RU2447289C1 - Method to identify outburst zones in coal beds - Google Patents

Abstract

FIELD: mining.

SUBSTANCE: method includes selective drilling of wells with depth of at least 5.5 m with a pitch of not more than 1.0 m, measurement starting from the distance of 0.5 m at each interval of drilling chip output and initial speed of gas release. For conditions of coal bed development by values of gas pressure and temperature of coal bed, the possibility is established for existence of gas hydrates in a coal bed. Specific electric resistance of the coal bed is measured in a drilled well, and a curve is built for dependence of the specific electric resistance of the coal bed on the distance along the well axis. Using the curve, width of the coal bed zone is detected, which contains gas hydrates of natural gas. Then the outburst hazard index is calculated depending on the width of the coal bed zone containing gas hydrates, and moisture of the coal bed. Afterwards the conclusion is made on outburst hazard of this section in the coal bed.

EFFECT: increased reliability of outburst-hazardous areas detection in coal beds inclined to sudden outbursts of coal and gas.

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Description

The invention relates to the field of mining, namely to underground mining of coal seams, inclined and dangerous for sudden emissions of coal and gas. It can be used during preparatory workings on coal seams.

A known method for predicting outburst hazard when opening a coal seam (Instruction for the safe conduct of mining on seams hazardous for sudden emissions of coal, rock and gas. - M., 1989), including drilling exploratory wells when approaching the bottom face of the opening to the coal seam at a distance not less than three meters normal for measuring gas pressure and sampling coal. The hazard of the formation is determined by three to four samples. Gas pressure is measured in at least two wells drilled at a distance of at least three meters. Gas pressure is monitored for several days until its maximum value is established.

The disadvantage of this method is that the outburst hazard indicator is determined at two or three points in front of the face of the cutting mine, and the outburst hazard of the whole face and its surrounding zone is evaluated, which reduces the reliability of the method.

A known method for the current forecast of the outburst hazard zones of a rock mass (Methods of differentiated current forecast of the danger of the manifestation of gas-dynamic phenomena, selection and control of the effectiveness of ways to prevent them for the conditions of the eastern regions. - Kemerovo: VostNII, 1979. - 16 pp.), The closest to the proposed technical the essence and the achieved result, including interval drilling of the well in the bottom of the preparatory mine with a depth of not less than 5.5 m in increments of not more than 1.0 m, measuring from a distance of 0.5 m, per House range output cuttings and the initial gas evolution rate. Its essence lies in the fact that each type of gas-dynamic phenomena corresponds to its own range of values of the initial rate of gas evolution and the yield of drilling fines. A zone is considered to be hazardous if:

1. The indicator R> 0, where R = (i _max -4) (S _max -1,6) -6,

where R is an indicator that determines the type of gas-dynamic phenomenon;

i _max is the initial velocity of gas evolution;

S _max - the output of drilling stuff.

2. The initial gas release rate drops sharply within one minute.

In a number of cases, wells are drilled heavily, up to one hundred liters of drill trifle comes out from one linear meter of a well, because of which it is practically impossible to seal and reliably determine the initial gas release rate. Currently, it is known that natural gas in coal seams can be in three states: free, sorbed and hydrated under natural conditions. The detection of gas hydrates of natural gas, which may affect the emission hazard, is not taken into account in the known method of the current forecast adopted as a prototype.

The technical result of the invention is to increase the reliability of the determination of hazardous zones in coal seams.

The specified technical result is achieved by the fact that in the method for determining outburst zones in coal seams, including interval drilling of a well in the bottom of a preparatory mine with a depth of not less than 5.5 m in increments of not more than 1.0 m, it is measured starting from a distance of 0.5 m, at each interval, the yield of drill fines and the initial gas release rate, according to the invention, first, for the conditions of development of the coal seam, the possibility of existence in the coal seam is determined by the values of the gas pressure and temperature of the coal seam e of gas hydrates, after which the specific electrical resistivity of the coal seam is measured in a drilled well and a graph of the electrical resistivity of the coal seam is plotted against the distance along the axis of the well, with which the width of the zone of the coal seam containing gas hydrates of natural gas is determined, and then the emission hazard index R ⁿ s taking into account the width of the zone of the coal seam containing gas hydrates, and the natural humidity of the coal seam.

The inventive method for determining the outburst zones in coal seams is illustrated by drawings, where figure 1 shows the equilibrium phase curve of the phase state of the system "water - natural gas"; figure 2 is a graph of the specific electrical resistivity (resistivity) of a coal seam from the distance along the axis of the well into the coal mass; figure 3 - dependence of the emission factor from the width of the coal seam zone containing gas hydrates of natural gas.

The method is as follows. In mine conditions, interval drilling of a well with a depth of not less than 5.5 m in increments of not more than 1.0 m is carried out and the yield of drilling fines and the initial gas release rate are measured at each interval.

For the conditions of the development of the coal seam by the values of gas pressure and temperature of the coal seam using the equilibrium curve of the phase state (figure 1) establish the possibility of the existence of gas hydrates in the coal mass. The region above the curve is the region of existence of gas hydrates, the region below the curve is the region of separate existence of water and natural gas.

, то эта зона содержит газовые гидраты.Then, in the drilled well, the resistivity of the coal mass is measured and a graph of the dependence of resistivity on the distance along the axis of the well is plotted (Fig. 2). According to this graph, the width of the zone of the coal seam containing gas hydrates of natural gas is determined: during the coal extraction zone, the resistivity value decreases by no more than 30%, and as it leaves the production influence zone, it takes on some constant value ρ ₁ . In the zone of the coal seam containing gas hydrates, the resistivity of the coal seam will be ρ ₂ . If the ratio

then this zone contains gas hydrates.

The emission hazard index R ^{n is} determined taking into account the natural moisture of the coal seam and the width of the zone of the coal seam containing gas hydrates. To do this, determine the number of moles of gas contained in a hydrated state in a coal seam:

,

,

where V _coal - the volume of coal in which crystals of gas hydrates are distributed;

ε is the humidity;

ρ _hydrate is the density of crystalline hydrates;

β - hydrate saturation;

µ _water is the molar mass of water;

n is the number of water molecules per one gas molecule in the unit cell of the hydrate.

Then, according to the Van der Waals equation, taking into account the number of moles of gas ν that are in a hydrated state in the zone of the coal seam, an increase in the pressure value P due to the release of gas from the hydrated state is calculated:

,

,

where R is the gas constant;

T is the temperature of the reservoir;

a and b are the van der Waals coefficients for a given gas;

V _pore is the volume of pore space;

ν is the number of moles of gas contained in gas hydrates.

The emission hazard indicator is determined as the ratio of the active forces F _a , striving to unleash a sudden release, and the passive forces F _n , which prevent this (Murashev V.I. Mechanism for unleashing sudden emissions of coal and gas in mining) / Fundamentals of the theory of sudden emissions of coal, rock and gas / Under the editorship of A.E. Petrosyan, A.P. Kulikov, G.K. Vasyuchkov. - M .: Nedra, 1978), according to the formulas

,

,

where F _a - active forces;

m ₀ - porosity of the array outside the zone of influence of the mine;

β is a parameter depending on the properties of coal and the depth of development;

h - the value of the extraction of coal on the edge of the face after the extraction of the next

sunset;

p ₀ - gas pressure on the coal seam;

p is the gas pressure at the edge of the face;

x is the length of the zone of influence of the preparatory workings on the stress state of the coal mass;

F _p - passive forces;

P - perimeter of the mine traversed along the coal mass;

S is the area of the exposed coal mass in the cross section of the mine;

- коэффициент сцепления угля на кромке забоя нарушенного участка пласта;

- coefficient of adhesion of coal at the bottom edge of the disturbed section of the reservoir;

ν 'is a parameter depending on the angle of internal friction of coal.

ρ is the angle of internal friction of the disturbed section of the reservoir.

After that, a conclusion is made about the outburst hazard of a given section of a coal seam: if R ⁿ > 0, then the portion of a coal seam is outburst hazardous. If the indicator R ⁿ <0, then the area of the coal seam is not emission hazardous.

An example of a specific implementation of the method for determining hazardous areas in coal seams. Interval drilling of a well with a depth of not less than 5.5 m in increments of not more than 1.0 m is carried out and the yield of drilling fines and the initial gas release rate are measured at each interval.

Next, determine the gas pressure and the temperature of the coal seam: let the gas pressure in the coal seam be p ₀ = 25 atm, the temperature of the coal seam T = 279 K with a natural moisture of the coal seam of 1.5% and a natural porosity of 5%. Using the equilibrium curve of the phase state (figure 1) determine the phase state of the system "coal matrix-moisture-natural gas." In this case, the “carbon matrix-moisture-gas” system is located at point 1 (Fig. 1) above the phase state curve; therefore, in the coal seam, gas and moisture are in a gas-hydrated state. Otherwise (if the parameters of the system are below the phase state curve, for example, at point 2), the existence of gas hydrates is impossible.

, следовательно, данная зона угольного пласта содержит газовые гидраты, а ее ширина составляет 0,7 м.Then, in the drilled well, the resistivity of the coal seam is determined. Build a graph of the resistivity from the distance along the axis of the well (figure 2). The resistivity of the coal seam at a distance of 3.4-4.1 m from the bottom of the mine exceeds the resistivity value characteristic of the zone of the untouched massif, and the ratio

therefore, this coal seam zone contains gas hydrates, and its width is 0.7 m.

The hazard factor is calculated taking into account the natural moisture of the coal seam and the width of the zone of the coal seam containing gas hydrates. To do this, determine the number of moles of gas contained in a hydrated state in a coal seam:

.

.

Then, according to the Van der Waals equation, taking into account the number of moles of gas ν that are in a hydrated state in a zone of a coal seam 0.7 m wide, the value of pressure gain P due to the release of gas from the hydrated state is calculated. The volume of pore space: V _then = 0.175 m ³ . We get:

.

.

That is, the pressure in the reservoir will increase with the release of gas from the hydrated state from p ₀ = 25 atm to 49.3 atm.

The outburst hazard index is calculated: R ⁿ > 0, therefore, the area of the coal seam is outburst hazardous.

Then, for a given coal seam, a graph of the dependence of the outburst hazard index R ⁿ on the width of the zone of the coal seam containing gas hydrates is plotted for different natural seam moisture (Fig. 3): 1 - 0.5%; 2 - 1%; 3 - 1.5%; 4 - 2%; 5 - 3%.

Next, the conclusion about the outburst hazard of this section of the coal seam is made taking into account the width of the zone of the coal seam containing gas hydrates and the natural humidity of the coal seam in Fig. 3.

The inventive method for identifying outburst zones in coal seams can improve the reliability of determining outburst zones in coal seams due to the fact that it takes into account an additional factor in the form of gas hydrates, the dissociation of which makes the main contribution to the gas balance in case of sudden emissions of coal and gas.

Claims (1)

A method for determining hazardous zones in coal seams, including interval drilling of a well in the bottom of a preparatory mine with a depth of not less than 5.5 m in increments of not more than 1.0 m, measuring, starting from a distance of 0.5 m, at each interval, the output of drill fines and the initial rate of gas evolution, characterized in that first, for the conditions of development of the coal seam, the values of gas pressure and temperature of the coal seam establish the possibility of gas hydrates in the coal seam, and then in the drilled well zmeryayut resistivity coal seam and plotted resistivity coal seam of distance along the borehole axis by means of which determine the width of the coal seam zone containing gas hydrates, the natural gas is further determined index outburst R ⁿ to the width of the coal seam zone containing gas hydrates and the natural moisture of the coal seam.

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