Electrical resistivity imaging of crude oil contaminant in coastal soils – A laboratory sandbox study

IF 2.2 3区 地球科学 Q2 GEOSCIENCES, MULTIDISCIPLINARY
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Abstract

Characterizing the subsurface distribution of crude oil after a spill in a coastal environment is challenging due to variations in the soil and fluid properties. In situ sampling is limited in capturing the lateral and vertical migration of the crude oil within the vadose and saturated zones. This study presents a laboratory sandbox framework used to assess the effectiveness of electrical resistivity imaging for investigating the spatiotemporal distribution of crude oil in coastal sandy soils. A sandbox with dimensions L = 240 cm, W = 60 cm, and H = 60 cm was constructed using a 10 mm plexiglass and filled to a 40 cm height with 2 mm medium to fine-grained sand. At each stage of the experiment, 20 kg of sand was mixed with 1 l of water to create moist sand, after which the mixture was flushed over 12 h to remove suspended fine particles. Both saturated and unsaturated conditions were simulated by setting the water table at 10 cm and draining a fully saturated system overnight. Two liters of crude oil were spilled and monitored for 30 h. A surface array of 98 electrodes, with a unit electrode spacing of 2 cm, was installed along two transects 12 cm apart. Resistivity measurements were collected using a dipole-dipole array before, during, and after the simulated crude oil spill. The time-lapse electrical resistivity results revealed an initial gravity-induced vertical migration under both saturated and unsaturated conditions; over time, lateral migration of crude oil became apparent. In the saturated zone, there was a noticeable reduction in the percentage difference in resistivity from 700 % to 400 % after 24 h, depicting a spatial and temporal redistribution of the crude oil attributed to variation in pore geometry. This highlights the sensitivity of electrical resistivity measurements to subtle but measurable anisotropy in the distribution of soil pores. Overall, electrical resistivity proved successful in imaging the non-ideal behavior of crude oil pollutants and the associated spatial changes in the pore-size distribution of subsurface sediments.

沿海土壤中原油污染物的电阻率成像--实验室沙盘研究
由于土壤和流体特性的变化,要描述沿海环境中原油泄漏后的地下分布情况非常困难。原位取样在捕捉原油在浸润区和饱和区内的横向和纵向迁移方面受到限制。本研究提出了一个实验室沙箱框架,用于评估电阻率成像在调查沿海沙质土壤中原油时空分布方面的有效性。使用 10 毫米有机玻璃建造了一个长 = 240 厘米、宽 = 60 厘米、高 = 60 厘米的沙箱,并用 2 毫米中细粒沙填充至 40 厘米高。在实验的每个阶段,先将 20 千克沙子与 1 升水混合成湿润的沙子,然后将混合物冲洗 12 小时,以去除悬浮的细颗粒。通过将地下水位设置为 10 厘米并将完全饱和的系统排水过夜,模拟饱和和非饱和条件。沿两个相距 12 厘米的横截面安装了由 98 个电极组成的表面阵列,每个电极的间距为 2 厘米。在模拟原油泄漏之前、期间和之后,使用偶极-偶极阵列收集电阻率测量值。延时电阻率测量结果表明,在饱和和非饱和条件下,最初都会出现重力引起的垂直迁移;随着时间的推移,原油的横向迁移变得越来越明显。在饱和区,电阻率的百分比差在 24 小时后从 700% 明显降低到 400%,这说明原油在空间和时间上的重新分布归因于孔隙几何形状的变化。这凸显了电阻率测量对土壤孔隙分布中微妙但可测量的各向异性的敏感性。总之,电阻率成功地成像了原油污染物的非理想行为以及地下沉积物孔隙大小分布的相关空间变化。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
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来源期刊
Journal of Applied Geophysics
Journal of Applied Geophysics 地学-地球科学综合
CiteScore
3.60
自引率
10.00%
发文量
274
审稿时长
4 months
期刊介绍: The Journal of Applied Geophysics with its key objective of responding to pertinent and timely needs, places particular emphasis on methodological developments and innovative applications of geophysical techniques for addressing environmental, engineering, and hydrological problems. Related topical research in exploration geophysics and in soil and rock physics is also covered by the Journal of Applied Geophysics.
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