| This article takes coal seams under red beds of the 33 ming area and 83 lower mining area and the overlying strata of the coal seams in Xutuan coal mine of the Sulin ore district as the main research object to evaluate comprehensively the sealing performance of coal seam gas of the overlying strata of coal seam sample,red beds sample and sample of quaternary loose bed from the diffusion and osmosis performance of the samples.In this paper,the adsorption potential theory is used to analyze the change trend of coal seam gas content with the depth of burial and predict the coal seam gas content corresponding to the depth of burial,combined with the burial history and gas generation history of the Xutuan coal mine.Based on the above research results and data of coal seam gas in a region,the gas occurrence rule of coal seams under red beds was reseached.Main conclusions are as follows:1)Coal seam gas loss is mainly divided into diffusion and seepage loss.In order to evaluate the sealing performance of the overburden on the gas,the diffusion coefficient and permeability of the rock samples were experimented in the laboratory.The integrated diffusion coefficient and average permeability of the coal strata are obtained by using the borehole stratigraphic data.The comprehensive diffusion coefficients of the coal strata in the 33 mining area and the 83 mining area are 2.49358 × 10-8 cm2 / s,1.74658 × 10-8 cm2 / s.The integrated diffusion coefficient of the red beds under the same condition is 3.06942 × 10-6 cm2 / s,and the diffusion coefficient of the Quaternary loose layer is 2.59016 × 10-6 cm2 / s.The average permeability of the coal strata in the 33 mining area and the 83 mining area is 0.0706 mD and 0.0490 mD.Under the same conditions,the permeability of the Paleogene red bed is 0.1454 m D,and the permeability of the Quaternary loose layer is 0.1609 mD.The red beds and the loose layer are less closed to the coal seam gas,and the coal strata play a closed role in the coal seam.2)When the adsorption characteristic curve between the adsorption potential and the adsorption space is studied,it is found that when K is equal to 1.5,the fitting degree of the characteristic adsorption curve is the best,reaching 0.98659.When K is equal to 1.5,the average relative error between the predicted quantity and the actual adsorption capacity is small,which is 4.4008% and 4.6746%.When the burial depth of the coal seam increases with the increase of the burial depth of the coal seam,the adsorption capacity of the coal seam increases rapidly and gradually decreases.When the burial depth reaches 1000 m,the adsorption capacity of the coal seam reaches the maximum value.When the depth is increased from 200 m to 300 m,the adsorption capacity of coal seam increases from 7.078m3/t to 20.716m3/t,and increases by 13.638m3/t.From 900 m to 1000 m,the adsorption capacity of coal seam increased from 36.130m3/t to 36.346m3/t,the adsorption capacity only increased by 0.216 m3/t.Depth of 1000 m deep,coal seam adsorption capacity gradually smaller.3)According to simulate the burial history of coal and coal seam gas adsorption amount with buried depth,the evolution history of coalbed methane(gas)in the Xutuan coal mine was studied.Containing plant strata in the late Permian began to deposit and the burial depth of coal seam is the largest in the Triassic period.During this period,the degree of metamorphism began to deepen under the condition of high temperature and high pressure,and the coal gas production gradually increased.Late coal-bearing strata began to rise,some coal seams in coal-bearing strata were eroded and coal seam began to form the ancient gas weathering zone in the early Paleogene.At this stage coal seam gas evolution was divided into two parts: When the burial depth of coal seam was less than 1000 m,the amount of coal seam increased with the uplift of coal seam.When the burial depth of the coal seams was above 1000 m,the adsorption capacity of coal seam gradually weakened,gas was from the adsorption state into a free state and began to lose a lot.Coal seam gas was the smallest in the shallowest burial.The coal seams had been affected by many tectonic effects from the Paleocene period to the present.During this period,the burial depth of the coal seam has been greater than the depth of the shallowest coal seam in the early Paleogene,there was no supply of effective gas source,and sedimentary strata(red beds and loose layer)have poor sealing performance to gas.Coalbed methane would have been lost and gas content will be lower than that in the shallowest burial.4)The data of the gas under red beds in the 33 mining area and the 83 mining area of the Xutuan Coal Mine show that the coal content is more closely related to the effective thickness of the overburden in the coal seam: The fitting degree of the gas content and the effective thickness of the formation is 0.96455,and the fitting degree of the elevation is 0.93161 in 33 mining area.The fitting degree of the gas content and the effective thickness of the formation are 0.89556,the fit of the elevation is only 0.54984 in the 83 mining area.And the relative emission of 3235 and 3237 working face under the red beds and the data of the occurrence of gas in the coal seam under the non-red layer in the 33 mining area are verified,and the regularity is better.On the basis of this,the outburst risk division of the coal seam under the red layer is predicted. |
