隧道磁共振全弛豫信号三维反演研究  

Research on full-relaxation signal 3D inversion of tunnel nuclear magnetic resonance

作　　者：赵威 李貅[2] 刘金鹏[2] ZHAO Wei;LI Xiu;LIU Jin-peng(China Railway Siyuan Survey and Design Group Company Limited, Wuhan 430063, China;School of Geology Engineering and Geornaties, Chang＇ an University, Xi＇ an 710054, China)

机构地区：[1]中铁第四勘察设计院集团有限公司,武汉430063 [2]长安大学地质工程与测绘学院,西安710054

出　　处：《地球物理学进展》2018年第2期900-908,共9页Progress in Geophysics

基　　金：国家重点基础研究发展计划(973)项目(2013CB036002);国家自然科学基金重点项目(51139004);国家重大科研设备研制项目(2011YQ030133)联合资助

摘　　要：磁共振探测反演近些年得到较多的关注.传统的磁共振反演多为基于地面大线圈采集,基于初始振幅的反演,这种方法未考虑地下复杂的多孔地质环境,且限制了磁共振方法的应用范围.针对上述问题,本文尝试建立了基于隧道磁共振全弛豫信号的三维反演方法,在传统的磁共振三维正演核函数基础上,加入指数衰减项,在充分考虑地下电阻率不均匀体的情况下,采用有限元方法模拟了磁共振全弛豫信号响应.针对三维磁共振灵敏度矩阵的病态性和隧道中的电磁干扰,建立了考虑罚项的最小二乘目标函数,并结合实际对函数的解加以约束,利用基于不等式约束的最优化算法实现了三维反演.模型计算表明:本文的三维反演效果良好,不仅能实现掌子面前方含水异常体定位,而且能给出不同弛豫时间下的含水量信息,从而间接获知灾害水赋存状态,为隧道磁共振数据处理提供了一个可供借鉴的方法.Nuclear Magnetic Resonance（ NMR） inversion has received much attention in recent years. The traditional NMR inversion methods are mostly based on surficial large loop collection and initial amplitude, which did not consider for underground complex porous geological environment and limit NMR application scope. Aiming at these problems,we attempted to establish tunnel NMR full-relaxation signal three-dimensional（ 3 D） inversion method. In order to simulate 3 D NMR relaxation signal, the exponential decay item was added to traditional NMR forward modeling kernel function,the finite element method was adapted in view of the various underground resistivity distribution. Aiming at the ill-condition of the 3 D NMR sensitivity matrix and the electromagnetic interference in the tunnel,a penalty term added least squares objective function was proposed. The solution of the function should be restricted and 3 D inversion was achieved by an optimization algorithm based on inequality constraints. Model calculations showed that this 3 D inversion method achieved good results. Not only to locate aqueous anomalies in front of the tunnel,but also to provide water content information under different relaxation time forecast disastrous water occurrence state indirectly.Totally,this paper provides a method for tunnel magnetic resonance data processing.

关 键 词：隧道核磁共振 弛豫信号 多指数拟合 三维反演 

分 类 号：P631[天文地球—地质矿产勘探]