Raman spectroscopy: an analytical tool for evaluating organic matter

Abstract

With the increase in production from shale oil and shale gas in North America during the last decade, many studies have been conducted in order to improve our knowledge from organic rich shale plays. Kerogen as one of their main constituents, is a complex macromolecule which generates hydrocarbons under adequate pressure and temperature. However, kerogen is still not fully known in terms of geochemistry and geomechanics. In addition, complexity of unconventional shale plays has led to employment new methods and analytical equipment for characterizing organic matter. In this study, samples from the Bakken Formation are collected and analyzed for thermal maturity and geochemical characteristics by Vitrinite reflectance (%VRo) and Rock-Eval (RE) pyrolysis. Then, Raman spectroscopy was performed on the samples as an analytical tool to provide us with deeper insight about molecular structure. To do so, organic matter properties in terms of thermal maturity were correlated with Raman signals. Furthermore, mechanical properties of organic matter that was acquired with PeakForce Tapping mode in atomic force microscopy (AFM) in-situ, was related to its Raman responses. Results showed a very good correlation between Raman signals and geochemical and geomechanical properties of organic matter reflecting molecular characteristics of this component of shale plays.