地面核磁共振找水方法在中国的应用效果

简要地阐述了地面NMR方法的直接找水原理及特点，并以实例说明了新的找水方法巳在中国11个省区地下水探查中取得出明显成效。建议在提高NMR找水仪抗电磁干扰能力和加大勘探深度方面进行研究，提高新方法的适应性。     

导电性对地面核磁共振信号的影响研究

与其它勘探方法相比,核磁共振(NuclearMagneticResonance,缩写NMR)的方法是直接勘探地下水中NMR信号的唯一有效方法,该信号的初始振幅决定了含水层深度及自由水的含量。但在实际工作中,大地导电性对含水地层中的NMR信号有直接影响,使得同样脉冲矩条件下,勘探深度有变化。为了评价大地(岩石)导电性对勘探深度的影响,建立了一个地面找水模型,对NMR信号进行数值模拟。仿真结果表明,NMR信号的振幅可以评价含水地层的结构,但大地导电性的增强将导致勘探深度的降低。     

探查地下水的新方法——地面核磁共振找水方法的应用研究

地面核磁共振方法是应用地球物理中新发展起米的一种直接找水方法,它利用水中的氢核在一定频率的外场作用下产生核磁共振现象实现对地下水的探测。对测量所得的NMR信号进行分析处理,可以确定地层的含水量、厚度和深度以及平均孔隙度。由于NMR信号微弱、信噪比低,因此所获资料需要进行综合解释和联合反演以提高反演解释的可靠性。以中国地质大学核磁共振科研组在西北某油田的找水工作和国外学者相关的研究成果为例,证实了这一研究方法的可靠性。     

利用核磁共振方法研究水文地质问题及应用实例

地面核磁共振找水方法是目前唯一直接找水的物探新方法。本文在介绍NMR方法原理的基础上,结合NMR方法技术特点和在中国的应用实例,论述了NMR方法在探测地下水、地下水资源评价等方面的效果,并提出了进一步开展新方法的工作建议。     

地球物理找水方法概述

水是人民生活、经济发展必需的宝贵资源,寻找地下水已是当务之急.文章简要介绍了当前找水使用的各种地球物理方法,重点介绍了最新的找水技术NMR的原理和方法特点.     

核磁共振地下水勘查的模拟退火反演

简要地介绍了NMR找水的理论方法,分析了核磁共振找水对于不同含水层的正演计算方法,并用模拟退火反演方法对一维含水模型进行反演,给出了三个不同含水层模型的模拟退火反演效果图。经对比验证,该方法在技术上是可行的,在理论上给出了对NMR反演进行改进的可行性方法。     

应用核磁共振方法在贫水地区勘探地下水

核磁共振(Nuclear Magnetic Resonance,以下缩写为NMR)找水方法是一种直接寻找地下水的物探新方法.以实例说明在岩溶裂隙水勘查中,以NMR方法为主,辅以电阻率法,进行资料的综合解释,可以获得好的效果.     

综合找水方法的应用——以内蒙古隆盛庄地区为例

隆盛庄地区属严重缺水地区，人畜用水严重短缺，找水任务重、难度大。为保证找水效果，本次通过水文地质测绘与水文地质物探确定找水方向和水井井位，然后利用水文地质钻探与抽水试验对找水结果加以验证，取得良好的找水效果，最后通过综合研究总结在找水工作中的经验与教训，形成了综合找水方法，在提高成井出水率的同时降低了风险，可为相似地区开展找水工作提供有益的参考和借鉴。     

岩溶含水介质充填水和泥识别的地球物理勘查技术探讨

岩溶含水介质中充填物性质(水或泥)的正确识别是目前制约岩溶水有效勘查与开发利用的主要“瓶颈”之一。充填物为泥或水时,均反映为低电阻率特性,无法区分充填物到底是水还是泥,从而往往造成打井的失败。作者在近几年岩溶区地下水地球物理勘查工作初步发现,利用水和泥的极化差异识别含水介质充填物性质具有较大的可行性。本文分别讨论了具有与水和泥极化特性相关的核磁共振找水法、激发极化法、频谱激电法三种物探方法识别含水介质充填水或泥的基本原理、野外试验效果。当岩溶含水介质充填水时,核磁共振找水法就会有核磁共振(NMR)信号反映,激发极化法中的极化率参数、频谱激电法中的时间常数均具有高值特征;当岩溶含水介质充填泥时,NMR信号无反应,激发极化法中的极化率参数、频谱激电法中的时间常数均具有低值特征。上述结论经几个不同类型的含水介质实例得到验证,效果明显。      

利用NMR研究三峡工程库区赵树岭滑坡稳定性

核磁共振找水仪(NMR)应用于滑坡地下水研究具有广泛的前景。本文以三峡工程库区巴东县赵树岭滑坡为例,说明利用NMR测试成果确定岩土层水文地质参数的方法,同时根据滑体含水量变化特征,进行滑坡的地下水含水层划分、滑动面确定,改进滑坡稳定性计算。利用NMR测试所测定的滑坡体地下水特征,进行赵树岭滑坡刚体极限平衡分析和有限元数值模拟,结果表明地下水特征对滑坡稳定影响很大,利用NMR可以更准确和有效地进行滑坡稳定性研究。     

地面核磁共振响应数值模拟研究

模型响应的数值计算是地面核磁共振勘探的一个重要组成部分，作者在本文中给出了地面核磁共振数值计算方法。在文中，作者借助直接数值积分方法，对回线源产生的磁场轴向和垂向分量进行计算，并采用不等间距空间坐标剖分技术，对地面核磁共振积分方程进行数值积分。利用这些计算方法，计算了在均匀导电半空间中的某一深度上，磁场的垂向分量沿轴向变化曲线，并给出了两层导电模型中存在一层含水层的地电模型的地面模磁共振响应的数值模拟结果。采用在本文中介绍的数值计算技术，可成功地进行一维含水模型地面核磁共振信号的数值计算。     

基于形态小波的核磁共振测井信号去噪及现场应用研究

核磁共振测井中采集到的回波串信号十分微弱,而背景噪声很强,使信噪分离困难。为解决这一问题,引入了结合数学形态学的特征识别和小波分解的多分辨率分析特性的形态小波方法。讨论了方法的数据基础和应用步骤,并与小波软阈值方法处理结果进行了对比分析。实测数据处理结果表明:形态小波去噪方法具有良好的细节保留和抗噪声能力,去噪效果优于小波软阈值滤波方法;在消除测井信号随机噪声的同时,能很好地保留信号的波形和特征,在较低信噪比下仍可有效地提取测井信号的有用信息,提高了T2谱的反演精度。     

Unfrozen water contents of submarine permafrost determined by nuclear magnetic resonance

Prior work resulted in the development of techniques to measure the unfrozen water contents in frozen soils by nuclear magnetic resonance (NMR). It has been demonstrated that NMR is a promising new method for the determination of phase composition (the measurement of unfrozen water content as a function of temperature) which circumvents many of the limitations inherent in the adiabatic and isothermal calorimetric techniques. The NMR technique makes it possible, in a non-destructive, non-intrusive way, to explore hysteresis by determining both cooling and warming curves. Corrections are made for dissolved paramagnetic impurities which have the effect of increasing the signal intensity at decreasing temperatures. The results demonstrate that NMR techniques can be effectively utilized both at and below the melting point of ice in frozen soils and that accurate melting points (freezing point depressions) can be determined.     

The H nuclear spin-lattice and spin-spin relaxation times at BEarth of some liquids associated with environmental spills

Assessing the extent of an environmental spill is the first step in soil remediation. Near-surface nuclear magnetic resonance (NMR) imaging is proposed as a possible technique for in situ imaging the extent of a spill because of the hydrogen or proton NMR signal associated with the most commonly spilled liquids. Before such a technique is developed, the available signal needs to be assessed. The hydrogen spin-lattice and spin-spin relaxation times of the spilled liquids are the best indicator of the signal. These relaxation times were measured for a variety of hydrocarbons that might be associated with spills. The relaxation times are measured at the Earth’s magnetic field, as these times are field dependent and a near-surface MRI will most likely operate at this magnetic field. With the exception of the more viscous hydrocarbons such as diesel fuel and motor oil, the lower viscosity liquids possess relaxation time values which should yield a good NMR signal from a near-surface MRI operating at the Earth’s magnetic field.     

Overestimation of the importance of phytate in NaOH-EDTA soil extracts as assessed by P NMR analyses

Solution ³¹P NMR analysis of NaOH-EDTA extracts is the most widely used method for determining the speciation of organic P in soils. In this paper, we bring together results from a number of our recent studies that highlight some of the difficulties in obtaining accurate quantitative results and propose that these difficulties may have resulted in the systematic overestimation of soil phytate concentrations. The first problem is peak identification, which is complicated by variations in chemical shift with pH and ionic strength, and the impracticality of the primary ³¹P chemical shift reference (85% H₃PO₄). Unambiguous peak assignment can be achieved by spiking suspected compounds directly into soil extracts prepared for NMR analysis; this ensures native and added compounds experience exactly the same chemical environment. The second problem is quantifying NMR signal for individual species in the crowded and overlapping phosphate monoester region. Spectral deconvolution has been employed for this purpose, but very different results are obtained depending on whether or not the fitting procedure includes a broad signal that probably comes from P in large, “humic” compounds. In particular, failing to consider this broad peak in the deconvolution procedure results in overestimation of small organic P compounds, including phytate. The ready decomposition of phytate is demonstrated with an incubation experiment in which phytate added at various concentrations to a calcareous soil is shown to be decomposed to produce orthophosphate. The decomposition follows a first order exponential decay with a half-life of 4-8 weeks.     

核磁共振找水方法的现状和发展趋势

简要介绍了利用核磁共振（ｎｕｃｌｅａｒ ｍａｇｎｅｔｉｃ ｒｅｓｏｎａｎｃｅ,缩写为ＮＭＲ）技术找水方法的发展状况、原理和方法特点,重点介绍了中国地质大学（武汉）ＮＭＲ科研组,利用ＮＭＲ找水方法在中国一些地区找水取得的成效,最后指出了ＮＭＲ找水方法的发展趋势。     

复杂条件下地下水磁共振探测与灾害水源探查研究进展

磁共振地下水探测是一种直接非侵害性探测地下水的地球物理新方法,与传统地球物理探测地下水方法相比,具有高分辨力、高效率、信息量丰富和解唯一等优点。近年来地下水磁共振探测技术发展迅速,不仅用于缺水地区的地下水勘查,还在地下灾害水源（由于地下水引起的灾害如堤坝渗漏、隧道/矿井水害、滑坡、海水入侵等）的探测预警中进行了探索性研究。综述了复杂条件下地下水磁共振探测技术的研究现状,包括强电磁干扰环境的自适应噪声压制、地下小水体的2D/3D磁共振探测、复杂条件的数据处理与反演、针对喀斯特地貌等地质环境的地下水磁共振与瞬变电磁联合探测研究成果,简要介绍了磁共振技术用于滑坡、海水入侵和隧道涌水等灾害水源探查的探索性研究示例,展望了地下水磁共振探测技术的未来发展趋势。     

A novel efficient inversion method for three-dimensional NMR and the optimization of activation sequences and acquisition parameters

A three-dimensional (3D) nuclear magnetic resonance (NMR) spectrum can simultaneously provide distributions of longitudinal relaxation time (T₁), transverse relaxation time (T₂), and diffusivity (D); thus, it greatly improves the capacity of fluid identification, typing, and quantitative evaluations. However, several challenges that significantly hinder the widespread application of this technique remain. The primary challenges are the high time and memory costs associated with the current 3D NMR inversion algorithms. In addition, an activation sequence optimization method for 3D NMR inversions has not been developed. In this paper, a novel inversion method for 3D NMR spectra and a detailed optimization method for activation sequences and acquisition parameters were proposed. The novel method, namely randomized singular value decomposition (RSVD) inversion algorithm, can reduce memory requirements and ensure computational efficiency and accuracy. Window averaging (WA) technique was also adopted in this study to further increase computational speed. The optimized method for pulse sequences is mainly based on projections of the 3D NMR spectra in the two-dimensional (2D) and one-dimensional (1D) domains. These projections can identify missing NMR properties of different fluids. Because of the efficiency and stability of this novel algorithm and the optimized strategy, the proposed methods presented in this paper could further promote the widespread application of 3D NMR.