Analysis of carbonaceous materials in shales using mid-infrared spectroscopy

Abstract The chemical analysis of carbonaceous and organic materials in geological samples (i.e., rocks) is an important and necessary step of hydrocarbon resource development. Despite some significant advances in the last several decades, there still is a need for improved analytical techniques that deliver greater sensitivity and reliable information regarding source rock properties and characterisation. Infrared spectroscopy is a promising technique in terms of providing both qualitative and quantitative information on carbonaceous materials. However, the application of this method for routinely determining parameters relevant to the organic geochemistry of geological systems has not been widely accepted. Here, we compare infrared spectroscopy to standard methods for deriving the total organic carbon content, number of free/volatile hydrocarbons and the hydrocarbon generating potential in shale rocks. Two common methods for collecting infrared spectra, namely Attenuated Total Reflectance (ATR) and Diffuse Reflectance Infrared Fourier Transform (DRIFT) spectroscopy, were evaluated to determine which one is most suitable for shale characterisation. It was revealed that the carbonate overtone band is largely responsible for causing quantitative interferences and errors. Although DRIFT was more sensitive, it was found that the ATR method is less prone to spectral interferences caused by the carbonate overtone band. Irrespective, both methods yielded reasonable correlations against established analytical techniques providing that the C H absorption band was corrected for variations in the carbonate content.