面向含水层的震电效应数值模拟  

Numerical simulation of seismoelectric effect of aquifer

作　　者：马杰 任恒鑫 汤井田[1] Ma Jie;REN HengXin;TANG JingTian(School of Geosciences and InfoPhysics,Central South University,Changsha 410083,China;Department of Earth and Space Sciences,Southern University of Science and Technology,Shenzhen 518055,China)

机构地区：[1]中南大学地球科学与信息物理学院,长沙410083 [2]南方科技大学地球与空间科学系,深圳518055

出　　处：《地球物理学进展》2023年第2期846-866,共21页Progress in Geophysics

基　　金：国家重点研发计划“深地资源勘查开采”重点专项(2018YFC0603202);国家自然科学基金项目(41922027,41830107)联合资助。

摘　　要：为了更好地理解和解释土壤结构、多相流混合物和流体矿化度对震电测量的影响,本文基于Pride和Revil分别提出的动电耦合控制方程组,采用LAC广义反射与透射系数法对均匀、横向各向同性的多层含流体孔隙介质进行数值模拟研究.本文分别研究了包气带、不同土壤结构的地层和污染物侵入含水层等三种不同地质背景的震电信号.数值结果表明:含水饱和度剧烈变化比均匀变化能激发出更强的动电效应;按照含水饱和度划分的地层层厚与主导的地震波长一致时,震电信号振幅最大;由于S波比P波波长短,所以S波转换的磁场分辨“薄层”能力更强;Pride与Revil的理论模型在地层富含黏土且孔隙中流体部分饱和时存在差异;当土壤为三孔的形式且富含黏土矿物时,基本上不满足“薄”双电层假设条件;黏土含量越高,砂土含量越低,电场总场及界面响应振幅越大;和依照饱和度划分的地层对比,震电信号不仅可以探测到含非水相液体(NAPL)地层的存在,而且分辨率远高于前者;非水相液体的密度和黏度会对震电信号产生明显影响;震电信号同样对流体矿化度变化敏感,非同震电磁信号对流体矿化度变化敏感主要体现于矿化度变化界面附近的隐失波,自由表面附近接收的震电信号无法辨别地层界面处流体矿化度的变化,地层界面附近接收的震电信号可以对依矿化度分类的天然水类型进行分辨.本文的研究对震电效应在地下水勘探的应用上具有借鉴价值.In order to better understand and explain the influence of soil structure,multiphase flow mixture and fluid salinity on seismoelectric measurement, the LAC generalized reflection and transmission coefficient method is used to simulate the homogeneous,transverse-isotropic multilayer fluid containing porous media based on the electrockinetic coupling control equations proposed by Pride and Revil respectively. In this paper, seismic signals in different geological backgrounds,such as vadose zone,stratum with different soil structure and pollutant intrusion into aquifer, are studied respectively. The numerical results show that the electrockinetic effect is stronger when the water saturation changes violently than when the water saturation changes uniformly. When the layer thickness divided by water saturation is consistent with the dominant seismic wavelength,the amplitude of seismoelectric signals is the largest,and the magnetic field of S-wave conversion is stronger in distinguishing “thin layer”due to the shorter wavelength of S wave than P wave. Pride and Revil's theoretical model have some differences when the formation is rich in clay and the fluid in the pore is partially saturated. When the soil is in the form of three pores and rich in clay minerals,it basically does not meet the“thin”double electric layer hypothesis.The higher the clay content and the lower the sand content,the greater the amplitude of the total electric field and interface response. Compared with the strata divided by saturation,seismoelectric signals can not only detect the presence of Non-Aqueous Phase Liquid( NAPL),but also have a much higher resolution. The density and viscosity of non-aqueous liquid have obvious influence on seismoelectric signals. Seismoelectric signals are also sensitive to fluid salinity changes. The sensitivity of noncoseismic electromagnetic signal to fluid salinity change is mainly reflected in the evanescent wave near the salinity change interface. The seismoelectric signals received near the free surf

关 键 词：震电效应 数值模拟 包气带 土壤结构 地下水污染 

分 类 号：P631[天文地球—地质矿产勘探]