RU2136890C1 - Method for degassing of coal seams - Google Patents

Abstract

FIELD: mining industry. SUBSTANCE: according to method, bore-holes are drilled from ground surface in direction of coal seam being worked with subsequent connecting these bore-holes to vacuum pumping station for extracting gases from coal seam. In process of drilling, assessed is strength of drilled layers of rock matter so as to separate strongest layer with exceeding arithmetic mean value of all other layers by at least 10%. This layer must be located at minimal distance from coal seam being worked. Thickness of selected layer must be not less than 0.1 a, where a - width of longwall in coal seam being worked. Bore-hole is drilled down to floor of this strong layer which is considered as gas-screening. Upper part of bore-hole is cased to corresponding depth which depends on descending angle of coal seam being worked, distance from axis of longwall of edges of next column, and also on angles of fracture on ascending, descending or extension selected with respect to orientation of longwall being worked. Application of aforesaid method gives higher efficiency in degassing due to long period of operating degassing bore-holes and reduced cost of preparatory activities. EFFECT: higher efficiency. 1 cl, 1 dwg

Description

 The invention relates to the mining industry and can be used to solve problems of reducing gas saturation of gas-bearing undermined coal seams and coal-bearing strata.

 A known method of preliminary degassing of a coal mass using exploration wells or wells specially drilled from the surface. Wells are drilled down to the formation or into the rocks of its soil, cased with pipes, the annular space is plugged, and the wells are connected to a vacuum pipeline (see, for example, SV Slastunov, “Early Degassing and Extraction of Methane from Coal Fields” M., Publishing House MSTU, 1996, p. 14-19).

 However, this method does not provide the necessary reduction in gas mobility, since the depth of drainage of the coal seam is limited to ten meters, and the method itself is characterized by the high complexity of the preparatory work and a significant period of their implementation, reaching 10-20 months.

 The closest in technical essence to the claimed one is the method of preliminary degassing of the produced seams through the wells drilled from the surface, described in the "Interim Guidelines for the processing of outburst and gas-bearing seams of coal and increasing the efficiency of degassing operations in the conditions of their intensive discharge at the mines of the Karaganda basin", L ., Ed. VNIMI, 1988, pp. 8-11; 21-26. The method includes drilling wells from the surface into the undermined reservoir before it is completed, casing the lower sections of the wells under the reservoir with perforated pipes and connecting them to a vacuum pipe.

 However, this method is also not effective enough due to the short life of the wells, since when mining the degassing sections, their lower part falls into the collapse zone of the formation roof rocks, the system fails, and additional labor is required to restore or create a new network of wells.

 The invention solves the problem of increasing the degassing efficiency of undermined gas-bearing coal seams by increasing the life of degassing wells and reducing labor costs in the preparation and conduct of early degassing measures.

 The essence of the method of degassing coal seams involves drilling wells from the surface in the direction of the undermined seam with its subsequent connection to the pump-vacuum station to extract gas from the undermined stratum. In the process of drilling wells, the strength of the drilled layers of rocks is estimated to highlight the most durable layer from them, exceeding the average value of the strength of all other packs in excess of 10% from the arithmetic average. This layer should be located at a minimum distance to the undermining layer, the undermining layer, and the thickness of the selected layer should be at least 0.1 a, where a is the width of the lava side. The well is drilled to the soil of a solid layer, and the upper part is cased to the appropriate depth, depending on the angle of incidence of the undermining layer, the distance from the axis of the lava to the edge of the next column, as well as the angles of rupture in rebellion, dip or strike, selected depending on the orientation of the producing lava.

 The method is illustrated in the drawing, which shows the layout of the degassing wells and degassed reservoir. The drawing shows: 1 and 2-part-time and part-time (degassed) layers, respectively; 3 - peeling, fissured layer; 4 - gas shielding strong layer; 5 - degassing well; 6 - section casing wells; 7 - pump-vacuum degassing station on the surface of the earth; 8 - the surface of the separation of rocks of the fractured pack 3 from the shielding layer 4; 9 - zone of collapsed rocks.

 The method is as follows. A well 5 is drilled towards the undercut formation 1 and the undercut formation 2 until the gas-draining fractured layer 3 comes into contact with the gas-shielding layer 4 from the earth’s surface. Moreover, the well is located so that it is located near the middle of the lava on the formation 1, which is planned for development. When drilling a well 5 in each intersected layer, formation or interlayer, characteristic pieces of rocks are selected and tested, for example, on a BP-14 device, in order to determine their physicomechanical properties. The test procedure is described, for example, in the "Instructions for choosing the method and parameters of softening the roof in excavation areas" L., VNIMI, 1982, pp. 86-87.

 Drilling of wells is carried out to the depth of the most durable gas-shielding layer of 4 rocks, usually sandstone, located above the zone 9 of the collapse of rocks at a minimum distance from the producing layer 1.

 The parameters of zone 9 are determined depending on the capacity m of the mined seam 1 based on regulatory documents for each of the existing coal deposits. In particular, for the Karaganda basin, this value is 6 m.

прочностей каждого из перебуриваемых слоев, т.е.The most durable layer 4 is identified as a layer of rocks with a strength exceeding at least 10% arithmetic mean value

strength of each of the drilled layers, i.e.

,
где X_i - значение прочности на сжатие каждого из породных и угольных слоев;
n - количество породных и угольных слоев в угленосной толще.

,
where X _i - the value of the compressive strength of each of the rock and coal layers;
n is the number of rock and coal layers in the coal-bearing stratum.

после чего выделяют отклонения с положительным знаком и определяют коэффициент вариации

Выделяют слой пород с V_Δ ≥ 10% и из них выбирают ближайший к упомянутой зоне 9. Значение коэффициента вариации 10% обусловлено обычной точностью определения физико-механических свойств пород. Кроме того, мощность защитного слоя должна составлять не менее 0,1а, где а - ширина лавы подрабатывающего пласта. Параметр 0,1а определен в результате аналитических исследований с привлечением статистики для прочных слоев (см. Герцен А.И., Гончаров Е. В. "Безопасные условия подготовки и отработки газоносных и выбросоопасных пластов". Подземное и шахтное строительство. М" Недра, 1991 N 12, стр. 11-13).Then calculate the simple average deviation

after which deviations with a positive sign are distinguished and the coefficient of variation is determined

A rock layer with V _Δ ≥ 10% is isolated and the closest to the mentioned zone 9 is selected from them. The value of the coefficient of variation of 10% is due to the usual accuracy in determining the physicomechanical properties of the rocks. In addition, the thickness of the protective layer should be at least 0.1a, where a is the width of the lava of the underburden. Parameter 0.1a was determined as a result of analytical studies using statistics for strong layers (see Herzen A.I., Goncharov E.V. "Safe conditions for the preparation and development of gas-bearing and outburst hazardous layers. Underground and mine construction. M" Nedra, 1991 N 12, p. 11-13).

 The conductor of the well (its upper part, to a depth of not more than f) is cemented, cased to a stationary pump and vacuum station 7, for example, PDU-50. The well further than the conductor can not be cased. The well casing depth f is determined depending on the angle α of the formation 1 dip, the distance Y from the edge of the next column, as well as the rupture angles, respectively, in the direction of rebellion, fall or strike, determined in accordance with the "Rules for the protection of structures from the harmful effects of mining in coal seams " Casing well 5 in its upper part is necessary for a longer and more efficient operation. The corresponding depth f of the casing will protect the well from destruction by sediments and groundwater in the conditions of underworking of loose and weak sedimentary rocks.

 Subject to the above conditions, above zone 9 of complete collapse of rocks caused by the mining process in formation 1, a fissured pack of rocks 3 is formed in contact with a strong gas-shielding layer 4 with identification of the surfaces (cavities) of delamination 8, defined as Weber cavities (see Goncharov E .V., Goncharova LA "Deformation and block formation of sedimentary rocks in dynamic zones of high rock pressure". Sat. Physical processes of mining. St. Petersburg, St. Petersburg State University, 1992, pp. 36-40).

 In this case, the gas is drained through the zone 9 of collapsed roof rocks through cracks in the exfoliating rock pack 3 and the cavities between the delamination surfaces 8 and the monolithic gas-shielding layer 4, from where it is released to the surface through the well 5 connected to the pump-vacuum station 7 and can then be disposed of .

 Using the inventive method in comparison with the known ones allows to increase the degassing efficiency of undermined gas-bearing coal seams by reducing the consumption of drill pipes, shortening the time of drilling of well equipment, and also increasing the duration of their operation.

Claims (2)

 1. A method of degassing coal seams, including drilling wells from the surface towards the roof of the produced seam, casing part of the wells, connecting them to the pump-vacuum station and extracting gas from the undermined coal stratum, characterized in that when drilling a well in the coal stratum, rock strength is evaluated layers, distinguish the most durable layer of rocks with a deviation from the arithmetic average value of the strength of the drilled rocks in excess of 10%, located at a minimum distance from the mining layer and having its own power of at least 0.1 a, where a is the width of the lava of the underburden, this strong layer is considered to be gas shielding, and the well is drilled to the soil of the gas shielding layer.  2. The method according to claim 1, characterized in that the well is cased in its upper part to a depth depending on the angle of incidence of the producing layer, the distance from the axis of the lava to the edge of the next column, as well as the fracture angles of uprising, dip or strike, selected in depending on the orientation of the working lava.