Evaluation of Mineralogical Composition and Organic Matter Content of Oil Shales by IR Microscopy

Abstract

Sedimentary rocks with different contents of organic matter (oil shales of the Bazhenov Formation and sandstones of the Tyumen Formation) from the West Siberian oil and gas province were used to demonstrate the simultaneous study of the mineralogical and structural-group composition, as well as semi-quantitative evaluation of mineral and organic matter contents in rocks by Fourier transform infrared (FTIR) microscopy. The following bands characterizing the stretching vibrations were used: Si–O and Al–O–Si of clay minerals (990–1090 cm–1), Si–O–Si of quartz (798 cm–1), CO2−3 of carbonates (1460 cm–1), as well as aliphatic C–H stretch (2800–3000 cm–1) and C=C ring stretch (1600–1650 cm–1) of organic matter. The obtained results are in good agreement with data obtained by traditional methods of bulk rock analysis: programmed pyrolysis, X-ray diffraction (XRD), and X-ray fluorescence (XRF) analyses. FTIR-ATR (attenuation total reflection) microscopy also provides the possibility of the distribution analysis of sample surface with color mapping, demonstrating the heterogeneity of the rock composition using the Bazhenov Formation as an example of unconventional reservoir. In addition, the method makes it possible to estimate the organic matter maturity and the rock residual generation potential based on the ratio of stretching band intensities of aliphatic and aromatic fragments.