顺磁性物质对冻土核磁共振信号的影响  

A study of the influence of paramagnetic material on the signal of NMR

作　　者：汤克轩 李俊丽 李振宇[2] 朱源婷 张文波[2] 

机构地区：[1]中水北方勘测设计研究有限责任公司,天津300222 [2]中国地质大学(武汉)地球物理与空间信息学院,湖北武汉430074 [3]中国地质大学(武汉)附属医院,湖北武汉430074

出　　处：《物探与化探》2017年第6期1268-1274,共7页Geophysical and Geochemical Exploration

基　　金：国家127专项"天然气水合物资源勘查与试采工程"项目(GZHL20110324;GZH201400305)

摘　　要：顺磁性物质的磁化率会随着温度的变化而变化,其引起的磁性不均匀对核磁共振信号有一定的影响。当利用NMR(核磁共振)技术研究冻土冻融物性特征时,冻土中所含的顺磁性物质造成的影响不容忽视。结合目前国内外冻土室内物性试验的研究情况,将顺磁性物质Fe_2O_3与马兰黄土混合,配制成Fe_2O_3含量不同、初始含水量相同的各样本,研究其弛豫特性。通过分析各样品的核磁共振信号幅值及横向弛豫时间随温度的变化特征,得到顺磁性物质含量对冻土核磁共振信号的影响规律。结果表明,顺磁性物质能够使孔隙介质中的流体弛豫时间显著减小,并在正温区间顺磁性物质的含量与横向弛豫时间满足某种经验关系式;顺磁性物质也使流体的核磁共振信号幅值显著减小,两者间也满足某种经验关系式;同时,在利用NMR技术分析冻土未冻水含量及孔渗结构时,顺磁性物质的存在会给计算结果带来一定的误差。Susceptibility of paramagnetic material changes when the temperature changes, and non-uniform magnetic field will have a certain influence on nuclear magnetic resonance （NMR） signal. In the study of physical properties of frozen soil with NMR, the effects caused by paramagnetic material in frozen soil cannot be ignored. In combination with the studies of physical properties test of frozen soil conducted both in China and abroad, the authors mixed Fe2O3 with Malan loess and water to make samples in which Fe203 values were different and initial water values were the same. Then the authors analyzed the relaxation characteristics of the samples. Through the analysis of the NMR signal amplitude and transverse relaxation time of the samples with the change of temperature, the influence of different paramagnetic values on NMR signal of frozen soil was summarized. The results show that the paramagnetic material can reduce NMR signal amplitude and transverse relaxation time of fluid in porous media significantly. The NMR signal and paramagnetic content meets some empirical formula below 0℃, and the paramagnetic material will cause some errors in the unfrozen water content calculation of the samples.

关 键 词：核磁共振 顺磁性物质 温度 冻土 弛豫时间 

分 类 号：P631[天文地球—地质矿产勘探]