基于多相流模型和探地雷达正演模拟的LNAPLs探测研究

doi:10.6038/pg2019CC0258

摘要/Abstract

摘要：

探地雷达(Ground Penetrating Radar: GPR)不仅可以用于估计土壤含水量,还可以用于探测和监测轻非水相液体(Light Non Aqueous Phase Liquids:LNAPLs)在土壤中的运移.建立接近实际情况的模型是利用GPR正演模拟开展LANPLs迁移和分布研究的关键问题.以往的地球物理模型大都属于概念模型,存在物性突变的界面.而在LNAPLs污染区域的各种物性参数通常是渐变的,大多数情况下并不存在突变的物性界面.因此,为了建立更符合实际的地球物理模型,本文基于多相流渗流理论模拟了LNAPLs在土壤中的泄漏过程,得到了渗漏后不同时刻土壤含水饱和度、含油饱和度的变化分布.然后利用混合介质的介电模型将流体饱和度分布转换为介电常数分布,获得了地球物理模型,显示了因LNAPLs迁移引起的土壤介电常数的细节变化.随后,基于时域有限差分开展了GPR正演模拟.正演模拟结果显示了雷达波对LNAPLs污染区域、潜水面的响应,与实验室实测数据具有很好的一致性.由以上分析、对比可知,本文提出的地球物理建模的方法和流程与污染场地的实际情况更为符合.基于多相流渗流理论建立的地球物理正演模型把地下LNAPLs迁移的水文模型与GPR探测相结合,为复杂的实际场地地球物理建模提供了思路,也为GPR更有效地探测LNAPLs在土壤中的渗流提供了分析和解释手段.

关键词: 探地雷达, 轻非水相液体, 多相流理论, 数值模拟, 相对介电常数

Abstract:

Ground Penetrating Radar (GPR) can be applied not only for estimating soil moisture but also for detecting and monitoring the migration of Light Non Aqueous Phase Liquids (LNAPLs) in soils. It is a key issue to establish a model close to the actual situation in the GPR forward simulation to study the LNAPLs migration in soils. Most of the geophysical models currently used for LNAPLs soil contamination can be considered as conceptual models with a sudden change of physical properties in interface. However, the the physical parameters usually change gradually in the LNAPLs contaminated area, and the sudden-change interfaces in physical properties usually do not exsit. In order to establish a more realistic geophysical model, this paper simulates the leakage process of LNAPLs in soil based on a multiphase flow theory, and obtains the distribution of water saturation and oil saturation at different times after leakage in soils. Then, a geophysical model is obtained by using the dielectric model of the mixed media to convert the fluid saturation distribution into a dielectric constant distribution. The obtained geophysical model shows the dielectric constant change caused by the migration of LNAPLs in detail. After that, the GPR forward modeling is carried out with the obtained model using the Finite Difference in Time Domain (FDTD) method. The results show the responses of the radar wave to the LNAPLs contaminated area and the water table, which correspond to the actual measured data in the laboratory. From the above analysis and comparison, the method and flow for establishing a geophysical model proposed in this paper are more consistent with the actual situation of the contaminated site. The geophysical forward model based on the multiphase flow theory combines the hydrological model with GPR detection, and provides ideas for geophysical modeling of complex sites, and it is a tool of analysis and interpretation for the GPR detection of LNAPLs.

Key words: Ground Penetrating Radar (GPR), Light Non Aqueous Phase Liquids (LNAPLs), Multiphase flow theory, Numerical simulation, Relative dielectric constant

中图分类号:

P631

佘松盛, 鹿琪, 刘四新, 李晔, 王焱, 张宫博. 2019. 基于多相流模型和探地雷达正演模拟的LNAPLs探测研究. 地球物理学进展, 34(1): 371-378. doi: 10.6038/pg2019CC0258.

SHE Song-sheng, LU Qi, LIU Si-xin, LI Ye, WANG Yan, ZHANG Gong-bo. 2019. Research on LNAPLs detection based on multiphase flow model and ground penetrating radar forward modeling. Progress in Geophysics. 34(1): 371-378. doi: 10.6038/pg2019CC0258.

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介质	相对介电常数
土体骨架(ε_s)	4
柴油(ε_o)	2.47
水(ε_ω)	78.52
空气(ε_a)	1