核磁共振T2谱换算孔隙半径分布方法研究

岩芯核磁共振T2谱和压汞分析数据均在一定程度上反映了岩石的孔隙结构特征，理论分析和二者频率分布图对比表明，这两组数据有较好的相关性，核磁共振T₂谱能够换算为反映岩石孔隙结构特征的孔隙半径分布图. 本文应用最大相关性原理、最小二乘法及插值算法等数学方法，给出了一个改进的将T2谱换算为孔隙半径分布图的实用有效新方法，求得了T2弛豫时间与岩芯孔隙半径r之间的换算系数C，计算过程中着重对比了T₂谱与压汞数据的主要分布区间，并考虑了压汞进汞饱和度小于100%对换算结果的影响. 天然砂岩岩芯核磁共振T₂谱换算为孔隙半径分布图的实际应用效果表明，着重对比T₂谱与压汞数据的主要分布区间，同时考虑压汞进汞饱和度小于100%对换算结果的影响是必要的，换算结果更加真实可信.

Methods for Calculating Pore Radius Distribution in Rock from NMR T2 Spectra

Both NMR T₂ spectra and mercury intrusion capillary pressure reflect pore structure of a rock, to a certain extent. Comparison and theoretical analyses of NMR T₂ spectra and mercury intrusion pore-throat frequency distribution curve indicate significant correlation between these two sets of data, thus it is possible to calculate pore radius distribution from NMR T₂ spectra. In this paper, several methods (e.g., interpolation arithmetics, methods based on least square principle and other mathematical methods) for converting NMR T₂ spectra into pore radius distribution were evaluated and compared, using mercury intrusion pore-throat distribution data as a reference. Mercury intrusion saturation was considered to be an important factor that can influence the result of conversion. The practical applicability of the methods was tested using sandstone samples. The results suggested that it is necessary to emphasize the main sections of NMR T₂ spectra and mercury intrusion pore-throat distribution, and consider the influence of inadequate mercury intrusion saturation in the conversion process. The conversion result was shown to be more reliable when both the factors were taken into consideration.