流动相石油在沿海土-水系统中的运移机制及电阻率响应特征研究

At present, the four domestic big oil reserve bases are all located in the coastal areas. The oil spill will cause serious pollution to groundwater and coastal waters. There are still many problems on how the mobile phase oil migrates in different soil-water environments and how we judge the pollution extent from the resistivity variation of the contaminated soil. The project chooses the migration of the mobile phase oil and the resistivity response in coastal aquifer as research object, and the following key issues will be studied based on laboratory and in-situ test combined with theory analysis. Firstly, the oil penetration, accumulation, and redistribution rule and mechanism will be investigated under the special geological or leakage conditions and when the hydrological conditions change on the basis of the transport simulation of the mobile phase oil in the case of the existence of the low permeable lens or lithologic mutation interface, internal oil leakage in the soil layer, water level fluctuation and rainfall leaching. Secondly, the characteristics and main influence factors of the contaminated soil resistivity will be revealed, and the resistivity formula will be established after the resistivity test of the oil contaminated soil with water. Lastly, the resistivity response mechanism will be expounded through monitoring the soil resistivity variation of the oil vertical permeability in the homogeneous soil and 3D migration in the heterogeneity soil, and it will be verified by in-situ test. Project results have theoretical significance to judge the pollution range and degree to the coastal soil-water system after the oil spill, and to take measures to minimize environmental damage.

目前国内四大石油储备基地均位于沿海地区，石油泄漏会对地下水及近岸海域造成严重污染。不同土-水环境下流动相石油的运移及如何通过污染土电阻率的变化判断污染情况仍存在许多问题。项目以沿海含水层中流动相石油的运移及电阻率响应为研究对象，采用室内试验、原位测试，联合理论分析的方法，开展如下关键问题研究：通过流动相石油在低渗透透镜体或岩性突变界面存在、土层内部石油泄漏、水位波动、降雨淋滤条件下的运移模拟，探讨特殊地质、泄漏条件及水文地质条件改变时石油渗透、聚集及重分布规律及机理；通过石油污染含水土壤的电阻率测试，揭示污染土电阻率特征及主要影响因素，建立污染土电阻率公式；通过石油在均质土层垂向渗透及非均质土层三维运移过程的电阻率变化测定，阐明电阻率响应机制，并通过原位测试进行验证。项目成果可为石油泄漏污染沿海土-水系统后快速判断污染范围及程度提供理论依据，以及时采取措施最大限度减少环境损害。

国内石油储备基地大部分位于沿海地区，流动相石油泄漏后会对土-水系统造成严重污染。通过地表布设电极的方式探测石油污染含水土层电阻率的变化，可获得某一深度范围的污染情况，但存在很多问题需要解决。研究内容如下：建立二维渗流槽模型，分别以低渗透透镜体和岩性突变界面存在为初始条件，以土壤表层和内部泄漏方式研究石油的运移规律；以升高和降低水位的方式研究水位波动对土壤中残留石油的重分布规律及机制；模拟降雨，研究其对残留石油的淋滤机制；以室内配样的方式研究污染土电阻率的影响因素及机理，建立电阻率公式；以土柱模拟石油在含水土层中的渗透，并利用电阻率探杆监测石油垂向渗透过程的电阻率响应规律和机理；以三维水槽模拟石油在含水土层中的泄漏过程，利用高密度电阻率映像法实时动态监测石油运移过程，获取相应电阻率图谱。主要结论如下：1）局部低渗透性透镜体、土壤质地、初始含水率、岩性突变界面、泄漏位置等因素影响石油在土层中的迁移速度和路径，垂向和横向运移相互关联，局部弱渗透层、岩性突变界面附近会形成油聚区，水位波动和降雨会造成残留石油进一步扩大污染范围；2）石油污染土的电阻率受含水率、含油率、孔隙率、土壤类型的影响较大，受石油种类的影响较小，计算污染土电阻率时应将含油饱和度引入公式；3）石油泄漏前期和后期分别以重力渗透和油水驱替过程为主，电阻率探杆可监测石油的垂向运移过程；4）高密度电阻率监测采用Wenner法结果较稳定，采用电极排可实现多条测线同时测量，水位波动或降雨后，油含量越高，电阻率越大，运移越快，电阻率变化越迅速；5）石油污染含水土壤的电阻率受初始含水率影响较大，在含水率15%时，随含油率的增加，电阻率呈总体上升趋势；而含水率5%时，随含油率的增加电阻率变化复杂，会呈现电阻率降低现象，故实际监测过程应首先明确土壤的含水率。研究结果可为沿海地区轻质石油泄漏后污染土-水系统范围和程度的快速判断提供技术支持。