Study On The Migration Law And Numerical Simulation Of Petroleum Hydrocarbon In Unsaturated Zone

The rapid development of modern life has a positive correlation with the increasing use of petroleum products,and petroleum products play an increasingly significant role in production.At present,the world needs more and more petroleum for its production,but at the same time,it also brings the increasingly serious oil pollution problem.The Petroleum Hydrocarbons are the chief chemical components of petroleum by products that produce landing oil in the petroleum exploration process and oil-bearing sewage in the petroleum processing engineering,which pose severe health risks to the environment.Under the normal circumstances,the surface petroleum hydrocarbon will enter the aquifer through the unsaturated zone under the action of its own gravity or external force,which will lead to the groundwater pollution.The unsaturated zone is the bridge from the surface to the shallow groundwater,and the petroleum hydrocarbon pollutants can enter into the groundwater through the unsaturated zone,so the control of the unsaturated zone is one crucial part of the management of groundwater pollution.Hence the exploration and research of petroleum hydrocarbon on how to migrate in the unsaturated zone have the far-reaching significance to the protection of groundwater resources.This research project based on the national natural science fund project"Chlorinated Hydrocarbon Pollution in the Process of Soil Restoration and Nonequilibrium Space Research on Migration Mechanism",and we will consider the petroleum contaminated land of the northern oil field as the object of the present study.After looking through the literature information and understanding the related hydrogeology survey,we first take advantage of the indoor experiment and numerical simulation in a bid to explore the research of petroleum hydrocarbon migration in the unsaturated zone,and then deduce the petroleum hydrocarbon migration process based on the results of numerical simulation.On the one hand,this study explains the actual migration process of petroleum hydrocarbons in the unsaturated zone;on the other hand,this study provides the specific data of groundwater pollution situations and supplies the theoretical basis for solving the groundwater pollution problems and protecting the groundwater resources.The specific contents of this project are as follows:1.On the basis of reading the relevant literature and documents,we carefully analyzed the geological and hydrological conditions of land as the research object,and conducted a targeted sampling survey of the unsaturated zone,and studied the petroleum hydrocarbon distribution in the unsaturated zone of the site at the same time.2.According to the literature,the self-made petroleum wastewater was used to conduct the isothermal adsorption experiment and adsorption kinetics research under the laboratory condition,and the relevant indexes of petroleum hydrocarbon in the unsaturated zone media were measured on purpose.3.The self-made soil column was used to simulate the unsaturated zone under the laboratory condition in order to carry out the Darcy seepage experiment,the dispersion experiment and the soil column leaching experiment of petroleum wastewater in the unsaturated zone media.The petroleum hydrocarbon migration law was analyzed with the help of the data obtained from the experiment,and then the model was properly established.4.We used the Hydrus-1d model to build a vertical one-dimensional solute migration model and verify the model parameter before the model calibration,and subsequently simulated and speculated the migration process of petroleum hydrocarbon in the unsaturated zone according to the degree of groundwater pollution,and finally analyzed the migration of petroleum hydrocarbon in the different actual environments.Based on the results of laboratory experiments and numerical simulation,we obtained the following results at last:1.The isothermal adsorption experiment results showed that the isothermal adsorption of the petroleum hydrocarbon in the unsaturated zone media of contaminated site as the research object conformed to the different isothermal adsorption formulas:the fine sand was of high fitting degree of the Freundlich model and the fitting equation was C_S=1.5·C_w^1.3;the silty clay had a high degree of fitting for the Langmuir model and the fitting equation was C_s=12C_w/（1+0.05C_w）.2.The results of static kinetic experiment showed that the adsorption equilibrium time of fine sand and silty clay on the contaminated site of this research object was about 200 min to the petroleum hydrocarbon.The difference is that the amount of petroleum hydrocarbon adsorbed by the silty clay was larger than the fine sand and the adsorption speed of the silty clay was faster than the fine sand.3.A vertical one-dimensional solute transport model was built in the Hydrus-1d model,and the model was verified and corrected by the soil column leaching experiment and outdoor monitoring data.The fitting degree between the numerical simulation results and the outdoor monitoring data was relatively high,which also proved that the model parameters conformed to the reality.4.The numerical model was used to predict the longitudinal migration of petroleum hydrocarbons.The simulation results showed that in the case of surface oil pits,the continuous pollution or one-time pollution of petroleum hydrocarbons would soon infiltrate into the aquifer and pollute the groundwater.The most serious groundwater pollution was caused by the continuous pollution.Because the total amount of petroleum hydrocarbon was relatively low during the one-time pollution,the concentration of petroleum hydrocarbon infiltrates into the groundwater became less,and the concentration of petroleum hydrocarbon would gradually decreases under the action of the unsaturated zone and the self-purification ability of groundwater.On the basis of our study,it shows that in the case of surface oil pits,the petroleum hydrocarbon will soon infiltrate into the aquifer through the unsaturated zone,which eventually leads to the groundwater pollution problems and causes the serious environmental pollution.So if the oil-bearing sewage of contaminated site overflow the surface,the relevant departments must immediately deal with the surface wastewater for fear of the existence of surface oil pits.Although this study has obtained certain achievements,there are some limitations:Firstly,it is when we explored the petroleum hydrocarbon migration process that we did not discuss the other possible influential factors such as the temperature and wind speed,and we also did not explore the change of chemical composition of the petroleum hydrocarbons under the action of the external force,so we should pay attention to going on the supplement and perfection in the research process for this work;Secondly,in the process of solute transport model establishment and use of the model to predict the migration,we derived the capillary negative pressure according to the empirical formula,definitely,which is not completely consistent with the reality;Thirdly,due to the lack of field measured data,the petroleum wastewater concentration and the rainfall evaporation conditions of the research object were conducted according to the data assumption,so in the future we will focus more on the research of petroleum hydrocarbon migration in the saturated zone and the establishment of multidimensional model in a bid to improve the accuracy of the model.Hence we should add the supplement and validation into the later monitoring work,and we also hope that there will be one clearer description about the process of petroleum hydrocarbon into the aquifer.