CO₂ Emission And Its Effects On Soil And Vegetation In CCUS-EOR System

Carbon capture,utilization and storage?CCUS?are useful methods for controlling greenhouse gas emission.It has been proved that CO₂ can be used to enhance oil recovery?named CO₂-EOR?.As a result,this promising technology,an important development direction of CCUS,has been widely adopted by many oil companies around the world.The latest literatures show that many scholars have paid much attention to the environmental effect of CCUS.However,most of these research works employed naturally CO₂ leakage points or simulate experiment to study the effect of CCUS on ecosystem.This thesis tries to analyze the characteristic of CO₂emission and detect the ecological effect of real CCUS project.Main study methods include ecological monitoring and simulation.The results show that there are three sources of CO₂ emission,which are CO₂transportation pipeline,oil production wells and CO₂ injection well respectively.The intensity of CO₂ emission is affected by injection rate and oil recovery rate.With the increase of the distance between emission source and testpoint,the concentration of CO₂ in air decline gradually.As for oil production wells and CO₂ injection well,the horizontal diffusion radius is about 100 meters and the vertical diffusion radius is approximately 5 meters.By comparison,the intensity of CO₂ emission from CO₂transportation pipeline is much lower than the other two sources,whose horizontal and vertical diffusion radius are 1.5 meter and 0.1 meter respectively.Another finding can be draw from the simulation and field ecological monitoring of CO₂ emission from underground CO₂ transport pipeline,which is the layered distribution of soil CO₂ at CO₂ leakage point.There is an interactive interface between soil and atmosphere?from-50cm to 0cm?,which is good for diffusion of CO₂.After CO₂ with high concentration pass through soil body,its concentration will drop immediately at-50cm.Once it meets air,the concentration of CO₂ in air will decline to normal level?380ppm?at+10cm above soil surface.When intensity of CO₂emission exceeds G2000,the concentration of soil CO₂ between-10 cm and-20 cm is higher than 20%,which will do harmful to plant growth.If the intensity is below G1000,soil CO₂ is lower than 20%while soil O₂ is higher than 10%,which will also cause an indirect impact on plant growth except that the CO₂ emission source can be removed promptly.It has been detected that there is chemical reaction occurring between CO₂,soil moisture and mineral substance,and these chemical process have an impact on the physicochemical properties of soil.On one hand,pH,electrical conductivity and nitrate nitrogen in soil decreased along with time of CO₂ emission while soil organic matter increased first and then deceased?within the first 18 days?.On the other hand,the impact on soil is heavier when the intensity of CO₂ emission is bigger.Apart from this,it also can be found that soil microbe is sensitive to soil CO₂ concentration.The total number of soil microbe reduces by almost 1/4 when intensity of CO₂ emission approach G800 and keeps stable when intensity of CO₂ emission exceeds G800.It can be inferred that G800 is a threshold for soil microbe.There is no significant impact of underground CO₂ emission on vegetation having been observed despite some ecological indicators?plant height,chlorophyll,Photosynthetic parameters?suffered a slight impact.According to the results obtained from remote sensing,the CO₂ emission form oil production wells and CO₂ injection well did not have noticeable impact on regional plant cover and productivity.One of the reasons is that there is no air mass with high CO₂ concentration having formed around the CO₂ emission source because of the fast diffusion of CO₂,and this means the circumjacent plant would not grow up in a greenhouse environment.Another reason is that the growth of filed plant mainly affected by soil and water conditions,cropping pattern and other factors.In conclusion,there are CO₂ emissions in real CCUS-EOR project.CO₂ emission from underground sources has impact on physicochemical properties of soil and growth of plant.Fortunately,its area is limited and can be easily controlled by the maintenance of CO₂ transportation pipeline.Filed plant has no significant reaction to CO₂ emission with high intensity from aboveground sources because that CO₂concentration of air is not a dominant factor of plant growth.