Application of Raman Spectroscopy as Thermal Maturity Probe in Shale Petroleum Systems: Insights from Natural and Artificial Maturation Series

Abstract

Raman spectroscopy was studied as a thermal maturity probe in a series of Upper Devonian Ohio Shale samples from the Appalachian Basin spanning from immature to dry gas conditions. Raman spectroscopy also was applied to samples spanning a similar thermal range created from 72-h hydrous pyrolysis (HP) experiments of the Ohio Shale at temperatures from 300 to 360 °C and isothermal HP experiments lasting up to 100 days of similar Devonian–Mississippian New Albany Shale. Raman spectra were treated by automated evaluation software based on iterative and simultaneous modeling of signal and baseline functions to decrease subjectivity. Spectra show robust correlation to measured solid bitumen reflectance (BRo) values and were therefore used to construct logarithmic regression relationships for calculation of BRo equivalent values. Raman spectra show considerable differences between natural samples and HP residues with similar measured BRo values, indicating as-yet undetermined differences in carbon chemistry. We ...