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Based on depth study of the influence law of key strata on the height of fractured water-conducting zone, this paper proposed a new method to predict the height of fractured water-conducting zone by location of key strata. The engineering measurements and theoretical research results show that the key stratum location affects the height of fractured water-conducting zone in the roof, when the distance from key stratum to the coal seam is less than a critical value, the fracture of key stratum will develop to water-conducting fracture, and the same goes to the fracture of the overlying strata controlled by key stratum leading to a synchronous breakage with key stratum. The critical height of key stratum fracture can be roughly estimated to be (7 ~ 10) M, where M is coal mining height. When it is less than (7 ~ 10) M from the primary key stratum to coal seam, water-conducting fracture will grow to the location above the roof of the bed rock, then the height of fractured water-conducting zone is equal to or greater than the height of the bed rock. When the distance from the primary key stratum to coal seam is greater than (7 ~10) M, water-conducting fracture in the roof will develop to the position below the nearest key stratum being (7 ~ 10) M more away from the coal seam ,and then the height of fractured water-conducting zone equals to the distance of the key stratum to coal seam. The prediction method is able to predict the height of fractured water-conducting zone in the roof with different mining heights, meanwhile, it also can be utilized to distinguish the abnormal development of the height of fractured water-conducting zone induced by structural changes of key stratum, and its reliability is verified by engineering measurements results. [ABSTRACT FROM AUTHOR]

This paper took Haishiwan coalfield as the background and CO2 in the No. 2 coal seam of Haishiwan mine area as the main study object, systematically carrying out study of various aspects on the causes of CO2, CO2 enrichment regularity, CO2 occurrence in coal seam of Yaojie coalfield, adsorption and desorption of CO2 in coal, numerical simulation and engineering practice applied to eliminate the risk of coal and CO2 outburst regionally, making some innovations. During the researches, the authors adopted all kinds of research methods that multi-disciplinary theory includes geochemistry, petrology, structural geology, surface chemistry, rock mechanics, mining engineering, mechanics, numerical simulation, theoretical analysis, laboratory experiments and field engineering practice. The main research content and conclusions are as follows: (1) The CO2 concentration range in the eastern coalfield is 18.79% to 96.6%. The δ13Cco2 values are mainly in the range of -5.0‰ to + 1.0‰ ( PDB ), suggesting an inorganic origin of CO2. The ³He/4 He ratios are (0.6 ~ 25.9) x 108, and the R/Ra is 0. 004 2 ~ 0. 185 0, which is a characteristic of crust-derived CO2 gas. The dynamic-thermal metamorphism of the F19 ductile-brittle shear zone is believed to result in the release of CO2 from basement marble formations, which shows an inorganic source of CO2 in the Haishiwan coalfield. The regional geological evolution and multi-periodical F19 fault movement control the formation, migration, and accumulation of CO2. The F19 fault plays multiple roles in the generation, transport, and sequestration of gas during the CO2 formation. (2) The studies on the characteristics of coal absorbing CO2 or CO2 and CH4 mixed gas are carried out under low pressure. The D-A model can fit the adsorption isotherms of CO2 well under low pressure. At the same time, the authors establish the modified D-A, which fit the present high-pressure adsorption data well. The modified model is applied to analyze the supercritical CO2 adsorption isotherms of Haishiwan coal field and abnormal adsorption isotherms introducing free volume theory of polymer. The result is preliminarily verified by desorption curve. (3) The mining depth of the Haishiwan mine coal is 600 to 1 000 m, where the coal reservoir temperature is in the range of 31.72 to 43.88 °C. The measured mixture gas pressure is not less than 7.3 MPa;the CO2 concentration range in the eastern coalfield exceeded 90%; statistical gas content is in the range of 50 to 60 m³/t. Supercritical CO2 is likely to exist in the No. 2 coal seam of the Haishiwan coalfield according to in situ measurement, experimental determination and theoretical analysis. (4) The numerical simulation results indicate that the range of pressure-relief and dilatational strain of lower coal-rock mass increases along with the pore pressure increases, the maximum absolute and the maximum relative amount of deformity reach 328 mm and 0.5 % under pore pressure of 9 MPa respectively. At the same time, the plastic area also increases along with pore pressure enlargement. It is indicated that the pore pressure plays strengthen role in the protected coal seam pressure relief according to plate theory. (5) High pore pressure acts on pressure relief of coal seam, which has been verified in practice of remote protective coal seam mining and pressure-relief gas drainage. The singe gas drainage flow reaches more than 2 m³/min. The coal seam permeability increases by 878 times. The gas content decreases from 53 m³/t to 12 m³/t. The risk of outburst has been eliminated with regard to the No. 2 coal seam. [ABSTRACT FROM AUTHOR]