岩心孔隙结构的空间分辨核磁表征

Spatially resolved NMR for rock core analysis

将低场核磁共振成像技术用于岩石物理研究中,结合拉普拉斯核磁共振(纵向弛豫时间T_(1)和横向弛豫时间T_(2))与核磁共振成像两种方法,获取岩心样品的局部区域孔隙结构、流体分布等信息。同时,对岩心样品的非均质性进行定性及定量分析,将岩心整体及局部区域的T_(1)和T_(2)分布进行对比,定性表征岩心样品的非均质性;利用地质统计学相关理论,得到岩心不同层面的非均质性大小,定量表征岩心非均质性。结果表明:定性与定量表征结果相符,岩心P的非均质性最强,岩心B最均质;岩心N与岩心P在同一层面以及不同层面之间均显示出明显的非均质性,实现了非均质性在三维空间的系统性研究;通过将多个像素点相加以获取更高的局部区域信号强度的方法,有效提升了低场强条件下空间分辨实验的信噪比。

This research applied low-field MRI technology to rock analysis,and combined MRI and Laplace NMR methods to get more comprehensive information about pore structure,fluid distribution and heterogeneity of core samples.In addition,heterogeneity of cores is analyzed qualitatively and quantitatively.First,the longitudinal relaxation time(T_(1))and transverse relaxation time(T_(2))distribution of the whole core are compared with that of local regions.The heterogeneity of the core sample can be qualitatively characterized by the T_(1) and T_(2) difference between the whole and local regions.Then,based on the theory of geostatistics,the experimental data obtained from the multi-layer spin echo imaging experiments are processed,and then the magnitude of the heterogeneity of different core layers is obtained.The results show that the rock core P is most heterogeneous while B is most homogeneous.The heterogeneity of N and P is quite clear in and among layers.In this way,both qualitative and quantitative analyses on heterogeneity of the cores in three dimension are achieved and the correspondence between the two methods is very well.In addition,the SNR is increased by adding multiple pixels in the same local region.