人民长江 ›› 2022, Vol. 53 ›› Issue (5): 213-220.doi: 10.16232/j.cnki.1001-4179.2022.05.033

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重塑黄土核磁共振T2谱的定量分析与应用

曹雪梅;詹永康;袁磊;舒中潘;张军;   

  • 发布日期:2022-06-27

Quantitative analysis on NMR T2 spectrum in remolded loess and application

CAO Xuemei1, ZHAN Yongkang2,YUAN Lei3,SHU Zhongpan4,ZHANG Jun4   

  • Published:2022-06-27

摘要: 核磁共振技术(NMR)凭借其便捷性、低成本、无损伤的优势被广泛应用于黄土孔隙空间研究领域中。但目前对于重塑黄土核磁共振T2谱的分析应用成果过于单一,从而造成了一定程度上的数据浪费。有鉴于此,基于核磁共振技术,利用数学分析手段对不同干密度重塑黄土的T2谱开展了定量分析;将分析得到的数学参数应用于石油领域中的SDR模型,并构建了重塑黄土的渗透率计算模型。结果表明:(1)不同干密度重塑黄土的核磁共振T2谱在数学分析参数(均值、几何均值、标准差以及峰度)中存在不同程度的差异,反映到物理意义上,则是重塑黄土干密度会对土体内部孔隙大小、分布及分选特征产生影响。相比传统的方法仅获取土体孔隙体积,数学统计方法获得的数学参数对孔隙的描述更全面也更精确。(2)借助于构建的重塑黄土的SDR模型,求解了试验黄土的渗透率,计算的最小渗透率约为0.3 mD,计算结果与前人总结的规律接近。(3)干密度会影响多个土体微观空间特征,从而引起土体渗透特性的改变。(4)从相关关系方面的分析来看,T2谱的均值和几何均值对土体渗透率影响较大。研究成果在一定程度上可为核磁共振技术在黄土领域中的应用提供新的思路,可为黄土渗透性的预测提供新的方法,也可为了解土体渗透机制提供新的思考。

关键词: 重塑黄土;孔隙空间;核磁共振技术(NMR);微观特征;定量参数;

Abstract: Nuclear Magnetic Resonance (NMR) is widely used in the analysis of pore space characteristics of loess due to its convenience, low cost, and no damage. However, the previous analysis and application of remolded loess T2 spectrum were limited to obtaining the distribution of pore size, and other spatial information contained in the T2 spectrum was not further extracted, which made the application results of the NMR T2 spectrum too single, resulting in a certain degree of data waste. Based on this, we used mathematical analysis method to quantitatively analyze the T2 spectrum of remolded loess with different dry densities, and applied the mathematical parameters obtained by quantitative analysis to the SDR model, so as to construct a permeability calculation model for remodeled loess. The main conclusions were as follows: (1) There are various differences in the statistical analysis parameters (mean, geometric mean, standard deviation and kurtosis) of the NMR T2 spectrum of loess remolded with different dry densities, which has physical meanings: different dry densities of remolded loess will affect the size, distribution and sorting characteristics of pores in the soil. Compared with the traditional method to obtain the pore volume of soil, the mathematical parameters obtained by numerical statistics method can describe the empty pores more comprehensively and accurately. (2) The permeability of each remolded loess was calculated by constructing the SDR model of the remolded loess, the minimum permeability was about 0.3 mD, and the calculated results were close to the previous experimental results. (3) Dry density affected micro-spatial characteristics of soil, and causing the change of soil permeability characteristics. (4) From the correlation analysis, the mean and geometric mean of T2 spectrum had great influence on soil permeability. To a certain extent, the research results can provide new ideas for the application of NMR in the loess study field, new methods for predicting the permeability of loess, and new thinking for understanding the mechanism of soil permeability.

Key words: pore space; Nuclear Magnetic Resonance (NMR); microscopic characteristics; quantitative parameters; remolded loess