Effects Of CO₂ Leakage On Soil Bacterial Communities In CO₂-EOR Project

Carbon Dioxide Recovery Enhanced Oil Recovery Technology(CO2-EOR)is a new technology.It can not only use Supercritical CO2 to increase oil recovery,but also achieve storaging of CO2 underground permanently.Although the technology is maturing,there are still many problems restricting its development,the most important issue is the risk of CO2 leakage.This study applied a simulated pot experiment combined with pipeline leak site monitoring in Shengli Oilfield,and tested the soil physicochemical properties,enzyme activity and soil DNA sequence.This study aimed at researching the influence of underground CO2 pipeline leakage on the soil properties and soil microbial community structure in CO2-EOR project.The following conclusion was get?1.The analysis of pipeline leak site monitoring in Shengli Oilfield each year showed that,with the increase of CO2 concentration,the soil p H decreased,the content of organic matter increased but the activity of enzyme had no obvious change.However,the enzyme activity decreased significantly when CO2 leaked extremely.The analysis of soil microorganisms Alpha diversity showed that microbial diversity decreased and the community structure tended to be single.With the increase of soil CO2 concentration,the abundance ratio of Proteobacteria,TM7 and Parcubacteria increased,while cyanobacterium,nitrospira,Chloroflexi decreased.2.The results of RDA analysis of pipeline leak site soil showed that the parallel samples in 2015 and 2016 were a bit different,but parallel samples in 2017 were similar.Organic matter had the greatest positive correlation with Actinobacteria and Verrucomicrobia.p H had the greatest positive correlation with Firmicutes,and greater negative correlation with Proteobacteria,meanwhile,the content of nitrate nitrogen had a significant correlation with Planctomycetes.3.The simulated experiments showed the following results,Carbon dioxide leakage causes changes in soil properties.CO2 leakage led to decreased soil p H.The higher the stress concentration was,the greater the drop in p H.The maximum decrease can drop from 8.2 to 7.29.There is a significant increase in ammonia nitrogen phenomenon,the maximum increase of 3 times.The electrical conductance did not change significantly.Available phosphorus and organic matter changed complex.CO2 leakage has an inhibitory effect on FDA hydrolase activity.The average level of FDA hydrolase in each group before simulated leaks was 22.69 mg.kg-1.h-1,and then decreased to 12.15 mg.kg-1.h-1 after CO2 leaked 100 days.4.Soil DNA sequencing was performed on simulated soil samples.The diversity of soil microbial communities decreased with the increase of soil CO2 concentration.Dominant species for test soil samples are Proteobacteria.With the increase of CO2 concentration,the abundance of Proteobacteria increased and the abundance of Acidobacteria decreased.The increase of nitrate nitrogen,urease and polyphenol oxidase concentrations was correlated with the change of some bacteria abundance.It shows that Increase in CO2 concentration can directly affect the environmental factors and bacterial community structure,and lead to the interaction of environmental factors and bacterial communities.