To test reproducibility of vitrinite and solid bitumen reflectance measurements in mudrocks, an interlaboratory study (ILS) was conducted using six samples from United States unconventional petroleum systems. Samples selected from the Marcellus, Haynesville, Eagle Ford, Barnett, Bakken and Woodford are representative of resource plays currently under exploitation in North America. All samples are from marine depositional environments, are thermally mature (Tmax >445°C) and have moderate to high organic matter content (2.9 to 11.6 wt.% TOC). The organic matter of the sample is dominated by solid bitumen, which contains intraparticle nano-porosity. Visual evaluation of organic nano-porosity via SEM suggests that intraparticle organic nanopores are most abundant in dry gas maturity samples and less abundant at lower wet gas/condensate and peak oil maturities. Samples were distributed to ILS participants in forty laboratories in the Americas, Europe, Africa and Australia; thirty- seven independent sets of results were received. Mean vitrinite reflectance (VRo) values from ILS participants range from 0.90 to 1.83% whereas mean solid bitumen reflectance (BRo) values range from 0.85 to 2.04% (no outlying values excluded), confirming the thermally mature nature of all six samples. Using multiple statistical approaches to eliminate outlying values, we evaluated reproducibility limit R, the maximum difference between valid mean reflectance results obtained on the same sample by different operators in different laboratories using different instruments. Removal of outlying values where the individual signed multiple of standard deviation was >1.0 produced lowest R values, generally ≤0.5% (absolute reflectance), similar to a prior ILS for similar samples. Other traditional approaches to outlier removal (outside mean ± 1.5*interquartile range and outside F10 to F90 percentile range) also produced similar R values. Standard deviation values <0.15*(VRo or BRo) reduce R and should be a requirement of dispersed organic matter reflectance analysis. R values were 0.1% to 0.2% for peak oil thermal maturity, about 0.3% for wet gas/condensate maturity and 0.4% to 0.5% for dry gas maturity. That is, these R values represent the uncertainty (in absolute reflectance) that users of vitrinite and solid bitumen reflectance data should assign to any one individual reported mean reflectance value from a similar thermal maturity mudrock sample. R values of this magnitude indicate a need for further standardization of reflectance measurement of dispersed organic matter. Furthermore, these R values quantify realistic interlaboratory measurement dispersion for a difficult but critically important analytical technique necessary for thermal maturity determination in unconventional petroleum systems.

Thirty-two organic-rich samples from the lower and upper shale members of the Devonian–Mississippian Bakken Formation were collected from eight cores across the Williston Basin, USA, at depths (~7,575–11,330 ft) representing immature through post peak oil/early condensate thermal maturity conditions. Reflectance results were correlated to programmed temperature pyrolysis parameters [hydrogen index (HI), production index (PI), Tmax], normal hydrocarbon and isoprenoid analysis of extractable organic matter (pristane/n-C17, phytane/n-C18) from GC analysis, and peak ratios from FTIR spectroscopy (branching ratio, A-factor).

This study presents Raman spectroscopic data paired with scanning electron microscopy (SEM) to assess solid bitumen composition and porosity development as a function of solid bitumen texture and association with minerals. A series of hydrous pyrolysis experiments (1-103 days, 300-370°C) using a low maturity (0.25% solid bitumen reflectance, BRo), high total organic carbon [(TOC), 14.0 wt. %] New Albany Shale sample as the starting material yielded pyrolysis residues designed to evaluate the evolution of TOC, solid bitumen aromaticity, and organic porosity development with increasing temperature and heating duration. Solid bitumen was analyzed by Raman spectroscopy wherein point data was collected from accumulations that ranged in size, pore density, and degree of association with the mineral matrix. Raman spectroscopy results show that with increasing temperature and experimental duration, solid bitumen aromaticity increases and compositional variability decreases. With regards to texture and composition, coarser-grained solid bitumen (>1.3 µm from nearest mineral grain) tends to have fewer pores (as identified with SEM) and consistently higher, but less variable aromaticity than thinner, wispy solid bitumen which is more intimately associated with the mineral matrix. The Raman data indicate that solid bitumen porosity development and molecular composition are linked, and these parameters are related to the textural relationships of the organic matter within the whole rock.

This study presents Raman spectroscopic data paired with scanning electron microscopy (SEM) to assess solid bitumen composition and porosity development as a function of solid bitumen texture and association with minerals. A series of hydrous pyrolysis experiments (1-103 days, 300-370°C) using a low maturity (0.25% solid bitumen reflectance, BRo), high total organic carbon [(TOC), 14.0 wt. %] New Albany Shale sample as the starting material yielded pyrolysis residues designed to evaluate the evolution of TOC, solid bitumen aromaticity, and organic porosity development with increasing temperature and heating duration. Solid bitumen was analyzed by Raman spectroscopy wherein point data was collected from accumulations that ranged in size, pore density, and degree of association with the mineral matrix. Raman spectroscopy results show that with increasing temperature and experimental duration, solid bitumen aromaticity increases and compositional variability decreases. With regards to texture and composition, coarser-grained solid bitumen (>1.3 µm from nearest mineral grain) tends to have fewer pores (as identified with SEM) and consistently higher, but less variable aromaticity than thinner, wispy solid bitumen which is more intimately associated with the mineral matrix. The Raman data indicate that solid bitumen porosity development and molecular composition are linked, and these parameters are related to the textural relationships of the organic matter within the whole rock.

This study tests the influence of environmental conditions on conversion of the maceral bituminite to a solid petroleum residuum (solid bitumen) during pyrolysis. The presence of water in sedimentary basins controls multiple processes during petroleum generation, migration, and storage. Four organic-rich (26–36 wt.% total organic carbon) oil shale samples were collected from thin-bedded (several cm thick), discontinuous outcrop exposures in the Neoproterozoic–Lower Cambrian restricted marine Salt Range Formation in the upper Indus Basin, Pakistan. Samples were from the Khewra Gorge (K-2) and Sohan Nala localities [SN-R(c), SN-5(b), SN-1]; a sample of Joadja torbanite coal from Australia containing terrigenous vitrinite was also included in the study for comparison. All samples were crushed, homogenized, and sieved to 4 (4.75 mm) or 8 (2.36 mm) mesh prior to pyrolysis experiments. Experiments used closed system batch reactors at subcritical water temperatures between 300 and 370°C for 72 hrs. The samples were pyrolyzed under hydrous and anhydrous conditions using distilled water, brine, or the absence of fluid as a condition of the experiment. These data tables represent the findings of this study and support an upcoming publication.

This data release contains reflectance measurements for eight samples submitted to the USGS Organic Petrology Laboratory in Reston. Samples include two artificial rock samples made from cement with organic matter added (samples 001-002), a coal and shale sample (samples 003-004, respectively), and hydrous pyrolysis residues for samples 001-004. The hydrous pyrolysis experiments were conducted at 330°C for 72 hours at the United States Geological Survey's (USGS) Denver Federal Center. Samples were mounted into 1-inch circular briquettes in USGS-Reston according to ASTM D2797 for organic petrographic analysis. Cement plugs (samples 001-002, and pyrolysis residues 005-006) were crushed to approximately 1 mm top-size whereas rock powders (samples 003-004, and pyrolysis residues 007-008) were prepared as-received (chips and powders of varying size). Samples were mounted in a thermoplastic medium using a heat-setting hydraulic press. Examination surfaces were ground and mechanically polished to a 0.05 µm finish with a silica colloid suspension. Reflectance measurements on the coal sample and the coal pyrolysis residue followed ASTM D2798 whereas reflectance measurements on cement plugs and shales followed ASTM D7708. A Leica DM4000 microscope equipped with LED illumination and monochrome camera detection was used for reflectance analysis with the computer program DISKUS-FOSSIL by Hilgers Technisches Buero. A YAG calibration standard (0.908% Ro) from Klein and Becker was used to calibrate the microscope for all reflectance measurements.

Solid bitumen is widely used as a thermal proxy in source-rock reservoirs, yet its texture and presentation may be affected by varying environmental constraints during its formation, e.g., water concentration, mineral catalysis, or salinity. Herein we investigated the development of solid bitumen properties during artificial maturation using three diverse (lacustrine to marine) oil shale samples containing abundant H-rich sedimentary organic matter (bituminite). Bituminite in the oil shales was treated via pyrolysis (320°C, 72 hrs) using hydrous, anhydrous, and brine conditions, causing the development of a newly formed solid bitumen in the experiment residues. The properties of the newly formed solid bitumen then were evaluated via geochemical screening tests, optical and electron microscopy, and infrared spectroscopy. Experimental residues also were treated via solvent extraction, allowing characterization of the effects of extraction to solid bitumen. Data from the experiments are provided here in 5 tables. Table 1 contains extract and fractionation data for untreated samples. Table 2 contains gas chromatography ratios. Table 3 contains reflectance and geochemical screening data. Table 4 contains gas yields for each sample under the various conditions. Table 5 contains Micro-Fourier transform infrared (micro-FTIR) data. For analysis findings, interpretations, and results, refer to the accompanying larger work publication, "Properties of solid bitumen formed during hydrous, anhydrous, and brine pyrolysis of oil shale: implications for solid bitumen reflectance in source-rock reservoirs".

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.

Bitumen reflectance data from a sample collected from the vertical EOG TATTOO D129 A28-F/094-O-10 ("Tattoo") well in the Horn River Basin, as part of the collection of a high-resolution geochemical data set.

Bitumen reflectance data from a sample collected from the vertical EOG TATTOO D129 A28-F/094-O-10 ("Tattoo") well in the Horn River Basin, as part of the collection of a high-resolution geochemical data set.