Brief introduction of gas geology in Changcun mine
A, mine profile
Changcun Coal Mine of Yima Coal Industry (Group) Co., Ltd. is located in the southeast of yima city, Henan Province, with a mine field area of13.63km2.
Changcun Coal Mine was founded in 1958. After reconstruction and expansion, the approved production capacity in 2004 was 210×104t0a, and the output in 2005 and 2006 exceeded 200× 104t. It is one of the main mines of Yima Coal Industry Group Company.
The mine adopts inclined shaft multi-level ascending and descending panel development. The main mining methods are longwall retreating slicing or comprehensive mechanization of full thickness mining at one time, and natural caving method to manage roof technology. Changcun Coal Mine has five air intake shafts-tank car inclined shaft, belt inclined shaft, material inclined shaft, gangue discharge shaft and No.81well, and two return air shafts-Hougou air shaft and Dongshan air shaft. The ventilation mode of the mine is two-wing diagonal mixed type, and the ventilation method is extraction type. At present, the exhaust air volume of main ventilator in Hougou air shaft is 5 170m3/min, and that of main ventilator in Dongshan air shaft is 6 16m3/min. All coal mining faces adopt full negative pressure "U" upward ventilation, and all tunneling faces adopt counter-rotating local ventilator forced ventilation.
In this field, there are four layers of coal-bearing group II of Yima Formation, 1- 1 coal, 1-2 coal is a non-recoverable coal seam, 2- 1 coal is a locally recoverable medium-thick coal seam with simple structure, and 2-3 coal is a thick coal seam with complex structure in the whole area.
The results of gas grade appraisal over the years show that Changcun mine belongs to low gas mine. The identification results of1999 ~ 2006 are shown in the table below.
Atlas of Coal Mine Gas Geological Map in Henan Province
Second, the mine geological structure and control characteristics
Changcun mine field is located in the east of Mianchi syncline, and the structural form is an asymmetric syncline with axial NE and SE inclination. Asymmetry is manifested in the gentle width of the north wing and the narrow and steep width of the south wing. The north and south wings are basically bounded by the F 16 fault, with the lower wall as the north wing and the upper wall as the south wing. The footwall coal seam is flat along the dip and strike, but slightly undulates along the east strike of 12 exploration line, and the footwall coal seam has obvious undulates along the dip or strike. The main body of the mine field is in the north wing, and the south wing is only shown on both sides of the exploration line F 16 12.
The main structures in Changcun mine field are distributed in E W direction, and the structural development degree is strong in the south and weak in the north, with the characteristics of strong in the east and weak in the west. The basic structural form to the west of 12 exploration line is gentle monocline, accompanied by five large faults, and small faults are developed in the shallow part and on both sides of the main fault, which has a great impact on mine production and the structural degree is moderately complex. The basic structural form to the east of 12 exploration line is oblique, and the secondary undulation is obvious. There are 7 large faults, and the small faults are more developed than those in the west, with serious coal seam fragmentation and complicated structure. The main body of Changcun mine field is in the west of 12 exploration line and the north wing of syncline, and the structural complexity is medium as far as the whole mine field is concerned.
Three, mine gas geological law
Controlled by the buried depth of coal seam, the gas content and gas emission have an overall trend of increasing with the increase of buried depth, and the gas emission increases obviously in the deep buried area of coal seam in the south of the mine field. As a gas-producing layer and a gas storage layer, the thickness of coal seam has an important influence on gas occurrence, and the gas in thick coal zone is obviously higher than that in thin coal zone. For example, the gas emission in the east wing of No.21 mining area in the mine field is obviously higher than that in the west wing, which is influenced by the thickness of coal. Affected by the merger and bifurcation of coal seams, the thickness of coal seams in No.21 mining area has the distribution law of thin in the west and thick in the east, forming a thick coal center with 160 1 borehole. It is absolutely necessary for the east wing to cross the thick coal belt that exceeds10/0, 2 103, 2 105, 2 107 and 2 109 five working faces.
The permeability of surrounding rock, especially the permeability of overlying roof, directly determines the gas storage capacity in coal seam. The direct roof of coal seam in 2 1 panel is mudstone, with a thickness of 35 ~ 66m. Only the sandstone direct roof appears near the borehole 1402, which has a certain sealing effect on gas and is one of the reasons for the relatively large gas emission in 2 1 panel. There are both normal faults and reverse faults in the mine field. The nature of the fault and its combination with coal seam and surrounding rock determine the conditions for gas preservation. The western part of 2 1 panel is a torsional normal fault with a drop of 60 ~100m, which can be broken to the bottom of Quaternary system. The tensile joints at the top and bottom of the coal seam on both sides of the fault are relatively developed, and most of the gas in the coal seam around the fault has escaped.
Four, the gas content distribution
Controlled by the buried depth, the gas content of coal seam has an overall trend of increasing with the increase of buried depth, and the gas content in the south of the mine field is larger than that in the north. Affected by the degree of coal metamorphism, the metamorphic degree of 2-3 coal seam is higher than that of 2- 1 coal seam, and its gas content is higher than that of 2- 1 coal seam; The gas content in thick coal seam is higher than that in thin coal seam, and the gas content in the east wing of No.21 mining area is higher than that in the west wing.
V. Characteristics of gas emission
(1)+320m level coal seam, due to shallow burial, low metamorphic degree and small gas content, its absolute emission does not exceed 2m3/min on average.
(2) The coal seam with+110m level has high gas content due to high burial depth and metamorphic degree, and its absolute emission is 2 ~ 5m3/min on average. The thickness of the horizontal coal seam changes greatly, and its gas content also changes obviously, that is, the gas content in the west wing coal seam of 2 1 panel is less than that in the east wing coal seam. 2 1 panel, the average absolute gas emission in the west coal seam is 2 ~ 3.5～5m3/min, while the average absolute gas emission in the east coal seam is 3.5 ~ 5m3/min.
(3) The gas content in the coal seam under the local sandstone body in the east wing of 21panel is large, and its absolute gas emission is 5 ~ 7.3m3/min on average.
(4) The gas emission of the working face with gob-side entry retaining arrangement is larger than that of the working face without this arrangement1.24 ~ 2.13 times.
(5) The gas emission in fully mechanized top-coal caving mining is1.47 ~ 3.21times larger than that in non-fully mechanized top-coal caving mining.
(6) For the same coal seam, the gas emission with fast driving and mining speed is1.18 ~1.94 times larger than that with slow driving and mining speed.