For sample mounting, organic petrology laboratories typically use cold-setting epoxy-resin (e.g., 40°C, used by Oklahoma Geological Survey, OGS) or heat-setting plastic (e.g., 180°C, used by U.S. Geological Survey, USGS). Previous workers have suggested a systematic vitrinite reflectance (VRo) increase was associated with the thermoplastic preparation process, relative to epoxy mounting, which was attributed to moisture loss from the transient high temperatures of plastic mounting. In this study, we evaluated thermal effects to low maturity organic matter from transient exposure to elevated temperatures. A subbituminous coal sample was subjected to long-term (4 to 38 weeks) exposure to temperatures of 85 to 120°C and afterward evaluated by multiple approaches to test thermal advance [elemental analyses, Rock-Eval pyrolysis, Fourier transform infrared spectroscopy (FTIR), nuclear magnetic resonance (NMR), pyrolysis gas chromatography, and petrographic analyses, including vitrinite reflectance and spectral fluorescence], all of which showed no detectable systematic changes between the original sample and its heat-treated products. We also compared vitrinite reflectance of six low maturity samples (those most likely to react to transient heating) mounted via both cold-setting epoxyresin and heat-setting thermoplastic. Results indicate measured VRo of a sample prepared by one mounting process was within the standard deviation of reflectance for the same sample prepared via the other process. Moreover, VRo results were not systematically higher in thermoset mounts. Contrary to previous work, these results suggest thermoplastic mounting or other transient exposure to elevated temperatures does not impact thermal maturity estimates from reflectance measurement for low maturity organic samples. Furthermore, the average interlaboratory difference in measured VRo (between OGS and USGS) for the same sample prepared by either epoxy-resin or thermoset mounting was 0.038%, about double the average difference between VRo for the same sample prepared via epoxy-resin versus thermoset in a single laboratory (0.024%). This result indicates interlaboratory variability impacts interlaboratory VRo measurement reproducibility to the extent that systematic differences could not be observed between thermoplastic and cold-setting sample preparation approaches, even if such differences were present.

The U.S. Geological Survey assessed undiscovered petroleum resources in the downdip Paleogene formations of the U.S. Gulf Coast in 2018. During the assessment new data and information were collected to evaluate thermal maturity, source rock character, and unconventional reservoir rock prospectivity for the Cenozoic-aged section in south Louisiana. Samples were analyzed using multiple analytical approaches, including programmed pyrolysis (Rock-Eval), Leco TOC, organic petrographic analysis including vitrinite reflectance (Ro, %), and X-ray diffraction mineralogy.

This data release contains Rock-Eval pyrolysis, organic petrographic (reflectance), and X-ray diffraction mineralogy data for subsurface Mesozoic rock samples from the eastern onshore Gulf Coast Basin (primarily Mississippi and Louisiana). Samples were analyzed in support of the U.S. Geological Survey (USGS) assessment of undiscovered petroleum resources in the Upper Cretaceous Tuscaloosa marine shale and evaluation of shale gas prospectivity in the Aptian section of the Mississippi Salt Basin.

This data release contains Rock-Eval pyrolysis, organic petrographic (reflectance), and X-ray diffraction mineralogy data for subsurface Mesozoic rock samples from the eastern onshore Gulf Coast Basin (primarily Mississippi and Louisiana). Samples were analyzed in support of the U.S. Geological Survey (USGS) assessment of undiscovered petroleum resources in the Upper Cretaceous Tuscaloosa marine shale and evaluation of shale gas prospectivity in the Aptian section of the Mississippi Salt Basin.

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.

Imaging of Niobrara Formation and Mowry Shale samples from a range of thermal maturities provided observations and data on pore systems, organic matter (OM) types and associations with mineralogy and fabric, wettability, and microporosity associated with both diagenetic and detrital clays. Imaging techniques included scanning electron microscopy, organic petrography and correlative scanning electron microscopy, and mapping of mineralogy through energy dispersive spectroscopy.

Imaging of Niobrara Formation and Mowry Shale samples from a range of thermal maturities provided observations and data on pore systems, organic matter (OM) types and associations with mineralogy and fabric, wettability, and microporosity associated with both diagenetic and detrital clays. Imaging techniques included scanning electron microscopy, organic petrography and correlative scanning electron microscopy, and mapping of mineralogy through energy dispersive spectroscopy.

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.