科研之友
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摘要
Samples of Late Devonian/Early Mississippian New Albany Shale from the Illinois Basin, having maturities ranging from early mature to postmature, were analysed using micro-Fourier transform infrared (FTIR) spectroscopy, ImageJ processing software and scanning electron microscopic X-ray spectroscopy to explore the distribution, connectivity and chemical composition of organic matter, clay minerals, carbonate minerals and quartz, and to further test the applicability of micro-FTIR mapping to study shale heterogeneity. Each sample was analysed in planes parallel and perpendicular to the bedding to investigate anisotropy in component distribution, with a possible implication for better understanding anisotropy in porosity and permeability in organic-matter-rich shales. Our results show that for low-maturity samples, organic matter is better connected in the plane parallel to the bedding than in the plane perpendicular to the bedding. Organic matter connectivity decreases with increasing maturity as a result of kerogen transformation. Clay minerals are very well connected in both planes, whereas carbonate minerals are not abundant whilst dominantly isolated in most samples, independent of maturity. This study demonstrates that micro-FTIR mapping is a valuable tool for studying shale heterogeneity on a micrometre to millimetre scale that becomes even more powerful in combination with scanning electron microscopy techniques, which extend observations to a nanometre scale. However, to obtain meaningful and comparable results, micro-FTIR mapping requires very careful standardization, precise selection of peak heights/areas and mapping conditions (such as aperture size, scan numbers, resolution, etc.) well suited for the analysed samples. Lay description Fourier Transform infrared (FTIR) spectroscopy is capable of effectively analyzing and documenting shale composition. Micro-FTIR complements this spectroscopic technique by offering a means to record heterogeneity in shales with diverse mineral compositions without destroying the surface of the sample that is analyzed. With micro-FTIR, a microscope is connected to a spectrometer, which can then map an area, which is set up as a grid of locations where FTIR data are collected, while the sample surface is viewed through microscopy. With this technique, we investigate the interconnectivity of clay minerals, carbonate minerals, quartz, and pore networks of organic matter (OM) parallel and perpendicular to the bedding in a New Albany Shale with high OM content. We are able to find out how interconnected these components are using ImageJ processing software, which allows us to use the maps collected from micro-FTIR to run an analysis based on high and low component concentrations. This gives us an interconnectivity index that we can compare to other information from other techniques. These other data include information from permeability measurements, porosity measurements, and scanning electron microscopy (SEM). While SEM can give an idea of mineral distribution, it is very small-scale. Micro-FTIR gives a better idea of the type of organic matter we find as well as the connectivity of the OM. Our study found that early-mature shales have a difference in OM distribution between planes parallel and perpendicular to the bedding, with OM being connected moreso in sections parallel to the bedding compared to those perpendicular to the bedding. This pattern becomes less evident in late-mature stage samples when OM is transformed into hydrocarbon products and occurs only in isolated areas. In the postmature stage, OM becomes better connected a result of secondary cracking of hydrocarbons. Clay minerals are very well connected in all samples, whereas carbonate minerals occur as isolated domains.
- 出版日期2017-1
