Geology topics

T.R. Menezes

Publications and source records attributed to T.R. Menezes.

4 recordsLinked to original sources

USGS2026

Characterisation of bituminite and testing reproducibility of vitrinite and bituminite reflectance measurements in organic‑carbon-rich intervals of the Kimmeridge Clay Formation: ICCP Identification of Dispersed Organic Matter Working Group round robin exercises

Three round robin exercises (RRE) aimed at characterizing bituminite and testing the reproducibility of random vitrinite (VR o %) and bituminite (BitR o %) reflectance measurements on samples of dispersed organic matter from organic‑carbon rich shale intervals of Kimmeridge Clay Formation were conducted in 2016, 2018, and 2020. This work was conducted by the Identification of Dispersed Organic Matter Working Group (IDOM WG) of the International Committee for Coal and Organic Petrology (ICCP). The Kimmeridge Clay Formation represents the major marine source rock for the North Sea hydrocarbon province. Samples collected from Kimmeridge Bay, Dorset, England, United Kingdom and Filey Bay, North Yorkshire, England, United Kingdom outcrops and the 16/17–14 well in the Tiffany oil field, Viking Graben, North Sea, were analyzed by 19 to 23 participants in 15 to 17 laboratories from 14 to 15 countries. Samples contain moderate to high organic matter content [5.32 to 12.10 wt% total organic carbon (TOC) content] with thermal maturity ranging from immature to thermally mature (T max 418 to 445 °C). Participants used a standard description sheet to record bituminite morphological characteristics, including its form, size, mode of appearance, and impurities, for use in the revision of the bituminite definition. The usage of previously published classifications of bituminite types (e.g., bituminite I sensu Teichmüller and Ottenjann, 1977 ) in the RRE was not found to be helpful. The indistinct, amorphous character of boundaries of bituminite, and the poor preparation of whole rock pellets for the 2018 and 2020 RRE hampered identification of bituminite. Mean random BitR o %, including outlying values, varied in all three RRE from 0.19 to 0.35% and is reported here for the first time. Application of the criterion standard deviation (SD) < 0.15 × BitR o % to exclude outlying BitR o % values showed virtually no change in modified BitR o % in immature samples (2016 and 2018 RRE) and an unexpected increase to 0.43% BitR o in the thermally mature sample (2020 RRE). Mean VR o values, including outliers in the three RRE, range from 0.47 to 0.71%, confirming the immature to thermally mature nature of samples of the Kimmeridge Clay Formation used in this study. Application of the criterion SD < 0.15 × VR o to exclude outlying values results in a comparable range of modified VR o values and a decrease in group standard deviation. Precision of VR o values (including outlying values) evaluated via the averaged unsigned multiple of the standard deviation rule (< 1.5) showed moderate to high precision comparable to historical values from similar RRE. An average reproducibility limit (RL) of 0.29% (including outlying values) showed an improvement in reproducibility relative to similar historical RRE (0.35%), which was attributed to the application of a common methodology (ASTM D7708, 2014b, 2023) to enhance the quality of data from the reflectance test method.

Kimmeridge Bay↗

USGS2017

Identification of alginite and bituminite in rocks other than coal. 2006, 2009, and 2011 round robin exercises of the ICCP Identification of Dispersed Organic Matter Working Group

The paper presents results of round robin exercises on photomicrograph-based identification of dispersed organic matter in source rocks that represent a range of marine and lacustrine deposits from worldwide localities and cover a range of thermal maturities. The round robin exercises were conducted by the Identification of Dispersed Organic Matter Working Group (IDOM WG) of the International Committee for Coal and Organic Petrology (ICCP). The round robin exercises aimed to (1) assess the applicability of the established ICCP definitions of bituminite, (2) identify deficiencies and improve the existing nomenclatures, and (3) provide a basis for the revision of the bituminite and alginite definitions in the ICCP Handbook (Taylor et al., 1998). Three round robin exercises performed in 2006, 2009 and 2011 involved 18 participants from research laboratories at universities and within government and industry. Participants were asked to identify macerals on the basis of existing definitions in 129 photomicrographs taken in incident white light and fluorescent mode and also in fluorescence light mode at prolonged (15 min) blue light irradiation. The results indicate that the definition of telalginite permits its positive and satisfactory agreement among the participants. In contrast, the descriptive characteristics of lamalginite referring to film-like appearance (filamentous) and lack of inner or outer structure are insufficient and inadequate to enable an unequivocal discrimination between it and telalginite. Furthermore, based on the amorphous nature of bituminite and lack of adherence to its established description and character (Taylor et al., 1998), the highest discrepancies were observed in its identification. Differentiation of bituminite from a fluorescent groundmass and in some cases from lamalginite proved to be particularly challenging. The findings of these round robin exercises are useful for improving the identification of sedimentary organic matter in source rocks and may be an important foundation for the modification of the ICCP definitions of alginite and bituminite.

International Journal of Coal Geology↗

USGS2011

Reply to Effect of concentration of organic matter on optical maturity parameters. Interlaboratory results of the organic matter concentration working group of the ICCP. Discussion by Vinay K. Sahay

This reply is motivated by Sahay's comments on the paper published by Mendonça Filho et al. (2010) dealing with the effect of concentration of an organic matter on optical maturity parameters. Four points were raised by Sahay: suggestion to use of chemical parameters to assess the effect of isolation, indication that suppression of vitrinite reflectance in liptinite-rich rocks was insufficiently addressed, discussion on the way to deal with the existence of multiple vitrinite populations in a dispersed organic matter, and contradictory explanation of results involving the influence of isolation procedure on fluorescence properties but no effect on vitrinite reflectance. The four points were separately addressed being the two first ones out of the scope of the paper. The existence of multiple vitrinite populations is a well-recognized problem whose importance in the results could be addressed because the participants provided individual records of vitrinite reflectance. These results indicated that election of different populations was not a major problem in the results. The influence of isolation procedure on the fluorescence spectra of alginite while the vitrinite reflectance remains unaltered is not considered contradictory because both parameters are measured on different components which may have a different response to the acid treatment.

International Journal of Coal Geology↗

USGS2010

Effect of concentration of dispersed organic matter on optical maturity parameters: Interlaboratory results of the organic matter concentration working group of the ICCP.

The main objective of this work was to study the effect of the kerogen isolation procedures on maturity parameters of organic matter using optical microscopes. This work represents the results of the Organic Matter Concentration Working Group (OMCWG) of the International Committee for Coal and Organic Petrology (ICCP) during the years 2008 and 2009. Four samples have been analysed covering a range of maturity (low and moderate) and terrestrial and marine geological settings. The analyses comprise random vitrinite reflectance measured on both kerogen concentrate and whole rock mounts and fluorescence spectra taken on alginite. Eighteen participants from twelve laboratories from all over the world performed the analyses. Samples of continental settings contained enough vitrinite for participants to record around 50 measurements whereas fewer readings were taken on samples from marine setting. The scatter of results was also larger in the samples of marine origin. Similar vitrinite reflectance values were in general recorded in the whole rock and in the kerogen concentrate. The small deviations of the trend cannot be attributed to the acid treatment involved in kerogen isolation but to reasons related to components identification or to the difficulty to achieve a good polish of samples with high mineral matter content. In samples difficult to polish, vitrinite reflectance was measured on whole rock tended to be lower. The presence or absence of rock fabric affected the selection of the vitrinite population for measurement and this also had an influence in the average value reported and in the scatter of the results. Slightly lower standard deviations were reported for the analyses run on kerogen concentrates. Considering the spectral fluorescence results, it was observed that the ??max presents a shift to higher wavelengths in the kerogen concentrate sample in comparison to the whole-rock sample, thus revealing an influence of preparation methods (acid treatment) on fluorescence properties. ?? 2010 Elsevier B.V.

International Journal of Coal Geology↗