Mechanism Of CO₂ Pools Formation And CO₂ Control Technology Of Haishiwan Coalfield

The Yaojie Coalfield is the only mining area with coal and CO2 outbursts in China. The CO2 is featured as the dominant gas component in coal seam. This paper takes the Haishiwan Coalfield as the background and the No.2 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 the 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. The main conclusions are as follows:1) The CO2 originates from inorganic crust sources according to carbon isotope and helium isotope in the Haishiwan Coalfield. The dynamic-thermal metamorphism of the F19 ductile-brittle shear zone is believed to result in the CO2 release. The F19 fault plays multiple roles in the generation, transportation, and trapping of gas during the CO2 formation.2) Studies on the characteristics of coal absorbing CO2 or CO2/CH4 mixture are carried out under low pressure. The D-A model fits the adsorption isotherms of CO2 well under low pressure. The modified D-A model is applied to analyze the supercritical CO2 adsorption isotherms of Haishiwan coal and free volume theory is used to explain abnormal adsorption isotherms.3) Taking the temperature, pressure of supercritical CO2 occurrence and the change of critical point of CO2 and CH4 mixed gas occurrence into consideration, and combining the basic parameters consist of earth temperature, gas pressure, gas content, gas concentration and so on, we raised the hypothesis that occurrence of supercritical CO2 occurs in the No.2 of Haishiwan coal field.4) Numerical simulation is used to analyze the stress and strain, damage characteristics, and evolution of protected coal seam under different pore pressure in the stope. The mechanism obtained that pore pressure helpful to pressure relief in protected coal can be used for pressure relief CO2 drainage of protected coal seam.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 2m3/min. The coal seam permeability increases by 878 times. The gas content decreases from 53m3/t to 12m3/t. The risk of outburst has been eliminated with regard to the No.2 coal seam.