Assessing thermal maturity beyond the reaches of vitrinite reflectance and Rock-Eval pyrolysis: A case study from the Silurian Qusaiba formation

Thermal maturity evaluation using Raman spectroscopy for oil shale samples of USA: comparisons with vitrinite reflectance and pyrolysis methods

“…It is worth mentioning here that RBS is found as a more robust parameter than G and D1 band area ratio while comparing with equivalent reflectance (%VR e ). The efficacy of RBS with thermal maturity was also observed by Sauerer et al (2017). The RBS versus vitrinite reflectance (%VR o ) shows a poor correlation suggesting a higher error in petrographic measurements.…”

“…Raman spectroscopy is potentially a better technique for nondestructive, rapid, and precise maturity evaluation of hydrocarbon source rocks (Kelemen and Fang 2001;Marshall et al 2012;Wilkins et al 2014). In recent years, Raman spectroscopy has emerged as a indispensable useful method that provides information about the structural and chemical properties of carbon materials (e.g., Ferrari and Robertson 2000;Beyssac et al 2002;Xie et al 2008;Wilkins et al 2014Wilkins et al , 2015Zhou et al 2014;Schito et al 2017;Sauerer et al 2017;Schmidt et al 2017;Khatibi et al 2018;An et al 2018;Hackley and Lünsdorf 2018). This method can also be used to study small, dispersed maceral grains that are difficult to study by other methods.…”

“…However, with an increase in thermal maturity, the D and G peaks shift toward lower and higher wavelengths, respectively. The distance between G and D peaks is called Raman band separation (RBS), and it has been used as a reliable maturity indicator (Kelemen and Fang 2001;Marshall et al 2012;Wilkins et al 2014;Sauerer et al 2017;Schito et al 2017).…”

“…The main problem is that the vitrinite reflectance itself shows a 10%-30% error, as the measurement is based on personal judgment. Recent studies such as Sauerer et al (2017) conducted on 11 samples that are all type II organic matter, while Kelemen and Fang (2001) worked on shale samples of type II and Spötl et al (1998) on type III organic matter (OM), respectively. The studies of Wilkins et al (2015) and Schito et al (2016) are based on core samples at different depths from a single well and were correlated with Raman spectroscopy, while Khatibi et al (2018) concentrated only on Williston Basin, North Dakota.…”

“…Pyrolysis was performed on an OCE-II oil-gas evaluation workstation following Chinese Technical Standard GB/T 18602-2012 (SAC 2012) at the China University of Geosciences in Wuhan. Previous work has explained in detail about different pyrolysis apparatuses-their operations, measured parameters, potential pitfalls, and applications to petroleum exploration (Behar and Pelet 1985;Espitalié 1986;Peters and Cassa 1994;Lafargue et al 1998;Cheshire et al 2017). The OCE-II oil-gas evaluation workstation performs temperature-programmed heating to (1) thermally distil "free" or adsorbed hydrocarbons (S1 peak) from the sample, (2) pyrolyze the kerogen to produce hydrocarbons (S2 peak) in a second oven, and (3) obtain residual organic carbon content in mg/g (S4 unit mass) of hydrocarbon source rock after pyrolysis.…”