Prokopenko Olga  

Institute of Mining and Geology

The Mine surveying Department

Speciality "Mining surveying"

Research of coal and gas outbursts forecast opportunities

Scientific adviser: Styagun Anatoly 

Contents

Introduction

1. Literature analis

2. Tectonic fracturing

3. Disruptive failures influent zone width determination

3.1. Main point of tectonic failures influence zones width determination

3.2. Methods of fractures frequency determination

Conclusion

Literature list

   Currently, the mining in Donetsk coalfield is more than half of the total coal production in Ukraine. Mines of Donbass are developing reservoirs at depths ranging from 800 m to 1250 m. Reservoirs developing does not stop, despite the fact that the mining and geological conditions are complicated, what caused increases the degree of outbursts and loss of human lives.

   The most vivid expression of the mismatch between the capabilities of modern industry and existing methods of deposits are sudden outburst of coal and gas (Animation 1).

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Animation 1. Sudden outbarst of coal and gas.
(Animation: format – gif; number of frames – 12; the number of repetitions – 7; duration between frames: 1–10 – 1 s., 10–12 – 1/10 s.)

   Exposure to sudden outbursts of coal and gas restricts the use of advanced systems in development, concentration of coal and improving of ventilation schemes.

   To solve the first–mentioned problem, you should clearly identify its causes. For this, we will analyze the sources in which the questions of a sudden coal and gas outbursts was examined.

   D.S., prof., Khodot V.V. [1, p. 10] wrote that there are removable and irremovable causes among the causes of the high frequency of sudden coal, rocks and gas outbursts. Irremovable causes include the reasons associated with the deepening of the rock and increasing gas pressure, as well as increased advancing speed of mining and the growth of coal mining. Development of measures to combat with sudden outbursts should be directed primarily at neutralizing of these reasons, among which there are the causes of organizational nature: lack of discipline, poor logistic support work for the prevention of dynamic phenomena and weaknesses in developing and implementing the results of scientific research.

   Chernov, O.I. and Rozantsev E.S., [2, p. 55] note that the majority of sudden coal and gas outbursts, is confined to the zones of geological disturbance of the strata. Sudden outbursts in coal seams of different basins and deposits at different depths from the surface can be explained by different complexity of the tectonic structure.

   M.I. Bolshinsky [3, p. 6] notes that the sudden coal and gas outbursts are confined to areas of geological disturbances with complexity of the tectonic structure of a mine field. The development of small plicative and disjunctive failures increase the danger of outbursts. The most dangerous zones are areas of 10-20 m width on both sides of the failure.

   After analyzing these and other sources we can say that among the most important factors there are effect of the stress field of tectonic plates, the structural features of rocks and other geological factors.

   Tectonic fractures are narrow slit-like cavity or the aggregate of such cavities, which are located close by and arose as a result of mechanical destruction of rocks, caused by tectonic processes.

Figure 1. – Tectonic the gap between the rocks.

These fractures are differ from each other with length, depth of penetration into the Earth’s crust, orientation, time of occurrence, etc.

   There are following tectonic fractures:

1. Very large with an amplitude of more than 1000 m, length of more than 100 km and which are boundary of the basin or deposits;

2. Large, with an amplitude from 100 to 1000 m and 100 km length;

3. Average, with an amplitude from 10 to 100 m and 10 km length;

4. Small, with an amplitude from 3 to 10 m and length from 100m to 1000 m;

5. Very small, with amplitude up to 3 m and length from tens to hundreds of meters.

   Fractures of less than 10 cm are cracks.

Figure 2. – Fracture of rocks.

Among the cracks there are following groups:

1. Endogenous;

2. Exogenous;

3. Cracks of the pressure;

4. Cracks of weathering.

   The fact that as we approach the failure rate of fracturing increases is put on the basis of prediction. A number of researchers to predict the distance to disruptive faults use relative frequency of fractures. The cracks manifestations frequency is determined only for the exogenous group of cracks. V.A. Bukrinskiy and A.V. Mikhailova [4, p. 76] have found that the relative frequency of fractures reaching its minimum value, as they approach the failure, then its value increases dramatically. The distance from the observation point, where the relative frequency of fractures is minimal before the failure is considered to be a zone of influence of disturbance on fracturing. This value is fairly constant for different areas. So for the southern zone of shallow folding it is 400-700 m. For areas with an open view of folds, it is 50–150 m. In addition, the value of influence zone depends on the amplitude of the failure. As the amplitude increases the value of influence failure zone increases too. Hence, knowledge of the value of influence failure zone at the fracture makes it possible to predict areas of high outburst in the Donetsk–Makeyevka area.

   In a number of sources the authors propose different methods of fractures frequency determination. For example, Bukrinskiy V.A. and Mikhailova A.V. [4, p. 88] use the notion of the intensity of fracturing. As intensity of fracturing they describe the manifestation of any crack system and express the number of cracks per length unit. and Mikhailov, A.E. [5, p. 67] notes that it is possible to attribute the number of cracks not only to the units of length, but also to the unit of area.

   The above data allow us to predict the approximate distance to the rupture. More accurate prediction can be made on the basis of changes in the relative frequency of fractures. In this case, the relative frequency of fracture is determined by the formula:

n=(ni-nв)/nв*100%,

     where: ni — the frequency of fractures in the zone of influence of the violation;

               nв — frequency of fractures outside the violations influence zone.

   It is determined that relative frequency of fractures not far from violation is increases by about 70%, compared with an unbroken area.

   Establishing relationships between influence violations zones and zones of high tension of the array, which are formed at some distance from the bursting tectonic faults and zones of increased outburst, creates the preconditions for research of coal and gas outbursts forecast opportunities*.

1. Collected papers of V All-Union Scientific Technical Conference of the struggle against sudden coal and gas outbursts. — Moscow: Nedra, 1969. — 455p.

2. Chernov O.I. ,Rozantsev E.S. Prevention of sudden coal and gas outbursts in coal mines. — M.: Nedra, 1965. — 210p.

3. Bolshinsky M.I. The theory of sudden coal, rock and gas outbursts. Central Bureau of Scientific and Technical Information Municipal Unitary Enterprise USSR. 1993.

4. Bukrinskiy V.A., Mikhailova A.V. Study of the connection between the jointing and tectonic structure of rocks. — M.: MIIRGEM, 1963. — 96p.

5. Mikhailov A.E. Field methods for studying cracks in the rocks. — M.:Gosgeoltechizdat 1956 — 132 p.

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* This work is under development, the final completion scheduled for the end of December 2011.