Analysis And Evaluation Of Soil Pollution In Jianghan Oil Field

XX Oilfield pollution survey were collected from120soil samples, which enable us to analyze pollution of petroleum hydrocarbons and polycyclic aromatic hydrocarbons in soil by means of GC/MS, then determine what the main source of pollutants is according to the characteristics of petroleum hydrocarbons distribution and polycyclic aromatic hydrocarbons (PAHs) molecular index.The survey analyzes the evaluation of soil pollution status on the basis of at home and abroad pollution standards of the quantity of oil and single-molecule aromatics in soil. In addition, the PAHs are carcinogenic, among which benzo (a) pyrene is the most representative. BaPeq of benzo (a) pyrene will be get by calculated the toxic equivalency factors (TEFs) of aromatics. That is to say, BaPeq of benzo (a) pyrene is the product of TEFs and16kinds of polycyclic aromatics’s mass concentrations. In the thesis, a preliminary study of the cancer risk of polycyclic aromatic hydrocarbons in soil will be done. The survey measures the mass of petroleum pollutants in soil by the means of gravimetric method and combined with chromatography-mass spectrometry techniques to study the content and distribution of16PAHs and in the study soil. The result shows that the well sites are polluted in varying degrees by petroleum hydrocarbons in the study area. The petroleum hydrocarbons especially aromatics content within500meters of the part of the oil region of XX Oilfield are more than several times European standards. This may be due to the most part of produced water in this area is high salinity and farming methods of the soil is dry land. On the one hand, the petroleum pollutants in plat surface are easy to migration and diffusion. On the other hand, the high soil salinity restricts petroleum hydrocarbons microbial degradation which cause petroleum hydrocarbons of this part exceed the standard.What is the rule of vertical migration and change when the crude oil and its products are leaking into the surface? Is groundwater polluted by them? All of those problems are the focus nowadays. In this survey, two abandoned wells such as WD12-7well (No.116) and ZX19well (No.117) are selected for the sampling point to analyze the petroleum hydrocarbons content and distribution of16PAHs in the soil vertically.After the process of Soxhlet extraction and concentration, weight the extract content respectively. As a result, the contents of petroleum hydrocarbons in the above two area are decreased with the soil depth increasing, also do the16PAHs contents. Furthermore, the soil with high contents is mainly concentrated in50cm below the surface. Although with the impact of crude oil gravity, rain flushing, and the soil is rich in water serve as capillary action, due to the crude oil is hydrophobic in nature, large migration of crude oil components in the soil is very limited. With a large number of oil spills, or after a long period of weathering, a large number of low molecular weight compounds disappear, and the polarity of crude oil increase at the same time. With the increasing of some non-hydrocarbons compounds such a Nitrogen compounds and oxy-compound etc., which produced by microbial degradation, the water phase polarity is also enhancing. In addition, the other non-hydrocarbons can strength emulsification and solubilization of the oil phase (organic phase). In this condition, a part of the low molecular weight compounds in crude oil disappeared, also lower migration occurred in the soil at the same time, if the petroleum hydrocarbon content is large enough, shallow groundwater will be polluted in varying degrees as time goes by.For this survey only investigated a little part of the oil field, the pollution point and its size are still unable to accurately identify. It needs more detailed research in the future.Nowadays, the critical value of oil in the soil is500mg/kg in China. However, there is no corresponding standard to formulate the residual quantity of polycyclic aromatic hydrocarbons in soil. Hence, there is an urgent need for establishing a range of organic pollutants monitoring methods and soil pollution judgment standards. Therefore, it is important to distinguish a variety of organic pollutants in soil pollution, especially to identify the location of the pollution and high-risk areas, scope, quantity and pollution characteristics. On that basis, further developmental and applied researches related to soil pollution such as physical, chemical and bio-remediation technology need to be conducted.