地下水位波动及降水对原油在非均质土层中重分布的影响

为研究原油泄漏后在非均质土层中的重分布过程及影响因素，建立3种不同组合的非均质土层物理模型（编号分别为L-a、L-b、L-c）进行原油泄漏后重分布过程的室内模拟，分别代表局部非渗透性透镜体（浅层泄漏）、大面积弱渗透性粉质亚黏土（内部泄漏）和土层界面（浅层泄漏）存在条件.待原油重力渗透稳定后分别进行升降水位和降水的模拟试验，由PET聚酯膜绘制、CCD相机拍摄和基于CMYK的灰度分析等图像采集和分析法获得平面运移分布图、纵剖面灰度变化图，采用风干法和紫外分光光度法获得采样点含水率和含油率对比图，分析原油泄漏后在非均质土层中的运移规律.结果表明:①在水位波动下，局部非渗透性透镜体和大面积粉质亚黏土弱透水层可有效截获原油，使原油在其左右及上侧大量聚集；3组试验中原油的重分布过程以垂向运移为主，但在粗-细界面和细-粗界面会因油水驱替和毛细压力导致其部分横向运移.②模拟降水时，受到淋滤和水位波动的综合效应，原油油聚区不能在短时间内随水位线移动，体现其滞后性；在模拟降水结束后油聚区大量分布于水位线位置和细-粗界面处；降水对土壤中的原油具一定稀释作用.③L-a和L-c组表层泄漏的原油分布面积（分别为800、538 cm2）较大，采样点含油率极差（分别为6.23%、6.80%）较大；而L-b组内部泄漏的原油分布面积（235 cm2）较小，采样点含油率极差（2.99%）较小.研究显示，地下水位波动及降水对非均质土层中原油的周期性聚集和释放有一定影响，尤其是局部非渗透性透镜体、大面积弱渗透性粉质亚黏土及岩性界面存在土层中影响更大. 

The Influence of Water Table Fluctuation and Rainfall on Redistribution of Crude Oil in Heterogeneous Soil

In order to study the redistribution process and influencing factors in heterogeneous soil after crude oil spill, three physical models of heterogeneous soil layers were established indoor (No.L-a, L-b, L-c respectively) to simulate the redistribution processes of crude oil after spill, which represented the conditions of the local impermeable lens (shallow leakage), the extensive low permeability silty clay layer (internal leakage) and soil layer interfaces (shallow leakage). The simulated experiments of rainfall, water table rise and fall were carried out respectively after the gravity infiltration of crude oil became stable. The plane migration distribution maps and the longitudinal profile grayscale variation graphs were obtained by image acquisition and analysis methods such as drawing on the PET polyester film, photography and the gray analysis based on CMYK. The contrast diagrams between water content and oil content at sampling points were obtained by air dry and ultraviolet spectrophotometry method respectively. Then the migration patterns of the crude oil in the heterogeneous soil layer were analyzed. The results showed that:(1) With the fluctuation of water table, the local impermeable lens and the extensive low permeability silty clay layer could effectively intercept the crude oil, causing crude oil to accumulate on the top and sides of them. The redistribution processes of the oil in L-a, L-b and L-c test groups were dominated by vertical migration, but the oil-water displacement and capillary pressure caused some crude oil to move horizontally at the fine-coarse interface. (2) In the case of simulated rainfall, the oil accumulation zone was often unable to follow the water table in short time because of the comprehensive effects of leaching and water table fluctuation, which reflected the hysteresis. At the end of the simulated rainfall, the oil accumulation areas were located at the water table and the fine-coarse interface. And the rainfall resulted in dilution of the crude oil to a certain degree. (3) The crude oil distribution areas in L-a and L-c test groups (800 cm² and 538 cm² respectively) were larger than in the L-c (235 cm²). The L-a and L-c were both under the conditions of surface leakage while the L-b group had internal leakage. After the tests, the oil content in different sampling points in L-a and L-c (6.23% and 6.80% respectively) were bigger than in L-b (2.99%). The comprehensive results indicate that the underground water table fluctuation and rainfall have influence on periodical accumulation and release of crude oil in the heterogeneous soil layers, especially in the presence of local impermeable lens, the extensive low permeability silty clay and lithologic interface.