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Reflectance, Raman band separation and Mean multivariant curve resolution (MCR) in organic matter in Boquillas Shale
The molecular composition of petroliferous organic matter and its composition evolution throughout thermal advance are key to understanding and insight into petroleum generation. This information is critical for comprehending hydrocarbon resources in unconventional reservoirs, as source rock organic matter is highly dispersed, in contact with the surrounding mineral matrix, and may be present as multiple organic matter types. Here, a combination of Raman spectroscopy and optical microscopy approaches was applied to a marginally mature (vitrinite reflectance ~0.5%) sample of the Late Cretaceous Boquillas Shale before and after hydrous pyrolysis (HP) at 300 °C and 330 °C for 72 hours. This experimental design allowed for correlative examination of micro-scale changes in organic matter compositional properties (e.g., aromaticity) for a variety of organic matter types across a thermal gradient at the single particle level. Results indicate that while the examined amorphous organic matter, solid bitumen, and vitrinite particles exhibit different aromatic signatures in the unheated shale, they effectively progress along a similar trend through composition space with thermal advance. Examined inertinite fragments were generally insensitive to the applied thermal stress, reinforcing the idea that reservoir temperature may be secondary for dictating the molecular composition of inertinite. Additional analysis of the Raman spectra for individual organic matter types was performed using multivariate curve resolution (MCR); correlation of standard Raman and reflectance-derived thermal maturity proxies against MCR parameters shows consistent trends. This trend suggests that MCR may be a fast and statistically robust method for extracting compositional information from Raman spectra of sedimentary organic matter that can be used to construct thermal maturity relationships. These findings inform the understanding of how different petroliferous organic matter types evolve throughout thermal reactions and further demonstrate that Raman spectroscopy combined with petrographic analysis can provide complementary estimates of organic matter composition and thermal maturity.
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Data Release for Application of Raman spectroscopy as thermal maturity probe in shale petroleum systems: insights from natural and artificial maturation series (2018)
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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-hour 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 an 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 speculate this result may be due to differences in the sampling interactions of Raman vs. reflectance measurements, and the incomplete nature of maturation reactions in the time-limited hydrous pyrolysis residues. Samples used in this study are similar in organic assemblage (dominantly solid bitumen) to other commonly exploited North American shale petroleum systems, i.e., Bakken, Barnett, Duvernay, Fayetteville and Woodford shales. Therefore, results presented herein may be broadly applicable to other important shale plays. However, caution is suggested and Raman spectroscopy as a thermal probe may need individual calibration in each shale play due to differences in solid bitumen carbon chemistry. Samples were collected and tested between 2013 and 2018, in studies preformed by Ryder et al., 2013; Hackley and Lewan, 2018; Hackley et al., 2017; Yang et al., 2017; Hackley and Lundsdorf, 2018.
Data Release for Application of Raman spectroscopy as thermal maturity probe in shale petroleum systems: insights from natural and artificial maturation series (2018)
공공데이터포털
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-hour 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 an 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 speculate this result may be due to differences in the sampling interactions of Raman vs. reflectance measurements, and the incomplete nature of maturation reactions in the time-limited hydrous pyrolysis residues. Samples used in this study are similar in organic assemblage (dominantly solid bitumen) to other commonly exploited North American shale petroleum systems, i.e., Bakken, Barnett, Duvernay, Fayetteville and Woodford shales. Therefore, results presented herein may be broadly applicable to other important shale plays. However, caution is suggested and Raman spectroscopy as a thermal probe may need individual calibration in each shale play due to differences in solid bitumen carbon chemistry. Samples were collected and tested between 2013 and 2018, in studies preformed by Ryder et al., 2013; Hackley and Lewan, 2018; Hackley et al., 2017; Yang et al., 2017; Hackley and Lundsdorf, 2018.
TOC, Reflectance and Raman Data from Eocene Green River Mahogany zone
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Geological models for petroleum generation suggest thermal conversion of oil-prone sedimentary organic matter in the presence of water promotes increased liquid saturate yield, whereas absence of water causes formation of an aromatic, cross-linked solid bitumen residue. To test the influence of exchangeable hydrogen from water, organic-rich (22 wt.% total organic carbon, TOC) mudrock samples from the Eocene lacustrine Green River Mahogany zone oil shale were pyrolyzed under hydrous and anhydrous conditions at temperatures between 300 and 370°C for 72 hrs. Petrographic approaches including optical microscopy, reflectance, Raman spectroscopy, and scanning electron and transmission electron microscopy, supplemented by geochemical screening measurements (TOC content and programmed pyrolysis), were used to quantify differences in relative appearance, abundance and composition of solid bitumen newly generated during the pyrolysis experiments. Results show hydrous residues contain lower TOC, comprised of solid bitumen with higher aromaticity, and textures indicative of lower viscosities, than anhydrous residues from the same temperature pyrolysis conditions. These observations suggest solid bitumen forming from thermal conversion of oil-prone sedimentary organic matter under anhydrous conditions is less aromatic, although more cross-linked, than solid bitumen forming under hydrous conditions at the same time-temperature combination. A radical disproportionation mechanism favored in the presence of hydrogen radical donation from water promotes aromatization in the solid residue with concomitant expulsion of saturated hydrocarbons.
TOC, Reflectance and Raman Data from Eocene Green River Mahogany zone
공공데이터포털
Geological models for petroleum generation suggest thermal conversion of oil-prone sedimentary organic matter in the presence of water promotes increased liquid saturate yield, whereas absence of water causes formation of an aromatic, cross-linked solid bitumen residue. To test the influence of exchangeable hydrogen from water, organic-rich (22 wt.% total organic carbon, TOC) mudrock samples from the Eocene lacustrine Green River Mahogany zone oil shale were pyrolyzed under hydrous and anhydrous conditions at temperatures between 300 and 370°C for 72 hrs. Petrographic approaches including optical microscopy, reflectance, Raman spectroscopy, and scanning electron and transmission electron microscopy, supplemented by geochemical screening measurements (TOC content and programmed pyrolysis), were used to quantify differences in relative appearance, abundance and composition of solid bitumen newly generated during the pyrolysis experiments. Results show hydrous residues contain lower TOC, comprised of solid bitumen with higher aromaticity, and textures indicative of lower viscosities, than anhydrous residues from the same temperature pyrolysis conditions. These observations suggest solid bitumen forming from thermal conversion of oil-prone sedimentary organic matter under anhydrous conditions is less aromatic, although more cross-linked, than solid bitumen forming under hydrous conditions at the same time-temperature combination. A radical disproportionation mechanism favored in the presence of hydrogen radical donation from water promotes aromatization in the solid residue with concomitant expulsion of saturated hydrocarbons.
Results from geochemical and mineralogical characterization of Boquillas Shale geochemical reference material ShBOQ-1
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This data release accompanies a Fact Sheet on the ShBOQ-1 geochemical reference material (Birdwell and Wilson, 2021). Average and standard deviations reported in the Fact Sheet were calculated using the values compiled here.
High Microscale Variability in Raman Thermal Maturity Estimates from Shale Organic Matter - Data Release
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Here the spatial variation in Raman estimates of thermal maturity within individual organic domains from several shale geologic reference materials originating from the Boquillas, Marcellus, Niobrara, and Woodford Formations are assessed from the respective Raman response. We show that for all four shales the thermal maturity parameters extracted from Raman spectra by iterative peak fitting can vary widely across distances of ≤5 µm within the same organic domain.
Analyzing Heterogeneity in Artificially Matured Samples of Bakken Shales (2018)
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Solid organic matter (OM) in sedimentary rocks produces petroleum and solid bitumen when it undergoes thermal maturation. The solid OM is a ‘geomacromolecule’, usually representing a mixture of various organisms with distinct biogenic origins, and can have high heterogeneity in composition. Programmed pyrolysis is a common conventional method to reveal bulk geochemical characteristics of the dominant OM while detailed organic petrography is required to reveal information about the biogenic origin of contributing macerals. Despite advantages of programmed pyrolysis, it cannot provide information about the heterogeneity of chemical compositions present in the individual OM types. Therefore, other analytical techniques such as Raman spectroscopy are necessary. In this study, we compared geochemical characteristics and Raman spectra of two sets of naturally and artificially matured Bakken source rock samples. A continuous Raman spectral map on solid bitumen particles was created from the artificially matured hydrous pyrolysis residues, in particular, to show the systematic chemical modifications in microscale. Spectroscopy data was plotted for both sets against thermal maturity to compare maturation rate/path for these two separate groups. The outcome showed that artificial maturation through hydrous pyrolysis does not follow the same trend as naturally-matured samples although having similar solid bitumen reflectance values (%SBRo). Furthermore, Raman spectroscopy of solid bitumen from artificially matured samples indicated the heterogeneity of OM decreases as maturity increases. This represents an alteration in chemical structure towards more uniform compounds at higher maturity. This study may signify the potential of Raman spectroscopy as an alternative to the conventional (pseudo) Van Krevelen diagram, by revealing the underlying chemical changes. Finally, observation by Raman spectroscopy of chemical alteration of OM during artificial maturation may assist in the proposal of improved pyrolysis protocols to better resemble natural geologic processes.
Analyzing Heterogeneity in Artificially Matured Samples of Bakken Shales (2018)
공공데이터포털
Solid organic matter (OM) in sedimentary rocks produces petroleum and solid bitumen when it undergoes thermal maturation. The solid OM is a ‘geomacromolecule’, usually representing a mixture of various organisms with distinct biogenic origins, and can have high heterogeneity in composition. Programmed pyrolysis is a common conventional method to reveal bulk geochemical characteristics of the dominant OM while detailed organic petrography is required to reveal information about the biogenic origin of contributing macerals. Despite advantages of programmed pyrolysis, it cannot provide information about the heterogeneity of chemical compositions present in the individual OM types. Therefore, other analytical techniques such as Raman spectroscopy are necessary. In this study, we compared geochemical characteristics and Raman spectra of two sets of naturally and artificially matured Bakken source rock samples. A continuous Raman spectral map on solid bitumen particles was created from the artificially matured hydrous pyrolysis residues, in particular, to show the systematic chemical modifications in microscale. Spectroscopy data was plotted for both sets against thermal maturity to compare maturation rate/path for these two separate groups. The outcome showed that artificial maturation through hydrous pyrolysis does not follow the same trend as naturally-matured samples although having similar solid bitumen reflectance values (%SBRo). Furthermore, Raman spectroscopy of solid bitumen from artificially matured samples indicated the heterogeneity of OM decreases as maturity increases. This represents an alteration in chemical structure towards more uniform compounds at higher maturity. This study may signify the potential of Raman spectroscopy as an alternative to the conventional (pseudo) Van Krevelen diagram, by revealing the underlying chemical changes. Finally, observation by Raman spectroscopy of chemical alteration of OM during artificial maturation may assist in the proposal of improved pyrolysis protocols to better resemble natural geologic processes.
Nanoscale Molecular Fractionation of Organic Matter within Unconventional Petroleum Source Beds (2019)
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Fractionation of petroleum during migration through sedimentary rock matrices has been observed across lengths of meters to kilometers. Selective adsorption of specific chemical moieties at mineral surfaces and/or the phase behavior of petroleum during pressure changes are typically invoked to explain this behavior. Given the current emphasis on unconventional (continuous) resources, there is a need to understand petroleum fractionation occurring during expulsion and migration at the nanometer to micron scale, due to the fine-grained nature of petroliferous mudrocks. Here organic matter compositional differences observed within kukersite petroleum source beds (containing acritarch Gloeocapsomorpha prisca) from the Ordovician Stonewall Formation are explored using a suite of optical and spectroscopic methods, most notably through a combined atomic force microscopy - infrared spectroscopy (AFM-IR) approach. The AFM-IR technique is capable of providing spatial resolutions approaching 50 nm and allows for an assessment of the molecular fingerprint of kukersite organic matter across transition zones from organic-rich ‘source’ layers into adjacent carbonate ‘reservoir’ layers ~150 μm away. Our results indicate that the composition of kukersite organic matter begins to vary immediately following expulsion from source layers, with loss of carbonyl groups and a concomitant increase in the CH3/CH2 ratio, indicating alkyl chain-length decrease, as migration distance increases. These chemical transitions correlate with fluorescence decrease, reflectance increase, and an increase in Raman proxies for aromaticity in the organic matter. These data are consistent with the retention of polar compounds onto mineral grains during expulsion and migration, and primacm-1ry cracking and bituminization of the Gloeocapsomorpha prisca kerogen, respectively.
Nanoscale Molecular Fractionation of Organic Matter within Unconventional Petroleum Source Beds (2019)
공공데이터포털
Fractionation of petroleum during migration through sedimentary rock matrices has been observed across lengths of meters to kilometers. Selective adsorption of specific chemical moieties at mineral surfaces and/or the phase behavior of petroleum during pressure changes are typically invoked to explain this behavior. Given the current emphasis on unconventional (continuous) resources, there is a need to understand petroleum fractionation occurring during expulsion and migration at the nanometer to micron scale, due to the fine-grained nature of petroliferous mudrocks. Here organic matter compositional differences observed within kukersite petroleum source beds (containing acritarch Gloeocapsomorpha prisca) from the Ordovician Stonewall Formation are explored using a suite of optical and spectroscopic methods, most notably through a combined atomic force microscopy - infrared spectroscopy (AFM-IR) approach. The AFM-IR technique is capable of providing spatial resolutions approaching 50 nm and allows for an assessment of the molecular fingerprint of kukersite organic matter across transition zones from organic-rich ‘source’ layers into adjacent carbonate ‘reservoir’ layers ~150 μm away. Our results indicate that the composition of kukersite organic matter begins to vary immediately following expulsion from source layers, with loss of carbonyl groups and a concomitant increase in the CH3/CH2 ratio, indicating alkyl chain-length decrease, as migration distance increases. These chemical transitions correlate with fluorescence decrease, reflectance increase, and an increase in Raman proxies for aromaticity in the organic matter. These data are consistent with the retention of polar compounds onto mineral grains during expulsion and migration, and primacm-1ry cracking and bituminization of the Gloeocapsomorpha prisca kerogen, respectively.
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