Petrographic maturity parameters of a Devonian shale maturation series, Appalachian Basin, USA. ICCP Thermal Indices Working Group interlaboratory exercise

• Published in: International journal of coal geology Vol. 130; pp. 89 - 101
• Main Authors: Araujo, Carla Viviane, Borrego, Angeles G., Cardott, Brian, das Chagas, Renata Brenand A., Flores, Deolinda, Gonçalves, Paula, Hackley, Paul C., Hower, James C., Kern, Marcio Luciano, Kus, Jolanta, Mastalerz, Maria, Mendonça Filho, João Graciano, de Oliveira Mendonça, Joalice, Menezes, Taíssa Rêgo, Newman, Jane, Suarez-Ruiz, Isabel, da Silva, Frederico Sobrinho, de Souza, Igor Viegas
• Format: Journal Article
• Language: English
• Published: Oxford Elsevier B.V 15-08-2014; Elsevier
• Subjects: Basins; Coal; Devonian source rock; Earth sciences; Earth, ocean, space; Exact sciences and technology; Fluorescence; Fluorescence parameter; Hydrocarbons; Interlaboratory study; Maturation; Reflectance; Reflectivity; Sedimentary rocks; Shale; Spectra; Spectral fluorescence; Standard deviation; Stratigraphy; Vitrinite reflectance; United States; Europe; Appalachian Basin; Ohio; France; Paris Basin; Western Europe; Interlaboratory study; Devonian source rock; Fluorescence parameter; Maturation; Spectral fluorescence; Vitrinite reflectance; Mesozoic; North America; Devonian; fluorescence; performances; clastic rocks; shale; carbonaceous rocks; detection; thermal maturity; hydrocarbons; maturity; reflectance; source rocks; Lias; windows; Lower Jurassic; Toarcian; Paleozoic; Jurassic; sedimentary rocks; upper Liassic; correlation; organic materials; coal; vitrinite; Phanerozoic; standard deviation
• ISSN: 0166-5162; 1872-7840
• DOI: 10.1016/j.coal.2014.05.002

This paper presents results of an interlaboratory exercise on organic matter optical maturity parameters using a natural maturation series comprised by three Devonian shale samples (Huron Member, Ohio Shale) from the Appalachian Basin, USA. This work was conducted by the Thermal Indices Working Group of the International Committee for Coal and Organic Petrology (ICCP) Commission II (Geological Applications of Organic Petrology). This study aimed to compare: 1. maturation predicted by different types of petrographic parameters (vitrinite reflectance and spectral fluorescence of telalginite), 2. reproducibility of the results for these maturation parameters obtained by different laboratories, and 3. improvements in the spectral fluorescence measurement obtained using modern detection systems in comparison with the results from historical round robin exercises.
Mean random vitrinite reflectance measurements presented the highest level of reproducibility (group standard deviation 0.05) for low maturity and reproducibility diminished with increasing maturation (group standard deviation 0.12).
Corrected fluorescence spectra, provided by 14 participants, showed a fair to good correspondence. Standard deviation of the mean values for spectral parameters was lowest for the low maturity sample but was also fairly low for higher maturity samples.
A significant improvement in the reproducibility of corrected spectral fluorescence curves was obtained in the current exercise compared to a previous investigation of Toarcian organic matter spectra in a maturation series from the Paris Basin. This improvement is demonstrated by lower values of standard deviation and is interpreted to reflect better performance of newer photo-optical measuring systems.
Fluorescence parameters measured here are in good agreement with vitrinite reflectance values for the least mature shale but indicate higher maturity than shown by vitrinite reflectance for the two more mature shales. This red shift in λmax beyond 0.65% vitrinite reflectance was also observed in studies of Devonian shale in other basins, suggesting that the accepted correlation for these two petrographic thermal maturity parameters needs to be re-evaluated.
A good linear correlation between λmax and Tmax for this maturation series was observed and λmax 600nm corresponds to Tmax of 440°C. Nevertheless if a larger set of Devonian samples is included, the correlation is polynomial with a jump in λmax ranging from 540 to 570nm. Up to 440°C of Tmax, the λmax, mostly, reaches up to 500nm; beyond a Tmax of 440°C, λmax is in the range of 580–600nm. This relationship places the “red shift” when the onset of the oil window is reached at Tmax of 440°C. Moreover, the correlation between HI and λmax (r2=0.70) shows a striking inflection and decrease in HI above a λmax of 600nm, coincident with the approximate onset of hydrocarbon generation in these rocks.
•The reproducibility of optical parameters for source rock maturation have been studied.•17 participants from 8 laboratories performed the ICCP exercise.•Vitrinite reflectance and fluorescence spectra were measured on 3 Devonian samples.•Overall good reproducibility was found.•Scatter was lower for lower maturity samples.