of the “VII Western” seam was determined as 117 m³ per 1 t of daily output (with a daily seam output of 27 t), while the total gas abundance of the mine was 24 m³ per 1 t of daily output.
The examples cited indicate the absence of proportionality between gas emission and output. Gas abundance, however, is determined on the assumption that gas emission is directly proportional to output; therefore gas abundance is not an indicative measure for determining the amount of air to be supplied to a mine.
The Necessity of Calculating Gas Emission for Districts
The gas emission of districts depends, as was noted above, on the gas content of the seam being worked, on its thickness and conditions of occurrence, on the development system employed, and also on the presence of “small-scale zoning” and zones of increased gas emission.
Professor Doctor I. M. Pechuk, who has been studying the gas content of the Kuznetsk Basin, points out that in the coal mines of the Kuznetsk Basin there is observed a fine zoning with respect to gas; that is, there exist areas—zones of increased gas content of small extent, even in deposits that are comparatively low in gas. Thus, for example, at mine No. 125 of the Prokopyevskugol trust there are areas with increased gas content (South mine 5). At mine No. 135 of the Kuibyshevugol trust, seam V is being worked in two folds, and in one of the folds (the Eastern) the gas content is greater than in the other (the Central).
In addition to zones with genuinely increased gas content, there are zones with increased gas emission (gas abundance), although the gas content may even be somewhat reduced. Such properties characterize places where tectonic activity was especially noticeable, for example, near faults and seam turns (in the hinge parts) [2, 37].
The phenomena indicated lead to uneven gas emission in the area being worked; within the limits of the area it varies both along the strike and along the dip of the seam.
It follows from the foregoing that, without knowledge of the magnitude and character of gas emission within the limits of the area, it is impossible to determine the quantity of air that must be supplied to this area in order to ensure normal operation during its exploitation.
The Need to Know the Gas Content of a Mine Field
The practice of developing individual deposits of the Kuznetsk Basin shows that, even at the present time, there are mines where, despite the shallow depth of working, considerable gas emission is observed, leading to the stoppage of work in some sections of the mine—for example, mine No. 125 in Prokopyevsk, mine No. 135 in Stalinsk, mine No. 120 in Kemerovo, and others. The main reason for the stoppage of mine operations is the unpreparedness of mines to combat increased gas emission.
In order to be able always to be prepared to combat increased gas emission, it is necessary to know the gas content of the entire mine field by seams and horizons, and the character of its manifestation. Only correct knowledge of the gas content of a mine field can ensure the development of measures that eliminate “contingencies” disrupting the operating regime of the mine.
It follows from the preceding that the selection of a rational ventilation scheme for a gassy mine—the basic element of proper ventilation—is impossible without knowledge of the variation in the gas content of individual seams and sections along strike and dip, as well as of the variation in the gas content of the entire mine field by seams and horizons.
The Impossibility of Determining the Gas Content of Sections from Gas-Emission Data of Neighboring Mines
As already indicated above, the gas content of seams depends on the nature of the coal and on geological and mining-technical factors. In a number of mines the geological conditions on adjacent horizons in a part of the mine field may be different; therefore, determining the gas content of a section from the gas emission of the upper horizon proves impossible in a number of cases. Thus, the gas content of the seams of mine No. 100 of the “Anzherougol” trust at the 300 m horizon is, in the greater part of the mine field, considerably higher than at the overlying 200 m horizon, which is caused by the presence of a fault passing approximately along the strike of the seams somewhat below the latter horizon.
Data on gas emission in neighboring mines may also be non-representative. Thus, the gas content of mine No. 103 of the “Kemerovougol” trust is considerably lower than that of neighboring mine No. 120.
The Need to Use Gas Maps
As established above, the gas content within a mine field, by seams and within a seam along the strike, does not remain constant. Therefore, in order to provide a clear representation of the distribution of gas content within each working horizon, by seams and within seams along the strike, it is necessary to compile a so-called gas map.
A gas map is a seam map of the working horizon on which the variation of the gas content of the seams within the mine field on the working horizon is plotted in conventional symbols.
The availability of a gas map facilitates the selection of a rational ventilation scheme and the proper distribution of the air supplied to the mine (Fig. 1).
Fig. 1. Gas map of Mine No. 135, horizon +85 m.
Existing methods for determining expected gas emission
The question of the need to forecast gas emission was first raised by Academician A. A. Skochinsky.
As the coal mines of the USSR move to lower, more gas-bearing horizons, where gas emission increases sharply, the forecast of gas emission acquires great practical significance. A forecast of gas emission is impossible without knowledge of the gas content of the seams. The basis for the correct determination of the expected gas emission of seams is the correct establishment of their initial gas content, i.e., the gas content that they have before mining operations are conducted in them. Knowing the gas content of seams makes it easier to establish the influence of mining-engineering factors on gas emission.
The gas content of coal, in turn, is determined by the gas capacity and gas permeability of the coal, which depend on the nature of the coal. Gas in coal is found in sorbed and free states. The ability of coal to sorb gas depends on the structure and composition of the coal, and on the temperature and pressure under which the gas is present in the coal. The principal factor determining the sorption capacity of coal of a given composition and structure is pressure. The ratio between the amount of sorbed and free gas in coal depends on the pressure under which the gas is present in the coal. When the pressure falls, part of the sorbed gas passes into the free state, and vice versa.
At the Institute of Mining of the Academy of Sciences of the USSR, engineer V. T. Palvelev, under the supervision of Academicians A. A. Skochinsky and M. M. Dubinin, carried out work in 1941–1945 on the study of methane sorption by fossil coals at pressures reaching 1000 atm. On the basis of this work it was established:
1) at a pressure of 100–150 atm, gas sorption by coal reaches a maximum; with a further increase in pressure, compression of the gas located in the pores in the free state occurs;
2) at pressures greater than 100–150 atm, the amount of methane contained in the pores exceeds the amount of sorbed gas. The amount of sorbed gas remains constant [3,3].
This work also indicates that the gas capacity of coal depends on pressure. The greater the pressure under which the gas is found, the more of it there is in the coal.
The gas-bearing capacity of seams depends to a considerable degree on the gas permeability of the coal and, chiefly, on the reduced gas permeability, i.e., the gas permeability of the coal under the conditions of its occurrence, taking fracturing into account. The greater the gas permeability of the coal, the more it is capable of being drained.
Drainage of coal seams depends not only on the gas permeability of the coal seams, but also on the geological conditions of their occurrence. Prof. Dr. I. M. Pechuk, on the basis of studying the gas-bearing capacity of coal seams, indicates that the drainage of coal seams is influenced by the chemical and petrographic composition of the coal, the angle of dip of the seams, the depth of occurrence of the seams, the relief of the locality, and the geological structure of the seams.
Consequently, a method for forecasting gas-bearing capacity must be based on the gas capacity of coal, taking into account drainage, which in turn depends on the reduced gas permeability of the coal and the geological conditions of occurrence of the coal seams.
Of the currently known methods for determining the gas-bearing capacity of seams, we shall consider the following four as having the greatest practical significance:
1) determination of the gas-bearing capacity of seams from data obtained in the investigation of coal samples taken at the face (the “Makeevka” method);
2) determination of gas-bearing capacity from borehole data during exploration (K. Buyanov’s method);
3) determination of the true gas-bearing capacity by an indirect route (I. M. Yarovoy’s method);
4) determination of gas-bearing capacity from tabulated gradients and geological conditions of seam occurrence (the method of Prof. Dr. I. M. Pechuk).
The first method, the so-called “Makeevka” method, is based on determining the content of occluded gas in the coal, for which observation points are laid out in the seams under study, covering the entire mine field along the strike and dip. At these points, coal samples are periodically taken as the face advances. The coal intended for the sample is crushed to 3–5 mm, and 50–70 g of this coal are placed in a hermetically closing flask with a capacity of 175 cm³. The sample is taken from the depth of the face, from the cut-in during the working shift. The shift preceding the sampling must also be a working shift. Analysis of the samples is carried out on the day of sampling. Extraction of gas from the samples is performed by heating it in a water bath to 100°. The gas extracted from the coal sample is analyzed in a Brockmann apparatus. Based on the results of analysis of the extracted gas, the methane content per 100 g of coal and the gas-bearing capacity of the coal are determined [4,11].
The second method for determining the gas-bearing capacity of seams, according to Buyanov, is based on the investigation of coal from boreholes. If it is not possible to obtain core, coal fines are caught with the aid of a No. 100–200 sieve installed under the stream of water from the borehole. The caught fines are placed in a hermetically closing flask with a capacity of 175 cm³. The laboratory part of the investigation does not differ from the method described above (the “Makeevka” method) [5,8].
The third method for determining the gas-bearing capacity of seams, according to I. M. Yarovoy, is based on measuring gas pressure in shotholes drilled in the coal mass and determining the amount of free and sorbed methane in the same coal, at the same pressure under laboratory conditions. From the pressure curve
methane measured in a drilled borehole, and by the amount of sorbed and free methane per unit weight of coal from the same seam, obtained under laboratory conditions as a function of pressure, determine the true gas content of the coal seam \[6, 9\].
The fourth method for determining the gas content of seams, according to Professor-Doctor I. M. Pechuk, is based on determining gas content from so-called tabular data, taking into account the geological conditions of seam occurrence. On the basis of geological sections along exploration lines, the following are established: the depth of occurrence of the seams, their dip angle, the presence of seam outcrops at the surface, the magnitude and character of overburden, the presence of breaks in seam continuity, anticlinal and synclinal folds, closed domes, etc. For the corresponding conditions of occurrence of the seam, depending on the grade of coal (gas, coking, lean), the gas content is determined from tables. For a clear representation of the distribution of gas content by seams and within seams along the strike at the projected level, a gas map is compiled. A gas map is a seam map of a level on which the change in gas content for each of the seams along the strike for the given level is recorded. The tabular gradients are established with allowance for the sorption capacity of coals \[2, 80\].
The first and second methods (the “Makeevka” method and Buyanov’s method) for determining the gas content of seams are almost analogous to one another.
The first method is possible when mine workings are present; consequently, it can be used only to establish the gas content of the seams of operating mines.
The advantage of the second method is that it makes it possible to determine the gas content of seams at the time of exploration; therefore it is more suitable for determining the gas content of the seams of projected mines.
Both the first and the second methods do not reflect the true gas content of seams, which increases with the depth of occurrence of the coal mass. Extracted coal contains a different amount of gas than coal located in a mass untouched by mine workings. This discrepancy is the greater, the more finely the coal has been crushed.
The third method, according to Yarov, although indirect, makes it possible to determine the true gas content of seams. It would seem to provide a more accurate establishment of the gas content of seams than any other method, but measuring the gas pressure in a borehole presents great difficulty. Drilling a borehole to determine the gas content of a seam where it is needed is not always possible.
Therefore, this method for determining the gas content of seams in a projected mine cannot be applied without its further development.
The greatest practical significance belongs to the fourth method for determining the gas content of seams, proposed by Professor-Doctor I. M. Pechuk. Only this method for determining the gas content of seams simultaneously takes into account the gas capacity of the coal and drainage, which depends on the reduced gas permeability and geological conditions (this method makes it possible to determine the initial gas content without carrying out special observations. Its accuracy is low, and, if possible, it is advisable to correct the results of gas-content determination using observational data).
Author’s observations on establishing the degree of accuracy in determining seam gas content
Determining the gas content of seams is a complex problem. Professor-Doctor I. M. Pechuk has come closer than all other scientists in the USSR to a practical solution of this problem. His method for determining the gas content of seams simultaneously takes into account the gas capacity of coal and drainage,
dependent on the geological conditions of seam occurrence, which is absent in all the other methods considered above for determining the gas content of coal seams. The correct solution of the question of the gas content of seams is impossible without taking into account the gas capacity of the coal and drainage.
The method for determining the gas content of seams proposed by I. M. Pechuk is the only method that has already found practical application in Kuzbass; therefore we studied this method in detail by conducting a series of observations. The observations were carried out in order to establish the conditions under which this method of determining the gas content of coal seams gives more accurate results. To ensure the successful conduct of the observations, mine No. 135 of the “Kuibyshevugol” trust was selected as the most gaseous. For this mine, the gas-content forecast was also compiled according to the method of Professor Doctor I. M. Pechuk, which makes it possible to establish the accuracy of the forecast from the actual gas emission.
As our observations have shown, the correct establishment of the conditions under which the gas-content forecasting method of Professor Doctor I. M. Pechuk gives the best results depends to a considerable extent on the methodology of conducting the observations. Therefore, a methodology for observations was developed in advance and tested at mine No. 140. The observations were carried out in development workings.
To establish the gas content of seams on the basis of actual gas emission from development workings, the following methodology was adopted.
- In the main and parallel drifts, at points 1, 2, 3, and 4 (Fig. 2), points were established for measuring the quantity of flowing air and for taking samples to determine the percentage content of methane in the air stream.
Fig. 2. Arrangement of points for air measurement and sample taking.
- From the results of measurements and chemical analysis of the air, the gas content of the seams was calculated according to the formula of Professor Doctor I. M. Pechuk [2, 68]:
\[ W=\frac{G}{\alpha \cdot m \cdot \gamma \cdot v \cdot \Gamma\left[1-\left(\frac{T-t}{T}\right)^2\right]}, \tag{1} \]
where \(W\) is the gas content of the seam, \(m^3/t\);
\(G\) is the actual gas emission, \(m^3/\text{min}\);
\(\alpha\) is the coefficient of gas emission from the walls of the working, an abstract number;
\(m\) is the seam thickness, m;
\(\gamma\) is the specific weight of coal, \(m^3/t\);
\(v\) is the average rate of driving of the working, m/month;
\(\Gamma\) is the limiting value \(s\), \(\frac{1}{43200}\) m;
\(T\) is the period after which gas emission practically becomes negligible, months;
\(t\) is the time elapsed from the beginning of driving the working, months.
This formula is valid for the case of continuous movement of the face; therefore the face for conducting observations was selected according to surveyors’ data.
Table 1. Results of observations for determining the gas-bearing capacity of seams at Mine No. 135 of the “Kuibyshevugol” Trust, horizon +85 m
| Sample No. | Date | Place of observations | Working cross-section \(S\) | Measurement duration, min | Air measurement by anemometer: I count | Air measurement by anemometer: II count | Air measurement by anemometer: count difference | Air measurement by anemometer: mean difference | Air velocity, m/min | Air quantity, m³/min | Brockmann sample analysis: bulb No. | \(CO_2\) | \(CH_4\) | \(O_2\) | Quantity of \(CH_4\), m³/min \(g\) | Incoming \(CH_4\), m³/min \(G\) | Mean rate of advance of workings, m/month | Time from the start of drivage, \(t\) | Gas-bearing capacity, m³/t \(W\) |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Seam 2, western | |||||||||||||||||||
| 9 | 31/VII | Main drift | 5.67 | 2 | 4110 4444 |
4444 4762 |
334 318 |
163 | 24 | 136 | 83 | 0.2 | 0.3 | 20.0 | 0.41 | 0.68 | 20 | 5 | 5.76 |
| 10 | ” | Parallel drift | 0.84 | 2 | 4762 7260 |
7260 9840 |
2498 2580 |
1264 | 162 | 136 | 60 | 0.2 | 0.8 | 19.5 | 1.09 | ||||
| 112 | 2/VIII | Main drift | 5.67 | 2 | 2820 3060 |
3060 3295 |
240 235 |
117 | 18 | 102 | 73 | 0.1 | 0.3 | 20.0 | 0.306 | 0.62 | 20 | 5 | 5.25 |
| 115 | ” | Parallel drift | 0.72 | 2 | 10609 2820 |
8448 609 |
2161 2211 |
1090 | 141 | 102 | 39 | 0.2 | 0.9 | 16.6 | 0.927 | ||||
| Seam 3, western | |||||||||||||||||||
| 5 | 31/VII | Main drift | 5.7 | 2 | 3676 4110 |
4110 4550 |
410 440 |
220 | 33 | 188 | 65 | 0.1 | 0.3 | 20.0 | 0.564 | 0.75 | 20 | 6 | 9.0 |
| 8 | ” | Parallel drift | 1.3 | 2 | 4550 5650 |
5650 6800 |
1100 1150 |
1125 | 144 | 188 | 70 | 0.1 | 0.7 | 19.8 | 1.315 | ||||
| 123 | 2/VIII | Main drift | 5.7 | 2 | 1880 2050 |
2050 2300 |
170 250 |
210 | 31.2 | 178 | 81 | 0.2 | 0.2 | 20.0 | 0.356 | 0.71 | 20 | 6 | 8.5 |
| 125 | ” | Parallel drift | 1.3 | 2 | 2300 3400 |
3400 4460 |
1100 1060 |
1080 | 137 | 178 | 79 | 0.1 | 0.6 | 20.0 | 1.07 |
Table 5 (continued)
| Sample no. | Date | Place of observation | Working section \(S\) | Duration of measurement, min | I reading | II reading | Difference of readings | Mean difference | Air velocity, m/min | Quantity of air, m\(^3\)/min | Bottle no. | CO\(_2\) | CH\(_4\) | O\(_2\) | Quantity of CH\(_4\), m\(^3\)/min \(g\) | Increment of CH\(_4\), m\(^3\)/min \(G\) | Mean rate of advance of workings, m/month | Time from start of driving, \(t\) | Gas content, m\(^3\)/t \(W\) |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 725 | 17/VIII | Main drift | 5.4 | 2 | 3818 4358 |
4358 4858 |
540 500 |
260 | 36 | 194 | 83 | 0.2 | 0.2 | 20.5 | 0.388 | 1.64 | 23 | 2 | 20.9 |
| 731 | — | Parallel drift | 2.2 | 2 | 5108 6608 |
6508 8048 |
1500 1460 |
740 | 96 | 191 | 65 | 0.2 | 1.2 | 20.1 | 2.33 | — | — | — | — |
| 130 | 2/VIII | Main drift | 5.64 | 2 | 2590 2900 |
2300 3230 |
310 | 160 | 25 | 141 | 23 | 0.1 | 0.3 | 20.0 | 0.282 | 1.41 | 23 | 2 | 15.9 |
| 130 | — | Parallel drift | 1.8 | 2 | 3261 4411 |
4411 5461 |
1150 1050 |
600 | 78.4 | 141 | 82 | 0.1 | 1.2 | 19.8 | 1.69 | — | — | — | — |
| 1208 | 28/VIII | Main drift | 5.4 | 2 | 1305 | 3105 | 1800 | 920 | 117 | 231 | 82 | 0.1 | 0.8 | 20.3 | — | 1.87 | 30 | 6 | 10.0 |
| 1208 | — | Parallel drift | 2.0 | — | — | 3105 | 4985 | 1880 | — | — | — | — | — | — | — | — | — | — | — |
| 1208 | 4/VII | Main drift | 5.4 | 2 | 5435 6785 |
6785 8235 |
1350 1450 |
700 | 90 | 189 | 48 | 0.1 | 1.0 | 20.1 | — | 1.89 | 30 | 6 | 10.1 |
| 1208 | — | Parallel drift | 2.1 | 2 | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — |
| 1212 | 28/VII | Main drift | 5.6 | 2 | 3750 4880 |
4880 6150 |
1130 1270 |
600 | 78 | 179 | 79 | 0.1 | 3.6 | 19.3 | — | 6.45 | 32 | 3 | 37.3 |
| 1212 | — | Parallel drift | 2.3 | — | — | — | — | — | — | — | — | 0.1 | — | 20.3 | — | — | — | — | — |
the dispatcher's office and only those were accepted which had had no stoppages in operation; after this, the condition of the ventilation and of the ventilation devices in the section of the seam under investigation was established on site. Seams with insufficiently good ventilation and ventilation devices were excluded.
Measurement of the air flowing through the workings was carried out with an anemometer. Air samples were taken by the “wet method,” using a set of bottles. The collected air samples were sent to the mine-rescue station, where the percentage content of methane was determined with a Brockmann apparatus.
The main observations were carried out at mine No. 135 of the “Kuibyshevugol” trust on the \(+85\) horizon. In all, five seams at mine No. 135 were subjected to investigation: 2 west, 3 west, 5 west, 2 east, and 5 east, and 150 determinations of methane content were made. The most characteristic results of the observations are summarized in Table 1. To compare the results of observations with the data of the gas-content forecast and with the data on determining the category of the seams, Table 2 was compiled. The data of the gas-content forecast for the seams were taken in accordance with the location of the face at the time of investigation from the gas map of mine No. 135 for the \(+85\) m horizon (Fig. 1), compiled by Prof.-Doctor I. M. Pechuk. The data on the gas abundance of the seams were taken from the acts on determining the mine category by half-years.
Table 2. Summary data on gas emission of the seams of mine No. 135 of the “KUIBYSHEVUGOL” trust for the \(+85\) horizon
| Name of seams | Gas content of seams according to the method of Prof.-Doctor I. M. Pechuk | Gas content according to observation results | Gas abundance according to PTE |
|---|---|---|---|
| Seam 2 west | 10–15 | 5.76 5.27 | 29.5 |
| Seam 3 west | 5–10 | 9.0–8.5 | 11.1 |
| Seam 5 west | 15–20 | 15.9–20.9 | 29.5 |
| Seam 2 east | 10–15 | 10.0–10.1 | |
| Seam 5 east | 15–20 | 37.3/18.6 |
From Table 2 one can see the complete similarity of the gas-content indices according to the forecast and according to the results of observations for seams 3 west, 5 west, and 2 east. The discrepancy between the forecast data and the observation results for seam 2 west should be explained chiefly by the unsatisfactory condition of the ventilation and ventilation devices during the observations, which made it difficult correctly to establish the actual gas emission. The reason for the sharp discrepancy between the observation results and the forecast data for seam 5 west is that the face passed through a zone of the seam with strongly crushed and comminuted coal; and, when calculating the observation results by the formula for determining gas content [1], the coefficient 2, recommended by Prof.-Doctor I. M. Pechuk for these bedding conditions of the seam, was not introduced into the numerator. In Table 2, in the denominator for seam 5 west, the recalculation results are given taking this coefficient into account.
The considerable discrepancy between the observation data and gas abundance confirms the non-indicativeness of gas abundance for the conditions of the Kuznetsk Basin.
The results of the observations carried out by us confirm that the gas-content forecast correctly reflects the character of the distribution of gas content by seams and especially the increase in gas content in the seams as one approaches
…to the closed-off part of the seam (seam 5 west), but quantitatively it does not provide great accuracy.
Of the five seams subjected by us to investigation, for four seams the forecast of gas content by the method of Prof. Dr. I. M. Pechuk was confirmed completely. Consequently, the method for forecasting gas content of Prof. Dr. I. M. Pechuk already at the present time has practical significance, but it requires additional scientific-research work to refine the tabular data so that this method will give sufficiently accurate results on the gas content of seams in all cases of occurrence—not only on the character of the distribution of gas content, but also on the absolute magnitude of gas emission.
Proposal of the Author of the Work
To achieve high accuracy in determining expected gas emission, it is necessary to know not the gas content of seams in general, but the initial (true) gas content, i.e., that which a coal seam possesses before mining operations are conducted along it. This gas content is more constant over a considerable extent of the seam. With the present state of science and technology, it is impossible to determine the initial gas content directly. Any penetration into the thickness of untouched coal in order to take a sample leads to a disturbance of the established equilibrium of pressures in the mass, and the sample taken loses part of the gas before it is enclosed in a hermetically closing vessel. Therefore, the initial gas content can be determined only indirectly.
The author of the work proposes, for determining the gas content of the seams of a projected mine, a combined method, which represents the aggregate of the positive qualities of the most advanced already known methods for determining the gas content of seams, with their shortcomings mutually excluded. At the same time, this method of determining gas content is based on the simultaneous consideration of the gas capacity of coal and of drainage, which depends on the reduced gas permeability and the geological conditions of seam occurrence.
The combined method is based on determining the gas content of the seams of a projected mine through boreholes. It unites Buyanov’s method and the method of Prof. Dr. I. M. Pechuk.
The method for determining gas content of Prof. Dr. I. M. Pechuk, which has already received practical application in the mines of Kuzbass, is indicative and does not lay claim to great accuracy under all conditions of seam occurrence. This method is directly dependent on the accuracy of determining the geological structure of the deposit. Errors made during exploration of the geological structure of the deposit lead to incorrect establishment of seam gas content. Therefore this method, despite its many positive qualities, does not yet fully solve the problem of determining seam gas content.
The second method (K. Buyanov’s), or rather its idea of determining the gas content of seams from coal obtained from boreholes, has purely practical significance. This idea is directed against the conservatism of certain geological-exploration organizations of coal deposits, which consider the determination of seam gas content simultaneously with exploration a matter of secondary importance. In addition to the great importance of establishing the gas content of a mine field by the time of design, simultaneous determination of the gas content of seams and of the geological structure of the mine field facilitates exploration, because every geological disturbance is associated with a change in the gas content of seams. This also contributes to mutual refinement of the gas content and the geological structure of the mine field. Determination of seam gas content by this method (K. Buyanov’s) does not hinder the application of the third method (I. M. Yaro…
On the contrary, it may serve as a control for sorption and desorption curves constructed on the basis of the results of I. M. Yarovoi’s method.
The proposed combined method for determining the gas content of the seams of a mine being designed consists of the following:
1) determination of the gas content of seams is carried out simultaneously with the exploration of the geological structure of the mine field;
2) coal extracted from a borehole when crossing a seam of the required fraction is placed in a hermetically sealed vessel and sent to the laboratory;
3) in the laboratory, the gas content of the extracted coal is determined;
4) on the basis of the gas content of the coal obtained in the laboratory, taking into account the data of Prof. Dr. I. M. Pechuk’s gas-content tables and the geological structure of the mine field for the planned horizon, a gas map is compiled (a map of the distribution of gas content by seams).
The theoretical and scientific value of this method lies in the fact that, at the present level of technology, it makes it possible to approach more correctly the determination of initial gas content and to verify the theoretical substantiation of the gas-content tables proposed by Prof. Dr. I. M. Pechuk, and to correct them in accordance with the geological conditions of seam occurrence.
The practical value of this method lies in the fact that design organizations will receive not approximate data, as is done now, but more accurate, scientifically substantiated initial data for designing the ventilation of newly laid-out mines, and will ensure the comprehensive design of mining operations at these mines as a whole. At the same time, exploration organizations will be able, by the character of changes in the gas content of seams, to establish additional seam disturbances.
Consequently, the combined method we propose for determining the gas content of seams is of theoretical, scientific, and practical interest.
References Used
- Skochinsky A. A.—Mine Atmosphere, 1932.
- Pechuk I. M.—Ventilation and the Struggle against Gas in the Mines of Kuzbass, 1946.
- Palvelev V. T.—Sorption of methane by fossil coals of Donbass at high pressures. Izv. AN SSSR, Technical Section, No. 5–6, 1942.
- Bykov L. N.—Exogas and the Theory of the Origin of Centers of Sudden Outbursts, 1932.
- Buyanov K.—Determination of the gas content of seams from borehole data during exploration, journal Occupational Safety in the Mining Industry, No. 2, 1935.
- Yarovoi I. M.—Determination of the methane content of coal seams, Coal, No. 12, 1947.