Martha (Rebecca) R. Stokes

Total neutron scattering of methane in Niobrara Formation samples at the wet-gas maturity level

Petroleum within unconventional source-rock reservoirs is hosted in organic matter and mineral pore space as well as in voids and microfractures. Recent work has shown that for source-rock reservoirs in the dry gas window, significant portions of methane (CH4), the main component of petroleum at elevated maturities, can be stored within fine organic matter porosity. However, within reservoirs at lower thermal maturities (e.g., peak oil or wet-gas conditions), the distribution and behavior of CH4 and the higher alkanes that comprise gas condensates across pore sizes is unclear, especially for fine pores with diameters <50 nm. Understanding CH4 within these settings provides insight for petroleum generation, movement,...

Categories: Data; Tags: Colorado, Contrast Matching, Denver-Julesburg Basin, Energy Resources, Gas Condensate, All tags... Geochemistry, Natural Gas, Neutron Scattering, Shale, USGS Science Data Catalog (SDC), Fewer tags

Textural occurrence and organic porosity of solid bitumen in shales

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...

Categories: Data; Tags: Clegg Creek, Energy Resources, Geochemistry, Hicks Dome, Hydrous pyrolysis, All tags... Illinois, Indiana, Organic petrology, Organic porosity, Raman spectroscopy, Thermal maturation, USGS Science Data Catalog (SDC), Fewer tags

Geochemical and isotopic data from glendonites and surrounding sediment, Carter Creek, North Slope Alaska

The dataset consists of geochemical and isotopic data from fine-grained sediments and glendonite crystals collected at Carter Creek on the North Slope of Alaska. Total Organic Carbon (TOC) values in the measured section were found to range between 0.5 and 3.5%, with a shift towards lower values in the uppermost 5 m of the section. Stable isotopes (13C) in organic matter were relatively stable throughout the section, ranging between -25.5 and -26, with a slight 0.3 per mil positive shift within this range approximately 57 m from the base of the section. Glendonites themselves were analyzed for δ13Ccarb and δ18Ocarb, with δ18O values relatively consistent between -0.22 and +1.28, and a much wider range of δ13C values...

Categories: Data; Tags: Alaska, Arctic, Carter Creek, Colville Foreland Basin, Energy Resources, All tags... Geochemistry, North Slope, Oligocene, USGS Science Data Catalog (SDC), calcite, glendonite, ikaite, isotope, mineralogy, raman, sedimentology, Fewer tags

Evidence for strain induced graphitization across a ductile fault zone

A suite of slate samples collected along a 2 km transect crossing the Lishan Fault in central Taiwan were evaluated to assess the role of ductile strain energy in natural graphitization at greenschist facies metamorphic conditions. Scanning electron microscope (SEM) imaging documents phyllosilicate and quartz replacement textures consistent cleavage development via dissolution-precipitation processes that increase in intensity from east to west. X-ray diffraction data reveal an east-to-west linear decrease in the full-width-at-half-maximum (FWHM) values of the 004 muscovite peaks and shifts towards higher 2θ (lower d) values. Rietveld refinements required two distinct muscovite populations and muscovite microstrain...

Categories: Data, Data Release - Under Revision; Tags: Electron Microprobe Analysis, Electron Petrography, Energy Resources, Energy Resources, Geochemistry, All tags... Graphitization, Greenschist, Raman Spectroscopy, Slate, Taiwan, Thermal Proxy, USGS Science Data Catalog (SDC), X-ray Diffraction, Fewer tags

Strain induced molecular heterogeneity in ancient sedimentary organic matter mapped at nanoscales using optical photothermal infrared spectroscopy

Here we report ultra-high resolution infrared mapping of organic matter functional group distribution in Tasmanites (algal microfossils) from the Upper Devonian Ohio Shale using optical photothermal infrared spectroscopy (O-PTIR). O-PTIR is capable of rapidly measuring the vibrational response of samples in situ with ~500-nm spatial resolution, well below the infrared diffraction limit. Our results indicate that organic matter within the fold apices regions (zones of greatest deformation) of relatively large Tasmanites is more aliphatic and less oxygen-rich than organic matter in the surrounding Tasmanites body. This contrasts with data from relatively thinner Tasmanites which show statistically invariant chemical...

Categories: Data; Tags: Huron Member, Mineral Resources, Ohio, Ohio Shale, Tasmanites, All tags... USGS Science Data Catalog (SDC), alginite, biota, deformation, optical photothermal infrared spectroscopy, organic matter, shale, Fewer tags