The Study Of Numerical Simulation Of CO₂-ECBM On The Deep Coal Seam In Shizhuangbei Block,Qinshui Basin

This paper accounted the 3# coal seam in Shizhuangbei block of Qinshui basin as the research object,and through the investigation of the data,the sample collection and the experimental test,ascertained the characteristics of the coal and rock quality,the physical property of the reservoir and gas adsorption,etc.Using numerical simulation software,this paper carried on CO₂-ECBM numerical simulation under different conditions aiming at 3# coal seam,and analyzed gas productivity and effect of CO₂ storage with CO₂-ECBM under different conditions.The results provided guiding significances for the development of deep coalbed methane in target area.The paper collected coal samples related with target coal seam from the three coal mines（Changping Coal mine-CP,Zhaozhuang Coal mine-ZZ,Shizhuang Coal mine-SZ）within the study and surrounding area.All three of coal samples are primary structure coal,and industry analysis results showed that the moisture content of three coal samples were very low with Sample CP and ZZ defined as Low ash-High fixed carbon coal and Sample SZ defined as High ash-Low fixed carbon coal.Vitrinite content of three coal samples was all above 60%,excluding the exinite,and their vitrinite reflectances have reached to anthracite（Ro>2.0%）.The N₂-Physisorption experiments results indicated that BJH total pore volume and BET surface area of three coal samples averaged 0.0061ml/g,and 1.52m²/g respectively,with sample SZ as the maximum of three samples.The results of CO₂-physisorption showed that the micropore development of samples CP and ZZ is superior to that of sample SZ,and it also demonstrated that micropore played a dominant controlling effect to the adsorption capacity of high-rank coal.The results of Mercury injection experiments showed that three coal samples had an average porosity of 5.5%,and all of their permeability were below 1×10-3μm²,belonging to low porosity and permeability reservoir.From processing experimental data using modified Langmuir equation for pure gas adsorption,we found the adsorption capacity to CH₄,CO₂,N₂ of the same sample behaved as CO₂>CH₄>N₂.In terms of the same gas,the adsorption capacity of samples CP and ZZ was higher than that of sample SZ because of more micropores.The results of multi-component gas adsorption/desorption experiments showed that the adsorption capacity of CP and ZZ is still higher than that of sample SZ with the condition of same ratio of multi-component gas,and under the condition of different ratio of multi-component gas,the higher the content of CO₂ in the mixed gas was,the more amount samples would adsorb,but the hysteresis of the desorption isotherm relative to the adsorption isotherm would also become more obvious.For the adsorption process,the concentration of CH₄ in the free gas showed a rapid increase initially as compared with the supply gas,and then decreased steadily,and the concentration of CO₂ changed contrary to CH₄.In the desorption process,the concentration of CH₄ in the free gas increased firstly,then decreased,and the concentration of CO₂ decreased first and then increased.CO₂-CH₄ separation factor calculated using the original formula was higher than that calculated by the Langmuir parameter,at the same time the lower concentration of CO₂ in original mixed gas was,the higher the corresponding CO₂-CH₄ separation factor was.The phase separation diagram showed,for the CH₄-CO₂ mixed gas that the adsorption rate of CO₂ in the mixture was from fast to slow,and the adsorption speed of CH₄ was from slow to fast.The CO₂-ECBM process under different production-injection well spacings and gas compositions has been carried out by SIMEDWin software.The results showed that 210 m is an economical and effective production-injection well spacing.When using N₂-CO₂ mixed gas for N₂&CO₂-ECBM,it was found that N₂ would only affect gas production rate and couldn`t increase CH₄ production capacity,therefore,the proportionof N₂ in injection gas should be adjusted according to specific production requirements.