磁共振测深技术的发展历程与新进展

磁共振测深(Magnetic Resonance Sounding,MRS)技术作为目前唯一能够实现地下水直接定量探测的地球物理高新技术已有近30年的历史,最近10年,MRS技术在仪器、正反演理论、信号影响因素、实际应用等方面都取得了一系列进展.死区时间不到10ms的商用型多道磁共振测深仪的推广使用,大幅改善了MRS方法的找水效果和仪器的抗干扰能力;正反演研究的重心已由简单的一维层状假设理论转入更符合实际情况的复杂地质条件下的高分辨率2/3D磁共振成像研究;信号影响因素与机制的研究也更加深入、全面;特别是实际应用方面,正在由单纯的地下水探测向水文地质调查、地下水管理与污染监测、灾害水源的超前探测等多个领域拓展.随着磁共振测深技术的进一步发展与完善,它定将在更多领域更好地造福于人类.     

羌塘盆地冻土层结构核磁共振信号响应研究与实践

为了了解羌塘盆地冻土层的结构,利用核磁共振测深(MRS)技术对羌塘盆地的两个研究区进行了野外勘探。结合室内实验及野外实际资料,冻土层基本无法引起仪器核磁共振响应是划分冻土层和探测水合物的重要证据。在钻井附近进行的MRS方法对试验点进行测量并采集到了NMR信号,分析认为是天然气水合物处在亚稳定状态,分解产生水或者液态烃,形成水-水合物-气三相共存的情况,引起了NMR反应。实践表明可以将MRS方法运用于探测陆域冻土带分布以及冻土带,该方法对于冻土层的结构划分具有十分重要的科学意义和应用价值。     

我国大地电磁测深研究新进展

回顾了我国80年代中期以来大地电磁测深工作的进展，包括资料采集、数据处理和反演解释着重介绍了大地电磁测深法在石油、天然气构造普查勘探以及地壳和上地慢探测方面应用的情况．     

核磁共振找水技术的研究现状与发展趋势

近20多年来,用核磁共振(Nuclear Magnetic Resonance,NMR)方法形成的一种直接非侵害性的探测地下水的地球物理新技术,与传统的地球物理探测地下水的方法相比具有高分辨力、高效率、信息量丰富和解的唯一性等优点,是一种很有发展前景的找水方法技术.我国的水资源短缺,对地下水资源的勘探、开发与利用十分重视,已将核磁共振找水技术研究列入国家十一五科技支撑计划.本文在广泛收集迄今为止的国内外大量资料的基础上,并根据作者近年来有关核磁共振找水技术的研究经历,综述了核磁共振找水技术的发展历史、现状和发展趋势,以推进我国核磁共振找水技术的发展.     

大地电磁测深反演方法现状与评述

如何通过改进大地电磁测深(MT)反演方法来提高数据解释的精确度一直都是大地电磁测深研究领域的重要课题.本文以作者所在研究组从事的科研项目为依托,介绍了国内外主要的大地电磁反演方法.通过总结将反演方法分为定性近似反演方法、基于目标函数的线性或非线性选代反演方法和全局搜索最优反演方法三大类,并从目标函数构建、灵敏度矩阵计算...     

一种多尺度电磁测深方法

电磁测深方法是地球物理勘探的重要方法.按照处理方式分为时间域和频率域电磁测深方法两类.但实质上时间域方法和频率域方法是等效的.而由于观测方式的不同,有时效果不能完全等同.本文介绍一种广义的时间域电磁测深方法.这种方法的最大优点就是在不改变激励和观测装置的前提下,通过改变激励波形,从而实现分段多尺度的电磁测深处理.     

利用核磁共振方法探查基岩裂隙水

基岩裂隙水是我国分布最为广泛的地下水类型之一。本文阐述了基岩裂隙水的特点：含水层产状不规则、其赋存空间介质不均匀、同一含水层埋深不同、地下水运动状态复杂等。这些特殊的地质、地球物理特征,给常用的物探找水方法带来许多困难。本文通过对直接找水的新方法一核磁共振（ＮｕｃｌｅａｒＭａｇｎｅｔｉｃ　Ｒｅｓｏｎａｎｃｅ,缩写为ＮＭＲ）测深与间接找水的电阻率测深的对比分析,论述了ＮＭＲ测深直接找水的实质。并以实例说明了ＮＭＲ测深在探查基岩裂隙水中的应用效果。     

地面磁共振测深分布式探测方法与关键技术

地面核磁共振方法(MRS)因具有对地下水探测定性、定量的特点而备受地球物理工作者关注.传统研究中,人们局限于一维探测方法,假设层状含水构造,导致复杂地质环境下难以确定井位、不均匀含水层小水体难以分辨的反演解释瓶颈.针对现有测量中的不足,本文提出了MRS二维分布式探测模式,依据激发场不均匀特性,定义了实际测量中的测线方位角α,推导了分布式接收线圈MRS响应核函数表达式,实现了二维正演计算,探索了α角与探测灵敏度之间的关系.在此基础上,首次将Occam方法用于MRS二维反演解释中,实现了磁共振断层成像MRT(magnetic resonance tomography).模型试算中,根据含水层位置以及环境噪声变化的磁共振响应,客观评价了分布式MRS探测适用范围.理论先行可推动仪器完善,本文通过分布式接收单元设计、接收线圈数量和匝数增加与调整、放大器参数自适应设置与矫正,成功研制了地面分布式磁共振探测系统,并进行了野外验证.本文的研究成果将为基岩裂隙水定位、堤坝渗漏灾害水源评价,喀斯特溶洞含水构造精确探测提供有力的科学支撑.     

一种广义时间域电磁测深法——单脉冲电磁测深方法

电磁测深方法可分为频率域测深和时间域测深两大类.时间域测深主要是在一次激励场结束后,观测二次涡流场.对于频率域电磁测深方法,研究问题时仅考虑边界条件即可,但对时间域方法,不但要考虑边界条件,还要考虑初始条件,所以时间域的研究往往比频率域的研究要复杂得多.在以往的时间域方法中,通常使用阶跃波作为激励源,这主要是由于阶跃波激励完成后,有充裕的时间间隙可以观测感应二次场.但由于阶跃波的时间域电磁响应的复杂性,往往采用分时段(分区间)的处理方式,分为远区(早期)、近区(晚期)、过渡区(过渡期)等方式.本文介绍一种利用?单脉冲函数的激励源的时间域电磁响应实现电磁测深的方式.它不需要将时间域分成多个区段,且可以借助任何的第三方激励源来进行激励.观测电磁响应也不需要在激励结束后进行.     

Inversion of resistivity in Magnetic Resonance Sounding

Magnetic Resonance Sounding (MRS, or Surface Nuclear Magnetic Resonance - SNMR) is used for groundwater exploration and aquifer characterization. Since this is an electromagnetic method, the excitation magnetic field depends on the resistivity of the subsurface. Therefore, the resistivity has to be taken into account in the inversion: either as a priori information or as an inversion parameter during the inversion process, as introduced in the presented paper. Studies with synthetic data show that water content and resistivity can be resolved for a low resistive aquifer even using only the amplitude of the MRS signal. However, the inversion result can be significantly improved using amplitude and phase of the MRS signal. The successful implementation of the inversion for field data shows that the resistivities derived from MRS are comparable to those from conventional geoelectric methods such as DC resistivity and transient electromagnetic. By having information about both the resistivity and the water content, MRS inversions give information about the quality of the water in the aquifer. This is of utmost interest in hydrogeological studies as this specific information cannot be determined solely by geoelectric measurements, due to the nonunique dependence of resistivity on water content and salinity.     

Pore size distributions and hydraulic conductivities of rocks derived from Magnetic Resonance Sounding relaxation data using multi-exponential decay time inversion

In hydrogeology there is a variety of empirical formulae available for determination of hydraulic conductivity of porous media, all based on the analysis of grain size distributions of aquifer materials. Sensitivity of NMR measurements to pore sizes makes it a good indicator of hydraulic conductivity. Analogous to laboratory NMR, Magnetic Resonance Sounding (MRS) relaxation data are of a multi-exponential (ME) nature due to the distribution of different pore sizes in an investigated rock layer. ME relaxation behaviour will also arise due to the superposition of NMR signals which originate from different layers. It has been shown, that both kinds of ME behaviour coexist in MRS and can principally be separated by ME inversion of the field data. Only a few publications exist that have proposed approaches to qualitatively and quantitatively estimate petrophysical parameters such as the hydraulic conductivity from MRS measurements, i.e. MRS porosity and decay times. The so far used relations for the estimation of hydraulic conductivity in hydrogeology and NMR experiments are compared and discussed with respect to their applicability in MRS. Taking into account results from a variety of laboratory NMR and MRS experiments mean rock specific calibration factors are introduced for a data-base-calibrated estimation of hydraulic conductivity when no on-site calibration of MRS is available. Field data have been analysed using conventional and ME inversion using such mean calibration values. The results for conventional and ME inversion agree with estimates obtained from well core analysis for shallow depths but are significantly improved using a ME inversion approach for greater depths.     

Resolution studies for Magnetic Resonance Sounding (MRS) using the singular value decomposition

We present a new approach to analyse the subsurface water content distribution obtained by inversion of MRS data in terms of resolution and penetration depth. It is based on a singular value decomposition (SVD) of the MRS forward operator to derive the model resolution matrix including regularisation parameters, i.e. including noise conditions. The approach takes loop size, subsurface resistivity distribution and noise conditions as input parameters affecting MRS into account and allows an assessment on resolution and penetration.The application of the new approach shows that the loop diameter must be carefully chosen depending on the investigation site to obtain optimal resolution and penetration. Using the introduced resolution measures the quality and reliability of the estimated model can be assessed.     

Widespread occurrence of aquifers currently undetectable with the MRS technique in the Grenville geological province, Canada

In the summer of 2003, a series of field tests were made over aquifers within or next to the Grenville geological province, Canada. Twelve sites distributed within three general areas of the province and nearby to its southern border were surveyed with the MRS (Magnetic Resonance Sounding) technique. Each site was characterized by saturated shallow water bearing layers of high effective porosity. The tests were planned to evaluate the MRS technology in such environments for groundwater resources quantification and aquifer/aquitard media characterization. A priori, the environmental conditions in Eastern Canada were assumed favorable for MRS work such as low to moderate ambient noise, earth's field value above 55,000 nT, targets consisting of shallow and high porosity aquifers. Despite such conditions, no clear MRS responses were observed. Following supplementary investigations, this is now attributed to the wide-scale occurrence of disseminated magnetite within the aquifers which shorten the signal decay time. Although the lack of MRS response over aquifers has been reported before, this was not the case for such widespread occurrence. This also supports the adaptation of the MRS technology to conditions similar to those observed in the Grenville province.     

利用核磁共振方法探查岩溶水

核磁共振（ＮＭＲ）找水方法是目前唯一直接找水的物探新方法,该方法可以探查各种类型的地下水。本文仅论述了在岩溶发育区常规电阻率方法找水时遇到的地质干扰。ＮＭＲ找水方法的原理,仪器的组成,并以实例说明了ＮＭＲ找水方法探查岩溶水的效果。     

我国大地电磁测深新进展及瞻望

简要回顾了上世纪60－80年代，我国大地电磁测深工作的起步和发展， 较全面地介绍了90年代以来的新进展，并瞻望了新世纪的发展方向。     

Cotton Fiber/ZrO2, A New Material for Adsorption of Cr(VI) Ions in Water

The natural cotton fiber was used to synthesize an anion exchange, containing ZrO₂ film on its surface, NCFZC (natural cotton fiber/ZrO₂ composite). This anion exchanger was produced by the reaction of the zirconium oxychloride and hydroxyl groups on surface of the natural cotton fiber. The material was used for Cr(VI) ions adsorption studies. Adsorption equilibrium time and optimum pH for Cr(VI) adsorption were found to be 6 h and 4.0, respectively. The Langmuir and Temkin isotherms were used to models adsorption equilibrium data. The adsorption capacity of NCFZC was found to be 1.33 mmol/g. Kinetic studies showed that the rate of adsorption of Cr(VI) on NCFZC obeyed a pseudo‐second‐order kinetic model.     

Geomorphic influences on the distribution and accumulation of pyrogenic carbon (PyC) following a low severity wildfire in northern New Mexico

The distribution, transport, and accumulation of wildfire‐generated pyrogenic carbon (PyC) has important consequences for contaminant transport and carbon cycling, but a conceptual model for PyC accumulation and loss that includes geomorphic processes is lacking. In this study we quantified PyC concentration in soil samples collected from the Jemez Mountains of New Mexico before and after the 2013 Thompson Ridge (TR) fire, and developed a conceptual model describing PyC redistribution. Pre‐fire samples were fortuitously collected 4 years before the TR burn and post‐fire samples were collected at the same locations 15 months following the TR fire. Samples were collected from the O and A horizon, with sites representing a range of slope angle, aspect, burn severity, and geomorphic setting. PyC was determined by a modified chemo‐thermal oxidation method to compare PyC to total organic carbon (TOC). The mean PyC/TOC ratio was significantly higher post‐fire than pre‐fire (0.14 vs 0.12), indicating increased PyC sequestration. O horizon PyC concentrations were more variable and more responsive to fire than the A horizon. Soil horizon, watershed, and geomorphic setting proved to be the most influential factors in predicting PyC concentration changes. PyC concentrations increased most on hillslopes and in low‐severity burn areas, suggesting higher rates of PyC production or post‐fire accumulation. Burn patchiness appears to facilitate PyC accumulation, with lower severity patches trapping PyC mobilized from high severity patches. While PyC content had greater point scale variance following the fire, the fire also homogenized pre‐fire PyC differences between soil horizons and among watersheds within the burn perimeter, differences that appear to develop over time between fires. The O horizon is a larger sink for PyC in the short term following fire, but based on pre‐fire concentrations the A horizon appears to be a more stable sink for PyC. Copyright © 2018 John Wiley & Sons, Ltd.     

High molecular weight (C_(35)~+) n-alkanes of high-waxy condensate and its source kitchen orientation in the Qianmiqiao burial-hill zone, Bohai Gulf Basin

Copyright by Science in China Press 2004 High-waxy condensate is a kind of special hy-drocarbon resources, i.e., the high molecular weight (HMW) alkanes, which usually appear in a solid wax fraction under normal temperature and pressure, but are dissolved by hydrocarbon gas as a high-waxy condensate of single gaseous phase under subsurface high temperature and pressure. Nevertheless, once produced in an oil-gas well, the subsurface condensate flows into the well-bottom, and then immediately …     

日本海沟俯冲带MW9.0地震震源区应力场演化分析

于2011年3月11日发生在日本东北部的M_W9.0级逆冲型板间地震是日本有地震记录以来震级最大的一次地震.本研究基于NIED F-net矩张量解目录中的震源机制解,选取两个长轴相互垂直的矩形区域进行应力场2D反演,获取了日本海沟俯冲带地区应力场的空间及时间分布图像.结果表明：主震前,俯冲带地区应力状态在空间上大体趋于一致,即应力轴（P轴、σ₁轴及S_Hmax轴）系统性地倾向板块汇聚方向,P轴、σ₁轴倾角整体偏缓（< 30°）,且远离震源区及日本海沟东侧区域内的应力轴倾角普遍大于主震震源区内应力轴倾角;主震前,受2003年5月26日在宫城县北部发生的M_W7.0地震影响,位于M_W9.0地震震源区西北侧的应力场出现明显扰动,σ₁轴倾向顺时针偏转150°~180°,并于之后大体恢复至震前状态,同期其他地区没有明显变化,这种情况可能和主震断层局部（深部）的前兆性滑动有关;主震后,距离震源区较远处应力场变化不大,主震震源区内应力场发生显著改变,P轴及σ₁轴均以大角度（>60°）倾伏于板块汇聚方向,S_Hmax轴顺时针偏转60°~90°且在日本海沟附近普遍平行于海沟轴.这项研究以时空图像的方式展示了大地震前应力场变化的特点,反映了大地震孕震过程中构造与地震的相互作用,对于理解大地震孕震过程有重要意义.