Gas prognosis

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Anthropogenic accumulation of methane in a disturbed coal rock massive

Translation from:

"Техногенні скупчення метану у порушенному вуглепородному масиві. Методика прогнозування зон підвищеної газонасиченності та визначення їх параметрів"

СОУ 10.1.05411357.007:2007

Видання офіційне

Київ, Мінвуглепром України, 2007

Автори: А.Ф. Булат, Д.П. Гуня, А.П. Клець, О.О.Кущ, Л.Д.Кузнєцова, В.В. Лукінов, О.В. Приходченко, М.Г. Тіркель

Інститут геотехнічної механіки ім. М.С. Полякова НАН України

CMM-forecast ukr.pdf


Gas prognosis or the parts with increased gas content and the determination of its parameters

Area of application

This norm is used for the parts with increased gas content and the determination of the parameters and is applied by geological departments for coal shafts (with increased gas hazards) that are dangerous because of the gas and geological departments of companies, that deal with coal mine methane extraction.

Some definitions

•Anthropogenic Accumulation of Methane (AAM) - methane accumulation in fractured zones of an undermined coal rock massive

•Disturbed coal rock massive – the rock massive that was released from the rock pressure as a result of undermining and where therefore coal mine methane arises

•Coal mine methane amount AAM - the amount of methane that arises in the layers of the coal rock after undermining.

•Contour map of AAM - contour lines with constant amount of coal mine methane that are shown on the mining map

•Areas with increased gas content (AIG) - areas in the disturbed coal rock with gas content that is higher than the average concentration in the whole massive and the depiction on the contour map

•Parameter of the AIG - size of the AIG on the map and on the vertical section and the average amount of coal mine methane

Forecasting methods and methods for the parameter specification of the AIG

1. For the prognosis of the gas content and the estimation of the coal mine methane amount following data are necessary:

- caracteristics of the coal extraction and the available methane amount in the goaf or the closed mine;

- mine working maps of the mined coal seams on the mining area or in the closed mine, that are considered for methane extraction;

- vertical cross section at strike and dip;

- data sheets of the working area with degasification activities;

- vertical cross section of the explatory borehole of the shafts and other mining areas;

- caracteristics of the coal seams and rocks in the strata above layer;

- information about gas deposit in the mine working area and about the boreholes of the prognosis area.

2. Prognosis procedure

2.1 The borders and the grid of the prognosis area are identified on the mine working map of the mined coal seam.

2.2 On this area the stock and the number of boreholes with the information of the vertical cross section of the layers, lithology, rock characteristics of the gas content, porosity, water content and gas pressure are determined.

2.3 The location of the borehole open end is determined according to the chosen grid for the prognosis.

2.4 For each borehole the coal mine methane amount in sandstones, caol seams and interlayers is estimated.

2.5 The contour map of the coal mine methane amount, the AIG are intergrated in the prognosis area in the mine working map and the parameters are determined.


3. Estimation of the coal mine methane amount in sandstone eaves for the strata of undermined rock layers from the hanging wall in direction (along the normal) of the hanging wall is calculated using an appropriate formula.

• For each borehole the amount of sandstones is determined.

• For each sandstone the thickness, the depth, natural porosity and the gas content are determined.

• For each sandstone besides each borehole the anthopogenic gas content in m³ gas referred to m³ of the rock is calculated.


4. Estimation of the coal mine methane amount in undermined coal seams for the strata of the undermined rocks with a distance of the normal to the hanging wall of teh extracted coal seam in the direction of the rock hanging wall

• For each borehole the number of the coal seams containing gas and interlayers with a thickness > 0,2m is determined. The thickness, layer density and teh natural methane content are determined.

• For each coal seam or each rock strata besides each borehole the anthropogenic gas saturation is calculated.

• Coal mine methane amount in undermined coal seams and interlayers for each borehole is determined.


5. Estimation of the coal mine methane amount in the undermined coal massive is the sum of coal mine methane amount in sandstones, coal seams and interlayers for each borehole.

6. Based on the data of the openend of the borehole and the coal mine methane amount for each borehole the contour map of the coal mine methane amount in undermined coal massive of the prognosis area is constructed (with the help of the interpolation method or other methods). A coordinate system is plotted on the contour map. The intervals correspond to the mid-distances between the boreholes on the prognosis area. Contour lines of the average coal mine methane amount are aligned on the contour map. The AIG are marked and their parameters are determined.