ABSTRACT
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 recrystallized 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(i1)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 separately 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 goall we should select a practical procedure.
ABSTRACT
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 (approximately 60%), feldspar (approximately 25%) and other impurity, a little recrystallized calcite (approximately 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 1000 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 1334.5 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 (indirect-imaging) procedure and imaging (direct-imaging) procedure, separately. In mapping (indirect-imaging) procedure, although the Raman spectra possess a high spectral resolution (approximately 1 cm(-1)) in every spatial dot, the restructured picture shows a low spatial resolution power (approximately 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 (approximately 10-20 cm(-1)), but the picture shows a high spatial resolution power (approximately 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.
