岩心显微拉曼光谱成像方法的研究

Microscopic Raman Spectral Imaging of Oily Core

虽然用激光拉曼光谱显微探针研究岩心中碳质物的工作已有很大进展,但是通常对诸如岩心等样品物性的光谱学(红外、拉曼和荧光等)微探针实验研究多是局限于对经过复杂处理分离出的微小样品或样品中个别点得到的结果,缺乏对复杂样品各组分(或基团)的空间分布及其相互关系的研究。近年来新发展起来的光谱成像分析系统将光谱技术与成像技术有机地结合起来融为一体,可在光谱和空间两个方面对目标样品进行分析和识别,但是用拉曼显微成像光谱研究岩心的工作则少有报道。文章报道了应用"串行-成像"(series-or indirect-imaging,Mapping)和"并行-成像"(parallel-or direct-imaging,Imaging)两种方式对含油岩心进行了显微拉曼光谱成像的研究。从光谱分辨率和空间分辨率以及工作效率等方面对两种方式所得试验结果进行了比较和评估。

In the present paper,the authors examined some oily core by Raman spectral imaging methods.Those methods can be classified into two categories,referred to as ＂parallel or direct imaging＂（Imaging） and ＂series or indirect imaging＂（Mapping） techniques.The observed oily core samples which belong to siltstone that was from LONG-HU-PAO structure in SONG-LIAO basin.The samples were made from quartz（～60%）,feldspar（～25%） and other impurity,a little recrystallized calcite（～1%） was in the pore,and the argillaceous matter was distributed along the edge of a pore.The experimental work was accomplished using Renishaw MKI2000 Model Raman spectrometer including System 1 000 plus filter wheel and filter set.The experimental condition is as follows： room temperature,back-scattering geometry,and excitation wavelength 514.5 nm（Ar ion laser）.In organic matter region,the microscopic Raman spectrum shows that there are two strong scattering peaks at 1 587.2 and 1 334.5 cm^-1,respectively.The former corresponds to intralayer bi-carbon-atomic stretch mode,referred to as ＂graphite peak＂;the latter is disorder-induced feature because of the relaxation of the wave-vector selection rule resulting from finite crystal size effects,referred to as ＂disorder peak＂.In pure core substrate region,we observed a sharper peak at 462.7 cm^-1,corresponding to Raman active nonpolar optical mode of quartz crystal.On the basis of the above-mentioned experimental result,we accomplished Raman spectral imaging using mapping（indirectimaging） procedure and imaging（direct-imaging） procedure,separately.In mapping（indirect-imaging） procedure,although the Raman spectra possess a high spectral resolution（～1 cm^-1） in every spatial dot,the restructured picture shows a low spatial resolution power（～1 micrometer） because the smallest laser beam radius on the sample plane was restricted by objective lens NA.In imaging（direct-imaging） procedure,the Raman spectra possess a low spectral resolution power（～10-20 cm^-1）,but the picture shows a high spatial resolution power（～0.25-0.30 micrometer） because we need not restructure the picture whose spatial resolution power was only restricted by the optical wavelength.According to the specific structural and spectral properties of sample,and the practical research goal,the authors should select either imaging（direct-imaging） procedure or mapping（indirect-imaging） procedure.