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Relating systematic compositional variability to the textural occurrence of solid bitumen in shales

September 18, 2022

This study presents Raman spectroscopic data paired with scanning electron microscopy (SEM) images to assess solid bitumen composition 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 solid bitumen aromaticity with increasing temperature and heating duration. Solid bitumen was analyzed by Raman spectroscopy wherein point data were collected from accumulations that ranged in size 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) has consistently higher, but less variable aromaticity than thinner, wispy solid bitumen which is more intimately associated with the mineral matrix. Collocated scanning electron microscope images were used to provide qualitative assessments of porosity hosted by the organic matter. These paired data sets suggest 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. These results are discussed with perspective towards understanding how rock fabric and texture can influence organic matter evolution during thermal maturation of organic-rich marine shales and inform our broader understanding of these important energy resources.

Citation Information

Publication Year 2022
Title Relating systematic compositional variability to the textural occurrence of solid bitumen in shales
DOI 10.1016/j.coal.2022.104068
Authors Martha (Rebecca) Stokes, Brett J. Valentine, Aaron M. Jubb, Paul C. Hackley
Publication Type Article
Publication Subtype Journal Article
Series Title International Journal of Coal Geology
Index ID 70236997
Record Source USGS Publications Warehouse
USGS Organization Eastern Energy Resources Science Center; Geology, Energy & Minerals Science Center