Experimental Study And Numerical Simulation Of Injection Of Co 2 Sub - N 2

China has huge CBM resources potential under depth of2000m, but coalseam permeability is generally less than0.1×mD, mostly belongs to tight coal reservoir, the current technology has not made any breakthrough yet. On the basis of hydraulic fracture stimulation technology, injecting CO2、N2and other non-hydrocarbon gases into coal seams has the dual advantage of CO2sequestration and recovery coalbed methane, which has broad application prospects. The adsorption of gas will make coal matrix swell and fractures narrow, resulting in permeability dcreased. The adsorption of gas also weaken mechanical strength of coal, resulting in coal seam instability during the process of gas injection. Therefore, based on the analysis of pore structure in coal, studies the effect of gas adsorption on properties of coal and mechanism of selective adsorption, which has positive significance in ECBM and optimizing the engineering work.This thesis focuses on the No.9coal seam in Ningwu Basin, based on the analysis of coal mineral composition, physical properties and pore structure properties, studies the coal selective adsorption characteristics to different gas in microcosm. By the high temperature/pressure triaxial gas adsorption-seepage experiment testing system studies the effect of gas adsorption on the permeability of coal, experiments on the effect of gas adsorption on the mechanical strength of coal, Carry out experiment and numerical simulation of displacing coalbed methane.Deepen understanding the pore structure characteristics of No.9coal. The results from integrated thin-section analysis, scanning electron microscopy (SEM), CT scan point out micro-fractures in coal are developed, yet poor in connectivity. It can be concluded from nitrogen adsorption that the pores in coal matrix are mainly nanoscale pores, the structure is quite complex, the connectivity between pores and fractures is poor.Make clear the gas adsorption capacity of coal to different types of gas on No.9coal, using molecular simulation methods analysis selective adsorption mechanism microscopically. The characteristic of single component and their binary or ternary gas adsorption on coal is tested by the HKY-Ⅱautomatic test system, analyze the gas adsorption heat and adsorption sites. The experimental results demonstrate that the CO2has the strongest adsorption capacity on coal, followed by CH4, and N2is the least; for binary and ternary gas adsorption, there is competition and mutual interference between the gases; with respect to the single component, adsorption sitesof binary and ternary gas trend to the right, resulting in the adsorption amount of the gas in the mixed gas is less than Separate adsorption.Explore the permeability and mechanical properties of coal under gas adsorption conditions. The results show that the gas permeability of coal reduce to varying degrees,the stronger adsorption ability of gas, the permeability reduction larger; The results show that the adsorption gas enhance the plasticity of coal, decrease the tensile strength, uniaxial and triaxial compressive strength, the more of gas adsorption on coal, the bigger the content of decrease.Make clear the influence of coalbed methane displacement efficiency and design the optimal scheme of gas injection. Within one hour desorption time, under4.5MPa injection pressure, compared to unlimited desorption, different gas injection approach can improve the efficiency of coalbed methane, binary gas displacing is better than pure CO2, the higher of N2proportion in binary gas, the faster increase in displacement efficiency, the same gas injection, the higher injection pressure, the sooner displacement efficiency increases; Gas injection pressure is4.5MPa,in the early stsge of gas injection, choose20%CO2+80%N2,when N2close to breakthrough, choose80%CO2+20%N2.Method and awareness have been gained from research provides certain references for understanding gas injection mechanism and implementing gas injection efficiently.