Vitrinite is a maceral group that is derived from the remains of woody material from vascular plants and is composed of the thermally evolved products of lignin and cellulose. A maceral group is a set of organic matter types with similar properties and appearance. Vitrinite reflectance measures the percentage of incident light that is reflected from the surface of vitrinite as calibrated to a standard of known reflectance. This measurement is often regarded as the gold standard thermal maturity parameter and is used in oil and gas resource assessment and basin analysis studies. The Organic Petrology Laboratory (OPL) in Reston provides vitrinite reflectance measurements and qualitative organic petrography of shale, coal, and other unconventional reservoir samples as a routine service for various USGS Science Centers and external collaborators.
Objectives:
This project area has two main objectives. The first is to provide routine vitrinite reflectance measurements for Energy Resources Program-funded projects, the broader USGS community, and external partners. The second is to provide routine laboratory support functions for sample preparation for various analyses and micro-Fourier transform infrared spectroscopy (FTIR) research. These objectives allow for collaboration or case study investigations that reduce uncertainty in energy resource assessments, energy processes research, and environmental assessments.
Methodology:
Using equipment for preparation of mounted sample briquettes and several optical microscope systems (vitrinite reflectance, spectral fluorescence, transmitted polarized light microscopy) with imaging capability, laboratory staff provide quantitative vitrinite reflectance and qualitative organic petrographic data to internal and external customers using a Laboratory Information Management System (LIMS) per the requirements of the USGS Quality Management System (QMS). Measurement of vitrinite reflectance follows ASTM International method D7708 or D2798. In addition to vitrinite reflectance measurement, current laboratory processes also include sample preparation (mounting, grinding, polishing, wafering), transmitted light petrography, creation of sample maps through image stitching, spectral fluorescence measurement, and micro-FTIR analysis. Petrographers in the OPL pursue external accreditation in the specialized techniques of organic petrology investigation. The OPL has participated continuously since 2005 in a quarterly coal petrography interlaboratory exercise as a quality control check and operates under the requirements of the USGS QMS since 2017 to ensure that all data are of known and documented quality.
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