Carbon Dioxide Transport In The Unsaturated Soil And Its Environmental Impact

It is necessary to conduct environmental risk assessment for the safety of CO2geologicstorage. This paper study the migration process and mechanism of the CO2gas in theunsaturated zone and the possible impact of it under a background of leak of CO2geologicalstorage happen and CO2migrates to near-surface soil. We combine physical simulation testand numerical simulation in study. Using a certain concentration of CO2released from thebottom of test columns to simulate the migration process. Through the measuring the CO2concentration, soil temperature, moisture content, analysis the soil components, monitoringgrowth of plant to research the migration rule of CO2in near-surface. Research thecharacteristics of CO2migration in the near surface, as well as the process how to affect soilcomponents and plant, etc. Assess the possible damage to the environment of the surface andpromote the study of CO2geological storage engineering safety. The main conclusions instudy are obtained as follows:(1) The concentration of CO2decreases on the process of upward movement from thebottom. The concentration is500~1700ppm when it arrived at the surface. It will equal to theatmospheric CO2concentration until at10cm on the ground. After a certain time, CO2concentration of soil achieves balance maintains a relatively stable. The concentration of CO2is low above0.5m depths of the soil. And it closes to the input of CO2concentration in thedeeper part.(2) The escape velocity of CO2mainly controls the distribution of CO2. Below0.5mdepths of the soil CO2concentration is high under a speed of more than4L/min inexperimental conditions. The upper soil is affected by soil-air interface and the concentrationis reduced considerably. According to the model calculation, the distribution of CO2in the soilis relatively flat in less than2L/min of escape velocity. There will be a lower trend at1mdepths.(3) CO2distribution in soil affected by the temperature during the experiment. Especiallyin the summer, It reach to maximum concentration at about17o ’clock, to minimum at4o’clock, which time lags the change of temperature. Rainfall process made CO2concentration significantly increased at0.5m depths of the soil, and the amplitude of increase is small in thedeeper part.(4) It proved that soil PH has a slightly rises from8.5to8.7under the influence of CO2gas for a long time. The content of soil carbonate, organic carbon and water-soluble carbonatehas little changes. The temperature of0.5m depths of soil increased1~2℃,1.5m and2.5mdepths increased0.5℃before and after the experiment. CO2improve carrots and peas betterin smaller concentration range (<8%). But have less effect on wheat. According to thecalculation of experimental model, the CO2escape make the O2decreased significantlyespecially in the deep soil. It has an influence on the plant belong straight root which the rootlonger than0.5m.