含油岩心显微红外光谱成像方法的研究

Microscopic Infrared Spectral Imaging of Oily Core

虽然用红外光谱显微探针方法研究岩心中碳质物已有很多工作,但是通常对诸如岩心等样品物性的光谱学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位点所得的结果,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并已得到广泛应用,但是用红外显微成像光谱研究岩心的工作则少有报道。文章报道了应用透射和衰减全反射(ATR)两种方式对含油岩心进行了显微红外光谱成像(Mapping)的研究。从灵敏度、信噪比、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实验结果进行了比较和评估。

In the present paper, the authors examined some oily core by microscopic infrared spectral imaging methods. Those methods can be classified in three modes, referred to as ＂transmission mode＂, ＂reflection mode＂ and ＂attenuated total reflection （ATR） mode＂. The observed oily core samples belong to siltstone. The samples were made of quartz（- 20%）, feldspar（- 50%） and other rock（igneous rock 25%, metamorphic rocks 1%, sedimentary rock 4%）; a little reerystallized calcite （-1%） was in the pore, and the argillaceous matter was distributed along the edge of a pore. The experimental work has been accomplished using SHIMADZU Model IRPrestige-21 Fourier transform infrared spectrophotometer plus AIM8800 infrared microscope. For IRPrestige-21, the spectral range is 7 800-350 cm^-1 , spectral resolution is 1 cm^-1 , and AIM8800 microscope with motorized stages has a resolution of 1 micrometer. The experiment was preformed at room temperature. In ＂transmission mode＂ infrared spectral imaging method, the spectral range was limited in wavenumbers greater than 2 000 cm^-1 because the base glass piece has strong light absorption. In contrast with ＂transmission mode＂, in ＂attenuated total reflection（ATR） mode＂, the depth of penetration into sample is very small （1-2 micrometer）, then the absorbance value has nothing to do with base glass piece light absorption. In microscopic infrared transmission spectra, the experimental result shows that there are some strong absorption peaks at 2 866, 2 928, 3 618 and 2 515 cm^-1. respectively. The former two peaks correspond to methyl（methylene） symmetrical and unsymmetrical stretch vibration mode, respectively. The latter two peaks correspond to hydroxyl-stretch vibration mode and S-H, P-H chemical bond stretch vibration mode, respectively. In microscopic longwave infrared ATR spectra, there are other stronger absorption peaks at 1 400, 1 038 and 783 cm^-1 respectively, corresponding to methyl（methylene） widing vibration mode and optical mode of quartz crystal, respectively. On the basis of the above-mentioned experimental result, the authors have sepa- rately accomplished microscopic infrared transmission and ATR spectral imaging using mapping procedure. The ＂transmission mode＂ and ＂ATR mode＂ have their own advantage and disadvantage. According to specific structural and spectral properties of sample and the practical research goal, we should select a practical procedure.