Study On The Migration And Transformation Of Typical Pollutants From Oil And Gas Field Drainage In Desert Soil Under Different Ecological Utilization Modes

With the rapid development of oil and gas field in northwest China,the production of oil and gas field wastewater is increasing year by year.The ecological utilization of oil and gas field wastewater is one of the most effective strategies to solve the contradiction of water resource shortage and the treatment of oil and gas field wastewater in northwest China.In this paper,by taking oxygen consumption organic matter（COD）and petroleum hydrocarbon（TPH）as the research objects,constructing in-situ desert soil column experiments,we studied the migration and transformation of oxygen consumption organic matter（COD）and TPH in oil and gas field wastewater under different ecological utilization modes（wetland mode and irrigation mode）in desert soil.（1）The effects of heavy oil water and fracturing fluid with different oxygen consumption organic matter（COD）contents on total organic carbon（TOC）in desert soil were studied under two ecological utilization modes.The results showed that the accumulation ability of desert soil for oxygen consumption organic matter（COD）was weak.The leaching of wastewater with oxygen consumption organic matter（COD）would lead to the reduction of TOC in surface soil and the accumulation of TOC in deep soil,but the increase of oxygen consumption organic matter（COD）in external drainage would slow down the loss of TOC in soil surface.The highest removal rates of oxygen consumption organic matter（COD）in heavy oil water and fracturing fluid are 94%and 98%compared with control group,respectively.This indicates that oxygen consumption organic matter（COD）is more likely to migrate to groundwater in soil,but it is also more likely to degrade in soil,there was no significant difference between the two ecological use models on TOC.（2）The accumulation and migration of TPH in desert soil under two ecological utilization modes were studied.The results showed that both of the two ecological utilization modes would lead to the accumulation of TPH in the surface soil,but the irrigation mode with low TPH concentration was beneficial to reduce the accumulation of TPH in soil.Regardless of the utilization mode,85%TPH was accumulated in 0-10 cm solum,and more than 90%TPH remains in 20 cm solum.The TPH content in 20 cm solum is similar to that in the blank soil sample.Since TPH is hydrocarbon,the accumulation of TPH in the surface soil leads to an increase in TOC,and the more leaching,the more TOC increases.Although TPH is not easy to migrate in soil,the large water flow in wetland mode increases the risk of TPH migrating to groundwater.（3）The degradation mechanism of typical pollutants in efflux water in desert conditions was preliminatively explored and the degradation behavior and mechanism of TPH and oxygen consumption organic matter（COD）by natural light and soil microorganisms have been investigated.The results showed that soil microorganisms play an important role for the reduction of oxygen consumption organic matter（COD）,and can effectively reduce the oxygen consumption organic matter（COD）migration to the deep soil.The maximum degradation efficiency of TPH by soil microorganisms could reach to 15%.Under both utilization modes,the relative content of TPH components below C₂₅decreased significantly,but the relative content of above C₂₆increased.The reason is that short chain TPH was degraded by microorganisms,while long chain TPH was not easy to degrade.Only ultraviolet light could degrade petroleum,and the degradation efficiency could reach to 17%.Natural light and soil microorganisms played important roles on the reduction of TPH in soil.This thesis studied the migration and transformation of typical pollutants from oil and gas field wastewater in desert soil under different ecological utilization modes,which can provide basic data and theory support for the ecological utilization of oil and gas field wastewater.