Adsorption Containment Mechanism Of Supercritical CO₂ In Deep Anthracite Coal Reservoirs With CO₂-ECBM

The research object of the paper is anthracite coal reservoir in southern Qinshui Basin.Based on the ScCO₂ isothermal adsorption experiments of deep anthracite coal reservoir,the paper discusses the relationship between ScCO₂ adsorption and the temperature,pressure,pore characteristic coal rank and so on.The paper selects the optimal theory adsorption model by comparing proximity of different adsorption models based on the experiments data and stablishes the relations between parameters of adsorption models and temperature,pressure,pore characteristic.Meanwhile the paper researches the mechanism of microscopic molecular forces and adsorption thermodynamics of ScCO₂ isothermal adsorption on anthracite coal based on the model.In addition,the paper tries to research the physical and geological significance of sorption containment.The result shows that:?1?Experiments of anthracite sorption with equilibrium water content under 1000,1500 and 2000 meters deep are simulated through isothermal adsorption experiment platform of high temperature and high pressure.The excess and absolute sorption is calculated and rule of adsorption is analyzed in the meantime.The result shows that excess adsorption that is different from normal pressure and temperature exists maximum points which migrates to the high pressure point with the temperature rising.Absolute adsorption has a rapid growth at high pressure.Pore volume and specific surface area of small pores become the key factor controlling the CO₂ adsorption.?2?Comparing the different adsorption theoretical models of Langmuir,BET,adsorption potential and Lattice,models of BET-3,D-R and Lattice are optimized based on excess sorption.Among the suitable models above,the absolute adsorption model,Lattice model is selected for its highest fitting precision and variable is free phase gas density.The absolute adsorption model is derived by the excess adsorption model.?3?From the point of view of microscopic particles,the dispersion force between coal macromolecule and nonpolar CO₂ molecules is the main force controlling CO₂ adsorption from the point of microscopic particle.From the point of view of adsorption thermodynamics,the results from adsorption thermodynamics in macrocosm shows that the surface free energy change reduces and difference between different samples declines with the temperature rising which reflects that the temperature accelerates sorption speed and fill in sites with lower surface free energy which CO₂ molecules tend to be in a more uniform distribution meanwhile.Qst0 is regarded as the most important index of sorption of CO₂ on coal which calculated by fugacity instead of pressure.Qst0 shows a rising trend with the increase of coverage that illustrates interaction between CO₂ molecules and coal surface weaken meanwhile and validates the existence of multilayer adsorption of ScCO₂ in anthracite coal reservoir.?4?Based on the sorption model,the physical and geological significance of the adsorption model are analyzed separately.The result shows that there is positive correlation relationship between ?0 and pore specific surface area;se is independent of coal pore characteristics.The paper establishes bi-directional model based on the adsorption space coverage to solve the bi-directional effect of temperature-water and diviedes the sorption sites on coal surface into three kinds of water-pro,gas-pro and water-gas-pro sites.From the point of view of absolute sorption model,the relationship between absolute adsorption and buried depth is established.