Supercritical CO₂ adsorption characteristics and their control factors in deep-seated coal seams in southern Qinshui basin

In order to reveal the characteristics and control mechanism of supercritical CO₂ (ScCO₂) adsorption in deep-seated coal seams, coal No.3 from Yuwu coal mine, Sihe coal mine and Chengzhuang coal mine was chosen as the research object, the isothermal adsorption experiments in different temperature(45℃, 62.5℃, 80℃)were conducted with the maximum pressure above the supercritical pressure of CO₂ by means of homemade isothermal adsorption instrument. The results show that the adsorption isotherm of ScCO₂ under the condition of high temperature and high pressure is different from the adsorption isotherm of CO₂ under normal temperature and pressure. The excess adsorption capacity of ScCO₂ had the variation of 4 sections, the absolute adsorption capacity of ScCO₂ had the variation of 3 sections. The pressure points matched with the maximum on excess adsorption capacity of ScCO₂ had the characteristics of drifting high pressure with increase of the formation temperature. The excess adsorption capacity of ScCO₂ was far below the absolute adsorption capacity of ScCO₂, they couldn't be explained ith the adsorption model of Langmuir. The temperature has an obvious inhibition to the adsorption of ScCO₂, the moisture content has no inhibition to the adsorption of ScCO₂, the high ash content has an obvious inhibition to the adsorption of ScCO₂, the high vitrinite and R_max have a relatively obvious promotion to the adsorption of ScCO₂. The adsorption capacity of ScCO₂ is controlled by micropore and transitional pore, is especially related to the amount of specific surface area from micropore, the decrease on the adsorption ability of ScCO₂ from high metamorphic coal may be caused by filling of the minerals in coal.